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Pictures and Illustrations.
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Frontispiece. Photographic Picture of the St. Louis Bridge, Taken 1880.
Plate I. Skeleton Plan and Elevation of the Bridge.
Plate II. Map, Showing the Location of the Bridge and Its Approaches.
Plate III. Profile of the Bridge and Its Approaches.
Plate IV. Strain Diagrams Resulting from Movable Loads.
Plate V. Strain Diagrams Resulting from Extreme Temperatures.
Plate VI. Strain Diagrams for the Main Braces.
Plate VII. Plan and Longitudinal Section of the Caisson of the East Pier.
Plate VIII. Details of the Iron-Work of the Caisson of the East Pier.
Plate IX. Method of Sinking the East Pier — Elevation of Caisson, Pontoons, Derricks, and Machinery.
Plate X. Method of Sinking the East Pier — Plan of Caisson, Pontoons, Derricks, adn Machinery.
Plate XI. Details of the Hoisting Machinery of Pontoons.
Plate XII. Drawings of a Sand-Pump.
Plate XIII. Method of Sinking the East Pier — Cross-Section Showing Air-Chamber and the Working of a Sand-Pump.
Plate XIV. Plan and Sections of the Caisson of the East Abutment.
Plate XV. East Abutment Caisson, Continued — Details of the Central Air-Locks.
Plate XVI. Caissons for the Approach Piers.
Plate XVII. The West Abutment and the West Approach, Complete.
Plate XVIII. The Masonry of the East Pier, Complete.
Plate XIX. Plan and Sections of the Caisson of the East Abutment.
Plate XX. Vertical Section of the East Pier.
Plate XXI. Cross-Section of the Center Arch at Joint No. 1 (Near the Springing).
Plate XXII. Cross-Section of the Center Arch at Join 22 (The Crown).
Plate XXIII. Upper Skewback-Joint of Rib A of Center Span.
Plate XXIV. Detail of Joint 1 of the Center Arch.
Plate XXV. Details of Joint 22 of the Center Arch.
Plate XXVI. Method of Supporting the Lower Road-way at Joint 0-7, 8 and 9.
Plate XXVII. Method of Supporting the Lower Road-way at Joints 10 and 11.
Plate XXVIII. Method of Supporting the Lower Road-way at Joint 13.
Plate XXIX. The Details of the Large Tubes.
Plate XXX. The Details of the Couplings and Steel Pins.
Plate XXXI. The Details of the Main Braces, Vertical Struts, Horizontal Tubular Struts, and Suspension-Bars.
Plate XXXII. General Plan of an Upper Wind-Truss.
Plate XXXIII. Details of an End of an Upper Wind-Truss.
Plate XXXIV. Details of the Anchorage of the End of an Upper Wind-Truss.
Plate XXXV. Drawings of the St. Louis Testing-Machine, and Measuring Apparatus.
Plate XXXVI. Drawings of the Philadelphia Testing-Machine, and the High-Pressure Steel Gauge.
Plate XXXVII. Method of Erection, Showing Arrangement of Cables and Towers.
Plate XXXVIII. Method of Erection, Showing Rams, Balance-Gauge, and Adjustable (Closing) Tubes.
Plate XXXIX. Method of Erection, Showing Details of Cables, Masts, Clamps, Etc.
Plate XL. Photographic View of the Construction of the West Pier.
Plate XLI. Photographic View of the Caisson of the East Abutment Showing First Courses of Masonry.
Plate XLII. Photographic View of the Erection of the West Arch, Showing the Cables to Joints Nos. 6 and 9.
Plate XLIII. Photographic View of the Erection of the West Arch, Showing Cables Nos. 6 and 9 (The Latter Under Strain).
Plate XLIV. Photographic View of the Erection of All Spans — The Western Arch is Closed.
Plate XLV. Photographic View of the Erection of the Road-ways Over the Arches.
Plate XLVI. Interesting Views (Four in Number) of the Completed Bridge, Taken in 1880.
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Preface.
Some apology seems to be necessary, in consequence of the fact that the history of the St. Louis Bridge does not appear in print till seven years after the Bridge was finished. The delay has been deeply regretted but inevitable. For several years it seemed probable that the history would be written by some one of the assistant engineers connected with its construction. Not till the end of 1876 did I consent to undertake it. I entered upon the task in the midst of arduous professional duties, and have given to it only such time and strength as my duties elsewhere fairly allowed. The work has grown unexpectedly in my hands: my first estimate of the number of pages was scarcely half of the least number into which, by repeated condensations, I have finally been able to compress the work; and what I had thought to do in two years has consumed all that I could give of nearly five.
I have labored to make the history both full and accurate without being tiresome. No engineering enterprise with which I am at all familiar ever involved so many difficult problems or developed so many interesting discussions and solutions. These problems have been to me the most interesting part of my work, and I hope that my statement of them will be satisfactory both to those whose ingenuity and enterprise this book commemorates, as well as to that vast army of mechanics, students, and engineers the world over, who may wish to know fully and accurately the details of both the Bridge and its building.
An eye-witness of many of the important operations attending the construction of the Bridge, and a frequent interpreter to those less familiar with the rationale of the work, I nevertheless feel as though I did not properly appreciate the magnitude, strength and beauty of the structure itself, nor the skill, courage, and energy displayed in its construction, until I had read the mass of correspondence and unpublished reports preserved in the office of the Company, and studied with the utmost fidelity every detail of both foundations and arches. I cannot expect to communicate to others the enthusiasm and admiration I myself feel, but if this book properly meets the wide-spread demand for information regarding the Bridge, and shall help to secure for the structure and the men who built it their true place in history, I shall be satisfied.
As is the fate of all great works, the building of this Bridge was attended with controversies more or less sharp, and striking differences of opinion. I have endeavored to deal with all such in an impartial and judicial manner. If I have reached conclusions on controverted points, it has been because the facts as I could get them forced the conclusions upon me. In some instances I have differed from personal friends with whom I would gladly agree; but as differences of opinion on professional matters are quite inevitable, there is perhaps no sufficient occasion for expressions of regret.
If, however, I have wrongly stated the position of any party on any point, I am very sorry. I have generally relied on documentary proof, and though I may have been at times in error, I have
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been innocently so. Unless it is explicitly stated otherwise, it should be understood that no one is responsible for the views set forth but myself.It is scarcely necessary for me to acknowledge my indebtedness to Mr. Eads, the chief engineer of the Bridge, for assistance and criticism. Though deeply engrossed in other enterprises, he has not failed to respond to every inquiry, and to live over again for my benefit the exciting periods of his seven years of bridge-building. To Col. Henry Flad and Mr. Charles Pfeifer, assistant engineers of the Bridge, my thanks have been repeatedly due. Fortunately, the city of St. Louis retains the services of both of these gentlemen — the former as President of the Board of Public Improvements, and the latter as Harbor and Wharf Commissioner.
To my valued friend Mr. Theodore Cooper, C. E., now of New York City, I desire to express my special obligation. His experiences as inspector at Philadelphia and Pittsburg, the responsible position he held in connection with the erection of the Bridge, his excellent memory and his admirable notebooks — all fitted him to be most useful to me, and I gratefully own my indebtedness.
To Dr. Taussig, the present manager of the Bridge and Transit Companies, and to Mr. Fabian, the secretary, I am under obligation for repeated courtesies in furnishing me with the documents and records of the Bridge Company. I am happy also to recognize the valuable aid of my former pupil, Mr. E. A. Engler, now a professor in Washington University, in the examination of documents and in the transcription of notes.
I am placed under peculiar obligation to Mr. Robert Moore, C. E., of St. Louis, who has kindly read the proof-sheets of the first three hundred pages of the book, and given me the benefit of his excellent taste on both literary and scientific matters.
Of those who have been concerned in the mechanical production of this book there is no need for me to speak: the book speaks for them. They have furnished what it was intended to secure — work of the best character.
WASHINGTON UNIVERSITY, C. M. W.
ST. LOUIS, September, 1881.
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Chapter I. The Basin and Regimen of the Mississippi River.
The Upper Mississippi unites with the Missouri River about twenty miles above St. Louis, so that the Mississippi, as it rolls by the city, contains only the waters of those two streams. The basin of the Missouri River includes an area of 518,000 square miles; that of the Upper Mississippi about 169,000 square miles; hence the drainage of 687,000 square miles of the earth's surface forms the river at St. Louis.
The great extent of this joint basin is better appreciated when it is compared with other areas well known. It is eighty-eight times as large as the State of Massachusetts or equal to the combined areas of England, Scotland, Wales, Ireland, France, Spain, Portugal, Holland, Belgium, Switzerland, and Italy. Again, it is equal to the sum of the areas of the basins of the Vistula, Oder, Elbe, Rhine, Seine, Loire, Garonne, Duro, Tagus, Gaudiaiia, Ebro, Rhone, Po, and the Danube. It is, however, probable that the volume of water discharged from this vast territory is not proportionally great.
The basin of the Upper Mississippi is wholly devoid of mountains, though the country is well wooded and abundantly supplied with lakes and streams. The average annual rainfall is 35.2 inches.
The Missouri basin includes the eastern slope of the Rocky Mountains, for a length of about 800 miles. From these mountains several large streams issue, and flow for hundreds of miles across the great barren plain, with little increase of size. "Comparatively little rain falls upon the mountains and plains, and hence the size of the main river is proportionately small when the drainage area alone is considered."
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The average discharge per second of the Upper Mississippi is given as 105,000 cubic feet, and that of the Missouri as 120,000 cubic feet. Hence the discharge of the river at St. Louis is 225,000 cubic feet per second, or 7,080,000,000,000 cubic feet per year. The maximum discharge must be at least four times the average.At the mouth of the Missouri the Mississippi takes on its peculiar character of a deep and boiling torrent. Its width is increased, but not so much as its depth.
The river is subject to great changes, both seasonal and irregular. The highest water is during the "June rise" (which may be a month or two early or late), and low water is usually in December. The greatest range ever observed at St. Louis between extreme low and extreme high water is 41.39 feet, the high water being that of 1844, when the water was 7.58 feet above the city directrix. The city directrix is the curbstone at the foot of Market Street, and marks the height of the water in 1828; it serves as the datum-plane for all the city engineering at St. Louis. The Bridge levels are generally referred to the same line. Its position is shown on several Plates. Thirty-four feet below the city directrix is known as "low-water."
The velocity of the current, where it is greatest, opposite to St. Louis, varies from 4 feet per second (or 2ž miles per hour) at low water, to 12Ë feet per second (or 8Ë miles per hour) at extreme high water. The average slope of the water-surface is about 6 inches per mile near St. Louis.
At all times the river-water is turbid, and when it is allowed to stand a few hours a sediment is deposited; but the amount of matter held in suspension varies greatly. The sediment consists of finely-divided vegetable and mineral matter, gathered from tributaries through alluvial districts and from the bed and banks of the stream. In order to appreciate the difficulties to be surmounted in bridging the Mississippi at St. Louis, it is necessary to clearly understand the laws which appear to obtain in the action of the river upon its banks and bed, and so determine its power to transport sedimentary matter.
This "carrying power" has reference, not only to the amount of sedimentary matter it can hold in suspension, but also to the amount of material which, under the influence of the impulsive force, or momentum, of the water, is driven along in a more or less fluid state. The distinction here made is one of degree rather than kind. Water moving slowly in a smooth, regular channel, can carry very little mineral matter; but increase its velocity and volume, and it will sweep along not only sand and mud, but gravel and large pebbles. When, from irregularities in the bed of a stream, the body of the river is full of whirl pools, — cross and vertical currents, — the action is analogous to that of jets driven by high pressure.
It appears that this transporting power of a river depends upon: (1.) The specific gravity of the sediment. (2.) The size of the sedimentary particles. (3.) The relative or internal velocity of adjacent masses of water. (4.) The depth of the stream. (5.) The absolute velocity of the stream.
1. Woody fibre and the tissues of vegetable cells, loam, clay, particles of limestone, sand, and gravel form the main burden of the river. The specific gravity varies from 1 to 3. The specific gravity of the strictly suspended matter is given as 1.9 by Humphreys and Abbott.
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2. The size of the particles is very important. The heaviest materials, if in a finely divided state, may be transported by the running water in rivers. If the particles are supposed to be similar in shape, we easily see that their stability in running water is less as they become smaller. Their weight, and consequently the resistance which they offer to being raised or pushed along by currents, varies as the cube of any one of their dimensions, as, for instance, their thickness; while the force to which they are exposed (the pressure, or impact of the waters upon their surface) varies only as the square of the thickness. For example, take two similar blocks of granite, or two grains of sand, the larger of which is three times as thick as the smaller; the weight, and therefore the friction, of one is twenty-seven times that of the other; while its surface, and hence the force with which water would press upon or strike it, is only nine times as great. It is evident that the smaller particle might be transported, or pushed along, while the larger would stand unmoved. It follows that, for a given current of water, there is a point of fineness for each substance at which the particles become transportable. As a consequence, we should expect in a diminishing river current to find the larger and denser particles deposited or left behind first, the smaller and lighter next, and so on, the finest and lightest being deposited only when the water is stationary.
3. In a stream full of whirlpools and boils (or vertical currents in opposite directions), the water is intermittently impinging upon the bed and banks. These currents not only prevent the deposit of what would otherwise come to rest on the river bottom, but when not fully loaded with sedimentary material, they seize upon all within their reach and carry it along. So far as velocity in the direction of the axis of the stream is concerned, the greatest "difference of velocity" in adjacent water-layers, or masses, is found near the bed and banks of a stream; but where cross and vertical currents exist, the resultant difference in velocity is likely to be greatest where the onward flow is greatest.
4. The modifying effect of depth on the power to transport solid matter in a sediment-bearing stream is shown in two ways: In the first place, as the depth increases, the internal, relative motion of adjacent layers is diminished ("still waters run deep," and conversely), — this alone lessens the transporting power. In the second place, the relative motions of a deep stream are powerful, and slowly moving masses of water produce great inequalities of pressure on the material of the bed. These unequal pressures suffice to keep the loose material on the bottom in continual motion, thus increasing the transportation. A paragraph in Mr. Eads's report of May, 1868, is so pertinent that I quote it here: "I had occasion," he says, "to examine the bottom of the Mississippi, below Cairo, during the flood of 1851, and at sixty-five feet below the surface I found the bed of the river, for at least three feet in depth, a moving mass, and so unstable that, in endeavoring to find a footing on it beneath my bell, my feet penetrated through it until I could feel, although standing erect, the sand rushing past my hands, driven by a current apparently as rapid as that at the surface. I could discover the sand in motion at least two feet below the surface of the bottom, and moving with a velocity diminishing in proportion to its depth." At Carrollton, gravel, sand, and earthy matter were found moving along the bottom at a depth of about 100 feet, by Professor Forshey. It is obvious that increase of depth diminishes rather than increases the "suspending" power per unit of volume, though it adds largely to the motive force of the stream.
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5. The absolute velocity of the water is, of course, a very important matter, both from the momentum with which it strikes all obstacles, and from the fact that increase of absolute velocity always involves increase of relative motion. With a given channel, depth of stream, and nature of sediment, there is a certain maximum load for each velocity, and the load increases as the velocity increases, though the law of increase is not exactly known. The practical limit to the power of the water to hold matter heavier than itself in suspension suggests that the solid particles afford each other a sort of protection from the impulsive force of the water, and that the amount of this protection increases as the number of particles in suspension increases, and that at a certain point the protection is so efficient that the water is unable to prevent their fall. This protection is, of course, mutual among the particles. Thus, if we suppose several grains of sand in contact and in a row, while the unequilibrated pressure of the water acts only on the end of the row, we see that the efficiency of the force is much less than with a single particle, as the surface of action remains the same, while the force to be overcome is increased. As the kinetic energy of the water is proportional to the square of its velocity, it is probable that the law referred to above would prove to be that the carrying power of a river is, other tilings being equal, proportional to the square of its velocity.
These main principles, derived partly by theory and partly by observation, are well confirmed by the behavior of the Mississippi at St. Louis. At "low water" the water is least turbid, the velocity is small, the stream shallow and confined to the main channel. It can carry but little solid matter, and it finds its load in the deposits made during the subsidence of the last flood. This is comparatively heavy material, and settles readily when the water is stationary. When, from any cause, a rise takes place, the increasing tide seizes upon the lightest and finest materials first, and it is noticeable that the suspended matter in samples of water at such times settles slowly and with great difficulty. But the demand of a flood is not easily satisfied. If the water enter the main stream comparatively clear (like the Upper Mississippi), it is much undercharged, and quickly attacks the old deposits along the river bed; and if the flood is great, it even scours out and carries away sand-bars and islands. It is generally true in the Mississippi that changes in level of the surface are accompanied by contrary changes in the bed, —
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The depth of scour of the river is sometimes very great. An obstacle in mid-channel, like the wreck of a boat,
The river ordinarily freezes over during the winter. The ice-coating is, however, generally composed of huge irregular fragments of ice from the North. No sooner does the cold weather set in than the river is full of cakes of ice. Under the influence of intense cold, the cakes freeze together and form large ice-fields. These in some narrow pass or across the head of an island gorge together, become stationary, and unite into a strong bridge of ice. The surface of the river above is soon crowded full of ice, and the river is closed. During the formation of an ice-gorge, large cakes of ice are carried by the current underneath the surface-layers to such an extent that the gorge is, at times, a solid mass 20 feet or more in thickness. The scouring action of the water under such gorges is obvious. Since the erection of the Bridge the piers have helped to form an ice-gorge above it, leaving the water clear below. This has proved of great value to the navigation of the lower river, and has caused very deep water between and above the piers. Foundations less deep and strong would have been exposed to great danger.
River ice is regarded as very treacherous. Previous to the construction of the Bridge, the river would occasionally, in mid-winter, be closed to boats and teams for days together; sometimes even the most daring footmen could not cross. At such times, when all communication with the East was suspended, when anxious travellers were visible on the other shore, the people of St. Louis earnestly prayed for a bridge which should put them beyond all danger of an "ice blockade." The river has been known to close early in December, and remain closed till the latter part of February. After freezing over, the water usually rises a few feet, from the action of the ice-gorge.
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There is something almost sublime in the immense volume and apparently irresistible power of this great river. The ease with which it devours island after island, and forms for itself a new channel the wild deluge of waters with which, without apparent loss of size, it covers thousands of miles of fertile fields; and the unequalled strength and depth of its current, — suggest a power so far beyond human control as to seem almost lawless: and yet nothing is more certain than that, in all its moods and phases, it is wholly obedient to nature's laws, and that the engineer who would grapple with the problems involved in the practical management of the Mississippi, must study and master those inflexible ordinances.
Said Charles Ellet, forty years ago: "The power of this great river does not prohibit any attempt to restrain, to force, or to change its current; on the contrary, it may be almost wholly subject to the control of art. Apparently, it varies its depth, alters its direction, reduces or increases its width, with regard only to its boundless power; but these movements are all made in obedience to certain laws, uniform and universal in their action, to the rule of which it is as completely subject as any other effect in nature to the cause by which it is produced. To govern it, the labor of man must be applied with a knowledge of the influences which it recognizes; and that power which renders it apparently so difficult to restrain may then be made the means of its subjection."
While Ellet thus wrote, James B. Eads was studying the habits of the river from the deck of a Mississippi steamboat, or on the bed of the river under a diving-bell. Over thirty years later, after an intimate acquaintance with the river for nearly forty years, Mr. Eads eloquently gave utterance to the same thought:
"It was necessary for this young engineer
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Chapter II. Historical Sketch of Attempts to Bridge the Mississippi at St. Louis.
In 1839, Dr. Carr Lane, then Mayor, addressed the following letter to the Council of St. Louis:—
"MAYOR'S OFFICE, ST. LOUIS, Aug. 20, 1839.
Gentlemen of the City Council: —
I submit a letter addressed to me by Mr. Charles Ellet, Junior, civil engineer, containing the outline of his project for erecting a permanent bridge over the Mississippi at this point, for a sum not to exceed $600,000, and respectfully ask that a joint committee may be raised, to consider and report upon this subject.
I have no hesitation in saying, that if a bridge of the strength and durability of the one described by Mr. Ellet can be built for the sum named in his estimate, the enterprise ought to be commenced, either by this city or a joint-stock company, as soon as the requisite authority can be obtained from our own State and the State of Illinois. Mr. Ellet promises leaving the city in a few clays.
I have the honor to be, etc.,
WM. CARR LANE, Mayor.
The joint committee consisted of Messrs. Hill, Glasgow and Trask from the Board of Delegates, and Messrs. Barry and Sarpy from the Board of Aldermen.
This committee reported August 26 in favor of accepting Mr. Ellet's proposition to make surveys and soundings, and to furnish full drawings and estimates, and present three hundred printed copies of the same to the city for the sum of $1,000. The report was adopted.
Accordingly Mr. Ellet made an examination of the river banks and bed at three points: namely, at Cherry Street, at Market Street, and at Hazel Street (which is referred to as a continuation of Chouteau's Avenue). In all cases rock was readily found on the western side of the river, but in mid-stream and on the eastern shore the sounding-auger met with so much resistance at the depth of about 20 feet that the power at hand was unable to force it further. In his report, Mr. Ellet said: "The material of which the bed of the river is composed is firm enough for the foundation of a basis for the piers of the edifice. It is in fact superior to the soil which sustains some of the most celebrated stone bridges in Europe."
The Council selected the site at Market Street as the one for which plans and estimates should be submitted. In his final Report (which was printed), Mr. Ellet stated that the breadth of the river at low water was 3,444 feet, and its extreme depth at that stage was
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but 12Ë feet. His plan contemplated a suspension-bridge of three spans, the central being 1,200 feet and the side spans 900 feet each, measured from center to center of towers. The available width of the bridge was to be 27 feet, giving two foot-ways of 4 feet each and a carriage-way of 19 feet. The towers were to be made of sufficient width and strength to admit of widening the bridge to 36 feet, "if ever the intercourse should be such as to call for the change." There was not even a thought of a railroad to the river, not to speak of one over it.When it is known that at that time the greatest bridge-span ever constructed was only 889 feet (that over the valley of the Sarine at Freiburg, erected by Mr. Chaley), it will be seen that in proposing to erect a span of 1,200 feet upon towers standing in the Mississippi river 1,000 feet from either bank, Mr. Ellet was entitled at least to the credit of great courage. Although it is probable that his bridge had it been built would have suffered during the high water of 1844 and other floods, there is no question but that his plan displays great originality and skill.
His river piers were to have bases 77 by 67 feet, and were to be about 200 feet high. His plan for securing foundation for a pier was first to construct a circular wall of sheet piling 140 feet in diameter; next to sink a circular curb 120 feet in diameter within the sheet-piling. This curb was to consist of twenty-five or more equal hoops, made of timbers 14 inches square securely bolted together. The lowest hoop was to have an iron cutting-edge, and the curb was to be loaded while the river-bed within should be excavated to a depth of 10 or 12 feet below the bottom of the river. Piles were then to be driven as far as possible (estimated at 40 or 50 feet) and as thickly as possible within the curb, and the spaces between them to a depth of 6 feet filled with concrete. A second curb 100 feet in diameter, similar to the first and concentric with it, was then to be sunk to the concrete. These two curbs were to form the walls of a coffer-dam. Two more feet of concrete in the centre and a complete filling of the space between the curbs with concrete and pudding would complete the dam. The water was then to be pumped out, the piles cut off and framed into cross-timbers which with the concrete would bind all the piles into one rigid mass. Two layers of cross-timbers imbedded in more concrete was to furnish the foundation for the first course of masonry. After the building of the pier the dam was to be filled with rock and an embankment of rock was to surround the whole structure.
"No apprehension need be entertained lest the piling should be undermined by the action of the river. The bed of the Mississippi, though very unstable, and composed of a material which readily shifts from place to place with changes in the regimen of the river, is not disturbed, where the width which it possesses at St. Louis is maintained, to a greater depth than would be protected by the sheet-piling." — Ellet's Report, p. 29.
There is no question of the stability of such a pier during ordinary stages of the river; but a rapid scour, such as occurred during the construction of the East Pier of the present Bridge [described on page 5], would have seriously imperilled if not overthrown Mr. Ellet's bridge. It is due to Mr. Ellet to say, however, that comparatively little was known at that time of the habits of the river. Had he been living in 1867, there is little doubt he
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would have opposed the construction of a river pier at St. Louis that should stand on any foundation less secure than the rock itself.Mr. Ellet's Report contains careful calculations based on actual experiment for his wire cables. They were to be formed by parallel wires, each about one-eighth of an inch in diameter, 1,200 in number, making a cylinder about 5 inches in diameter. Ten such cables were to support each span. The ultimate strength of iron wire was assumed to be 98,560 pounds per square inch. He added: —
"Experience has taught us that it is injudicious, if not unsafe, to load a bar with a permanent charge exceeding the third part of the weight which could draw it asunder. The greatest weight, therefore, with which a cable presenting a section equal to one square inch should be permanently charged is 32,853 pounds."
In discussing the limit to the length of spans in suspension-bridges, he said that the greatest distance to which the points of support of a wire cable carrying only its own weight could be safely removed from each other, the versed sine being one-twelfth, was one and one-fifth miles. Suspension-bridges may approach, but they can never reach, that length of span!
It is not strange that the Mayor and City Council stood aghast at such language, and held the views of their engineer as extravagantly wild and unsafe. It is certain that the report fell very flat upon the city fathers, and that they felt relieved when they had paid Mr. Ellet his $ 1,000, and he was safely away. The Mayor closed all discussion by saying, in the communication accompanying the 200 copies of the Report he sent to the Council: "The time is inauspicious for the commencement of an enterprise involving such an enormous expenditure of money." The entire estimate was $737,566.
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In 1855 Mr. Josiah Dent, then a resident of St. Louis, obtained charters from the States of Missouri and Illinois, authorizing the formation of a company for the purpose of erecting a railway suspension-bridge over the Mississippi at St. Louis. The bridge was to be 90 feet clear above high water. This great height was intended to disarm the jealous opposition of the steamboat interests. The only railroad leading into St. Louis at that time was the Missouri Pacific, which had been built as far as Washington, Mo.; but roads were building from the East. Mr. Dent was assisted by Gen. Frank P. Blair, Mr. Benjamin Farrar and others in St. Louis, and Col. "Waite and Gov. Palmer of Illinois. John How, Esq. of St. Louis was elected President of the company, and Maj. J. W. Bissell, who had been connected with Charles Ellet in the construction of the first Niagara bridge, was retained as engineer.The site selected was near the foot of Cass Avenue. Drawings and estimates were made for a bridge containing a single span of 1,500 feet. The cost was placed at $1,500,000. It is doubtful if the plan was fully matured. Subscriptions amounted to only $25,000 or $30,000, and then the project was abandoned. The railroad interest was not at the time sufficiently powerful for such an enterprise.
It was at about this time that Mr. John A. Roebling, having successfully built the Niagara bridge, prepared a plan for a suspension-bridge over the river at St. Louis containing a very long span.
Later in 1868 he prepared several plans for a bridge at St. Louis, combining both suspension cables and parabolic arches. The spans shown on the drawings were 500, 600, and 800 feet in length. The plans were published in 1869, after the death of Mr. Roebling.
In 1865 Council of the City of St. Louis moved again in favor of a bridge.
Premising that it had "become indispensably necessary to erect a bridge across the Mississippi River at St. Louis, for the accommodation of the citizens of Illinois and Missouri, and the great railroad traffic now centering there," it was resolved to appoint a committee who should consider and report on the exigency; and to instruct the city engineer, Mr. Truman J. Homer, to report information touching the erection of a bridge, accompanied by general plans and approximate estimates of cost, etc.
Four days afterwards, "as the result of much thought and extended inquiry upon the subject," Mr. Homer submitted a very elaborate report, which was printed.
Mr. Homer proposed a tubular bridge of three spans of 500 feet each between centers, at a height of only 30 feet above the city directrix, or about 22 feet above high water. His tube was Stephenson's Britannia Bridge slightly enlarged. His method of erection was not given. The foundation of his piers was to be on the rock, if that could be found within 40 feet of low water; otherwise, large iron cylinder piles were to be sunk to the rock by the pneumatic process. At that time no borings had been made to the rock on the Illinois shore. In defence of the small head-room for steamboats, Mr. Homer asserted that all steamboats could easily be made to pass under an object 44 feet high, and that
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during 343 days in a year, the clear space was at least 44 feet. Hon. Erastus Wells was chairman of the committee referred to. In his report he said: —"The chimneys of steamboats may be so constructed as to admit of their being conveniently and expeditiously raised and lowered at will, so as to admit of their passing under an object 35 feet above the surface of the water; and Congress may as legitimately legislate upon these particulars as upon the construction and operation of the steam apparatus."
The estimated cost of the bridge, including approaches, as given by Mr. Homer, was $3,332,200.
It does not appear that anything was effected by the publication of these reports beyond the creation of a livelier interest in the subject, and a growing conviction that a good bridge was to cost a good deal of money.
12
Chapter III. The Organization and Work of the St. Louis and Illinois Bridge Company.
The initiatory steps in the formation of this Company were taken by Hon. Norman Cutter in 1864. This gentleman was at that time a member of the State Senate. He drew up the charter, inserting the names of such St. Louis men as were likely to aid the enterprise. Previous charters, and the discussions to which they had given rise, enabled him to frame a liberal charter and to secure its passage by the General Assembly. In the House, Mr. Cutter's name was added to the list of incorporators. The charter was approved February 5, 1864. The list of incorporators was as follows: Norman Cutter, E. O. Stanard, Joseph Cabot, Edward C. Pike, John A. Lightner, Hugh McKittrick, S. G. Read, Rufus Fitch, George D. Hall, John H. Beach, Chas. Miller, H. A. Doan, John H. Bowen, E. H. Sterling, James H. Wear, James E. Blackmail, Clinton O. Dutcher, John H. Siegrist, Wm. D'Oench, C. Reuss, Robert Heinrichshofen, Jacob Woodburn, Chas. F. Meyer, Robert H. Ober, Chauncey I. Filley, B. E. Bonner, Charles H. Howland, E. H. E. Jameson.
In January, 1865, Mr. Cutter visited the Legislature of Illinois at Springfield, and procured the introduction of a bill granting the supplementary charter. The bill met with strong and bitter opposition from the friends of the Wiggins Ferry Company, a wealthy and influential corporation at St. Louis, having a practical monopoly of transfer privileges. The bill was finally passed with amendments which were intended to render the charter useless. The chief amendment required that the Bridge should be located within 100 feet of Dyke Avenue in East St. Louis. It was the openly-confessed object of this amendment to kill the enterprise by rendering the acquisition of depot-grounds and the construction of a road through the city fatally expensive. It is doubtful if the idea of a tunnel under the streets of the city ever occurred to the managers of the Ferry Company. Now that the Bridge has been actually built on the ground thus grudgingly granted, the location seems so wise that one is almost inclined to regard the amendment as a blessing in disguise. The bill was approved February 15, 1865.
At about the same time (February, 1865) the Missouri charter was amended. The charter had stipulated that "said bridge shall be constructed of stone, iron, and wood, but mainly of iron and stone. The Company shall have power to determine what kind of abridge shall be built, — whether suspension, tubular, draw, or otherwise; but whatever kind it may be, it shall be so constructed as not to obstruct or impede the navigation of the river." It was to be both a highway and a railway bridge, and if built with a draw, was
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to have at least two openings, each 100 feet wide. The amendments repealed the above section, and provided that "said bridge shall be built of such materials and upon such plans as the Board of Directors shall decide to be most suitable for the uses required of it." They also required that the Bridge should be "sufficiently high to admit of steamboats and all other river craft passing under it, at all ordinary stages of the river, when the chimneys, pipes, and other projections are lowered down." A section was added authorizing the City of St. Louis to subscribe for any amount of said stock, "not to exceed one million dollars," etc. The following names were inserted among the incorporators: Truman J. Homer, Carlos S. Greeley, J. D. Barlow, E. W. Fox, John M. Krum.Thus furnished with proper authority from the two States, the friends of the enterprise asked for the authority of Congress, as it alone has jurisdiction over navigable rivers. Hon. B. Gratz Brown, at that time in the United States Senate, took a lively interest in the matter. He introduced a bill confirming the charters of Missouri and Illinois, and granting the right to cross the channel. This bill encountered great and unexpected opposition from railroad companies interested in lines of trade and travel across Northern bridges, and from steamboat interests. It was amended and made a part of a bill to "authorize the construction of certain bridges, and to establish them as post-roads," which, in July, 1866, passed through both houses of Congress and received the signature of the President.
The original bill had been so amended that it seemed almost impossible to construct a bridge under its provisions. This act forbade the use of a suspension-bridge, but required either two spans of at least 350 feet each in the clear, or one span of 500 feet, and a height of 50 feet from the lower chord to the city directrix. A span of 500 feet was regarded as wholly out of the question, and two spans of 350 feet each seemed to involve so much masonry in the midst of a deep and rapid stream, that the construction of the bridge under the provisions of the act was not generally regarded as probable.
The act of Congress making the Bridge and its approaches a post-road, virtually placed it under the protection of the United States, and made it independent of State legislation.
Pull authority having now been obtained, it was time for the corporators to act. A meeting of five of the corporators, Messrs. J. D. Barlow, E. W. Fox, Charles H. Howland, E. H. E. Jameson, and John H. Lightner, had been held February 19, 1866, at which the charter and its amendments had been accepted. Mr. Lightner was chosen president, and Mr. Fox vice-president, Mr. Howland secretary, and Mr. Barlow treasurer. They had then adjourned, to meet at the call of the president. This first meeting had been held at Jefferson City, and was pro forma.
Meanwhile Mr. Cutter kept possession of the charter and endeavored to interest capitalists and bridge-builders in the undertaking. Several parties visited St. Louis to examine the location and to discuss plans. It was reported that negotiations had been entered into with English and other capitalists, but that none would invest their money in the enterprise without first obtaining certain amendments to the Illinois charter. Prominent among such outside parties was Mr. L. B. Boomer, of Chicago. He sought out Mr. Cutter and endeavored to get the contract for the Bridge. Mr. Cutter had no authority from the corporators, but he nevertheless after much controversy came to an understanding with Mr. Boomer substantially like the following: First, that Mr. Boomer and a committee of
14
the Company should go before the next Legislature of Illinois and ask for certain amendments to the Illinois charter, to wit: one, giving them the exclusive right to bridge the liver for the next twenty-five years, and that their bridge must be begun within two years and completed within five; a second, repealing the clause limiting the location of the bridge; and a third, providing that a majority of the directors of the Company should be residents of St. Louis. It was further agreed that Mr. Boomer should have the contract to build the Bridge. Mr. Boomer was a bridge-contractor by profession.Consequently a meeting was called December 18, 1866, at the office of Judge John M. Krum, in St. Louis. There were present besides Judge Krum, Messrs. Barlow, Pike, McKittrick, Miller, Lightner, Howland, Beach, Cutter, and Fitch. Judge Krum was chairman. The charters were read, and a committee was appointed to open books and solicit subscriptions to the capital stock. This committee consisted of Norman Cutter, Judge Krum, and John H. Beach. The necessary amendments to the Illinois charter were discussed and the same committee of three were instructed to secure the amendments, if possible. One amendment thought to be desirable, was to modify and simplify the methods of condemning ground for the use of the Bridge Company. Others were those agreed upon by Messrs. Cutter and Boomer.
Messrs. Krum and Cutter went to Springfield to get their charter amended. Mr. Boomer and his lawyer, Judge Beckwith, met them. They experienced no difficulty in getting the necessary bill introduced. It passed the House almost unanimously, and as there seemed to be no opposition in the Senate, the committee were satisfied to leave the matter in the hands of Judge Beckwith. After several weeks of what appeared to be very unnecessary delay, the committee in St. Louis were astounded to hear that a bill had been introduced to repeal the charter which they had sought to amend, and that they were opposed by their former allies, Messrs. Boomer and Beckwith. Delegates from St. Louis did what they could for their bill, but the tide had turned. Fortunately the repeal-bill was defeated, but the amendments were hopelessly lost. In fact they had been met in the Senate by a substitute embodying the amendments originally asked for by Messrs. Cutter and Boomer (including the exclusive right to build a bridge, etc.) in the provisions of a full and liberal charter, under the title of, "An Act to Incorporate the Illinois and St. Louis Bridge Company," and in which both Messrs. Boomer and Beckwith were named as incorporators.
When it was reported on the streets of St. Louis that legislation adverse to the interests of St. Louis was pending at Spring-field, the excitement was intense. Charges of corruption and treachery were plenty, and the friends of the Company were troubled lest the result should be a delay of several years in the building of the Bridge. Meetings, of which Mr. James B. Eads was chairman, were held on 'Change, and a committee consisting of "Wm. A. Pile, Judge Krum, and Josiah Fogg, were selected to visit Springfield and protect the interests of St. Louis. In spite of all that could be done by this committee, the bill granting the new charter passed, and was approved by Gov. Oglesby February 21, 1867.
The action of the Illinois Legislature seems at first quite unaccountable, as it was clearly irregular for them to grant a charter in direct conflict with a charter previously granted and still valid. Personal explanations subsequently made, however, leave no doubt
15
but that the general impression was that the friends of the two charters were substantially the same, and no controversy was expected in the matter. Those who understood better the motives of Mr. Boomer and his friends, saw in the new charter a means of either preventing the building of a bridge, or of giving its construction into the hands of Chicago capitalists, or of forcing St. Louis to an expensive compromise.Meanwhile, finding that nothing was to be gained from the Legislature of Illinois, the friends of the enterprise had resolved to organize and commence operations under the charters already granted. At this time Mr. James B. Eads came forward and took a leading part in the undertaking. February 17, 1867, a meeting of the stockholders was held at the Southern Hotel. The record shows that Charles K. Dickson, James B. Eads, Joseph C. Cabot, John M. Krum, John H. Beach, and James R. Blackman were present. At this time the pledged subscriptions to the stock amounted to $300,000. March 23, at the Planters' House, the stockholders organized by the election of C. K. Dickson as president pro tem., and on motion of Josiah Fogg, Esq., James B. Eads was elected engineer-in-chief. Mr. Eads at once secured the services of Henry Flad as his first assistant engineer. Col. Flad was at the time a member of the Board of Water Commissioners of the City of St. Louis. New surveys, soundings, and borings were made, and the outline of a plan was soon prepared.
May 1, the first Board of Directors was chosen by the stockholders; they were: Charles K. Dickson, James R. Blackman, James B. Eads, Amos Cotting, William Taussig, Barton Bates, Thomas A. Scott, Josiah Fogg, John R. Lionberger. The Directors immediately organized by the election of Mr. Dickson president, Mr. Blackman vice-president, Mr. Cabot secretary, and Mr. Cotting treasurer.
The action of the stockholders appointing Mr. Eads chief engineer was confirmed, and fifteen per cent of the capital stock was called for, to be paid during the succeeding three months.
On the 5th of June Messrs. Robert Lenox Kennedy and Henry F. Vail of New York City were admitted to the new Company as stockholders. In September and October the following new subscribers were received: Messrs. E. D. Morgan and John A. Ubsdell, of New York; Mr. Thomas D. Gaylord, of Cincinnati; and Messrs. John J. Roe, Gerard B. Allen, John Knapp, and Wm. M. McPherson, of St. Louis. The subscriptions of these gentlemen, as well as of the earlier stockholders, were arranged to be 200 shares, or $20,000 each. During the summer Mr. Blackman, the vice-president, and Mr. Cabot, the secretary, resigned, and their places were respectively filled by the election of Mr. Barton Bates and Mr. John A. Dillon.
On the recommendation of Mr. Thomas A. Scott, the assistance of Mr. J. H. Linville, of Philadelphia, bridge engineer of the Pennsylvania Central Railroad, was secured as consulting engineer. Mr. Linville was known to be an eminent engineer, and it was hoped that his connection with the Pennsylvania Central would help to secure the co-operation of that powerful company. His connection with the St. Louis Company, as engineer, was of short duration. Outline sketches of Mr. Eads's plans, involving the long span arches, were submitted to him for suggestions in regard to the still undetermined details. From the first Mr. Linville was opposed to the use of either the braced or the ribbed arch, and doubted if
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steel in pieces of sufficient size could be obtained to construct the ribs. He wrote, in reference to the first skeleton sketch: "I cannot consent to imperil my reputation by appearing to encourage or approve of its adoption. I deem it entirely unsafe and impracticable, as well as in fault in the qualities of durability." He then submitted his views of the character of structure required, which was that of a truss-bridge, supported by three girders or trusses, each having an arched upper chord with a versed sine of 25 feet for the 500 feet span. The method of erecting Ms. bridge, which he regarded as an "undertaking of not much practical difficulty and involving no great risks," was to construct each truss complete on temporary piers at a sheltered point below the site of the bridge, on eight or ten pontoons, haul it into position between the piers of the bridge by cables, and then raise it vertically to its final resting place by hydraulic presses placed under its ends.Mr. Linville's hasty condemnation of plans not yet matured, and the uncalled-for submission of plans of his own, could have but one result with a Board of Directors who were satisfied with the skill and resources of their own engineer. It was voted, July 11, to dispense with the services of a consulting engineer.
On the 15th of July Mr. Eads had so far progressed in his investigations as to be able to present to the Directors an outline of his plans. The general features, as then determined upon, were adopted. They included the use of steel arches, the approximate length of the spans, and the construction of stone foundations for the river piers reaching to the solid rock. All these points were then settled and published to the world. The details were properly left for future determination. At this time Mr. Eads was authorized to commence active operations as soon as, in his judgment, it was for the interest of the Company to do so.
At the same time an Executive and Financial Committee of four was appointed, with Dr. Wm. Taussig as chairman. Dr. Taussig filled this difficult and responsible position until the completion of the Bridge, with great credit to himself and benefit to the Company. He was immediately authorized to open negotiations with proper persons in Europe with a view to effecting a loan secured by a mortgage on the Bridge and its franchises.
Permission having been granted by the Mayor of the city (Hon. Jas. S. Thomas) to appropriate a portion of the levee at the foot of Washington Avenue, work was actually begun August 20, 1867.
The coffer-dam for the West Abutment was completed November 25, and excavating and lifting machinery was then erected. The unexpected difficulties encountered in the construction and maintenance of an efficient dam (see page 32) had a discouraging effect upon the friends of the enterprise. But these material difficulties were not by any means the worst which the Company had to face. The active opposition of a powerful company was a much more serious and costly affair than sunken wrecks and leaky dams. This book would be very incomplete did it not contain the full history of both the rise and progress and the decline and fall of Mr. Boomer's Company. That history, therefore, will soon be given.
For the sake of complying with all legal forms, a meeting of the incorporators named in the Missouri charter
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the amount of $400,000 was immediately subscribed. After due notice the stockholders of the St. Louis and Illinois Company met at the National Hotel, East St. Louis, on February 22, 1868, and elected a Board of Directors, who immediately organized by the election of officers. The organization was throughout the same as that of the Missouri Company. It only remains to be said of the St. Louis and Illinois Bridge Company, whose corporate existence under that name and style was less than a year, that it has the credit of actually laying the first stone in the great undertaking. With great difficulty the coffer-dam had been partially freed of mud and water, and the underlying rock had been properly dressed and prepared for the masonry of the Western Abutment. On the 25th of February, 1868, the ceremony of laying the corner-stone was observed. In the presence of the officers of the Company, the city government, and invited guests, a massive piece of Grafton limestone was lowered to its resting place, some twenty feet below the surface of the river. It was adjusted to its proper bed by Mr. Eads in person, assisted by Mr. Benjamin E. Singleton, the superintendent of the work. In the language of a reporter, amid much applause "Mr. Eads stepped in triumph upon the corner-stone" and announced that the Bridge was actually begun.18
Chapter IV. The Boomer Company and the Consolidation.
Meanwhile the rival company was in the field. As soon as it was certain that his charter would he granted, Mr. Boomer and nine other persons, all residents of Illinois, organized a company in Missouri, under "An Act Concerning Private Corporations," on the 19th of February, 1867. The name was declared to be the Illinois and St. Louis Bridge Company, "and under that name and style [it] shall continue to exist for the term of one hundred years." Messrs. L. B. Boomer, K. P. Tansey, W. E. Morrison, Geo. Judd, and C. Beckwith were named as directors to manage the affairs of the company for the first year. The capital stock was fixed at $1,000,000.
The Board of Directors of the above company met on the 11th of March, and organized by the election of Judge Beckwith as president, Mr. Tansey as secretary, and Mr. Boomer as treasurer. Measures were at once taken to unite the interests of this company with the Illinois and St. Louis Bridge Company just organized in Illinois. Later (October 6, 1867) all the other stockholders assigned their stock to Mr. Boomer, and then he assigned all his to the Illinois and St. Louis Bridge Company of Illinois, which thus became the sole stockholder and owner of the franchise of the Missouri company. For this transfer Mr. Boomer was allowed $10,000. On the 6th of January, 1868, the Missouri company voted to unite with the Illinois company bearing the same name.
On the first day of March, 1867, the incorporators named in the charter just granted by the State of Illinois met at Springfield, Illinois, and organized. The subscriptions to the stock of the company showed that Mr. Boomer took 5,250 shares and all others 192 shares. Messrs. Boomer, Tansey, Judd, Beckwith, and Morrison were elected directors; Mr. Boomer was elected president, and Mr. Tansey secretary. Eight days later Mr. Boomer was elected treasurer, and he was authorized to employ the best engineering talent in the country to assist in the enterprise. Accordingly Mr. A. Anderson of Kansas and Mr. S. S. Post of New Jersey were engaged as chief and associate engineers, while Messrs. W. J. Mc Alpine of New York, George A. Parker of Pennsylvania, E. S. Chesborough of Chicago, Gen. W. S. Smith of Michigan and L. J. Fleming of Alabama were engaged for professional work upon the problem of bridging the Mississippi at St. Louis.
It is but just to all parties for the writer to record here after a very full and impartial examination of all the facts that he is of the opinion that Mr. Boomer and his associates
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were at this time entirely sincere in their expressed intention to build a bridge at St. Louis and according to the terms of their charter. With full legal authority on the Missouri shore and an exclusive charter in Illinois, what rival or what opposition could he find? With the approval of his charter it was expected that all faith in the "defunct Cutter charter," as the charter of the St. Louis and Illinois Company was called, would be lost, and Mr. Boomer was doubtless very much surprised to find that Mr. Eads, instead of abandoning the field, pushed on with renewed energy to get his plans before the public and to secure the co-operation of capitalists. Where Mr. Boomer expected to have things all his own way he found himself opposed by one who possessed to an uncommon degree the confidence of his fellow-citizens, and who united to the skill of an engineer great executive power and unusual resources as a financier. With dismay Mr. Boomer saw capitalists both at home and from New York coming to the support of the St. Louis Company, while he and his entire enterprise were popularly regarded with distrust. It was, beyond question, unfortunate for his undertaking that Mr. Boomer was from Chicago, a rival city. To many, that single fact was sufficient to subject his motives to suspicion, and frequent utterances from Chicago men and in Chicago papers gave color to this suspicion.The strong determination on the part of St. Louis men to build and control their own Bridge, and an obvious firm reliance on the validity of their charters, left Mr. Boomer only the alternatives of driving the other company from the field or of withdrawing himself. Two bridges were clearly out of the question. Of the two courses open to Mr. Boomer he chose the former; he resolved to break down the St. Louis Company. We shall see with what success his efforts were crowned.
Three methods of breaking down his opponents offered themselves to Mr. Boomer. The first was to bring discredit upon their plans while recommending his own. This was to be done through the instrumentality of a
Preparations were accordingly made and elaborate reports were prepared. At least nine different engineers of reputation were set to work by Mr. Boomer upon the various problems involved, while especial prominence was given to the question of a 500 feet span for the Bridge. The convention called by Mr. Boomer met at St. Louis on the 21st day of August, 1867. The following is a complete list of the engineers invited to be present (according to what appeared to be an official list given in the St. Louis papers): W. J. McAlpme, C. L. McAlpine, Gen. W. S. Smith, Geo. A. Parker, E. S. Chesborough, W. S. Merrill, E. B. Mason, T. B. Blackstone, L. H. Clark, E. H. Johnson, S. S. Post, S. F. Johnson, T. McKissock, J. B. Moulton, O. Chanute, Jas. H. Morley, A. Anderson, T. J. Homer.
On motion of Col. Anderson, Mr. Boomer's chief engineer, Wm. J. McAlpine, who
20
had been engaged at the request of Mr. Boomer upon the subject of the Foundations, was chosen president. In the appointment of the committees it was natural that Mr. Post should be the chairman of the "Committee on Superstructure and Approaches," and that the entire "Committee on Foundations and Piers" should be composed of Mr. Boomer's employees. Mr. Boomer's name nowhere appears in the published Report of the Convention, though he was present and took part in the business meetings. When the question as to the time when the various committees should report came up, Mr. Boomer objected to delay. The convention met on Wednesday. The Missouri Republican of the succeeding Monday morning contained the following carefully written paragraph: —"These investigations [of the convention] have covered the entire ground. The most intricate problems of engineering science have been patiently solved; the strength of materials estimated; the safe length to which spans may be extended calculated; the comparative value of different kinds of piers and foundations determined upon; and every point connected with practical bridge-building elucidated in the light of the most thorough and scientific knowledge and the most varied and extensive experience."
This was certainly doing remarkably well. The greater part of the convention left St. Louis within a week, but certain gentlemen remained to make up the Report.
No sooner was the convention over than an effort was made to spread the impression that it had discussed the general question of spans and foundations "without reference to any particular plan or company." Some little pretence of the same thing appeared during the first day of the convention. On page 8 of the Report we find: —
"On motion it was ‘Resolved, that an invitation be extended to any parties having plans to suggest to attend the meeting and submit them for the consideration of the convention.’
Pursuant (?) to the above the following invitation was sent: —
ST. LOUIS, August 21, 1867.
Sir: A Board of Engineers and gentlemen interested in the question of crossing the Mississippi River at St. Louis by a highway and railroad bridge have met at St. Louis this morning and on motion it was
‘Resolved, that the gentlemen of St. Louis most interested in this question be invited to attend the meetings and unite in the discussion of the various important questions connected with this subject.’ In accordance therewith the Board respectfully invite you to meet them at the Southern Hotel, Parlor No. 6, at your convenience. * * *
Respectfully yours,
WM. J. McALPINE, President."
From their own Report it is obvious that the resolution passed by the convention was not the one sent. It is said that a copy of this note was left at the office of Mr. Eads and another was sent to Col. Flad. It thus appears that Mr. Eads was not invited to submit his plans to the convention.
Again, an effort was made to create the belief that Mr. Eads's plans were made the object of special examination by the convention. This was done by incorporating into the printed report of the president's opening speech parts of two other speeches, and some things which he never said. There is nothing in any of President McAlpine's speeches as reported
21
at the time in the newspapers to show that he referred at all either to the St. Louis Bridge Company or to the plans of Mr. Eads.The Report of the Convention puts into his month this entirely unauthorized statement: —
"Your attention will also be called to a plan for building stone piers based upon the rock, the details of which have been recently published in this city and which will be laid before you. This published plan contemplates the use of three spans of about five hundred feet each."
This positive statement with not even a subsequent hint that the promised plans never appeared before the convention, was plainly intended to give to those who should rely upon the printed Report for then knowledge of the proceedings the idea that the plans of Mr. Eads, as well as those of Mr. Boomer's engineers, were under discussion and that the former were disapproved. Under the circumstances, one can hardly understand why the Committee on Foundations and Piers were allowed to adopt the following honest resolution: —
"Resolved, that in the opinion of this committee it is safe and practicable to construct a bridge at St. Louis of the character of the one which we have had under discussion." [The italics are mine. — ED.]
No other form of superstructure nor even any other truss than Mr. Post's patent truss was considered by the convention. A fine drawing, 12 feet long by 4 feet wide, giving an elevation of the truss-bridge designed by Mr. Post, was displayed to the convention and was much admired. It had two spans of 368 feet, and four of 264 feet.
Had Mr. Boomer been really anxious to make a just comparison of various plans and to call out the views of the best engineering talent in the country, he would not while sending his invitations in all directions have failed to include among the first such widely known engineers as James B. Eads and Henry Flad. In fact it is so clear that neither the engineers nor the plans of the St. Louis and Illinois Bridge Company were wanted that nothing more need be said on that point.
Although not formally discussed, nor even explicitly mentioned, it is clear that Mr. Eads's plans were continually in the minds of the prominent actors, and especially were they kept in view by those who framed and edited the reports. In asserting (General Report, p. 80) that "in no case does the scour extend to a greater depth than 30 feet below low water," Mr. Eads's deep foundations were of course aimed at.
The convention contained much ability and the contributions of several of the engineers were worthy their authors; but there was a common theme upon which every set of resolutions was most emphatic, namely, a disapproval of a 500 feet span either on the ground of safety, or economy, or "authority." This, the main point of the convention, is best shown by a few quotations from their resolutions and reports: —
"Resolved, that we as practical engineers cannot conscientiously recommend to the parties in interest to venture upon the construction of spans of as great length as the maximum one prescribed by law [500 feet]. * * *
"Resolved, that in view of all the circumstances of this case, we would recommend spans of less than three hundred and fifty feet in the clear, if the Federal law permitted such reduction." — Committee on Foundations and Piers.
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The "Joint Committee on Foundations and Superstructure" expressed by resolution "their unqualified disapprobation of spans of 500 feet."
"The Joint Committee on the Regimen of the River, on the Foundations and Piers, and on the Superstructure discussed the alternative proviso of the law in regard to the length of the spans across the main channel, and unanimously agreed that it was inadvisable to adopt the span of 500 feet clear opening, on account of the difficulty of procuring suitable materials of the proper form, size, and workmanship required to meet the extraordinary strains to which some of the members of the truss would be subjected; the increased hazard of its construction and maintenance; the large additional cost of the whole structure by the use of the long span; and because the necessities of this case do not require the use of one of such great length for which there is no engineering precedent." — General Report, p. 79.
When the Report had been properly revised to suit Mr. Boomer's plans, it was
"Resolved, that all the members present [there were very few left] be requested to sign the same [the General Report] before its publication, and that a copy be sent to each member not present, with the request that he shall affix his name thereto and return to the president at St. Louis." — By the Convention, August 31, 1867.
In consequence of this last resolution, the Report as printed is signed by twenty-eight gentlemen, all engineers, about one-half of whom took no active part in the convention.
This convention fell quite flat upon the community of St. Louis. Its object was so well understood and so little sympathized in that no one was deceived. It is even probable that such ex parte proceedings made friends for the St. Louis Company. Work on the West Abutment was begun the very day the convention met, and, in spite of difficulties of all sorts, the work was continued through the autumn and winter without break. Stockholders of the St. Louis Company continued to pay their monthly assessments and new stockholders were added. About September 30, Mr. Eads's plans were shown in drawings exhibited on 'Change and compared with those of Mr. Post. The stability of his piers which were to have no other foundation than the solid bed-rock below the river the wide and lofty spans; the beautiful proportions of the Bridge and the open view commanded by its spacious high way, did not fail to arouse the admiration of all. Said the Republican: —
"The steamboat men seem much pleased with its great arches, and the fact that but two piers will be placed in the channel."
Thus this grand move of Mr. Boomer failed, but it narrowly missed success. Had there been less courage, less indomitable energy, less engineering ability in the St. Louis Company, it would have surrendered. As it was, its operations have seriously embarrassed. A feeling of distrust and uncertainty was created, especially away from home, which, when the real difficulties of the great undertaking came to be better understood, rendered its progress extremely slow and costly. It is not easy to say what "might have been," but it
23
is strictly within reasonable limits to say that the measures of Mr. Boomer cost the Bridge Company hundreds of thousands of dollars and delayed the erection of the Bridge more than a year.Mr. Boomer's first attempt to break down the St. Louis Company having failed, he resorted to his second move.
This consisted in a reorganization of his company which should, apparently at least, throw its management into the hands of St. Louis men. Whatever success the convention achieved abroad, it certainly failed at home, and Mr. Boomer deemed it essential to the end in view to make friends in St. Louis. A few St. Louis gentlemen had by this time been prevailed upon to take some stock in Mr. Boomer's company; and it was thought that their names would serve to give to the company such standing as would render it popular with the citizens of St. Louis. Consequently, on November 25, 1867, Messrs. Boomer and Beckwith resigned, the former as director and president, and the latter as director. Mr. Boomer had already been relieved of the duties of treasurer by Mr. Tansey. The vacant directorships were filled by Messrs. J. R. Stanford and D. Gillespie, both of Illinois. The number of directors was also increased by the election of Messrs. D. E. Garrison, C. P. Chouteau and James Harrison of St. Louis. Mr. Garrison was then elected president. The next day and for about a month subsequently, the following advertisement appeared in the Missouri Republican: —
"ILLINOIS AND ST. LOUIS BRIDGE COMPANY. — Daniel K. Garrison, president; E. P. Tansey, secretary and treasurer; S. S. Post, engineer. Board of Directors: D. B. Garrison, James Harrison, C. P. Chouteau, H. C. Creveling, Luther C. Clark, J. E. Stanford, W. E. Morrison, David Gillespie, George Judd, E. P. Tansey."
It is perhaps a matter of small importance, and yet it indicates better than anything else can the loose and provisional nature of this new organization, to say that as far as the records of the company show there is no evidence that Mr. Clark of New York and Mr. Creveling of St. Louis had any connection with the company, while Messrs. Chouteau and Harrison had not yet subscribed for any stock. On November 25 the stock was held as at first (see p. 18) except that Mr. Garrison had subscribed for 150 shares. In December, 1867, Mr. Harrison, who represented large manufacturing interests, offered to subscribe heavily, provided his shares could be paid for in iron. Mr. Boomer objected, and his offer was after some delay declined.
No sooner was Mr. Boomer freed from the responsibilities of office in a company where he owned fifteen-sixteenths of all the stock than he rushed into print, obviously for the purpose of calling public attention to his new move. On the very day of Mr. Garrison's election, he wrote the following letter to the editor of the Republican: —
"ST. LOUIS, November 25, 1867.
Recent publications in your columns, and in those of other city papers, charging ulterior purposes on the part of the company which I have heretofore represented, require a brief reply. Fairness requires that you should give this reply as prominent a place in your columns as you gave the unfounded charges referred to.
First, then, it is not true that I represent Chicago, or any parties in that city except myself.
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Second. The Illinois and St. Louis Bridge Company is duly incorporated under the laws of Missouri, and, by special legislative act, under the laws of Illinois, with an exclusive right in that State, in St. Clair County, for twenty-five years.
Third. Every step so far taken by this company has been with a view to the earliest, safest and most economical construction of a bridge opposite this city on the best scientific principles; and in furtherance of this end it is true, as charged, that I have succeeded in enlisting in the enterprise prominent gentlemen of this city, whose names are identified with her growth and prosperity.
I have not sought, and do not now desire, a newspaper controversy for the purpose of interfering with the plans of others; but as this has been begun and persistently continued against the Illinois and St. Louis Bridge Company, I will merely say that the structure now being commenced at Washington Avenue is, in my judgment, if not IMPRACTICABLE, needlessly and extravagantly costly in plan, and the so-called St. Louis and Illinois Bridge Company has no legal existence or chartered rights in Illinois, and, as held by some of the best lawyers in this city, is yet a mere copartnership in Missouri.
The first proposition, as to the cost and impracticability of the plan, I am prepared to discuss before any board of engineers in the country, and abide the decision of such tribunal.
The question of the legal existence of that company in Illinois, the Illinois and St. Louis Bridge Company is willing to submit, on an agreed case, to the decision of either State or United States Court, and perfectly willing to abandon the field if the decision shall be adverse to it.
An early settlement of these practical questions would tend more to the speedy construction of a bridge than bandying epithets or abusing Chicago in the columns of the newspapers.
Respectfully,
L. B. BOOMER."
This was followed the next day by a rejoinder from Mr. Eads: —
"ST. LOUIS, November 26, 1867.
MR. EDITOR: My attention has been called to the communication of Mr. L. B. Boomer of Chicago in your issue of this morning. It is unnecessary for me to notice more than one portion of his letter.
Mr. Boomer pronounces the plan of the bridge I am constructing at Washington Avenue impracticable and extravagantly costly.
I have only to reply that Mr. Boomer has never examined the plans of this Bridge, and knows nothing whatever of the estimate of its cost, save the gross sum that has been published by newspaper reporters, and which is $1,500,000 less than the published estimates of his own bridge.
The plans and calculations for the Bridge I am building have been most cheerfully shown by me to every engineer who has called to inspect them. I am, and hall continue to be, most happy to show and explain them to any engineer of respectable standing in the country at all times, and shall esteem it an especial favor if any one or more of them will point out anything impracticable or unnecessarily costly in its details and construction.
I feel confident that no engineer who regards his reputation will, after a careful examination of the plans and estimates of this Bridge, assert that it is either impracticable or extravagantly costly.
JAS. B. EADS,
Chief Engineer St. Louis and Illinois Bridge Company."
The authoritative tone of Mr. Boomer's letter and the unexpected prominence given to his St. Louis recruits completely spoiled the effect of this second move. The motive was too open, the artifice too shallow, and the company remained as unpopular as ever. In fact, considerable feeling was aroused in the public mind against those citizens of St. Louis who had become identified with Mr. Boomer's company.
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The expected influx of new subscribers demanding- stock in the Illinois company and the long looked for defection from the ranks of the St. Louis Company never occurred. It is true, the unexpected difficulties encountered in the construction of the coffer-dam for the West Abutment greatly disheartened some of the more timid stockholders, and, at the same time, cheered the hearts of Mr. Boomer and his friends. On one occasion, one of Mr. Boomer's secretaries wrote to him referring to these difficulties: "The dam leaks again; water boils up in it faster than two pumps can remove it. Eads is about to put in a second sheet inside and pack between the two. F — is exceedingly discouraged. Mr. Garrison [thinks] that a general desertion of the enterprise is not improbable!" Again, the secretary said officially: "Our bridge will not cost over $3,000,000, nor over three years to build it. The other will probably cost $9,000,000 and take nine years to erect it."
By such means did Mr. Boomer and his friends endeavor to weaken the public confidence in the other company. A chance utterance in the Republican of December 18, 1867, pictures truthfully the state of despondency in the public mind at the time. A writer on "Railroads vs. Rivers" said: "As illustrative of what is thought of our enterprising character, I will mention what I recently overheard while crossing the Mississippi by the cumbersome omnibus mode. A gentleman pointing out to another where the Bridge is supposed to be erected, the stranger inquired what it would cost to build it. The reply was: ‘Seven million dollars.’ — ‘How long will it take to build it?’ — ‘Seven million years,’ was the sarcastic reply."
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their charter. The result should be either surrender or compromise. Proceedings were begun thus:—"PRESIDENT'S OFFICE, ILLINOIS AND ST. LOUIS BRIDGE COMPANY,
320 NORTH THIRD STREET, ST. LOUIS, Mo., December 4, 1867.
Chas. K. Dickson, Esq., President St. Louis and Illinois Bridge Company
DEAR SIR: The great importance of a bridge over the Mississippi River at this place, and the interests of our citizens in its early and speedy construction, render it desirable that the rights of the companies which we respectively represent should be settled as early as practicable. Our legal advisers and the community may differ in opinion as to our respective rights, and so long as these differences continue and are unsettled they tend to diminish the confidence of the public in both enterprises and hinder that which we most earnestly desire and are endeavoring to accomplish, — the speedy construction of a bridge.
The company which you represent claims the right to construct a bridge in Illinois, while the company which I represent claims the exclusive right. The question is an important one to capitalists who might desire to invest money in the enterprises.
In view of these facts, I propose that proceedings be commenced in Illinois, in an amicable manner, to test the rights of your company, and that an agreed case can be made and heard at Springfield, Illinois, at the coming January term of the Supreme Court of that State.
If this proposition should meet your views, our legal advisers can at once agree upon the details, and under such an arrangement I have no doubt the matter can be settled before the first of February next.
Yours truly,
D. E. GARRISON, President Illinois and St. Louis Bridge Company."
"ST. LOUIS AND ILLINOIS BRIDGE COMPANY,
OFFICE, N. W. COR. THIRD & PINE STS., ST. LOUIS, December 6, 1867.
D. R. Garrison, President Illinois and St. Louis Bridge Company.
DEAR SIR: Your communication to me of the 4th of December has been received, and I have given it the attention that the importance of the interest involved demands, and concur with you in the desirableness of having the question at issue between the companies settled at as early a day as possible, and will join you in endeavoring to have the matter presented to the Supreme Court of Illinois at the ensuing term of that court. If, therefore, the counsel for your company will prepare such papers as they deem essential for presenting the case properly and fairly before that court I will at once submit them to our counsel for their examination, and, if they deem it necessary, for such additions or alterations as they may think essential in order to present the questions at issue between the companies.
Respectfully,
CHAS. K. DICKSON, President.
The friendly tone of Mr. Garrison's letter and the soundness of his premises naturally led Mr. Dickson to look with favor upon any plan which should terminate this unprofitable warfare. In his anxiety for peace, it is possible that he did not sufficiently consider the one-sided nature of the proposition. Matters were soon in the hands of the lawyers. Messrs. Glover & Shepley represented the St. Louis and Illinois Company, and Messrs. Sharp & Broadhead, the Illinois and St. Louis Company. As was to be expected the interviews and correspondence between the lawyers were exceedingly unsatisfactory. Their published letters were flatly contradictory on important points, and no results were reached. Instead of adhering to Mr. Garrison's own proposition and carrying the matter
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directly to the Supreme Court, his lawyers proposed to bring the officers of the St. Louis Company before Judge Gillespie of the Circuit Court of St. Clair County on a writ of quo warranto. This would only call in question the Illinois charter of the St. Louis Company, which, it was claimed by Mr. Garrison, had through some informality been forfeited. No account was to be taken of the ratifying effect of the Act of Congress; and the validity of Mr. Boomer's charter was not to be questioned. It thus appeared that all the risk was to be on one side. There was nothing to lose and everything to gain for the Boomer company. It is obvious that both Mr. Garrison and Mr. Dickson wrote without first consulting their lawyers. It does not appear that the officers of the St. Louis Company had any lack of faith in the validity of their charters, but they wished to avoid the risk of an adverse decision from an inferior court which was generally thought to be unfriendly, and refused to subject themselves to the danger of indefinite delay during which no capitalist could be expected to contribute to their funds.The prospect of endless litigation with perhaps no bridge after all was exceedingly exasperating to the community. The bridge quarrel was the theme on all lips. A report on bridge matters was presented to the Board of Trade January 6, 1868; it reflected strongly upon those who were apparently working against the interests of the city, and earnestly deprecated "harassing lawsuits." After the discussion which attended the presentation of this report, the Board of Trade adopted the following resolution: —
"Resolved, that a committee of ten be appointed by the Chair whose duty it shall be to urge upon Congress the granting of any additional authority that may be deemed necessary to empower the St. Louis and Illinois Bridge Company to proceed with the construction of their Bridge at the foot of Washington Avenue, and thus avoid any delay that said Company may otherwise be subjected to by reason of suits in law brought by parties inimical to its completion; and, if necessary, to require said committee to visit Washington to obtain such legislation."
The action of the Board of Trade brought from the president of Mr. Boomer's company the following hasty letter: —
"ST. LOUIS, January 7, 1868.
Editors Missouri Democrat: —
Permit us a brief reference to the action of the Board of Trade on the bridge question, as reported in the Democrat of this date.
A majority of the stock of the Illinois and St. Louis Bridge Company is not held by one gentleman, a non-resident, but on the contrary a majority of said, stock is held and controlled by several of the most prominent citizens of St. Louis.
In regard to the charge of ‘black-mail,‘ the fact is, the company I represent is not in the market, either to buy or sell, and a reference to the St. Louis men who control the stock and operations of this
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company is a sufficient vindication from the charge. Confident of our exclusive right to build a bridge, we are inclined to prosecute the work with vigor. We have already purchased, of the Wiggins Ferry Company a right of way on the Illinois side, for the foundation and approaches of the bridge.
The St. Louis Company have not acquired any right of way for their bridge on either side of the river, either by purchase or otherwise, as we are advised.
We have to-day on the Illinois side, delivered and being used in the construction of our bridge, material exceeding in value all the material with which the St. Louis Company are ornamenting the levee near Washington Avenue.
We have a large force of men employed, not amusing themselves for months past in an idle effort to pump out the Mississippi, but practically engaged in making excavations for the foundations of our bridge.
Without in any manner delaying the progress of our work, we shall seek through the courts (as speedily as possible) to assert our exclusive authority to bridge the river.
We are content with the rights secured by our charter, believing it to be ample authority for our work. The St. Louis Company, however, have confessed to the Board of Trade that they are not authorized to complete their work, and now invoke the power of Congress, if it has any (which we deny), to aid them in their unauthorized and illegal enterprise.
Very respectfully, D. R. GARRISON,
President Illinois and St. Louis Bridge Company."
No sooner did Mr. Eads commence operations on the Illinois shore than the threat contained in Mr. Garrison's letter was put in execution. The officers of the company were served with a writ of quo warranto, requiring them to appear before the St. Clair County Court and prove the validity of their charter. Once in court it was evident to all that whatever might be the merits of the case it was in the power of either party to fatally prolong the suit and cripple its antagonist, though it might be, and probably would be, at the cost of its own life. Little was to be hoped from Congress in the face of opposition from Mr. Boomer's company, from the Ferry Company, and from steamboat interests in general. Things had reached such a pass on the 13th of January that Mr. Eads wrote to Messrs. Graylord & Co. of Cincinnati that he was unwilling to give any orders for iron until he had secured further legislation in favor of the company he represented.
Under such circumstances the only hope of a bridge lay in a compromise and the withdrawal of one company.
Through the mediation of mutual friends, conspicuously Hon. Wm. A. Pile, M. C., Mr. Eads and Mr. James Harrison had an interview in Washington City and drew up some articles of agreement which were to be submitted to the respective companies on their return to St. Louis. The main points of the agreement were: first, to submit the plans adopted by the two companies to an impartial board of five engineers; and secondly, the company whose plans should be decided inferior was to resign to the other all its property and franchises, and in return to receive indemnification for all its expenses.
These articles were duly submitted to the two companies, and committees were appointed to effect a consolidation. The original propositions were somewhat modified. A new consolidated company was to be formed bearing the name of the "Illinois and St. Louis Bridge Company," to which all the property and franchises of the two companies were to be transferred. The stock of the new company was to consist of 6,000 shares, 3,000 of which were
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to be divided among the stockholders of each company in proportion to the number of shares held in the same. The Board of Directors of the consolidated company was to consist of twelve members, six from each company, as follows: —Prom the St. Louis and Illinois Company: Chas. K. Dickson, Wm. Taussig, Gerard B. Allen, Wm. M. McPherson, Barton Bates, John B. Lionberger.
From the Illinois and St. Louis Company: D. R. Garrison, James Harrison, R. M. Renick, C. Beckwith, Wm. R. Morrison, R. P. Tansey.
The plan and location were to be determined by a vote of the Board of Directors, or, could they not decide, by a board of referees. "Any stockholder of the company the plan of which should be rejected, who should be dissatisfied with the plan or location adopted should, upon his giving written notice of his dissatisfaction with such adopted plan within fifteen days after said adoption, upon surrendering his stock, have his stock subscription or liability therein cancelled at once, and be entitled to have the amount already paid by him thereon, if anything, refunded by said consolidated company. All expenses by either company on any account and all liabilities were to be assumed by the consolidated company."
Considerable time was occupied in arriving at these articles of consolidation. In form they were prepared for the adoption of either plan and the withdrawal of either company, but it was throughout understood that the new company was virtually to be the old St. Louis and Illinois Company, and the point most difficult to agree upon was the "expenses and liabilities" of the other company. Finally $150,000 in cash and $25,000 in full paid up stock in the new company was agreed upon and allowed. One of the articles of agreement bound the members of either company who should withdraw from the consolidated company not to engage in building any bridge across the Mississippi River opposed in interest to the one to be built by the consolidated company.
The articles of consolidation were signed March 5, 1868. The new Board of Directors met immediately and adopted the plans and location of the St. Louis and Illinois Company. They also elected Mr. Eads as the chief engineer. As Mr. Boomer had been the banker of his company, no assessments having been made on the stock, the president of the new company, Mr. Dickson, was instructed to pay the amount agreed upon to him (Mr. Boomer). Thus the consolidation was effected and the Boomer company was no more. An Act authorizing this consolidation was within a few days passed by the General Assembly of Missouri and approved March 19, 1868. As required by this Act the articles of agreement were redrawn and signed, bearing date April 4, 1868. The final meeting of the stockholders of the uniting companies was not held till the 9th of July following. In due time the several stockholders from Mr. Boomer's company declared in writing their dissatisfaction with the plan and location adopted by the new company, and were allowed to withdraw; their stock subscriptions were cancelled and their names appear no more in the history of the Illinois and St. Louis Bridge Company.
Reference has already been made to the Act of the Missouri Legislature authorizing the consolidation. Similar recognition on the part of Congress was asked for. The passage of the Act of Congress was attended with lively discussion and strong opposition. The question of bridging the Ohio at Cincinnati was exciting considerable interest, and it is probable that the legislation asked for by the Illinois and St. Louis Company would have been refused
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had not the provision requiring a span of at least 500 feet in the clear been inserted. There could be no reasonable objection to a bridge with such a span, and it was thought that there was little chance of its being built. After considerable delay, the bill passed and was approved July 20, 1868. This Act confirmed the consolidation and recognized the new company as one with full power and authority to build a bridge across the Mississippi opposite to St. Louis, and "provided further that in constructing said Bridge there shall be one span of at least 500 feet clear between the piers."As soon as the consolidation was an assured fact, the community and all the friends of the Bridge breathed easier. Confidence in the ultimate success of the Bridge Company was very general, and it was thought probable that the City of St. Louis would in its corporate capacity assist the enterprise. The Company had already resolved to issue 4,000,000 first mortgage bonds on the property and rights of the Bridge Company, but no purchaser had been found. On the 10th of March, 1868, Mr. Eads had addressed a letter to Hon. James S. Thomas, Mayor of the city, stating the intention of the Bridge Company to ask the General Assembly of Missouri to authorize the Mayor of St. Louis, so soon as $1,000,000 had been subscribed to the stock of the Company, to cause an election to be held to vote upon the proposition to have the City of St. Louis guarantee the bonds of the Bridge Company to the extent of $4,000,000, payable in gold, with 6 per cent interest, twenty years after date. This plan was indorsed by the Mayor and by the press, and although the bill met with bitter opposition from various parties, chiefly the ferry interests and those who had been in sympathy with the Boomer company, it passed the Legislature March 24 and was approved by the Governor the following day.
By the provisions of this act two-thirds of all those voting should be in favor of the proposition to guarantee the bonds of the Company in order to give the city the requisite authority. The Mayor, the City Comptroller and the President of the City Council were to decide when the Company had spent $1,000,000 in the work of constructing the Bridge, and they were to indorse the bonds a million at a time, provided the proceeds from the sale of previous guaranteed bonds had in their judgment been properly used.
The passage of the "enabling act" was very satisfactory to the city, and when the time came for the people to vote upon the question, the vote was in favor of the Bridge by a very handsome majority.
Mature deliberation, however, led the Bridge Company to decline the proposed guarantee. The acceptance of the city's credit involved the risk of falling completely into its control, in case of failure to pay the accrued interest on its bonds; and the power which the officers of the city would have had in supervising the expenditures of the Company and in passing judgment on its management might in unscrupulous or unfriendly hands have greatly embarrassed the Company.
At the date of the consolidation, the total subscription was small and the stockholders were few. It was desirable to offer the largest liberty to new subscribers, and it seemed probable that among the citizens there might be many who would gladly become stockholders. Accordingly, for one month books were kept open at several places and great efforts were made to obtain subscriptions both large and small. In order that new stockholders might have voice in the management, the election of officers and the making of
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contracts were postponed for a month. It was, however, all to no purpose; no new subscriptions were obtained during the month.On the 9th of June the stockholders held an election and the following Board of Directors was chosen: Chas. K. Dickson, Barton Bates, John R. Lionberger, Amos Cotting, Gerard B. Allen, James B. Eads, Josiah Fogg, Wm. Taussig, Wm. M. McPherson, David Gillespie, Wm. K. Morrison. The old officers of the Company were re-elected. The Executive Committee consisted of Messrs. Taussig, Lionberger and Allen.
Mention should be made of still another company, which sprang into being during the bitter warfare described in Chapter IV., but which quickly disappeared below the horizon as soon as the consolidation of the other rival companies was effected.
The "exclusive right for twenty-five years" given to the Boomer company was limited to St. Clair County, Illinois, the northern boundary of which is about 2Ë miles north of the present Bridge. No difficulty had been met in securing a charter for building a bridge from Madison County about two weeks after Mr. Boomer received his charter. The principal parties in interest were Messrs. J. J. Mitchell and Zepheniah B. Job of Illinois, and Col. Henry C. Moore of St. Louis.
This company organized and combined with a company formed in Missouri in December, 1867, and decided to build a railway truss-bridge at Venice (about three-quarters of a mile north of the boundary line of St. Clair County) and opposite to the northern part of St. Louis.
Some prospecting was done and an outline of a plan with approximate estimates of cost was submitted by Messrs, Benj. H. Latrobe and C. Shaler Smith, civil engineers. They recommended a truss-bridge of seven spans of 300 feet each, about 8 feet above high water, the central span being counterweighted over lofty piers, so that when not needed for a passing train it could be raised vertically 62 feet, thus giving about 100 feet clearance at ordinary stages of the river. The cost of this bridge and approaches was put at $1,314,000.
Published appeals to railroad men show that it was the hope of this third company to divert the railroad interests to the northern location and leave Mr. Eads or Mr. Boomer to build a bridge for highway purposes alone.
Failing to attract the railroads, the St. Louis and Madison County Bridge Company soon sank into oblivion.
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Chapter V. The West Abutment — The First Report of the Chief Engineer.
It was an unfortunate circumstance that at this time the rising Mississippi flooded the coffer-dam and stopped for a few months all work on the Western Abutment. The masonry was only about 12 feet high and all this was now some 15 feet under water. It is proper to state here more fully than was done in Chapter III. the peculiar difficulties encountered in the construction of the West Abutment.
Although the bed-rock at the site of this abutment is 73Ë feet higher than at the East Pier, the difficulties encountered in building its foundation were of a much more perplexing and tedious character than those encountered at either of the others. Its site had been for over sixty years a part of the steamboat wharf of the city, and as such had received every kind of useless material thrown overboard from the various steamers lying over it during that time. The old sheet-iron enveloping their furnaces, worn-out grate-bars, old fire-bricks, parts of smoke-stacks, stone-coal cinders and clinker, and every manner of things entering into the construction of a Mississippi steamer seemed to have found a resting-place at this spot, and constituted a deposit averaging 12 feet in depth over the rock. During the memorable fire of 1849, when twenty-nine steamers were destroyed at the levee, the wrecks of two of them sunk upon the site of this abutment. One of these was partly covered by the hull of the other, which probably sunk immediately afterwards. The lower one was but 2 or 3 feet above the bed-rock. After this terrible conflagration the city authorities determined to widen the wharf. Its front was extended to a line inclosing about one-half of these two wrecks by filling in with stone and rubbish from the city. During this extension several other vessels were burnt at the wharf, and the wreck of one of these also sunk upon the site of the abutment. The coffer-dam constructed to inclose the site had to be put down through these three wrecks, the hulk of either of which was not probably less than 400 tons measurement. Their bottom planking was all of oak, 3 or 4 inches in thickness. To drive the sheet-piling down through these hulks, an oak timber 6 by 10 inches, armed with a huge steel chisel, was first driven down as far as a steam pile-driver could force it. It was then withdrawn and a sheet-pile 5 by 10 inches was driven down in its place. The coffer-dam was formed of two courses of sheet-piling, 6 feet apart, and a solid filling of clay. When this was completed and the water pumped out and the excavation prosecuted within it, the discovery was made that from one-third to one-half of the length of each of the three steamboats
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boat hulks was inclosed within the dam, and that some of the sheet-piling had not been driven, through the lower one, owing to the great resistance of the hulk and the mass above it. Before the space between the lower wreck and the bed-rock could be made secure on the inner side of the dam, the water came through and flooded the inclosure. A stream from a powerful Gwynne pump, having an 8-inch diameter of jet, was then directed against the material deposited over these wrecks on the outer side of the dam, where the water was 15 feet deep, and enough of the deposit was washed away to enable another course of sheet piling to be driven down 6 feet from the dam through all of the wrecks to the rock. After this that part of the wrecks inclosed between this last course of piling and the dam was removed by a diver and the space filled in with clay, and the inclosure again pumped out. A portion of the dam, about 50 feet in length, was by this construction made double.As the excavation within progressed it revealed the fact that another portion of the dam had been built and made water-tight through and over a paddle-wheel of one of the wrecks. The crank of an engine of 7-feet stroke, attached to the head of the shaft of the wheel, was just within the inclosure, while the flanges, arms and braces of the wheel were within the walls formed by the sheet-piling. From the inclosure within the dam were taken parts of several engines from the burnt steamboats, the iron parts of some of which had to be cut off at the dam. Wrecks of four barges, some of them in use doubtless before the era of steam, were also found within it; likewise several oak saw-logs, some anchors, chains, and a great variety of smaller articles lost or thrown overboard from the river craft, or dumped in from the city.
This incongruous deposit made it exceedingly difficult to maintain the integrity of the dam, which at times had to resist a pressure of 30 feet of water. Frequent floodings consequently occurred, which delayed, and increased the cost of the work. These difficulties were, however, finally overcome, and the bed-rock within was at last exposed to view. On the 25th day of February, 1868, after thoroughly testing the solidity of the rock by drilling, the first stone was laid 55 feet below high-water mark, about four months after commencing the construction of the dam. The coffer-dam was 112 feet from end to end, and its extreme width was 80 feet.
The failure of the plan to increase the subscription to the stock of the Company, coupled with the rise of the river, rendered a temporary suspension of active work necessary. The misleading Report of Mr. Boomer's convention had been scattered far and wide, creating in the minds of railroad men and eastern capitalists a deep feeling of distrust in Mr. Eads and his plans.
Under such circumstances it was absolutely necessary for the chief engineer to publish the fullest report of his plans; to justify the adoption of every novel feature; and to explain how it would be practicable to found piers upon the rock in the channel of the river, when such serious difficulties had been encountered at the water's edge.
The first Report was published in May, 1868. It tells its own story of careful preparation and profound study. This Report was eagerly sought and carefully read by engineers and capitalists the world over. It is doubtful if a bridge report of equal interest had ever been published. Nearly every scientific journal of importance reviewed it; without exception, the reviews were highly commendatory. The distinguished ability it displayed
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completely disarmed criticism, and few writers were bold enough to attack any of its main positions; and even where the critics ventured to differ, they did so with feelings of the highest respect for the engineering skill and brilliant daring of Mr. Eads and his assistants.To the President and Directors of the Illinois and St. Louis Bridge Company.
GENTLEMEN: I have the honor to submit the following Eeport of the operations of the engineering department of your Company.
In view of the great importance of your enterprise, the deep interest manifested in it by our citizens and the public generally, and because the plans adopted by you have been frequently misrepresented and unfairly criticised, I have deemed it proper that everything of interest connected with my department should be placed in such form as to be clearly understood, not alone by your stockholders, but also by every person of ordinary intelligence in the community. I have, therefore, endeavored to explain the plan of structure, the principles involved in its construction, and the reasons for its preference, in the simplest language I can command, and with an avoidance, as far as possible, of the use of all technicalities not understood by every one. At the same time you will be furnished, in an appendix, with all the scientific data, principles and formulae involved in investigating and calculating the various strains to which each and every part of the Bridge is liable to be subjected. These are so arranged, together with the results deduced therefrom, as to furnish to the most critical and scientific engineer the materials in convenient form whereby he may be able, with great economy of labor, to investigate the correctness of every step that I propose to take in constructing your Bridge.
Fully estimating the great responsibility assumed in undertaking to design and complete this important work, I have felt that in no way could I so certainly insure a successful result, and at the same time manifest my appreciation of the obligation imposed upon me, as by securing the aid of the ablest talent in every department of the work, and proving by careful experiment, as far as possible, everything connected with it that has not been already fully, demonstrated in practice, so that when the whole is finally consummated you can feel assured no step was taken that was not well considered with due regard to the safety, durability and economy of the structure.
The mathematical investigations and calculations for the Bridge were confided to my chief assistant, Col. Henry Flad, C. E., and in this laborious duty he has been faithfully and efficiently aided by Mr. Chas. Pfeifer, C. E. Several months of patient labor have been spent by these gentlemen in the investigation of the arch with spandrel bracings, the ribbed archwith pivoted ends (as in the Coblentz bridge), and with fixed ends and of various depths. After careful revision by Col. Flad, the results obtained from time to time were submitted to me, and finally, to guard against any possible error in the application of the principles upon which the investigations were made or in the results arrived at, they were referred by me to the patient analysis and careful examination of Chancellor TV. Chauvenet, LL.D., of the Washington University, formerly Professor of Mathematics in the U. S. Naval Academy at Annapolis. His certificate, affirming their correctness in every particular, will be found appended to this Report. For the interest this gentleman has taken in the enterprise, for the care bestowed in
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examining and verifying the scientific data required for the work, and for many valuable suggestions and simplifications in the investigation, I feel under many obligations.
It gives me great pleasure also to state in this connection that Chancellor Chauvenet, whose eminent ability as a mathematician is known and acknowledged throughout Europe as well as America, accords high praise to Col. Flad and also to Mr. Pfeifer for the correctness and ability shown by them in discharging the important duty confided to them.
Mr. Eads first discusses the subject of location at some length, and points out the great advantage of the site selected. He closes this discussion as follows: —
As a matter of convenience to the marine interests, the location at Washington Avenue must be deemed judicious. It is idle to talk of bridging the river and planting piers in its channel without obstructing navigation. No matter how wide the spans may be, every pier that is placed in the river is an obstruction, calculated to create danger and cause anxiety to those who navigate it. By the location at Washington Avenue the wharf is nearly equally divided above and below the Bridge. This will make it unnecessary for the steamers trading on the upper rivers to pass under the structure, whilst those engaged on the Ohio and the lower rivers will seldom be required to pass above it. If the Bridge were located in the upper portion of the city, all of the upper river boats would have to pass and repass it every trip.
From all these facts I feel confirmed in asserting that at no other location could the Bridge be erected so cheaply, at no other one would its revenues be so great, and at no other point opposite your city would the public at large be so welt accommodated.
ARCH AND TRUSS BRIDGES.
Because of the frequent assertion that your structure will be needlessly extravagant, I deem it proper to illustrate, in as simple a manner as I possibly can, enough of the general principles involved in the construction of bridges to enable any one to satisfy himself that the plan adopted for the construction of this Bridge, instead of being needlessly expensive, is really the most economical of all known methods. The general principles involved in the construction of an arch or a truss are not so intricate or difficult but what any one with ordinary intelligence can, with a little explanation, comprehend them sufficiently to judge for himself of the truth of this assertion. I shall do this before proceeding to an explanation of the plan of your proposed Bridge, as the method adopted in it will then be more readily understood and its merits appreciated.
Any one who can be made to understand the principles of the simplest of all the mechanical powers, the lever, can readily comprehend the explanation I propose making, and though he may never
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have reflected upon the subject, a few minutes spent in carefully considering the following illustrations will be sufficient to enable him to understand the economy of the arch over the truss for long span bridges.
Suppose the lever A B (Fig. 1) to rest on the fulcrum C, so that the long arm is six times the length of the short one; then it is evident that 1 ton placed at B will balance 6 tons at A. If the short arm of the lever be bent down, as in Fig. 2, 1 ton at B will exert a force equal to 6 tons at A in the direction of the arrow; and it will create a pulling or tensile strain on the hook at C of a little more than 6 tons. If two such levers be placed together, as in Fig. 3, with 1 ton weight on each at B (2 tons on the two), then the strain of 6 tons on the hook in Fig. 2 will be transferred to B, where the two ends of the levers will press against and mutually support each other. To retain the short ends of the levers at D and E from separating, it will be necessary to tie them together with a chord, D E, capable of sustaining a strain of 6 tons, that being the strain at A (Fig. 2) in the direction of the arrow. Anything interposed between the levers at B would be subjected to a crushing or compressive force of 6 tons.
The two long arms of the levers (Fig. 3) here represent the upper or compression member of a truss sustaining a crushing force of 6 tons, while the chord is the tension member, and is resisting at the same time a strain of 6 tons that is endeavoring to tear it asunder. If the upper member fails to resist the crushing force, or the lower one is rent asunder, the truss must fall.
To avoid complicating the explanation, the illustration assumes that the levers are perfectly rigid, and makes no account of their weight. If, instead of placing the 2 tons at B (Fig. 3), we suppose their long arms were each of 1 ton weight, then the strains would be only half as great; for if we remove the weight at B (Fig. 1), and suppose the long arm of the lever to weigh just 1 ton, then this arm will only balance 3 tons at A, for the center of gravity of the arm will be at the point 3 on the lever, and at this point a ton weight will only produce half the strain it would if placed at the end of the lever, the point 3 being only half the distance from the fulcrum that B is. The strain upon the chord (Fig. 3) comes from the weights at B acting in the direction of the dotted lines, F and G; hence, by substituting the straight members, K and L (Fig. 4), for the bent levers, these members will be subjected to very nearly the same crushing strain, and being shorter, will be more economical in material. This simple, triangular truss represents the most economic of all forms of short trusses known. If we desire to extend the span of this truss, the members K and L are liable to bend downwards with their own weight. To obviate this difficulty many expedients are resorted to; one method is shown in (Fig. 5), which is by the introduction of a third member, M
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(forming the top of the truss), the braces N, N., and the tie-rods O, O. Here K, M and L sustain the entire compressive force exerted by the weight of the whole structure. These members may be made with less material by curving them in the form of an arch, as in Fig. 6. This constitutes the bow-string girder. It will be observed that as the compressive and tensile strains are about equal, the truss requires about the same quantity of material in the lower member for tension that it does in the upper or compression member, when the material is the same in both, while the latter is really the sole supporting member of the structure.
The illustration of the lever shows that the strain on the compression and tension members is increased by diminishing the height or depth of the truss. For instance: if the short arm of the lever is only one-twelfth of the length of the other arm, instead of one-sixth, as in Fig. 2, the same weight would create twice as much strain at A as before. The truss, in that case, would be twenty-four times its height in length, instead of twelve times, as in the illustration at Fig. 3. Thus, making the height less, requires more material in the upper and lower members, and making it greater requires more in the braces N N and in the tension-rods O O, as they must then be longer. The proportions that insure the greatest economy are found to be about one-tenth of the length of span for the height, varying, however, in different systems from one-eighth to one-twelfth.
The bow-string girder (Fig. 6) requires theoretically probably as little material in its construction, in proportion to the weight to be sustained, as any form of truss known. If we support the compression member or arch of this truss (Fig. 7) between stone abutments strong enough to bear 6 tons of horizontal thrust, or exactly what its lower member must sustain, we can then dispense with the latter altogether, for it must be evident that its only purpose is to keep the bow or arch from spreading at its ends. If the truss must be supported on piers, it will at once become an interesting question, what will be the difference between the cost of the light piers needed to uphold the truss and the heavier ones required to sustain the horizontal thrust of the arch. By the horizontal thrust of the arch we mean the strain thrown by it upon the tension member in the truss. Of course, if this member be dispensed with, the abutments must sustain this thrust; and their ability to sustain it is simply a question of weight and arrangement of stone. The force of the thrust is easily known by calculation, and when we know that one cubic yard of stone will require a certain force to move it, we can readily calculate how many cubic yards of it will be required to resist a given force or thrust. As no account of the bond of the cement is taken in the calculation, we will have that much additional safety in the abutment. If the excess of masonry required for abutments be found to cost less than the tension member, then the arch (or the bow without the chord) will be the cheaper structure. It may occur, too, that because of floods, ice, and drift, it may be prudent to use heavier piers than would otherwise sustain the truss. This would be an additional argument favoring the use of the arch.
By referring to Fig. 6 it will be seen that the bracing between the arch and the chord, as well as almost the whole of the chord itself, is suspended from the arch. In a span of 500 feet these braces at the center of the arch would be from 50 to 75 feet long, and their weight and that of the chord would be enormous; yet they bear no part of the load, but serve only to preserve the form of the bow. The
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sole sustaining member of this truss is therefore the compression member or arch. It must be evident, then, that by sustaining that member between abutments we not only save the cost of the tension member and bracing, but we relieve the arch of this constant and enormous weight also. Now, if this bow-string truss were simply strong enough to bear its own weight before, the same arch supported between abutments, as in Fig. 7, and relieved of this weight, would then sustain an imposed load on the Bridge equally as great as the weight of the tension member and braces taken away. Indeed, if the span of the truss were 500 feet, these needless members would equal the weight of two loaded trains of cars throughout its entire length. It will be asserted that the tension member is all that is saved by using the abutments, because the bracing is needed to preserve the form of the arch also, when but one-half of the span is loaded, whether we use the tension chord or the abutments. This is true, but in the latter case a much smaller quantity of bracing material is needed, as I shall soon prove. I have purposely taken that form of truss which is of all others the most favorable to those who may be disposed to question the propriety of using the arch in the Bridge at this location, because in no other form of truss with the distributed load, even in theory, can the braces be omitted. (In the tubular girder the vertical plates forming the sides of the truss constitute the bracing between the upper and lower members.)
Referring to Fig. 7, if this arch be of equal weight throughout its length and parabolic in form, with a load equally distributed, it will be self-sustaining and will require no bracing; but when a moving load at A (Fig. 8) has covered that end to the arch, it will be straightened and the unloaded portion at B will be bent upward. As the strength of the arch is dependent upon its form, it is necessary to adopt such means as will preserve it in shape under all trials to which it may be subjected. The usual method of counteracting the effect of the moving load is by spandrel bracing (Fig. 9). Here A B is a member extending over the arch from pier to pier. To this member are secured braces and tension rods, extending from it down to the arch, to which they are also secured. The spaces thus occupied by the bracing are called the spandrels of the arch. We here have the member A B extending over the whole length of the span, sustaining no part of the load, but adding so much weight to the arch. Although it is not subjected to so much strain as the chord in the bow-string truss (Fig. 6), and is consequently much lighter, still it may be dispensed with altogether, if we divide the material in the arch and place one-half of it a few feet below the other, and thus two form two arches with about half the original material in each, as in Fig. 10, and brace these two arches or ribs thus made in such manner that they will preserve their form and relative distance from each other, under all circumstances. This is what is usually termed the ribbed arch, and is the form adopted for
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your Bridge. The roadway above it may be of wood, and can be carried by light struts resting on the arch. We require only a little more material in the arch thus formed to carry a given load than is required in the compressive member alone of the bow-string girder, and we only need the two parts of it far enough asunder to insure sufficient stiffness to resist the strains produced by the partial load. In a 515 feet span, if made of cast steel, 8 feet from center to center of the ribs is found to be sufficient to sustain the form of the arch when one-half of the span has two tracks covered with locomotives, and the roadway is densely packed with people, the other half of the span being entirely unloaded. The braces for that depth of rib are about 9 feet long, whilst in the bow-string girder of the same span and similar curve of arch the bracing would be greatly longer and would weigh four or five times as much. Hence, by using the stone abutments we save weight (and consequently cost) in the superstructure in three ways: firstly, by dispensing with the long, heavy bracing; secondly, by dispensing with the tension member of the truss; and lastly, by using less material in the arch — for it is plain that, as this member must sustain in either case the entire load that crosses the Bridge, it must have more material put in it when it has the heavy bracing and the tension member to support also. In a long span the saving in these three items is really enormous, as will be presently shown. The 515 feet span for this Bridge, with the arch, made of cast steel, weighs about 1,400 tons, exclusive of timber; with the timber it weighs about 2,000 tons. If the arch were held by a tension member, instead of abutments, that member would weigh about 450 tons, supposing the steel used in it to bear a strain of 20,000 pounds per square inch. But as the arch is only calculated to bear about 3,600 tons, including its own weight, the extra weight of this member would require the arch to be increased in its dimensions by the addition of about 50 tons of steel, making 500 tons in all for one span. At $350 per ton for the steel this would increase the cost of the span $175,000. The three bowstring girder spans, if made of cast steel, would therefore cost over half a million dollars more than the three ribbed arches. They would then weigh 1,500 tons more than the arches, while the saving in the cost of the four piers for their support could not exceed $250,000.
It matters not what truss be used, a proportionate excess of cost over the arch will be found to prevail in every one of them. Where there is no saving in the cost of masonry, or peculiar features of location excluding the arch, there can be no substantial argument in favor of the truss for long spans.
By the word truss, I include every known method of bridging except the arch. In all of them there must be both a compression and a tension member. In the arch, but one of these two members of the truss is required: the compression member when the upright arch is used, and the tension member when the catenary or suspended arch is adopted. This principle limits the length of the span in trusses by rapidly increasing their cost, so that we will seldom see them used in excess of 350 feet; whereas, the span of the upright or suspended arch may be almost unlimited. If it can be shown that the arch will be as safe and durable, and the entire structure can be made at less cost, and that its form is suited for the location, then there can be no reason why it should not be adopted where a long span is desirable. This explanation will enable any one to understand, if he will take the trouble carefully to consider it, why an arch for the superstructure is cheaper than a truss.
CAPACITY OF THE BRIDGE.
On consulting your Board as to the capacity which the Bridge should possess, I found you were unanimously in favor of the erection of one that should be capable of accommodating the local trade and travel now existing, or likely to exist for many years to come, between this city and those immediately opposite in Illinois, and at the same time serve for crossing all the trains required by the ten railways radiating in every direction from St. Louis. To accomplish this it was deemed necessary to provide a carriage-way of sufficient width to admit of four wagons abreast, two foot-ways each 8 feet wide for pedestrians, and a double railway track for steam trains.
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The accommodation of steam railway traffic and ordinary travel on the same structure and at the same time is not an untried experiment. It has been done with entire success on the Niagara Bridge, on the High Level Bridge at Newcastle-on-Tyne, and on several structures of minor note in Europe and America.
To provide a single roadway wide enough to accommodate all of these currents on one level, in such manner as to prevent any annoyance from or interference with each other, would involve the necessity of a much wider superstructure than if the railways were placed above or below the carriageway. This wide superstructure would require wider piers and abutments, and thus increase the cost of the entire fabric.
The great number of steam trains to be accommodated by the Bridge makes it absolutely necessary that each track shall be at all times open for their transit, and precludes the possibility of having the rails occupy a roadway to be used, even at stated intervals, by ordinary travel, as is done on some railway bridges where the steam trains cross less frequently. In like manner the great tides of local travel that must constantly occupy the carriage-road throughout the day and part of the night preclude its being used in common for steam trains. Hence there would be no alternative, if they were all on the same level, but to widen the superstructure to accommodate them. In placing the railways alongside the carriage-road, it would be absolutely necessary that the tracks should be separated from the latter by close partition walls or fences, to prevent the frightening of animals on the Bridge. These walls would increase the weight of the structure, expose a much greater surface to be acted upon by winds, and destroy the attractiveness which the Bridge would possess if it afforded an uninterrupted view of the river and harbor. For these reasons it was decided not to place the railways on the same level with the carriage-road.
The Federal law requiring the lowest part of the Bridge to be 50 feet in the clear, "measured at the center of the span," above the city directrix (or ordinary high water), and the level of the railways on the Illinois shore being but a few feet above the directrix, it is plain that if the railways of the Bridge were placed above the carriage-ways it would greatly increase the length of the necessary railway approaches in Illinois. Instead of their being 52 feet above the directrix at the center of the Bridge, they would have to be at least 70 feet if they were placed over the carriage-way. This would involve difficulties at the western end of the Bridge also, as the grade would be too great to run the trains under Washington Avenue. To have these trains leave or enter upon the Bridge through this crowded avenue would not be desirable, even if the citizens of St. Louis should permit it. To substitute horse-power for steam in moving the trains through the avenue would cause extra expense and would not remedy the difficulty, for the street does not possess the capacity to accommodate the railway business as well as the local traffic of the Bridge; and if used for the former, it would be liable to be blocked up at times from the effect of snow-storms, accumulation of trade or other causes, and would so interfere with the business of the city and the convenience of the people as to become an unbearable nuisance. The accommodation of railway traffic by the Bridge therefore, if located at Washington Avenue, involves the necessity of a tunnel under that street, and the railroad grades on both sides of the river fix the position of the railway tracks on the Bridge below the carriage-way.
By this arrangement it was found that the carriage-way would be on the same level with Washington Avenue at each end of the Bridge, and it would thus form a continuation of that avenue eastward from Third Street 2,700 feet long, entirely level, except the slight rise that will be given to the Bridge between the two abutments to obtain the requisite height over the channel at the center of the middle span.
The width of the structure and the position of the roadways being thus determined, the next important step was to decide upon the system that should be adopted on which to construct the Bridge.
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The determination to accommodate railway and local traffic on the Bridge, involving as it does the necessity of an upper and lower roadway, increases the magnitude of the structure to such a degree as to render a drawbridge out of the question, even if it were not an absurdity to think of opening and closing, thirty or forty times a day, a highway that must be as constantly and as densely thronged as any street in the whole city. As a drawbridge at this city has been, I think very wisely, prohibited by law, I only allude to it to record my disapprobation of such a structure if it were considered desirable to obtain a repeal of the restriction. The objections to the use of one at this location are so numerous and, I think, so well understood, that I will not occupy your time in detailing them.
In deciding upon the method of superstructure to be adopted, so much depends upon the difficulties presented in securing proper foundations that it becomes necessary to explain something of the magnitude and character of those difficulties in this case to enable you to understand fully the reasons which impelled me to the adoption of the arch in spans of about 500 feet.
ACTION OF UNDERCURRENTS.
Examinations made by myself and other engineers have revealed the fact that the bed-rock of the river, which is limestone, is overlaid with a deposit of sand about 15 feet deep near this shore and perhaps 100 feet at the other, the increase in depth being very regular as we proceed towards the Illinois shore. The borings, as far as made, indicate a regular slope of the rock from this shore, which has been traced as far as the location of the Eastern Channel Pier, where it is about 79 feet below the deposit. Near the Illinois shore 90 feet of boring has failed to reach the rock. The sandy bed of the river in low water is nearly level.
Soundings made by me prove that this deposit is scoured out to a great depth in time of floods and freshets. Although I have not had any extreme stage of water in which to make my observations, I found that a rise 13 feet less than high-water mark caused a scour of 18 feet. The greatest variation in the height of the river known at this place is about 41 feet. An average depth of about 8 feet, with a width of 1,600 feet, represents the volume of the river at extreme low water at the location selected. Extreme high water covers an immense area of bottom-lands above and opposite to the city, and the construction of numerous railway-dykes across these from East St. Louis reduces the water-way at Washington Avenue to about 2,200 feet in width at high-water mark. On this shore and on the other this water-way is thoroughly revetted below the low-water line with rubble-stone and protected by the wharf pavements above that line. The concentration into this narrow channel of the vast volumes that are sometimes poured out of the gigantic net-work of streams above St. Louis, the main artery alone of which is navigable over a thousand leagues above this city, assures me that in time of floods it is not improbable that this deposit is removed to twice or thrice the depth shown by my soundings, and perhaps to the rock itself.
I had occasion to examine the bottom of the Mississippi, below Cairo, during the flood of 1851, and at 65 feet below the surface I found the bed of the river, for at least 3 feet in depth, a moving mass, and so unstable that, in endeavoring to find footing on it beneath the bell, my feet penetrated through it until I could feel, although standing erect, the sand rushing past my hands, driven by a current apparently as rapid as that at the surface. I could discover the sand in motion at least 2 feet below the surface of the bottom, and moving with a velocity diminishing in proportion to the depth at which I thrust my hands into it.
It is a fact well known to those who were engaged in navigating the Mississippi twelve years ago, that the cargo and engine of the steamboat America, sunk 100 miles below the mouth of the Ohio, was recovered, after being submerged twenty years, during which time an island was formed over it and a farm established upon it. Cottonwood trees that grew upon the island attained such size that they were cut into cord-wood and supplied as fuel to the passing steamers. Two floods sufficed to remove
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every vestige of the island, leaving the wreck of the America uncovered by sand and 40 feet below low-water mark, where, in 1856, the property was recovered. Pilots are still navigating the river who saw this wreck lying near the Arkansas shore, with her main deck scarcely below low-water mark at the time she was lost. When the wreck was recovered the main channel of the Mississippi was over it, and the hull of the vessel had been let down by the action of the current at the bottom, nearly 40 feet below the level at which it first rested; and the shore had receded from it by the abrasion of the stream nearly half a mile.
These remarkable but well attested facts came under my own observation and occurred at Plum Point, 100 miles below Cairo, where the Mississippi is more than one mile wide, and where the lateral action of the current is not confined as it is here by stone, and where the depth of the action of the undercurrents must be much less than at this narrow passage.
Singularly enough, it is well established that at seasons of lowest water, this deposit is also liable to be removed to an extent probably sufficient to lay bare the rock in mid-channel. The current being much less when the water is low, the sand accumulates to its greatest depth. When the river freezes over, which only occurs when it is quite low, a strong crust of ice, from 10 to 15 inches thick, is formed in this narrow gorge, while there are frequently great stretches of the river above unclosed. The floating ice formed in these open spaces is carried down in large masses, which accumulate in this and other narrow passages of the river, and form what are termed ice-gorges. These accumulations sometimes extend several miles above the contracted channels of the river, and cause the water to rise, or in river parlance, "back up," 10 and even 20 feet in some instances, above its former level. The firmly frozen crust serves to hold the masses that are accumulated beneath it, and the great height attained by the "backing up" of the water above the gorge increases the currents that are sweeping below the ice to a degree probably greatly exceeding that of the floods, if we may take the water levels above the gorge as an index to the current created by this hydrostatic pressure. These currents, I believe, would prove too great to be resisted by any ordinary rip-rap (or loose stone) usually used to protect foundations not resting on the rock. The ice being lighter than the water, it follows that these currents will be constantly acting beneath the gorged ice, and in direct contact with the sand. As rapidly as the latter is cut away, fresh supplies of ice are driven under, and thus the mass continues to grow in depth, and the current to be directed nearer to the rock. After a few weeks the pressure of the back-water becomes so enormous as to sweep the gorge away, and on such occasions the open space of water below the gorge is at once filled for miles with the submerged ice thus liberated. This ice can readily be distinguished from the crust or surface ice by its scarcely floating, and by the quantities of sand and mud with which it has been saturated during its imprisonment.
On two occasions I undertook to cut a channel in the ice through which to remove from gorges two valuable diving-bell boats to places of safety. The undertaking was only successful in one case. The surface ice being removed from the canal and hauled off on its sides, I found the quantity of submerged ice which continually arose, when that in sight was removed, was so great that the supply seemed inexhaustible. In the case where I was successful, I was able to cut the channel from an open part of the river up to the vessel, and through it the submerged ice was floated out and the channel thus cleared.
In the winter of 1855, the steamer Garden City, of about 800 tons burden, was inclosed in the ice-gorge which formed in this harbor. Many of our citizens will remember that a partial movement of the gorge caused her sides to be crushed, in consequence of which the vessel filled with water. She was lying at the upper part of the city in front of a large stone-quarry, the debris from which had been for several years thrown into the river by the quarry-men, and had formed a steep, rugged shore of such slope as the broken stone naturally assumed. The water where the vessel sunk was 25 feet deep,
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but she was sustained upon the gorged ice beneath her, so that her deck was scarcely under the surface. She was in this condition when I was called upon to save her. Her hull being about 9 feet in depth, it is evident that the ice which sustained her must have been packed to the bottom, and 16 feet deep. This ice supported her with her engines and boilers and a cabin over them about 150 feet long, until the bank was removed, ways placed on the ice under the steamer, powerful purchases secured ashore, and the vessel hauled broadside in to, and upon the bank in safety, before the gorge gave way. The time occupied in doing this was about ten days, nearly all of which time the steamer was resting on ice that had been driven under the surface by the action of the current.
The establishment of piers in the channel of the river must facilitate the formation of an ice-gorge at the Bridge in the winter, and they will certainly tend to its retention until the sand is scoured out about and between them to an unknown depth.
For these reasons I have maintained and urged that there is no safety short of resting the piers for your Bridge firmly upon the rock itself. On no other question involved in its construction does my judgment more fully assure me that I am correct, although the convention of engineers assembled here last summer announced in their Report that they did not consider it essential to go to the rock with all the channel piers of Mr. Boomer's bridge. The convention assumed that the greatest possible scour would not exceed 30 feet below low-water mark (equivalent to the removal of 22 feet of deposit). [See Report, p. 80.] I am supported in my opinion upon this matter by many eminent engineers with whom I have exchanged views upon the subject.
The recent destruction of many of the bridges in British India, by having their foundations undermined mined by the action of floods upon the sandy bottoms of the streams in that country, furnishes a warning that we should not neglect.
MAGNITUDE AND NUMBER OF FOUNDATIONS.
The necessity for basing the channel foundations upon the rock being considered imperative, the next question was to determine the most judicious number of piers.
By shortening the spans the cost of the superstructure would be lessened, and a reduction in the size of the piers be possible. This would, in ordinary cases, result in a proportionate lessening of the cost of the entire structure. The law, however, requires that at least two spans shall each be not less than 350 feet, and the remaining spans 200 feet in the clear. Therefore, the reduction in cost of the structure by lessening the length of spans is limited to a certain extent by this provision. There are reasons, however, involving the safety of the Bridge, which make it necessary to provide, by an increase of masonry in the piers, the ability to resist the extraordinary casualties to which they will be liable at this location. When we take into account the great height required for the piers, from the rock to the lower roadway of the Bridge (145 feet in one, and 174 feet in the other), and remember that by the scour of the current they will be, at times, without the supporting pressure of the sand to resist the strains to which they will be subjected, we have an imperative reason for increasing the size of the piers to a degree sufficient to insure their stability, without reference to any other question whatever.
In another part of this Report I have explained why an arch is a cheaper method of superstructure than a truss; and that the advantage which the truss has to recommend it, is that it creates no thrust, but simply a vertical pressure upon the piers, thus enabling the latter to be built with less material than when the arch is used. But here we have an absolute necessity for using massive piers, and hence are unable to avail ourselves of the chief features of economy that might otherwise make the truss available, and the smallest spans permitted by the law desirable. If we bear in mind that the bedrock deepens as we approach the Illinois shore, it will be seen that by adopting shorter spans it becomes necessary to erect piers nearer to that shore, and these must be put down through a greater depth of deposit than the two contemplated in the plan. The deepest foundation we have to put down will be
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79 feet below the bottom of the stream, and we shall probably have an average depth of 20 feet of water during the season that is occupied in placing it in position, making in all 99 feet below the surface of the river. It is certainly not desirable to undertake a deeper one, except for more potent reasons than I can discover in the premises. Shorter spans would make it absolutely necessary to do this, if the piers were placed on the rock. It has been asserted that the erection of 500-feet spans is more hazardous than 350-feet ones. This is admitted; but with ordinary care and judgment the danger of casualties in the erection of either cannot be great. It is certainly more hazardous to erect a structure at this location whose channel piers are not placed upon the bed-rock below the river bottom; and if this be done, and shorter spans adopted, the difficulties attendant upon putting down the foundations must necessarily be increased, not only by increasing their number, but also because of the greater depth required for one or more of them. The hazard avoided in erecting the superstructure would simply be added with interest to that attending the construction of the piers.
The magnitude and height of the piers required is so great, even if the spans were lessened and four arches substituted, and the season favorable for their economic erection is so short, extending only from the middle of August to the middle of December, that it would not be advisable to attempt the erection of more than one of them in one year. Hence an additional one would delay the completion of the Bridge and absorb in interest on capital as much as could be saved by shortening the spans. It is possible to use the same false works and machinery for each pier unless we undertake to put in two of them in one season. This would involve the additional expense of duplicating these works and machinery. But little could be saved in the masonry of the piers by substituting three for the two contemplated, as the three would contain nearly as much as the two. There would be more saved in the abutments, but it would be chiefly in that class of masonry (the backing) which is least expensive. The cost of putting down the necessary false works, removing the deposit, and erecting the three piers, would be considerably greater than for two.
The masonry of your Bridge being so massive in character, has been contracted for at a price greatly under that paid for other large bridges now being constructed in the West. The reason for this is that the slender piers used in the latter require that every stone in them be cut to an exact size. This is only necessary with the exterior work in yours, and hence it can be and is being executed for about thirty per cent less than the masonry of those bridges.
The question of relative economy of shorter spans has not been determined by guesswork, or decided by judgment alone, but the conclusions arrived at in favor of the spans adopted have been shown by careful estimate and calculation to be not only the most judicious, but also the most economical arrangement compatible with the safety of the structure.
It is not considered advisable to place the abutment at the Illinois shore upon the rock. The cost of doing this would be very great, and as the piles upon which the masonry will be erected can be thoroughly protected at the shore from the action of the current, it will not be necessary to do it. The sand on the site of the abutment will be excavated to a point about 25 feet below the bottom of the river, and piles will then be driven to the greatest depth possible and sawed off a few feet above the sand. The spaces between the piles will be carefully filled, and the masonry laid upon a timber platform on the bed thus formed. The face of this abutment below water will then be thoroughly revetted with stone. (See p. 63.)
The rock has been laid bare 13 feet below low-water mark on the Missouri shore, and the Western Abutment commenced upon it within the coffer-dam built for the purpose.
METHOD OF SINKING THE PIERS.
A number of designs and estimates were made by me to determine the most practicable, economical and reliable method of constructing the parts of the channel piers below low-water mark. These
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designs and estimates included the use of cast-iron cylinders of diameters varying in the different plans from 3 to 15 feet, which were to be sunk to the rock and filled with concrete. The danger of scour, and the difficulty of binding these cylinders together beneath the surface of the sand, so as to insure stability under the strains produced by the thrust of the arches, induced me to increase their diameters in subsequent designs, until they became so great that wrought iron was substituted, and finally two cylinders, each of a diameter equal to the width of the pier, were tried with smaller ones about them, to complete the entire dimensions of the foundation. The same difficulty of binding these together in a manner to insure safety to the superincumbent masonry, in the event of deep scour, as well as to give promise of any great durability, still remained.
Cast-iron cylinders may be used with great advantage in forming subaqueous foundations in situations where there is no scour, but the dangers to be guarded against in this location would render them, I think, less reliable and more expensive than other methods.
My experience of the effects of fresh water upon wrought and cast iron, submerged for many years in the Mississippi, assures me that the latter can be relied upon as almost indestructible, but that wrought iron will oxidize or rust out so rapidly that in twenty years the strength of a bolt an inch and a half in diameter would probably be reduced one-half. To bind these cylinders together beneath the sand would greatly increase the cost of adopting them, and to use wrought iron to secure them above the sand would fail to insure durability. To undertake to do it with cast iron would be more expensive, and the slightest unequal settlement of the different ones composing the mass would be likely to fracture a material so brittle. To sink these cylinders, either by the pneumatic process or by any of the methods known, to the requisite depth, would be exceedingly expensive. The great quantity of iron required in them and the fact that they must be filled with masonry would render a foundation of the necessary dimensions, if composed of them, much more expensive than if made of stone alone.
Having arrived at this point in the solution of the most important problem connected with the design and erection of your Bridge, I determined to construct the base of the pier entirely of solid masonry, within a water-tight floating coffer-dam, whose sides should be extended above water from time to time, as it sunk deeper and deeper with its increasing burden of stone and cement. Piers of smaller dimensions have been constructed in a similar manner and placed upon foundations favorable to their permanent reception. When sand or mud has been interposed, and its removal rendered necessary, the sides of the floating vessel have been extended downward below its bottom, to form a chamber or kind of diving-bell beneath the masonry. Through the masonry tubes were provided by which workmen and materials could descend into the chamber, and through these tubes air was forced to expel the water from the chamber and enable the workmen to remove the sand or mud beneath the pier. These tubes required to have two or more air-locks or valves in them, that were closed behind the workmen or materials in their passage, to prevent the escapement of the compressed air in the chamber. This of course retarded the rapid progress of the work. To facilitate the excavation of the deposit an extra tube was introduced in the middle of the pier and extended to the level of the bottom of the air-chamber. The water stood within this tube at the level of the surface of the river, and through it an endless chain, carrying scoops or excavators, was made to rotate around a pulley at the bottom of the tube, and another at the top. In this way the sand was rapidly excavated without permitting the escapement of air from the chamber, and without passing the deposit up through the air-locks. The workmen in the chamber were enabled to shovel it to the bottom of the tube, where it was taken by the excavator and discharged in vessels above.
The gradual descent of the pier was managed by screws, supported upon false works erected around and over the site of the pier. As the sand was removed below, the pier was allowed to settle by slacking the screws, as it was only partially water-borne. When it had passed through a considerate
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considerable depth of sand, the friction of the latter upon the sides of the pier held it to such a degree as to take all the strain off the screws, and when it moved downward it was sometimes so suddenly that the supports were strained severely.
The shortness of the season in which each one of the piers for this Bridge must be put in position, because of the floods of summer and the ice of winter, and the great amount of deposit to be removed, renders the pneumatic process just described too slow for this case, as well as too expensive. For the safety of the workmen beneath the pier, it is absolutely necessary to regulate its descent by screws or similar means, and to do this with piers of such magnitude would not be advisable. The removal of the sand will be accomplished by sinking an elliptical-shaped caisson or curb of plate iron through the deposit to the rock. This caisson will be open at top and bottom, and will be strongly braced on the inside with heavy angle irons placed horizontally around it. It will be larger at bottom than top, to facilitate its passage through the sand and relieve it of the friction. The caisson will be suspended by false works erected around the site of the pier, and will be regulated in its descent by screws supported on the false works. As it is lowered into the sand, that which is inclosed by it will be excavated by steam machinery, until the caisson is finally sunk to the rock. It is not intended at any time to remove the water within the caisson, but only the sand it incloses; the object of the caisson being only to exclude the sand outside of it until that which it incloses has been removed, the
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rock leveled off with, concrete, the floating coffer-dam placed in position within the caisson, and the pier so far built up in the latter as to sink it down to the concrete bed prepared for it.
The bottom of the coffer-dam will be formed of squared timbers, thoroughly calked, and will be about 2 feet in thickness. Its sides will also be of timber, and so constructed as to admit of being disengaged from the bottom when the latter has reached the bed formed to receive it. The interior of the coffer-dam will be larger than the pier, and the latter will be constructed with certain cavities in it to be filled with masonry after the pier reaches the bottom, so that the weight of the pier will bear such proportion to the displacement of water as to insure the top of the masonry being kept but little below the surface of the river while the pier is being built within it. This will enable the sides of the vessel to be thoroughly braced against the pier, so as to resist the pressure of the water.
It is known that timber is indestructible when completely submerged in fresh water. Piles placed in the Rhine by the Romans nearly two thousand years ago have been found to be entirely sound when removed within the present century. There are many other similar instances on record establishing the fact of its durability, whilst the soundness of the timber found in the bogs of Ireland and elsewhere indicates that it is unlimited by time.
When the bed-rock has been prepared to receive the pier the coffer-dam will be floated within the caisson, and will be guided by the latter as it descends with its load. It will be understood that the pier is completely water-borne by the coffer-dam until the quantity of masonry in it has become so great as to cause the dam to touch the bed on which its bottom, with the pier, is to rest permanently. When the pier has been completed above water the dam is permitted to fill, and its sides will then be disengaged from the bottom and removed to be used in putting down the next pier. The caisson for the smaller pier can be withdrawn and used for the other one, and the larger one may possibly be saved also.
As before stated, the floating coffer-dam is not an untried experiment, but has been frequently used to place piers in position where the bed-rock or other substratum was favorable for their reception. The caisson has also been frequently used to exclude the sand or mud and enable that within it to be removed sufficiently to facilitate the driving of piles to a greater depth and in firmer soil than would be otherwise practicable.
The estimates made for the cost of this work prove that it will be much less expensive than any other method yet devised; while the superiority of the foundations thus made will be beyond all question.
PLAN OF STRUCTURE.
The Bridge will have three spans, each formed with four ribbed arches made of cast steel. The center span will be 515 feet and the side ones 497 feet each in the clear. The rise of the center one will be one-tenth of the span that of the side ones 47 feet 10 inches each.
The four arches forming each of these spans will each consist of an upper and lower curved member or rib extending from pier to pier. Each of these members will consist of two parallel steel tubes, 9 inches in exterior diameter, placed side by side. The upper and lower members will be 8 feet apart, measured from the center of the upper to the center of the lower tubes. At regular intervals of about 9 feet these members will be braced from each other by a vertical system of cast-steel bracing on each side of them. These braces will be secured at each end to cast-steel plates, formed something like the voussoirs of a stone arch, and against which the tubes will be abutted and secured every 9 feet throughout the arches. A horizontal system of bracing will extend from pier to pier between the four upper curved members, and a similar system between the four lower ones, for the purpose of securing the four arches in their relative distances from each other and to sustain them against lateral pressure.
The two center arches of each span will be 13 feet 9Ë inches apart from center to center, and will
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have, in addition to the upper and lower horizontal bracing just described, a system of diagonal bracing, securing the upper member of one arch to the lower one of the other arch, and the two other members in like manner. The outside arches are each 15 feet 1ž inches from the middle ones, and are joined to the latter by three systems of bracing similar to those described as between the two center arches. These systems, however, on the outside of the middle arches, extend only from the piers to the under side of the railways, the latter being carried between the two outer and the two inner arches near their crowns. The outside arches being supported in this interval against lateral movement by rigid connections from both the upper and lower roadways.
The roadways are formed by transverse iron beams, 12 inches in depth, supported by iron struts of cruciform section resting on the arches at the points where the vertical bracing of the latter is secured. That portion of the railways which passes below the crown of the arches is suspended from them. Between the iron beams forming the roadways, four parallel systems of longitudinal wooden members are introduced, extending from pier to pier and serving to maintain the iron beams in position. These wooden members are each about 9 feet long, and their ends rest upon the flanges of the beams, and are there secured from moving. On these, the wooden beams for the carriage-way rest in one roadway, and the cross-ties for the railways in the other. From the opposite ends of the iron beams a double system of diagonal horizontal iron bracing serves to bind the whole together, and gives additional support against wind pressure.
The upper roadway is 34 feet wide between the footwalks. The latter are each 8 feet wide, making the Bridge 50 feet wide between the railings.
The railway passages below the carriage-way will each be 13 feet 6 inches in the clear and 18 feet high, and will extend through arched openings of equal size in the abutments and piers. The railways will be carried over the wharves on each side of the river on five stone arches, each 26 feet wide, and will be inclosed throughout this distance by a cut-stone arcade of twenty arches supporting the upper roadway. After passing over those stone arches, the railways will be carried through the blocks between the wharf and Third Street on brick arches into the tunnel at Third Street and Washington Avenue. Over the intervening streets they will be carried on wrought-iron trusses.
* * * * * * * * * * * * *
MASONRY.
The greater part of the stone for the Bridge will be taken from the Grafton quarries, on the Mississippi, in Illinois, about forty miles above St. Louis. This stone is a magnesian limestone, of fine, firm texture, yellowish in color, and is found in regular strata, varying from 1 to 3 feet in thickness. From severe chemical tests, and the proofs of its durability given in many of the large buildings in this city constructed with it, it is believed to be well suited for the intended purpose. It will not, however, be used on the exterior of the work above water. From 2 feet below low-water mark to 2 feet above high-water mark, the exterior of the piers, including those on the wharves as well as the abutments, will be of the best quality of granite. This will be laid in courses not less than 30 inches thick, with an arris cut around each block to indicate the joints of the work, while the remainder of the block will retain the quarry or rough face upon it. Above the granite, the exterior will be entirely of cut sandstone. A granite course 8 feet in thickness will be laid through the channel piers, and in the abutments, to receive the skew-backs or heavy cast-iron plates, against which the ends of the arches will rest.
STRENGTH OF THE BRIDGE.
The arches have been designed with sufficient strength to sustain the greatest number of people that can stand together upon the carriage-way and foot-paths from end to end of the Bridge, and at the same time have each railway track below covered from end to end with locomotives. With this
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enormous load the strength of the arches will be taxed to the extent of less than one-sixth of the ultimate strength of the steel of which they will be constructed. The piers and abutments have been designed with a view to sustain either span when thus loaded, even if the others were entirely unloaded, and to sustain either span entire if from any cause the adjoining ones should be destroyed. The arches have also been designed to resist the effects of any portion of the span being loaded, as above stated, with any other portion of the same span entirely unloaded.
It will be seen, therefore, that the Bridge has been designed to sustain a greater load than will ever be placed upon it. No occasion can possibly occur requiring it to be densely packed with human beings on the upper road-way, and at the same time have its railways covered with locomotives below. Yet the ultimate strength of the materials of which it will be composed is such that the three arches are capable of sustaining 28,972 tons, before they would give way under it.
The superabundant strength of the piers to resist the effects of ice, and the ability of the superstructure to withstand the most violent tornadoes, is clearly demonstrated in the appendix to this report. It has been asserted by some of your opposers that the pressure of such long arches upon the abutments would be so great that the stone would crush under the effect of it. The ridiculous absurdity of this statement is exposed by the fact, that one block of ordinary limestone, 6 feet square, requires a greater load to crush it than the heaviest burden that can possibly be imposed upon all three of the arches of your Bridge with the entire weight of the three spans themselves added to it. The weight of the three spans, and the maximum load they are designed to bear, is 7.2 tons per lineal foot, or 10,865 tons. The 6-feet block of limestone would require 5,000 pounds per square inch, or 12,960 tons, to crush it. I have already stated that the thrust of the piers would be taken upon granite courses, 8 feet thick. Granite being more than twice as strong as limestone, the absurdity of this notion is still more apparent. As the thrust of each end of each arch will be received on a surface of granite equal to 24 square feet, and as each span has four arches, it follows that the thrust of the three spans is taken on a surface of 576 square feet of granite. This would require, at 10,000 pounds to the square inch, 414,720 tons to crush it, proving that of all the ridiculous assertions advanced this is the most extravagant. It could only be excelled by the fear that the tremendous thrust of these 500-feet arches will prove so great as to force the banks of the stream asunder and let the fabric into the abyss through which the mighty river would then escape.
EFFECTS OF TEMPERATURE.
By making the longitudinal members of the roadways of wood we avoid the expansion and contraction of those long level platforms between the piers, and leave them to be affected only by the action on the arches.
The longest of the arches will rise at the center a little less than 8 inches by the expansion of the steel when under the greatest extreme of heat, and with the most intense cold it will fall as much below the point at which it will be maintained under a medium temperature. This supposes a range of temperature from 20 degrees below zero to 141 degrees above (Fahr.). In the appendix it will be seen that in determining the size of the several parts of the arch we have duly considered the strains resulting from this change of form. The severest strain produced by temperature occurs at the abutments, and does not amount to over 4 tons per square inch.
The effect on the roadways is simply to raise and lower them at the center of the arches so imperceptibly that the eye could not detect it. The rise and fall of the roadways of the Niagara Bridge is stated by Mr. Roebling to be 2ź feet at the center of the span, under a change of 100 degrees of temperature
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That is, the roadways are 2 feet 3 inches higher at zero than when the thermometer marks 100 degrees. No inconvenience has been found to arise from this change of form in that bridge, and none can be apprehended from it in yours, where it will be so much less.
There is no truss combined with the arch in the method adopted. The roadways being simply carried on vertical supports by the arches, form no part of a truss system. The arches are the sole supporting members of the structure, and by the vertical bracing between their upper and lower parts are made amply rigid to sustain their burdens without the use of a truss in combination with them. I am thus particular in stating this fact, as one of the misapprehensions existing in regard to the plan adopted by you is that it is a combination of the arch and truss. The well-known difficulties caused by the unequal expansion and contraction of each, when the two systems are combined in a metal structure of a long span, would naturally create a want of confidence in your plans, if this impression were permitted to prevail. * * *
CONVENTION OF ENGINEERS.
The organization of two companies about the same time for the purpose of bridging the river at St. Louis, and the rivalry existing between them for nearly twelve months prior to their consolidation under the present organization, was the cause of many difficulties thrown in the way of the construction of your Bridge. One of these companies, generally known as the Boomer company, called together a convention of engineers last August to consider the question of bridging the Mississippi River at this point. Although composed in part of many distinguished and able engineers, it was known to have been held solely in the interest of that company. The plans designed for that company by Mr. S. S. Post, C. E., were laid before it and approved by the convention. The plans designed for your Bridge and adopted by you were not solicited by the convention for its examination, and at no time were those plans under consideration by it. At no time did the convention take up the subject of bridging the river by arches but simply by trusses, and it therefore very properly recommended that no spans exceeding 350 feet in the clear should be adopted.
Notwithstanding all these facts, it was industriously reported by your opponents that the plans adopted for your Bridge had been condemned by that convention as unsafe, enormously extravagant, and utterly impracticable, and that it had also condemned the location of it as very injudicious. It is because these statements are even yet repeated by parties interested in defeating the erection of the Bridge and because they are credited by many persons really anxious for its completion that I call your attention to them, and pronounce them one and all utterly untrue. One effect of these misrepresentations has been to create a belief in the minds of many that the plans adopted by you will involve a much greater outlay than is really necessary. This impression has been strengthened, no doubt, by the fact that those plans represent piers and abutments much more massive and a superstructure far more graceful and elegant than any form of truss-bridge yet constructed. Yet one of the most beautiful and graceful structures in this or any other country, with its massive masonry and enormous span, is one of the cheapest ever erected. I refer to the suspended arch bridge of Roebliug's at Niagara.
We are too prone to associate our contemplation of the beautiful in architecture and engineering with an idea of costliness, which is not always just. It is easy to prove, beyond the possibility of a question, that in no other form could the material in those members of your Bridge which impart to it the chief feature of its gracefulness be used with such economy.
The effort to create a want of confidence in the safety of your Bridge was supported, to a certain extent, by the fact that this convention declared in its Report that there was no engineering precedent for a span of 500 feet, and also by stating that "there has been no bridge of the character of that which (in our judgment) is required at this place yet constructed, to furnish us with any reliable and certain data on the serious questions of materials and workmanship in spans of such great length."
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By reference to a copy of the official publication, in my office, made by the Dutch Government in January, 1866, of the details and plans of the Kuilinburg bridge over the Leek, an arm of the Rhine in Holland, you will see that its greatest opening is spanned by a truss of 157 metres, or 515 feet in length, constructed on the method used in the bridge at Hartford, Connecticut. This bridge has a double-track railway through it, and this truss weighs nearly 2,400 tons, and is partly of steel.
In 1801 the great Scottish engineer, Thomas Telford, proposed to replace the old London Bridge with one of cast iron, having a single arch of 600-feet span. His suspension bridge over the Menai Straits is one of the most substantial structures of the kind in the world, and spans 570 feet.. A cast-iron arch bridge of a single span of 500 feet was proposed by him in preference to the suspension one, but was rejected by the government, because the arch gave less room on each side of the channel for sailing vessels.
For forty years this remarkable man continued to enrich Scotland and England with some of the most stupendous and successful triumphs of engineering skill to be found in Great Britain. The erection of more than twelve hundred bridges by him, many of them of cast iron, made his ex-experience in bridge construction superior to that of any man of his period. Many of those erected by him are among the largest and most substantial structures in that country.
A select committee was appointed by Parliament to examine his plans for the 600-feet arch, and the opinions of the most eminent, practical, and scientific men of the British Empire were taken before it on the subject, among whom were James Watt, John Rennie, Professors Robinson and Playfair of Edinburgh, and Hutton of Woolwich. The plans were approved and adopted, and the work upon this stupendous arch was actually begun.
Although this great work was ultimately abandoned, it was from no want of confidence in the plan, but because (according to Stephenson) the height of the arch (65 feet) involved the necessity of raising the streets leading to it, by which too much valuable property would have been depreciated. In a private letter to a friend, Telford informs him that his plans were adopted for this bridge, and says: "If they will only provide the means, and give me elbow room, I see my way as clear as mending the auld brig at the burn."
Surely, the recorded judgment of such a man as Telford, when sustained by the most eminent men of his day, asserting the practicability of a cast-iron arch of 600 feet span in 1801, furnishes some "engineering precedent" to justify a span of 100 feet less in 1867.
When we take into account that the limit of the elastic strength of cast iron in compression is only about 8,000 pounds to the square inch, and that in cast steel it is at least seven or eight times greater, and consider the advance that has been made in the knowledge of bridge building since the days of Telford, it is safe to assert that the project of throwing a single arch of cast steel, 2,000 feet in length, over the Mississippi, is less bold in design, and fully as practicable, as his cast-iron arch of 600-feet span. Engineering precedents have nothing to do with the question of length of span in a bridge. It is a money question altogether. The problem to be solved is simply, what length of span will pay best? This being decided, and profit enough assured to justify the outlay, engineering skill and knowledge will be found fully equal to its accomplishment, no matter what may be the length required. That one made, of a material eight times as strong as cast iron, is unsafe or impracticable 500 feet long, is almost too ridiculous to be noticed, in a country where the assertion is rebuked by Wernwag's wooden arch of 340 feet, which spanned the Schuylkill at Philadelphia.
It must be remembered that the Report of the convention has the names of several able engineers appended to it who were not present at its meetings; that those who were present considered no method
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of construction except trusses; that its deliberations for the solution of the grave questions involved in bridging this river occupied scarcely ten clays; and that it was convened almost solely in the interest of Mr. Boomer, who then controlled one of the charters of your consolidated company, and the patent for the truss-bridge he intended building. When these facts are considered, in connection with each other, it will be understood why the plans for your Bridge were not solicited for comparison with Mr. Post's patent truss; and when you take the statement of Mr. Post himself, as chairman of the committee on superstructure, that to span a clear opening of 500 feet with his truss would cost as much as to span two openings of 350 feet each, and one and a half of 250 feet each in addition; or that the superstructure of the Bridge, if built on his plan, would cost $750,000 more with one 500-feet span than if two of 350 feet were used, you will understand fully why the preference was given (on the score of economy) to spans of 350 feet.
An investigation by the convention of the plans adopted by you would have revealed the fact that the superstructure of your Bridge, possessing greater strength than the one it indorses, and with its great openings, could be erected for about $400,000 less than the truss-bridge approved by them, with its greatest spans of but 350 feet; and no part of this saving is absorbed by cost of foundations, as those approved by it, on account of the great quantity of iron required, are more expensive also than yours. The proof of these facts will be found in another part of this Report, and they are set-forth in a manner that admits of no refutation.
It is, however, not so easy to understand why a body so intelligent as this convention should forget the authority of Telford and his eminent contemporaries, and the 500-feet truss-bridge over the Leek at Kuilinburg in Holland, and be led into the error of asserting that there was no "engineering precedent" for a span of 500 feet. If it were expected to span this river with an exact copy of some bridge now standing elsewhere, the necessary data could be obtained and applied without convoking so much ability. Any respectable bridge-building firm in the country has, no doubt, sufficient engineering talent constantly in its service for such an emergency, and could have had the requisite plans copied and the structure erected without calling a convention of such distinguished gentlemen to deliberate upon them. Where no "engineering precedent" exists, however, and where data "on the serious questions of materials and workmanship in spans of such great length" are not supplied by structures of equal magnitude, there is a necessity for bringing to the consideration of the subject the profoundest thought, based upon such a thorough acquaintance with the strength of materials as experience and experiment alone can furnish, together with a knowledge, obtained by careful study and observation, of the laws which guide us in the combination of those materials.
For increasing the dimensions of a truss beyond any now existing, a knowledge of the strength of materials and the laws that govern their application was sufficient to enable the convention to deduce with entire safety such data from the experience furnished by the 450-feet truss of Brunei, over the Tamar, the 397-feet trusses of the Dirshau bridge over the Weichsel, and a dozen others of lesser span, if the Kuilinburg truss were not in existence.
The wording of the Report, inconsiderately (and I believe quite unjustly to the members of the convention), makes that body seem to condemn the adoption, not simply of a truss of 500 feet, but a span of that length, whereas it really investigated no other methods of construction to determine their relative economy with the truss. It simply compared the 500 and the 350 feet trusses with each other; and instead of being content to condemn the use of the long one on the score of economy alone, which would certainly have been sufficient, it thoughtlessly gives a reason for not using a 500-feet span that is not only unsupported by truth, but which is also a discreditable one to a profession whose greatest merit lies in its ability to overcome difficulties by the application of physical laws, without the aid of precedents. By this negligent (or adroit) wording of the Report, the professional reputation of the
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members is made to injure a kindred enterprise of whose existence they were not ignorant, by making each one of them appear to condemn the plans of a rival structure they had never seen; a thing which no one of them would do deliberately if he valued his own reputation.
The biographer of Telford relates that a scheme for a broad ship-canal was started to connect the Mersey, opposite to Liverpool, with the estuary of the Dee, the object being to enable shipping to avoid the shoals and sand-banks that obstruct the entrance to the Mersey. Telford entered on the project with great zeal, and his name was widely quoted in connection with it. It appeared, however, that one of its projectors, who had secured the right of preemption of the land on which the only possible entrance to the canal could be formed, suddenly sold out for a large sum to the corporation of Liverpool, who were opposed to the plan. His biographer says that "Telford, disgusted at being made the instrument of an apparent fraud upon the public, destroyed all the documents relating to the scheme, and never spoke of it afterward, except in terms of extreme indignation."
Considering that the convention was assembled solely in the interest of a rival company, and after the fact of your adopting 500-feet spans had been published, the inference drawn from this part of the Report is quite conclusive that the eminent reputation and distinguished standing of its members have been used for a purpose quite similar to that related of Telford; and knowing that the same keen regard for rectitude displayed by that engineer is shared in by almost every member of a profession based on laws incapable of deception, and the daily application of which, in the routine of their duties, naturally inculcates a love of all that is truthful and correct, I feel assured that they have cause to feel, and doubtless do feel, equally indignant with Telford.
If there were no engineering precedent for 500-feet spans, can it be possible that our knowledge of the science of engineering is so limited as not to teach us whether such plans are safe and practicable? Must we admit that because a thing never has been done, it never can be, when our knowledge and judgment assure us that it is entirely practicable? This shallow reasoning would have defeated the laying of the Atlantic Cable, the spanning of the Menai Straits, the conversion of Harlem Lake into a garden, and left the terrors of the Eddystone without their warning light. The Rhine and the sea would still be alternately claiming dominion over one half of the territory of a powerful kingdom, if this miserable argument had been suffered to prevail against men who knew, without "an engineering precedent," that the river could be controlled, and a curb put upon the ocean itself.
* * * * * * * * * * * * *
MANNER OF USING THE STEEL.
To obtain the highest value of cast steel in compression, with the greatest economy in construction, I think it should be used in the tubular form. Although cast-steel tubes have been recently drawn cold by hydrostatic pressure, in France, from steel expressly prepared for the purpose, I cannot learn that the process has been carried to any extent beyond the production of gun-barrels. It is quite possible that this method may in the future furnish steel much superior for bridging to anything we can now obtain. I have but little doubt that methods of manufacturing and tempering steel in this form for bridge construction will soon be discovered, by which a much higher value of strength may be safely used in construction. As the use of cast steel in bridge building is comparatively in its infancy, I have deemed it proper to use the material at a much safer limit as regards its ultimate strength than my judgment would otherwise dictate. I feel assured that the structure would be entirely safe to bear a far greater load than can be placed upon it if its arches contained but one-half of the steel that will form them. When this material comes to be universally used in bridge construction in the place of wrought and cast iron (as it inevitably will be because of its greater economy), the very large margin for safety provided by the liberal use of this material in your Bridge will be more fully appreciated.
To insure a uniform quality and high grade of steel at the lowest prices, and at the same time avail
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myself of the advantages of the tubular form of construction, I propose to have the steel rolled for the arches in bars of 9 feet length, and of such form that ten of them shall fill the circumference of a 9-inch lap-welded tube one-eighth inch thick, in the manner that the staves of a barrel fill the hoops. This would virtually form a steel tube 9 inches in diameter and of 6 inches bore, the steel being about 1Ë inches thick, and would be much less expensive than if the tube were rolled or drawn in one piece. The manufacture of the steel in such small bars will insure a more uniform quality in the metal, and in the tube each bar will be supported against deflection in every direction. The tubes will be retained in their positions by an effective system of bracing, which will sustain the voussoirs or pieces against which the tubes are butted throughout the arch. The upper and lower members of each arch will each be formed of two courses of these tubes, from end to end of the arch, each tube having a sectional area of 36 square inches at the summit of the arch. As each span will be made up of four arches, and each arch of four of these tubes, the span will have an aggregate sectional area at that part of 576 square inches of steel. The tubes, for about 20 feet of their lengths nearest the abutments, will require one-half more sectional area to resist the greater strains at those points. The tubing in which the steel bars will be inclosed will effectually protect the latter from the weather.
I am gratified in being able to state that proposals from several of our leading steel-makers in the United States have been received, and also from some of the most celebrated in Europe, among whom I may name Naylor & Co., of England; Petin, Gaudet & Co., of France; and Fred. Krupp, of Prussia; all offering to furnish the steel, and agreeing to guarantee its strength fully up to the standard required.
The importance of being guided by the very best lights that can be obtained from practical and careful experiment, and the great interests involved in the safety and permanency of the structure, fully convinced me at the inception of this enterprise of the necessity of instituting a careful series of experimental tests of the materials to be used, and also determined me to have every part of the structure thoroughly tested to a degree of strain much beyond what it can by any possibility be subjected to when in the Bridge. For this purpose I am having a powerful machine made that will be capable of carefully testing every member used in its construction. * * *
Mr. Eads's estimate of the cost of the superstructure was $1,460,418, and of the substructure, $1,540,080. The Report closes with an estimate of revenue.
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Chapter VI. Financial Matters — Mr. Eads in Europe — The Sinking of the Three Great Piers.
In July, 1868, Mr. Eads's health failed. A dangerous and distressing cough led his physician to order him to Europe without delay. He sailed from New York for Liverpool July 22. With his departure, in the words of Col. Flad, "all the life of the Company seemed to go out."
Mr. Eads had tendered his resignation, but it was declined, and he was requested to name an engineer to take his place during his absence. He first conferred with Mr. O. Chanute, then engaged in the erection of the Kansas City bridge, but his engagements prevented his acceptance of this position. Mr. Eads then consulted Col. W. Milnor Roberts of Pennsylvania, whom he knew only by reputation. Col. Roberts was glad of an opportunity to join in such a notable enterprise, and accordingly he was appointed associate engineer; he did not, however, come to St. Louis till the middle of October, He was in the service of the Bridge Company about two years.
For months the work of construction was in statu quo. Owing to the high water, progress on the masonry of the West Abutment was impossible. Col. Flad, however, measured a base line on the eastern shore of the river, and made the triangulations necessary to locate the river piers with great accuracy. Further work for the time was out of the question. On the 1st of September all the employees of the Company, except Col. Flad, Mr. Pfeifer, and two men, were discharged. Drawings and estimates had been prepared for a large testing machine designed by Col. Flad, but the Company was at the time unable to order its construction. In October, the water being low, Mr. Roberts suggested to Col. Flad the preparation of an estimate of the cost of raising the West Abutment to a height of 12 feet above low-water. The cost, including the excavation of sediment, the removal and storage of the frames and machinery, was given at $40,000. The contractor, Mr. Andrews, agreed to do the work as required on the immediate payment of $25,000, the rest of the account remaining till more complete financial arrangements had been made. As it was very desirable that the masonry should be above danger from ice, some of the Directors subscribed $25,000 outside of their stock subscriptions, and work was resumed October 28. With some interruptions it was continued till the 10th of January, 1869, when the masonry was 5 feet above low-water; on account of unusually high water the work was then stopped.
The return of Mr. Eads to New York in December was the signal for more active efforts in behalf of the Company. There seemed to be a better feeling among capitalists
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and railroad companies, the legitimate result of the publication of the first Report. The magnitude of the enterprise seemed to be better understood, and it was clear that those who had already contributed heavily had no alternative. They must go forward, and cash subscriptions sufficient to construct the two channel piers must be secured before the bonds of the Company could be negotiated.Mr. Eads did not dare to expose himself to the climate of St. Louis, and after a stay of about a month in New York City he returned to Europe.
Meanwhile the Directors of the Company were very active in St. Louis. A prospectus was drawn up by Dr. Taussig and Wm. M. McPherson, Esq., and a financial policy was adopted. In brief it was: to increase the capital stock of the Company to $4,000,000; to increase the subscriptions to $3,000,000, forty per cent of which should be in cash as required. This would yield, in available funds for the building of the foundations of the Bridge, $1,200,000, including that already spent. It was thought that this amount would suffice for bringing all the foundations above low-water, and that they could then negotiate $4,000,000 of first mortgage bonds, the proceeds of which would complete the Bridge. At ninety percent these bonds (which were to be seven per cent gold bonds) would yield $3,600,000, which, added to the forty per cent of the subscriptions, — $1,200,000, — would give $4,800,000, and this, according to the estimates of the chief engineer at the time, was ample allowance for the building of the entire Bridge. It was thought that two-fifths of the $3,000,000 subscription could be raised in St. Louis, and Mr. McPherson of St. Louis and Mr. Amos Cotting of the firm of Jameson, Smith & Getting, New York, were appointed a committee to receive subscriptions in New York. These gentlemen visited New York in February, 1869, and were entirely successful. In a few days the entire amount asked for, $1,800,000, was made up, and on the return of Mr. McPherson the required $1,200,000 was secured in St. Louis in two days' time.
The success of this measure was announced as follows: —
"FEBURARY 21, 1869.
Editor Missouri Democrat: —
The St. Louis Bridge is a fixed fact, so far as the subscription is concerned. The inclosed is the list of subscribers to the stock of the Company, whose aggregate subscriptions amount to $3,000,000. This was deemed a sufficient amount to ensure the completion of the Bridge, and therefore the books have been closed.
Very respectfully,
WM. M. McPHERSON.
Morris K. Jesup, E. D. Morgan & Co., John A. Stewart, Jameson, Smith & Cotting, Horace Fairbanks, James H. Benedict, Dabney, Morgan & Co., Thomas W. Piersall, J. Boorman Johnson & Co., A. B. Baylis, Wm. Whitewright, Jr., Paul Spofford, John G. Copelin, Wm. Taussig, Barton Bates,
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Charles K. Dickson, Greeley & Gale, George & John Knapp, John D. Perry, Josiah Fogg, S. E. Filley, Thomas Slevin, Robert Lenox Kennedy, John A. Ubsdell, James Low, Thomas Eakin, Gardner Colby, Edwin Hoyt, Junius S. Morgan, Morton, Bliss & Co., A. Boody, Alex. M. White, E. A. Quintard, Amos E. Eno, Wm. M. McPherson, John E. Lionberger, Gerard B. Allen, John J. Roe, Wm. J. Lewis, Hudson E. Bridge, James B. Eads, James H. Britton, John Jackson, Taussig, Livingston & Co., A. Iselin & Co., Rufus Fitch, Geo. C. Fabian, Charles Bond, Lorenzo Blackstone, T. P. Morton, James Loyd, Geo. D. Phelps, Gardner Greene, T. A. Walker, John Jeffries, James L. Hubbard, Jno. J. Taussig, James M. Carpenter, Joseph Taussig."
This success was largely due to the influence of Mr. Eads's first Report, supplemented by the energetic efforts of Messrs. McPherson and Cotting. It was now evident that at least a year had been lost in overcoming groundless prejudices and in reaching a strong financial basis.
On March 22 the Directors resolved to push matters with vigor, and with a view to hastening the completion of the Bridge determined during the ensuing season to commence operations on both of the river piers and the East Abutment.
Complete drawings and specifications for the caissons of the two channel piers were prepared, and proposals for their construction were solicited. The design of the previous year (fully explained on page 46) had been slightly modified. Instead of elliptical caissons, it was thought best to make them circular. A vertical section of the larger caisson is shown in Fig. 11, on p. 46. It was to be 114 feet high, with an internal diameter of 86 feet. The lower part for 72 feet of its height was to be formed of two shells of plate iron connected by skeleton frames of cast iron. The outer shell had a batter of one-half inch per foot for 72 feet. The inner shell was vertical excepting for 6 feet at the bottom. The top of the caisson for 42 feet consisted of a single shell stiffened on the inside by cast iron frames and vertical posts. The distance between the two shells varied from 4 feet 3 inches at a height of 6 feet from the lower edge, to 1 foot 6 inches at the top of the inner shell. The whole caisson was to be built as nineteen separate rings, each 6 feet high. The lowest ring was wedge-shaped in section, and its cutting edge was armed with steel. The outside diameter of the steel ring forming the cutting edge was 95 feet. The two lowest rings were strictly circular, and were riveted so as to form one continuous body. All others were regular polygons of 48 sides, put together and to each other with bolts. Ring No. 1 was wholly of wrought iron and steel. It had plates 1 inch thick in each shell with radial stiffening plates, triangular in shape, one-half inch thick and 3 feet apart. The thick plates were connected by heavy T-irons; the stiffening plates were secured by angle irons. The plates of the upper rings diminished in thickness to three-sixteenths of an inch in the last six. The cast-iron frames were horizontal, three in each segment of a ring. The segments were
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to act like the voussoirs of an arch to resist the horizontal thrust of the sand, and the impact of the water. All rings were to be put up complete on shore, and two rings were to be put together before the lower was accepted.Though not water tight, the caisson was to have nicely fitting joints. All materials were to be of the best quality.
The caisson was to be supported and regulated in its descent by forty suspension rods attached to brackets riveted to the second ring. This caisson (for the East Pier) was to have contained — of cast iron, 587,000 pounds; plate iron, 780,000 pounds; angle and T-iron, 334,000 pounds; bolts, nuts, and heads, 20,000 pounds; steel, 16,800 pounds. It was proposed to fill the caisson for 30 feet with closely fitting blocks of concrete. This admirable and carefully matured design was destined to be superseded, but it stands as a part of the history.
Mr. Eads's second visit to Europe was fraught with important consequences. Messrs. Petin, Graudet & Co., iron and steel manufacturers of France, had been much interested in the proposed superstructure, and entertained the thought of bidding for the contract of erection. On their application Mr. Eads sent them detailed drawings of the Bridge, with a request to Mr. Petin that he and his engineer would carefully study them and suggest any modification of detail that would insure greater economy without sacrifice of strength and durability.
More anxious than ever to furnish the iron and steel, Mr. Petin asked for another interview to which he would invite the distinguished engineer, Mr. Moreaux, who was reported to have built a thousand bridges and who was then building a bridge at Vichy, France. The interview was held March 15, and lasted three hours. There were present: Messrs. Petin and Gaudet, the manufacturers; Mr. Moreaux, the eminent engineer; Mr. Weld, a director of the Vichy Bridge Company; Mr. Eads; Mr. Champin, the New York agent of the manufacturers; and Dr. Chas. A. Pope, a distinguished surgeon, formerly of St. Louis. The last two gentlemen acted as interpreters.
Mr. Moreaux had never before seen the plans and his first criticisms were very severe. It was evident that he thought it a piece of presumption on the part of an American engineer to publish plans for a bridge having arches with spans more than 200 feet greater than any arch in Europe, and he doubtless expected to find the details deficient and faulty. Closer study, however, convinced him that every part of the design had been carefully considered and the most rigid economy observed. At the close of the interview Mr. Moreaux told Dr. Pope that the whole investigation of the subject and the entire design seemed to him to be of the most complete and thorough character, and that the engineering ability displayed was of the first order. Finally Mr. Moreaux expressed himself as entirely satisfied with the design, but advised the use of a lower grade of steel with a maximum resistance to compression of 18,000 pounds per square inch.
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Mr. Eads submitted to the inspection of the French engineer his plans for constructing the river piers. They were without hesitation pronounced "good" but in order that Mr. Eads might see the best usage in France in the matter of foundations, he was invited to visit the river piers then building at Vichy. He went accompanied by Dr. Pope. The resident engineer was Mr. Audernt, who had been engaged fourteen years in building foundations by the pneumatic process, and had put down forty piers by the method of compressed air. His deepest pier, at Piacenza for the bridge over the Po, reached a depth of 75 feet below the river's surface. The piers building at Vichy were to be sunk seven metres below the bed of the stream. Their dimensions were 10.10 by 3.90 metres. Mr. Eads spent some days studying the construction of the caissons and their methods of conducting the work. Subsequently Mr. Eads conferred with several eminent English engineers, both as regards the manufacture of steel and the use of compressed air for deep foundations. He especially felt under obligation to Mr. Brereton, an engineer engaged on the Saltash pier under Brunei, for much valuable information and for good suggestions.
The result of all this examination and study was a complete change in the method adopted for building the channel piers of the St. Louis Bridge. The general method used at Vichy, with important modifications and on a greatly enlarged scale, was followed at St. Louis. The details of the method with the modifications introduced are given in subsequent Chapters. Mr. Eads was entirely convinced of the practicability and reliability of the method already devised for building the piers of his Bridge, as were Col. Flad and Col. Roberts; but the new method by compressed air was adopted as less expensive and more expeditious. Col. Flad was inclined to regard the old plan as on the whole the safer, and abandoned it with considerable reluctance. Expensive as the piers proved to be, there is not the slightest doubt but that the system was wisely chosen and skillfully used. In the opinion of Mr. Eads, fully $200,000 were saved by the change, as it is probable that the cost of executing the original plan would have exceeded the estimates.
The proper construction of the river piers was unquestionably the most difficult engineering problem connected with the Bridge. The utmost care had been exercised from the first to obtain all available information as to methods of laying foundations. The method used at Kehl, and described by Mr. Eads in his first Report, had been fully discussed and rejected as slow and extremely hazardous; but the latest improvements were unpublished, and the accident of Mr. Eads's second visit to Europe must be considered as a fortunate one. He exchanged views with the most eminent engineers of England and France and was fully confirmed by them in his conclusions. His subsequent invention of the Sand Pump completed the features of a design already distinguished by many valuable improvements. Mr. Eads returned in good health in the month of April, 1869.
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step on the ground that the great bugbear to all parties who might wish to take the first-mortgage bonds was this East Pier, which involved engineering difficulties not yet successfully met; and that although it would seem to be the path of wisdom to bring to the larger pier the experience gained in sinking the smaller, time was too precious and money too much needed.A barge had been anchored over the site of the East Pier in March and careful measurements were taken to ascertain the distance to the rock. A 10-inch tube 40 feet long was sunk in an upright position till it penetrated about 15 feet into the bed of the river. Within this, a 4-inch pipe was driven to the rock. Measurements gave: From surface of water to rock, 96.15 feet; depth of water, 14 feet; depth of sand, 82 feet; rock below city directrix, 122.50 feet. In the Report of 1868 this last depth had been assumed to be 123 feet.
The change of plan as regards the method of founding the piers involved the execution of new drawings, new estimates of cost, and an entire remodelling of all the floating machinery.
The greatest activity at once prevailed both in the offices of the chief engineer and at various other points. The din of preparation was heard on all hands: limestone was being quarried at Grafton and stored on the levee; granite was being dressed at Richmond, Va., to be sent via New Orleans and the Lower Mississippi to St. Louis; the caissons were being built; barges were being fitted up with engines for pumping air and water, and with derricks and travellers for handling stone; sand-pumps were being made and tested; brick and sand and cement were being piled hard by; a blacksmith's shop built at the foot of Washington Avenue was in full blast; timbers for piles, scaffolds, and caisson girders were being dressed; the testing machine was in process of construction; barges and tug-boats were being put in working order; and breakwaters above the sites of the piers were being constructed.
By the middle of June one thousand men were engaged upon these preparations for building the Bridge, and the number was increased to full fifteen hundred by September 1. At the latter date there were in use, or ready for use, some twenty-four boats, thirty-seven engines with a proper supply of boilers, thirty-one pumps for air and water, twenty-nine derricks, forty travellers erected on strong frames, and twenty-four hydraulic hoists with jacks, pulleys, ropes, and frames, complete.
Mr. James Andrews
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The rapid progress of the work was delayed by the failure of the iron-plate contractors to deliver the iron as fast as it was required, and the caisson for the East Pier was not launched at Carondelet till October 17, 1869. It was immediately towed to its place within the rows of "guide piles" already arranged, and the operation of sinking was begun. A full description of this caisson and its history during its progress to the bed-rock of the river will be given in Chapter XVIII. The floating machinery used in the construction of the East Pier was of the most elaborate and complete character. The skilful use of steam in transferring the heavy blocks of stone from barges to their final resting places on the pier was the continual theme of admiring crowds that thronged every available foot of observation. (See Plates VIII. — XII.)
It was a cold raw day in October when the corner-stone of the great pier was laid; the wind whistled through the frames and network of wire ropes; the sky was black with huge volumes of smoke from the engines and boats on either side of the floating caisson; the din of hammers calking the air-chamber below and riveting new plates above was deafening; the furious wind had lashed the yellow Mississippi into something of an angry whiteness, yet the enthusiastic friends of the Bridge did not fail to be present. The ceremony was simple, the speeches were short, and the laying of masonry went rapidly forward.
The work thus begun was not suspended, day nor night, for five months. Steadily day by day the masonry was laid above, and the caisson descended through water and sand below. The pier rested upon the sand November 17 in 34 feet of water. The sand pumps worked to perfection. On the morning of February 28 the crashing echoes of cannon and the discordant shrieks of a dozen steam whistles announced to the people of St. Louis that the great pier had reached the bed-rock! The hardest problem of the Bridge had been solved, and there was general rejoicing. Congratulations poured in from all sides. The filling of the air-chaixtber, which was begun March 1, was finished May 27, the work having been interrupted nearly four weeks.
When the caisson of the East Pier reached the rock it was 95 feet below the surface of the river, and on the 13th of April, when work in the air-chamber was suspended by the temporary flooding of the pier, the river was 110 feet and 6 inches above the bottom of the caisson.
In addition to the presence of the general superintendent, Mr. W. K. McComas, who was almost constantly at the works, it was made the duty of three civil engineers, familiar with the plans, machinery, etc. (Messrs. Roberts, Mad, and Pfeifer), to give their personal superintendence to the sinking of the East Pier, one being constantly on duty, watching and directing the progress of the work, and keeping a record of everything of interest occurring. Extracts from their "log-book" will be given later.
To prevent the possibility of delay arising from the failure of any one piece of machinery, duplicate pumps, engines, boilers, boats, etc., in perfect order, were always held in reserve. That the work proceeded without interruption or accident speaks volumes for the thoroughness with which all plans were laid and the careful supervision with which the work was done.
The winter was fortunately open and the ice did not gorge, though it ran heavily at times. During fifteen, days it was impossible to tow a barge of stone to the pier, and during
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several days all ordinary communication with the shore was suspended. This contingency had been provided for by laying in bedding for all hands, provisions and fuel and material for two weeks. During this blockade the din of hammers and the clouds of smoke did not cease, and regularly morning and evening Mr. McComas posted conspicuously on a placard the progress of the work, to be read by an observer with a telescope on shore. All such bulletins closed with the cheerful words, "Ice-breaker all right." As this was the supreme moment when the safety of the whole work hung upon the efficiency of these defences such information was cordially welcomed by the engineer-in-chief.Later, when the pier had reached the depth of 66 feet, a telegraphic instrument was placed in the air-chamber, and a wire was led to the office of Mr. McComas on one of the derrick boats at the pier, and also to the office of Mr. Eads in the city. By this means messages were sent to and from the air-chamber and between the offices of the superintendent and the chief engineer at all times. This telegraph proved not only convenient to the engineers in charge, but the knowledge that a means of communication with the upper world was always at hand in the air-chamber, and one not likely to be broken by any accident endangering the lives of the workmen in it, was productive of a very salutary moral effect upon the men.
The caisson for the West Pier was launched and towed to its position January 3, 1870. The masonry was begun January 15; the caisson rested upon the sand February 2, and on the rock by April 1. Its air-chamber and shafts were filled with concrete by May 8. The West Pier is somewhat smaller than the East Pier, and its caisson reached the rock through about 86 feet of sand and water. Its construction contained some improvements suggested by the experience with the other pier which are fully pointed out in Chapter XIX.
During the summer of 1870 the river piers and the West Abutment were built several feet above the ordinary surface of the river with masonry faced with granite from the Atlantic coast, though the granite arrived very slowly. Two sailing vessels from Portland, Me., laden with granite were lost on the coast of Florida, thus adding to the unfortunate delay. The Bridge Company spent considerable money in efforts to find granite in the neighborhood, but the search was for the time in vain. At a later date it was found that the red granite of Missouri was well suited apparently to the wants of the Bridge; it could have been quarried more cheaply and far more promptly.
Originally both channel piers were to be faced with granite on all sides from 2 feet below low-water to 2 feet above high-water, a height of 46 feet. Now, however, in their anxiety to render the permanency of the foundations doubly sure, and to give to the masonry a finish more in harmony with the superstructure, the Directors decided to face both piers and abutments with granite quite to their tops. Only those parts of their sides which are above the springing of the arches and beneath the roadways (and consequently very little exposed to the weather) are of sandstone. This extra granite item added to the cost of the Bridge about $73,000.
The complete success which attended the sinking of the East Pier convinced Mr. Eads of the practicability of sinking the East Abutment in the same manner and to a greater depth. The original plan of the Bridge did not contemplate resting this abutment
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on the rock. The depth to the rock, at its site, had been ascertained by borings to be 8 feet greater than at the East Pier, or about 136 feet below high-water mark. The original plan was to place the masonry on piles driven to a depth of 50 feet below low-water, and then to protect the foundation by riprap. When, however, the Directors of the Company were assured of the practicability of resting this abutment on the bed-rock itself, and of thus terminating forever all doubt as to the absolute stability of each one of the great supports of the Bridge, they unanimously resolved that the East Abutment also should stand on the rock. The estimated extra cost involved in this change of plan was $175,000. Ten thousand cubic yards of masonry were required to build the abutment up to the point where originally the first course of stone was to be laid.Accordingly, preparations were made for sinking the abutment during the fall and winter of 1870-1. The drawings, and specifications of the East Abutment caisson were completed early in 1870, and the contract for its construction was made in May. It contained several new features and improvements which will be fully pointed out in the Chapter devoted exclusively to the East Abutment. The caisson was launched November 3; the first stone was laid on the 16th; and the rock was reached March 28, 1871, the immersion being 109 feet and 8 inches. So complete were the arrangements for the execution of the work, that the supervision was left wholly to the efficient superintendent, Mr. McComas, instead of making it the joint and exclusive duty of three experienced civil engineers, as was done at the East Pier.
The construction of the East Abutment was a signal triumph in engineering. It was quite unparalleled both in size and in the depth to which it was sunk, and it stands to-day the deepest subaqueous foundation ever built. While the work was in progress it attracted much less attention than had the channel piers. The novelty of the methods had worn off, and improvements in the apparatus and in the management of the work rendered the execution of the great undertaking an apparently easy matter. No accidents, no delays (except that caused by the tornado) were suffered; no insuperable obstacles were met, no serious difficulties of any kind were encountered; everything worked beautifully, and the cost in material and time was well within the estimates. One can point with confidence to the East Abutment of the St. Louis Bridge as the most brilliant example of deep foundations the world has ever seen; and though by the adoption of a similar plan it might readily be surpassed in mere magnitude, it will unquestionably mark an era in deep-water engineering. On the 28th of November, when the cutting edge of the caisson was 17 feet below the surface of the water, having sunk 8 feet of the 95 it was destined to pass through, Mr. Eads wrote to Messrs. J. S. Morgan & Co., London: —
* * * "The future is wisely hidden from our view, and I cannot therefore tell what disaster may befall me in sinking the East Abutment pier; but when I left it to-day, I could not help being impressed with the feeling that I had never undertaken any mechanical or engineering performance before with such full assurance that failure was absolutely impossible as in the case of this, the greatest work of my life. Every difficulty that presented itself in the sinking of the two channel piers has been fully provided for in this one, and I cannot believe anything can possibly occur that would prevent my assistants from safely placing the monster mass of masonry exactly where I intend it to rest, even if I were
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stricken out of existence to-morrow. We may encounter considerable masses of drift logs imbedded in the sand, or possibly a steamboat wreck; these would only delay the sinking a week or a month, but could not possibly stop it, as we have every facility for removing them."
The tornado just referred to was one of unprecedented violence. It occurred March 8, 1871. It came from the southwest across the City of St. Louis to the river, doing but little damage, being either some distance above the ground, or not yet at the height of its fury. But it struck the east bank of the river with great violence, and for about one-half a mile wrought most fearful havoc. Scattering the scaffoldings about the East Pier, it fell with terrific force upon the derricks and engine-boats lying at the East Abutment. Stout timbers were snapped like straws and the wire ropes and cables were twisted in utter confusion. Four days after the storm, Mr. Eads thus described the damage to his works: —
* * * "In an instant the frames [derricks, travellers, etc., of the East Abutment], with all their ropes of wire, pulleys, chains, etc., were levelled with the water in one confused and shapeless mass. Hydraulic lifting machinery, air pipes and hose, sand and water pipes, and all the various devices for the rapid prosecution of the work were bent, broken, and carried down by the large timbers of the framework. These latter were mostly 12 inches square and from 50 to 65 feet long, and in falling were broken to atoms. The violence of the storm carried these frames with their top hamper over on to the cabin within which were the air and water pumping machinery and boilers. Copper steam-pipes were here bent and twisted and some little damage to the air-pumps was done. Fortunately, the boilers with their usual pressure of seventy-five pounds of steam in them remained unbroken in spite of the tons of timber and iron suddenly thrown upon the slender roof above them, carrying it down in the general crash upon the engineers and firemen beneath. The men in the cabooses up in the frames of the "Allen," forty feet above the deck, went down with their little cabins. * * *
Strange to say in this general ruin, with men almost as thick as bees in a hive, but one man was killed and eight wounded, only two of these seriously."
Among the injured was the superintendent, Mr. McComas, who was rendered momentarily unconscious both of what happened around him and of his own acts. Every engine was disabled, including those pumping air into the caisson. The men in the air-chamber were at once signalled to come up, and in a few hours the caisson, filled with water. It remained thus filled with water for four days. The destruction of machinery, scaffolding, etc., caused by the tornado, with the incidental expenses caused by it, cost the Company about $50,000. Three large blocks of granite were knocked from the East Pier into the river as the scaffolding was thrown down. They were subsequently recovered.
The path of the storm across Bloody Island gave evidence of a wind-force surpassing anything on record. Lumber-yards were swept clean; all frame houses in the ill-fated path were completely dismembered and blown away. Not a stick was left to mark the site of the station of the Belleville Railroad, but the piles upon which the building rested. Huge sycamore trees about three feet in diameter were torn asunder and whole trains of cars were thrown from their tracks. Several empty freight-cars were lifted from the ground and carried hundreds of yards through the air, their trucks falling during the flight and burying themselves in the earth or striking the tracks with such force as to bend the rails completely out of shape. A heavy sleeping-car was taken squarely from the track and thrown across a body of water against an embankment some seventy-five feet distant, the couplings
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of the car being torn asunder. The most astonishing feat, however, remains to be told. A locomotive of the Wabash Railway, weighing some twenty-five tons, was actually lifted bodily from the track and thrown upon its back at the foot of an embankment some fifteen feet high. A personal inspection of the wreck by the writer showed that the track was undisturbed and that the top of the embankment had not been touched by the engine in its course.The lesson of this tornado was not lost upon the engineer of the Bridge. The original design contemplated an upper roadway wholly of wood, the sub-structure of which was designed to act as a truss to resist the action of hurricanes upon this part of the Bridge. The possibility of a tornado like that just described striking the Bridge itself, led to the adoption of a wind-truss in the form of a flat or horizontal girder 54 feet wide extending from pier to pier and formed entirely of plate iron. This design was subsequently modified, resulting in an iron truss of great strength and stiffness but involving a less amount of material. The admirable method employed to properly secure the ends of these wind-trusses and the details of the trusses themselves are shown in Plates XXII, XXXII-XXXIV. It is believed that as constructed the Bridge is abundantly strong to withstand a tornado as furious as that of March, 1871. At the date of the tornado, the East Abutment was only ten feet from the rock. Owing to the crippled state of machinery (for the damage was never fully repaired), subsequent progress to the rock was rather slow. The caisson reached the bed-rock March 28. By April 21 the concreting under the cutting edges and the girders of the caisson was all done. The chambers were packed solid with sand,
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Chapter VII. Contracts, Controversies, and Specifications.
On the 26th of February, 1870, before the bonds of the Bridge had been negotiated, even before either channel pier had been sunk to the rock, a contract was made with the Keystone Bridge Company of Pittsburg for the construction and erection of the superstructure of the Bridge. The officers of this company at that time were J. H. Linville, president; Andrew Carnegie, vice-president; J. L. Piper, general manager; and Walter Katte, engineer.
By the terms of the contract the Keystone Bridge Company agreed to complete the erection of the Bridge, ready in all its parts for use within seventeen months from the delivery of working drawings; provided they were not delayed in waiting for the completion of the masonry after the 1st of March, 1871.
All workmanship and materials used were to be subject to the tests, inspection, approval, and acceptance or rejection of the chief engineer of the Bridge. The prices agreed upon were, for all crucible-steel work, 15 cents per pound; for all wrought-iron work, except as hereinafter mentioned, 7.9 cents per pound; for all cast-iron work, 4 cents per pound; for all spikes, bolts, etc., in roadway, 6 cents per pound; for all pine timber and plank, 5 cents per foot, board measure; for all oak timber and plank, 7 cents per foot, board measure; for all galvanized-iron lining, 20 cents per square foot; for cornice, $1.50 per lineal foot; for painting, $36,000; for testing material, $36,000; for raising superstructure, $104,000. It was also agreed that the cost of planning one or more of the steel staves of each tube, as might be necessary, should be paid in addition to the above.
Any differences as to construction of contract or any ambiguities were to be decided by the chief engineer of the St. Louis Company.
Any work or materials not specified in the contract and which might be necessary to fully complete the superstructure of the Bridge were to be paid for at rates which would allow ten per cent profit to the Keystone Bridge Company.
Ten per cent of all amounts thus agreed upon was to be retained as security for faithful performance, and this should be forfeited by a failure to complete the Bridge at the time named.
The last clause of the contract read as follows: "It is distinctly understood that all risk as to the raising of the superstructure is assumed by said party of the second part" [the Keystone Bridge Company].
At the time of signing this contract the specifications for the steel had not been made
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out, and the details of the arch were still matters of investigation. The design complete and finished in itself as published in 1868 had been essentially modified: One tube 13 inches in diameter had taken the place of two smaller ones in each member of the rib; the depth of the rib had been increased; the couplings were to be of cast iron, with projections like trunnions to receive the main braces; the envelopes of the tubes were to be of rolled iron; — but none of these matters were irrevocably fixed. The size of the tubes, the number and shape of the staves in each, the depth of the rib, the character and form of the tube couplings, the size of the anchor-bolts, — all the more important parts were still liable to be changed by tests of materials, new calculations, and practical considerations. The signing of a contract under such circumstances was an unusual procedure and one fruitful of serious misunderstandings; but there were good reasons for this course. The magnitude of the work undertaken by the contractors rendered necessary the most extensive preparations for the manufacture of the materials. Tests of steel already made had shown that there was no difficulty in obtaining crucible steel in small bars of the quality desired from several different manufacturers, both in Europe and in the United States. Their ability to produce equally good steel in large masses, in the shape of bolts, staves, and couplings, was yet to be shown.It will be impossible to give a full history of the failures and successes of the several subcontractors, but a brief sketch of all important events and experiences will be given. The great delay and unexpected cost of the superstructure were largely due to the failures and difficulties experienced by the subcontractors, and the history of the Bridge would be far from complete if these matters were omitted. Controversies between companies cannot, of course, be discussed here any further than to state clearly the admitted facts in the case.
Working drawings were delivered in April and May. After the receipt of working drawings, Mr. Piper, the general manager of the Keystone Bridge Company, visited St. Louis and carefully went over all the details of the iron and steel work with Mr. Eads and his assistants. He was invited to suggest and did suggest modifications, which, without impairing the strength and efficiency of the parts, should render their construction more simple and inexpensive. Mr. Eads also introduced a few very important modifications in the details of the arched rib. In the design of 1868, the railways were 8 feet lower than the arches at the middle of the spans. To increase the openings below and to improve the appearance of the Bridge, the railways were raised 4 feet at the center of the Bridge, and the crowns of the arches were lowered 4 feet. In consequence of this, the versed signs of all the spans were diminished 4 feet and their radii were increased. To lessen the grade of the railways at the abutments, the crowns of the side spans were lowered 9 inches more by lowering the springing lines at the abutments 18 inches, the springing lines at the piers remaining the same. The curve of the railway tracks over the Bridge was thus made parabolic. These changes added much to the beauty of the Bridge. (See Plate I, and Frontispiece.)
The width of the Bridge was also changed from 50 feet to 54 feet and 2 inches; the depth of the rib was increased to 12 feet; the exterior diameter of the tubes was increased to 18 inches, with envelopes and couplings of steel and separate steel pins; and the anchor-bolts
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were made smaller. As a consequence of these extensive modifications, all the old drawings were returned and revised ones were substituted.The Keystone Bridge Company had made comparatively little progress in the execution of its contract by the end of the year 1870. Of the various establishments for making steel in the United States only two sent in bids, and of these only one was in accordance with the specifications, — that of the "Butcher Steel Works" of Philadelphia. As one manufacturer in England and another in France had expressed a desire to bid for the steel contract, bids were solicited from them, and some months were lost in fruitless delay.
The subcontract for all the steel was awarded to the Butcher Steel Works, October 24, 1870, the price for the steel delivered at their own works being 10ž cents per pound. The Butcher Company agreed to furnish all the steel "within ten months from the time the testing-machine was set up" [that is, should be in working order]. This machine, which was to be used for testing anchor-bolts, staves for the tubes, etc., was to be furnished by the Keystone Bridge Company from designs made by the St. Louis Company, but the cost of making the tests was to be borne by the Butcher Company. The Illinois and St. Louis Bridge Company was, however, to furnish an inspector, who should be under the orders of the chief engineer.
In view of the delay in subletting the contract for steel, and the character of the contract with the Butcher Company; in consequence of the probable failure of the Bridge Company to complete their masonry by March 1, 1871, at least to such a point as to require bolts and skew-back plates; on account also of the extensive changes in the form and material of the arches, — the Keystone Bridge Company felt entitled to an extension of time. They first asked for about three and a half months, but soon demanded more, and on the 7th of February, 1871, an extension of ten months was granted in a supplementary contract approved by both Companies. According to this contract the Bridge and its approaches were to be ready for traffic by the 15th of May, 1872, provided: (1.) The Butcher Company carried out its contract. (2.) That the Bridge Company furnished full working drawings and specifications for the Bridge within ten days and for the approaches within sixty days. (3.) That the masonry was ready for the superstructure as follows: Western Approach by August 1, 1871; Bridge by September 1, 1871; Eastern Approach by November 1, 1871. It was further agreed: —
"That for every day gained upon the time for opening for traffic as above determined, the Keystone Bridge Company were to receive a bonus of $500 per day; and for every day lost beyond this date as above determined, they were to pay a penalty of $250 per day. Provided, that no penalty should be exacted should delay be caused by a failure to receive steel, masonry, drawings, or specifications as above, or should extraordinary accidents occur, or should the back of steel staves be required to be planed or turned."
In this new contract certain disputed points were settled and certain changes in the design of the arch were recognized. The Keystone Company claimed that they supposed the skew-backs were to be of cast iron. The Bridge Company claimed that in the beginning they were designed to be of cast steel, but that upon adopting the plan of using one large tube in the place of two small ones, it was determined to use wrought-iron skew-backs, and
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that this change was made before the contract was made with the Keystone Company. At no time was it intended to make them of cast iron. It was agreed now that the Bridge Company should pay their actual cost, allowing the Keystone Company no profit. Forty-eight skew-backs were required, each weighing about 6,850 pounds, making a total of 328,800 pounds. The average cost of the forged skew-backs was 23 cents per pound, thus making an extra item of about $50,000.Among the changes recognized were the use of steel for the couplings of the tubes and the large pins through the same; the use of steel envelopes for the staves and steel laps for the same; the use of tubes 18 inches in diameter and a depth of 12 feet in the rib; the use of wrought-iron bands on the ends of the tubes; the use of "grooves" instead of "screws" for the couplings and tubes; and the change in the material and form of the wind-truss. It was also agreed that all questions of cost arising from changes in form, material, or design since February, 1870, should be referred to three experts, one to be selected by the Keystone Bridge Company and one by the St. Louis Company and the third by the two first chosen.
Complete revised drawings of the main superstructure were furnished February 10, 1871; they are given with great fidelity in the Plates of this book. To every engineer they will have great interest, and they will repay the most careful study.
No sooner were preparations made for the construction of the arches than practical difficulties appeared. It is true many of them had been anticipated, but it is equally true that the difficulties actually met far surpassed the shrewdest conjecture. The steel-makers found that their facilities were inadequate to the magnitude of the work undertaken; their workmen were unskilled; and their foremen without experience in working steel in such large masses.
Both iron and steel makers were unaccustomed to the rigid tests required. The insertion into specifications of the items of elastic limit and modulus of elasticity was a new feature in bridge contracts. Moreover, the detail drawings and specifications indicated a grade of workmanship altogether exceptional. To be sure they involved nothing as regarded accuracy either impossible or even difficult, but they were unusual and of course expensive. All these things now add to the value and fame of the great work; without them this Bridge would be merely one of a thousand bridges, and this history never would have been written; but in 1871, '72, and '73 the fame of the Bridge had little weight with a contractor or with a stockholder.
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Most of the real difficulties were actually overcome; and through the influence of Mr. Eads's specifications, the standard of good workmanship was raised throughout the world. In the construction of the St. Louis Bridge, engineering made rapid progress. Let me quote on this point from so eminent an authority as London Engineering. In its issue of October 10, 1873, the editor said: —
"Our present requirement being to select some example of the most highly developed type of bridge-building of the present day, we have no difficulty in passing before ourselves in mental review the different works now in progress throughout the world, and we have still less difficulty in electing as our example the magnificent arched bridge now almost completed by Capt. Eads at St. Louis. In that work the alliance between the theorist and the practical man is complete. The highest powers of modern analysis have been called into requisition for the determination of the strains, the resources of the manufacturer have been taxed to the utmost in production of material and perfection of workmanship, and the ingenuity of the builder has been alike taxed to put the unprecedented mass into place. In short, brain power has been called into action in every department. * * * One long-sighed-for result — the welding of the theoretical and practical man into one homogeneous mass, without which no truly great undertaking could possibly be carried out — has at last been attained."
Thus wrote the accomplished critic, unmindful for the time of the perplexities of the manufacturer, the misgivings of the contractor, the anxieties of the capitalist, and the trials of the engineer. Each in his place was abundantly exercised. When cross-examined before the tribunal of actual work, the steel and iron makers who had given such repeated assurances of their ability to construct all that was required, confessed themselves less confident, and sometimes completely at a loss. And more than all, after careful study of the drawings and specifications, even when numerous changes had been made with a view to lessening the cost of construction, the contractors claimed that the quality of workmanship required was far beyond their expectation, and that on many points Mr. Eads demanded impossibilities. Every detail was sharply discussed, and agreements were reached at the expense of time, and generally money. I cannot better give a glimpse of the peculiar difficulties encountered by the engineer of the Bridge than by quoting a few words from the letters of some of the principal actors, written just before the new contract of February, 1871: —
Dr. Taussig to Andrew Carnegie, Esq., — December, 1870:
* * * "I entertain a fear as to the willingness, not as to the ability, of the Keystone Bridge Company to complete the Bridge in time, if at all. I am led to this by official letters to Capt. Eads, every one of which evinces a spirit of fault-finding, of captiousness, and a supercilious disregard of the spirit and letter of the contract, coupled with an open avowal that they do not consider themselves bound by that instrument as to time and specifications. It is not contended in any of the numerous communications on this subject that the difficulties are insuperable, or that the specifications are beyond the possibility of execution; but it is found: that the material will cost much more than was anticipated; that skew-backs are to be forged, instead of cast; that holes are to be drilled, instead of punched; that upset links for this Bridge are designed differently from those of ‘ordinary’ bridges; etc., etc., ad infinitum; and consequently that the cost to your Company will be increased much beyond what was calculated on when they signed the contract. * * * Every difficulty resolves itself finally into a question of more or less profit to your Company." * * *
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Mr. Andrew Carnegie to Dr. Taussig, — December 30, 1870:
* * * "Capt. Eads had expected that the steel would be rolled so as to require no planing. Now, every bar must be planed. All holes are to be drilled — a thing unheard of!. Piper wanted to substitute our upset links [for the iron main-brace bars], but no, — they must be made in a different way, and Mr. Klomau had to decline until he experiments. All links in all lands are hammered only; these have to be planed. [See specification X, p. 74.]
Capt. Eads must only require the custom of the trade. Everything beyond that must be allowed for in time and money. Piper thinks the Bridge as now designed will require fifty per cent more time than as designed when our contract was made. This Bridge is one of a hundred to the Keystone Company — to Eads it is the grand work of a distinguished life. With all the pride of a mother for her first-born, he would bedeck the darling without much regard to his own or others' cost. Nothing that would please and that does please other engineers is good enough for this work. All right, says Keystone, provided he allows the extra cost and the extra time.
In all that I have written, remember I do not infer that Eads could have reached practical grounds earlier; on the contrary, we have all reason to be pleased that so novel a work has been carried through so well to this point, — but it is a new work emphatically. The very machinery to make the raw material has in large part to be created; the tools to finish are mostly special ones. That the result will be a magnificent success I do not doubt, but it may be three, it may be six months later than office figures. Only let every point be finally settled as to plans, etc., and if the Keystone doesn't surprise even the irrepressible Captain himself then its record is to be completely changed.
Meanwhile Keystone is only experiencing the fact that of all men your man of real decided genius is the most difficult to deal with practically. But he will come out all right. The personal magnetism of the man accounts for much of the disappointment. It is impossible for most men not to be won over to his views for the time at least. Piper and Katte come to us after their sober second thought prevails and give way to expressions of fear of pecuniary results, while the same men in St. Louis seem incapable of telling the Captain how far he travels out of the safe practical path. * * * You must keep Eads up to requiring only what is reasonable and in accordance with custom."
Mr. Linville to Mr. Eads, — December 19, 1870:
The planing of the ends of arch [main] braces is quite unusual and really appears unnecessary. I am not aware that such nicety has been practised heretofore in this country or elsewhere. * * * The extreme nicety indicated by the specifications and details places the whole work in a very different class from that understood by our officers who conferred with you before closing our contract.
The majority of the Board and officers that will have to do with your work will be a unit in their determination to execute it promptly and successfully, just as soon as you have furnished us with the plans and specifications reduced to a certainty, and determined satisfactorily in advance the principles that will govern the rates for work which in every respect thus far appears by the detail drawings and specifications to be much more expensive than we were warranted in anticipating from existing plans at the time the contract was made."
Mr. Eads to Andrew Carnegie, Esq., — January 9, 1871:
"I note your remarks that Kloman [of the firm Carnegie, Kloman & Co., Pittsburg, subcontractors for the rolled iron of the superstructure] ‘cannot upset bars so much thicker in the eye, of such shape
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and size as you desire,’ and also your assertion that if he cannot, no one else can. If this be the case, it would probably be as well to ascertain if that is the only manner of making them, without losing the time that would be involved in modifying the drawings and plans in an effort to avoid a difficulty that may be easily overcome in some other manner. I am sure Klomau will not undertake to say that it is impracticable to attempt to make these links or braces of the form given in the drawings.
* * * In this connection I cannot refrain from suggesting that the interests of your company will in my opinion be promoted by its moving promptly forward to the execution of the contract it has made, without raising the question of extra pay for every deviation from ‘custom,’ in the execution of a work which it knew at the time the contract was made was so totally out of the line of ordinary bridge work as to constitute a novelty not only here but abroad in bridge construction."
ADDENDUM. — SPECIFICATIONS FOR STEEL AND IRON WORK FOR THE ST. LOUIS BRIDGE.
I. CAST-IRON BED-PLATES. [Plate XXIII, Fig. A.]
(1.) The cast iron in the bed-plates must be of such material as is used in making guns. The tensile strength of specimen bars of the metal of these castings is to be not less than 20,000 pounds per square inch of section. Two of these specimen bars shall be 11 inches in diameter by 16 inches in length, and shall be poured from the ladle before and after the bed-plates have been cast. To prevent unequal contraction the castings shall remain in their moulds for at least 36 hours after the casting is made.
(2.) The castings must be free from scale and flaws of every nature.
(3.) The face which is to receive the wrought-iron skew-back must be planed and the bolt-holes drilled at the exact angle given in the drawings.
II. CAST-IRON ANCHOR-PLATES. [Plate XVII, Fig. 3.] [Material and tests same as in No. 1.]
Bolt-holes and recesses for nuts are to be drilled.
III. ANCHOR-BOLTS THROUGH PIERS AND IN ABUTMENTS. [Plate XXIII, Fig. D.]
A. Wrought-iron Bolts.
(1.) The wrought-iron bolts must be forged of the best American iron, and of the exact dimensions shown by the drawings. The enlarged ends are to be turned off as far as the thread of the screw extends.
(2.) These bolts will be tested after being finished and with their nuts in position. [To save transportation to Pittsburg and back to Philadelphia, they were tested before the threads were cut See p. 80.]
(3.) Each bolt will be tested in tension to 20,000 pounds per square inch of section without permanent set under this strain. [This was afterwards changed to 18,000 pounds per square inch.]
(4.) A specimen bar of the material composing each bolt will be required to possess an ultimate strength of 60,000 pounds per square inch of section.
B. Steel Bolts.
(1.) They are to consist of cast steel and are to be finished as stated for wrought-iron bolts.
(2.) Tests will be made of the finished bolts in the same manner as the wrought-iron ones, and they must be able to stand without permanent seta tensile strain of 40,000 pounds per square inch of sectional area.
(3.) A specimen bar cut from each end of each bolt must have an ultimate tensile strength of 100,000 pounds per square inch of section.
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IV. NUTS FOR ANCHOR-BOLTS. [Plate XXIII, Fig. C.]
They are to consist of the same material as the bolts to which they belong, and their faces resting on skew-backs and anchor-plates must be turned.
V. WROUGHT-IRON SKEW-BACKS. [See Plate XXIII, Fig. B.]
They must be forged of the best American iron, and accurately finished according to the drawings. A test-bar from each of them must stand an ultimate tensile strain of 60,000 pounds per square inch of section.
VI. TUBES. [See Plate XXIX.]
(1.) The modulus of elasticity [see p. 77] of the steel in the staves shall not be less than 26,000,000 nor more than 30,000,000 pounds. This variation should be avoided if possible; in which case the lower amount will be preferable. Each bar will be tested by the contractor, and the modulus stamped on it by the inspector of the Illinois and St. Louis Bridge Company.
(2.) Each tube is to be composed of six staves having, as near as possible, the same modulus of elasticity.
(3.) Before proceeding to turn the ends and grooves, the inspector will have the six staves temporarily formed into a tube by bringing them in close contact by means of collars at the ends of the tubes. If they fail to form a true circle or to come into close contact, the inspector will have them straightened, and if this cannot be done, the defective staves must be rejected. [See method of forming tubes, p. 149.]
(4.) The ends of the tubes having been turned, and the grooves cut, the tube will be carefully tested as to its length, the finish of the grooves, and the correctness of the bevel angle, and if defective must be rejected. The center line of the shaft of the boring tool must pass in all cases through the center of the tube, at a point half way between the outside limits of the grooved portion of the tube. [See p. 149.]
(5.) One specimen bolt from each twenty staves will be made by which to test their limits of elasticity and ultimate strength in tension. The inspector for this purpose may either have specimen bolts cut from staves rejected on account of imperfect workmanship or procure them from pieces cut off from staves of extra length. These will be selected by the inspector from such staves as he may choose. If, however, a failure of such a percentage of these test-bolts should occur as to create a want of confidence in the remainder, the chief engineer may cause such additional numbers of them to be made as he may deem necessary to insure the requisite strength in each stave. These specimen bolts must be able to sustain a tensile strain of 40,000 pounds per square inch, without permanent set, and must have an ultimate strength of 90,000 pounds per square inch of section.
(6.) Wrought-iron bands on tubes must be turned on the inside and faced on each edge, as shown in drawings, and must be heated and shrunk on.
VII. STEEL ENVELOPES FOR TUBES. [See Plate XXIX.]
(1.) For the purpose of testing the material of the plates which form the envelopes, the inspector will select the plates from which the butt-straps are to be cut, and retain one cutting of each plate as selected. The specimen bars so obtained must have a limit of elasticity of 40,000 pounds, and an ultimate tensile strength of 90,000 pounds.
(2.) The envelope plates must have their edges planed and brought closely together to insure accuracy of diameter of the tubes before riveting on the butt-straps. These latter will be calked.
VIII. COUPLINGS. [See Plate XXX.]
(1.) The couplings for tubes may be of rolled steel. The portions next to the main braces of the arch must be true and parallel, to insure accurate contact and adjustment of the braces on them; but these surfaces and the outside of the couplings need not be finished work. The surfaces where the halves core in contact with each other, and with the tubes and pins, must be accurately finished.
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(2.) For the purpose of testing the material, the inspector will have one specimen bolt cut from the plates used in the manufacture of the couplings for each ten pairs, and subject them to the same tests as those used for forming the envelope. The failure of these test bolts will in all cases involve a rejection of the pieces they shall have been cut from, and if the percentage of failure is considerable, the number of tests may be increased according to the judgment of the chief engineer.
IX. STEEL PINS. [See Plate XXX.]
(1.) The steel pins will be accurately finished according to the drawings. The central part where they are reduced in size will not require turning off. The conical portions must be large enough to fill tightly the holes in the tube couplings.
(2.) For the purpose of testing the material of the pins about two out of every forty pins should be forged in one piece, with au intermediate bar of the same size as the middle of the pin and about 12 inches in length between the two pins, or every twentieth pin shall be made with a projection at one end 12 inches long and of the same diameter as the middle of the pin. From these specimen bars, test bolts must be cut out which shall stand a tensile strain of 40,000 pounds per square inch without permanent set, and have an ultimate tensile strain of 100,000 pounds per square inch. These extra 12-inch lengths will be paid for by the [St. Louis] Company.
(3.) Should any of these test bolts fail to stand the test, the entire forty pieces shall be rejected. The contractors in this case may, however, cause a test bolt from one of the rejected pins to be made, and if this should stand the test, the inspector shall select nine of the lot and accept them, and so on of the remainder, one of the pins being in this manner tested for nine that were rejected. In this event the pins thus cut and destroyed shall not be paid for by this Company. Should the inspector have cause to suspect the material in any of the finished pins, he may resort to a test by inserting the doubtful pins into nippers provided for this purpose and subjecting them to a direct tensile strain, or to a test by a transverse load as the nature of the case may suggest. But these latter tests shall be so arranged, that no part of the pin will be strained beyond 40,000 pounds per square inch.
X. MAIN BRACES. [See Plate XXXI.]
(1.) The main braces are to be made of the best American iron, and to conform as closely as possible to the dimensions given in the drawings. The upset ends are to be planed on both sides to the exact thickness required, and the holes which are to receive the pins are to be drilled.
The inspector will pay particular attention to the distance between centers of pin-holes and to the exact fitting of the pins to these holes.
(2.) Each brace will be tested by inserting proper pins into the pin-holes and subjecting the braces to a strain of 20,000 pounds per square inch of sectional area, which strain must not produce any permanent set. Specimen bars of the metal selected by the inspector must have an ultimate tensile strength of 60,000 pounds per square inch of sectional area. [See pp. 96-101.]
(3.) The rivet-holes in the braces are to be drilled. [See p. 102.]
(4.) The rivets are to be of the best American charcoal iron, and are to be driven hot.
XI. STEEL EYE-PLATE WASHERS. [See Plates XXIV, XXV.]
(1.) The eye-plate washers, where they come in contact with the braces and horizontal straps, must be planed or turned.
(2.) The lip containing the eye must be bent to the exact angle given in the drawing, and tested by templets to be provided by the contractor under the directions of the inspector. Specimen pieces of the material of which these are made, not exceeding two and one-half per cent of the number of washers, will be made at the steel works and tested to 100,000 pounds per tension.
(3.) The inspector may, if he considers it proper, select some of these eye-plate
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them before being bent in regard to their ultimate tensile strength, which is to be not less than 100,000 pounds per square inch of sectional area. These extra ones will be paid for by the Company.
XII. TENSION-RODS BETWEEN STEEL RIBS. [See Plates XXIV, XXV.]
(1.) The tension-rods, eye-washers, connecting straps, and bolts will be tested after being finished to 40,000 pounds per square inch of section, and shall show no permanent set. Test pieces of about five per cent of the number of the rods will be tested to an ultimate strength of 100,000 pounds per square inch at the Steel Works.
XIII. HORIZONTAL STAYS BETWEEN STEEL RIBS. [See Plates XXIV, XXV, XXXI.]
(1.) The horizontal tubular stays, nuts, and sleeves must be made of the best charcoal iron. Specimen pieces of the material of which they are made shall be equal in strength when tested to that used in the braces.
(2.) Their ends must be turned off square to the exact length shown in the drawings, and the nuts and sleeves carefully prepared so as to make a close fit.
(3.) The inspector may select one tube out of twenty for the purpose of testing its strength under compressive strain. With 15,000 pounds per square inch of section, they must not show any permanent set. The inspector may also apply a hydraulic test to them, which, however, will be limited to a strain of 20,000 pounds per square inch tensile strain on the section of the tube.
(4.) Two extra tubes selected from the whole number will be tested for their ultimate tensile and compressive strength, and will be paid for by the Company.
(5.) The inspector will, by a gauge provided for the purpose, or by drilling, measure the thickness of the metal in the side of the tubes at different points if found necessary, and will reject all tubes showing inequalities in the thickness, if such inequalities exceed one-fifth of the thickness of the metal in the sides.
XIV. DIAGONAL BRACES BETWEEN BARS OF MAIN BRACES. [See Plate XXXI.]
The T and strap iron forming the diagonal bracing must be of the best rolled iron. The inspector shall cut and test specimen bars from the iron which is to be used for this bracing, to the number of at least one out of two hundred pieces, and test it as to ultimate strength and permanent set. These test-bars must stand a tensile strain of 18,000 pounds per square inch without taking a permanent set and 50,000 pounds per square inch before rupture. Failure of three pieces out of a lot of two hundred to stand this test, shall involve the rejection of the whole lot. All the holes in T and strap iron may be punched, but the greatest accuracy will be required in the location of the rivet-hole, and the inspector may reject any piece in which the centers of any of the rivet-holes are more than one-fourth of an inch from the center of the corresponding rivet-holes in the pieces to which they are to be riveted.
XV. WROUGHT-IRON BEAMS. [See Plates XXVII, XXVIII.]
Made-up beams must consist of best iron which will stand an ultimate tensile strain of 60,000 pounds per square inch for plate iron, and 50,000 pounds per square inch for angle-irons. Edges of plates unless rolled straight are to be planed to the exact size required by drawings. The inspector will select such specimen bars from the iron used in the construction of these beams as his judgment may dictate for the purpose of testing.
Rolled beams must be rolled to the exact size shown in drawings, perfectly straight with full edges. The inspector may test one out of fifty by deflection as to permanent set and modulus, and test-bars occasionally selected must stand an ultimate tensile strain of 55,000 pounds per square inch.
XVI. SUSPENSION BARS, [See Plate XXXI.]
Heads of suspension bars must fit closely to braces; if the distance of their heads from brace exceeds in any part one-sixteenth of an inch, the face next to the brace must be planed. The two uppermost rivet-holes at lower end of suspension bar must be drilled; all others in the bars may be
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punched. Each suspension bar shall be tested as to permanent set to 15,000 pounds per square inch tensile strain, by inserting pins at the upper end and proper bolts at the lower end. The inspector may also test a few of these bars as to their ultimate strength, which must be 60,000 pounds per square inch. The Illinois and St. Louis Bridge Company will pay for bars tested to destruction.
XVII. JAW NUTS. [See Plate XXVII.]
Jaws supporting cross-beams at special joints must be made to the exact dimensions given in drawings. When they come in contact with eye-plate washers they must be turned.
XVIII. VERTICAL STRUTS. [See Plate XXXI.]
The specification and tests for T, channel, and strap iron in the struts are the same as for the diagonal braces between bars of main braces given in Section XIV.
XIX. WROUGHT-IRON TENSION-RODS. [See Plates XXI, XXII.]
The test-bars of iron used in these rods must stand an ultimate tension strain of 60,000 pounds per square inch, and a tensile strain of 20,000 pounds per square inch without permanent set.
Each rod with its sleeve-nut attached shall be tested to 15,000 pounds per square inch by inserting bolts in the eyes. They must not show any permanent set under this strain.
Right and left sleeve-nuts are to be used in all parts of the structure.
XX. IRON WIND-TRUSS OF UPPER ROADWAY. [See Plates XXXII, XXXIII.]
All plate iron is to stand 55,000 pounds per square inch. For the purpose of determining this strength, strips may be cut by the inspector from one out of every two hundred plates. Failure of three pieces out of a lot of two hundred pieces to stand this test shall involve the rejection of the whole lot. Angle and T irons must stand the same tests as already specified for channel and T iron in a previous section. All joints in the upper roadway to which water has access are to be calked. The cornice to be of galvanized iron, the curved part of No. 20 and the remainder of No. 14 as shown in drawings.
[See p. 110 for record of change in the cornice.]
XXI. ANCHORAGE OF WIND-TRUSS OF UPPER ROADWAY. [See Plate XXXIV.]
The steel is to be of same quality, and the steel rods are to be tested with their nuts on, the same as provided for bolts passing through piers. Castings to be of the same quality of iron and to stand the same tests as required for anchor-plates. [Iron anchor-bolts were used. See p. 103.] The inside of guide box and the end of wind-truss resting in the same are to be planed on sides and lower surfaces. None of the other castings need to be planed, provided castings are neat and true, unless otherwise ordered.
XXII. CASTINGS FOR SUPPORTING STRUTS ON SKEW-BACKS. [See Plate XXIII, Fig. F.]
Are to be of the same quality of iron and to stand the same tests as specified for other iron castings. Surfaces resting on skew-backs and on collar of bolts are to be turned.
XXIII. GENERAL AND MISCELLANEOUS.
(1.) All holes through steel work must be drilled, and all bolts turned, unless otherwise directed by the inspector in writing.
(2.) The strains will be computed in all cases from observations of the pressure of water in the rams by gauges tested and approved by the chief engineer.
(3.) Test-rods of wrought iron and cast steel for testing in tension for ultimate strength will be 8 inches long by 1 inch in diameter, and must be turned down to three-fourths of an inch in diameter, leaving a shoulder at each end. [See p. 302.] The bolts for ascertaining elastic limit must be 14 inches long. These dimensions may be reduced according to the judgment of the chief engineer. In all cases the sectional area referred to is the area before testing and not the area after fracture.
(4.) Steel templets will be provided by the contractor, under the direction of the chief engineer,
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and they will be verified and stamped by him before they can be used. The various parts of the work must be made to fit these templets with the greatest attainable accuracy, and it will be the duty of the inspector to reject any piece which in size and direction of its parts shows the least imperfection.
(5.) Each piece after being examined and accepted by the inspector is to be marked in some indelible manner by the inspector, so as to show its exact position in the structure. Every piece when finished is to be covered with a coating of paint or other material, as directed by the inspector, to prevent rusting.
(6.) The arches for the two side spans are intended to be exactly alike.
(7.) The main tubes of the three spans will all be of the same diameter and with the same section. Any difference between the middle span and the side spans in the section of the staves will be in their areas alone.
(8.) The steel shall be of the kind known in commerce as "crucible cast steel."
(9.) Any modifications which may be suggested by the contractor to lessen the cost of this part of the work will be agreed to by the engineer, provided such proposed modification will not delay the execution of the work and will not impair the strength of the structure; no modifications, however, will be permitted without the written approval of the engineer indorsed on the working drawings.
(10.) Should it be deemed important by the engineer to alter or modify these drawings or specifications, the right to do so is especially reserved by him; but in case of such alteration involving the contractor in extra cost, a just allowance will be made to him for the same.
Inasmuch as this phrase has been used by different writers in different senses, it seems best to clearly define its use here. Every bar of metal is perfectly elastic under certain moderate compressions and tensions, that is, it yields instantly to the least strain, whether in compression or tension, and if the strain is only moderate the shortening or lengthening is proportional to the strain, and when the strain is removed the bar assumes exactly its original dimensions.
If the strain exceeds a certain point, which is called the "elastic limit" of the bar, the bar fails, when released from strain, to resume its original length; the internal arrangement of its particles has received a permanent modification, and the bar is said to have taken a "set." A slight set may be received without injury; it is only when each new application of the strain produces a new set that a bar is injured, and is, as it were, on the road to speedy destruction. When the set continues under repeated application of the same strain, it generally increases in amount. Now the modulus of elasticity is determined by the amount of yielding under a strain which produces no set, and is that strain which bears to the imposed strain the same ratio that the original length of the bar does to its change of length. For example, suppose that under a strain of 10,000 pounds per square inch a bar 30 feet long lengthens one-eighth of an inch. Now the original length of 30 feet or 360 inches is 2,880 times the increase in length, hence the modulus of elasticity is 2,880 times 10,000 pounds, or 28,800,000 pounds. Had the material been more yielding the modulus would have been lower. Suppose we test an oak post by compression. A length of 30 feet would be shortened one-fourth of an inch by a load of about 2,000 pounds per square inch. The original length being 1,440 times the contraction, the modulus of elasticity is 1,440 times the load, or 2,880,000 pounds. It thus appears that the modulus of elasticity is the best possible measure of the ability of a substance to resist a change of form under strain. Moreover, it is easily seen that in order that the strains may be equally distributed over the six staves of a tube, for instance, and through the tubes of the upper and lower members of the rib under different loads, the modulus of elasticity must be constantly the same in all the steel of the arch. Should some of the staves of a tube when under compression yield more than others, it is obvious that
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those others would be forced to bear more than their share of the load. It must not be assumed that a high elastic limit is always accompanied by a high modulus, nor that "hard" substances have relatively high moduli. Mr. Eads tested a bar of Butcher steel in April, 1870, which had an elastic limit of 64,000 pounds per square inch and a modulus of 24,000,000 pounds. He reported that it suited him exactly. Again, he tested several specimens of wrought iron which showed moduli of over 40,000,000 pounds.79
Chapter VIII. The Construction of Anchor-Bolts and Staves.
The first important work the Keystone Company was required to furnish was the anchor-bolts which were to secure the ends of the arches to the abutments and piers. Each of the lower skew-backs was to be secured by four bolts, and each of the upper by three. The bolts through the piers secured the skew-backs on each side. There were therefore twenty-eight bolts for each abutment and each pier, or one hundred and twelve bolts in all. (See Plates XVII, XVIII, XXIII.) Eighty of these bolts were to be of steel, and thirty-two of the best wrought iron. The latter were for the upper holes of the upper skew-backs. Messrs. Macpherson, Willard & Co., of the "Union Steam Forge," Bordentown, N. J., had taken the contract to forge the iron ones. They were sent to the steel works in Philadelphia and tested by Mr. Dahlgren. They were subjected to a tension of 18,000 pounds per square inch, and measured for permanent set. The total tension applied to each bolt was a little over 232 tons, and the uniform extension of the bolt between the collars (see Plate XXXV, Fig. 5 ), which were 31 feet apart, was one-fourth of an inch. The bolts were a little over 34 feet long, and all stood the test perfectly, contracting to their original length when relieved of the strain.
Messrs. Macpherson, Willard & Co. also took the contract to furnish the wrought-iron skew-backs, forty-eight in number. (See Plate XXIII, Fig. B .) In April, fourteen had been forged and sent to finishing works in Philadelphia. At the request of Mr. Eads, Mr. Henry W. Fitch, engineer of the United States Navy, inspected the forgings. Their great size rendered it impossible for the light hammers at the Union Steam Forge to force the cinder out from between the layers and make the welds complete. Consequently the forgings were somewhat laminated, but as the tubes were to screw through to the base, good judges decided that they were abundantly strong, and they were finally accepted. Their apparent ill success, however, led the contractors to sublet the remaining thirty-four, — twelve to the Patterson Forge of New Jersey, and twenty-two to the Bridgewater Forge of Massachusetts. The latter forge had the heaviest hammer in the country. All the forgings produced by these firms were excellent in material and workmanship, and all were accepted. The Butcher Company of Philadelphia had included the steel bolts in their contract. Each of the bolts was to be tested to the extent of 40,000 pounds to a square inch, or 516 tons to a bolt. The machine on which the tests were to be made was constructed by the Keystone Company, its main features having been suggested by Mr. Eads. (Plate XXXVI.) On February 9, Mr. Linville reported that the testing-machine was "set up," and that Mr.
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Butcher desired an inspector who should test specimens to determine the proper quality of steel. Accordingly, Mr. Paul Dahlgren left St. Louis February 13, and reported to Mr. Linville on the 15th. The machine appeared to be in order, but there was nothing suitable to test. Mr. Dahlgren was not prepared, nor was he instructed, to test various small specimens of Mr. Butcher's steel to aid him in arriving at a knowledge of the proper mixture to be used. Moreover, it was thought that sufficient tests had already been made at St. Louis during the previous year to test the best grades of steel. Mr. Butcher appeared to be much disappointed at this. He claimed that all his works were waiting for the testing to be done. He was told that the large machine was intended only to test the finished work or actual pieces of the Bridge; small specimens that were to be tested for modulus, permanent set, and ultimate strength, could be tested on the machine in St. Louis or elsewhere at the option of the manufacturer.Under one pretext or another Mr. Butcher continued to delay. Because the steel gauge was not at hand, he refused to forge anchor-bolts, although the gauge ordered by Mr. Eads was waiting in the shop. It is probable that the real reason for the delay was the high price of coal, caused by a strike among the miners. Whatever margin of profit had been expected from the contract to furnish steel seemed now destined to be eaten up by the ruinously high price of fuel.
The masonry at St. Louis was waiting for the bolts, and yet the delay continued. By April 1, Mr. Huston, the president of the Steel Works, reported that he had bought a supply of coal, though at a great loss. The steel gauge to be used in testing was made in St. Louis and sent to Philadelphia about April 12. For a description of this admirable instrument, the joint product of Messrs. Eads and Flad, see Chapter XXV. By May 1, 1871, Mr. Butcher had "roughed down" ten anchor-bolts under the hammer, but they were not finished ready for testing. On May 9, Dahlgren wrote: "A few more anchor-bolts have been turned out at the Steel Works. Neither they nor those previously made are ready for testing."
On the 24th of May the first steel anchor-bolt was tested. It was a little more than 34 feet long and 5ž inches in diameter, excepting about 3 feet on each end, where the diameter was 6Ë inches. On these ends threads were to be cut for the steel nuts. It was at first intended to test the bolts by applying the tension directly to the nuts after they had been carefully fitted. As, however, the threads were to be cut and the nuts fitted in Pittsburg and the bolts afterwards tested in Philadelphia, Mr. Eads consented to a change of plan to save time and to relieve the Butcher Company of the risk of great unnecessary loss; for in case the bolts failed to stand the test, the steel-contractors were to lose not only their bolts and the freight, but the cost of all the work done on them by the Keystone Company. It was therefore held by the president of the Steel Works to be a large concession to them when permission was given to forge the bolts with a second small projection on each end, which when turned should accurately fit the clamps of the testing-machine, as in Fig. 23. These projections were to be afterwards
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turned off by the Keystone Company. Mr. Butcher the superintendent, however, protested, declaring that the little projections were going to give him an immense deal of trouble. He claimed that he would have had no trouble whatever in rolling to the diameter of the part where the thread was to be cut, and reducing the middle under the hammer in another heat. This additional projection would prevent him from using this simple method and compel him to use fourteen or fifteen heats. The method he actually used in all cases was to cast the ingots in rectangular blocks and then draw them out under the steam hammer. No rolling was ever attempted. It was heavy work, and required skill and judgment.Specimens from the bolt first tested had shown great strength, one breaking at 101,000 pounds, the other at 100,000 pounds per square inch. The bolt, however, broke at 30,000 pounds per square inch of the cross-section at the point of fracture. Several men engaged in making the test narrowly escaped injury when the bolt gave way, as the long end sprang out of the machine a distance of over thirty feet and the clamps which held it were flung off with great violence. The ram came out so far that it cleared the packing. No flaw in the steel was visible, and the surfaces of fracture seemed sound.
Three or four days later a second steel bolt was tested with similar results. At a strain of 33,000 pounds per square inch in the body of the bar, it broke under the clamps at the end, where the diameter was about 6Ë inches. The concussion forced the ram out of the cylinder, breaking off the steel plates, besides doing other damage to the machine. The fracture showed a good quality of steel, being close-grained, uniform, and silvery in appearance. The strains came on squarely, and a fair hold all around the circumference of both heads was observed in the nippers, insuring a tight fit. The strains were gradually imposed; there was no jerking of any land. No vibrations took place in the bolt which could be detected by the eye. (Two men were watching the bolt carefully for this during the entire time of testing.) The violent reaction of the same arose not only from the elasticity of the bolt and the material of the machine, but chiefly from the presence of a small amount of air in the cylinder, which expanded the instant the bolt broke. Later, the cylinder was tapped at its highest point and the air let off through a stop-cock. This remedied the matter in great measure, but as the thrust on the machine was taken by oak timbers, whose modulus of elasticity was much lower than that of iron and steel (and which reacted, therefore, through a greater distance), the liability of fractured bolts to "kick" was never wholly removed.
The injury to the testing-machine was not repaired till June 9, and five days later a third steel bolt was tested in the presence of Mr. Eads. It broke at 26,000 pounds per square inch. Small specimen bars cut from a fragment of this broken bolt showed sufficient strength, and it was suggested that the evil, arising from whatever cause, would be remedied by annealing. A furnace was therefore built by the Steel Works, in which several of the forged bolts were annealed. They were not ready to test, however, till July 25. On that day one was tried and broke at a strain of 12,000 pounds per square inch, owing to a flaw near one end. The following day another was tried, and when 38,000 pounds per square inch were on the bolt, the pulling-bolt of the machine broke. This pulling-bolt, which was the piston-rod of the hydraulic cylinder of the machine, was of steel and 6 inches in diameter,
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but the screw cut on the outer end diminished its diameter to 5Ë inches. It broke at the beginning of this thread, discovering a slight flaw.Thus the first four of these massive steel bolts broke under a test which was supposed to impose less than two-fifths of the breaking tension, while the fifth bolt broke the machine. Six months of time had been lost, while all the foundations of the Bridge were waiting. The loss of the bolts, which cost not less than $300 each, and the burden of keeping the testing machine in repair, which was no small matter, fell upon the Steel Works; while the Bridge Company was the heaviest loser of all from delay. But Mr. Eads was not wholly unprepared. Drawings of iron bolts to replace the steel ones had already been made, and the moment the machine broke down, as described above, he decided to order iron bolts for the Western Abutment without delay. Eight were ordered of Willard, Macpherson & Co., and twelve of the Trenton Forge.
But Mr. Eads's chief reliance in this emergency was upon the Chrome Steel Company of New York. No sooner had the third bolt broken than he arranged with this company to make a 6-inch bolt and send it to Philadelphia to be tested. He also ordered some, ingots of chrome steel in order to test its fitness for making staves. For some time he had been familiar with many of the peculiar properties of chrome steel.
The utility of annealing the bolts was still a matter of doubt, and there seemed to be no other prudent course except to effect an arrangement with the Chrome Steel Company as soon as possible whereby it should furnish such amounts of steel as might be required. "The proprietors of the Butcher Works are considerably demoralized," wrote Mr. Eads, July 26, adding, "and certainly if I had no reason to expect better results in the tubes, I should feel very anxious myself. But I have no fear about the success of the staves." Yet there were not wanting men who declared in the most positive manner that the steel demanded could not be made, that "the ablest men in the country pronounced it impossible," etc., etc. Chrome steel was made by a patented process, and as the two steel companies were naturally rivals it was not easy to effect an arrangement between them. This was, however, done at a later date.
As I have said, the turning point in steel matters was the breaking of the pulling-bolt of the testing-machine on July 26. Duplicate bolts were at once ordered by Mr. Linville, one of chrome steel and one of superior Butcher steel. The chrome-steel bolt was put in the machine August 15, after a delay of twenty days. For the purpose of avoiding the risk of breaking again, Mr. Fitch, the inspector, postponed the testing of steel bolts till he had tested seven wrought-iron ones. The iron bolts were all tested and accepted by August 18.
Three short steel anchor-bolts were then tested. They all stood the test required, but the steel sleeve-nut (the shaft of which was 6 7/16 inches in diameter) on the end of the pulling-bolt of the machine broke August 22, completely disabling the machine for pulling purposes for about three weeks more. The nut is shown in Fig. 14, p. 89. It broke at the shoulder, A A, The dimensions in the cut are those of the new nut.
In view of all these very serious mishaps to bolts and testing-machine, Mr. Linville wrote as follows August 29: —
These breakages "prove that Butcher's steel has heretofore been of very inferior grade, and also prove that the making of large masses of the required strength is still experimental, with no definite
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data as to ultimate strength and security. We are not responsible for this nor the delays caused by the accidents. It was not supposed by Mr. Eads nor any other person that the steel which stands 100,000 pounds in small specimens would break at 26,000 to 30,000 pounds per square inch in large specimens. The results of these breakages have been the racking and injury to the testing-machine, and annoying delays in repairs. * * * If the 6-inch pulling-bolt of the machine breaks, then I should have no confidence in the anchor-bolts. While the duplicate bolt is being used I would order an 8-inch pulling-bolt and new couplings. These will be very expensive, difficult to adapt to the machine, and will cause several weeks' delay. It is unreasonable to ask their introduction; but to get over the hitherto undetected difficulty in dealing with large pieces of steel and the consequent delays, I have offered to provide such a bolt."
All the steel bolts thus far tested were made of Mr. Butcher's carbon steel. Four only had remained unbroken, apparently uninjured. Various attempts had been made to determine their moduli of elasticity, and the exact amount of set caused by the tests; but he results were only rough approximations. Nearly every kind of measuring apparatus had been broken, and, according to the statements of Messrs. Dahlgren and Cooper, it was at great personal risk of life and limb that the inspector came near enough to the bolt when under strain to use his micrometers.
I have thus grouped together several important events in the history of the testing-machine and anchor-bolts, because they bring out into strong relief the peculiar difficulties under which both engineer and contractors labored, and because they partially explain the protracted delay of the summer of 1871. It must not be supposed that the whole has been told even on this topic, but it is necessary, before going further in this direction, to mention other important matters.
It may be well to say a word in this connection as to the use of the anchor-bolts, and the consequence of their all giving way in the Bridge, if such a contingency may be supposed possible. The anchor-bolts merely serve to fix the ends of the ribs. Without them there might be a slight motion of one of the skew-backs in cases of extreme cold or heat, nothing more. Thus, in the extreme heat of summer, the ribs would rise at the crown, and the lower skew-backs might be drawn away from their backing a small fractional part of an inch, the entire weight and thrust of the rib being carried by the upper skew-backs; but this would do no sort of harm. The fixing of the ends of the tubes introduces greater stresses into the rib, and has the effect of diminishing the motion of the whole under extreme temperatures. In severe cold the crown falls, and the entire weight is carried by the lower skew-backs. Hence, while the greatest possible strains in the anchor-bolts are less than the elastic strength of iron, it should be remembered that the arches would be perfectly safe even if every anchor-bolt should break.
Mr. Paul Dahlgren had resigned his position as assistant inspector of iron and steel work on July 16. He had been in the employ of the Bridge Company since March, 1870, and had been constantly employed in testing either specimens of materials or finished work. The records of all his tests were kept by him in complete order, and furnish the materials for one of the most valuable Chapters in this work.
In May, 1871, Mr. Eads applied to President U. S. Grant for the services of assistant engineer Henry W. Fitch of the United States Navy. Mr. Eads was well acquainted with
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Mr. Fitch and knew his eminent qualifications for the very responsible position of chief inspector of iron and steel work. Leave of absence was granted as desired, and in June Mr. Fitch was appointed. He had already inspected some of the forged skew-backs, and now about the 1st of July he took up his position at the steel works in Philadelphia. Mr. W. H. Harrison was appointed to assist him when Mr. Dahlgren resigned.During the months of June, July, and August Mr. Eads spent the most of his time in Philadelphia, New York, and Pittsburg. All this while his advice and ingenuity were in constant demand. Not only were the Butcher Steel Works making, or trying to make, steel anchor-bolts, but they were casting and forging steel pins for securing the main braces to the tubes, and steel nuts for the anchor-bolts, and steel rivets and steel tension-rods for diagonals between the arched ribs, and, more important than all, the steel staves of which the tubes were to be formed. No difficulty was expected or experienced in the manufacture of either pins, rivets, nuts, or rods. Such was not, however, the case with the staves, and upon their fabrication ever since the beginning of the enterprise all eyes had been turned.
No sooner had the subcontract for the manufacture of steel been awarded, than Mr. Butcher began his preparations for rolling staves. Six staves were to form a tube 17Ë inches in external diameter; their thickness varied in different tubes. For the purpose of increasing the rigidity of the tube, Mr. Eads had wished the staves to be made with flanges on their inner edges as shown in the figure. Repeated experiments on model tubes (see Chapter XXV) had, however, convinced him that as finally designed his tubes would be sufficiently rigid with plain staves; he therefore gave Mr. Butcher his choice to roll them as channel bars, as in Fig. 13, or as sectors of a regular tube. (Fig. 3) Mr. Butcher decided to roll them as channels, but after repeated failures, fell back upon the other form. The total sectional area was the same in either case. The steel envelope was one-fourth of an inch thick.
Each stave was to be just 9 1/6 inches wide on the back, bent to an arc of 60 degrees, and 12 or 13 feet long. The thickest staves had a cross-section of 17.11 square inches, and weighed about 750 pounds each; the thinnest had a cross-section of 10.14 square inches, and weighed about 400 pounds. Compared with the steel bolts these staves were light work.
The machinery for rolling these staves was of the most massive character. Each of the rolls weighed several tons, and any modifications made in the acting surfaces were at the expense of much time and money. In his Report of October, 1871, Mr. Eads stated very concisely some of the causes of the delay in producing staves: —
"Several attempts were made to roll these staves before the rolls were perfectly formed to accomplish it. Each failure necessitated the removal of the rolls for alteration from the mill to the machine shop, several miles distant; this usually involved a loss of two or three weeks before they were in place again and ready for trial. An option had been given to the contractors to have these staves rolled with a rib on each edge of the stave and projecting into the tube, or to roll them without these ribs. The Steel Company elected to roll them with the ribs. After three or four alterations of
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the rolls, they determined to abandon the attempt and to roll them without the ribs. This involved the making of an entire new set of rolls, ten or twelve in number; and when these latter were tried they had to be twice or thrice returned to the machine shop before perfect staves could be turned out with them. In this way at least six months were consumed before a stave could be offered for testing. When this was done the steel proved inferior."
The first stave tested took a set at 17,000 pounds per square inch. A specimen bolt 1 1/8 inches in diameter and 9 inches long, cut from the stave, took permanent set at 18,000 pounds, and completely crippled up at 34,000. This steel was of course too soft. One part of the problem was, however, nearly solved: they had rolled staves in the correct form. It was now necessary to secure the right quality.
The only resource seemed to be chrome steel for staves as well as for bolts, and Mr. Eads regretted exceedingly that they had not decided to use it from the first. Before July was over, Butcher had rolled some staves which when tested showed good results, but he seemed to lack confidence in the uniformity of his own mixtures and delayed positive action. In the mean time Mr. Eads procured two ingots of chrome steel from New York and had them rolled into staves at the Butcher works. They worked beautifully and the mill men were much pleased with them. They were tested with the most satisfactory results. Mr. C. P. Haughian, the superintendent of the New York company, offered to come over to the Butcher works and make a hundred staves exactly like them without a single failure, provided they would give him $25,000 for the use of his patent if he did what he promised. Mr. Butcher's lack of success both with bolts and staves led the officers of the company to seriously consider this proposition, and an arrangement was effected on the 6th of August, 1871. By the terms of this agreement Mr. Haughian was to superintend the necessary mixtures at the Butcher works and the manufacture of a hundred chrome-steel staves and some chrome-steel bolts until the use of his mixtures should be well understood. For his services and the use of his patent he was to receive $15,000. In recognition of this contract and to help the Steel Company out of its difficulties, the Bridge Company agreed to give the Butcher Company a bonus of $10,000 provided they should complete the delivery of the Bridge steel in accordance with their agreement with the Keystone Bridge Company, and within ten months from the 10th of April, 1871, at which time it was agreed that the testing-machine should be considered as "completed" — i. e., in complete working order as contemplated in the supplementary contract of February 7, 1871.
At the time this arrangement was completed Mr. Eads was fairly worn out and sick at Philadelphia.
On the 18th of August staves were rolled from ingots of chrome steel cast at the Butcher works; on the 23d the first chrome-steel ingot for anchor-bolts was cast. Inspector Fitch wrote: "Nine chrome and eight carbon staves were rolled. The chrome staves looked fair, but not equal to the two sent from New York. The carbon staves were an improvement." Two of the thick staves rolled of Mr. Butcher's carbon steel showed good results, sustaining 60,000 pounds per square inch without injury. On September 12 the maximum compression to be applied to staves was reduced to 55,000 pounds per square inch, and the next day to 50,300 pounds. On the 21st of September Mr. Fitch finished the testing of the entire lot of one hundred staves. Not one had failed to stand the test in
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the machine through weakness of the metal. The modulus of elasticity of the steel in the chrome staves averaged about 29,000,000, and of the carbon staves 30,000,000. "The testing-machine has been kept in steady operation," wrote Mr. Fitch, "but with the best efforts fourteen staves is the highest number yet tested in one day. I think it doubtful if that number can be exceeded if we measure and examine each stave carefully."These reports show that things were in a very hopeful condition at this time, and there
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was good reason to believe that so far as steel was concerned there would be no further difficulty in manufacturing it rapidly of the proper quality, quantity, and form. Mr. Eads, in his October Report, 1871, after detailing the many mishaps and disappointments of the year, adds: —"I feel every assurance that the difficulties in the way of supplying steel for your Bridge are now surmounted. The steel we are now testing is of a quality entirely satisfactory, and the workmanship is unexceptionable. The tests made of its ultimate tensile strength are considerably in excess of the specifications. In compression almost any degree of resistance can be obtained by the addition of chrome. To avoid unusual difficulty, however, in finishing the steel in the lathes, it is only made sufficiently hard to meet the requirements of the specifications."
The great strength and hardness of the first specimens of chrome steel used was remarkable. Mr. Haughian cast an ingot at his works in New York and sent it to the Butcher works, where it was forged into an anchor-bolt and tested. It stood the test of 40,000 pounds per square inch without injury, and was sent to Pittsburg to be finished. The end projections were turned down and screws were cut on each end. Mr. Baily, the assistant steel-inspector at Pittsburg, reported that this bolt required thirty-four hours for turning down the ends and cutting screws; the carbon-steel bolt of the same size took only sixteen hours. He added: "If the staves and pins are not made softer than this, it will make rather a serious delay." The strength of the steel was shown by the small specimens cut from each end of the first two chrome-steel bolts cast at the Butcher works. These
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specimen bolts broke under tensile strains of 142,900, 142,800, 119,000, 161,900 pounds per square inch respectively.But the end of difficulties was by no means reached. Not to mention the insuperable obstacles encountered in rolling the couplings, it was not exactly "plain sailing" in other matters. On the 21st of September Mr. Fitch telegraphed: "Gas-flue leading to heaters of rolling-mill exploded last night." The mill was disabled for over a month. The same day the chrome-steel anchor-bolt made by Mr. Butcher was tested. It broke at the largest section at a strain of 16,800 pounds per square inch. Mr. Haughian's bolt made at the same time had stood the test of 40,000 pounds. The next day the pulling-bolt made of chrome steel by Mr. Haughian for the testing-machine broke across the thread at 40,000 pounds per square inch on the anchor-bolt.
The duplicate pulling-bolt made of Butcher steel was put in the machine, and the same anchor-bolt was tested again to ascertain if it had sustained any injury. No defect was discovered and it was accepted. The carbon-steel pulling-bolt proved to be sound. The next three anchor-bolts of Butcher steel broke on first test at 17,400, 21,300, 35,600 pounds per square inch respectively. The testing of steel anchor-bolts was continued till seven more, all that were ready, were tested. One of these broke, and six were accepted and sent with all haste to Pittsburg. A new pulling-bolt was immediately ordered by Mr. Linville as a reserve.
Mr. Butcher seemed quite dispirited by his lack of success, and the works reflected the feelings of the superintendent. The need of a reorganization and a change in the management of the works was so apparent that a change of superintendent was made on the 1st of October. Mr. Butcher retired and Mr. W. F. Durfee took charge.
Under Mr. Durfee things began to mend. A new foreman was employed in the forging-shop, and a skilful metallurgist in England was at once sent for to take charge of the melting and mixing of the steel. He arrived at his post about November 1. November 29 Mr. Fitch writes: "The young man who came out from England to take charge of the melting-shop gives good satisfaction, and the stock he turns out is much superior to the old lot." From this time forward no serious difficulties were met with in the manufacture or testing of staves. The inspector reported: —
December 14, 1871. — "The new mixture [of chrome steel for staves] is very uniform, very hard, modulus about 26,000,000, and none [of the staves] have upsetyet."
January 27, 1872. — "All the staves stood the test. The tests of the last three days show a higher modulus and less set than some of those tested previously, and they appear to work easier on the planer, and from the manner the steel is worked here I think there will be no great difficulty in turning the metal after the outside scale is removed. The fin, or ragged edge, left by the rolls is much the hardest part of the stave, and thus far there appears to be great difficulty in removing it."
This "fin" only was removed by the planer, which could finish but nine in a day and night. Others were chipped by hand, two men finishing five or six in a day. A few weeks later large shears were provided with which the fin was removed the moment the staves left the rolls and while they were still hot. A little practice enabled the men to remove it so
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neatly that no finishing upon the body of the staves was needed. Many of the staves came from the rolls slightly twisted, and required reheating to be straightened."A great number of the staves are heated only to a very low red heat, and many not even as high as that; there is no doubt reheating makes them staffer and increases the modulus."
February 3, 1872. — "The staves appear to roll well as far as the material is concerned, and they come from the rolls very true and straight."
February 7, 1872. — "The power press straightens them [the staves] as fast as they are rolled now, by taking them from the hot-bed as soon as they are sufficiently cooled down to handle."
February 10, 1872. — "The staves rolled yesterday and to-day come from the rolls very fair in shape, and the sections made up [into a tube] are very satisfactory as regards the diameter and the joints. Rolling the staves is a very simple problem now, though it cost a round sum to solve it."
It will be remembered that the first stave was rolled May 1, 1871, and that about ten months had been spent in rendering the problem "simple." Very great uniformity was finally attained in the manufacture of staves, and under test they exhibited results so nearly identical that it was found unnecessary to actually test more than about one stave in three; still later not more than one in ten. Small specimens of the steel were, however, continually tested to destruction to ascertain both the modulus of elasticity and the ultimate strength. The modulus was kept at about 27,000,000, and the ultimate strength at about 120,000 pounds per square inch.
Returning now from this special consideration to the anchor-bolts once more, we find the subject still interesting. The chrome-steel anchor-bolts proved stronger than Mr. Butcher's carbon-steel ones, but the problem of their construction never became "simple." Every bolt had to be tested, and in spite of the strength of small specimens of the steel and the utmost care in the forging, the bolts broke occasionally at astonishingly low figures; while fully half the bolts made by Mr. Butcher broke. The breaking of an anchor-bolt under test soon ceased to be a matter of much interest. The inspector had learned to run the tension up to 40,000 pounds without having the measuring-bar on the bolt. If it remained intact, the measuring-bar was put on and the test repeated while the point and amount of set were noted. This permanent set was usually very small. In the two bolts accepted December 9, it amounted in a length of 25 feet to 0.0053 and 0.0035 of an inch respectively.
On December 13, while testing an anchor-bolt, two nuts were broken in quick succession on the end of the pulling-bolt of the machine. The shape of this nut is given in (Fig. 14). They each broke at a a, just at the end of the screw-hole. The cross-section was about 30 square inches — a little greater than that of the bolt under test. One of these nuts had repeatedly stood much higher tests; the other was the reserve nut. These are the two nuts of which Mr. Linville wrote August 29: "We are having duplicates of this nut made; of superior steel." After their destruction two more of chrome steel and greater thickness were ordered by Mr. Fitch, one of which was finished with all dispatch, work being continued on it day and night till it was done.
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Four more steel bolts were tested December 80. One broke at 19,300 pounds per square inch; the others showed no set. The one which broke had been cast by Mr. Butcher, the other three by Mr. Durfee.
Meanwhile another change from steel to iron anchor-bolts had taken place. It was brought about in this manner: —
About the middle of September Mr. Eads received a box of six specimens of what he supposed to be "tension-rod steel" from the Butcher Steel Works. No letter of information came with them, but as they were neatly prepared for the St. Louis machine they were soon tested. They broke at strains ranging from 61,600 to 63,610 pounds per square inch, averaging 62,973 pounds. Mr. Eads at once wrote to Mr. Fitch: "The steel is soft and beautiful, but none of the samples stood over 64,000. The elastic limit was about right — 40,000. If these are a fair sample of the steel rods already rolled there is no alternative but to reject them." Now, it afterwards appeared that what was supposed to be steel from the Butcher Works was really wrought iron of the finest sort from the Bridge-water Forge, Mass. It was intended to show the quality of the iron used in the skew-backs they were making. Its great toughness and high elastic limit naturally suggested to Mr. Eads the possibility of using such iron in lieu of steel for those anchor-bolts where the strains were less severe, viz., the upper bolts of the lower skew-backs. In quality this iron was all that was required for any of the bolts.
Twenty-one iron bolts were therefore ordered of Macpherson, Willard & Co. at 9Ë cents per pound. Each of these iron bolts used as substitute for steel was tested to 20,000 pounds per square inch. Though scarcely equal to the specimen iron of the Bridge-water Forge, the iron furnished by Macpherson, Willard & Co. was excellent. The former lot of iron anchor-bolts were made by this firm for 7Ë cents per pound. The Bridge Company agreed to pay the actual cost of these bolts, and to allow the Keystone Company a profit equal to what they would have made had the steel bolts been used as first proposed. The last steel anchor-bolt made for the Bridge was tested June 15, 1872. Of the last fifteen tested, but two had broken and they were both forged from ingots cast long ago by Mr. Butcher. Both the material and the workmanship on the later bolts seemed to be of the best quality.
There are fifty-nine steel anchor-bolts in the Bridge. Each one of them was subjected twice to a tension of 40,000 pounds per square inch, which was in every case below the limit of elasticity.
Twenty-seven bolts were, however, broken under test. Several of the fractures showed flaws. Several bolts broke near the ends where the diameter was 6 7/16 inches. Some showed injury by excessive heat; in others the steel seemed perfectly sound. Small specimen bars from the bolts showed in every case an ultimate strength of over 100,000 pounds. Over eighty iron anchor-bolts for the arches and the wind-trusses had meanwhile been tested without a single failure. Nearly all were tested to 20,000 pounds per square inch, which was far within the limits of their elasticity. Thus the iron showed itself always strong enough to bear the maximum strain which was calculated for the steel bolts. It is altogether probable that all the anchor-bolts would have been made of iron, if Mr. Eads had not been assured by the steel-makers that sound steel bolts could be forged without difficulty.
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The large testing-machine had been a severe sufferer. It had been broken repeatedly, and racked with every fracture. Curiously enough, the machine broke down while testing the last bolt, when the tension on the anchor-bolt was 40,000 pounds per square inch. It will be remembered that Mr. Linville had ordered in August, 1871, two new pulling-bolts for the ram (two having been broken), each 6 inches in diameter, one of chrome steel, and one of superior Butcher steel, and that he based his faith upon the 6-inch bolt of Butcher steel. The chrome bolt broke in September on the first severe test, but the reserve proved sound. It survived nearly a hundred tests of iron and steel bolts, but, as I have said, it broke with the very last.
It is not easy to account satisfactorily for the behavior of the large steel bolts under test. A large proportion of those first made broke, while very few of the later ones failed. It was admitted by all that much greater care was taken in working the bolts under Mr. Durfee than under Mr. Butcher. The anchor-bolt ingots were rectangular, about 15 inches square by 48 inches in length. They were examined, and if cracks were found, they were cast out. They were then forged down under steam-hammers, the finishing dies being suited to the body of the bolt, 5 7/8 inches in diameter. Several reheatings were necessary and it is probable that many of the first bolts made were overheated, through Mr. Butcher's desire to diminish the number of heats, since many of the fractures gave evidence of burning. Moreover, it appears from the fact that ingots cast by Mr. Butcher but forged with all care by Mr. Durfee were conspicuously weak, that the mixing and melting of the steel had much to do with the quality.
But the occasional breaking of sound steel both in anchor-bolts and in the pulling-bolts and nuts of the machine seems to be still unaccounted for. Mr. Eads believes that the following is the true explanation: In finishing the bolts under the trip-hammer when the steel was at a low red heat, the light strokes had the effect of extending the outer surface of the steel longitudinally, thereby causing a high initial strain throughout the core of the bolt. It is quite possible that in some cases the exterior of the bolt may be so extended by light hammering as to fracture the interior even before it is under test.
A finished bolt, with its interior in a state of tension and its surface in a state of compression for three-eighths or one-half of an inch in depth, is somewhat analogous to a piece of unannealed glass or a Prince Rupert's drop. The application of a tensile strain to such a bolt at once tended to neutralize the compression on the surface, while it greatly increased the tension at the core. It is quite probable that sometimes the center was fractured before the surface was under tension. Mr. Fitch, the inspector, made a note of the fact that one of the steel bolts "commenced to rupture from center of bolt." It is easy to see that a bolt thus at war with itself might yield to a moderate strain, while specimen bars an inch in diameter cut from the broken end should exhibit great strength. The remedy for such a bolt would seem to lie in annealing at a high temperature; on the other hand, it would seem that the use of light hammers should have been avoided. The iron bolts were spared this peculiar danger, being worked at a higher heat and having great ductility. An annealing-furnace was built by Mr. Butcher and some of the steel bolts were annealed, but with little apparent effect. It is probable that the experiment of annealing was not thoroughly tried.
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An examination of the fractured bolts and nuts suggests another reason for several of the failures, which I venture to add. There was a decided tendency to break at the shoulder where the tension was applied. As the bearing surface was turned down, any initial compression in the steel induced by the hammering was removed. If any effect of the surface hammering did remain, it completely failed to account for the fractures at the bolt-heads, for there the surface must have parted first. The reason is readily seen.
Suppose a bolt has a circular plate for a head, as in (Fig. 15). Were the plate perfectly rigid and the applied stress on its outer ring evenly distributed, the tension on the end of the bolt would be uniform. With an elastic disk, however, the stress would be very unequal, varying from a maximum at the circumference or to a minimum at the center, where it might be negative. Under a tension, which at the surface is below the limit of elasticity of the material, there is a certain neutral circle, or line of no stress, in the end of the bolt.
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Chapter IX. Rolled-Iron Work and Steel Envelopes — Changes in Specifications.
Messrs. Carnegie, Kloman & Co. of Pittsburg had taken the subcontract to furnish nearly all the rolled iron for the Bridge. The most important parts were the main braces. Each brace consisted of two bars, with T irons riveted on their inner faces, and a lattice web. The bars for the end braces of each rib are about 15 feet long, 13 inches wide, and 1.787 inches thick.
Specimens of brace iron tested in St. Louis showed about the same strength, and the question of reducing the test to 55,000 was discussed. Inspector Baily felt satisfied that the Union Iron Mill could make and had made 60,000-pound iron. If they were permitted to begin with 55,000, it wouldn't be long, he thought, before they would be down to 50,000. Meanwhile, Messrs. Carnegie, Kloman & Co. claimed that the method of testing their iron as required by the specifications was unfair. "No iron," said they, "will stand 60,000 pounds when tested in cylindrical bars." They claimed that "the cylindrical test is unusual, and not in accordance with the practice of engineers throughout the country," and that the specimens should have a circular groove cut around them as shown in the upper drawing in Fig. 16. The second form shown was approved by Mr. Eads.
In addition to the claim that the specimen bars should be grooved, the Iron Company asserted that it was customary to determine the intensity of the strain by measuring the area
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of the broken end after test. They claimed that both in the War and Navy Departments or the government and among an bridge engineers the area of the section diminished by stretching is the one measured. They said that the tests already made, if measured correctly, would show that their iron was fully up to 60,000. Mr. Carnegie claimed that his company was "delayed by the novel mode" of testing insisted upon by Mr. Eads.Three grooved specimens prepared by the makers were sent to St. Louis, and tested by Col. Flad. One specimen broke at 60,000, the other two at 60,300 each. Mr. Linville wrote August 7: "If the iron is tested in the usual manner, which we believe we are justified in asking at your hands, I have no fears that Carnegie, Kloman & Co. will [not] be able to furnish iron that will stand 60,000 pounds per square inch." By "the usual manner," Mr. Linville meant in grooved specimens as shown in (Fig. 16).
Mr. Eads protested against the grooved specimen as unsatisfactory as well as unusual. He said the form of the bars was so different from the plain cylinders he had used in his tests, that he could "make no correct comparison of the relative strength of the different kinds" of iron.
"I am not willing," he wrote August 19, "to accept an iron for the braces inferior to other qualities in the market, and I am not willing to have any particular method of testing it prescribed by the makers, which does not represent the manner in which it will be strained in the Bridge. By grooving it, as urged by Carnegie, Kloman & Co., no idea of its limit of elasticity can be obtained, nor can any reliable idea be formed of the quality of the sample except at one particular point in its length. The test is not only empirical, but I believe, so far as I can learn, unusual. The standard of strength required is not excessively high. On pages 110, 112, and 114 of Kirkaldy's Experiments on Wrought Iron and Steel are recorded the tests of sixty-nine samples of iron tested to an average of 60,000 pounds per square inch of original area, and by inspecting the first plate in the book you will see that the form of the samples are cylinders of several diameters in length."
He also quotes the published experiments of the United States Navy officers, Wade and others, on the strength of cannon metals, in which the specimens, "though not exactly cylindrical, were nearly so." "By reference to Hodman's experiments on metals for cannon, you will find that all of his tests are made on cylinders."
For the purpose of learning the practice among American bridge engineers, the question of the usual form of specimens was referred to Col. C. Shaler Smith, C. E., and Mr. Albert Fink, C. E. These gentlemen confirmed the views of Mr. Eads.
For the purpose of determining the effect of grooves upon the apparent ultimate strength of specimens, Mr. Eads requested Col. Flad to make a careful series of experiments upon various grades of iron. The very significant results of over eighty tests are given elsewhere (p. 319). The grooved bars appear to be ten or fifteen per cent stronger than the cylinders, original sections being measured in all cases.
Mr. Eads adhered, therefore, to his original plan as regards the form of the specimen bolts, but he finally consented to concede 5,000 pounds on the ultimate strength. He wrote
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to Mr. Linville, August 25, 1871, notifying him that he had agreed with Mr. Kloman to accept such iron for the braces as would stand 55,000 pounds in cylindrical bars. Numerous specimens of American iron had exceeded these figures. He adds: —"I am not willing to accept an iron inferior to this standard, and as it is 5,000 pounds less than the numerous results I referred you to in Kirkaldy's work, and 1,000 pounds lower than the English standard (25 gross tons) required in Great Britain in bridge constructions, I feel that I am making quite as great a concession as you should demand. A greater one would certainly not be creditable to your own establishment, and I do not feel justified in assuming the responsibility of permitting a lower grade of iron to be used in these important members of the Bridge. In channel-bars and angles [subject to compression alone] I will accept iron at 50,000 pounds. The plate iron for wind-truss must likewise not be less than 55,000 pounds."
Up to this time, tests made on cylindrical specimens from the brace-bars showed an average strength somewhat below 50,000 pounds. In this connection it should lie stated, that Mr. Gerard B. Allen, the vice-president of the Bridge Company and the chairman of the Construction Committee, was opposed to the concession of the 5,000 pounds on the test. During July and August, Inspector Baily was at the steel works in Philadelphia assisting Mr. Fitch. On his return to Pittsburg, in September, he found that Mr. Kloman had finished about one hundred brace-bars, and about two hundred more were ready to have their ends upset. Although the heavy bars would be first needed, he had made some lighter ones, in order to give practice to his men. In regard to these braces Mr. Eads wrote the inspector, September 18: —
"As this is the most important iron-work about the Bridge, it is my wish that you be entirely satisfied that none is used that will not stand 55,000 pounds per square inch of section, when tested in the manner described in the specifications. To this end you will from time to time, as the work progresses, select samples from the iron being used and have them tested, sending a few specimens to this office. It may be well, in case there is any question as to the quality of the iron used, for you to notify the subcontractors that none of the braces will be accepted unless I am well assured that the quality of the iron is satisfactory."
Eleven samples cut from these bars broke at strains ranging from 50,000 to 53,000 pounds per square inch. When Mr. Baily remonstrated with Mr. Kloman as to the order in which he was making the bars and the quality of the iron, he answered, "I want to first find out if this iron I have made is acceptable; if it is not, I will withdraw from the contract. I have always given satisfaction before, and if this iron is not good enough for St. Louis I will withdraw." Further tests showed an average ultimate strength of only a trifle above 50,000 pounds. To accept the bars already made was out of the question. Mr. Eads promptly (September 25) gave official notice to Mr. Linville that his subcontractors were not furnishing iron of the proper quality. He thus closes his letter: —
"As I distinctly stated to you and to Mr. Kloman also, I will accept no iron in these braces bearing a less strength in tension than 55,000 pounds per square inch. I shall therefore reject all braces in which iron of inferior strength is used. It may perhaps be well for you to notify the parties interested of this fact."
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The reader will bear in mind that the subcontract for these braces had been let over six months, and yet not an acceptable brace-bar had been made. I have been minute in my account, for the reason that the delay of these contractors was a matter of growing importance, soon to become very serious, and when coupled with the difficulties encountered in the steel-work, gave an exceedingly discouraging aspect to affairs. Mr. Eads was convinced that, as modified, his requirements were not excessive, and that so far as iron was concerned the difficulties were only of a pecuniary character.
At this juncture the bars of Bridgewater iron were tested on the St. Louis machine, showing an average strength of 62,973 pounds. Here was a gleam of light. Mr. Eads immediately wrote Mr. Linville, giving him the facts in regard to this iron and suggesting that the subcontractors be requested to supply iron of the proper quality for the brace-bars at once, or in case of their default, that he obtain it elsewhere without further delay and controversy.
In response to this letter, Mr. Linville asserted that the parties in Pittsburg were willing "to furnish specimens until tests are satisfactory," and then to make the iron. He then urged upon Mr. Eads the importance of a personal visit to Pittsburg. "Your personal influence and an interchange of views is required there just as it was at the steel works, and I believe in a few days you can reconcile all differences and start the work of supplying iron for braces, straps, tubes, plates, &c." Accordingly, Mr. Eads made haste to Pittsburg. He left St. Louis October 13. On the 12th Mr. McPherson had written as follows:
"OCTOBER 12, 1871.
J. H. Linville, Esq., President Keystone, Bridge Company, Philadelphia.
DEAR SIR: At a meeting of the Board held two days ago, the chief engineer presented his Report on the progress of the work, and among other things it appeared that all the specimens of iron furnished by the Union Mills had fallen short of the requirements of the specifications in your contract. It was also shown that specimens from other iron-works had exceeded the requirements several thousand pounds. The engineer also read a letter from C. Shaler Smith giving the tests made for St. Charles Bridge, from which it appeared that iron from the Norway Works at Wheeling stood tests ranging from 60,000 to 67,000 pounds. It was further represented that some of this iron would soon be needed here, and great apprehensions were expressed by the Board that the work here would be further delayed for want of this iron. Under these circumstances the Board expressed great anxiety about the matter, and requested me to address you officially on the subject.
Having made the statement of the case, I do not know that it is necessary to say more. As an engineer, you know the importance of having every part of the work pressed to completion.
If the Union Mills fail to come up to the requirements of the contract, then justice to this Company requires that you should engage other manufacturers to make the iron. Mr. Allen, of our Board, questioned the propriety of the engineer conceding to you the 5,000 pounds, and all the Board were unanimous in now adhering to the 55,000, the specimens being tested as required by our engineer. * * *
Very respectfully,
WM. M. MCPHERSON, President."
To this Mr. Linville replied, that he had done everything possible to procure the iron under his contract with Carnegie, Kloman & Co. As the last effort to effect this, he had urged Mr. Eads to visit Pittsburg, and also written Mr. Carnegie, urging every consideration
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of honor, reputation, etc., to induce them to furnish the iron. "If these all fail," said he, "then we must procure the material elsewhere, including special shapes of iron, which I fear will be very difficult to obtain without perhaps modifying some of the special sizes and shapes."While Mr. Eads was in Pittsburg, Carnegie, Kloman & Co. rolled some of their iron a third time; its strength then reached 55,000 pounds. They also turned out some highly carbonized iron (or rather puddled steel) which gave fine results; but in spite of promises to produce iron of the required strength without further delay, little progress was made for two months. The fact of the matter was, Carnegie, Kloman & Co. had contracted to deliver 60,000-pound iron for 6 3/8 cents per pound, and now it seemed probable that it would cost them 8 cents per pound to manufacture the brace-bars of the quality demanded, — i. e., having a strength of 55,000 pounds per square inch.
An important crisis in iron and steel matters was reached in December, 1871. I have followed the history of making steel staves and steel bolts through into the year 1872, but I was concerned chiefly in mechanical matters. I stated incidentally that the test as applied to the staves was reduced from 60,000 to 50,000 pounds per square inch, but it was not necessary just then to mention the reason, nor the complications to which the redaction led; but I must now give a connected statement of the conclusions reached in December, 1871, and partially embodied in a new supplementary contract signed December 21, 1871.
During October, 1871, Mr. Eads, finding that the steel which was strong enough to Dear 60,000 pounds per square inch without injury would prove harder to work than he had anticipated, and that it was more liable to fracture from sudden shocks and blows than that a little milder, voluntarily reduced the test standard to 50,000 pounds. The first hundred staves had been tested to but a little over 50,000 pounds, yet Mr. Eads was entirely satisfied both with their limit of elasticity and their ultimate strength. Even after the reduction to 50,000 pounds had been made, tests were frequently made to 60,000, with a resulting set in all cases so minute as to be detected only by the delicate measuring apparatus then in use. The arrangement made between the Steel Works and Mr. Haughian, by which they were to be allowed to continue the manufacture of chrome steel, was agreed to by Mr. Huston, the president of the Steel Company, only on condition that he should be released from all obligation to furnish steel that should uniformly bear a pressure of 60,000 pounds without set, as required by his contract with the Keystone Company.
When officially notified of the reduction of the test, and asked to indorse his acceptance of the same on the contract with Mr. Haughian and his associates of the Chrome Steel Works, Mr. Linville refused. He gave two reasons for his refusal:
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able for failing to finish the Bridge by that date. Mr. Linville was, therefore, unwilling to sanction this reduction without a corresponding concession to his Company.A second reason for refusing the desired indorsement was his unwillingness to sanction the use of chrome steel in the place of carbon steel, without halving first clearly arranged for the extra compensation his Company was to receive in consequence of the expected greater difficulty of working it. Their experience on a few specimens of chrome steel had led them to expect both a higher price and a longer time for finishing the work at their shops in Pittsburg. The position taken by Mr. Linville led the chief engineer of the Bridge Company to withdraw the concession he had made in reducing the test of ultimate strength of iron from 60,000 to 55,000 pounds per square inch. It seemed to him but fair to meet Mr. Linville on his own ground. The change to chrome steel had been made because it seemed impossible for the contractors to furnish the specified carbon steel; and the proof-strength was reduced in order to facilitate both the manufacture of the raw material and the finishing of the work. In the face of these modifications of original requirements, both of which were in the nature of concessions, Mr. Eads felt that the claim for extra compensation was uncalled for, and, besides, he thought that the supposed extra hardness of the steel then being made was without foundation in fact.
"Before we consent to accept iron of less strength than 60,000 pounds, we should at all events have it definitely understood by Mr. Linville that no such claim will be set up as he proposes on account of extra hardness of steel, which I think is all imagination. * * * The standard [on iron] was lessened to 55,000 pounds three months ago in the hope of expediting its delivery by Carnegie, Kloman & Co., and they have not yet offered a bar of it, while samples have been recently furnished by Spang. Chalfant & Co. and by Willard, Macpherson & Co. from 58,000 to 66,000. Brown & Co. of Pittsburg; Bailey, Lang & Co., New York; and the Bridgewater Forge, Mass., offer to guarantee 60,000. * * * If I had not so many tests of my own, such assurances from other engineers, and the evidences of so many published reports, I might doubt the ability of iron-masters to furnish what my specifications call for." — Mr. Eads to President McPherson, November 4, 1871.
This sharp construction of contracts on both sides had a very wholesome effect on the subcontractors. The Butcher Steel Works bent every nerve to carry out their contract as to time, proposing to get a great deal of their steel made and rolled in other shops. As soon as Mr. Carnegie learned that the concession of 5,000 pounds had been withdrawn, he made haste to assure Mr. Eads that his firm had made every effort to make iron that would stand 55,000 pounds, and that "they intended doing it, if it cost as much as silver!" In spite of this brave resolution, however, the specimens of iron he offered rarely went above 52,000, averaging about 50,000.
When Carnegie, Kloman & Co. came to the conclusion that they could make the iron, but that it would cost them as much as they were to get for it, they again protested against the severity of Mr. Eads's tests, and tried to extort from him a promise that he would accept their iron if they could prove, by taking out a few bars from the St. Charles Bridge
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there was at that time a large supply of Norway iron at the establishment of Mr. Gerard B. Allen in St. Louis. A barge-load of links, made for the St. Charles Bridge, had been sunk somewhere in the Ohio River, and its place had been filled by a second cargo. Subsequently, Mr. Allen bought and recovered the sunken iron. He speedily furnished four specimens taken from one of these links, and Col. Flad tested them on the St. Louis machine. Their ultimate strength was over 58,000 pounds per square inch, the extremes being 55,200 and 60,050. Thus the good name of the St. Charles Bridge was vindicated.Another discouraging feature of the iron-problem was the delay in the manufacture of the plate iron for the upper wind-trusses. Messrs. Spang, Chalfant & Co. of Pittsburg had taken the subcontract in April, 1871, to furnish this iron for 4 cents per pound. It was to have a tensile strength along the fiber of 60,000 pounds per square inch. This was reduced to 55,000 pounds in August. Up to December, however, none of their iron had shown the required strength. A large number of plates had been rolled while Mr. Baily was in Philadelphia. On his return to Pittsburg he found the iron too weak, and the work stopped. The manufacturers claimed that their iron "stood between 58,000 and 60,000, and some as high as 64,000 pounds, on the Fort-Pitt machine." Mr. Baily tested a large number of specimens; the breaking strength ranged from 43,200 to 54,000, the average being 48,100. A specimen sent to St. Louis broke at 48,700. In September the contractors had declared they could make no better iron for the money. They seemed to take their cue from the Union Iron Mills, and proposed to wait till, worn out by the delay, the Bridge Company should be "worried into accepting inferior iron."
On the 1st of December, 1871, affairs were in a very misettled state. Mr. Linville claimed that the adoption of chrome steel upset all the contracts, and he proposed to abrogate all contracts relating to steel, and to agree anew to accept a low percentage on the actual cost of all the material, and to make the subcontractors for steel directly responsible to the Bridge Company. Meanwhile the Butcher Company had made their arrangements with the Chrome Steel Company on the strength of Mr. Eads's personal pledge that they should be held harmless in the matter. Mr. Eads was unwilling to concede anything as to the strength of the iron, unless certain claims were withdrawn by the Keystone Bridge Company. To bring about the settlement of all disputed points, a meeting was arranged between Messrs. McPherson, Allen, Taussig, and Eads, of the Bridge Company; Mr. Samuel Huston, president of the Butcher Steel Works; and the officers of the Keystone Company at Pittsburg, December 14, 1871, at which the provisions of the contracts of December 21, 1871, were adopted. A week later they were signed by the presidents of the three Companies. The importance of these contracts to a right understanding of the whole matter justifies the insertion of one of them in extenso: —
SUPPLEMENTARY CONTRACT OF DECEMBER 21, 1871.
"WHEREAS, it has been decided by the chief engineer of the Illinois and St. Louis Bridge Company that ‘chrome steel’ be used for certain portions of the work in place of ‘carbon cast steel’;
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and whereas, the substitution of said chrome steel may involve additional expense in working the same to the Keystone Bridge Company, and also may require longer time for its execution: Now, in order to determine the equitable increase of compensation and extension of time for completion, and in order to further explain and determine certain clauses in previous contracts, by which disputed points are to be decided by arbitration, therefore it is agreed by and between the Keystone Bridge Company and the Illinois and St. Louis Bridge Company as follows: —
1. John L. Piper, of the Keystone Bridge Company, and Gerard B. Allen, of the Illinois and St. Louis Bridge Company, are hereby agreed upon as the referees to decide all questions which, under the original or supplementary contracts, are to be decided by arbitration, and they shall have power to appoint an umpire in case of their disagreement; and it is agreed their decision, or in case of their disagreement, that of the umpire, shall be binding and final on both the above-named referees.
2. Inasmuch as the contracting parties cannot agree upon the principles and methods that shall control the manner of arriving at a just and equitable solution of the question as to whether the ‘chrome steel’ is more difficult to work than the ‘carbon steel,’ and the measure of increased compensation and extension of time that should be allowed the Keystone Bridge Company for working it, if it should prove more difficult than ‘carbon steel,’ it is agreed that all questions involved in the decision of this matter, — whether 60,000 pounds ‘carbon steel’ should or should not be tested against 50,000 pounds ‘chrome steel:’ or whether the ‘carbon steel’ should be of one or another kind of specimen, large or small; or whether it should be of such forms, sizes, and qualities as will make the pieces tested suitable for use in the Bridge; together with all other incidental questions whatever, which have already arisen or may hereafter arise respecting this question; and the question, what expense, if any, may arise to the Keystone Bridge Company from a too late delivery of couplings, — shall be left entirely to the decision of the referees, they being fully authorized to obtain such specimen pieces of ‘carbon steel’ to be tested as they may deem proper.
3. The said Piper and Allen shall, so soon as sufficient material is delivered to make complete tubes, couplings, and connecting-pins, meet and determine from their experience derived in making the same, the date at which the Bridge should be completed ready for traffic, and they shall have power to extend the time beyond that date; and in determining said extension they shall take into consideration: —
First. Any delay occasioned by unforeseen or unavoidable accidents, or by failure on the part of the Butcher Steel Works to furnish steel within the time stated in the supplementary contract agreed upon between the Butcher Steel Works and the Keystone Bridge Company, dated the twenty-first day of December, 1871, including such delays as may be incurred by non-delivery of couplings in suitable proportions, shall entitle the Keystone Bridge Company to as many days in addition to the time they may fix for completion as the delays and circumstances above recited may occasion.
Secondly. In event of ultimate failure on the part of the Butcher Steel Works to furnish steel as agreed in the original and supplementary contracts, and if the Keystone Bridge Company is then called on to procure steel, whether it be the ‘chrome steel’ or the ‘carbon steel,’ elsewhere, then the time incident to failure by the Butcher Steel Works, and so much time as may be required to procure steel of another manufacturer, shall be added to the extension above granted, provided that due diligence be exercised by the Keystone Bridge Company in obtaining the same.
4. The said Piper and Allen shall have the right to determine what additional tools, plant appliances, and men the Keystone Bridge Company shall provide in its own establishment to insure a just and reasonable prosecution of the work.
5. The Illinois and St. Louis Bridge Company agree that the staves composing the tubes shall not be required to stand a compressive strain exceeding 50,000 pounds, or a tensile strain exceeding
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40,000 pounds, per square inch of section, without permanent set, and that the Keystone Bridge Company, in event of failure on the part of the Butcher Steel Works to furnish the steel which is provided for in the supplementary contract above referred to, then the Keystone Bridge Company may furnish in lieu thereof any kind of crucible steel, and that the staves, if made of such crucible cast steel, shall also not be required to stand tests exceeding those above stated.
6. It is understood that the right of the chief engineer of the Illinois and St. Louis Bridge Company to substitute iron anchor-bolts for steel ones of the same size, without affecting the obligations of the Keystone Bridge Company in undertaking to erect the superstructure, is unquestioned; the Keystone Bridge Company having the right, if it so elects, to take out such iron ones as it may think proper, and substitute steel ones where originally designed, while raising the superstructure; the Illinois and St. Louis Bridge Company agreeing on its part to pay such compensation to the Keystone Bridge Company as will insure them an equivalent profit for what they would have earned on the steel bolts if such iron bolts had not been substituted.
7. It is agreed upon that the said Piper and Allen, after they shall have decided the matters in controversy, shall submit their joint decision, made either with or without an umpire, to their respective Boards for ratification; in event, however, that either of said Boards disapprove their decision, then in that case the said Boards shall each immediately appoint another referee, to whom shall be referred the matters in controversy, and these two referees shall have the right to select an umpire, and the decision of a majority of these three shall be final, and binding on both Companies.
8. In case of death or inability of either or both of the above named, Piper and Allen, the respective Company or Companies whom he or they represent shall each have the right to select another party as substitute." [Duly witnessed and signed by Mr. Linville and Mr. McPherson.]
About the same time, another important matter was settled which does not appear in this contract. The very day of the meeting in Pittsburg, Mr. Eads received from Col. Flad a report of the tests made on the iron made for the St. Charles Bridge (mentioned on p. 99). This report he took to the office of Carnegie, Kloman & Co. with most convincing effect. Arguments and protests were no longer to be tolerated. The iron could be made, and parties stood ready to make it, but it would cost both time and money. To save both, though most unwillingly yielding the point of quality, Mr. Eads offered them the alternative of executing their contract or of reducing the price in proportion to the reduction in the test. The latter proposition was accepted. The following letter serves as an official record of the change: —
"PITTSBURG, December 14, 1871.
Mr. J. H. Linville, President Keystone Bridge Company.
DEAR SIR: I will accept all wrought iron for the Bridge of the quality tested by us from the brace-links now made for the Bridge by Carnegie, Kloman & Co., having a tensile strength of not less than 50,000 pounds per square inch, provided a discount of nine per cent is made from your charges on all the brace-links required, and on all iron required in both chords of the wind-trusses and in the lower chords of the street and alley bridges and built beams of the St. Louis approach. If this proposal is accepted, you will at once increase the thickness of each of the remaining brace-links one-tenth more than shown on drawings, but leave the size and thickness of heads of the links unchanged.
Very respectfully,
JAS. B. EADS, Chief Engineer.
Plates, T-bars, angles, I-beams, rolled and channel bars will be accepted if not less than 46,000 pounds tensile strength.
J. B. E."
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Mr. Linville's official acceptance of the proposition was sent the next day. As the brace-bars already rolled were in quality up to the new standard, they were accepted, but their destination in the arch was changed. In each rib there are several different sizes of brace-bars. (See Plate XXXI.)
By this new arrangement, as is readily seen, both the total strength and the total cost of the iron involved remained substantially unchanged. It was impossible to thicken the circular ends of the brace-bars (already about forty per cent thicker than the body of the bar), as the greater part of the steel pins were already made, but by the omission of some bolt-holes through the ends (designed for the purpose of securing the braces to each other independently of the pins), the proper increase in strength was gained. Moreover, it is worthy of notice that the bars as modified were more readily made, for the reason that the ends required less "upsetting," consequently there was a greater probability of soundness in the eyes. Inspector Baily was instructed, while lowering the standard of ultimate strength, to insist upon an elastic limit not less than 20,000 pounds per square inch, just as before.
Not till July, 1872, did the contractors furnish main-brace bars with strength as last agreed. After that date they were turned out rapidly.
The same reduction in the test for ultimate strength was made for the plate iron furnished by Messrs. Spang, Chalfant & Co., but as the design of the wind-truss was changed from a plate girder to a truss soon afterwards, the reduction of the test was less important.
The iron which was to be accepted at 46,000 was used only in compression. The adoption of a lower grade of iron in the main braces involved an increased amount of metal in those pieces; this in turn made necessary a series of changes which should be here explained.
The additional weight of metal in the braces would have required additional strength in the steel tubes to support the "dead" weight of the Bridge, had it not then found possible to lighten some other parts by an equal amount.
"I have determined to lessen the quantity of iron in the wind-trusses by substituting 3/16 inch iron for theź inch plates, andź-inch for the 5/16-inch plates, shown on the ground plans of these trusses, and beg that you will make these changes accordingly without further notice or drawings. The precise dimensions of the chords for the trusses are now being worked out, and will be forwarded to you shortly. I have endeavored to lessen these weights in proportion to the increased section given to the brace-links required in accepting Carnegie, Kloman & Co.'s iron. As a result, less of the wind-strains of the upper roadway will be conveyed to the tops of the piers [by the wind-trusses], and more of them to the arches. This will involve higher strains in the steel diagonals in the arches [between the arched ribs] than the maximum of 20,000 pounds, assumed in the event of a tornado as violent as that of last March. As,
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however, they will be tested to 40,000, [the elastic limit, the tensile strength being about 100,000 pounds] and as the excessive strain will perhaps not occur oftener than once in a century, or a generation, I presume it will be safe, although I should have preferred leaving the whole as originally designed. This change will make steel bolts [to secure the ends of the wind-trusses on the tops of the piers] unnecessary, and you will please have iron ones made for them in the place of steel ones, without awaiting further instructions or drawings. These iron bolts will be tested to 20,000 pounds, and will be of the same quality as those being made by Willard, Macpherson & Co. for the anchor-bolts." — Mr. Eads to Mr. Linville, January 5, 1872.
All these bolts (thirty-six in number) were made for 9Ë cents per pound. The Bridge Company allowed the Keystone Company ten per cent profit on them. The cost of the wind-truss was diminished some twenty or twenty-five per cent, though at the expense of a large factor of safety, which, after all, may not be desirable more than "once in a century." If a tornado like that of March, 1871, ever strikes the St. Louis Bridge, some of the lateral bracing will be subjected to one-fourth of their breaking strength, instead of one-fifth as originally intended. A tornado might tear up and blow away the planking of the upper roadway, but it would scarcely endanger the arches or the wind-trusses themselves.
The horizontal struts in the systems of bracing between the ribs consist of wrought-iron tubes about five inches in diameter secured to the ends of the steel pins. (See Plates XXIV, XXXI.) Mr. Linville wrote Mr. Eads January 1, 1872, suggesting that he alter the size of these struts to the regular sizes in the market, and "vary the specification slightly for compression, also for tension. I think we can succeed in getting the tubes promptly and at greatly reduced price." Mr. Eads consented to this provided the change in quality did not require an increase in weight. "Please let me know," he wrote, "exactly what changes will facilitate your work, and what alterations in drawings you require." The making of these struts had not yet been sublet. The testing of one tube out of twenty kept parties from bidding. They would prefer, Mr. Linville thought, to make a single specimen tube and have all the tests made on that. Mr. Eads, however, did not wish to trust specimens too implicitly. The compressive test of 15,000 pounds per square inch in the full form of a tube was held by makers to be too high. Mr. Linville suggested 14,000. Messrs. Spang, Chalfant & Co. took the contract in May, 1872.
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This was practically the end of all controversy as to the quality of iron. The subcontractors had no difficulty in delivering it of the specified strength and as rapidly as was wanted. True, there had been great delay, which would have been a very serious matter had not the much greater delay in the manufacture and delivery of the steel completely overshadowed it.
In the contract of December, 1871, between the Keystone Company and the Butcher Steel Works, the right of the latter company to sublet the manufacture of two hundred and fifty tons of steel and the rolling of the same into plates was distinctly admitted. This was for the purpose of confirming an arrangement already brought about by Mr. Eads, between the Butcher Steel Works and the Chrome Steel Company of New York, according to which the New York company was to furnish two hundred and fifty tons of chrome-steel ingots, which were to be rolled by Messrs. Park Brothers & Co. of Pittsburg into envelope plates for the large tubes.
In effecting this arrangement Mr. Eads recognized that without aid the Butcher Company was quite unable to furnish all the steel during the next four or five months, and that the entire capacity of the works would be in demand to produce the other items. A few ingots for envelope plates had been cast, and various attempts had been made to roll them. An ingot of chrome steel, cast by Mr. Haughian in September at the Butcher works, had been rolled at the mill of Distons & Sons, Philadelphia. It was successfully rolled to a thickness of a little more than five-sixteenths of an inch. At that point it was too large for their reheating furnace, and further rolling was impossible.
The great width of the plate (about five feet) and the low heat at which it was worked subjected the rolls to great strain, and the proprietors were unwilling to try a second ingot. Specimen straps cut from the end of this plate showed an ultimate strength in tension, across the grain, of nearly 90,000 pounds per square inch. In November two envelope ingots of chrome steel were sent to a mill in Coatesville, Penn., to be rolled. One, of Mr. Haughian's make, was overheated, and broke to pieces in the rolls. The other was rolled down to a thickness of five-sixteenths of an inch and then abandoned. These parties likewise were afraid of breaking their rolls, and refused to, roll any more.
On the 27th of November the large plate-rolls were in order at the Butcher works, and Mr. Durfee attempted the rolling of an envelope plate. The result was just what was anticipated in the other shops, — his upper roll broke, and the machinery was disabled for eighteen days. Meanwhile, thirteen envelope ingots had been shipped to Park Brothers, Pittsburg, to be rolled there. Mr. Huston had also ordered twelve plates of Park Brothers, which were to be made of their own homogeneous (carbon) steel. They were to supply the immediate demand for plates, and enable the steel-makers to compare the workings of the two kinds of steel.
The plates rolled from the chrome-steel ingots proved to be altogether unsuited for envelopes; they were excessively hard and brittle, and they rolled to great disadvantage. An attempt to form an envelope of one at the Keystone shops totally failed. On the other hand, the plates rolled from Park's homogeneous steel worked beautifully, both in the rolls
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and at the shops. Mr. Eads had already pronounced the material of these latter plates "entirely satisfactory." The specimens sent to St. Louis showed a tensile strength of 90,000 pounds and an elastic limit of 40,000, and bolts three-fourths of an inch in diameter had been bent double when cold without a break.When informed of these facts, Dr. Taussig, at that time in Pittsburg, proposed to Messrs. Park Brothers that they contract with the Butcher Company to make all the envelope steel. This they were willing to do. The emergency was one requiring promptness and decision. Dr. Taussig therefore telegraphed Mr. Huston that he was satisfied that chrome steel would not answer for envelopes, and asked authority to contract with Park Brothers & Co. for making and rolling two hundred and fifty tons of plate steel at 12 cents per pound. He agreed to have the arrangement already made with Messrs. Haughian and Cotting cancelled, and pledged the Bridge Company to pay the extra 1ź cents per pound over Huston's contract price. Mr. Huston telegraphed his consent, and the contract was signed on the 28th of December. The steel was to conform with the specifications of the chief engineer of the Illinois and St. Louis Bridge Company, except that the tensile strength need not exceed 80,000 pounds per square inch. The steel plates were to be delivered in quantities not less than fifty or sixty tons per month, and the delivery was to commence on or before January 15, 1872.
Mr. Eads had no question of the unfitness of those particular chrome-steel plates rolled at Pittsburg for envelope uses, and was altogether satisfied with the homogeneous steel; but he believed that the chrome steel would have been equally good had Mr. Haughian's mixture been strictly adhered to by Mr. Durfee. The latter insisted that Mr. Haughian's mixture would have been too soft, and, in spite of Mr. Eads's advice to the contrary, had added more chrome. The result was very unfortunate for the interests of the Chrome Steel Company though fortunate for the Bridge, for no further trouble or difficulty was experienced in this direction. Messrs. Park Brothers & Co. furnished the steel as rapidly as it was needed, and of excellent quality.
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Chapter X. Reports and Suggestions of Mr. James Laurie, C. E.
Before detailing the eventful history of the sleeve-couplings, it is both logically and chronologically necessary for me to turn the reader's attention from the manufacture of iron and steel to engineering matters of a very different character.
The available funds of the Company were clearly inadequate to meet the increased cost of the Bridge, and there seemed to be no practicable method of procuring the additional money needed except that of calls upon stockholders. The stock subscription amounted to $3,000,000; of this only forty per cent had been paid in, and though farther calls had not been expected, there seemed to be no other course to take.
The great delay in the construction of the Bridge superstructure, coupled with the exaggerated reports of practical difficulties encountered by the contractors, made some of the stockholders uneasy, and it was thought best to call a meeting in New York, where the larger part of the stock was held. The meeting was held December 20, 1871. Mr. Allen.
Dr. Taussig, and Mr. Eads were present. Mr. McPherson, the president of the Company, was detained at home by the dangerous illness of several members of his family. The action of the meeting was embodied in two resolutions. In one it was resolved to make calls for money as it should be required, and to give second-mortgage bonds in equal amounts, reckoned at par, for the first million dollars paid in. The other resolution, offered by Mr. Andrew Carnegie,
"Resolved, that a committee of stockholders be appointed to obtain the services of an engineer of eminence in his profession, and of experience in bridge-building, who in connection with the chief engineer shall have authority to alter the details of, and amend or curtail, existing plans, should the same be found to be necessary as the work progresses, to insure the completion of a satisfactory bridge at the earliest possible day and at the least possible expense; provided, that should the recommendations of the engineer fail to be acceptable to the chief engineer, they shall first be submitted to the Board of Directors for adoption."
Though the motive of Mr. Carnegie in offering the resolution was evidently a desire to see the chief engineer overruled in the interest of the contractors, Mr. Eads favored its
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adoption, and invited the fullest and most searching examination, to the end that the confidence of all, if in any way shaken, might be fully re-established. Hence the resolution was adopted unanimously. The chairman, Mr. E. L. Kennedy, appointed Messrs. Boody, Humphreys, and Low as the committee Mr. Kennedy himself was afterwards added. This committee secured the services of Mr. James Laurie, C. E. His appointment dated January 3, 1872, and his duties were defined to be, "to examine into and report the present condition and probable cost of the Bridge."Mr. Laurie immediately visited St. Louis and made a thorough examination of plans, estimates, contracts, workmanship, and accounts of the Bridge and Bridge Company. Every facility was afforded him by Mr. Eads and his assistants, that every point might be embraced in his examination.
His first report, made February 28, 1872, was at once referred by the Directors to Mr. Eads. Much of it is unimportant, but that its exact force and scope may be seen I give it in full, and immediately after it the remarks of Mr. Eads in relation to the same. It will be seen that many of Mr. Laurie's suggestions had been anticipated: —
"ST. LOUIS, February 28, 1872.
Wm. M. McPherson, Esq., President Illinois and St. Louis Bridge Company.
DEAR SIR: The following are the items of work in connection with the Illinois and St. Louis Bridge, heretofore mentioned to you, on which possibly some saving of expenditure may be made, and which, in view of the probable increased cost of the Bridge over previous estimates, appear to me to be deserving of consideration: —
1st. Arcade Work across the Levees in St. Louis and East St. Louis. — The contractor has given notice that he will claim extra pay for this work, as no arcade was shown in the original plan. None of the work has yet been built, although a considerable quantity of the stone, I am informed, has been quarried and cut. I suggest that some understanding be had in relation to the price. If the original plan had been adhered to, there could be no claim.
The contractor also makes a claim for the profit he would make on using limestone or standstone, as originally intended, in the piers and abutments above the spring line of the arch, where granite furnished by the Bridge Company is now being used.
He also claims extra for the increased cost of laying masonry around the main and side shafts and the pipes for air and sand pumps, in the piers and the East Abutment, the original plan showing solid masonry. These shafts were filled with concrete by the Bridge Company. So far, the contractor has been allowed $3,600 extra on this item, but he makes further claim.
2d. Four Towers for Stairways and Elevators — Two on each Side of the River. — The foundations are all laid, and one tower on the St. Louis side is half-way up to the upper roadway. To complete the three others, including elevators, will cost $48,000 to $50,000, to which must be added the amount to be paid for land damages, not yet determined, for the north tower on the St. Louis side; $9,000 is asked for the lot, and $4,600 has been offered for the portion required for the tower. All three towers can be dispensed with by making a wooden stairway on the East St. Louis side, costing about $1,000. Two of them certainly may be omitted, and until you have determined where to place
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the toll-houses, and whether to use elevators, I recommend that any tower built be carried up only to the level of the carriage-way. This will reduce the cost about one-half. By the plan, they are carried 43 feet higher.
From Col. Flad I learn that the contractor is willing that they be omitted, and that he will make no claim in connection therewith, — that the stone he has quarried and dressed for them can be used in other parts of the work. To operate four elevators will require eight employees, and there would be a considerable rent to be paid for the use of water-power to operate them.
3d. Cornice on Bridge Superstructure, 3,108 Feet in Length. — Originally, this was intended to be a galvanized-iron cornice, costing by the first contract $1.50 per running foot, but the plan having been changed to a wrought-iron cornice, it is provided in the supplementary contract to be paid for at cost, which will amount to about $10,000 or $11,000. Its weight will be about fifty tons, and as it projects beyond the side railings one foot on each side, it adds two feet to the width of the platform on which snow may accumulate, giving an additional load to be supported by the Bridge. Cornices are not often used on wrought-iron river bridges.
4th. Cast-Iron Cornice on Piers and Abutments. — This takes the place of a stone cornice originally intended, which, if built of sandstone or limestone at the contract price, would have cost about $4,000. It will weigh about 205 tons and cost about $22,000, and the concrete and masonry for its support about $1,000 more. A cornice may be considered necessary to give finish to the stone-work, but is not required in order to obtain the use of the Bridge, although a temporary expenditure of perhaps $1,000 would be necessary to continue the sidewalks.
5th. Blocks of Masonryto support the Upper Roadway and Ends of Wind-Truss across Piers and Abutments. — These blocks average about 35ź feet in length, 14Ë feet in thickness, and 22 feet in height, and contain 1,554 cubic yards of masonry, which will cost fully $20,000. They have but little weight to support, and possibly a saving may be made by constructing them hollow. If the weight is wanted, they can be filled in with ballast.
6th. Tramways on Upper Roadway. — There are two railway tracks intended for street-cars, and two tramways laid with 9" X 3/8u rails to be used by common vehicles, extending the whole length of the Bridge and approaches, — from Third Street, St. Louis, to Fourth Street in East St. Louis, a distance of 4,680 feet. The street-railway tracks must of course be preserved, but the question may be raised: Are the tramways desirable?
The inclination of the common travel road on the side spans of the Bridge is 1 foot in 35.7 feet, and on the trestle-work in East St. Louis 1 foot in 25 feet, or 211 feet per mile, — inclinations that, with heavy loaded wagons on smooth rails, will require the application of brakes. Again, so many tracks being on the Bridge (eight lines of single rail) will make it difficult for vehicles going in the same direction to pass each other, and thus in a great measure limit the speed of private conveyances to that of heavy freight-wagons, which, for so long a distance, would be objectionable. Besides, the plan of the tramways makes it necessary to have nine separate lengths of plank in the width of the Bridge, and thus the rigidity and strength of a continuous floor is lost. The cost of the tramways, if laid by the Keystone Bridge Company, will be about $15,000.
7th. Wind-Truss and Upper Roadway Covering. — The wind-truss, so called, consists of a continuous plate girder of the length and width of each span, the web being composed of iron plates three-sixteenths of an inch thick. It is placed immediately below the floor beams supporting the upper roadway, and forms a good protection against fire and smoke from the locomotives below, but will have the serious disadvantage of collecting and retaining the dirt and offal from the traffic of the road above.
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And if soft coal, building-sand, or material of such character as will readily pass through between the joints of the planking is largely carried over the Bridge, the accumulation will be rapid, and it can only be effectively removed by lifting the planking. A single inch in thickness of such material allowed to accumulate on the center span would weigh about 112 tons.
Originally the upper roadway was proposed to be laid with Nicolson pavement, which is substantially water-tight and would prevent the dirt from passing through, and for a bridge having a large traffic would be much superior to single planking, but its weight would be considerably more. If either Nicolson pavement or double planking was adopted, an iron trellis or lattice could then be used for the wind-truss, the weight and cost of which would be less than that of a plate girder, and as a protection against fire, thin galvanized iron sheeting, as in the approaches, could be used.
Very respectfully yours, etc.,
JAMES LAURIE."
To this report Mr. Eads responded as follows: —
"To the President and Directors Illinois and St. Louis Bridge Company.
GENTLEMEN: I have the honor to report upon the letter of Mr. James Laurie, C. E., referred by resolution at your last meeting to the chief engineer, as follows: —
1st. With reference to the masonry-contractor's claim for extra pay for work on stone arcades in East and West Approaches over the levees: The original plan involved the construction of a total of 1,056 cubic yards of masonry in this part of the work. By the change made, 481 cubic yards are saved. At $14 per cubic yard, this amounts to $6,734. It would be but just to allow the contractor extra for the difference in substituting the piers and arches for walls that were to be built with three circular openings only. His contract, however, only provides for the measurement of the actual cubic contents of the work, without allowance for openings, and contemplates the use of limestone, which is more expensive than the sandstone that is being used. A just compensation to him for the difference in the plans should leave a saving in favor of the one adopted. I have seen and conversed with the contractor on the subject of the claims referred to by Mr. Laurie, but have as yet been unable to either obtain a definite amount of such claims or an adjustment of them. The Company has a large bill of charges against the contractor for use of mules in hauling about the yard, for glycerine used in the hydraulic jacks, etc., and I think this will be quite sufficient to offset the claims referred to.
2d. Towers for Stairways. — Elevators were not included in the estimates for the four towers, for the reason that their use was supposed to be contingent upon the discretion of the Company after the Bridge should have been earning its revenues. The cost of the towers is not increased by designing them to admit of the use of one elevator at each end of the Bridge, — that is, two in all, — should it ever be found desirable to use them. Four elevators were never thought of by me. I should not even recommend building the stairways in the towers until after the Bridge is fairly opened for use.
At the regular meeting last October, I suggested that none of these towers be built above the carriage-way until after the Bridge is opened, and it is my design to build but one (the south-west one) even that high now. This one is now about twenty-six feet below that level. The masonry of the other three will only be laid sufficiently to bond the work in with the adjoining piers in such manner as to admit of completion hereafter at the leisure of the Company, thus postponing until that time the work of fully three-fourths of each of the three remaining towers. I think it would be injudicious to release the contractor from his contract for the towers without a large abatement of payment on the other work on the West Approach, as the price he has taken them at is an extremely low one, — $8.92 per cubic yard. This general price was fixed on all the stone-work between Third Street and the Levee, including the towers at each end of the Bridge. If he were released from this part, he would have that part which is by far the least profitable of the whole taken off his hands.
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3d. Cornice on Bridge Superstructure. — Within the last four weeks I have been having the plans of the wind-trusses modified, by which I shall effect a saving in their cost that I think will be fully equal to $17,000. These plans are not yet quite ready, but will probably be finished in a week. Mr. Linville assures me that the change will cause them no delay, and that they will be glad if it is made, as the work will be more quickly and easily put in place. By this change the cornice will be modified also, and its cost will fall considerably below the original estimate of $1.50 per foot. The wooden sidewalk of the Bridge will project 12 inches outside the railing and form the top of the cornice; the remainder of the cornice will be constituted simply by iron brackets fastened to the face of the wind-truss for the purpose of supporting the extension of the wooden beams on which the sidewalks and the posts of the railing will rest, — the beams being about 6 feet apart. [See Plate XXII.] To place the railing flush with the very edge of the sidewalks would constitute such a mutilation of design as I am sure no stockholder would advocate for the saving, when compared with the modified arrangement just described. The plank saved would amount to about 7,500 feet, worth $525, and the iron-work to probably $1,000 more. The extension of the sidewalks, or a cornice beyond the railings, gives an appearance of strength and support to the railings that would be wanting without them. I should certainly discourage such an alteration.
4th. Oast-Iron Cornice on Piers and Abutments. — Some discrepancy occurs in the estimates of cost, of the stone and iron cornices as made by Mr. Laurie and those made at my request by Col. Flad. The limestone cornices at only $14 per yard would amount to very nearly double the amount ($4,000) stated by Mr. Laurie. Col. Flad's estimate is $7,840. The estimate for the cast-iron ones is $4,000 less than the $22,000 stated by Mr. Laurie. I do not think they will exceed $18,000. The size of the mouldings of these cornices are proportioned to that of the piers, and they are too large, I think, to be safely constructed of anything but iron or granite. Designs were made for granite, but it was found that they would cost three or four times as much as the cast iron. For this reason the latter was adopted.
Since the suggestion of Mr. Laurie, I have given the question of these cornices much thought, but have not yet been able to devise a reduction of cost that would not involve either danger to their stability or a mutilation of the design of the main piers and abutments, which four masses of masonry are among the most prominent and important features of the Bridge. Many difficulties interfere to prevent leaving these cornices off until after the completion of the Bridge, while on the other hand I would not risk their construction in limestone or sandstone.
5th. The blocks of masonry between the railways in the main piers and abutments are not only needed for weight, but for strength also. The wind-trusses are secured to them, and to give these blocks of masonry the requisite strength, large bolts are carried down into the body of the piers from the wind-trusses. [See Plate XXIV.] To build them hollow and fill them with ballast as suggested would diminish their weight. To fill them with concrete would entitle the contractor to charge the same price as at present. Either plan would give less strength.
6th. Tramways. — Two of the tramways will be required for horse-railways, and cannot be dispensed with without cutting off one source of revenue that should be secured. Tramways for common travel on road bridges have been found very economical devices. Those proposed will be simply plates of 3/8-inch iron, 8 inches wide, with a very slight flange rolled on each edge to insure the tracking of the wheels. I have no doubt if they were left off an additional expense for repairs the first year would be incurred almost sufficient to pay for them. I do not think, judging from our experience with street-car tracks, that either the car-tracks or the broad tram-rails will prove to be a serious obstacle to light carriages which may wish to pass slow teams. The use of the tramways does not prevent planking the Bridge lengthwise The plan adopted, it is believed, will make the roadway more easy to repair, and
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is equally cheap in construction.The use of the wooden planking as a means of strengthening the Bridge against winds is impracticable in connection with the iron truss. This may be illustrated by an exaggerated example, such, for instance, as the strengthening of an iron wire-rope by increasing its diameter with india-rubber or manilla. The iron truss would give way before the strain would be sensibly transferred to the planking.
7th.Wind-Trusses. — The weight of the iron in the three wind-trusses will be reduced, by the alterations I have been devising during the last four weeks, about 124 tons. All of the objections named by Mr. Laurie will be avoided in the modified design, without using the heavy Nicolson pavement mentioned, or in any way increasing the weight of the wooden work.
JAS. B. EADS, Chief Engineer."
Mr. Laurie's main Report of April 10 is a document of great interest and bears evidence of marked ability. It is clear in all its statements, and, better than almost anything-else gives the exact status of Bridge affairs in St. Louis at that date. Mr. Laurie was exceedingly careful and conscientious in his investigations, and, so far as his knowledge of ordinary bridge-work went, he was an accurate observer and a good judge he was, however, less familiar with the arch. That such should be the case ought not to surprise any one, for very few engineers, either at home or abroad, felt competent to give an opinion upon the details of the arch. The single sentence with which Mr. Laurie disposes of the peculiar difficulties already encountered in the construction of the arch ("so much drilling and turning"), shows that he had little knowledge of what had been doing at Philadelphia and Pittsburg.
The Report begins with a statement of the financial condition of the Company. I omit this statement, as well as a brief description of the Bridge and its approaches. Under the head of "Masonry," Mr. Laurie said: —
"The following table exhibits the dimensions of the several piers and abutments: —
Dimensions at Foundations. Dimensions at Top. Height from Foundations to Top of Masonry. Foundations below Extreme Low Water. Length. Thickness. Length. Thickness. Feet. Feet. Inches. Feet. Inches. Feet. Inches. Feet. Inches. Feet. Inches. East Abutment 83 70 6 64 3Ë 47 6 192 9 93 3ź East Pier 82 60 0 63 0 24 0 197 4 86 21 West Pier 82 48 0 63 0 24 0 172 1ź 61 2ź West Abutment 94 62 8Ë 64 3Ë 47 6 112 8Ë 13 3ź
The great mass of masonry in the piers and abutments is due to the calculations and plans having been made with a view to make each span self-sustaining independent of the others, so that, if one span of the superstructure from any cause should be destroyed, the others would not necessarily fail. If this consideration had not been kept in view, but the masonry been built merely to sustain the vertical load of the Bridge and its traffic, and to resist the shock and pressure of ice and blows from vessels or rafts, the amount required would have been reduced to about one-half."
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Mr. Laurie pronounced air the masonry to be of "a very superior and substantial character." He proceeded as follows under the head of
SUPERSTRUCTURE:
"So far, only the cast-iron bed-plates and part of the steel and iron bolts for securing the skew-backs to the masonry, and a few other castings, have been delivered at St. Louis, but there appears by the estimates to have been labor performed and material delivered at Philadelphia and Pittsburg on February 1, to the value of $220,010.46; on March 1, the value amounted to $318,643.11, and on April 1, to $380,633.38.
Many modifications have been made of the plan of superstructure on which the contract was based. Of the whole estimated weight of metal in the Bridge and approaches, say 6,141 tons, only 643 tons remain at the original contract prices, the prices for the rest having been changed by supplementary and special agreements. Twenty-two hundred and six tons of steel have been submitted by agreement to referees to determine the price, or rather to determine the difference in cost between working chrome steel and crucible cast steel; 1,242 tons of wrought and rolled iron, for various reasons, are left to the same referees to determine the price; 156 tons of skew-backs are to be paid for at cost; 1,079 tons of wrought iron at cost, with ten per cent added; 797 tons of wrought iron at 7 cents per pound; 18 tons of wrought iron at 10 cents per pound; and on 304 tons of envelope steel an allowance of 11 cents per pound has been agreed to; — leaving at the original contract prices of 15 cents per pound for steel, 7 9/10 cents for wrought iron, and 4 cents for cast iron, only 396 tons of steel and 247 tons of cast iron.
Under these circumstances, an estimate at the present time of the cost of the superstructure must be considered only as approximate. I have not thought it advisable to make any guess of what the referees may decide upon, but have estimated the work at the prices stated, except in the two following instances: The skew-backs, weighing 156 tons, have by supplementary contract to be paid for at cost, and, being nearly completed, I have entered them at $72,000, which makes their cost per pound about 23 cents. And for 1,079 tons of wrought iron agreed to be paid for at cost plus ten per cent, I have added the percentage to the original price for wrought iron.
Of the 1,036 tubes required for the Bridge, there are only about fifty on which any work has yet been performed. It is very important that they should all be completed during the summer and autumn, and at least two-thirds of them put in place by December next, as, from the plan of the structure and proposed mode of erection, it will be difficult and costly to make the connections in the centers of the several spans except during very cold weather. By calculation, the arch ribs, to preserve their form, require to be united when the temperature is not higher than 20° Fahrenheit, or 12° below the freezing point. In fact, I think it is questionable whether the junctions can all be made without resorting to artificial means of lowering the temperature of the tubes to obtain the necessary contraction in length. It is true that the responsibility rests with the contractors, but any failure to make the connections in a proper manner will be a serious injury to the work.
TIME NECESSARY TO COMPLETE THE WORK.
As much of the stone is on hand, dressed, ready to lay, and the balance required can readily be procured, there should be no difficulty in completing the masonry in four or five months, or even sooner. The trestle-work in East St. Louis is quite an extensive structure, but may readily be completed in six or seven months after the plans are furnished to the contractors, and it certainly would be an advantage to them to have the plans, and time to procure the timber and have it sawn to the proper dimensions.
But small progress has been made on the superstructure of the Bridge. A considerable amount
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of material has been manufactured or purchased and is on hand at Philadelphia and Pittsburg, but of the workmanship necessary to fit it but a small amount has yet been done, and it is this workmanship which will control the time of completion. There is so much drilling and turning required, especially on the steel-work, which must be done by machinery, some of which has to be got up specially for the purpose, and it is of an expensive character; and from the delays heretofore and the small progress still making, I do not think it is probable that the Bridge will be completed for use until next spring or summer.
In a few weeks the masonry of the West Pier and Abutment will be so far completed that the erection of the superstructure could be commenced if a sufficient quantity of material was on hand.
The estimate of cost includes four towers and elevators. If the completion of three of them be omitted and wooden stairways be substituted, and the fourth tower, which is now in a state of forwardness, be carried up to the level of the upper roadway only, there will be a saving of about $60,000. The wind-truss, which had been reduced from 965 tons to 750 tons when the estimate of quantities was made, has since been reduced about 120 tons more and the wrought-iron cornice omitted, which will make a saving of about $20,000; and if the tramways for common vehicles are dispensed with, there will be a further saving of $15,000.
The inside railings along the footways, and the iron sheathing for protection against fire and annoyance of smoke from the locomotives below, originally contemplated, have been omitted. If found necessary, they can be added at a future time.
Since preparing the estimate I am informed that it was not intended to place elevators in more than two of the towers for the present. This will reduce the saving above mentioned $12,000; but I have only allowed $3,000 for two toll-houses against $15,000 in the original estimate for station and entrance on Third Street."
Mr. Laurie's estimate was taken from the books of the Company, and is given in great detail. His footings only are of special interest; he gave: —
| Amount expended on the Bridge and its two approaches up to March 1, 1872 | $4,023,703 95 |
| Amount required to complete the work | 2,815,082 94 |
| Total cost | $6,838,786 89 |
On the 30th of April Mr. Laurie submitted several suggestions to the president of the Bridge Company, which I will consider seriatim. They were, like the previous Reports, referred to the chief engineer. Mr. Eads did not deem it necessary to report upon them in detail. He, however, assured the Company that Mr. Laurie's suggestions would receive the respectful consideration which the high professional standing of that gentleman, and the confidence reposed in him by the stockholders, demanded at his hands.
Mr. Laurie suggested as follows: —
"1st. At the east end of the Bridge the grade of the railroad, from the middle of the side span to the abutment, is 79.2 feet per mile, and from the abutment to the trestle-work it is only 16Ë feet per mile. By continuing the 79.2-feet grade to the end of the masonry the height of the trestle will be reduced 3 feet, or from 45 to 42 feet; and the same reduction may be made in the height of the trestle for common travel, making it 63Ë feet instead of 66Ë feet.
The railroad-trestle or embankment will be about five-eighths of a mile in length, and averages 35 feet in height. The common-travel trestle to Fifth Street is 1,365 feet in length, and averages fully 40
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feet in height. A reduction of 3 feet will effect a considerable saving, and I know of no serious objection to making the alteration.
2d. The common-travel carriage-way at the abutments is 19 feet above the railway, but at the piers it is elevated 4 feet 9 inches higher, making a parabolic curve different from that of the railway, with a grade at the ends of 184 feet per mile. If the upper roadway was made to run on a curve parallel with the railroad tracks at an elevation of 19 feet above them, there would be a reduction in weight of the iron uprights and bracing equal to about 60 tons, and the inclination of the roadway would be reduced from 184 to 79.2 feet per mile."
It must be said that the adoption of these suggestions would have effected some saving, but in each case it would have been at the cost of grace and beauty in the Bridge. The general architectural features of the Bridge, including the stone approaches, had been the result of careful study. The design in all its parts was that of Mr. Eads, but on certain matters of detail he had consulted Mr. Gr. I. Barnett, a St. Louis architect of good taste and judgment, and had adopted the style of ornamentation for the piers and the arcade over the approaches on his suggestion; and to mar the appearance of a bridge costing several millions for the purpose of saving a few thousands, would have been unpardonable. The slightly increased rise of the upper over the lower roadway at the center gives the design a lightness and grace it would otherwise lack,
"3d. There are sixty-four pillars or uprights, composed of trough and T-iron bars, supporting the upper roadway, which are 30 to 54Ë feet in length. It is questionable if these bars can be obtained over 30 feet in length, and if they cannot, splice joints will have to be adopted, and plans ought to be furnished for them."
The longest vertical struts in the Bridge are in the center span near the piers. Each contains two 10-inch channel-bars 54 feet 6ž inches long. The total weight of every complete strut of this size is about 4,900 pounds. Subsequent investigation showed that when Mr. Laurie wrote this "suggestion" all the large channel-bars had been rolled.
"4th. I am of opinion that light diagonal bracing is necessary to prevent dangerous vibration in the pillars mentioned in item No. 3 from the passage of locomotives. They can be braced in couples or triplets, with slip-joints if thought necessary."
In this fourth suggestion Mr. Laurie shows his unfamiliarity with the theory of the ribbed arch. The insertion of stays between adjacent vertical struts would have constituted a sort of spandrel bracing entirely inadmissible. What any system of bracing would amount to with "slip-joints," it is difficult to see. The shape and composition of these upright struts is shown in Plate XXXI. As a matter of subsequent observation, I will say that they suffer no dangerous vibration of any kind.
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"5th. The angle-iron bars underneath the railroad tracks are 48 feet in length. It is probable that they will have to be formed by connecting two bars together, and, to resist thrust, they require bolts and distance-pieces."
It had been decided to use channel-bars in place of angles, and at the time Mr. Laurie wrote this Report they were all rolled the full length of 48 feet. (See Plate XXI.)
"6th. The Main Street and Second Street bridges are weak at the ends;ź-inch plates with 5-inch pitch of riveting does not give sufficient bearing area for the strains. In the end panels intermediate rivets should be put in, — making them 2Ë-inch pitch, — if the plates themselves are not increased in thickness."
In deference to Mr. Laurie, Col. Flad reviewed his calculations for these bridges and re-examined the dimensions and riveting of the iron girders. He found them abundantly strong. Nothing better illustrates the extreme fidelity of Mr. Laurie, so far as his investigations went, than a bit of conversation he had one day with Col. Flad. Mr. Laurie was revising the estimate of weight on the arches used in the calculations of the office. He found that every bolt, rivet, nut, and plank had been included. At last he said, "Are you to run a water-pipe over the Bridge?" "Yes," answered the Colonel; "that is all in." After a moment of thought Mr. Laurie asked again, "Have you included the weight of the gas-pipe too?" "No," said Flad, with a smile; "I think we didn't figure on that." Mr. Laurie thought it should go in. "Yes," said Flad, "but there is a correction. We must allow for the buoyancy of the gas!"
"7th. From experiments made on four small model tubes 8 inches in length, bored out of the solid, received a few days ago, the breaking strength of the chrome steel now being used has been found to be about 100,000 pounds per square inch, including the envelope as part of the solid ring of chrome steel; but as the envelope in the large tubes is made of homogeneous steel, which is known by other experiments to have a compressive strength of only 48,000 to 58,000 pounds per square inch, a correction is necessary. And making this, we get 90,000 pounds per square inch as the ultimate strength of the tubes, which will make the possible working strains fully one-third of the ultimate or breaking strength of the metal of which the tubes are composed."
In this last observation Mr. Laurie refers to a very interesting point, which requires at my hands a very full and detailed account.
Mr. Laurie was considerably in error in regard to the strength of the envelopes. To be sure, the steel had frequently shown an ultimate strength as low as that named by him, but the contractors were required to furnish steel whose average tensile strength was 80,000 pounds per square inch, and as a matter of fact its average strength was between 70,000 and 80,000. Between June and December, 1872, more than four hundred tests were made on scraps cut from envelope plates. If the tensile strength was less than 70,000 pounds the plates were rejected. The strength often ran up to 90,000. On September 23, fifteen tests were made on specimens from envelopes and butt-straps. The least strength shown was 73,000 pounds, the highest was 93,000, the average being 81,867 pounds per square.
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inch. For a full discussion of the maximum strains in the finished arches of the Bridge, see pages 355, 356.From the first sight of a steel tube for the Bridge (and he probably saw one at the Keystone shops in Pittsburg while on his way to St. Louis) Mr. Laurie had questioned its strength. To him, as to all, the form was novel for a working member of a bridge, and he perhaps had little or no experimental knowledge of the strength of tubes. He therefore very fitly represented a certain amount of popular skepticism upon the subject. About thirty steel tubes, variously constructed, had already been tested by Mr. Eads for the purpose of ascertaining the strength of steel and the best design for a tube. Mr. Laurie's misgivings led Mr. McPherson, the president of the Bridge Company, to ask Mr. Eads's views upon the subject of testing a tube made of chrome steel. All the model tubes tested thus far had been made of carbon steel. Mr. Eads's reply is so full of interest that I give it entire: —
"ST. LOUIS, February 12, 1872.
Hon. Wm. M. McPherson, President.
DEAR SIR: In answer to your note requesting my views as to the propriety of making and testing one or more small model tubes of chrome steel, I have to reply that for the purpose of determining the quality of steel and the proportions of the tubes to be used in the arches of the Bridge, and the strains that could be safely imposed upon the material when in the structure, I instituted a series of careful experiments upon a variety of specimens furnished by different makers throughout the country. To determine with the utmost exactitude the values of the three most important qualities of the steel, namely, its limit of elasticity, its ultimate strength in tension and compression, and the ratio of extension and compression to the intensity of the strains or loads imposed, a testing-machine capable of exerting a force of one hundred tons was designed and built, and several novel and delicate instruments to be used with it were devised and provided, the whole costing about $4,000. The accuracy and delicacy of the tests made on this machine are admitted by engineers and scientific gentlemen familiar with its construction to be unequalled by anything of the kind ever before known. On this machine I have had three hundred and sixty-seven specimens of steel tested and the results carefully noted. Of these tests, seventy-eight have been made on specimens of chrome steel.
Before the completion of this machine, specimens of steel were tested on the government machine at the Washington Navy Yard for this company by Chief Engineer Wm. H. Shock, U. S. N., who took unusual pains to insure the most accurate results. These tests, made on one of the most perfect machines in the country at that time, were carefully reported to me in full.
At the same time (1868) Mr. Kirkaldy, in London, tested for this company thirty-two specimens of chrome steel furnished to him by me.
In addition to these numerous tests, model tubes of steel were made and tested to determine the best manner of constructing the large tubes; to ascertain the proper strength of the envelope which encloses the staves; and also to determine the relative strength of the steel when in the tubular form as compared with solid cylinders. These tubes were about 21 inches long by 2ž inches in diameter, and cost from $137.50 to $150 each.It is true that none of these tubes were made of chrome steel. My numerous experiments establish the fact that perfect safety is assured through the simple requirements in the specifications for the steel — to wit: that it shall possess a certain limit of elasticity, a certain ultimate strength in compression and in tension, and a certain modulus of elasticity. These conditions being fulfilled by the steel-maker, I am indifferent as to whether he furnishes carbon or
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chrome steel for the tubes, just as I would be in receiving iron for the Bridge; if it fulfilled the specifications, I should not deem it important to know whether it was Sligo, Lowmore, or Swedish.
I added to the specifications that the steel should be crucible cast steel, because I believed that a greater degree of uniformity of product and a finer article would result therefrom. I am glad that the makers are making chrome steel, because I believe it to be more uniform than carbon, by which more prompt delivery will be insured and some relaxation in testing be permitted.
There can be no reasonable ground whatever for assuming that where two brands of steel (as carbon and chrome) possess the same ultimate strength in the testing-machine, the same modulus, and the same elastic limit, they will not possess equal strength to resist either a direct tensile or a crushing force when in the Bridge. It is possible that the one may be more liable to break under sudden shocks or concussion. For such contingencies the tougher material will certainly be the better. I am absolutely positive from my own investigations that chrome steel of equal ultimate strength is tougher and will bend more than any carbon steel of which I have knowledge. I should therefore prefer it for tension members in the structure. The tubes, however, can have no bending strains of the slightest consequence compared with their strength, nor are they liable to any concussions that carbon steel would be at all liable to fracture from. With chrome such casualties are, in my opinion, simply impossible. In making the tests of the model tubes, I was most anxious to form them of steel of a certain elastic limit, and being reasonably satisfied of their relative strength, I feel safe when I know that I am getting steel fully equal to that in them. Besides, at the time these were made and tried the Wm. Butcher Works were the subcontractors, and were not making chrome steel. If any more money is to be expended in experiments on tubes, they should be made in a manner so convincing that no cavillers among the public could carp at the result. This could not be the case by simply crushing one or more small models.
No person who has made the subject of cast steel a study is ignorant of the fact that its quality and strength is greatly modified by the amount of work it receives, either under the hammer or in the rolls. The large staves are from 1 3/16 to 2 1/8 inches thick. Those of the model tubes would be about one-fourth inch thick. If drawn down under the hammer or in the rolls to this small dimension, it could reasonably be inferred that although an ingot prepared for the large ones was used, these small pieces, having received so much more work or compression, would be stronger relatively than the large ones. If the result proved favorable, it would be largely discounted when applying it to fix the value of the large tube.
On the other hand, if the test proved unfavorable, it might be reasonably inferred that the smith had injured the steel in heating it, or that some of the staves had been more suddenly cooled than others; and such want of uniformity would be deemed sufficient cause for an unfavorable result. Tests on small tubes could not be absolutely conclusive unless the smaller staves were planed down from the large ones. The great expense of doing this is admitted to make such method impracticable. Even if this were done, some might raise the question as to whether the planing off the skin or outside of the large stave did not give a different degree of strength to the small ones made from it. I believe the testing of such tubes would lead to discussions involving the making and testing of several more and the expenditure of a considerable sum, with no more absolute result than what we have already. For my own part, I have no doubt whatever of the abundant strength of these tubes. I am led to this result by the deductions drawn from the numerous tests I have made of specimens of steel, and by the fact that the staves we are receiving are fully up to the standard of strength required and are of great uniformity. Each one of them is tested to 50,000 pounds, although in the structure the maximum strains will not put over 28,000 pounds in reality upon them.
After the elaborate professional report and indorsement of the plans of the Bridge by Mr. Julius
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W. Adams, C. E., containing his statement that he would not hesitate to use the steel with a maximum strain of 40,000 pounds per square inch on it; and after the fact that the plans of the structure and the manner of using the steel have been discussed and approved by many of the most eminent engineers in this country and in Europe, I do not believe that there exists any one stockholder in the Company who doubts its strength. If, however, there be a desire to open this question of the strength of the Bridge, I earnestly trust it will be met in a way to quiet forever all controversy on the subject. If it is deemed necessary, I hope the Company will authorize the construction of such devices as I will design for crushing one of the large tubes. Let this be indiscriminately selected from among those now being made to go into the arches, and tested to destruction. I believe this experiment can be made at a cost (including the tube) of not over $3,000. Such an experiment would demonstrate absolutely the strength of the tube and therefore the strength of the Bridge; it would silence all controversy, and would pass into the history of the structure and constitute a reliable certificate of its safety.
Very respectfully,
JAS. B. EADS, Chief Engineer."
Mr. Eads's proposition to test one of the large tubes was very satisfactory to the officers of the Company and to Mr. Laurie. Col. Flad was consulted on the matter, and as he pronounced the project entirely feasible, he was asked to devise the method of testing and submit a proposition. The plan he proposed to adopt was substantially as follows: To procure from Haughian, of the New York Chrome Steel Works, a steel ring made like the tire of a car-wheel, about 9 inches thick and 12 inches long, with an internal diameter of 45 inches. This was to be turned on the inside, and a plunger of cast iron fitted into each end with proper packing. The exterior ends of these plungers were to be accurately planed and capped by chrome-steel plates of several inches thickness. Thus arranged, the apparatus was to be placed in a recess cut out of the solid rock of a stone-quarry. The axis of the ring and plungers was to be horizontal. One steel plate was to rest against a dressed vertical face of the solid rock, while the other was to receive the carefully squared end of the tube to be tested. The other end of the tube was to rest against a third steel plate supported by the face of the opposite quarry wall. The accompanying sketch shows the arrangement proposed.
Fig. 17. — METHOD PROPOSED BY COL. FLAD FOR TESTING A LARGE TUBE.
"When all was in adjustment, as shown in the figure, water was to be forced into the space within the large ring and between the plungers by a powerful pump till the hydrostatic pressure should be 8,000 or 10,000 pounds per square inch. The compressive force
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on the tube would at 8,000 pounds amount to 12,800,000 pounds, — an amount greater than the entire weight of the iron and steel in the three arches of the Bridge! The sectional area of one of the strongest tubes was 117 square inches, including the envelope. The breaking (or buckling) pressure was expected to be about 100,000 pounds per square inch, or 11,700,000 pounds for the tube. It is therefore evident that the apparatus would be able to crush any of the tubes.The quarry selected by Col. Flad was "Nipper's Quarry," where the rock was seamless and exceedingly solid. In the place of the steel ring, Mr. Eads suggested a thin cylinder of cast iron, upon which wrought iron or steel bands should be shrunk. Col. Flad proposed to test three tubes for the sum of $4,000.
At this stage of the question it seemed highly probable that the tests would actually be made. Mr. Laurie had requested it, and Mr. Boody of the Stockholders' Committee had seconded the request; and yet just there the subject was dropped, and small model tubes were substituted. Col. Flad, though willing to undertake the grand test, regarded it as a useless waste of money and material, and freely said so. Mr. Eads thought the experiment would develop no new facts, though it might silence "cavillers among the public." It is probable that Mr. Laurie was unconsciously influenced by the strong confidence shown by the Bridge engineers in consenting to the test, and he certainly wished to avoid unnecessary expense. He therefore consented to waive his request and substitute model tubes of chrome steel. Accordingly, March 15, Mr. Eads wrote to Mr. Fitch at the Philadelphia Steel Works: —
"I enclose you a tracing of four small models, which I want you to have made as soon as possible and sent to Pittsburg to be tested. Let me know as soon as they are done.
These model tubes represent the proportionate dimensions of the large ones. They should be made as accurately as possible. The enlargement at each end represents the couplings. Make them out of a stave of 11 inches thickness or over, and of the chrome steel we are using. Put the work in hand as soon as you can, and report to me what it will probably cost."
The order was promptly executed. For the sake of increased evidence of the strength of the steel, Mr. Eads soon ordered four more cut from the same stave.
The first four model tubes were sent to Pittsburg April 5. The work on the four cost $60. They were tested April 16 by Mr. Bremermann on the St. Louis machine, in the manner specially indicated by Mr. Laurie. He did not care to know either the modulus or the limit of elasticity. "What he wanted was the total compression at 55,000, 60,000, 70,000, and 80,000 pounds per square inch, and the ultimate strength under compression. Some of the first four tubes had a small hole drilled in the side. It was at the time proposed to bolt the staves together internally, though the idea was subsequently abandoned. The hole in the model tube had no sensible effect upon its strength.
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The second set was ordered by Mr. Eads for the purpose of determining the limit and modulus of elasticity. I give the results in the following table, with a section of the specimen tubes: —
| No. | Length. | Area in Inches | Dist. betw'n Collars | Compression in inches at | Strain per Sq. Inch in Ibs. | Compres'n between Collars. | Modulus of Elasticity. | Limit of Elasticity. | Ultimate Strain per Square Inch. | |||
| 1 | 7.986 | 0.269 | 6.0 | 0.0062 | 0.0173 | 0.0364 | 0.0500 | — | — | — | — | 102,000 |
| 2 | 8.005 | 0.286 | 6.25 | 0.0083 | 0.0193 | 0.0410 | 0.0546 | — | — | — | — | 102,900 |
| 3 | 8.000 | 0.364 | 6.09 | 0.0072 | 0.0184 | 0.0503 | 0.0653 | — | — | — | — | 98,100 |
| 4 | 7.992 | 0.356 | 5.75 | 0.0065 | 0.0183 | 0.0426 | 0.0576 | — | — | — | — | 102,100 |
| 5 | 7.998 | 0.280 | 6.1 | — | — | — | — | 35,000 | 0.0074 | 28,900,000 | 55,000 | 110,000 |
| 6 | 7.972 | 0.287 | 6.25 | — | — | — | — | 20,000 | 0.0049 | 27,600,000 | 55,000 | 108,000 |
| 7 | 8.004 | 0.358 | 6.3 | — | — | — | — | 19,000 | 0.0045 | 26,600,000 | 50,000 | 97,000 |
| 8 | 8.008 | 0.360 | 6.25 | — | — | — | — | 27,000 | 0.006 | 28,100,000 | 50,000 | 101,000 |
The tests of the first four tubes are quite anomalous, but I give them for what they are worth. The amount of set was neither asked for nor obtained for the various pressures. The most remarkable discrepancy lies in the small amount of contraction under the load of 55,000 pounds per square inch. As the tests were made with great care, there is no reason to question the record. An explanation may perhaps be found in this, that instead of applying the pressures gradually, adding 500 pounds every time, noting the compression, then relieving the specimen entirely, watching for the first evidence of set (as was the inspector's usual method), Mr. Laurie required the immediate imposition of 55,000 pounds per square inch. Apparently the amount of compression was scarcely more than one-third of what it would have been had the pressure been gradually applied and the tube frequently relieved.
The stave, from the end of which these specimens had been taken, had been tested to but 50,000 pounds per square inch. Its modulus of elasticity had been found to be 30,340,000. The specimen tubes taken from the interior of the stave showed a lower modulus, thus indicating that the surface layers of steel were more rigid than the interior.
Mr. Laurie expressed his satisfaction at the strength shown. As was seen in his letter of April 30, he figures out the greatest possible working strain as one-third the breaking strain, and he probably was inclined to regard the factor of safety as low. In regard to that it should be said that more and more, in carefully designed bridges, actual tests of the working pieces are taking the place of large factors of safety. It is unnecessary, for instance, to reduce the maximum working stress (combining maximum effects of dead and live loads and temperature) below 30,000 pounds, when the limit of elasticity is known to
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be between 50,000 and 60,000, and the breaking strain of the pieces as used, is between 90,000 and 100,000 pound.As to the large tubes of the Bridge, it must be remembered that there was nothing problematical in regard to the strength of their staves. At first, all the staves were tested to 50,000 pounds, which was always below the elastic limit. Later, when the material was found to be very uniform, one in three or five, and finally one in ten, was tested. Moreover, the composite nature of a tube was a consideration in its favor. It was of course possible that a stave might pass the inspectors with some imperfection, but that two such staves should find their way into one tube was so altogether improbable that the contingency may be regarded as out of the question.
"With the letter of April 30, Mr. Laurie's labors in connection with the St. Louis Bridge ceased. For his services he was paid $4,057.
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Chapter XI. The Manufacture of Sleeve-Couplings.
So far as practicability was concerned, all the questions regarding the construction of the various members of the arch had been settled save that of rolling steel couplings for the tubes. This was still an open question and of daily increasing importance. It does not appear that special difficulty was expected in this quarter, and no early efforts were made to solve this, the knottiest problem in the whole work of construction.
The specifications required that the couplings should be made of steel which had a limit of elasticity of 40,000 pounds, and an ultimate tensile strength of 90,000 pounds. The quality of the steel was to be determined by test-bolts cut from the plates actually used in making the couplings. Accurate drawings showing both the size and shape of the couplings are given in Plate XXX. The weight of a complete coupling varied from about 365 to 500 pounds.
Although the Butcher Steel Works had contracted to roll the 1012 couplings needed, they postponed their manufacture till the steel bolts which were to be first used should be well under way. Mr. Fitch reported the casting of the first ingot for couplings in his letter of November 25, 1871. Mr. Durfee was already superintendent, and the ingot was of chrome steel. Four days after, Mr. Linville writes that, "They [the Butcher people] have promised, after repeated urging, to be ready to make couplings next Monday" (December 4). The promise was not kept, however. Accidents, repairs, additions to the works, and changes in the force of men employed prevented the trial till January 2, when three ingots for couplings were rolled. The metal did not roll well, — two ingots showing cracks and rough edges, as though the steel were hard and brittle, and they did not fill out sideways, showing that the moulds were too small. The rolls being of unequal size, the plate bent as it came out. An attempt to saw off a half coupling failed, owing to the cooling of the steel and it was feared that they would require cutting cold.
The cast-iron moulds were planed out, new ingots cast, and a second attempt at rolling was made January 16. The upper roll broke in the middle on the first trial, and stopped the mill until another roll could be made. The new roll arrived at the works January 27, and another trial was made on the 29th. Three ingots were rolled with fair success, but the outside flange of the roughing roll was broken. Inspector Fitch reported: "From the observations I made during the trials, I think there will be great and constant risk of breaking the rolls in making this work, as the great width and section of the pieces and the
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impossibility of any relief to the sides brings great strain on the rolls, and any error of judgment in estimating the temperature or in lowering the roll will cause another break." The ingot was passed three times through the roughing-rolls and once through each of the other sets, making six passes in all. It was always" noticed that the steel cooled rapidly. Only three passes could be made before reheating was necessary. The rolled plate was cut in lengths of from 16 to 20 inches, which were bent into semi-cylinders, as shown in Fig. 19. The internal diameter of the larger couplings was a little less than 16Ë inches, admitting of deeper grooves than the shorter ones. The bending was done under a large hammer furnished with proper dies, the steel being at a red heat. The success was fair at the first trial, February 8. Some slight changes were made in the rolls and in the moulds, and six more couplings were bent March 1, with some improvement. Some coupling-ingots only one- half as long as the former were cast about March 15, in the hope that they would roll more easily; but so busy was the mill with other matters that no attempt at rolling was made till March 29. Only two halves were obtained out of a lot of eight pieces; both of these were defective on the flanges, the metal being broken and cracked. No suitable means for handling the ingots had yet been provided. The material used was carbon steel, and chipped readily.In spite of promises to the contrary, several weeks were allowed to slip away before the couplings were touched again. Meanwhile Mr. Fitch had resigned, his leave of absence from the navy having expired, leaving Mr. Harrison in charge of the inspection at Philadelphia, with Mr. Bremermann as his assistant.
Mr. Eads protested earnestly against the repeated delays. Promises to vigorously take hold of the couplings had been freely made, but not kept. He foresaw that the work was difficult, and that some experimenting would be necessary, but the ready answer was that it would soon be well in hand, and that no fears need be entertained of the result. In truth, the mill was engaged on more profitable work, and it is probable that the superintendent was really less sanguine than he wished to appear. Mr. Huston admitted that the problem was a difficult one, and "pronounced by some expert rolling-mill men of very questionable practicability, but the superintendent [Mr. Durfee] hoped that in the early part of the following week he would roll them satisfactorily."
Twelve days later, on the 12th of May, no progress in making couplings having been reported, Col. Flad left St. Louis to examine into the coupling problem and other matters of construction. Should the rolling not be successful by the 16th, he was to see on what terms couplings could be got in Pittsburg; and if parties were unwilling to undertake to manufacture them of steel, he was to arrange for making the first needed of iron, leaving the contract for the whole number to depend on the success achieved.
On the 18th Col. Flad was present at the Butcher Steel Works, when a new trial was made at rolling couplings. Huston telegraphed, "Have rolled sleeve-couplings successfully!" The lower rolls were too large, however, causing the steel to bend upwards, so they were sent away to be turned down. By the 22d, the coupling bars had been heated,
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straightened under the hammer, cut off, and bent. Mr. Harrison reported, "One looks well, but is not of the right shape or thickness." A pair of half-couplings were sent to Pittsburg for trial. A few weeks previously the ingots had been thought too thin, and the moulds were planed out to make them thicker; they were now thought too thick, and the moulds were planed on the flanges to make them thinner. Col. Flad returned to St. Louis the last week in May, leaving the coupling problem in statu quo, and Mr. Eads spent the entire month of June in Pittsburg and Philadelphia.Meanwhile more changes had been made among the inspectors. Mr. Harrison resigned May 31, and Mr. E. L. Bremermann, C. E., who had been acting as his assistant, was promoted to his place. Mr. Theodore Cooper, engineer U. S. N., was appointed to assist Mr. Bremermann. About August 1, Mr. Bremermann returned to Pittsburg. Mr. Cooper remained at the steel works as long as the manufacture of steel continued.
Rolling couplings was not resumed till June 14. The lower roll seemed still too large. The ingot bent upwards and fatal cracks appeared on the lower surface. By the use of a milder steel, and a reheating after each passage of the ingot, good results were reached, and Mr. Durfee was sanguine of ultimate success. On the 17th the lower finishing-roll was broken, and a new roll was ordered and turned with all speed. It was in place for a new trial June 26. Rolling was then continued day after day with frequent modifications, all results being unsatisfactory. Relief to the ingot at one point seemed to involve tearing at another.
On June 28, Mr. Dwelle, inspector at Pittsburg, wrote: "The six steel couplings have arrived. Two of them have been planed preparatory to being bored. They look very badly." The main defect appeared to be "blow-holes." Two pairs of these couplings were rejected by Mr. Eads after the work on them was all done.
On July 9, couplings were rolled apparently perfect. When, however, a few days later, ten were bent under the hammer, only three proved to be fit for use. The seven exhibited a uniform tendency to crack along the edges of the plane surface, as shown in the section. (See a a, Fig. 19.) The lower rolls were still too large.
Thus change after change was made till the 20th of July was reached; results were not at all satisfactory. Nevertheless, all parties were sanguine of success. Mr. Eads received a bid from Wm. Miller of Pittsburg to forge iron couplings, and the Steel Casting Company proposed to cast and hammer steel couplings. The propositions were declined, as he had faith that the Butcher Steel Works would "turn them out all right." On the 26th of July seventeen half-couplings were shipped to Pittsburg. They proved to be better than the first lot sent, yet nine out of the seventeen were rejected.
On August 1, the open-hearth furnace, on which Mr. Durfee relied to cast five tons of sleeve-coupling ingots at one charge, gave out, and a general overhauling was found necessary. The same day, the lower roughing-roll was broken. An extra pair of rolls was, however, on hand. At this time it seemed probable that the steel works would soon be able to turn out about thirty half-couplings per day, which was faster than the Keystone Company could furnish them at Pittsburg. Rolling was not resumed for twenty-seven days. There were several reasons for the delay: repairs and changes were going on, the weather was very hot, and the Steel Company preferred to roll staves, inasmuch as they turned them out beautifully and they were paid promptly as the steel was accepted.
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August 30, 1872. — "The men at the rolls have improved in handling the ingots so that they can pass one through all the passes [six] and get a cut by the saw at one heat. Yet the results are poor; from thirty-two pieces of sleeve-couplings, I accepted only four."
September 4. — "The rolling has been continued, and with great improvement over the last batch. They are forming to-day a pile of forty-six couplings, and judging from those which are finished, I hope to be able to accept at least twenty-five of them, — a much larger percentage than ever before." — Extracts from Mr. Cooper's Diary.
He did accept twenty-eight of the forty-six, and sent eight more to the planer to test them further.
Such was the state of affairs when Mr. Eads found it necessary to visit London in the interest of the Tunnel Company. To all appearances the coupling problem was solved, and it was hoped that the erection of the arches would soon commence. The masonry was finished, or nearly so, and nearly half the material of the superstructure was ready to be embodied in the arch. Mr. Eads sailed from New York September 11, 1872; he returned to New York just six weeks later.
A visit by Mr. Cooper to Pittsburg to see how the couplings looked when finished, was most discouraging. He wrote September 24: —
"I was in Pittsburg last week and saw the last shipment of couplings on the lathes and planers, and was not satisfied with the appearance of the material, shown after the tool. It was much honeycombed, — very few of the couplings appeared to be solid. Some were good in parts only. Whether they will have sufficient tenacity, considered as a whole, to answer the purpose required, can only be satisfactorily determined by experiment."
On the 24th of September the top finishing-roll broke, and as there was no reserve roll, the train was delayed once more for some weeks.
It is evident that no reliance could be placed on the uniformity of material in the couplings. Certain ingots were full of cracks, while others were free from them. Some pieces were extremely hard, while others worked readily. The steel-makers were at liberty to mix their steel to suit themselves, and the lack of evenness in the results proved that the proportions of carbon and chrome steel were by no means definitely fixed. Chrome scrap was occasionally used, but though I have no positive information on this point, I am pretty well convinced that chrome steel according to Mr. Haughian's formula was not made. At the time of Mr. Cooper's visit to Pittsburg, Mr. Allen, then president of the Bridge Company, was there, and together with inspectors Dwelle and Bremermann carefully examined the couplings. Mr. Allen had one of them cut into three pieces longitudinally, and holes bored in the ends of each piece, that their tensile strength might be tested in the large machine. It seemed impracticable at the time to test a finished coupling entire. These pieces proved to be poor steel. They had in each case a breaking cross-section of between four and five square inches, and they broke at 34,000, 33,000, and 37,000 pounds per square inch respectively.
All this while very little had been done in the matter of tests of small specimens cut from the couplings. The material was supposed to be similar to that used in the steel anchor-bolts and staves, and repeated tests of it had shown an abundance of strength.
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Moreover, although it was assumed that the steel of the couplings would be as strong as that described in the specifications, it was well known that that degree of strength was not absolutely necessary. While great anxiety was felt that the couplings should come out sound and with correct dimensions, no solicitude was felt lest they should not be sufficiently strong.In the absence of Mr. Eads, Col. Flad went to Pittsburg to see the couplings himself. He met Mr. Allen in Philadelphia. Together they visited the steel works, and reported to the president and superintendent the failure of their couplings. Messrs. Allen and Flad believed that the only way to remedy the evil of blow-holes was to hammer the steel ingots previously to rolling, and they urged strongly that the experiment be tried.
It was objected that they (the Steel Works) had been doing their best, spending their money freely on alterations and experiments of all kinds, and that the hammering involved new expense which they were hardly able to bear. Mr. Durfee felt convinced that he could turn the work out all right yet, and claimed that the last couplings rolled were the best of all. A subsequent examination of the twenty-four half-couplings last rolled revealed the fact that not more than six or seven of the lot were worth putting finishing work on, and that even they might prove defective when planed and turned.
Finally Mr. Huston agreed to hammer the ingots before rolling them if the Bridge Company would pay the expense of the cast-iron die required. Mr. Allen agreed to this, and steps were taken to have the experiment tried. The ingots already cast, some eighty in number, were thought to be too thin for the hammering; they were therefore set aside to wait the result of the new method, and new moulds were made for new ingots.
On his return to Pittsburg, Col. Flad took the second precaution to order the casting in a sand mould of a steel half-coupling in finished form by the Steel Casting Company, who had a patent process of casting steel (it was claimed) free from air-holes and flaws. This company thought their steel would stand 40,000 pounds per square inch without permanent set. The hammering was decided upon October 3, but was not tried till the 30th day of the month, and then — it proved a failure. The ingots under the hammer "‘pulled’ (or cracked open) more or less on the flanges or center ribs." Another difficulty was encountered in the jamming of the ingot between the guides of the die, when struck by the hammer. It was necessary to keep the forged ingot at a certain width on account of the subsequent rolling, and the time lost in releasing the forging when jammed allowed the steel to cool so much that the opportunity to hammer effectively was largely lost. It was, moreover, very hot work for the men. Mr. Huston, after reviewing the attempts at rolling without hammering, and the hammering alone, lost courage. "We look upon the rolled coupling," said he, "as a practical impossibility!"
This was not a very cheerful state of things. Two other plans were still to be tried. The Pittsburg Steel Casting Company had by this time produced two pairs of steel couplings cast in nearly the finished form, and their strength was to be tested; and, at the suggestion of Messrs. Flad and Allen, the Butcher Works had cast three half-couplings in finished shape of a material called by the makers "semi-steel," one of which had been broken in the presence of Mr. Eads, soon after his return from Europe, by one hundred blows with a heavy sledge. The material seemed both tough and strong, and the Steel Works were very sanguine that the solution of the problem lay in that direction.
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Mr. Bremermann had by this time devised and put in practice an ingenious method of testing couplings by hydrostatic pressure which I must now explain.
A complete coupling was formed by planing, drilling, and bolting the halves together, turning the grooves on the interior, and boring the pin-holes. Two wrought-iron plugs were then fitted into the ends, filling completely the grooves as the ends of the steel tubes were to do. These two plugs, though meeting each other along their circumferences, contained an interior cylindrical cavity, as is seen in Fig. 20, which shows a section made by a plane passing through the axis of the plugs and the pin-holes of the coupling. The diameter of the cavity or chamber was 13Ë inches. A circular sheet of packing covered the circular end, and was kept in position by a flat iron ring bolted to the plug A. A hole 2 inches in diameter through plug B admitted a plunger to which pressure was applied by the St. Louis testing-machine, the coupling, with plugs, etc., being placed in the compression end of the machine. Plug mA rested against the cross-head, and the whole force of the ram could be brought to bear on the plunger, P.
The tension exerted on the coupling was measured by the pressure exerted by the water on the annular surface around the 2-inch hole. The area of the end of the plunger was 3 1/7 square inches; the area of the base of the chamber was 143.19 square inches; the difference was about 140 square inches. A pressure of 63,000 pounds on the plunger gave ten tons per square inch as the hydrostatic pressure in the chamber, and a tension on the couplings of fourteen hundred tons. A cross-section of 70 square inches (measured through the pin-hole) gave an average tension per square inch of 40,000 pounds. The chamber was first filled by a hand-pump through the pipe F, and then the pipe was closed. By this admirable device, the largest couplings could be tested to destruction if necessary. Another capital feature of the test was this: The strain was applied to the couplings in precisely the same manner as it would come upon them when under tension in the arches of the Bridge. The great intensity of the pressure forced the water at times through the apparently solid wrought-iron plugs, causing considerable trouble.
The couplings of the Steel Casting Company (three pairs) broke at 35,000, 29,000, and 26,300 pounds per square inch respectively. The first of these couplings was called by the makers "forged," and was delivered at 12 cents per pound. The forging consisted, I believe, of only gentle hammering with a hand-sledge while the casting was still very hot. The second pair was not forged, and cost 11 cents per pound. Six specimens cut from the fragments were tested, with the following results; all specimens were turned to the shape of small cylinders: —
No. 1 ultimate strength, 57,000 pounds per square inch
" 2 " " 49,000 " "
" 3, hammered " " 73,000 " "
" 4 " " " 94,000 " "
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No. 5, hammered and annealed ultimate strength, 77,000 pounds per square inch." 6 " " " " 86,000 " "
The same company made a steel plug to be used in testing couplings, but on trial the raised rings fitting the grooves on the interior of the couplings sheared off.
The failure of these couplings to stand the test of 40,000 pounds put an end to all idea of using them in the Bridge, and Mr. Eads was so afraid of flaws in castings that he would consent to no modification of the tests.
The semi-steel of the Butcher Works gave very poor results. A semi-steel coupling broke at an average tension of 14,000 pounds per square inch. Some specimens of the material showed an ultimate strength of about 56,000 pounds. That was the end of the matter of semi-steel.
As has been said, Mr. Eads returned from England October 24. On the 28th he was at the steel works in Philadelphia, and on the 29th at the Keystone shops in Pittsburg. He was much disappointed at the condition of the coupling problem, but detected a ray of hope in the hydraulic tests on couplings already made by Mr. Bremermann. The rolled couplings which looked so unpromising, and about which so many hard things had been said, proved to be of abundant average strength. Six had already been tested to 40,000 pounds per square inch without fracture. Mr. Eads at once telegraphed, "Proceed without delay with rolled couplings." Mr. Huston answered, "It will be ruinous to this concern [the Steel Company] to roll these couplings;" and he proposed to await the result of test on his semi-steel coupling. The Bridge Company was in such straits that delay was certain to call out some new proposition.
On his arrival at St. Louis, October 31, Mr. Eads wrote more fully to Mr. Huston: —
"From what I have seen, I feel sure the greatest certainty of a successful production of the couplings will be found in the system of rolling so nearly perfected by Mr. Durfee. If this is abandoned, the experience gained will be lost and a new field of experiment must be explored. I am, however, ready to receive any couplings you may deliver, if the metal tried in small samples will stand 80,000 pounds and the finished couplings 40,000 pounds per square inch. I think it of the first importance that a duplicate pair of rolls be provided at once, so in case of breakage there will be less delay, and I am willing to defray the cost of such duplicate pair if you will at once provide them."
In his letter to Mr. Cooper of same date, Mr. Eads says: —
"I am sure our best hope lies in the rolling of the couplings, and as twenty-four pairs have already been tested with but three failures, I am satisfied that many of the rejected ones will pass when tested. Especially do I think so because the smaller sizes will not need nearly so severe a test as these large ones have to stand."
Accordingly Mr. Bremermann was instructed as follows, November 1, 1872, in regard to test of couplings: —
"1. For Rolled Couplings. The large couplings, 20 inches long, forming the joints on the ends of the upper skew-back tubes are to be tested to 800 tons, which will not exceed 32,000 pounds per square inch.All other couplings, to 25,000 pounds per square inch of section.
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2. For Cast-Steel Couplings, not Rolled. Forty thousand pounds per square inch for finished couplings, and 80,000 pounds ultimate strength of material in specimen bars."
None of this second class had yet been tested. So long as it was thought possible to invent a method of casting a half-coupling in its final form and of the requisite strength, the door was left open for its use. For a time a great deal was said, particularly by Messrs. Linville and Piper, about "steel castings," though the instructions given Mr. Bremermann as to couplings "not rolled" were sufficiently clear. After Mr. Bremermann's tests, as I have before said, all idea of using them was abandoned.
The receipt of Mr. Huston's opinion that rolled couplings were a practical impossibility, and that further attempts in that direction would ruin his company, left Mr. Eads no leisure. A letter from Mr. Linville, dated November 1, protesting against the use of couplings whose strength should not come up to the specifications, made it doubly necessary that he should visit Philadelphia again immediately. He found the Steel Company on the verge of bankruptcy. The urgent necessity of the case led him to propose as follows: —
"1. To pay the Steel Company an extra price for the remainder of the rolled couplings required, sufficient to cover the actual cost of supplying them, including duplicate rolls, on condition that the Steel Works supply the cast unrolled couplings, if any are needed, at the price already contracted for the rolled ones (10ž cents).
2. To relinquish all claim for damages growing out of the failure to supply couplings as agreed upon, provided the couplings needed be now furnished without unnecessary delay. The extra price for one hundred and seventy pairs of rolled couplings, including those already delivered, shall be fixed at $10,000.
3. The Bridge Company is also to bear the expense of annealing the cast couplings, if annealing is thought necessary."
These propositions were accepted. Under the stimulus of this agreement the Steel Company proceeded vigorously. New rolls were ordered, and the ingots on hand were rapidly rolled. As was anticipated, they did not turn out very well. Out of about eighty ingots, which should have yielded between two hundred and three hundred half-couplings, only about ninety pieces were passed by Mr. Cooper, though a few more were afterwards accepted by Mr. Eads.
The protest against the use of steel of less than the specified strength made by Mr. Linville proved to be quite embarrassing to the Bridge Company. In spite of assurances that the tests applied to the couplings would certainly secure ample strength, the Keystone Bridge Company declared that the use of steel of less strength than was required by the specifications, which were a part of their contract, invalidated their contract; and if such steel was used they proposed to throw the whole risk of the erection of the arches upon the St. Louis Bridge Company.
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In response to Mr. Linville's protest, Mr. Eads wrote, November 6, 1872, as follows: —
"In the matter of couplings, I propose to accept for the Bridge only such as shall fulfil the following conditions: —
First. Each coupling may be subjected to a strain in tension equal to twice that of the calculated maximum strain it is afterwards to bear, whether the calculation is for the strain in raising or for the finished structure (the test, however, not to exceed 800 tons on any coupling).
Second. No couplings shall be used which show permanent set under the test strain.
Third. No couplings shall be tested to less than 275 tons.
Fourth. Reliable samples of the quality of metal used in the various couplings shall stand ultimate tensile strains six times as great per square inch as the maximum strains estimated to be borne at any time by the respective couplings.
Fifth. Wrought-steel couplings will be required where the greatest tensile strains occur, and no cast steel or wrought of less than 50,000 pounds per square inch tensile strength will be used in any part of the structure.
If you object, on account of the danger of raising the arches, to using any steel couplings of less strength than that named in our contract with the Steel Company, it is imperatively incumbent upon you at once to enforce from that company the immediate delivery of such couplings, and stop further loss to this Company from delay in completing the Bridge. I am willing to accept any which fulfil the above conditions, feeling confident that the use of wrought-steel ones, where the strains are low, will add nothing to the safety of the structure. With those above described, I have no doubt of the safety of the arches in erection, so far as the strength of the coupling-joints is concerned. I have, however, no authority to release you, as requested, from the responsibility you have assumed in contracting to erect them. The ownership and early use of the structure are matters of such deep interest to my Company that they will assure you that nothing but an error of judgment on my part could induce me to permit any material to be used in the Bridge that would endanger the safety of its erection."
On the 11th of November Mr. Linville sent to Mr. Eads a copy of the resolutions adopted by the Keystone Bridge Company, "after a long and careful discussion of the engineering and financial questions involved." One of the resolutions read as follows: —
"Resolved, that the president be directed to reply to Mr. Eads's proposition of November 6: That, after a careful consideration of all points involved, the Keystone Bridge Company does not consider it safe for them to attempt to erect the Bridge upon the plans they have adopted,based upon the specifications, if the strength required by the specifications be reduced. But that it is believed that a plan may be devised by which, at an additional expenditure, it would be safe to use cast-steel couplings (steel castings) somewhat in the manner suggested by Mr. Eads; and, provided the St. Louis Bridge Company deem it advisable to pay the additional expenditure, this company will endeavor to meet the wishes of Mr. Eads in regard to the use of cast-steel couplings (steel castings), as far as they can, in their opinion, be used with safety, the material, tests, and places where used to be subject to their approval; it being first understood that the Butcher Steel Works agree that the change of material shall not disturb their original contract."
It does not appear that this resolution had much effect. Mr. Linville telegraphed as follows on November 19: "Our company proposes to employ plan of erecting works now
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designed, and proceed with erection to completion, or until it is found unsafe to proceed, your Company adopting such couplings as you consider safe, and assuming all risks of erection."The Directors of the Bridge Company at once voted that Messrs. Allen, Eads, and Taussig should visit Pittsburg and "enter into contract to secure the early completion of the Bridge."
A meeting was held at Philadelphia. After a full discussion of all points, including the strains produced in the couplings by different methods of erection, and the tensile strength of wrought and of unwrought steel, and of cast and wrought iron, an agreement was reached with the Keystone Bridge Company, and also with the Midvale Steel Works (formerly known as the "Wm. Butcher Steel Works"), on December 7, 1872, which is of sufficient interest to be given in full. It will be observed that provision is made for the use of cast-iron couplings.
The points agreed upon were as follows: —
"First. That in the event of wrought-steel couplings being used, no additional charge be made for erection, except as hereinafter provided for in clause No. 4; provided, that the Keystone Bridge Company may, if not satisfied with the tests made by the St. Louis Bridge Company, obtain specimens of the steel used and turn them of the prescribed form for testing; and these specimens shall show an ultimate average tensile strength of 90,000 pounds per square inch. They shall also have the right to test any finished wrought-steel couplings to an ultimate strain of 800 tons without perceptible injury; couplings which fail to stand the above tests to be replaced by the Illinois and St. Louis Bridge Company. Any doubtful couplings shall, at the request of the Keystone Bridge Company, be subjected to a tensile strain four times greater than that calculated to be put on them in erection, and sustain this strain without perceptible injury.
Second. Should steel castings for couplings be used, in accordance with Mr. Eads's letter dated November 6, 1872, the Keystone Bridge Company is to be allowed the additional sum of $25,000 for erection.
Third. Should cast-iron couplings be used at points to be hereafter agreed upon by the chief engineers of the two Companies, the Keystone Bridge Company is to be allowed the additional sum of $15,000.
Fourth. The necessary apparatus for inserting the last tubes in the arches, and the cost of said insertion, is to be allowed to the Keystone Bridge Company at actual cost; said apparatus to be approved by the chief engineer of the Illinois and St. Louis Bridge Company.
It is further provided and expressly agreed by and between the parties hereto, that no change in the material in the couplings from rolled (or wrought) cast steel to steel castings or to cast iron shall be made unless the Midvale Steel Works first agree with the Keystone Bridge Company, in writing, that such change of material shall not vitiate or annul the existing contracts between the last-named companies; and if such changes are proposed to be made, the Keystone Bridge Company shall have early notice of the same, to the end that they may make the necessary arrangements to execute and erect the work."
Although this contract admits the possibility of using cast couplings (unrolled) of steel or of iron, and extra payment for erection, by this time there was very little faith left in their availability.
A final effort was therefore made to procure the rolled-steel couplings of the old (now
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the Midvale) Steel Company. To go elsewhere would have been to lose the experience already gained. The expensive nature of the work and the urgency of the case forced from the Bridge Company the following proposition: To pay to the Steel Company a bonus of $30,000, provided they delivered an average of thirty complete couplings per week for the rest of December, and sixty per week thereafter, till the entire number required was delivered. To do this the capacity of the shop was to be increased, and work was to continue day and night. The Steel Company undertook to earn this bonus.Under this new arrangement the casting of more sleeve-couplings began December 19, the furnaces having in the meantime been overhauled and new flasks for ingots furnished. One point had in the meantime been gained, or was supposed to be gained, — to cast the ingots in dry sand. This suggestion came from Mr. Durfee. Their chief trouble had been the "pulling" of the ingots cast in iron moulds. To avoid this evil, he had "swept up" a mould in dry sand for an ingot about four inches thick. The ingot, which was entirely free from cracks when removed from the mould two days afterwards, was then drawn down about seven-eighths of an inch under a hammer, still showing no signs of flaws or cracks. Mr. Cooper thus reported the success with which it was rolled:
"It looks exceedingly well. Appears perfectly sound and smooth."
Here, then, was the solution at last! "Without waiting till these new plates could be bent, patterns were made for casting in sand ingots that were of the full width of a coupling-plate and scarcely more than three inches thick; these were to be rolled, but not hammered. No more were cast in iron moulds.
On the 23d, rolling commenced with apparently good results, and was continued with little interruption through the month. By the 28th of December ninety pieces, including seventeen accepted by Mr. Eads December 10, were ready for shipment to Pittsburg. There was now a fair prospect of the delivery of sixty pairs of couplings per week, and with good reason the coupling problem was thought to be solved. Thirteen months had elapsed since the first coupling ingot was cast, and the first attempt at rolling had been made a year ago. Only one hundred and fifty pairs out of the ten hundred and twelve which were required had been delivered, and much of the work was necessarily waiting for them. I find it necessary to extend the history of the couplings into another chapter, but before closing this it will be well to speak of a change which had taken place in the management of the Bridge Company, and give a brief glance at the progress thus far made in construction.
Mr. Wm. M. McPherson had for several months been unable, from loss of health, to attend to the duties of president of the Bridge Company. On the 18th of March, 1872, he sought relief in the milder climate of the Gulf States; but the change availed him little, and he never regained his health. He lingered through the summer, and died November 2, 1872. The next day the Board of Directors met and bore testimony to the character and ability of the friend and officer they had lost, in such fitting language that I can not do better than quote it here: —
"In addition to the masterly qualities which were innate in the man, — the clear perception, accurate judgment, firm purpose, high courage, tempered but not impaired by thoughtful prudence, patience under sore trials and disappointments, and entire devotion to duty, — he brought to the service of this
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Company rare wisdom, acquired by wide experience of many kinds of business, which had brought him in contact with nearly all classes of men, insomuch that often his anticipations of results seemed like prevision. In the administration of the affairs of the Company, as its president, he was as efficient as in counsel he was wise, and the Company could sustain no more serious loss."
Mr. Gerard B. Allen, who from the first had been chairman of the Construction Committee, and who during Mr. McPherson's sickness had been acting for him, was unanimously chosen president. Of Mr. Allen's fitness for the position there had been already abundant proof. Himself the builder and owner of large iron-works, foundries, and machine-shops, he was familiar with all kinds of machine work, and a shrewd business manager. As one of the referees to decide in regard to compensation not otherwise provided for by the contracts with the Keystone Company, Mr. Allen had repeatedly visited Pittsburg, and was fully informed of the capacity of the shops and the progress of the work. On his return from his visit in December, 1872, just after the contract last named, he wrote the folio whig letter, which sufficiently explains itself: —
"J. H. Linville, President Keystone Bridge Company.
DEAR SIR: You are aware that our Company has arranged terms with the Midvale Steel Company by which the latter have agreed to furnish sixty pairs of rolled-steel couplings per week, beginning January 2, 1873.
This agreement is a perfectly safe one as to quantity, as the capacity of the Steel Company at the above date will be equal to at least sixteen couplings per day; and as late experience has shown that less than thirty per cent have been rejected, the probabilities are that they will furnish twelve pairs per day. In addition to this they design casting the ingots long enough to get one more niece from each, and if they succeed in this the product will be increased one-fourth.
You are also doubtless aware that by a previous agreement made between Col. Piper and myself, acting as referee, it was determined that all the tools in the shop at Pittsburg should be worked day and night, when required, so as to facilitate the work.
There are twenty-one lathes in the Pittsburg shop, each capable of working on tubes and couplings (this is exclusive of the small lathes that will work on pins, etc.). There are three hundred and sixty tubes to finish. Each lathe is capable of finishing a tube every twenty-four hours. Hence, if we take six lathes working day and night, all the tubes can be finished in seventy-five days [adding twenty-five per cent].
There are say one thousand couplings to finish. Each lathe can finish a coupling in twenty-four hours. If we take the remaining fifteen lathes on couplings, working day and night, all can be finished in eighty working days [with a fair margin].
There are seven planers, each of which will plane two pairs of couplings per day, so that seventy-two days would finish the entire lot.
There are four drill-presses that can drill the first pin-hole in twelve tubes per day, making say eighty-three days for the whole. [Pin-holes were drilled simultaneously through tubes and couplings; hence very few had been made.]
There are four horizontal boring-machines. This number must be increased to six. These six machines would finish and taper the pin-holes of twelve per day, or say eighty-three days for the entire lot.
All these calculations are based on night and day work, and are based on Col. Piper's estimates of time, which in many cases exceed mine. From this you will perceive that if the Midvale Steel
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Company perform their contract as to time (for which they have very strong inducements), all the couplings will be delivered by the 1st of April, as a considerable number are already done; and all your shop-work can be done about the same time. Col. Piper intends beginning on erection in January, and calculates that each span (or, rather, span-and-a-half) can easily be set up in twenty-two days; on this basis, if commencement be made January 15, one and a half spans would be up about February 10, and the remaining one and a half spans about the 10th of March. But realizing as I do that many unforeseen things may occur to prevent and interfere with so prompt an execution of the work, I will say that if your company will erect one and one-half spans by the 15th of March and the remaining one and one-half spans by the 1st of May, the Illinois and St. Louis Bridge Company will pay you a bonus of $20,000, and furnish the additional horizontal boring-machines required for finishing the drilling. (These machines are to be the property of the Bridge Company.)
Please inform me if you accede to this proposition, and if you do, have a contract to that effect prepared; of course you will understand that in this contract there will be no penalty for failure, but there will be the bonus in case of success.
Very truly yours,
GERARD B. ALLEN,
President Illinois and St. Louis Bridge Company."
In default of any explicit record of Mr. Linville's reply, we will contemplate for a moment the agreeable prospect presented by Mr. Allen's letter, and then return to the rolling-mill of the Midvale Steel Company. We shall find that the coupling question is not yet devoid of interest.
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Chapter XII. The Manufacture of the Couplings Concluded.
The Steel Works, under the stimulus of the inducements contained in the last arrangement, continued to turn out couplings with great rapidity. The form of ingot now used was the "corrugated," and was cast in common molding-sand. A cross-section of the ingot was about as shown in Fig. 21.: —
The ingot was brought to the roughing-rolls as hot as the integrity of the steel would allow, and passed through as rapidly as possible. If this figure is compared with Fig. 19, on page 123, it will be seen that very little work was required of the rolls; the length of the ingot was to be about doubled.
As has been said of the ingots which had been hammered and then rolled, they came from the rolls looking exceedingly well; but they all cracked badly when reheated and bent into semi-cylindrical form under the hammer. Even the pieces from the hammered ingot were condemned by the inspector. The cracks were generally along the convex portions, near the edges of the plane face, marked a a, in Fig. 19. In some, the plane face was seamed with cracks from a quarter to an eighth of an inch in depth. Nevertheless, out of about eight hundred pieces, six hundred were accepted and sent to Pittsburg to be finished and tested. Many of them had, besides cracks, flaws and blow-holes which the rolling could not obliterate. Though faulty in appearance, they might still be strong. Such as they were, the Steel Company were turning them out rapidly.
The first twenty-eight couplings tested had been subjected to a tensile strain of 40,000 pounds per square inch of finished cross-section, and while under that strain the couplings had been struck several blows with a heavy sledge. Three had broken, — one at a strain of 39,000 pounds, one at 33,000 pounds, and a third at 27,000 pounds per square inch. As has been shown, a tension of 40,000 pounds per square inch of section of a large coupling involved a total tension of about 1,400 tons, a strain many times as great as could by any possibility ever be brought on the couplings, either during erection or in the finished arch.
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It is obvious that under this excessive test, pieces might fail which would still have been abundantly strong for the work required of them in the Bridge. With the exception of a few couplings near the skewbacks and the crown, cast iron would have sufficed. The strength of a chain is the strength of its weakest link; and, as Mr. Eads afterwards said, it would not add to the safety of the arch to make the couplings stronger than the braces.The test was therefore reduced, as has been said, on the 6th of November, and the hammering was omitted. The specific tests to be applied were as follows: 20-inch couplings, total strain 800 tons; 19-inch couplings, total strain 600 tons; 18-inch couplings, total strain 500 tons; 17-inch couplings, total strain 450 tons; 16-inch couplings, total strain 400 tons; 15-inch couplings, total strain 400 tons.
The thirty-eighth coupling split under the hammer, while being fitted to the testing-plugs; no other of the first seventy-six rolled-steel couplings broke. It is probable that all were from ingots cast in iron moulds. Specimen bolts from the coupling-plates had shown a strength of about 90,000 pounds.
The sand-moulded rolled couplings now began to come in, and speedily the record changed. Of the first forty, six broke under test at strains of about 20,000 pounds per square inch, and three others split under the hammer, after test, while being fitted to tubes. These results showed unusual weakness and brittleness for wrought steel, and Mr. Eads ordered small specimens from the broken couplings to be tested for ultimate strength. As the composition of the steel was precisely the same as that in the staves and the iron-moulded couplings, there was no suspicion of its quality, and the tests for ultimate strength had been omitted. The average of ten specimens was less than 60,000 pounds: the highest was 87,000; the lowest, 45,000. This result was sent at once to the steel works. On the 27th of January, Mr. Eads reports again to Mr. Huston: "Six samples taken from a broken coupling showed but 67,000 pounds tensile strength, — the highest being 92,000, the lowest 51,000 pounds."
It will be remembered that the Keystone Company had the right to demand an ultimate strength in specimen bars of 90,000 pounds, and that each finished coupling, large or small, should be tested to 800 tons total tension. In view of these facts, Mr. Eads declined to receive any more couplings till tests should establish the required strength of the material. The Steel Company could of course continue to make them, running their own risk as to strength. Those already referred to as broken had been accepted by Mr. Cooper, and the loss of both material and workmanship fell upon the Bridge Company. Before getting Mr. Eads's letter, Mr. Huston had decided that it was "unsafe" to proceed, and had telegraphed Mr. Allen and Mr. Eads to come to Philadelphia. Accordingly, the work stopped January 28.
Meanwhile, the alarm was sounded in another quarter. On January 24, Mr. J. L. Piper, general manager of the Keystone Company, wrote to Mr. Linville as follows: —
"PITTSBURG, January 24, 1873.
J. H. Linville, Esq.
DEAR SIR: Allow me to call your attention again to the steel couplings for the St. Louis Bridge. Are you aware that they are only testing these couplings to 23,000 pounds per square inch, and that a large portion of them break under this strain, and that others, after being tested, fall to pieces in our
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putting them on the tubes to finish the pin-hole? Now this is not as good material as the cast iron we put in the Steubenville bridge, and does not require one-half the pounding to break it that good cast iron would. It does not possess the tensile strength required by the government for cast iron to be used in machinery that is to be operated by men hired to be killed, and I am as certain that if this thing is not stopped that the Bridge is a-going to go to the bottom of the Mississippi River as I am that you will attempt to put it up in the way you propose to raise it; and just so sure as this Bridge falls, just so sure the Keystone Bridge Company is a thing of the past."
Mr. Piper's absence from the works for two or three weeks, on account of sickness in his family, must explain his wrong impression in regard to the proportion which broke under test, and the number which fell to pieces after test. Out of one hundred and seven couplings tested when he wrote, nine had broken under tension, and two under the hammer. This letter from Mr. Piper called out emphatic letters from Mr. Linville. January 28, 1873, he wrote Mr. Allen: —
"We do not propose to undertake the erection at our risk and responsibility if it is true as stated that the material is more brittle and less reliable than cast iron, or not of a quality contemplated in our contract by the term ‘wrought steel.’ * * * Unless satisfied that the couplings have the tensile strength and toughness requisite, we must decline to undertake such risks."
Mr. Linville also demanded all the tests required by the specifications and contracts. He reported the test by Mr. Cooper of three specimen bars cut from one of the couplings last made. They gave results, 54,900, 49,030, and 47,500 pounds per square inch. The metal was described by Mr. Cooper as "very coarse, soft fracture." A piece was then cut from the same coupling and forged down under the hammer. Two specimens turned from this steel showed strength of 80,000 and 78,600 pounds per square inch. "Fracture fine-grained," All the tests on specimens allowed by the contract of December, 1872, were then applied, both at the steel works and at Pittsburg. Mr. Cooper tested six specimens cut from sleeve-couplings, and reported the results to Mr. Linville. The average breaking strain was 71,150 pounds, the extremes being 90,700 and 44,000 pounds per square inch. On January 29, Mr. Linville wrote to Mr. Eads that it was his firm conviction that the material was "not suitable for use in the erection of the Bridge," and he consequently gave formal notice of his refusal to assume the risk of erection. He believed that no test whatever to which such couplings could be subjected would establish to a reasonable certainty their safety and reliability. His company, therefore, felt compelled positively to decline to use, under any existing arrangement, the wrought-steel couplings that had been furnished, whether originally cast in iron or sand moulds. He believed that wrought iron of suitable quality and well worked, and subjected to the requisite tests, would furnish the only secure coupling to be employed in erecting the Bridge, and he earnestly hoped that any intention of employing steel, either cast or wrought, would be abandoned.
The next chapter in this interesting history is best given in the words of Mr. Eads: —
REPORT ON THE STRENGTH OF STEEL COUPLINGS.
"FEBRUARY 19, 1873.
GENTLEMEN OF THE BOARD OF DIRECTORS: On receipt of the letter of the president of the Keystone Bridge Company dated January 24, inclosing a copy of a letter from the manager of that company,
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Mr. Piper, respecting the quality of the steel couplings now being worked, I proceeded without delay to Pittsburg and carefully examined the couplings. I found that the average tensile strength of those delivered since the last arrangement with the Wm. Butcher Steel Works is about 60,000 pounds per square inch, as shown by testing a great number of specimens cut from rejected couplings, and selected from various parts of these couplings with a view to obtain a correct idea of their actual average strength. The strength guaranteed by the Steel Works is 90,000 pounds per square inch tested by specimens, and this strength the Keystone Bridge Company claim they are entitled to have, as it is stated in the specifications of their contract with this Company.
This unusual degree of strength is not needed in these members after the Bridge is erected. They were originally designed to be of cast iron. An objection made by Mr. Piper against using cast-iron couplings in erecting the Bridge, before the contract with the Keystone Bridge Company was made, led to the adoption of cast-steel couplings.
The assurance on the part of the Butcher Company that these members could be produced without any difficulty, and no extra price over 10ž cents being demanded, made them cheaper than wrought iron. The assurance also by the Butcher Company that there would be no trouble in producing steel that would stand 100,000 pounds led to the fixing of the standard for all tensile strength of the steel to be delivered at 90,000 pounds, and no exception was made in the case of the couplings. It was well known by me that this degree of strength would not be needed in them, but an excess of strength could not be objectionable, and the Steel Works were perfectly willing to guarantee it.
The claim of the Keystone Bridge Company to have this material stand 90,000 pounds seems to be sustained by the letter of the contract; but it is an unreasonable one, inasmuch as it would be impossible in the erection of the Bridge to get anything like the strain on them which they are tested to, for the simple reason that other members (the brace-links) would cripple up before such strain could come upon the couplings. Very few of them will ever have any strain on them compared with what they are tested to. The highest strain that can be brought on any coupling in erection is 200 tons; such couplings are tested by actual strain to 800 tons, and no one of them to less than 400.
Much stress is laid upon the fact that some of the couplings break under test with a strain of 16,000 to 18,000 pounds per square inch of the section of the couplings. The manner in which the strain is thrown on the coupling is such that it is simply impossible for them to show as high a strength according to the section of the coupling as in the specimen.
The strain in the coupling is wholly on the inside of it, and has a tendency to tear the inner surface out. In the specimen it comes fairly on the piece, and all the fibres are strained alike. In the coupling the whole strain is thrown on the fibres of the interior, or on one side only of the metal.
A coupling has a section of about sixty-eight square inches; and a strain of 6,000 pounds per square inch on this section is the greatest strain that can come on any one of them in erection. About five hundred pairs, or one-half of all needed, are now made. [The total number of couplings is ten hundred and twelve.] Ninety-nine of these were made of steel of the requisite standard. About three hundred more have been received at Pittsburg of the inferior strength, and the remaining one hundred are at the steel works awaiting your action in the premises.
About one hundred and twenty-five couplings have been fully finished, and perhaps one hundred more are in various stages of finishing. About five per day are being fully finished, and during this week this number per day will probably be increased to seven.
Being satisfied by the various tests made that the strength of the couplings was very much underestimated by Mr. Piper, and that they were abundantly strong for all strains which can possibly come upon them, and believing that it would involve not only serious loss, but great delay, to cast aside these couplings, I endeavored to effect some understanding by which they should be used without invalidating
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the Keystone Bridge Company's obligation of responsibility in erection. I am sure no engineer will deny that it is quite practicable to erect the arches, even on the plan adopted, without putting tensile strain on any coupling in it, simply by using additional guys and other simple devices to sustain the arches at intermediate points not before contemplated. I strove to obtain some assurance from Mr. Linville and Mr. Piper that their Company would do this, on condition that we would pay for such extra appliances as they might deem needful to insure safety, but was unable to obtain such promise. I was likewise unable to get an assurance from them that they would erect the Bridge, even if wrought-iron couplings were furnished, unless the question was first settled as to the disposition of the present steel couplings, and also all questions of liability between them and the Steel Works.
The Steel Works assure me that there has been no change whatever made in their mixtures for the couplings, nor in the quality of the iron used, and that the difference in strength is simply the result of casting in the one case in iron moulds and in the other in dry sand. The iron-mould ingots, however, crack so badly that but one-half or less of it is good when rolled, whilst the whole of the dry-sand ingot is available; and that they can not undertake to do any better than the last deliveries.
I instructed Mr. Piper to finish the steel couplings for the present, all for the lower tubes, where they will have but little tensile strain on them in erection.
Under the circumstances, I deemed it advisable to accept a proposal made by Carnegie, Kloman & Co. for the delivery of five hundred, or any additional number, of iron couplings, at 15 cents per pound, or 14 cents if nine hundred be used. This contract is herewith submitted, and is made subject to your approval before the 26th inst.
A solution of this controversy cannot be reached, I think, without getting Mr. Linville and Mr. Piper together; this I was not able to do. Mr. Linville's knowledge of the couplings comes almost wholly from Mr. Piper's representations, and these have been very highly colored, to say the least of it. To show that I am not unjust in saying so, I will state that the couplings, when under the highest strain imposed on them in the testing-machine (which is 800 tons for the largest, 600 for the next size, 500 for the next, and 400 for the smallest), have been subjected to vigorous blows from a twenty-three-pound sledge-hammer, and that under this severe ordeal only one in twenty-three failed. To pretend that such material, which is only about 11/4 inches in thickness, is no stronger than cast iron, is absurd. Another proof of the unfair statements respecting these members is as follows: In Mr. Linville's office I was shown a letter from Mr. Piper, stating that in lifting off two of the tubes from the boring-mill the coupling broke by which they were joined together. This coupling I had seen. It was made of two pieces, and one-half of it had doubtless been cracked in testing. The extent of this crack (which was not discovered until the piece was fitted to the tubes) is shown at C in the accompanying sketch. [See Fig. 22, next page.] I immediately wrote to Mr. Dwelle, after seeing this statement, to support these tubes on the middle coupling and load the tubes at their outer ends, and report how much was required to break the coupling asunder.
This was done, and not until nearly ten tons was borne on each end did the cracked half give way, and even then only down to the pin-hole; the under part of the cracked one still remaining sound. Seventeen tons was finally placed on each end, and the effort to break it was then abandoned through fear of breaking off one of the tube-staves."
The manner of making these tests is shown in Fig. 22, which is taken from Mr. Dwelle's report. The coupling C is the one to be tested. The couplings D and E were securely bolted to the outer ends of the tubes A and B, so as to prevent any slipping of the staves under the envelope". These couplings were turned 90° for the purpose of offering planed surfaces for the loads. The length of the tube B (i. e., the distance from the fulcrum to
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the center of gravity of the weight at E) was 146 inches. The exact central area of the tested coupling was 69.25 square inches. The load, including one-half the weight of the tube, required to break the injured half down to the pin-hole was 21,311 pounds. The increased load, by which Mr. Dwelle then tried in vain to pull in two the still uninjured half-coupling, was 36,391 pounds.Mr. Eads's report continues as follows: —
"On my return to Pittsburg I had this coupling turned upside-down, and 10 tons placed on the outer end of one tube while the other end was heavily weighted down. Then a piece of iron weighing 700 pounds was let fall 2 feet upon the end carrying the 10 tons, and again let fall 4 feet, and again raised as high as the crane would raise it, 4 feet 8 inches, and again let fall, without any injury whatever. The deflection of the tubes was found to be, with 10 tons, over five-eighths of an inch at the outer ends. When the weight fell from the greatest height, the end struck sprung down under the blow one inch farther, and vibrated until it came to rest at its original position, thus showing a great degree of elasticity as well as strength."
Mr. Dwelle's report gives still further tests on this same coupling. After the trial of the falling weight, a load of 22,991 pounds was allowed to remain on the end of the tube for thirty-six hours. An addition to the load was then made, making the total 36,207 pounds. The total deflection caused by this load was fifteen-sixteenths of an inch. It was now noticed that openings of about one-sixteenth of an inch had been formed on each side of the iron ring near the top of the coupling under test. An additional load of 6,608 pounds caused an additional deflection of about one-fourth of an inch. The tube then remained loaded with about 21 tons for twenty-seven hours without sensible change. Sixty-six hundred pounds more were then gently placed on the load, making the total 49,173 pounds. Under this great strain the injured half-coupling gave way in the line of the former break. The whole load then came upon the half-coupling still sound; it withstood the strain, but the middle and upper staves on that side of the tube broke and ended the test.
Mr. Eads's report concludes as follows: —
"To reject these couplings would, in my judgment, be very unwise, as it would certainly delay the completion of the arches about two months, if all goes right in rolling iron ones; and it would
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involve a loss certainly four or five times as great as the cost of any appliances needed to remove all tensile strain absolutely from them during erection. The strength shown in the above experiment on a defective coupling is much greater than any strain it will have to bear in erection by the method already adopted.
Respectfully submitted,
JAS. B. EADS, Chief Engineer."
The manufacture of steel couplings, which had been stopped by telegraph January 28, was never resumed. Mr. Bremermann continued to test the couplings as they were finished. Out of one hundred and twelve rolled Philadelphia couplings, sixteen broke under test. As was said in Mr. Eads's report, this strain was not applied favorably, and should not be taken as a fair test of the strength of the material. The tension being on the interior rings, the tendency was to tear the steel on the inside before much strain was brought on the exterior layers. However, the couplings were tested just as they should be, viz.: as they were to be strained when in the Bridge.
A cast-iron coupling had been made and finished as a model in working the steel, and when it had served its purpose as a model, it was tested as the steel ones had been. It broke at 11,500 pounds per square inch.
The conclusion of Mr. Huston was that "it is simply impossible as a practical question to make these wrought-steel couplings and have them stand the test, because we cannot get enough work on the steel after it is cast. The quality of the material can be demonstrated at any time by samples which prove that when worked they stand 96,000 pounds; but pieces taken out of the same coupling, without additional working, break at from 50,000 to 60,000 pounds." Later experiments by Mr. Cooper on specimens from bent and unbent couplings showed that the steel wraps much injured by bending. Nine specimens from bent couplings gave an average of 64,900 pounds per square inch; while nine specimens from the plates before bending, the metal being the same, gave an average of 82,500 pounds per square inch. Some parts of the plates were more strained than others during the bending, thus causing a great range in the strength shown.
Mr. Cooper makes the following interesting statement in regard to the strength of the sand-moulded couplings: "On testing the metal it was found to be much weaker than those cast in iron moulds, though Mr. Durfee insists, and I believe him, that the metal is precisely of the same composition. This would go to show that casting in iron moulds was equivalent to additional work on the metal." This fact appeared to be a new one to Messrs. Huston and Durfee.
It was clearly out of the question for the Bridge Company to spend more time over the problem of steel couplings. The Butcher Company took the contract to roll the couplings October 24, 1870. The first coupling ingot was cast November 25, 1871, and the first attempt to roll couplings was made January 2, 1872. Now, after experimenting thirteen months, the attempt to roll the couplings specified was abandoned. Thus the coupling question had consumed two years and four months, and it was still to be seen whether any out of the five hundred couplings made were to be used.
Under the contract with the Union Iron Mills, made by Mr. Eads, work was pushed with great energy. Everything was waiting for the couplings, and Carnegie, Kloman &
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Co. bent all their resources to the task. Nearly all the iron specified in their previous contracts for the Bridge work had been furnished."While preparations were making for the rolling of iron couplings, a very interesting test was made, the object of which was to determine the strength of iron as compared with that of cast steel when subjected to a shearing and tearing stress. Figure. 23 shows the size and shape of the test pieces. A was a piece of cast steel; B a piece of wrought iron. The method of clamping them together is omitted in the plan. The ultimate tensile strength of both steel and iron had been previously determined by breaking a specimen cylinder of each in the testing-machine. The steel broke at a steady uniform tension of 89,507 pounds per square inch, the iron at 48,989 pounds per square inch; yet in this tearing test the steel gave way as is shown in the figure, at an average strain of 23,111 pounds per square inch. In the cylindrical test the iron stretched 1.7 inches in ten inches before breaking, while the steel stretched only 0.05 of an inch. In this last test, the iron yielded until the main tension was brought upon the extreme point of the steel shoulder; this placed the steel at a great disadvantage.
Meanwhile, the plans for the erection were carefully revised and modified so as to relieve the couplings of strain, and arrangements were made for a meeting of the officers of the Keystone Company, the Midvale Steel Company, and the Bridge Company at Philadelphia, to come to final understanding in the matter. Mr. Linville's health, which was always precarious, would not allow a trip to Pittsburg. On March 5, 1873, an elaborate contract was concluded which effectually disposed of the matter of couplings.
This contract recognized the failure of the Steel Works to furnish the steel under all previous contracts — of October, 1870, December, 1871, and December, 1872; it cancelled all these contracts, and released the Keystone Company from their obligations under the same; it assumed the insufficiency of the "cables, guys, anchorages, and apparatus deemed necessary and provided" by the Keystone Company for the erection, provided the steel
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couplings already made were used; and it permitted the Bridge Company to use wrought-iron couplings.The contract also agreed: that the Keystone Company should be relieved of all obligation to furnish steel couplings, and all damages on account of delay in completing the Bridge arising from the failure to deliver steel; that the Bridge Company should pay for all the steel furnished by the Steel Works, and turn over to the Keystone Company such steel as should stand the required tests at the rate of 10ž cents per pound; that the Bridge Company should furnish working drawings for the additional apparatus for erection, and pay the cost of all such extra apparatus at shop rates, with fifteen per cent added; that the Bridge Company should pay for "all labor at the Bridge, and work done in any manner in erecting and removing the extra guys, cables,
The Steel Company had of course failed to win the heavy bonus offered for completing their contract at a certain time, and were liable to heavy damages for non-fulfilment of their contract. Their contract was cancelled on condition that $35,000 should be allowed the Bridge Company out of the reserved payments, to help pay the extra cost of the iron couplings and the additional erecting apparatus. It will be remembered that 15 cents per pound were to be paid for the wrought-iron couplings. The original contract for steel was 10ž cents.
In February, Mr. Cooper left Philadelphia and took charge of the testing and inspection of steel in Pittsburg.
On visiting Philadelphia, in March, he accepted one hundred and twenty-seven pairs of couplings on the conditions named in the last contract. It appears that there were on hand, March 19, five hundred and twenty-four steel couplings, of which ninety-nine were from ingots cast in iron moulds, and four hundred and twenty-five were "sand-moulded."
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About one hundred and seventy-five coupling's were finished. The number of iron coupling's needed would then be four hundred and eighty-eight, and as many more as might be required on account of failure under tests.
As has been said, Mr. Eads contracted with the Union Iron Mills for five hundred iron couplings in February. In spite of active preparations, no attempt to roll couplings was made till April, and then considerable difficulty was experienced in discovering the correct form for the "pile." Five different forms of pile were rejected, the rolled plates being either torn or not properly welded.
Messrs. Carnegie, Kloman & Co. were much disappointed at their lack of success in rolling couplings, and at first submitted to Mr. Dwelle certain defective pieces, affirming that their contract with Mr. Eads only required that the couplings should be acceptable to the Keystone Company, and that they were satisfied. The inspector took the ground that first of all the couplings must be satisfactory to the Illinois and St. Louis Bridge Company.
On April 18, Mr. Dwelle gave the following hopeful account: "Work on wrought-iron couplings at last under full headway."
On the 23d he wrote: "Couplings are coming along at the rate of forty or fifty a day. They look well, and are being finished as fast as possible."
The material of which the couplings were made proved to be of excellent quality. One only was destroyed by test, and this had been condemned on account of imperfect weld, — a hole about one-half of an inch square ran entirely through one of the pieces from end to end. By direction of Mr. Piper it was finished up, so that it might be tested to destruction. Under a tension of 38,000 pounds per square inch the packing gave way. The coupling took a permanent set, but did not give way. Specimens of coupling-iron gave an average strength of 50,000 pounds.
By the terms of the last contract none of the couplings made from sand-moulded ingots were to be used unless re-tested, and even then only in the lower tubes of the ribs. At the date of the contract, however, many of them had been finished for the upper members, and some had even been shipped to St. Louis.
On the 3d of April, Mr. Eads telegraphed Mr. Linville, asking that certain couplings finished for upper members should be re-tested and sent forward, as they were wanted for immediate erection. Mr. Eads suggested that if any doubt existed after the tests as to the strength of the couplings, he would supply clamps which would relieve the couplings of all tension during erection. Great delay would otherwise ensue, as the iron couplings were not yet ready.
Mr. Linville replied: "I have ordered all couplings at works fitted for upper members to be re-tested. When I get report of tests, length and position of couplings, I will decide whether they can be used as you suggest. Please send copy of revised calculations for strains on couplings. Tension clamps and bolts, if used by us, must be proportioned to bear the greatest calculated strain from weight of Bridge together with effects of gales of wind, with factor twelve at least in order to provide for jars and incidental strains caused when guys at abutments are removed."
Under the modified plan of erection the maximum tension in the couplings would be
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38.7 tons. The couplings in question had already been tested to twelve or fifteen times that amount, and it seemed but reasonable to consider them safe even without clamps, when again tested, including the six hammer-blows. If clamps capable of resisting twelve times the entire tension that could possibly come on the couplings were added (according to the demand of Mr. Linville, which completely ignored the strength of the coupling itself), one would have supposed them safe yet the Keystone Company declined to use the couplings as proposed. Mr. Linville afterwards justified his use of the factor twelve in the clamps on the ground that the elongation of the clamp under even a small strain would bring the steel coupling into full bearing, owing to the length of the clamp as compared with the distance between grooves on the abutting tubes, and probably a lower modulus in the iron than in the steel; and that having calculated the maximum possible strain and used a factor of safety of six, it should then be "doubled for contingencies."The delay in the erection of the Bridge in consequence of the rejection of the steel and the non-appearance of the iron couplings was about a month.
The story of the couplings has now been told in its main features. As Mr. Piper sagely remarked: "Back-sights are better than fore-sights." At the end of two and a half years it was easy enough to say what "should have been done," yet Mr. Kloman was not more confident of his ability to roll couplings of iron than was Mr. Butcher to roll them of steel. Had the attempt been made in the days of the elder Butcher, the result might have been the other way. In every exigency Mr. Eads strove to adopt the most expeditious course, and he naturally followed the advice of those who ought, at least, to have been the best judges, — namely, the steel-makers themselves.
The delay and partial failure of the Steel Works to supply the couplings cost the St. Louis Company heavily. The cost of certain apparatus and fixtures at the Steel Works; the value of material and workmanship on couplings rejected at Pittsburg; the increased cost of all above 10ž cents per pound; the, salaries of engineers and inspectors the cost of frequent experimental tests and, above all, the loss of revenue while interest was aggregating, — all these fell with fatal effect upon the Company.
As has been already intimated, the erection of the Bridge had been begun, but so little had been done that I have postponed the subject till another chapter. I shall close this with President Allen's Report to the stockholders of the Bridge, made May 7, 1873. It was thought that a report by the chief engineer would of necessity discuss quite fully the circumstances which had led to the appointment of Mr. Laurie, as well as to the more recent points in controversy with the Keystone Company, and as such a discussion was not likely to hasten the completion of the Bridge, which was of course the most important end to be gained, the Directors excused Mr. Eads from the duty of making an annual Report, and called for a brief one from the president in its stead.
Mr. Allen's report was as follows: —
"ST. LOUIS, May 7, 1873.
GENTLEMEN: It affords me great pleasure to announce to you that all the difficulties attendant on procuring material of a fitting character for the superstructure of our Bridge have been removed, and I think I may with safety promise completion of the entire work ready for traffic before the close of the present year.
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You are doubtless aware that great delay in prosecution of the work has been caused by inability of the steel-contractors to furnish couplings of required strength and in quantity to insure a speedy erection; this inability became so manifest, notwithstanding the earnest efforts of these gentlemen to fulfil their contract, that when the steel couplings for the lower members of the arches were all made, the chief engineer, with consent of the Board of Directors, abandoned the use of steel for couplings required for the upper members, and in its place substituted wrought iron from the works of Carnegie, Kloman & Co., of Pittsburg, who are now making them successfully at a rate that will insure delivery of all required within two weeks. The solution of this coupling problem removes the last of the many very serious troubles the chief engineer has had to contend with in getting the work executed, and little now remains in the direction of the superstructure but an energetic action on the part of the Keystone Bridge Company in the erection to bring our labors to a speedy and successful termination.
The construction of the East Approach, excepting the wooden trestle, has been let to the Baltimore Bridge Company at the following cost: —
Cost of Approach with iron trestle $377,900.00 Land for East Approach (estimated) 75,000.00 Cost of wooden trestle-work 40,000.00 $492,900.00
President Allen gave a brief summary of the financial condition and prospects of the Bridge Company, as follows: —
RECEIPTS. Payments on stock $3,205,220.00 Sale first-mortgage bonds 3,671,134.39 $6,876,354.39 Due by the Company for percentage retained from contractors, deferred payments on real estate, land damages, less sundry assets $167,249 20 And there has been expended as follows: — For masonry, superstructure, engineering, salaries, machinery, boats, and general expenses $5,170,982 83 For Approaches in this city and East St. Louis, and other real estate connected therewith 695,204 34 And for interest 986,831.37 Charter account 190,585.05 $7,043,603.59
These figures are taken from the footings of the ledger items on our books, and embrace, among the apparent expenditures, the percentage retained from contractors, which is charged up, and most of which will not become due until after the completion of the structure; as well as deferred payments on real estate and land damages, etc., most of which do not mature for several years.
From the estimates of funds necessary for completion, you will perceive that after estimating for interest on first and second mortgage bonds falling due respectively in July and October of this year, and for payment of the total cost of the East Approach, there will be a deficiency of $856,468.34. To meet this deficiency we have $1,050,000 of second-mortgage bonds, which, if sold at even as low a rate as eighty-five per cent of par value, will realize more than sufficient for all requirements. In addition
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to which we have two thousand shares of unsold stock. With the exception of retained percentage, which is not due until the work is completed, this Company may be said to owe nothing except the unmatured notes for real estate, land damages, and sundries; and if, on completion, there should be any indebtedness, there can be but little difficulty in liquidating it, as the revenue will rapidly provide for such obligations as they mature, besides yielding a profitable return to the stockholders for the capital invested.
That our anticipations of revenue are not over-sanguine requires, in my opinion, no better proof than a glance at the statistics of the railroad traffic of this city for the past three years, which we have obtained chiefly from the Union Merchants' Exchange, as follows: —
Tons. Railroad tonnage for 1870 2,379,206 " " " 1871 3,258,208 " " " 1872 4,043,028
Thus you will perceive that the railroad tonnage of St. Louis has nearly doubled in two years, with every probability that a like increase will continue for many years to come.
Basing our estimate, however, on the traffic of last year, and adding the coal tonnage for the same period, which amounted to 781,627 tons, we have a total of 4,824,655 tons received and shipped in this city during the year 1872.
If one-third of this traffic crosses our Bridge, it will, at the average charge of 50 cents per ton, pay the interest on the first and second mortgage bonds, and yield an annual dividend of over seven per cent to the stockholders. If we add to this revenue the income to be derived from the forty-eight passenger-trains which now arrive, and from as many which depart daily, together with the charge for mail and express cars ($10 for each), one of each of which is attached to nearly every passenger-train; and if, finally, we consider the immense traffic that will cross the upper carriage-roadway, the number of foot-passengers, transfer and other teams, which now keep eight large transfer steamers occupied busily, it will not be difficult to arrive at the financial results of this enterprise.
When another year shall have rolled around, we trust that the above figures will be substantially demonstrated to the satisfaction of the stockholders, in the shape of a dividend large enough to give promise of a future that will amply compensate for the unavoidable delay in the construction of this great work.
Very respectfully,
GERALD B. ALLEN, President."
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Chapter XIII. The Work at the Keystone Shops, Pittsburg.
Before proceeding to give an account of the erection of the Bridge, it seems to be necessary to devote a few pages to the important work doing and done at the shops of the contractors in Pittsburg. There all the rollings, forgings, and castings were properly fitted and finished. It is my privilege and pleasure to pay high tribute to the zeal and ability of Mr. Shiner, the master-mechanic, and of Mr. Nichols, the foreman of the shops. The excellence of the workmanship is largely due to their skill and fidelity. And I ought not to fail to recognize the unquestioned mechanical skill of Mr. Piper, the general manager of the Company. His suggestions were often of great value, and Mr. Eads and his assistants always treated them with great respect. It will be best to describe the work in logical order.
These were forgings weighing nearly three and one-half tons each. They are correctly shown, as finished, in Plate XXIII. As they were forged solid, it is easily seen that the amount of boring was great. The central hole was cored out and finished with a screw-thread for the skew-back tubes.
Fifty-nine of these were of steel, and fifty-three of iron. The work done on them in Pittsburg consisted in turning off the enlarged ends by which they were clamped in the testing-machine, and in cutting the threads. The length and weight of these bolts required the construction of special lathes. The longest were 35 feet 11Ë inches when finished, and weighed 3,400 pounds each.
Fifty-six being octagonal and one hundred and sixty-eight hexagonal. Some of these were of wrought steel, and others of wrought iron. A special "tap" was made for cutting the thread. A tap is a steel bolt upon which a thread has been cut exactly similar to that on the bolts for which the nuts are to be made. This thread is then turned down at the entering end, leaving it with a taper from no thread to a full thread; and the thread is notched at points, and tempered. When its edges are properly sharpened, it is inserted into the smooth-bored hole of a nut, and, as it advances, it cuts the thread for itself to work in. This process was employed by Mr. Nichols without a suspicion of difficulty. The nuts were turned out in fine shape; but to the surprise of all, they would not work on the anchor-bolts. Several were tried, but with the same result. They worked without difficulty on the tap, which had been cut exactly like the bolts. The mystery was finally explained by Mr. Nichols, who discovered by careful measurements that the tap had contracted during the tempering about one-tenth of an inch in a foot, thus changing its pitch. A new tap
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was therefore made, sufficiently large to leave it of the exact size after tempering. No further difficulty was experienced.An envelope plate was cut to about the correct size, and its edges were planed till it was exactly 55.76 inches wide. Two rows of rivet-holes were next drilled along each of the long edges, and then the plate was bent into the form of a perfect cylinder 17Ë inches internal diameter. The bending was effected by repeatedly passing the plate, cold, under a roll which was brought down between two fixed smaller ones. The upper roll was lowered gradually till the plate assumed the proper shape. When it was properly bent, a steel butt-strap was riveted on, as is shown on all the tubes. The rivets were countersunk on the inside, and if, after riveting, any chipping was necessary on the inside, a small boy was sent in to do it. The ends of this envelope were then accurately faced off in a lathe. Five staves, having as nearly as possible the same modulus of elasticity, were then placed in position, within the envelope, all resting on a machine. A tapering piece of iron about ten inches long, called a "pilot," was next inserted into the vacant stave-space, with its edges and convex surface well greased. The sixth stave, also well greased, was then placed behind the pilot and forced into its place by the machine. Not more than one-third of the staves had ever been planed at all, and consequently they were not exactly of the same size, and the sixth was selected with careful reference to the space to be filled. It was desirable that the staves should fit tightly, but it was not necessary to create much initial tension in the envelope. The tube thus formed was of course perfectly straight. The staves varied in different tubes from 127 to 157 inches in length, the large majority being about 146 inches.
The next work to be done on the tube was to shrink a wrought-iron band on each end. Cross-sections of these bands are shown on Plate XXX
The next step was to face all the ends of the staves to the correct bevel. The drawings of a tube being made to scale, exhibit so slight a bevel that without explanation it would almost escape notice. To make my description of the subject clear, it will be better to use an exaggerated drawing of the ends of two tubes abutting, and without the coupling. The reader is warned against the dimensions of Fig. 24. It is intended to illustrate the fact that the coupling had but a single axis.
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and that it intersected the axes of the two tubes, not at a common point, but at separate points. It was specified (see p. 73) that "the center line of the shaft of the boring-tool must pass in all cases through the center of the tube, at a point half-way between the outside limits of the grooved portion of the tube."
The center line of the boring-tool (which is the same thing as the axis of the coupling) is represented by the line c c; it intersects the axes of the tubes at a and a. By this adjustment, the amount of steel to be turned from the exterior of the staves was reduced to a minimum.
The work of bevelling off and turning down the ends, as well as the cutting of the parallel grooves on the same, was at first done by a double-ended lathe, the main features of which had been suggested by Col. Flad. The design was fully worked out and the machine was built by Mr. Nichols. In this machine, the tube was held stationary while the ends were simultaneously operated on. The angle between the axis of the coupling and the axis of the tube was 179° 31' 45".27 for the tubes of the side spans, and 179° 32' 1".74 for those of the center span. These angles were laid off with a radius of 10 feet. Later, large ordinary lathes were adapted to the work of turning tubes.
The degree of accuracy of the bevels was ascertained by careful test. It was generally found sufficient, in case of inaccurate bevel, to put the tube in the lathe and adjust the machine just as it had been adjusted before; the tool passed a second time over the surface, making a very slight cutting where before it had sprung out of position. The adjustments of the lathe were made and tested upon two cast-iron tubes made for the purpose. The tests of the bevels were made with the greatest care, as it was necessary in erecting the arches to make it possible to put on the main braces without springing a tube, and without bringing an initial tension on one side of the coupling.
The process of testing the angles of the bevelled ends was substantially as follows:
The tube whose bevels were to be tested was placed on two stout trestles, its turned wrought-iron rings resting in turned bearings. While in the lathe, four points 90° apart were marked on each of these rings. If we suppose the tube to be resting on the trestle right side up, — that is, with the butt-strap uppermost, as it was intended to be placed in the arch, — one of the marks on each ring would be found exactly on top. By means of the marks and indices on the trestles the tube could with accuracy be placed upright, inverted, or resting on either side.
Suppose the tube right side up, with its main axis horizontal. A straight-edge, with telescope and spirit-level attached, was then placed against the end of the tube. It was adjusted till the contact edge intersected the axis of the tube and was horizontal. Parallel with the axis of the tube and in the same horizontal plane with it, seventy feet off, was a finely
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graduated scale. Let (Fig. 25) A B be the tube under test, x x a line of sight along the straight-edge, and C D the graduated scale; x x represents a second straight-edge and telescope on the other end of the tube. Before taking readings on the scale, it was so adjusted that an observer looking along x x should read zero on the scale at d. A second zero had been placed on the scale at a distance from d exactly equal to the required length of the tube, measured on its axis; if then the lines x x and x x were parallel, and the tube of correct length, a reading from the telescope at x x would give zero also. If the reading was to the left, it was recorded as f; if to the right, d. This observation tested only the parallelism of the lines x x and x x. Both should be perpendicular to A B; to test them in this respect the tube was rolled over 180°, and the straight-edges and telescopes were applied again. Great care was taken that the tube suffered no motion except rotation. If the telescope x x still gave d, the diameter x x was perpendicular to A B. If the reading was to the left or right it was recorded under c or e respectively, and the same for the other end. The angles made by x x and x' x' are now fully determined. It is obvious that these observations, taken with the direct measurement of the length of the tube, have several checks. A careful study of the records shows, as would be expected, inevitable instrumental errors; but the "probable errors" are readily deduced. To illustrate fully this important point, I take at random the record of eight consecutive tests made by Mr. E. L. Bremermann, inspector at Pittsburg: —| Test No. | a | b | c | d | e | f | g | h | a' | b' | c' | d' | e' | f | g' | h' | Remarks. |
| 176 | — | Ë | — | 0 | 1/4 | 0 | — | 1/16 | 7/16 | — | 3/8 | 3/16 | — | — | 7/16 | — | |
| 177 | 5/16 | — | 7/8 | 0 | — | 0 | 5/8 | — | — | 1/4 | — | — | Ë | 9/16 | — | 3/4 | |
| 178 | — | 3/4 | — | 0 | 11/16 | 0 | 0 | 0 | 1/8 | — | 0 | 3/4 | 0 | — | 11/16 | — | |
| 179 | Ë | — | 1 | 0 | — | 0 | Ë | — | — | 1Ë | — | — | 3/4 | 5/16 | 11/16 | — | Tube 1/64 in. too long. |
| 180 | 0 | 0 | 9/16 | 0 | — | 0 | 1 | — | — | Ë | — | 3/16 | 3/4 | — | 0 | 0 | — |
| 181 | 1/8 | — | 7/16 | 0 | — | 0 | — | — | 1/8 | — | — | 1/8 | — | — | — | 1/8 | Tube 1/64 in. too short. |
| 182 | — | 1/8 | — | 0 | 3/16 | 0 | 1/16 | — | 3/8 | — | — | Ë | — | 0 | 0 | 0 | Tube 1/64 in. too short. |
| 183 |
— | 1/8 | — | 0 | 3/8 | — | — | Ë | 1 5/8 | — | 1/4 | 0 | — | 0 | 0 | 0 | Tube 1/32 in. too short. |
In the first of these tests e is 1/3 of an inch; this indicates that x x is not perpendicular to A B, but that the foot of a true perpendicular would be 1/8 of an inch to the right of d; in other words, the tangent of the obliquity of x x is (1/8)/ 840, or tan i = 0.000149. The error at the surface of the tube was about 1/756 of an inch.
Now in considering the readings at the other end of the scale, we must bear in mind
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the fact that the zero which was taken to correspond to the first position of x x was 1/8 of an inch too far to the left. The reading d' = 3/16 should have been d' = 1/16, showing an error in x' x' only one-half as great as that in x x. When, however, the tube had been turned 180° the reading was c' = 3/8. Consistency with the other readings required that this reading should be c' — 1/16. Judged from the readings c and d', the zero was too far to the left by A of an inch; averaging these two determinations of the error in the position of the scale (the index error), we may for the present assume that the scale was 13/64 of an inch too far to the left.Wow turning the tube 90° and adjusting the straight-edges along the faces in the direction y z and y z, the observer tested the accuracy of the bevel angles. The angle x A y or tubes of the center span was intended to be 27' 58".26; for side spans this angle was about 16" greater. The reason for this difference lies in the fact that the tubes of the side spans are about an inch and one-half longer than those of the center span. The distance between A B and C D being 70 feet, and x d being perpendicular, the zero point for the line y z was for tubes of the center span 6.83 inches from the zero at d. For tubes of the side spans this distance was 6.90 inches. When we remember that the tubes of the upper members were longer than the tubes of lower members, we see that four graduated scales C D were required, and that each had six zero points on it.
Returning now to our tube No. 176, we see by the record b =Ë that the line of sight y z falls to the right of the zero point; at the other end of the tube we have d' = 7/16 also to the right a nearly equal amount. While turning the tube again 180° and reversing the straight-edges, we find h and g' both to the right again. As a' = g', we see that the bevel is exactly right on the end B; it would appear to be out 1/33 ofË of (b — h) =Ë976 of an inch at the end A. (A x is 1/93 of 70 feet.) The bevels, therefore, are almost perfect.
In the next tube, Wo. 177, we find that the zero points were too far to the right, as follows: (c/2) = (14/32) inches: (f' + e' inches)/2; (a + g)/2 inches; (b'+h')/2 = 16/32 inches.
The bevels appear to be out on the scale (i.e., when multiplied 93 times) at A, (g — a)/(2) inches, and at B, (h' — b')/(2)of an inch. In the same way all the records may be discussed. The bevel on tube 183 at the B end was out according to the scale 13/16, and hence was returned to the lathe. The error thus detected (and afterwards remedied) amounted on the end of the tube to 1/93 of 13/16 of an inch, or 0.0087 inches!
Inspector Baily made the preliminary tests on tubes. He was greatly annoyed at first by the effect of the sun's heat, which, though not great, distorted the tube sufficiently to produce very anomalous results. When the true cause of the trouble was discovered,
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and awnings were erected, protecting tube, trestles, observers, and instruments, all striking anomalies disappeared.About one tube in five required sending back to the lathe. No tube was ever rejected on the ground of inaccuracy. The time required to turn and groove one end of a tube varied from nine to ten and one-half hours according as the grooves were shallow (3/16 inch) or deep (3/8 inch). The grooves were cut, and the edge of the iron band was faced, parallel with the bevelled end.
The finishing stroke to a tube was the turning of the pin-holes. Plates XXIX, XXX show that the pin-hole is through the coupling and the staves of two tubes. The only practicable method of boring the hole accurately was to place the coupling tightly on the tubes it was destined to unite, and drill through both couplings and tubes at once. Hence we must first prepare the —
1,012 Sleeve-Couplings. (See Plate XXX.)
The first work was to plane the inner surfaces of the flanges of the two pieces which were to come in contact; next, to finish the outer plane faces. Two half-couplings were then clamped together and bolt-holes were drilled through the flanges. By steel bolts and nuts they were then securely bolted together and placed in a large lathe, where the interior was bored out and grooved to a tight fit with the ends of the tubes. All this was simple machine-work, accuracy in widths and depths alone being required. More or less was always to be turned from the ends of the couplings in finishing. When the grooving was done, the coupling was fitted to the two tubes and bolted. This fitting was no simple matter. The grooves had been made strictly rectangular in cross-section, in order that no initial strain should come on the projecting rings of either piece in consequence of inaccurate fit.
It is obvious that much nicer workmanship was required than would have been necessary with bevelled grooves. Mr. Linville protested against the rectangular grooves, and considered the requirement as based upon an "erroneous idea." The coupling first finished required over four days of "scraping and fitting," in getting it upon the tubes. As Inspector Dwelle remarked, there was no "give" to either the coupling or the tube. The process of fitting involved the danger of splitting the coupling. If for any reason the grooves and rings did not fit, the tube acted as a wedge, with a tendency to split a half-coupling through its center. Heavy hammer-blows on the plane face in several cases broke the coupling.
The tubes of each arch were finished in order from the skew-backs, so that in every case one of the two tubes coupled as we have said had previously been fitted either with a skew-back or with a coupling and pin at the other end. This exterior coupling and pin were adjusted so that the two tubes were placed as shown in the Fig. 26figure.
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A. represents the coupling and pin previously fitted, the pin resting in an iron support. The coupling to be bored is shown at B, where the tubes rest on the iron bands. The distance between centers of the pin-holes at A and B is of course accurately known, say (for an upper tube of the middle span) 144.965 inches. This distance is laid off from A with a trussed steel rod (made and graduated with the greatest care in St. Louis), and the required position for the axis of the boring-machine accurately determined. It is obvious that a small error in the lengths of the tubes was readily corrected here. It was not necessary that the pin-hole should be cut equally from the two tubes; a deviation of even half an inch would have done no harm. However, the errors in the lengths of the tubes when noticeable varied only from one-sixty-fourth to one-eighth of an inch. As the errors in length just about balanced each other (as the record of tests shows), a deficiency in one tube was most likely to be soon made up by another. Where all the workmanship is fine, it is difficult to feel sure of one's ground when calling one point more accurate than another, but it can scarcely be doubted that the steel tubes and their immediate connections were the most exact and thorough work on the Bridge. No appreciable resultant error was made in the length of the large tubes.
The boring of a pin-hole was a tedious job, particularly through the steel couplings and the thicker staves. Some seven inches of solid steel were to be penetrated with a hole about six inches in diameter. The steel of the first tubes made was very hard. Mr. Dwelle wrote August 6, 1872: "It is now more than three weeks since work was commenced on couplings, and yet there are but two pin-holes bored, the work on the pin-holes themselves occupying the greater part of the time."
The first coupling was in the boring-mill five days. A two-and-one-half-inch drill was first worked through the coupling and tubes, and the hole was then finished with a boring-bar. Later, with practice and better tools, the steel worked more rapidly, the number of hours for one hole being reduced to eighteen.
Simultaneously with boring the hole, the steel pin was turned to a close fit with the same. Both pins and holes had a slight taper, and the fit was to be such that the pin required driving home, but the blows were to be given with a heavy wooden mallet. It must be remembered that the pins were made of the finest steel, and that the largest weighed nearly three hundred pounds. It will be noticed that in the adjustments of the supports of the tubes and the fastenings of the boring-mills great care was necessary that the axes of the pins should be parallel. When the steel pin had been fitted, and all pieces so marked that there could be no mistake about their assigned positions, they were uncoupled and the coupling was tested as required. After the contract of March 5, 1873, the "sand-moulded," rolled-steel couplings were tested as soon as grooved, in order to save expense and time in case the coupling should fail. After being fitted and bored they were tested again.
1,024 Main Braces. (See Plate XXXI.)
The ends of the bars were forged solid, and the pin-holes were cut out by a machine. The rivet-holes in the body of the bar at first were drilled, but finally they were punched, as already explained on page 102. The size of the pin-holes was accurately tested by disks dropped into them. The distance between pin-holes was a matter of the greatest importance.
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A. represents the coupling and pin previously fitted, the pin resting in an iron support. The coupling to be bored is shown at B, where the tubes rest on the iron bands. The distance between centers of the pin-holes at A and B is of course accurately known, say (for an upper tube of the middle span) 144.965 inches. This distance is laid off from A with a trussed steel rod (made and graduated with the greatest care in St. Louis), and the required position for the axis of the boring-machine accurately determined. It is obvious that a small error in the lengths of the tubes was readily corrected here. It was not necessary that the pin-hole should be cut equally from the two tubes; a deviation of even half an inch would have done no harm. However, the errors in the lengths of the tubes when noticeable varied only from one-sixty-fourth to one-eighth of an inch. As the errors in length just about balanced each other (as the record of tests shows), a deficiency in one tube was most likely to be soon made up by another. Where all the workmanship is fine, it is difficult to feel sure of one's ground when calling one point more accurate than another, but it can scarcely be doubted that the steel tubes and their immediate connections were the most exact and thorough work on the Bridge. No appreciable resultant error was made in the length of the large tubes.
The boring of a pin-hole was a tedious job, particularly through the steel couplings and the thicker staves. Some seven inches of solid steel were to be penetrated with a hole about six inches in diameter. The steel of the first tubes made was very hard. Mr. Dwelle wrote August 6, 1872: "It is now more than three weeks since work was commenced on couplings, and yet there are but two pin-holes bored, the work on the pin-holes themselves occupying the greater part of the time."
The first coupling was in the boring-mill five days. A two-and-one-half-inch drill was first worked through the coupling and tubes, and the hole was then finished with a boring-bar. Later, with practice and better tools, the steel worked more rapidly, the number of hours for one hole being reduced to eighteen.
Simultaneously with boring the hole, the steel pin was turned to a close fit with the same. Both pins and holes had a slight taper, and the fit was to be such that the pin required driving home, but the blows were to be given with a heavy wooden mallet. It must be remembered that the pins were made of the finest steel, and that the largest weighed nearly three hundred pounds. It will be noticed that in the adjustments of the supports of the tubes and the fastenings of the boring-mills great care was necessary that the axes of the pins should be parallel. When the steel pin had been fitted, and all pieces so marked that there could be no mistake about their assigned positions, they were uncoupled and the coupling was tested as required. After the contract of March 5, 1873, the "sand-moulded," rolled-steel couplings were tested as soon as grooved, in order to save expense and time in case the coupling should fail. After being fitted and bored they were tested again.
1,024 Main Braces. (See Plate XXXI.)
The ends of the bars were forged solid, and the pin-holes were cut out by a machine. The rivet-holes in the body of the bar at first were drilled, but finally they were punched, as already explained on page 102. The size of the pin-holes was accurately tested by disks dropped into them. The distance between pin-holes was a matter of the greatest importance;
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it was laid off and afterwards tested by steel rods in the same manner as has been explained for the distance between pins. The whole number of brace-bars in the three spans is two thousand and forty-eight. They were used in pairs, to form one thousand and twenty-four main braces. The T-irons were riveted to the bars at the Keystone shops, but the light lattice-bracing could be put in only at St. Louis, after the bars were in place. A similar course was adopted with the vertical struts and other built-up pieces.There was a great amount of machine-work in addition to the above to be done at the shops of the Company, but the details are not of sufficient novelty to require mention here. When the number of tubes, couplings, and pins is considered, with the amount of machine-work required on each, some idea may be gained of the amount of "drilling and turning," which so bewildered Mr. Laurie that he ventured on no close examination of it.
As we have seen, a lathe in charge of a good workman could turn and groove both ends of a tube in about two and one-half working-days. To turn one thousand and thirty-six tubes would take one lathe two thousand five hundred and ninety days; another lathe would be about equally long facing, boring, and grooving couplings; another in turning pins, facing envelopes, and turning wrought-iron bands. A boring-mill would have been equally long boring pin-holes and drilling bolt-holes in the couplings. Two thousand five hundred and ninety days for three lathes and one boring-machine!
When Mr. Allen visited Pittsburg in March, 1872, and conferred with Mr. Piper, some such calculation as the above was made, though they both under-estimated the work on couplings.
Mr. Allen was much pleased with the excellence of the work done and of the novel appliances designed for doing it, but he found that the number of tools employed was far too small. They had but six lathes on the heavy work, and were intending to fit up four more, making ten in all. On Mr. Allen's estimate, which, as I have said, was low, these ten lathes would require five hundred and seventy-eight days, or nearly two years of ordinary working-days. He urged the Keystone Company to obtain twenty-seven more lathes. This Mr. Piper flatly refused to do. He agreed to employ two gangs of men and run his machines day and night, but he would not agree to provide the twelve new lathes which Mr. Allen thought necessary even with night-work.
It was so important to turn the work out rapidly that Mr. Allen finally proposed on the part of the Bridge Company to purchase six new lathes and give the use of them to the Keystone Company, provided the latter company would set up six more. This was agreed to, and the twelve lathes were at once ordered. The Bridge Company got three of its lathes from Worcester, Mass., and three from Newark, N. J. All the new lathes were of 36-inch swing. It was agreed to begin night-work early in April. The Newark lathes had all arrived by May 28, in "miserable condition," being unpainted and covered with rust. The last of the Worcester lathes did not arrive till July 5, but they were in fine condition. There was no great amount of night-work till midsummer, and then all was in full blast.
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Mr. Dwelle reported as follows for the work done during the week ending August 17, 1872: —
10 large lathes, including the "double-header," turning ends of tubes, with a total of 51 days and 40 nights.
3 lathes boring and grooving couplings, with a total of 18 days and 7 nights.
4 lathes turning steel pins, — 24 days and 7 nights.
2 lathes turning wrought-iron bands, — 11 days and 6 nights.
lathes turning ends of envelopes, — 6 days and 2Ë nights.
5 planers at work on staves, couplings, and envelopes, — 16 days and 6Ë nights.
6 drill-presses, drilling pin-holes and bolt-holes in couplings and rivet-holes in envelopes, — 30 days and 14 nights.
6 riveters, 4 helpers, and 2 machinists, at work on envelopes and couplings, — 6 days and 2Ë nights.
At other times men would be reported "forming tubes." Laborers in sufficient numbers were of course employed, but it was not necessary to report on the matter. When, in the fall of 1872, couplings began to arrive with considerable rapidity, and it was necessary to fit them to tubes already made, the drill-presses were found inadequate, and on another visit Mr. Allen agreed to supply two additional horizontal boring-mills. They were made in the shop itself, thus withdrawing the lathes for a time from other work. In January, 1873, night-work, which had been suspended for about three months, began again, and eight drill-presses were in nearly continuous use. By the middle of February every tool, including eleven drill-presses, was at work night and day. It will be remembered that in December, 1872, Mr. Allen proposed to give Mr. Piper $20,000 bonus to complete the Bridge by May 1, 1873.
Having now followed the work of construction up to the completion of all the parts of the Bridge, it will be of interest to know the decision of the referee experts upon the various matters which by contract were left to them. They were to take into consideration changes in the design, cost of material, cost of special tools, the amount and quality of work required, in order to arrive at a fair estimate of how much was to be charged or credited to the contractors. T give only the more interesting items: —
Steel Couplings. — The cost of finishing each wrought-steel coupling used was put at $45.34. The referees decided that the contractors would have lost $6.82 on each coupling had they executed the original design and made them of cast iron; they were, therefore, allowed $38.52 extra on each coupling.
Steel Tubes. — The work on each 18" tube over the original 13" tube was worth $18.75. For the two wrought-iron bands they were allowed for material and work 10 cents per pound, or $11.80.
Jaw-Nuts (See Plate XXVII). — For each nut an extra allowance of $26.37 was made.
Chipping and planing Staves. — A gross amount was allowed of $2,270.58.
Main-Brace Bars. — The St. Louis Company was allowed $10.10 on each brace bar, for simplifying the form; and the Keystone Bridge Company was allowed 2 cents per pound extra for the iron.
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Lateral (Steel) Tension-Bods complete, including the Eye-Plate Washers. — The Keystone Bridge Company was allowed extra for each rod, $6.25.
Steel Pins. — The contractors were allowed extra for work on each pin, $13.74.
The wrought iron under the railway tracks was put at 10 cents per pound.
Suspension-Bars (carrying the railways near the centers of the spans). — On 244 of these bars, $12.45 instead of $10 was allowed per hundred, making an extra of $2,090.56.
The sum of all these allowances amounted to about $110,000, — in favor of the Keystone Bridge Company.
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Chapter XIV. The Erection Begun.
I have at no point given a formal description of the superstructure of the Bridge, nor is it necessary now to describe the arches. It will suffice if I say that each span had four ribs, and that each rib had two lines of tubes connected by a single system of bracing. The depth of a rib from center to center of tubes was 12 feet. The distances between the ribs (from centers) was 16Ë feet for the outer spaces and 12 feet for the central space. All the details are shown in the Plates.
The erection began with the putting in place of the steel anchor-bolts of the West Abutment. These were followed as soon as possible by the bolts in the other piers. When the bolts intended to secure a skew-back were in position, the cast-iron "bed-plate" upon which the skew-back itself was to rest was carefully adjusted in its bed. In the first place, a recess was made for it in the granite facing of the masonry. In the second place, instead of lime or cement mortar, a thick paste known as a "rust joint" made of iron filings and salammoniac, was used. This paste set in a few hours, and formed an exceedingly solid and durable support. About twelve hundred pounds of filings were used for each joint. The plates had parallel longitudinal ribs on their under surfaces. They were brought into correct position by wedges, and the nuts on the anchor-bolts were tightened. The paste was then inserted between the ribs, and rammed home by long iron punches. The paste was soon almost as hard as cast iron, and the joints were perfect. As the inclination of the outer face of the bed-plate was a very important matter, the adjustment was made under the supervision of Col. Flad. In some cases, when the joint was made in cold weather, the paste was kept artificially warm till it was thoroughly set. Twenty-four of the forty-eight plates had been adjusted by June 1, 1872.
The next step in the erection consisted in placing the skew-backs in correct position. (See Plate XXIII.) After a skew-back and its tube
2d. The error in "azimuth" of the tube, i. e., the angular amount by which the tube tended towards the right or the left of the skew-back on the opposite side of the span. 3d. When the four tubes composing the upper or the lower set of the skew-back tubes were in
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position, a horizontal line was drawn through the pin-holes at their extremities to determine the variation in the resultant lengths of these tubes due to variation in the thickness of skewbacks or the positions of the bed-plates. 4th. The vertical and horizontal distances between the pins of an upper and the corresponding lower skew-back. 5th. The horizontal distances between the skew-backs of different ribs. 6th. The level, or height above the city directrix, of the center line of each pin-hole at the extremity of a skew-back tube.As additional checks upon the correctness of the adjustment, the distances of the pins in the upper skew-backs from the pins in the extremities of the lower skew-back tubes — the length of first main-braces — were taken; also the vertical and horizontal distances between the centers of the pin-holes at the extremities of the skew-back tubes.
From these measurements the amounts and directions of the changes necessary to bring a skew-back and its connected tube into correct position were determined. Errors in height were corrected by cutting out bolt-holes. Angular changes were made by inserting between the skew-back and its bed-plate wedge-shaped iron plates. They were made of cast iron, and were planed to calculated thicknesses at the corners. They covered the whole bed of the skew-back, and were generally put in in segments, after being well painted.
These adjustments necessarily required much time and care. The same measurements were always repeated after an adjustment, and if necessary further changes were made.
The first and second observations named above — that is, the measurements of the angle of elevation and of the angle of lateral deviation of the skew-back tube — were made by means of a mirror very accurately adjusted upon the planed end of the tube. The method is roughly shown in this sketch: —
The telescope was mounted in a determined position on the adjacent pier, its axis being in the plane of the rib to be adjusted. Knowing the distance and position of the instrument and the required inclination of the planed end of the tube, it was easy to calculate the angle which the plane of the mirror should make with the end of the tube in order to be perpendicular to the line of sight from the instrument. Having accurately adjusted the mirror, the observer at the telescope saw in the mirror the reflection of his own instrument, provided the tube was in correct position. If he failed to see himself, as it were, it was easy to so place a target in the immediate vicinity of the telescope that its image could be seen through the telescope. The error in the elevation of the tube was readily determined
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by the distance of the target above or below the object-glass of the instrument; the lateral error, by the distance of the target horizontally from the telescope.The first skew-backs adjusted were those of rib "D" (the northern one), at the west end of the west span. They were reported as in adjustment March 13, 1873. The corresponding skew-backs of the other ribs were in adjustment on the next day.
In adjusting the skew-backs of the channel piers it was found necessary to take them in pairs, one on each side of the pier, as they were secured by the same bolts.
The erection was under the general charge of Mr. Walter Katte, the engineer for the contractors.
The method of erection was on the plan devised by Col. Flad in 1870, modified to meet the requirements of the contract of May 5, 1873. (See Chapter XII.) By this plan, the arches during erection were partly self-supported and partly upheld by a system of cables passing over the masonry of the abutments and piers, and over towers built upon the same. The arrangement of the cables, main and secondary, is clearly shown in Plates XXXVII — XXXIX.
Platforms supported by the masonry were used in the erection of the skew-backs and first tubes, but no sooner were tubes in position than they themselves furnished supports both for platforms and the apparatus for hoisting additional parts of the arch.
As the parts were needed for erection they were placed upon a barge at the river's edge and towed into position directly under the hoisting-gear and anchored. The hoisting was all done by hand.
Mr. Cooper has furnished me with the following sketch of the method of erection: —
Fig. 28. —
The half-coupling (7, first fitted to the tubes at T, contains the larger end of the steel pin. (As already mentioned, the steel pins were slightly tapering.) As soon as this half-coupling was fitted, the pin was brought up by the same hand-line L, and loosely inserted. The other half of the coupling followed, and the two were bolted together. The fit of the grooves could be observed on withdrawing the pin, and the adjustment circumference
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was effected by driving the pin tightly home with a wooden mall. The brace-bars B were then sprung over the ends of the pin.Without moving the balance-beam H H, an upper tube, coupling, and pin were erected, the hand-line L being run over the pulley at n. The next step was to hang the inner brace-bars over the ends of the pin at D.
At this stage of the work, it is obvious that there would be a sensible deflection of the joint at D in consequence of the weight of the additional tube and the load upon the two; hence before the outer brace-bars from T to D could be put on, the joint D was raised by a jack supported by the tube K.
At the other end of this same rib the order of erection was somewhat different, on account of the necessity of coming out right at the center, but the method was equally simple.
Before the insertion of the brace T D it is obvious that the weight of two tubes, one coupling, and two brace-bars brought a bending strain on the coupling at P. This strain the coupling was abundantly able to bear, as was shown by the experiment described in Chapter XII, where the strain upon a coupling was equivalent to the support of five tubes and four couplings, forming a single projecting tube about sixty-one feet long. On one occasion, in the early part of the erection, Mr. Eads learned that the foreman had erected and coupled on a third tube before the outer end of the first had been supported by a brace. He at once called the attention of Mr. Katte to the fact, with the warning that the strain was unnecessarily great, and one which would jeopardize a coupling under the added effect of a heavy blow, should one chance to fall upon it. (In the completed arch the only strain of any importance on the couplings is that of direct tension. Under normal influences and ordinary loads there is no strain at all on the couplings.)
The riveting of the diagonal bracing of the main braces and the insertion of the tubular struts and steel diagonals between adjacent ribs followed the erection of the tubes as rapidly as possible.
The first difficulty encountered was the misfit of the steel pins. It appears that it was the opinion of Mr. Piper that it would be sufficient to fit them until they would enter the holes bored for them, to within one-fourth or three-eighths of an inch of their destination. The taper of the pin was so gentle that no trouble was expected in driving them home when erecting the Bridge. It was found, however, that a large amount of filing was necessary. This was very annoying, and the work was done at some inconvenience. Mr. Eads accordingly ordered that the pins be fitted in Pittsburg and driven home. Besides, both the pin and the coupling should be so marked that when put together at St. Louis, the angular position of the pin could be precisely repeated.
On the morning of April 7, 1873, three sections of tubes and braces were up at the West Abutment, and an equal amount on each side of the West Pier, and work was begun on the fourth section. Two additional sections at all three points were put up, and then the erection stopped for a month for want of material. Meanwhile, the tower on the West Abutment had been completed and that on the West Pier had been begun.
On June 4, Mr. Theodore Cooper was ordered by Mr. Eads to report at St. Louis to
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take the important position of inspector of the work of erection. Mr. Cooper entered upon the discharge of his new duties June 9.On the last day of June Mr. Eads returned to St. Louis, after an absence of three weeks. He was greatly surprised and disturbed by the small progress made in the erection during his absence. He protested against the management which resulted in entirely unnecessary delay. He complained that many parts had been sent to St. Louis far in advance of any demand, while there had been unaccountable neglect in providing such as were wanted at the very beginning of the erection. "For instance," he wrote Mr. Linville, "the coupling-bolts should have long since been made and shipped. The steel for them was rolled and delivered eighteen months ago, and any bolt-factory in the country could have turned out the entire order in a few weeks. Today we are in receipt of a dispatch from Col. Piper stating that they are being shipped as fast as he can make them. This indicates that the erection must await the arrival of holts yet to he made."
There was great want of steel rods for the diagonal bracing between ribs. In the entire structure of the center span, then extending 72 feet out from the pier, there was not a single diagonal tension-rod. Had a tornado or the upper works of a steamboat struck these ribs, thus devoid of lateral bracing, the shock would have brought a strain upon the couplings which they were not designed to bear, and which would be much more severe than those which the Keystone Company had insisted should be provided against, at the expense of the Bridge Company, by extra cables. The steel for these rods had been delivered in Pittsburg fully a year and a half before.
By the evening of July 3, seventy-five additional tubes had been erected, being an average of less than four tubes per working-day. The small progress made (nine sections in ten weeks) was altogether unexpected. To be sure, the work was new and but few men were engaged on the erection, but many days went by in which nothing was done. "Everything stands idle," wrote Dr. Taussig to Mr. Piper, "for want of material. Bolts, tension-rods, eye-plates, etc., all articles about the making of which there never was any difficulty, which might have been turned out and shipped a year ago just as well as to-day, are not at hand."
The officers of the Keystone Bridge Company were evidently much disappointed as regarded the rate at which the arches could be erected. Col. Piper had estimated the time to erect one-half of the entire Bridge at twenty-two days. (See Mr. Allen's letter, p. 134.) He now declared that his estimate did not include the work of putting up cables and their supports. He admitted that there had been some delay in furnishing material. Mr. Linville was of the opinion in May, that the first span would be closed by June 15. On July 12, a plank, upon which were standing three men engaged in the erection of the center span, broke and precipitated the men into the river. One of the men was drowned.
Prom the nature of the work of erection there was great personal risk. None but careful, cool-headed men could be employed. When this accident was reported to Mr. Eads, he at once gave orders that the foremen would be held responsible for the safety of their men.
The work of erection went on slowly. The Keystone Bridge Company were under no explicit obligation to push the work, and their arrangements seemed to be dictated solely
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by a desire to erect the Bridge at the least cost to themselves. Not till the 3d of July were three gangs of men at work erecting the arch simultaneously at three points. The reader does not need to he told that the bonus offered by Mr. Allen in December, 1872, was never earned. In fact, Mr. Piper had as much as declared that he had no idea of earning it. It was evident that experience was necessary to a rapid erection.In response to urgent appeals more men were furnished, and later in July as the lacking material came to hand, progress was for a time quite satisfactory.
By August 1 the work of erection seemed pretty well understood, and the prospect good. Under that date Mr. Eads wrote: —
"Work is progressing with great regularity. The novelty and magnitude of the work made calculations as to the rate at which it could be put up necessarily uncertain. The contractors predicted that it could be put together more rapidly than any large bridge they had ever erected, and in this they are able to do even better than they expected; twelve feet, or a panel of arch, was put in place in five hours, and thirty-six feet was recorded as a day's work last week, — twelve feet on the end of each segment (twenty-four tubes). But every third panel the cables from the piers have to be put together and fastened to the arches to sustain them, and in this work much more time is expended than was expected.
On the whole, I feel greatly encouraged. Progress at the West Abutment 168 feet, and 156 feet opposite to it. The contractors assure me they will close the gap (176 feet) in fifteen days. I give them twenty."
Although the contractors had assured Mr. Eads that they would close the gap of sixty-four tubes in the center ribs of the first span in fifteen days, only four tubes were erected on that span during the next seventeen days. The time was spent in putting in the lateral bracing, in doing "odd jobs," and in the erection of the main cables to the twelfth joints. These cables were the longest and the strongest, and every detail of their fitting and adjustment was of the utmost importance.
The first suspension-cables used were those to joints "No. 3" of the upper members of each rib. They were similar in all respects to those to joints 6, shown in Plate XXXIX. Although required by the contract of March, 1873, the "No. 3" cables were entirely unnecessary, and in some cases they were not used. "No. 6" cables were an essential part of the plan of erection; they supported the weight of the ribs till the ninth joints were reached. For each rib they had a cross-section of thirteen square inches, and were attached to all ribs. "No. 9" cables were of the same size as "No. 6;" they were attached only to the inner ribs, and they were removed when the main cables were under strain. The main cables supported the twelfth joints of the inner ribs.
The secondary system of cables comprised the iron masts at joints 12, the back-stays to the skew-back pins, and the suspension-cables to joints 15 and 18 of the inner ribs. Cables to joints 15 were removed when those to joints 18 were under strain. These cables contained a cross-section of 22 square inches for each rib.
Plate XXXVII shows clearly the use of the main or "No. 12" cables. The tension on them was always to be sufficient to support all the weight of the ribs at the twelfth joints, including the load on the masts from the secondary cables. The main towers (Figs. 3-9, Plate XXXVII) stood upon the plungers of powerful hydraulic jacks, by means of which
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the tower could be raised as required. A very ingenious provision was made by which the tension on the cables was kept uniform while the temperature changed. A few words will explain its main features.In the first place it should be seen that the towers required raising with a rising temperature, and lowering with a falling temperature. The expansion of the stone pier and the wooden towers caused by heat was practically nothing, while the expansion of the ribs and cables was measured by inches. Uniform stresses in a structure possessing rigid members and fixed angles depend upon proportional changes of figure; hence, with a rising temperature the tension in the cables could not be maintained without artificially raising the towers. This was automatically effected by connecting the hydraulic chambers of the rams with the chamber of a small cylinder several feet in length, in which a loaded plunger was free to move either up or down. This plunger was loaded according to the pressure required, and so long as it rested upon the liquid (glycerine) alone the pressure could not change. A man was on hand night and day to see that the plunger was kept in "mid-gear," as it were, by forcing more liquid into the pipes, or allowing some to escape, according as the towers rose or fell. The small plunger, with its series of weights, all constituting the "balanced gauge," are seen in Figs. 14-16, Plate XXXVIII.
The main cables had each a constant cross-section of 42 square inches. The tension on them was of course measured by the weights on the balanced gauge. The number of these weights was increased as the erection progressed. The tension on all the other cables was regulated by sleeve-nuts, and was measured by the extension of one of the bars, the original distance between two marks on the bar having been carefully noted, and the modulus of elasticity of the bar obtained. As will be seen, the labor of putting up and removing cables was unexpectedly great.
All at once the eyes of the Bridge Company were opened to the probability of its taking several times as long to erect the Bridge as had been expected. On the original plan of main and secondary cables, Mr. Piper had expected to erect the three spans in forty-four days. Mr. Allen had allowed him one hundred and five! Now, however, after the adoption of three sets of additional cables, that estimate seemed no index of the actual demand. The chief engineer was accordingly instructed to prepare a careful estimate of the probable time required to finish the Bridge, based on the experience of several months, and making no allowance for lack of material.
On the 9th of August Mr. Eads submitted the following report to the Directors: —
"GENTLEMEN: In compliance with your instructions, I have the honor to submit estimates of the time required to close the arches: —
1st. On the supposition that the Keystone Bridge Company continues the work on the system proposed by them.
2d. In case an additional tower and one additional set of cables Nos. 3, 6, and 9 should be supplied.
3d. On the supposition that all-towers and cables now used should be duplicated. I also give the extra cost arising from the use of additional towers and cables.
These estimates have been submitted to Walter Katte, Esq., engineer of the Keystone Bridge Company, and are concurred in by him."
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The contractors had proposed to use but two towers and two complete sets of cables. Their plan was to erect the west span and one-half the center span simultaneously. After closing the west span, the tower and all the cables on the West Abutment were to be moved to the East Pier. The eastern half of the center span and one-half of the third span were then to be erected, and the center span closed. Finally, the tower and all the cables on the West Pier were to be moved to the East Abutment, and the third span completed.The estimates submitted by Mr. Eads had been prepared by Col. Flad and Mr. Cooper, and were based upon the work done during the month of July, when, on an average, four-tubes were put in position daily.
I. They allowed ten days for adjusting and closing the center ribs of span I, and two days for closing the outside ribs. The removal of the tower and main cables from the West Abutment to the East Pier was estimated to take two months after the first span was all closed. The same allowance was made for removing the tower and main cables from the West Pier to the East Abutment after the center span should be closed. Two months were allowed for time lost during the winter. The closing of the last arch, on the plan of the Keystone Company, would not be effected till September 6, 1874!
II. The date of closing the last span, on the second plan, was given as June 5, 1874. The estimated net cost of this plan over the first was only $5,400.
III. The third plan proposed that the towers and cables then in use be duplicated as soon as possible. No transfers or removals to other spans would then be necessary. The estimated date of closing the last arch on this plan was (making allowance for loss of time in winter) December 18, 1873.
The net extra cost of the third plan over the first was estimated to be $30,000, and the saving in time eight and one-half months.
In either case it appeared that the cost would be nearly, if not quite covered by the saving in the cost of engineering, etc. When the vastly more important matter of revenue was considered, there was not a moment's hesitation. The directors at once resolved "that the Company could no longer endure the slow progress of erection." President Allen officially protested against "such intolerable delay." "No effort, no sacrifice, nothing that men and money can do, ought to be spared to bring the three arches to a close this winter." Mr. Eads was requested to deliver this protest in person, and was fully authorized to make any arrangements with the Keystone Bridge Company which he might deem best calculated to secure the earliest possible completion of the Bridge.
Two days later he telegraphed from Pittsburg that he had sent the protest and demand of the Bridge Company to Mr. Linville, and had received the following reply: "Duplication of towers and cables can be made only at expense of your Company; will call meeting to act on definite proposition to this effect. Have requested meeting Thursday morning." On receipt of the above, the executive committee delegated Dr. Taussig, its chairman, to proceed to Philadelphia, and assist Mr. Eads in coming to an agreement. Dr. Taussig was "instructed to consent to no arrangement looking to a payment, in part or whole, by the Bridge Company for duplication of towers, cables, etc., unless such duplication was accompanied by a corresponding increase of force, tools, and plant; by quick and rapid shipments of material, and by a positive assurance of closing the arches on a fixed date."
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The meeting of the officers of the Keystone Company was held in Philadelphia on August 14, the day named by Mr. Linville. The estimates of time required to close the arches were read and discussed. The result of the conference is shown in the following official papers: —
"PHILADELPHIA, August 14, 1873.
J. H. Linville, Esq., President Keystone Bridge Company.
DEAR SIR: In answer to your proposition that you will erect duplicate towers and cables, provided we will pay for the actual cost of the same, we make you the following counter-proposition: —
1st. We will pay you the sum of $35,000 if you will complete the three arches on or prior to January 1, 1874.
2d. We will pay you the additional sum of $30,000 if you will have the Bridge ready for railway and highway traffic on the 1st of March, 1874, and the sum of $250 for each day prior to the 1st of March on which the Bridge is opened for railway and highway traffic, provided that you agree at once, without delay, and give a telegraphic order for the execution of the following necessary appliances: —
I. For the making and framing of the necessary cables in duplicate.
II. For immediate framing of the towers and the making of hydraulic rams.
III. To procure additional flats, crabs, balance-beams, and a steam-hoist for the East Abutment.
IV. To ship material which is finished in shop, during the present season of inactivity on the railroads, and not to wait for shipments in the order and succession in which it is wanted.
V. To replace any pieces which maybe accidentally lost, with the utmost dispatch, and to authorize your engineer to have such pieces, if practicable, made in St. Louis.
VI. To appoint an additional competent engineer to aid Mr. Katte, who shall devote his whole time to and at the work.
VII. To give us the benefit of the presence of Messrs. Linville and Piper: the first to be there at least once every thirty to sixty days, if ill-health does not prevent; the latter, at least one or two weeks of every month.
Should you accept this proposal and comply with its conditions as to date of completion, we hereby agree that no claims shall be made as to delays which we think have hitherto occurred in the prosecution of this work. It is understood, of course, that should you complete the arches by January 1, 1874, and the Bridge be opened for traffic by March 1, 1874, the sums named will have been earned, no matter how you do it. The details referred to in the above are urged as important suggestions to insure your success.
Respectfully, etc.,
ILLINOIS AND ST. LOUIS BRIDGE COMPANY,
By JAS. B. EADS, Chief Engineer.
Approved.
WILLIAM TAUSSIG, Chairman Executive Committee."
"PHILADELPHIA, August 14, 1873.
James B. Eads, Esq., Chief Engineer Illinois and St. Louis Bridge Company.
DEAR SIR: In reply to your letter of this date we beg to state that we accept your proposition, and will, in pursuance thereof, proceed to act upon it. We will put in hand at once the necessary work, including the duplication of the necessary cables, rams, etc., and we will duplicate correspondingly our force of men as soon as possible, supply the necessary additional tools and plant, and ship the material as fast as cars can be obtained, and use our best efforts to meet your views.
In arranging for payment upon new cables, rams, etc., it is to be understood that you allow us the
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$35,000 upon the same when they are shipped to St. Louis, and should we fail to meet the terms of your offer as to time for completing the arches, — say January 1, 1874, — you shall then charge us with the said sum upon account.
Very respectfully yours,
J. H. LINVILLE, President Keystone Bridge Company."
This contract was approved at the time by the Board of Directors of the Keystone Company. The executive committee of the Bridge Company approved it on the return of Dr. Taussig to St. Louis.
Orders were issued for the manufacture of the additional cables, towers, etc., and the employment of a large force in St. Louis. The erection began vigorously. Although the additional cables, held to be unnecessary by the engineer of the Bridge but insisted on by the Keystone Company, and authorized in the contract of March 5, 1873, had already cost some $30,000, and this new contract of August, 1873, called for $65,000 more, making about $100,000 not included in former estimates of erection, the new contract seemed in every way a good one for the Bridge. A reasonable prospect of its rapid completion was of immense value to the financial interests of the Company. The Bridge was still an unsolved problem, and would remain such till it was finished. European capitalists, with millions of dollars already invested in the Bridge, refused to advance more till the feasibility of closing an arch had been practically demonstrated. The contract was a plain one. The Keystone Company was to close the arches by January 1, 1874, or it would lose the $35,000, and the Bridge must be ready for use by March 1, 1874, or it would fail to earn the $30,000. The contract was without other conditions.
Meanwhile, the state of Mr. Eads's health made it absolutely necessary that he should take a leave of absence and seek a milder climate. He had recently returned from a three weeks' visit to Texas and the Passes of the Mississippi, with a severe cough and bleeding lungs. His physician advised an ocean voyage. The Directors of the Bridge Company had therefore given him leave of absence for two months. At the conclusion of the conference in Philadelphia on the 14th of August, he went to New York, whence he sailed for England on the 20th. Before he left St. Louis he had delegated to Col. Flad all the powers and functions of the chief engineer, in the following letter: —
"ILLINOIS AND ST. LOUIS BRIDGE COMPANY,
CHIEF ENGINEER'S OFFICE, ST. LOUIS, August 6, 1873.
Col. Henry Flad, C. E.
DEAR SIR: In view of my temporary absence on an ocean trip for the restoration of my health, I hereby, with the approbation of the president and directors of the Company, fully authorize you to act in my stead, and sign my official signature as engineer of the Bridge and Tunnel, whenever necessary. It is needless to add that it is my urgent wish, as well as in the interest of the Company, that you push the work with all possible vigor, and to this end I wish you not to hesitate for a moment to take such responsibility as may arise in the progress of the work, but decide in the premises on your own good judgment all questions that would otherwise be referred to me for my decision, and your action will be approved by me.
Very truly, etc.,
JAS. B. EADS, Chief Engineer."
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Chapter XV. Erection Continued — Closing of the West Span.
Mr. Eads had scarcely sailed from New York before the Keystone Company gave notice that they would not execute their last contract. On the 23d of August, Messrs. Linville, Piper, and Carnegie were on their way to St. Louis to submit new propositions. Some one had discovered that their Board had met on the 14th without legal notice, and as the contract involved some risk to their company, they took advantage of the oversight to repudiate their bargain. The reasons given by Mr. Linville (August 25, 1873) were as follows: —
"Upon consultation with our engineer and general manager, we find that our ability to close the arches depends very largely upon the state of the weather and river. In the estimate made by Col. Flad, no time is allowed to meet these and other contingencies.
When action was taken by our Board in Philadelphia we were informed by your Company that the estimates referred to had been concurred in by our engineer. This we find was in no just sense the case.
Under these circumstances, protest has been duly entered against the action of said meeting, and proceedings will be instituted to restrain me from attempting to comply with the arrangement. I have therefore visited St. Louis, together with Messrs. Piper and Carnegie, to confer with you as to the most feasible method of securing the object we all have in view, — the earliest possible completion of your work, — and I beg to submit for your consideration and acceptance the following proposition: —
The Keystone Bridge Company will provide the cables, rams, towers, and apparatus required to proceed without delay with the erection of the remaining portions of the Bridge, and furnish the forces of men that your acting chief engineer, Col. Flad, and our general manager, Col. Piper, upon consultation with each other, may determine to be necessary to secure the erection of the arches, ready for the insertion of the closing-tubes of the interior arches, by January 1, 1874, with a view of securing the completion of the Bridge at the earliest possible date with the force agreed upon.
And we will further pledge our best efforts and the best efforts of our company to the attainment of this end, agreeing to work our men at such time as is practicable.
Your Company to agree that for the cables, rams, and apparatus furnished by us you will pay current monthly estimates, as materials are delivered, to the amount of $35,000.
Upon the acceptance of this proposition by you, we will order by telegraph the necessary cables. I have no hesitation in expressing the opinion, in which I am supported by my colleagues, that, weather and river being favorable, and no extraordinary contingencies arising, we can have the arches all ready for the insertion of the last tubes on or about January 1, 1874, and that it is our intention to do this if practicable.
This opinion is based upon data and experience, and therefore entitled to consideration; hitherto, all opinions were necessarily hypothetical."
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When this letter is compared with the letters of August 14, it is obvious that the objects the Keystone Company "had in view" were, first, to avoid the risk of losing the $35,000; and, second, to disclaim the responsibility of inserting the closing-tubes. The letter contains nothing else. The date on which the arches are to be closed remains substantially the same, and the appliances are the same; yet on the 14th the estimate was "hypothetical," on the 25th it was based on "data and experience!"
The officers of the Bridge Company had no alternative. Possibly the contract of August 14 was not valid, and even if it had been valid a suit would not have hastened the erection of the Bridge. They therefore agreed that if the Keystone Company would "at once provide cables, rams, towers, and apparatus, and proceed without delay with the erection of the remaining portions of the Bridge, and would provide such additional plant and machinery and furnish such a force of men" as should be named by Messrs. Flad and Piper, the Bridge Company would pay the $35,000 "irrespective of the date for closing the arches."
For the purpose of preventing further protests, it was agreed that the modified contract should "be submitted to the respective Boards of the two companies, at legally called meetings thereof."
From various causes, there was no formal ratification of this contract. Messrs. Flad and Piper agreed upon "the number of men and amount of apparatus necessary to carry on the work of erection in the most rapid and systematic manner," and their agreement was substantially carried out, and the $35,000 was paid.
This agreement was as follows: —
First. A sufficient number of extra balance-beams, crabs, flat-boats, etc., are to be obtained as soon as possible to commence erection at all points. (Three additional — six in all.)
Second. For the purpose of raising tubes, couplings, and main-braces, and connecting the same, eighteen men are considered the proper number at each point of erection as long as four ribs are being raised. (Fifty-four additional men at three points.)
Third. To fit and connect tension-rods and tubular stays as fast as the "tube-raising" gang are out of the way, seven men at each point are allowed. (Twenty-one additional men at three points.)
Fourth. On each flat-boat from which tubes, etc., are being raised, three men are allowed to clean, uncouple, and "make fast" the material.
Fifth. Enough riveters and helpers are to be employed to keep up the riveting of the main-braces as the work progresses.
Sixth. Sufficient carpenters and laborers are to be employed, independent of the above gangs of men, to frame and erect the towers, trestling, and frame-work, as fast as timber can be obtained and the work of erection of tubes will allow.
Seventh. It is understood that as long as the erecting-gangs can be kept at work by a proper supply of material, they are not to be taken from it to do work which other men can be employed to do. It is hereby understood that the spirit and intent of this agreement is: that the work of the erection of the Illinois and St. Louis Bridge is to be carried on in as rapid and systematic a manner
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as possible, all portions of the work being kept as far advanced as can be done without interference between the different gangs of workmen, and that as many men are to be employed by the contractors as can contribute to this result, to wit, the closing of the arches of all the spans by the 1st of January, 1874."
Let us now go back a few days, and then carry the work forward to completion. By August 1, work had been begun on the main cables of the West Abutment. The anchorage had long since been arranged, and the clamps fitted upon the tubes at joint 12. (See Plate XXXIX, Figs. 2 and 5.) When all the supports were ready the cables were raised to their places. As each bar was 27Ë feet long, six (or seven) inches wide and an inch thick, and as each length of the cable consisted of seven (or six) bars, the putting together of a cable four hundred and ninety feet long was no small matter. The main cables with their supports, including the towers and rams, are fully shown in Plate XXXVII. On August 9, the cables over the West Abutment towers being fully connected, the pressure was applied to the rams. The packing proved to be useless, and the pipes leaked badly. The next day the packing was renewed, and glycerine was substituted for water in all the hydraulic apparatus.
Not till the 14th could pressure enough be secured to raise the towers half an inch.
I cannot do better than to draw largely from the very valuable and interesting "daily record" kept by Mr. Cooper during the erection.
August 16. — "At 5 P. M. hoisted abutment towers 4Ë inches, bringing full strain on cables. Levels taken at joint 12, when pressure was on, showed that rib B was stillË inches higher than C, and that both were about 1 inch higher than before the strain was put on the cables."
Plates XLII and XLIII give excellent pictures of the work at this time. The first view is from the wharf north of the West Abutment. Cables to joints 6, 9, and 12 are all in position, but the main cables are not under strain. The trestling for the secondary systems of cables is begun.
Plate XLIII shows that the No. 9 cables have been removed, the main cables being under strain. This Plate gives a general view of the whole work. The view is from below the West Abutment. The main cables over the West Pier are clearly shown, while the details of the guides to the towers on the West Abutment are well brought out. It is hardly necessary to say that the apparent confusion of wood-work on the pier vanished on a closer inspection. The remnants of the old ice-breaker are seen above the West Pier.
"August 18. — At [West] Abutment, raised four tubes (15th section). Only seven men at work on abutment. At [West] Pier packed rams afresh. Put on bottom guides to towers. Raised towers six inches to full strain for present load. Rams very well packed. Not being quite ready with balance-gauge, etc., let pressure off again. (At first had difficulty in lowering towers.)"
August 20. — "Raised towers this morning, pumping until balance-gauge showed a balance. This afternoon found balance-gauge did not work the same, and on examination found towers were four inches too high; lowered them till spring-gauge showed proper pressure per square inch (1,150
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pounds), as we could make nothing of the irregular manner of action of the balance-gauge. Carefully examined ribs to see if any part had been overstrained. Could find no indications of such."
Meanwhile six or eight tubes per day are raised on the central ribs. No. 9 cables were removed and the secondary system got ready.
August 23. — * * * "A man fell from the Bridge near the West Abutment and was killed."
August 28. — "Connected cable 15 at all points. Raised 12 tubes, 17th sections of middle ribs, at three points." * * *
August 29. — "Raised 12 tubes, 18th sections." * * *
August 30. — "Raised 12 tubes, 19th sections." * * *
September 1. — Could not connect No. 18 cables, as the short links are not here. Telegraphed to Pittsburg for them. Getting ready to hoist the 20th sections without waiting for this cable." * * *
September 2. — "Received last evening by express (in anticipation of telegram) the missing links for 18th cables. * * * Erected 6 tubes to-day."
September 3. — "Connected 18th cables and slacked 15th." * * *
September 4. — "Raised 12 tubes. This brings the side span within one tube at the top and two at the bottom member. Set up 18th cable on C rib, and slacked off No. 6 a little in order to raise joint 16 and beyond for connecting tube-stays, the rib C being much lower (about 1Ë inches) than B. Very strong wind last night, but had no effect on the work except blowing off some loose planks from scaffolding."
Ribs A and D were not erected beyond the 11th joint until ribs B and C had been closed.
September 5. — * * * "Raised at abutment end the two lower tubes of 21st section, reducing the open space between semi-arches to a single tube, — the 21st at the top and the 22d at the bottom."
September 6. — "This morning at 7 A. M. (temperature 60°), distance between semi-arches was only 0.295 inches short on upper and 0.54 inches short at lower members. The abutment portion was one foot lower than the pier portion at extreme points. [Its proper position was 1 3/5 inches lower. The western end was actually 8 1.2 inches too low, and the eastern end about 1ž inches too high. The abutment end was three inches too far north, and the pier end one inch too far north, at extreme points."
This lateral curvature was ascribed by Mr. Cooper to the fact that the men had screwed up one line of the diagonal tension-rods, which had sleeve-nuts, more tightly than the opposite line, fitted with swivels.
The condition of the arches was very satisfactory, and it was expected that by means of adjustments of diagonals between ribs, and an increase of cable-strains, with a lower temperature the closing-tubes could be readily entered.
It should be understood that during the erection thus far little reference was had to correctness of line or elevation of the semi-ribs. All the parts had been accurately made, and during the erection care was taken to fit the joints perfectly. It must not be supposed, however, that all joints were perfect, and that any subsequent change in position depended upon elasticity alone. Some ribs were unaccountably flexible, while others were very stiff. Mr. Cooper mentions the important fact, that the first ribs were built low, — i.e., the cable
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strains during the erection were insufficient to keep the ribs at their proper height, — and that it was found later that in raising them they had to use strains much greater than would have been necessary to equilibrate the same had they been kept at their correct elevation during erection.Although the Keystone Bridge Company had contracted to erect the Bridge, and for nearly two years had been endeavoring to find the most practicable plan for closing the arches, they had not been able to solve the problem to their satisfaction; finally,
Several days were spent putting in and adjusting diagonals between the ribs B and C, so as to draw them into correct line, and in riveting the main-braces to prepare them for the work of compression in a completed rib.
The tubes, as well as all other pieces of the Bridge, were painted on all sides before they left the shops of the Keystone Bridge Company. But it was also necessary that the interior of the tubes, and especially their joints, should be thoroughly painted after the tubes were in place. This was done as follows: —
A spindle-shaped vessel, small enough to pass freely inside the tubes beneath the steel pins, perforated on the top and sides with fine holes, ballasted with lead and set upon rollers, was connected by a universal joint to a gas-pipe which was put together in 12-feet lengths. This apparatus was prepared and put in use within twenty-four hours. It was first sent down the whole length of a semi-rib, joint by joint, until it reached the skew-back. Thin asphaltum varnish was then forced down the pipe and through the holes of the spindle upon the interior of the skew-back tube, and the steady spray of varnish was maintained as the spindle was slowly withdrawn. The surplus varnish ran down the interior and completely filled the skew-back tube, whence it worked its way into every crack and crevice around the bed-plate and the anchor-bolts and nuts. In place of the spindle mounted on rollers, a simple gas-pipe with numerous small holes was afterwards found to be equally efficient and less clumsy. This plan worked readily when the weather was warm enough to keep the varnish thin, and was so satisfactory that it was used for all the arches.
In order to better understand the problem of closing an arch, let us consider the situation. The "normal arch" was the position of a rib under its full permanent load, and at
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a temperature of 60° Fahrenheit. Moreover, each tube had been made about one-sixteenth of an inch longer than its normal length, to provide for its compression. During the erection there was very little load to be supported compared with the weight of the finished Bridge, and that little was carried almost entirely by the upper tubes, which were under compression, and by the suspension cables. The lower members were under very little compression; hence all the tubes were abnormally long, particularly those in the lower members.Fig. 29. —
Fig. 29 gives a skeleton plan and elevation of the erected portion of the western span at this date. The inner ribs lacked two tubes and five braces each. Cables to joints 3, 9, and 15, shown by dotted lines, had long since been removed, and the long semi-ribs were supported by the cables shown by full lines. The strains on the cables at this time were as follows: —
No. 6 cables 65 tons, or 5 tons per square inch.
No. 12 (main) cables 176 4 1/5
No. 18 (secondary) cables 73 3 1/3
The space found by Mr. Cooper on the 6th, when the temperature was 60° (only 0.54 of an inch less than the length of the closing-tube), was therefore greater than was to have been expected from the unloaded state of the rib. The deficiency should have been at least three inches. Evidently there was some mistake in the calculated length of the span (502.075 feet), which was the basis of the construction. This view is supported by subsequent measurements. (See Chapter XVI.) Whatever may have been the cause of the discrepancy, the fact was that the immediate difficulties in the way of closing the ribs were less than had been anticipated.
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The position of the ends of the semi-ribs depended greatly on the temperature. No mercurial column more certainly indicated fluctuations in temperature than did the steel arches of the Bridge. Their ends rose and fell, approached and receded, with increased heat and cold; while, under the direct rays of the sun the southern half-ribs expanded so much more than the northern ones (which were somewhat protected by scaffoldings, etc.) that both ends moved towards the north.
September 12. — The arches having been drawn into correct line by adjustments of diagonals, an effort was made to get the proper elevation. Col. Flad directed Mr. Cooper to slack No. 6 cables and increase the strain on main and secondary cables. The day was wet, with a prospect of a cold night, and Mr. Cooper was anxious to bring up the western half-ribs before night. Men were wanting, however, and not much was gained. Mr. Katte was still in charge of the work, and he was unwilling to add much to the cable strains.
September 13. — Col. Flad, as acting chief engineer, assumed the responsibility of increasing the cable strains so as to bring up the western semi-ribs, and of closing the arches. The strain on each main cable on the west side was increased from 176 tons to 181.6 tons, raising the endsË an inch. No. 6 cables were slacked entirely off the inner ribs, and the ends of the semi-arches rose two inches. In the course of an hour, however, the free ends of the arches sunk two inches automatically, the cable strains remaining the same. Cable 18 was then tightened up with little effect, and the strain was increased on the main cables to 198.4 tons, but the gain was only 7/8 of an inch. The ribs were very stiff, and as the cable strains were very nearly sufficient to support the entire weight of the ribs,
September 14 (Sunday). — The men were ordered to come as usual, as all the adjustments were to be completed on that day, that the arch might be closed on Monday. The morning was very cool, — 44° at 6:30 A. M. Mr. Cooper was at the Bridge at 6:15; he found that there was one-fourth of an inch to spare between lower tubes, and three-eighths of an inch between upper tubes. Moreover, the western ends had risen during the night, and were then only 3Ë inches too low.
When these facts were reported to Col. Flad at 7 o'clock, he resolved to improve the opportunity and if possible close the arches at once. He knew that if he could properly enter the lower tubes, the rising temperature would increase the openings in the upper members (by the rising of the crowns of the arches), and the upper tubes could be inserted
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easily. Mr. Cooper thought that the lower tubes could be entered, and then the eastern semi-ribs (which were readily raised and lowered) brought gradually down to a correct relative height.When it was known among the workmen that the tubes could be entered, and that Col. Flad had decided to close the arch, the greatest enthusiasm prevailed. The tubes (which, unfortunately, had not been hoisted) were brought out and raised with all speed. From a plank spanning the gap Col. Flad anxiously awaited their arrival, for the sun was shining brightly, gradually but surely reducing the tube spaces. The north lower tube entered without difficulty; the south one would only enter partway, on account of the unequal elevation of the semi-arches. The strain on the abutment cables was increased as far as was permissible; the rib seemed inflexible. Sledges were of no avail. Mr. Cooper found it impossible to make the connections properly, so he took the tubes out again. Little time was to be lost. Had one got caught by the expanding arch, the consequences might have been serious. "I was glad enough," said Col. Flad, "to see them both safely out again."
During the day the other two tubes were hoisted up to the balance-beams, and all preparations made for the morrow. On the western side, diagonal rods were slacked, relieving the interior ribs from the weight of the eleven sections of the outer ribs; more strain was put on the secondary cables (to eighteenth joint), in order to compress the upper tubes and slightly raise the extreme points. Very little was gained, however, in this particular way. Two more "weights" were also added to the "balance-gauge," increasing the lifting power of the hydraulic jacks under the cable towers on the West Abutment: each "weight" increased the tension in the main cables 2.83 tons. This additional pressure gave a total strain in each cable of about 198 tons.
Monday, September 15. — "All hands out at 5 A. M. Temperature, 52°. Space too small (being of an inch short on lower tubes). Put 6 tons additional strain (total, 204 tons) on west main-cables, in order to raise the ribs, but without benefit. Then lowered pier towers to get the arches to proper level with reference to each other. — [Mr. Cooper's Diary.
While the eastern half-arches were being lowered, Mr. Cooper tried the experiment of putting some wooden struts between the ends of the upper tubes, to see what effect they would have on the lower openings. The unstable nature of the device seemed to involve too much risk, however, and the struts were removed. The pressure was light, and yet on their removal the lower space was shortened 1/8 of an inch.
The central tubes of the two side-spans were to be very nearly alike, and one set had been already made by the Keystone Bridge Company. When Mr. Linville gave notice that he would not undertake the insertion of the central tubes, Mr. Eads immediately undertook the solution of the problem himself. He had duplicates of those for the west span altered according to a design of his own, so that the tubes could be shortened before insertion and extended to their normal length again after they were entered in the arch. Each tube was cut in two, and about five inches of its length taken out. Screw-threads were then cut on the interior of the staves on both sides of the section, the threads being right-handed on one side and left-handed on the other. Wide wrought-iron bands were shrunk over the ends of the tube-staves on each side of the opening. A wrought-iron ring or thick cylinder was made, with right and left threads on its extremities to fit those in the segments of the
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tube. All the details of one of these "adjustable tubes" is shown in Plate XXXVIII. Six holes in the interior screw received the levers by means of which it was to be turned, shortening the tube before insertion in the arch and lengthening it afterwards. Mr. Eads was willing that the experiment of trying to insert the original tubes should be tried, by straining the cables if necessary to 12,000 pounds per square inch of their section, inasmuch as plain tubes were cheaper than the others, though he had little faith in the success of the attempt.Col. Flad held different views on this point, and was very sanguine of his ability to insert plain tubes. The order for the manufacture of the closing-tubes of the other spans was delayed till the result of the trial should be known.
The trial of the 14th had convinced Col. Flad that the regular tubes could be used, and he felt perfectly sure that by waiting a few days for low temperature, they could easily be inserted. But the immediate outlook was unfavorable. For several days the temperature, especially at night, had been quite cool; it now became very warm, with no prospect of change.
Some of the Directors of the Company were much disappointed at the failure of the first attempt to close the arch; and as the loan of half a million dollars effected by Mr. Eads in London depended upon the closing of the first span by September 19, Col. Flad had no time to lose; nevertheless he determined to make one more effort to use the plain tubes, not wishing to resort to the adjustable tubes until all chances for inserting the others had been tried. He believed that he had failed on the 14th from his inability to keep the temperature of the tubes down to 44°. He thought this could be done by ice. In the execution of his plan, all the tubes of these inner ribs, over both halves of the span, were wrapped with gunny-cloth. Boards, on edge, were placed between the brace-bars on the sides of the tubes, thus forming continuous troughs, in which ice was placed. The water from the melting ice saturated the cloth, so that the latter served the double purpose of protecting the tubes from the warm wind and the direct heat of the sun, and of facilitating the cooling by promoting evaporation.
The ice (fifteen tons) arrived about 9:30 P. M., Monday, September 15, but the troughs were not ready until 2 o'clock next morning. The gunny-cloth was then wet down with water pumped from the river, and the ice put in as fast as possible. So few men were furnished by the Keystone Bridge Company that they could not keep the tubes covered with ice, and as the wetting by river-water was thought to be of advantage it was continued. The day had been quite warm, — about 80° in the shade. Col. Flad reports the temperature as being "98° in the shade at 5 P. M." At sundown, the space wanting between lower tubes had been 2ź inches; at sunrise on the 16th it still lacked 5/8 of an inch, — "having had a very warm night of it." The ice and wetting down with ice-water was applied all day. At sundown the space lacked 1 1/8 inches. At 11:30 P. M. the deficiency wasž of an inch, and it remained at that point till morning. A warm southerly wind prevailed all night. During the day and night some forty-five more tons of ice had been used.
On the morning of the 17th, there being no prospect of a change to cooler weather within the time to which he was limited (namely, the 19th), Col. Flad gave the order to use the extensible tubes.
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Their insertion was effected with very little difficulty. The two lower ones were first entered, and one end of each was connected by means of its coupling and steel pin. The S tube pinched, in consequence of the interior screw-threads not being cut far enough. It could be shortened only aboutË inches below the "normal" length. Before the other ends could be connected it was necessary, by means of links and clamps, to draw the tubes into correct line with the projecting tubes of the opposing ribs. The steel pins belonging to these joints were then placed in the pin-holes of the tubes; they served to hold the tube ends in line vertically, and clamps kept them from moving horizontally. The bearing faces were then brought together by means of the adjustable screws and a slight lowering of the eastern ribs. The couplings were next entered upon the grooves of the tubes, and the connection of the lower members completed. Having, by means of the tubular stays and tension-rods, secured the lower members against any tendency to buckle horizontally, Mr. Cooper watched the arch carefully all day to see if the upper space would be increased when the rising temperature should expand the arch and bring compression on the lower tubes. The space increased, however, only 1/8 of an inch, and at 4 P. M. Mr. Cooper commenced to raise the upper adjustable tubes. It is evident that Col. Flad had still hoped to use plain tubes in the upper members. In view of the fact that the opening between upper tubes increased 1/8 of an inch instead of closing 1Ë inches during the day, as had been usual, we see that the action of the lower members affected the upper to the amount of 1 5/8 inches. The upper tubes were entered in the same manner as the lower. The braces connecting the upper and lower members were all put on, excepting one set; the last brace on each rib could not be put in place until the adjustable tubes were screwed out to proper lengths. At 10 o'clock P. M., September 17, two ribs of the first arch were successfully closed.
The next morning the following telegram was sent to Mr. Eads in London: "Arch safely closed. Last tube at 9 yesterday. Flad."
This dispatch was opened by Mr. Morgan in London and forwarded to Mr. Eads, who had gone to Paris. The English capitalists had not been free from considerable anxiety in regard to the novel and delicate operation of closing an arch, especially since Mr. Linville had so emphatically declared the unwillingness of his company to assume any responsibility attaching to the insertion of the closing-tubes. Mr. Eads promptly responded that his chief pleasure at the receipt of the news was in the knowledge that the anxiety of his friends was removed. As for himself, he assured them that each of the other arches would be completed without the possibility of disaster; that his plans were so perfectly matured and every point so guarded that failure was impossible that little causes might occur to create unexpected delays, but he felt as comfortable about the safety of the operation and its certain accomplishment as a banker did when he knew he had an abundance in his vaults to meet every demand that could be made on his house. In a letter congratulating Col. Flad, after referring to the above response to Mr. Morgan's note, Mr. Eads adds:
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"I think good engineering will always give us this kind of feeling, and that disasters and serious accidents are always an evidence of bad engineering."Various plans had been suggested for artificially increasing the arch-openings on the very contingency which actually happened.
To attempt to force the ends of the ribs apart by direct thrust was deemed unsafe, if not impracticable.
Another method of reducing the temperature of the tubes had been suggested by Col. Flad. It was to discharge a stream of compressed air into each skew-back tube. It was thought that the expanding air, as it flowed along the connected tubes, would extract so much heat from the steel that the desired contraction would readily be produced.
When the suggestion was made to Mr. Eads by Col. Flad to insert the tubes by cooling the semi-arches, he expressed his disbelief in its success, because of the impracticability of cooling at the same time the extensive system of main-bracing; and hence he thought that the brace-bars would supply heat to the tubes almost as fast as the ice could cool them. He was likewise in doubt as to the practicability of inserting the plain tubes, even if the cables could spring the segments of the arch far enough, apart, owing to the fact that four pairs of braces would have to remain unsecured to their respective pins until all their central tubes were in place; and if the lower tubes fitted exactly, the upper ones would not do so, and hence the lower couplings only could be put on. The upper tubes could subsequently be brought together only by loading the arch, or by a very low temperature.
On all points, however, the adjustable tubes left nothing to be desired. Mr. Eads knew that under all circumstances they could be readily inserted, as they could be adjusted to the exact length required, and all but the free ends of one pair of braces on each rib could immediately be put on; and he anticipated no serious difficulty in finally screwing out the tubes to their proper lengths.
The current interest in the problem of closing the arches was very great. All engineers admitted that under certain conditions of temperature and strains it would be possible to enter a closing-tube of the full calculated length, but the difficulty lay in the realization of those conditions. There was no serious difficulty in bringing the ends of the half-ribs into correct line and elevation by means of the suspension cables and the lateral bracing, but beyond that point the engineer's power over the rib was small. Temperature was evidently the most important factor in the problem, and under the circumstances it was largely beyond human control. Let us examine the subject a little in detail.
Steel at ordinary temperatures, and between moderate limits, expands or contracts about 0.0000066 of its length for a change in temperature of 1° Fahrenheit. An entire rib of 502 feet span would therefore contract horizontally 0.0398 of an inch for each degree in the reduction of its mean temperature.
A change of 50° between a cool September morning and the direct heat of the afternoon sun reduced the openings for the last tubes two inches.
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From Mr. Cooper's record we can compute approximately the effect of Col. Flad's "ice poultice." From the facts already given, and from the record of maximum and minimum temperatures carefully kept by Dr. A. Wislizenus at his residence in the city of St. Louis, I have prepared the following table for the greater convenience in comparing figures. The last five temperatures in the last column are calculated from the spaces for the closing-tubes at the rate of 1° for 0".0398, assuming that the mean temperature of the ribs at 5 A. M. September 14 was 44°, and allowing Ë of an inch as the effect of lowering the extremities of the eastern semi-arches on the 15th.
| Date — 1873. | Temperature (Cooper). | Temperature (Wislizenus). | Condition of tubes. | Deficiency of opening. | Indicated temperature of tubes. |
| Sept. 14. — 5 A. M. | 44° | 45°.0 | Uncovered. | +ź inch. | 44° |
| 15. — Sunrise | 53° | 51°.5 | " | + 1/16 " | 53° |
| 15. — Sunset | 80° | 82°.0 | " | + 2ź inch. | 95° |
| 16. — Sunrise | "warm." | 57°.0 | Under ice. | + 5/8 " | 54° |
| 16. — Sunset | "hot day." | 79°.5 | " | + 1 1/8 " | 67° |
| 16. — 11:30 P. M | "warm south | — | " | +ž " | 57° |
| 17. — Sunrise | " | 62°.0 | " | +ž " | 57° |
From these figures it appears that while the temperature of the atmosphere fell 25° between sunset on the 15th and sunrise on the 16th, the temperature of the tubes fell 41°, — i.e., from a point 13° higher than the shade temperature by day to a point 3° lower than the minimum air-temperature at night.
Again, while on the 16th the temperature of the air rose 22°.5, the temperature of the tubes rose only 13°.
As was to be expected, the ice was much more efficient by day than at night. A comparison of the sunset temperatures of the tubes on the 15th and the 16th shows that the day effect was a reduction of about 28°, while the night effect was very much less, — according to the table, not more than 5°. This last result is so small that I am led to believe that the night temperature of the air blowing along the surface of the river (in which the water had at the time a temperature of 72°
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hours, less than sixty pounds of ice per foot of tube were used. The influence of the main-brace bars, as pointed out by Mr. Eads, is evident from the fact that in spite of the ice application the temperature of the tubes rose 13° during the day. It would be the height of extravagance to say that the tubes were "packed in ice."Had they really been so packed, the result would have been different. As it was, nothing useful was gained, and nothing would have been gained by continuing the application indefinitely.
I find in Mr. Cooper's published paper on the erection a statement that the first adjustable tubes could be shortened but 1Ë inches, — i.e.,ž of an inch on each end of the screw, — so that even they could not have been entered on the 17th, "after the effects of the ice had disappeared." It is obvious that they could not have been entered in the heat of the day, for the lack of space would have exceeded 1Ë inches; but, on the other hand, there can be no question as to the possibility of inserting the adjustable tubes on the morning of either September 14, 15, 16, or 17, the ribs being uncovered.
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Chapter XVI. Erection Continued — Closing of Center and Eastern Spans.
When the closing-tubes of Span I were inserted, the openings were less than the calculated length by about three-fourths of an inch. The expanding screws fitted snugly, and required a moderate power to turn them, even without pressure against the threads. When under either compression or tension it became very difficult to move them. The main brace crossing the panel of the last section in each rib could, of course, not be put on until the tubes were screwed out to their proper length. The tension on the cables was therefore maintained, with a view to take up the thrust of the arch, and gangs of men were set to watch by night to take advantage of the contraction produced by a lowering of the temperature. The tubes were liable to both tension and compression, according to the temperature and their position. Only when the stress was zero could the screw be moved by simple hand-levers. Hence a constant torsion strain was kept on each of the screws by means of ropes from four "crabs" to the steel levers. On the 22d, measurements from pin to pin across the closing panels showed that the required length between pins had been reached, and on the morning of September 23 the remaining braces were put on.
Riveters were immediately set to work, and all the bracing of these inner ribs was soon complete. Only ten or eleven sections had been as yet erected on the semi-arches of the outer ribs of this span. As soon as the inner ribs were closed, work on the outer ones was resumed (September 19). Their only support thus far had been the cables to the sixth joints; new sections were to be supported by the inner ribs. The horizontal tubular struts, and the diagonal suspension-rods from the lower outer to the upper inner tubes, were amply sufficient to support these unfinished ribs in their proper positions. These suspension-rods were not all permanent parts of the arch; the spaces near the center of the span between the ribs A and B on the south and C and D on the north were to be kept free for the lower (steam) road-ways. Hence, diagonal rods designed for the other spans were borrowed to erect the outer ribs of Span I through these spaces. It was necessary, however, to furnish them with clamps or straps enclosing the tubes.
October 4, a line stretched from the centers of pin-holes in the outer ribs at the fifteenth joint showed that the outer ribs projected one-half an inch beyond the corresponding joints in the inner ribs. This was due, undoubtedly, to the compressive effect of the cables and the combined weight of the ribs.
By October 15, the ribs A and D lacked only the four closing-tubes.
The four adjustable tubes were ready for erection October 20, and were readily entered
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on the 21st and 22d. The openings were considerably short, and the upper tubes were shortened quite to their limit. Meanwhile, a capital improvement in the order of erection consisted in the omission of one coupling for each closing-tube. The pins were inserted and the uncoupled ends were secured laterally. The advantage of this arrangement was that when the upper or the lower member opened a trifle, as the temperature rose or fell, the tube could be screwed out with perfect ease.Measurements of spaces for closing-tubes, taken October 22, showed as follows: —
Rib A, upper tube 144.06 inches.
Calculated normal space 147.29 inches.
44.72
Rib A, lower tube 143.136
Calculated normal space 144.92
143.158
The night of October 22 was very cold; in the morning, openings were found at the uncoupled ends of all the tubes, which were immediately closed by screwing out the tubes. As the temperature rose, the crown of the arch rose, bringing an increased compression upon the lower tubes, and then the upper tubes showed a separation allowing those tubes to be still further screwed out. As the temperature fell at night, the crown of the arch fell, and the upper tubes, being a little longer than previously, took all the compression, and the lower ones opened. In this way a little was gained with every marked change of temperature. Nothing, however, was more obvious than the impossibility of forcing the semi-arches apart by means of the screws with the apparatus then in use. Steel bars four or five feet long were inserted in the six holes of the screws and connected at their outer ends, forming a sort of wheel; a rope from the drum of the lifting apparatus of a crab passed over a pulley on the end of a balance-beam to the circumference of this wheel of bars. Four men at the crab could easily exert all the force the bars could withstand in fact, many steel bars were broken by overstrain. The necessity for some improvement in the screwing apparatus led to the construction of an efficient wrench. This wrench is shown in Fig. 30. It was made of railroad iron, and resembled in form an elongated letter A. Each foot was fitted with a T-shaped nipper, sufficiently narrow to enter the opening between the bands of the tubes. This wrench was about seven feet long, and acted by direct shearing-strain upon the steel pin passing through the screw and projecting sufficiently at each side for the nippers to catch it. With the use of this wrench the power of six men on a double-geared crab could be transmitted through a six-ply purchase to the end of the wrench. Three of these
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wrenches were broken, two by tearing apart the tension side (of the rail bar) and one by an inclined shearing of the compression side. The fourth one was strengthened on both sides y the addition of a six-inch channel-bar riveted to the foot of the rail.On November 12, Mr. Cooper tried to screw out the lower tube of rib C, but he could not start it with all the power of the wrench. This rib was fully connected by couplings, braces, etc., and success depended upon his hitting the proper moment when the temperature was changing the strains from compression to tension, or vice versa.
The slow progress made in screwing out the outer ribs of the first span will be seen by comparing the length of the tubes October 22, as already given, with their length November 13. On the latter date they had gained, —
Rib A, upper tube 0.81 inches; lower 0.864 inches.
" D, " " — 0.61" " — 0.962 "
Meanwhile, the strain on the main and secondary cables of the west half of Span I was diminished, and on November 15 the secondary cables on that side were disconnected; this threw a part of the thrust of the semi-arch against the structure of the West Pier.
Mr. Cooper wrote December 10 (the men had been so busy on other portions of the Bridge that they could hardly attend to the matter earlier): On Span I, had a gang engaged screwing out adjustables; succeeded, by means of a double-geared crab with five men and a double set of triple blocks, in gaining 1 1/32 inch on D upper tube." Three days later the upper A. tube was screwed out five-sixths of an inch, and then the wrench broke.
On the 15th the wrench had been repaired, and the gang of painters (who were also the wrench-men) had brought the repaired wrench to the center of the arch, when one of the men by some mishap lost his footing and fell from that dizzy height into the river below. The man was recovered with but slight injuries. In the excitement of the moment the wrench fell into the river and was lost.
By March, the spaces around the screws and between the ends of the staves were filled by segments of steel rings. The width of these rings shows the final adjustments.
Upper A had been screwed out 2 1/8 inches, leaving it short of the drawing length 1.1 inches.
Upper B had been screwed out 7/16 inches, leaving it short of the drawing length inches.
Upper C had been screwed out 7/16 inches, leaving it short of the drawing length inches.
Upper D had been screwed out 1ž inches, leaving it short of the drawing length inches.
Lower A had been screwed out 1 1/16 inches, leaving it short of the drawing length inches.
Lower B had been screwed out 7/16 inches, leaving it short of the drawing length inches.
Lower C had been screwed out 1/11 inches, leaving it short of the drawing length inches.
Lower D had been screwed out 1ž inches, leaving it short of the drawing length inches.
These results were deemed on the whole satisfactory, and the ribs of the first span were finished.
We see that all the upper closing-tubes of Span I are about an inch short, while the shortage on the lower tubes averages about half an inch; but as the bracing between ribs was adjusted accordingly, and as the ribs themselves when finished had no abnormal strains on them, we may feel certain that the ideal arches were approximately realized. While the inner ribs of Span I were being erected and closed, preparations were making for the rapid erection of the remaining half of the Bridge. On August 7, the sixteen skew-tubes
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backs of the East Pier were all in place, and the eight skew-backs of the East Abutment were in position just a week later. The last one was not satisfactorily adjusted till October 6. Filling-plates were required in several cases, and some of the skew-backs were removed several times.Under the agreement of August 25, the Keystone Company had largely increased its force of men, but in many cases there was lack of material. By the middle of October they were at work raising tubes, braces, etc., at four points. Besides the work on Span I, as already described, there was a gang on each side of the East Pier and one at the East Abutment.
On October 24, seven tubes of the eighth section from the East Abutment were raised. As yet these ribs were not supported by cables; that is, the braced ribs supported themselves from the skew-backs while projecting nearly 100 feet. It is obvious that all parties had great confidence in the wrought-iron couplings of the upper members. The want of cables at the proper time, and of men to erect them, prevented any more erection on that end of the span for five days. On the 25th of October, as the cables (3 and 6) for the East Abutment had not arrived, the No. 6 cables of the West Abutment were slacked off and removed to the East Abutment. On the 30th of October, twelve tubes were erected on three ribs from the East Abutment. This shows the rapidity with which, under favorable circumstances, the arches were raised. During the month of October, two hundred and forty tubes were erected, as follows: Span I, 67 tubes; Span II, 46 tubes; Span III, 127 tubes. Mr. Eads reached St. Louis, on his return from Europe, during the last week in October. By November 20, the hydraulic jacks, towers, etc., were all in position both at the East Pier and the Abutment, and everything was waiting for the No. 12 cables. The anchorage in the East Approach had cost much time and labor, and was at last ready. On the 25th, the No. 12 cables were connected with the ribs on each side of the East Pier.
"November 28. — Finished balance-gauges at [East] Pier this forenoon, and this afternoon put main cables under proper strain for present condition of arches. This raised the towers 4 inches.
November 29. — At East Pier raised sixteen tubes (15th and 16th sections of inner ribs on each side of pier).
November 30 (Sunday). — A gang of men employed all day at East Abutment straining cables. Raised towers 2ź inches, giving cables proper strain for present load." — [Inspector's Record.
In Mr. Cooper's "log" for the 2d of December, I find the following interesting entry: "The inspector (present writer) tripped on an unbalanced plank, on outside of joint 30, rib G, Span III, at 11 A. M., and fell to the river below, a distance measured this afternoon and found to be 90 feet. Escaped uninjured, excepting a stiffness resulting from the shock."
The above is all that Mr. Cooper wrote on that subject. The "daily record" continues, however, in spite of that fearful fall. The only further reference to the effect of his bath was a parenthesis thrown in a few days later: "(I was not on work to-day, being too stiff in joints.)" This absence was on a wet, snowy day, when everything was covered with ice. It was the only day Mr. Cooper lost from personal supervision of the erection. He afterwards gave me a full account of his experience while falling and in the water.
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He was conscious (he said) of its taking him a long time to fall 90 feet. He thought of the probable force with which he would strike the water, and rolled himself into the shape of a ball as much as possible. He struck the water he hardly knew how, and went very deep into the river, — nearly to the bottom, he thought. After what seemed another long interval, he reached the surface and struck out vigorously for the shore. He then found that he still held in his hand the lead-pencil which he was using when he stepped on the treacherous plank. A boat from the East Abutment soon picked him tip. In an incredibly short time he changed his clothes and walked into the office of the company as though nothing had happened.
"December 6. — Snowing this forenoon, and a sleet falling this afternoon. At East Pier raised sixteen tubes, 18th and 19th sections of inner ribs at each side of pier. At East Abutment, finished straining cables to joint 15 this forenoon. Erected four tubes (17th section) this afternoon. Found it necessary to use salt on planking to clear ice formed by the falling sleet. The ropes were also very stiff from ice. The sleet likewise filled the grooves of the tubes and couplings so as to delay making connections until it could be cleared out."
It was thought the better plan to paint the interior of the tubes, a few sections at a time, as opportunity occurred, while the cables were being adjusted. Hence, a gang of painters was kept continually busy going from rib to rib. By this plan advantage could be taken of favorable weather, and there was little chance that the closing of the arches would be delayed by the necessity of painting in severe weather.
On December 9, the opening in the center span was reduced to a length of three tubes, top and bottom and Span III lacked but one tube at the top and two at the bottom. The openings were spanned by timbers, and a foot-passage established over the whole Bridge.
So rapid had been the process of erection, compared with former work on the Bridge, that to the thousands of spectators who daily flocked to the river's edge to see the work in progress, it was a continual wonder and surprise.
Nothing could be more striking and full of interest than the sight of the East Pier and its novel load of towers, cables, and semi-arches, stretching far out over the dark torrent of the Mississippi on either hand. The visible portion of the pier itself was about 115 feet high; the towers rose to an additional height of over 50 feet; the semi-arches, like the wings of a mighty bird, stretched over the water, embracing between extreme points a reach of over 500 feet, and all with no other support than the pier of masonry, less than 40 feet in thickness as it rose from the water. From numerous photographs taken at the time, I have selected Plate XLII to illustrate this stage of the erection.
On the morning of the 13th of December, the last of the ordinary tubes were erected on the inner ribs of these spans, bringing the ends of the semi-arches within one tube-length of each other. The remainder of that day was employed in putting in such tube-stays and tension-rods as were on hand, preparatory to bringing the arches into a true line. The level and line of both spans were determined, with the following results: —
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Center Span. — The two semi-arches were approximately at the same level, each being a little above the normal line of the finished arch. The western half was correct as to line. The eastern half curved slightly to the south, commencing to bend at the fifth joint from the East Pier, and attained a maximum deflection of 1ź inches at the extremity.Span III. — The semi-arches of this span were relatively out of level 1 foot, measured at the extreme points, the western half being 5 inches above the normal line, and the eastern half 7 inches below same line. The western semi-arch curved to the north, commencing at the sixth joint from the East Pier, and reached a maximum deflection of 3Ë inches at the extremity. The eastern semi-arch commenced bending towards the north at the fifth joint from East Abutment, attaining the maximum northerly deflection of 1Ë inches at the eleventh joint; it then reversed the curve and bent south, crossing the right line at the eighteenth joint, and at the extremity of the semi-arch wasž of an inch south of the true line.
Sunday, December 14, was occupied in drawing the lower members of both spans into line by means of the tension-rods. The strain on the eighteenth and the main cables of the eastern half of Span III was increased, raising that semi-arch 4 inches, measured at joint 18.
As soon as the arches were approximately in line, the spaces between the extremities of the semi-arches were measured, and also the minimum lengths of the adjustable tubes. It was found that the spaces in the center span (measured at a temperature of 34° Fahr.) were in excess of the minimum lengths of the adjustable tubes for these spaces by one and a half or two inches. The spaces in Span III were by no means favorable, as they were two or three inches less than the calculated lengths of these tubes, and too short for even the adjustable tubes.
The tubes were therefore cut down an inch or two. During the 15th the alignment of the upper members of the ribs was completed, and the internal painting of all the tubes of these inner ribs was finished.
The eastern half of Span III being too low, the No. 18 cables were tightened till joints 18 rose 2 inches. They were still 2 inches too low, and joints 12 were 3 inches too low. As it required time for any additional strain put upon these cables to distribute itself throughout the number of joints in the arches, it was deemed a necessary
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caution to raise this semi-arch only a little at a time, so as not to throw a great and sudden strain upon any one point of the arch, cables, or anchorage.December 16. — All preparations being completed, the final connection of the inner ribs of the center span was made without difficulty; the arches expanded very rapidly from the extremely warm weather, and it was necessary to screw in the tubes to their minimum lengths. To bring the ends of the semi-arches to the same level, the towers on the West Pier were slightly lowered. The tubes were permanently connected at one end by means of the couplings, pins, and braces, while at the other end they were secured in line and pins only were entered. As the central tubular stays had not arrived, temporary wooden struts and tie-rods were used between the ribs. During the day the eastern half of Span III was raised to the normal line by increasing the strains in the main cables.
December 17. — This morning the adjustable tubes of center span were extendedž of an inch, the ribs having contracted that amount during the night. The eastern half of Span III was raised 2 inches above the normal line. The closing-tubes, cut down as above stated, were screwed together preparatory to raising. Mr. Cooper found that, as the day was very warm, the distances were still too short, though he would have had about f of an inch clearance had the temperature remained at 34° Fahrenheit. At noon Mr. Cooper received from Mr. Eads positive orders
The work of connecting the other ends commenced by drawing the tubes into exact
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line and entering the steel pins. The B rib was connected without much difficulty, by 4:30 A. M. The western half of rib C was about two inches higher than the eastern, and the main cable over the East Pier was slacked to bring this semi-rib to proper level, and the connection was completed within the time specified.It will be observed that there was a striking analogy between the conditions of the ribs of Spans I and III when the erections had reached the points of inserting the closing-tubes, while there was a wide contrast in the subsequent treatments and the results. In each case the pier portions were above the normal line, while the abutment portions were several inches below it, the difference being about twelve inches. In each case there was an error in the length of the span, Span I being at least two inches longer than was expected, and Span III being fully three inches less than the drawing length. In each the abutment semi-ribs were "stubborn," yielding slowly and with difficulty to increased cable-strains. In Span I, Col. Flad was unwilling to impose more than 204 tons tension on the main cables, and consequently he closed the ribs with their crowns several inches below the normal line of the arch. In Span III, however, the cables on the East Abutment were strained to 216 tons, thus raising the ribs 2 inches above the normal, at which point they were closed.
The result is, that the arches of Span III are where they should be, while those of Span I are too low.
Nothing, however, could have been more simple than the closing of the arches of the center (the longest) span. Slight differences in the positions of the semi-arches were readily corrected by means of the cables and the lateral diagonals, and the openings for final tubes were found to be just what had been calculated. All four tubes were satisfactorily entered and screwed out to bearing in a single forenoon, and no difficulty was experienced afterwards in screwing them out to their full drawing lengths.
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Chapter XVII. The Completion of the Bridge.
The closing of the inner ribs of the central and eastern spans completed the solution of the great engineering problems connected with the Bridge. It was comparatively simple work to finish the outer ribs and build the road-ways.
The winter of 1873-4 was a severe one, yet the work of erection went on with little interruption. Occasionally, snow, ice, or extreme cold stopped the work. At such times watchmen were kept on duty to see that the hydraulic rams did not spring a leak or become in any way deranged; that the contraction of the cables did not bring undue strain upon them, and to allow the towers to descend slowly as might be necessary. Blocks were ordered to be kept within half an inch of the base of a tower, so as to check the motion of the tower should the hydrostatic pressure be accidentally lowered. On one occasion, as the weather was rapidly changing to severe cold, Col. Flad sent a man to the towers to warn the watchmen that they should see that the towers did not get caught on the blocking. In a few moments the messenger returned in hot haste, with the report that one of the towers had fallen so rapidly that it had caught the blocking with a great and increasing pressure. No a moment was to be lost. Col. Flad made all haste to the tower, and ordered the blocks to be cut out with axes with all speed. In ten minutes the tower was free and the danger was over.
The contraction of the arch was accompanied by a corresponding contraction of the cables, but by no sensible contraction of the masonry of the pier and the wooden towers. With an unyielding tower the result would be a bending up of the end of the rib, with a tendency to increase the angle of elevation at the springing of the arch. The automatic motion of the tower, however, when unchecked by the blocks, gave just the contraction to the tower required to preserve the uniform action of the cables on the arch. (See also Chapter XV, p. 164.)
Mr. Cooper's record shows that special pains were taken to give a better support to the outer ribs of Spans II and III than was done at Span I, with a view to facilitate the screwing out of the last tubes. As a new feature, "supplementary" cables connected the tops of the masts which stood upon the twelfth joints of the inner ribs with the twelfth joints of the outer ribs. By this means the weight of the outer ribs was quite directly transferred to the main cables.
On January 3, the wind was so furious that it was dangerous to go upon the arches. The "Hewitt" (steam tug) was unable to bring in an empty barge anchored under the arches. In spite of the wind, however, three tubes were raised on Span III. To prevent delay by heavy ice, which might interfere with the movements of the barges
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containing tubes and braces, all the material to be used in closing the ribs was raised and stowed on skids placed across the inner ribs. Rib D of the center span was closed January 12. The next day the adjustable tubes of this rib were screwed out to their full length, and the last couplings were put on. It had already been found that the outer ribs could readily be relieved of all compressive strain at the crown by lifting them by the diagonals attached to the inner ribs; hence, by alternating the use of the wrench on the screws with the tightening up of the suspension-rods, the adjustable tubes were soon extended to full length. The error in the length of the adjustable tubes of the inner ribs of Span III was of course repeated in those for the outer ribs, for all were ordered at the same time. Careful measurements showed that they were too long by about four inches. All were, therefore, shortened by that amount, each of the segments of a tube being cut off at its screw end, the larger amount from the short end.On the 16th, rib A of Span III was closed, and on the 19th the last rib of the center span was finished.
Mr. Cooper's diary of January 19 contains this startling record: —
"At 4 P. M. one of the men reported a broken tube at Span I, lower joint, O 18, in tube 18-19. I examined, and found it true; the staves were ruptured through the first groove near the wrought-iron band; coupling apparently intact: I also found B 20 broken in lower tube 19-20. Ordered these tubes stayed as soon as possible, to keep them in line, and also ordered suspension clamps from outer ribs to take center weight of these ribs; but could get no rods, as all are in use on Spans II and III."
Mr. Eads was at the time in New York, and Col. Mad was sick in bed. By direction of the latter, Mr. Cooper immediately telegraphed these facts to Mr. Eads and asked instructions. The dispatch reached Mr. Eads at 11 o'clock at night, just as he was retiring to bed. Its effect upon him for an instant was almost equal to a thunderbolt. He said that the first thought which crossed his mind was the question," Can it be possible, after all the care I have used to ascertain the modulus of elasticity of the steel and the strains that would result from the alterations in the form of the arches which must follow the changes of temperature, that our investigations have been erroneous, and that the steel is actually not strong enough to withstand extremes of temperature?" An interval of intense oppression followed, during which the immense responsibility of his position as chief engineer of the work was more fully realized by him than at any other one moment throughout the entire seven years of his connection with the Bridge. In a moment, however, he recovered from the stunning blow, the feeling of distrust vanished, and he coolly proceeded to analyze the situation and to discover the cause of the accident. A few moments' reflection sufficed to convince him that it was the result of an undue strain upon the main cables, and that it could result in no serious harm. Nevertheless, he carefully wrote out his telegram of instructions, and to be absolutely sure of its proper delivery he went in person to the telegraph office.
To fully appreciate the intensity of Mr. Eads's feelings during the first few minutes after the receipt of the dispatch, it should be stated that on the morrow he was to have a conference with some of the stockholders of the Bridge Company, preliminary to a general stockholders' meeting in New York, at which some means were to be devised for raising the funds necessary to complete the structure. At that meeting he was to report the condition and progress of the work.
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The telegram he sent was as follows: "Secure tubes in position by draw-bands; screw out lower B and C so as to close openings shown by fractures; after this reduce strain on each cable to 100 tons, and all other cables to one-half."
The fractured C tube had slipped out of the coupling, and was pressing against its end. Mr. Cooper at first doubted his ability to get it in line again without the removal of the coupling, and he suggested its removal to Mr. Eads. After eight hours of hard work, however, the fractured tube was sprung back into its place. When it did enter, "it slipped inź of an inch with a jump." Meanwhile Mr. Cooper had received from Mr. Eads a second telegram, forbidding the removal of the coupling and ordering all main-cable strains reduced to 75 tons. As yet no change had been made in the cable-strains, as it was necessary first to get the end of the above tube in place. The lower adjustable tube in rib B had been screwed out as directed, till the opening in the fractured tube of that rib was closed, and there was, therefore, no valid objection to reducing all cable-strains, thereby relieving the ribs of distortion. As all the ribs of the west and central spans were closed, there would have been no objection to removing all cable-strain on the west span, according to the original plan of erection adopted by the Keystone Bridge Company. The order to reduce the strains gradually and simultaneously was given in order, that the effect upon the diagonals between the inner and the outer ribs might be more carefully noted. However, Mr. Cooper thought it best not to reduce the strains in the main cables, as directed by Mr. Eads, until the last rib of the eastern span was completed. Rib D of that span was not yet closed. Its weight was supported partly by the supplementary cables at joints 12 and 30, as just explained, and partly by temporary diagonals from rib C. To diminish the tension in the main cables would, Mr. Cooper thought, endanger these diagonals. Hence he used all possible exertions to get in the last tubes of this rib. The lower tube was inserted on the 20th, but the couplings and pins for the upper tube needed so much fitting that it could not be closed till the morrow, and no change was made in the cable-strains. Daily reports relating to this accident were telegraphed to the chief engineer.
On the 21st, the last tube of Span III was inserted. The cable-strains were then slightly reduced and a watch was set in each tower for the night, with instructions to lower the cable-strains if the weather turned cold. The weather had been quite warm, and the expansion of the steel kept the fractured ends closed. During the night all cable-strains were reduced to about 125 tons. In the morning there were small openings at the fractured tubes, which became still less during the day. It rained hard all the forenoon. Mr. Eads arrived from New York at noon on the 22d. He examined the condition of the arches, and learned why the cable-strains had been so little changed. He directed that they should remain as they were till the morrow, and that the towers should have plenty of clearance for contraction during the night. At 11 P. M. there was a very high wind and falling temperature.
January 23. — This morning (temperature 25°) the openings stood: C,ž of an inch; B, 3/8 inch. They closed towards noon, until C stood at 3/16 of an inch, and B at 0. Mr. Eads then ordered the cable-strains on the west span to be reduced to 100 tons per cable. This reduction caused no appreciable change in the openings. Meanwhile, parties were screwing out closing-tubes and putting in internal bracing.
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On the 24th, Mr. Eads gave the order "to have all cables removed, as they were not heeded further."
The cable-strains were gradually reduced, and at 5 P. M., January 29, Mr. Cooper records that "there is now no cable-strain on any part of the work." By January 31 all cables and towers were removed.
Mr. Cooper's record contains all that is known in regard to the breaking of the two tubes. Nothing is clearer than that the ribs were subjected to an immense and altogether unnecessary strain. Had the hydraulic apparatus been properly managed, no harm could have come upon the arch. Some watchman had evidently been unfaithful to his trust. Mr. Cooper's diary says that he "suspected that the rupture was caused by an excessive strain on the cables on January 14," but "he could not reduce it to fact." This excessive strain could have occurred only by the towers getting caught on the blocking, as they did on a former occasion, or through the neglect of the man in charge to free the balance-gauge by drawing glycerin from the rams.
At this point it will be interesting to note the occurrences of the five days preceding the discovery of these fractured tubes.
January 14 was a very cold day, — in fact, the coldest of the month, — and no men were at work; Mr. Cooper, however, was on duty. He found three tension-rods (diagonals) broken between the C and D ribs at the east end of Span I. These rods ran from joints 31, 32, and 33 of the upper member of rib C to corresponding joints on the lower member of rib D. The main cable on the east side was attached at joint 30. Singularly enough, the three rods broke in very different ways: one through the "eye" of the rod, one through the "connecting straps," and one through the "eye-plate washer." (See Plates XXIV and XXI.) The outer ribs of this arch were wholly closed, but as the closing-tubes had not been fully screwed-out, their weight was largely carried by the inner ribs. These rods had a large strain thrown upon them in consequence of the removal of the temporary rods supporting the outer ribs. The break of these rods took place at 7 o'clock in the morning. The full extent of the injury was not known, but it was afterwards ascertained that "there was a heavy concussion," and that "the arch shook very much, so that planks at the center jumped clear of their supports." The workmen who were present when the break occurred were forbidden by the general foreman to say anything about it, under penalty of immediate discharge.
January 15 continued bitter cold, and little work could be done. Mr. Cooper was anxious to close the outer ribs of the other spans in order to free certain temporary suspension-rods for use on Span I. It was Mr. Cooper's intention to make a final effort, by means of his new and powerful wrench, to screw out the adjustable tubes of this span, and to that end he wished to throw the weight of the outer ribs upon the inner ones. The few rods connecting rib D to C were under heavy strains.
On the 17th, a lateral tension-rod between the lower members of ribs B and C, from joint 17 to 18 of Span I, broke, causing considerable vibration. The weather was now warm again.
January 19. — Mr. Cooper examined the cable-strains at noon. He found that at the West Abutment and West Pier they had earn a tension of 152 tons; at the East Pier, 161 tons; at the East Abutment, 141 tons. These were according to previous directions.
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The extreme cold of the 14th caused such a contraction of the material of the arch that the joints 12 and 30, where the main cables were attached, must have slightly settled, in common with every joint along the central portion of the arch, or at least tended to settle. When the accident occurred, the state of the case was this: —
Only the main cables attached to the ribs B and C at each end were remaining on this span. Each cable was supposed to bear a strain of about 150 tons. The effect of these strains, at a normal temperature, was to raise two haunches at the twelfth joints, sharpening the curve of the arch at those points and flattening it at all other points. This distortion produced compression on the lower tubes near joints 12 from each end, and tension in the lower tubes near the crown and near the springing. The stresses in the upper tubes due to the cables was nearly the opposite of those in the lower at all points. Now suppose a great contraction to take place in the arch from severe cold. The tendency of the contraction would be to diminish the span of the arch; as, however, the length of the span must remain unchanged, the effect upon the arch would be like that of drawing the ends asunder, thus flattening and lowering the crown. The tendency would also be to diminish the angle at the springing but as the ends were fixed, the contraction would produce tension in the upper tubes and compression in the lower ones near the ends, thus neutralizing the strains produced there by the cables. At the center, however, the effect of the cold would be similar to that of the cables; the result would be a great tension in the lower central tubes, though by no means sufficient to cause a fracture unless the cable-strains were greatly in excess of the amount named in Mr. Cooper's orders. Now make the supposition that the towers were not lowered as the cold increased. The massive cables, nearly 400 feet long from the unyielding anchorage to the twelfth joint of the arch, would continue to contract and gradually raise the twelfth joint of each rib by a mighty tension, which must more than overcome the tendency of the cold to make it fall. This union of stresses would produce immense tension in the central lower tubes and couplings of the arch. The steel couplings of the lower member, whose tensile strength had been so generally abused and questioned, proved equal to the emergency; a steel tube, however, in each rib gave way to the strain, in each case at the very point where the tube was weakest, namely, at its inner groove. The unquestionable strength and soundness of the tubes makes it almost certain that the strain on at least one set of main cables was in excess. The tension-rods which broke on January 14 were between rib C and the outer rib D, and adjacent to the thirtieth joints. All such rods helped to distribute the strain of the cables to the outer ribs, and, so long as they were intact, prevented the excessive distortion of the two central ribs. It is probable that these diagonal rods broke first, throwing the whole cable-strains upon the inner ribs and causing them to break in succession, — C and then B.
On Mr. Eads's return from New York he ordered the erection of the superstructure over this span to proceed without reference to these fractured tubes, being well assured they could be replaced by sound ones at any time.
New tubes were, however, ordered without delay. To prevent all chance for mistake, the couplings at the ends of the broken tubes were opened sufficiently to get templets of the grooving. The new tubes reached St. Louis March 21. Preparations had been made for inserting them by slightly setting up the tension-rods so as to carry the weight of the inner
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ribs on the outer ones, and screwing back on the lower adjustable tubes of B and C. One adjustable tube was shortened 3/16 and the other 5/16 of an inch. On March 23 the broken tube of rib C was removed and the new one inserted. Owing to some errors in the boring of the pin-holes, couplings and braces were not put on till the next day.The fractured tube in rib B was removed and the new one inserted March 26, all parts being put in place within eighteen hours. Col. Flad reported that the work of removing and inserting tubes was done so quietly that workmen engaged within a few feet on the upper road-way did not know what was going on.
The advantage of the adjustable feature of the central tubes was apparent from the fact that although the new lower C tube was 1/8 of an inch too long it was readily entered, and the proper allowance was made subsequently in screwing out the adjustable tube of that rib. All diagonals between ribs were then adjusted to legitimate strains. Only seven men were employed in all the operations connected with the insertion of the new tubes. It is evident from the facts connected with the removal of these fractured tubes and the insertion of others in their stead, that it is possible to remove and replace any part of the arches without the use of cables above or of supports beneath.
A little trouble was experienced with the adjustable tubes of rib A, Span III. When an attempt was made to put the coupling on at the long end of the tube, it was found that the staves were twisted in the envelope, the ends having moved around f of an inch. This was caused by a very tight screw.
The appearance of the arches after the completion of the ribs and before the erection of many of the struts is given in Plate XLV It shows mainly the unloaded ribs, and helps the layman to separate the supporting arches from their load. The upright struts merely carry the two road-ways and the upper wind-truss, transferring their weight directly to the ribs.
On February 5, the first upright strut for the upper road-way was placed in position. It stood upon the skew-back of rib B at the East Abutment. One of these struts stands upon each upper skew-back and each coupling-pin in upper members; hence the whole number of struts is five hundred and twenty-four. The last one was in place March 6. In connection with these struts, and attached to them at the top, are cross-beams to support the upper road-way. These were, of course, erected at the same time, and all were riveted together.
At a meeting of the officers of the St. Louis and Keystone Bridge Companies, held on the 7th of February, 1874, it was agreed that a bonus of $1,000 should be paid to Andrew Carnegie, an officer of the Keystone Company, for every day prior to the 1st of June on which the Bridge (so far as contracted for by that company) should be ready for railway and highway traffic; and, on the other hand, it was agreed by the Keystone Company that it would pay a penalty of $500 for every day in June required to complete their contract. Under the stimulus of this arrangement, the work progressed at a most rapid rate. The arches actually swarmed with workmen, and the struts and cross-beams went up as though by magic. The noise of riveters was almost continuous. In one day fifty-two struts, or thirteen panels, were erected.
The employment of so many new workmen naturally led to some serious accidents. On February 19, James Brant, assistant foreman on center span, fell from the center of an
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arch. In his fall he passed within one foot of the barge, striking the water on his face and shoulders. He was bruised considerably. On March 2, James Lemars fell from the top of the upper road-way of the center span. He struck a timber on an upper member of a rib, then a lower tension-rod, and then 90 feet to the water, striking flat on his face. He was not seriously hurt. On March 22, one of the rivet boys (Nolan) fell from center of Span I and was killed. He struck a tension-rod and a timber, then fell into the river and disappeared.Following close upon the erection of the upright struts and upper cross-beams came the wind-trusses over all, one for each span. The construction of those trusses is clearly shown in Plates XXXII and XXXIII. Each end of a truss terminated in a wrought-iron parallelopipedon called a "nose," which is of great strength, and which rests in the channel of a large cast-iron plate capping the masonry, to which it is secured by a system of powerful iron bolts firmly anchored far down in the body of the pier. These are shown in Plate XXXIV.
It will be noticed that the noses of the wind-trusses have considerable freedom of motion longitudinally in the castings. The necessity for this will be obvious when we consider that the extreme length of the central wind-truss, whose normal length is about 540 feet, varies more than six inches under a change of temperature from 20° below zero to 120° above.
The numerous details of the iron-work erected on the arches went together well and rapidly. On March 27, Col. Flad reported the progress of the work as follows: "The upper road-way of Span III has been nearly finished, with the exception of the side-walks, which are laid one-third of the span. The wind-trusses of the three spans will all be riveted by to-morrow afternoon. Track stringers have been laid over Spans III, II, and one-half of Span I. The riveting on strut work is about two-thirds done." On April 2, Col. Flad reported the wind-trusses all riveted, tension-rods nearly all in, railroad stringers all in place, and upper road-way half laid. "All the iron of the Bridge is now in place." Dr. Taussig wrote, April 6: "On the whole, I believe that the Keystone Bridge Company will have completed its contract by the 1st of May, a feat which they frequently declared, in answer to our former appeals, to be physically impossible." The steel rails required for the Bridge and its approaches were ordered of the Cambrian Iron Works, Johnstown, Pa. The rail weighs 67 pounds per yard, and shows almost exactly the section designated in the office of the chief engineer. The rails for the Bridge were cut to exact lengths, as follows: —
88 rails 23' 3Ë" long.
96 rails 23' 11Ë"
72 rails 24' 4 " "
In all 509 tons were required, and the price, not including freight, was $100 per ton.
They were to be delivered by May 1.
The tramway rails or sheets for the upper road-way were procured from the American Sheet and Boiler Company, of Cleveland, Ohio.
On the 15th of April the upper road-way was done. On Saturday, the 18th, the Keystone Company agreed to allow the upper road-way to be opened to the public on the following day, and it was so announced in the papers of the city. Manager Piper and Mr.
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Andrew Carnegie, with their attorney, were in the city. Mr. Piper had given the Bridge work his personal attention. Mr. Carnegie was, of course, much interested in the prospect of a large bonus.This action of the Keystone Company was considered extremely outrageous; and though, as Col. Flad wrote to Mr. Eads, who was at the time in Washington, it went sorely against the grain to quietly submit, there was no other proper course to be taken.
On Tuesday the upper road-way was torn up at the east end of the Bridge, as it had been at the west; the railway stringers were taken up at each end, and the force of men was reduced. The men retained were chiefly on "watch" duty, day or night. However, a compromise was effected in New York, according to which the upper road-way of the Bridge was opened to foot-passengers and visitors on the 23d of May. On the 24th, which was Sunday, between 15,000 and 20,000 people paid for admission to the promenade of the Bridge. The East Approach was not in a sufficiently finished condition to allow of the use of the Bridge by vehicles till the second day of June.
Meanwhile, a few men were putting the finishing touches to the steel and iron work of the Bridge. Every nut and rivet was inspected, every tension-rod was properly "set up," and every combination of pieces was carefully "lined up." The wind-trusses and arches, as wholes, were adjusted with the greatest care.
Early in June, it was my good fortune to be invited to join a small party of Bridge officials, engineers, and other invited guests in a trip across the Bridge. At this time the tunnel under the streets of St. Louis was nearly completed, and the long eastern approach was finished. The railway tracks were laid over all to within a few feet of what is now the Relay House in East St. Louis, where the party of the afternoon was directed to rendezvous. We found workmen laying a track across one road, to connect with another on which an engine and two cars were waiting to make the passage of the Bridge. The visitors cheerfully lent their hands to the work, and the honor of driving the last spike to connect the Bridge with the railways of the land was assigned to Gen. Sherman, one of the guests. Our feelings as the train slowly ascended the approach and smoothly crossed the Bridge
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were those of quiet rejoicing and deep satisfaction. At last the great work was finished! The Bridge was done! That which we had pictured so often, but which we had at times almost despaired of seeing, was now realized; and for myself, though there was nothing to identify me with the work, I can truly say that my enjoyment was closely akin to that which attends a personal triumph, so lively was my interest in the undertaking.This pioneer train entered the tunnel as far as Eighth Street, and then, after an exceedingly disagreeable delay in the thickest of coal-smoke, withdrew to the purer air of the Main Street Station.
On the 29th of June a locomotive was run over both tracks, stopping at each joint until all nuts and fastenings could be inspected. All was found in place, and generally in proper adjustment. On June 30, the deflections due to the load of a 80-ton locomotive and tender were noted. On July 1, a locomotive and ten cars loaded with gravel and iron-ore were used to test the Bridge.
On the 2d of July there was a public test, and thousands of citizens flocked to witness the interesting spectacle. Fourteen locomotives, with their tenders full of coal and water, were loaned for the occasion. All were heavy machines, and all were crowded with spectators. Seven were coupled together, and crossed and recrosssd the Bridge on each track, stopping on the middle of each span. Then the fourteen locomotives, in two divisions of seven each, moved out on the two tracks, and stopped on the center of each arch side by side. Finally, the fourteen locomotives, all in a line on one track, slowly moved across the Bridge. Such a combination is rarely seen. It extended the length of nearly a span and a half. Meanwhile, the upper road-way was open, and was crowded with spectators and passing teams. The sight was an impressive one. The levee north and south was crowded with people. The excitement was intense, as with almost breathless interest they watched the immense load move from the West Abutment upon the western span. To the unskilled it seemed incredible that the slender arches could support such a burden. Men swarmed over the engines, and to the crowd below a thousand lives seemed hanging by delicate threads.
When, however, it was seen that the arches supported this load of 700 tons, whether moving or at rest, with the greatest apparent ease, a conviction that the Bridge was immeasurably strong settled into every heart, and a joyful shout of triumph went up from the vast throng, that will not soon be forgotten.
It was observed that there was some little trepidation among the engine-drivers. One asked me in an undertone, as he started his engine in obedience to an order which he had not the slightest idea of disregarding, "Do you think she will hold us?" I answered promptly that in my opinion "she" certainly would, and bade him have no fears. Another engineer was so excited that he forgot to reverse his engine (as would have been proper in his case). The strength and weight of the six locomotives with which this one was coupled were sufficient, however, to drag out upon the Bridge an apparently unwilling companion, whose driving-wheels were turning the wrong way.
Careful measurements of deflections at different points and for different positions of the various loads gave very satisfactory results. Everything seemed to be in order, and the steel yielded to the stress put upon it in the exact manner and to the degree that was expected. These tests are all given below.
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On the 4th of July, 1874, the city celebrated the completion of the Bridge in magnificent style. The usual festivities of Independence Day adapted themselves to the event which stood foremost at that time in all minds. The first feature was a ride over the Bridge. A long train of coaches, crowded with passengers who had gone over from the city for a "trip on the first train," left East St. Louis, crossed the Bridge, and passed through the tunnel to the Union Depot grounds. In that simple trip many actually realized the accomplishment of what they had stoutly declared during the previous two or three years they never expected to live to see.
Next followed in the streets of the city a mammoth procession of trades and occupations, fifteen miles long, crossing and recrossing the Bridge. Near the entrance to the West Approach, in what is a part of Third Street, and a public square, a large tent had been erected, and after the procession had passed, a large company of invited guests joined in congratulatory exercises. Addresses were made by Hon. Joseph Brown, mayor of St. Louis; Gov. Beveridge, of the State of Illinois; Gov. Woodson, of the State of Missouri; Gov. Hendricks, of the State of Indiana; Hon. Thomas W. Ferry, of Michigan; Mr. James B. Eads, the chief engineer of the Bridge; and Hon. B. Gratz Brown, of St. Louis. The last-named speaker pronounced the main oration of the day.
All the speakers entered heartily into the spirit of the occasion, and gave utterance to the feeling of triumph and rejoicing which pervaded all classes in the community.
In the evening the Bridge was still the center of attraction. Ten thousand dollars' worth of pyrotechnics were displayed from the upper road-way, while a vast concourse of people beheld them from the levees and from the decks of a numerous flotilla of steamboats that covered the river below the Bridge. The spectacle of the thronged boats and the crowds which completely covered the banks, lighted up by the brilliant colored lights on the Bridge, was exceedingly fine; but the fire-works themselves were dwarfed into comparative insignificance by the height and length of the Bridge and by their distance from the spectators, and the effect of the mottoes and other elaborate designs was less impressive than was expected.
Engine No. 40 of the Vandalia Road, total weight 50 tons, was run over both tracks, stopping at every third joint, while the depression at the centers of the spans was noted.
| 50 Tons on North Track at Joint. | Deflection in Inches at Center of Rib C. | ||
| Span I. | Span II. | Span III. | |
| 3 | 0.084 | 0.072 | 0.048 |
| 6 | 0.120 | 0.072 | 0.048 |
| 9 | 0.144 | 0.096 | — |
| 12 | 0.228 | 0.144 | 0.252 |
| 15 | 0.360 | 0.240 | 0.360 |
| 18 | 0.408 | 0.513 | 0.540 |
| 21 | 0.636 | 0.600 | 0.636 |
| 24 | 0.480 | 0.540 | 0.504 |
| 27 | 0.300 | 0.504 | 0.360 |
| 30 | 0.156 | 0.288 | 0.264 |
| 33 | 0.024 | 0.192 | 0.120 |
| 36 | 0.000 | 0.132 | 0.024 |
| 39 | — | 0.060 | — |
Engine No. 40 of the Vandalia Road, total weight 50 tons, was run over both tracks, stopping at every third joint, while the depression at the centers of the spans was noted.
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While the load was on the south track of the west span, the deflections of rib A were noted; when on the south track of the center span, the deflections of rib B of that span were noted. The results agreed so closely with the above that I have not thought it necessary to give them. In all cases, as there was but a single set of observations, allowance should be made for instrumental and personal errors.
The next test consisted in placing the load in succession at the three points, — the center, and the eleventh joint from each end, — and noting the deflections or rise of a loaded rib each time at all three points.
With 50 tons at the center, the deflections at the center agreed with those given above, namely, from 3/10 to 6/10 of an inch. The eleventh joints were generally depressed a trifle, though on III B they rose 1/32 of an inch.
When an eleventh joint was loaded, the deflections at that joint varied fromź of an inch tož of an inch, — the most of the readings beingË inch.
When one eleventh joint of a rib was loaded, the other eleventh joint generally rose, the amount varying from nothing to 1/8 inch.
Center deflections were also noted as the engine ran over the different spans at various speeds: five, ten, and fifteen miles per hour. The results did not differ essentially from those with the engine at rest.
Next, a locomotive and ten loaded gravel-cars was run over the Bridge and back; the load was not very great, for the maximum deflection did not reach 1Ë inches.
The grand tests were on the 2d of July. The record is given in the following table and observations. In the load, no allowance is made for the human freight, which at one time must have aggregated more than 50 tons: —
| Load (allowing 15 Tons for each Tender). | Deflection (Inches) at Center of | ||||||
| Locomotives. | Weight in Tons. | Placed on Middle of | Rib A. | Rib B. | Rib C. | Rib D. | |
| 7 | 350 | South track of | Span I | 2.48 | 1.80 | 1.27 | 0.82 |
| 7 | 334 | " " | " II | 2.80 | 2.15 | 1.37 | 1.10 |
| 7 | 334 | " " | " III | 2.48 | 1.84 | 1.33 | 0.83 |
| 7 | 334 | North | Span I | 3.048 | 2.892 | 2.616 | 3.00 |
| 7 | 350 | South " | |||||
| 7 | 334 | North " | Span II | ||||
| 7 | 350 | South " | 3.48 | 3.44 | 3.89 | 3.92 | |
| 10 | — | " " | " II | 2.37 | — | — | — |
The greatest vertical deflection of Span II, when one-third was loaded with locomotives, was 1.43 inches, and at the fourteenth joint; when one-half was loaded, this maximum deflection was 1.67 inches, and at the fourteenth panel; and when five-eighths was loaded, it was 2.25 inches, and at the seventeenth panel.
The ten engines and tenders covered an entire span, thus putting a maximum load on two ribs while the other two were unloaded. Observations were made to see if the arch as a whole was twisted. Rib C was a little deflected, but none of the ribs were thrown out of vertical planes.
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The greatest negative deflection or rise of the same span, when twelve of the forty-four panels were loaded, was 0.63 inch, and at the twenty-ninth joint.
North track of Span I Rib C of Span II rose 0".3
South II B 0".12
South B 0.216
South I, moving east B II 0".48
In each case the measurement was at the center of the rib.
After each test, the load was entirely removed and observations were made for permanent set; none was at any time detected, nor was any lateral motion discernible in the outer ribs under the various loads.
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Chapter XVIII. Special Subject No. 1. — The Sinking of the East Pier.
I propose in this chapter to give a full account of the construction of the East Pier. It will be followed by other chapters also on special subjects.
As has been told in Chapter VI, the caisson of the East Pier was towed into position on the 18th of October, 1869. The plan of the construction works given in Plate X shows the position of the caisson between the guide-piles (which are marked IF), and the situations of the pontoons "Allen" and "Johnson." Plate IX gives an end view of the floating caisson and the full length of the guide-piles. Of the latter, the two at the south end were not to be sunk till the caisson was in position.
These guide-piles were 3Ë feet in diameter and 80 feet long. They penetrated the river-bed about twenty feet. Twelve feet of the lower extremity was a hollow iron tube with open end; above this, for a few feet, the tube, with the exception of an opening about one foot in diameter, was filled with pig iron to give it weight. The rest of the pile was built of timbers strapped and bolted together as shown in Fig. 31. To sink the pile, the sand was removed from the end of the tube by a sand-pump inserted through the hollow center. When the pile had reached the proper depth the interior was filled with sand. The tops of the guide-piles were securely framed together as shown in Plates IX and XL. The latter, though taken from a photograph of the West Pier, shows equally well the construction of the frames, etc., about the East Pier. This frame-work supported the nuts of ten large screws, each 20 feet long, whose lower ends were secured to the wall of the caisson. These screws were not intended to support the entire weight of the caisson, but were to keep it from tilting, and regulate its descent till it should rest in the sand.
The construction of the caisson is fully shown in Plates VII, VIII, and XIII. When launched it had a temporary wooden bottom, made water-tight, which rendered it more buoyant and served as a floor to the riveters, who were kept busy for several days stopping leaks. The entire enclosed space within the caisson was known as the "air-chamber." Its three compartments were connected by permanent openings in the division-walls. After air was forced into the chamber, its pressure counteracted the water-pressure, and in due time the bottom was drawn out in sections by a tug-boat. The uniform depth of the chamber, measured to the "cutting-edge," was nine feet.
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The iron plates in the walls of the air-chamber werež of an inch thick; those in the roof,Ë an inch thick. As the roof was to support the entire weight of the 100 feet of masonry laid during the sinking process, it was made very strong. It was riveted to the lower flanges of thirteen plate-iron girders, 5 feet high, which cross it from side to side at intervals of 5 feet 6 inches. The roof was also supported by two heavy walls of oak timber, 7 feet high, in the air-chamber itself. These walls were hung from the roof at first, but furnished support as soon as the sand was reached.
The walls of the air-chamber had been extended above the roof 10 feet before the caisson was launched, thus constituting a sort of open coffer-dam above the air-chamber. The weight of the caisson when launched was 437Ë tons, and its immersion with false bottom and without masonry was about three and a half feet. The base of the air-chamber contained 4,020 square feet.
On the "Allen" there were four air-pumps, each 14 inches in diameter, with 4 feet stroke, driven in pairs by two independent engines with 20-inch cylinders and a 24-inch stroke. Engines and pumps had been thoroughly tested. The "Alpha," fitted up in the same manner, was at first put in working order and held as a reserve, though destined for the caisson of the West Pier, soon to be launched.
As soon as the caisson was placed in position between the guide-piles, the air-pumps were set to work pumping in air and forcing out the water. The unavoidable leakage of air required the continual use of the pumps, and as the river was always either rising or falling, the suspension-rods required continual inspection and the nuts frequent turnings, so as to keep the tension both slight and even until the caisson rested on the bottom. Hence, at all points it was necessary that work and supervision should be continuous day and night. A week was spent by riveters, engineers, and carpenters in getting the caisson ready for the masonry.
Entrance to and exit from the air-chamber was through air-locks, seven in number. These air-locks were in form vertical cylinders, made ofË-inch plate-iron. The central lock, which was 6 feet in diameter and 6 feet high, was wholly within the air-chamber; in fact, the roof of the caisson formed its upper base. Adjoining this lock was a second iron cylinder, 5 feet in diameter and 5 feet deep, sunk through the roof of the caisson and entirely open at the top. The air-lock had two strong, tight-fitting doors, — one communicating with the open air-cylinder just mentioned, and swinging into the lock; the other opening into the air-chamber and swinging from the lock. The other six air-locks were 5 feet in diameter and ten or twelve feet high, being partly above and partly within the air-chamber. Each had two doors, — one on the side near, the bottom, and one on the upper end. These six locks were intended to be used for the admission of concrete and for the removal of logs, etc., should any be met with in the bed of the river. Workmen generally passed in and out through the central lock.
The method of going in or out was very simple. The outer door of the air-lock being open, and the inner one, of course, closed, the party of visitors for example, descended into the open cylinder by the central lock, crawled through the opening into the lock, and closed the door. A cock was then opened which allowed the compressed air from the chamber to enter the lock. When the air-pressure within, the lock equalled that in the chamber, the
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other door readily swung open and the party entered the air-chamber. The time required in entering depended upon the pressure in the chamber and the ability of the persons in the lock to endure the change. If the air was let on rapidly, and the pressure was considerable, the sensation produced was very disagreeable. The compression of the air in the lock was attended by the evolution of heat, and though the air was saturated with moisture, as well as warm, there was no difficulty connected with one's breathing. The only serious difficulty to a visitor was felt in his ears. The pressure upon the exterior of the drum was very painful unless soon balanced by internal pressure. This could generally be produced by vigorously blowing the nose, thus forcing air into the interior cavity of the ear. Mr. Eads found that the act of swallowing would often give relief, and had a pail of water and a cup placed in the lock. In some cases, however, these simple remedies were of no avail, and intense pain was the result. In that event the air was admitted very slowly.In returning from the chamber the operation was equally simple. The party entered the lock, closed the inner door, and opened a lock which allowed the air of the lock to escape to the outside.
As soon as the air-pressure was reduced to that of the atmosphere, the outer door was readily opened. The physical effects of reducing the pressure were very different from those experienced when going in. The expanding air absorbed heat, and one literally felt the chill to the very marrow. So much vital heat was lost that in some cases the effect was very disastrous. There was much in the habit of undergoing these changes. Certain airlock men, whose duty it was to take parties of visitors, engineers, and workmen in and out, became so used to sudden changes that they could, without apparent injury or even inconvenience, endure surprisingly rapid changes of pressure.
Soon after the sinking of the caisson began, a small air-lock, an inch or two in diameter, was attached to the wall of the open air-cylinder, by means of which written messages could be quickly sent to and from the air-chamber.
The derricks and machinery employed in taking the blocks of stone from a barge and placing them in position on the floating or sinking pier are well shown in Plates IX, X, XI, and XL. Nevertheless, a few words are necessary to make clear their theory and use.
The wire cables, 2ź inches in diameter and about one hundred and five feet long, were supported by the frames some fifty feet above the decks of the pontoons. On each cable ran a truck or "traveller," with a possible lateral motion of 100 feet, which was sufficient to carry a stone from a barge moored alongside a pontoon to the center of the pier. Over the two lower wheels of the truck passed a wire rope 1 inch in diameter, whose devious course is shown in Plate IX and Figs. 1 and 2 of Plate XI. In the latter Plate the plies of the rope are numbered in order, with arrows, so that we can easily follow them. The first ply comes from the fixed pulley on the end of the derrick, and passes under one of the fixed pulleys at the base of the hydraulic jack (Figs. 1 and 2); the rope then rises to a pulley on the top of the jack, and thence down into the hold of the pontoon and several times around a drum seen in
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Fig. 1. From the drum the rope (ply No. 4) rises again to the second pulley on the top of the jack, then falls to the second fixed pulley at its base, whence it runs off diagonally to the end of the frame at the other end of the cable, and thence to the traveller again. Several feet below the traveller the two ends of the rope are secured to the lifting-block, from which hang the chains and grappling-hooks.If now the drum be turned, it is evident that the traveller will be drawn along the cable to the right or the left, according as the rotation of the drum is right or left-handed, while the lifting-block will remain at the same height above deck. There was, of course, a separate drum, jack, etc., for each traveller but there was only one engine for moving the six travellers on a pontoon, and each was to be operated at will by means of attachments to a single main-shaft running at uniform velocity in one direction. How one traveller could be moved in either direction, and stopped without interfering in any way with the other travellers, I will now explain.
Fig. 3 of Plate XI gives atop view of two drams, and the main shaft, which is driven directly by the engine, and also a parallel shaft connected with the former by gearing, and turning in the opposite direction. Both shafts extended over all six drums. On each of these shafts, and for each drum, there was a conical friction-wheel turned by a key, which pierced the shaft in a slot which allowed the wheel several inches' motion along the shaft. Adjacent to each of these wheels was a second friction-wheel, larger than the first and conical internally, attached to a sleeve pinion, and turning freely on the shaft. This pinion worked with a spur-wheel keyed tightly to the shaft of the drum, as shown in Figs. 1, 2, 3. Thus two pinions, one on each shaft, moved or stood still with the drum.
Now the two friction-wheels, which were movable laterally, turned continuously and in opposite directions. Hence, if one was forced firmly into its follower, it drove it and the drum in one direction if it was withdrawn and the other forced upon its friction-follower, it drove the drum in the other direction, and in either case motion was imparted without jar or blow. A friction-driver was moved in and out by a cam secured to a vertical shaft and acting on the projecting rings of a sleeve attached to the wheel, as seen in the lower part of Fig. 3.
To suddenly check the traveller at any desired point, a brake was attached to the cam-shaft in such a way that the complete withdrawal of the friction-wheel applied the brake to the narrow rim of a wheel on the drum-shaft. The brake was a single strap of iron surrounding the wheel and attached to both cam-shafts at the bottom. The cam-shafts were about thirty-three feet long, ending in the little cabins upon the frames, as seen on several plates, where each was furnished with a long handle or lever, as shown in Fig. 4 of Plate XI.
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it is evident that both handles could not at the same time be turned outward without throwing in both friction-wheels and endangering the gearing. Hence a flexible strap connected the two handles, which prevented their separation, while it allowed them to be drawn towards each other, with the invariable effect of instantly stopping the traveller. Again, the motion of the handles was towards the pier when the traveller was to go in that direction, and away when the traveller returned. Hence there was little chance for mistake on the part of the man in the cabin who had charge of the handles. It is obvious that but little power was needed to transport the stone and return the travellers, the main expenditure of power being in hoisting the stone.This hoisting was done by the hydraulic jacks. A jack, clearly shown in Figs. 1 and 2 of Plate XI, consisted of a cast-iron vertical cylinder 11 feet long, with a 5-inch solid plunger, which carried upon its upper end a cross-head and the two pulleys for the wire rope already spoken of. The maximum rise of the plunger was 10 feet, by which motion 10 feet of length were added to each of the plies 2, 3, 4, and 5; and as the rope was of fixed length, that motion of the plunger raised the lifting-block 20 feet. The motion of the plunger was caused by the admission of glycerine,
As the immersion of the caisson increased, the wall of plate-iron, which at first was all around 10 feet high (from the roof of the caisson), was extended by the regular addition of more plates, and then stiffened by timber braces, as shown in Plate XIII. This iron wall was indiscriminately called the "shell," the "skin," or the "envelope" of the pier. Its top was generally five or six feet above the surface of the river.
So long as the caisson was floating, it was supported by the upward pressure of the air upon the roof of the air-chamber (omitting, of course, occasional slight tensions in the suspension-rods). As the laying of the masonry progressed, the immersion increased, and the air-pressure required to keep the air-chamber free from water increased proportionately. After the caisson reached the bed of the river, the bearing-sills along the outer and inner walls of the caisson were given a bearing, and the load of masonry was then greatly
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increased without materially increasing the immersion. All the sills were 2 feet above the cutting-edge of the caisson. The sill along the outer wall was originally 21 inches wide, while the sills of the interior walls had bearing-surfaces 3 feet and 6 inches wide. The sills are shown in Plates VII and VIII . The total bearing-surface was about eight hundred and fifty square feet. The details of the iron brackets, which helped support the roof and stiffen the walls, are shown in Plate VIII .To Col. Roberts, Col. Flad, and Mr. Pfeifer was assigned the responsible duty of personally directing the work of building and sinking the pier. On October 25, Mr. Eads issued the following instructions: —
"Col. W. Milnor Roberts, Associate Chief Engineer Illinois and St. Louis Bridge Company.
DEAR SIR: The laying of the masonry in the caisson of the East Pier having commenced to-day, the safety of the work as it progresses demands the strict observance of the following rules: —
1st. The caisson must be kept as nearly level as it is possible to keep it. The safety of the work will be imperilled in proportion as this rule is departed from.
2d. The quantity of stone laid on the opposite sides and ends of the caisson should be as nearly equal as possible. (Until the guide-piles at the south end shall have come to their bearings and the two screws supporting that end of the caisson are connected with it, a preponderance of from five to ten tons should be maintained in the forward end, but not afterwards.)
3d. One set of air-pumps alone should be constantly kept running, at a speed of engine of not less than fifty revolutions and not more than ninety-five per minute, the smaller number being preferable. An escapement of air from under the edge of the air-chamber must be constantly kept up. If fifty revolutions fail to do this, more must be made; and in case of necessity, the one engine failing to provide such escapement, the other should be put to work. This can only occur from some new leakage of air from the chamber; and in the event of one engine being unable to supply an excess of air, the laying of masonry must be stopped until the leak be discovered. Each one of the air-locks in such a case should be first examined, as the leak will most likely be found there.
4th. The object of the suspension-screws is not to carry any part of the weight of the caisson or masonry when the latter is evenly distributed. When an excess of masonry or other load is on one side or on one end, the screws are designed to hold that excess. They should, therefore, be evenly slacked from time to time, until all weight is off of those on the side or end having the least load, and the laying of a farther load on the side or end where the screws are loaded be stopped, and the other side or end built up. The screws should then be gradually lowered until they become slack. If the screws on the deeper side or end of the caisson be lengthened, the strain on the screws will be increased. Therefore this must not be done. They can at once be relieved of the strain by placing more stone on the higher side of the caisson. In no case should the screws on the deeper end or side of the caisson be slacked until the level of the caisson is restored.
5th. At least 7 feet 6 inches of the enveloping wall should be above water at all times, so long as we have the full air-pressure in the air-chamber.
6th. The strain on any one of the suspension-screws should not exceed 20 tons, and some of them (two at least) should always be slack.
7th. Notes of the depth of each side and of each end of the caisson must be taken once every half hour, and also of the speed of the air-pumps, and of the air-pressure. Any matters of importance occurring must be recorded in the note-book by the engineer on duty at the time.
8th. In case the escapement of air from the bottom of the air-chamber should cease, and cannot be restored by the action of both sets of air-pumps, immediate observation must be made to ascertain if the water is rising in the air-chamber. If this is taking place the screws should be slackened down as
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evenly as possible, so as to let the caisson settle in the water in proportion as the buoyancy of the air is lost. In case of an accident of this kind, it will only be necessary to let the caisson settle 6 feet 3 inches, even if a loss of all the air in the air-chamber should occur. This loss would be equivalent to a displacement of about 8.25 feet, and the difference between that and 6.25 feet could be sustained by the screws.
9th. To avoid accidents to men and injury to the boats or caisson, stones must not be raised above the deck of the derrick-boats, or above the caisson, any higher than is necessary. Especial care must be taken in this respect where the roof of the air-chamber or an air-lock is exposed.
You will oblige me by giving a copy of this letter to Col. Flad, Mr. Pfeifer, and Mr. McComas.
The instructions herein contained relate chiefly to the management of the work before the caisson obtains a bearing on the sand.
Very respectfully,
JAMES B. EADS, Chief Engineer."
The laying of the masonry was begun October 25, and continued day and night without serious interruption. At night a calcium light was run for each end of the caisson. A few extracts from the "log," written before the novelty of the work had worn off, and while little defects and shortcomings were being found out, will be of interest. The engineer on duty made the entries at intervals during his watch: —
"Monday, November 8, 1869.
11:00 P. M. — Mr. Pfeifer relieves Col. Flad.
11:30 P. M. — Air-pressure, 8.70 pounds. Revolutions, [of-one of the air-pump engines] 86. Immersion, 20' 2". The minimum immersion for 9 pounds pressure (air-chamber full of air) is calculated at 20' 9".
As the pressure will probably reach nearly nine pounds during the night, a further sinking of the caisson will be necessary. The masonry inside is now, all around the circumference, 18' 9" above lower edge of caisson, or 1' 5" below present stage of water. We may, therefore, safely lower the screws 7" more, so as to get an immersion of 20' 9".
Tuesday, November 9, 1869.
12:30 A. M. — Pressure, 8.75 pounds per revolutions, 88; immersion, 20' 2" all round. Masonwork stopped at 12, and resumed work at 12:35.
1:15 A. M. — Pressure, 8.65 pounds; revolutions, 92; immersion, 20' 2" all round. Mr. Duffy is lowering screws 2 inches.
1:45 A. M. — Pressure, 8.70 pounds; immersion, 20' 4" all round. Screws have all a little strain; Nos. 1 and 2 are tightest. Told Duffy to lower screws 2" more. Instructed Mr. Eberley and the ‘foreman of masons&Rsquo; not to lay more backing than is absolutely necessary for the next course of face-stones, which has to be set 10" back from the iron shell. Vertical timbers 10" X 10", 30" apart from center to center, will be put on top of the course already laid for supporting the iron shell. Order of Capt. Eads given to me November 8, 1869, at office.
2:30 A. M. — Revolutions, 90; pressure, 8.73 pounds; immersion, 20' 7" all round.
2:40 A. M. — Screws not quite loose yet; changed revolutions to 98.
3 A. M. — Pressure, 8.75 pounds. There are nine masons and nineteen laborers working to-night.
3:30 A. M. — Pressure, 8.73 pounds; revolutions, 90 — changed to 103; immersion is now 20' 7" all round. I think some bracing for the iron shell should be provided, even before the next course of face-stone is complete.
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Thursday, November 11, 1869.
11 P. M. — Mr. Pfeifer relieves Col. Flad.
11:30 P. M. — Immersion 24' 10" all round; pressure, 11.25; revolutions, 80 — changed to 88. Screws a little strained all round. North engine of air-pumps [broken down during the day] not yet repaired; will be probably in order again early in the morning. The safety of the work now depends on one engine. The caisson can only be lowered 3 feet more, and even then it has to be braced. If the screws were all loosened we should have 8 feet of air in the air-chamber. To hold the caisson up without air, the screws would have to carry a load corresponding to 5 feet immersion, or 630 tons. This would be 63 tons on one screw, instead of 20 allowed by the letter of instructions. By attaching all the hydraulic jacks, each screw could be relieved of about eight tons, leaving 55 tons, or a strain on the iron of 30,000 pounds per square inch; good wrought-iron ought to stand that. As the laying of stone during the night will not make the case much worse, and as the engine will probably be repaired in the morning, I did not stop the masonry. But I would suggest that, at least for a few days, riveters should be at work day and night to bring the shell up to 7' 6" above water. Calcium lights very poor.
Friday, November 12, 1869.
12:30 A. M. — Immersion, 24' 10"; pressure, 10.25 pounds; revolutions, 110 — changed to 85. North engine nearly fixed. Broken bed-plate tied together by two heavy bars and two screws.
1:15 A. M. — Immersion, 24' 10" all round; pressure, 11.25 pounds; revolutions, 81.
2 A. M. — Immersion, 24' 10" all round; pressure, 11.20 pounds; revolutions, 72 — changed to 100. North engine is repaired now.
2:45 A. M. — Immersion, 24' 10"; pressure, 11.25 pounds; revolutions, 106.
3:15 A. M. — Immersion, 24' 10"; pressure, 11.27 pounds; revolutions, 102. Twelve masons and nineteen laborers at work to-night. New links should be put on screw-chains. Are more links on hand? [Henceforth log entries are made only once an hour.]
4 A. M. — Immersion, 24' 10"; pressure, 11.30 pounds; revolutions, 100. One of the timber braces running from north to south was knocked out by careless handling of a heavy stone. This brace, however, could not have had much strain, as I cannot discover the least bending in the cross-brace.
5 A. M. — Immersion, 24' 10" all round; pressure, 11.35 pounds; revolutions, 103. Screws tight yet.
6 A. M. — Immersion, 24' 10" all round; pressure, 11.37 pounds; revolutions, 90 — changed to 105. The engineer of the air-pumps thinks that the high speed will ruin the machinery in a short time. Would it not be better to run both engines at a moderate speed — say 55, not more? This would give us the same degree of safety, in case one engine should break, as running one engine at 110 or 120 revolutions; and the danger of breaking would be much smaller. [This suggestion was approved by Mr. Eads and adopted next day.]
6:40 A. M. — Immersion, north, north-east, north-west, south-east, and south-west, 24' 9"; south, 24' 8"; pressure, 11.40 pounds; revolutions, 105. Screws all under strain yet, but near south-east corner they become looser. Stage of river, 22' 5Ë" below directrix.
7:05 A. M. — Masons and laborers going home; new gangs coming over. North engine at air-pump started, and southern one stopped for purpose of examining it, as the engineer supposed the crank loose. Everything found in order. North engine is running now at 105 revolutions.
Sunday, November 14, 1869.
3:00 P. M. — Col. Flad relieves Col. Roberts. Gauge out of order. Immersion 27'9". Airblowing out at bow. Severe strain on all the screws. Ordered screws to be lowered at once, Revolutions, 45 and 47.
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4:00 P. M. — It takes four to six men with block and tackle to turn one of the screws, and then it takes about ten minutes for a turn. Air blowing out Revolutions, 45 and 46, north and south engines.
5:00 P. M. — Have not been able as yet to lower more than about two inches. Strain on screws very severe yet. Have sent all spare men to the screws and requested Andrews not to bring in any large stones until we could lower a little more. Brick-work and filling going on. Air blowing out freely. Revolutions, 48 and 45.
6:00 P. M. — Air blowing out. Revolutions, 45 and 43. Examined engineers' records and found them all in order. Nothing new since Col. Roberts left.
7:00 P. M. — Have by incessant work since 3 P. M. succeeded in lowering caisson about seven inches, or to 28' 3". New set of hands coming on under Duffy. I ordered them to lower caisson 3 inches more at once. Screws have considerable strain on them yet. Air blowing out at bow. Masons are going to work. Revolutions, 48 and 54. Found one of the timber ties between large piles on east side grinding heavily against the derrick-timbers. As soon as I can spare some of the men at the screws I will have it cut out.
8:00 P. M. — Immersion, south-east, 28' 8"; north-west, 28' 6"; north-east and south-west, 28' 7". Ordered masonry to proceed in north part of the caisson. Screws rather tight yet. Air blowing out at bow. Gauge at air-pumps, 20 pounds. Greatest strains on Nos. 7 and 8.
9:00 P. M. — Immersion, 28' 9" all round. Revolutions, 45 and 48. Screws have very little strain. Air blowing out at bow. Gauge at air-pumps, 20 pounds.
10:00 P. M. — Immersion, 28' 10'°. Revolutions, 45 and 46. Screws easy. Air blowing out a bow. Let caisson down to 29' just before 10 o'clock.
Monday, November 15, 1869.
7:00 P. M. — Mr. Pfeifer on duty. Some boiler-makers are coming over, but not many. Revolutions — south, 40; north, 46. No discharge of air could be seen for a long while. I ordered the pumps run at about 55, which made the air blow out in about five minutes. I then directed the engineer to run at 47 revolutions. Very bad weather; constantly raining. As there are only few riveters, for whom we have lights enough, I allowed the men tending the calcium lights to go home.
8:00 P. M. — Immersion, 30'. Revolutions, 45 on both engines. Moderate discharge of air at bow. North-east corner-sheet is in place now, and at present they bring the north-west corner-sheet. Temperature, 41° Fahrenheit. Weather not better — rather worse.
9:00 P. M. — Immersion, 30'. Revolutions — north, 45; south, 47. Moderate discharge of air at bow. Mr. Hutton over; also Mr. Nelson. As the rain becomes heavier, the few men of Mr. Nelson quit work entirely. The two corner-sheets have been put in. Temperature, 39° Fahrenheit.
11:00 P. M. — Col. Roberts relieves Mr. Pfeifer. Raining quite hard. No work going on. The only things requiring special attention to-night are the running of the air-pump engines and the bailing of water. Thomas Malvern is here in charge of the water-bailing. Mr. Duffy is in charge of screw-men. The screw-men work at bailing water.
11:45 P. M. — Immersion, 30' full. Revolutions, 46 and 46. Air-pressure at pumps, 21 pounds; blows off freely at bow. Temperature, 38° Fahrenheit. Raining quite hard.
Tuesday, November 16, 1869.
5:15 A. M. — As nearly as I can tell, the river has risen 2.5 inches since the rain commenced.
6:00 A. M. — Raining steadily.
6:30 A. M. — From "lower regions" [i.e., from air-chamber] Thomas Malvern reports soundings 2' aft, and 5' forward. * * * Malvern had a hard night's work at the water. He emptied six
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times at south air-look and three times at north air-lock after 12 o'clock. The gauge now shows 24 inches of water in the middle air-lock.
[The water which leaked or rained into the shafts was allowed to accumulate in the air-locks to a reasonable depth, and then by passing through the lock in the regular way the attendant took all the water through with him. The inner air-lock door was nearly a foot and a half lower than the outer one.]
7:00 A. M. — River has risen 3 inches.
8:00 A. M. — Col. Flad relieves Col. Roberts. Still raining."
The "log" extends through seven volumes of note-books. It is scarcely necessary to add that I am greatly indebted to their interesting pages.
The soundings indicated that the current of the river was washing out the sand beneath the caisson at the bow, and as it was desirable to place the caisson evenly on the sand as soon as possible, the chief engineer gave orders that as soon as the iron plates on the envelope were properly in and braced, the caisson should be lowered as far as could safely be done, so as to check the scour.
The sinking was readily done, as follows: The nuts were all turned 3 inches and the air-pumps were stopped; gradually the caisson settled 3 inches from leakage of air; then the air-pumps were started at their former rate and the nuts were again turned, and the stopping was repeated. In this way Col. Flad lowered the caisson 29 inches in forty-five minutes. An observer hi the air-chamber noted and reported the rise of the water.
On November 17 the southern edge of the caisson entered the sand at a depth of 33 feet 7 inches. Under the bow there were still about four feet of water.
No sooner had the caisson touched the sand than two logs were discovered under the bow. One was of hard wood, about eighteen inches in diameter, extending under the caisson some ten or twelve feet from the cutting-edge. At first sight it was an ugly customer. The other timber had been dressed. Both were removed without special difficulty, by drawing them into the air-chamber, cutting them in pieces, and taking the segments out through the locks.
By November 22 the bearing-timbers of the caisson rested on the sand, excepting at the north-east corner. The scour at that point had produced quite a depression. To equalize the surface and to bring the timbers to an equal bearing, wheelbarrows were sent into the air-chamber and used for carrying sand from under the girders and walls to the bow. At the same time a sand-pump was put in order near the stern, preparatory to removing the sand.
At this stage of the work the immersion of the caisson was about 36 feet 4 inches; the walls of the iron coffer-dam above the caisson extended 4Ë feet above the water. The top of the masonry was twelve or fifteen feet below the surface of the water. The walls of the dam were supported by posts and struts from the masonry. The leakage of water above the roof of the caisson was considerable, but it did not interfere with the laying of masonry. Steam-pumps were in constant use to keep the water down. The main shaft to the central air-lock was 10 feet 6 inches in diameter, with brick walls containing a winding staircase. Wear each of the smaller air-locks was a similar shaft 5 feet in diameter, containing an iron ladder. In spite of careful masonry, the water oozed through the cement into
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all these shafts. It was, however, readily removed in the way already explained. For the purpose of diminishing the leakage into the shafts, Mr. Eads gave each a lining of wooden staves 3 inches thick, and supported them on their inner surfaces by horizontal iron rings at intervals of about ten feet.The progress of the sinking pier thus far had been through the water, which readily gave place as the work advanced. The sand, however, must be removed; and here came into play the sand-pump. It is necessary to give a description of this apparatus and the manner of its working. A longitudinal section of a sand-pump, with its supply and suction pipes, is shown in Plate XII. Remembering that all the surfaces and openings are either cylindrical or conical, the construction is seen at a glance. The motive power of the sand-pump was received from a powerful Cameron water-pump on one of the pontoons, which supplied a 4-inch hose with water at a pressure of from eighty to one hundred and fifty pounds per square inch.
During the months of July and August, 1869, repeated and careful experiments had been made to determine the best shape of the suction-pipe, the most efficient thickness of the annular jet of water, and the necessary pressure in the supply-pipe. Mr. Eads, in his Report of September 1, 1869, stated that a pump having a 3-inch bore had been tried in 40 feet of water, and found capable of discharging ten cubic yards of sand per hour. On one occasion it had pumped for eleven minutes at the rate of eleven cubic yards per hour.
The action of the pump is easily explained. The annular jet assumes a conical shape, and as the water at 100 pounds pressure issues against ordinary atmospheric pressure with a velocity of about one hundred and twenty feet per second, it, by friction, almost entirely removes the atmosphere from the upper end of the suction-pipe. When the lower end of the suction-pipe was closed air-tight, the pressure of the air remaining in the inside sufficed only to support 1ź inches of mercury, — showing a very fair vacuum. Now if, instead of closing the end of the suction-pipe, it is inserted in water, the water will be forced up the pipe and through the jet by a force proportional to the head of the water above the pump and the atmospheric pressure on its surface. Thus, at a depth of 44 feet in the open river, the pressure which would force water and sand into the suction-pipe would be about thirty-five pounds per square inch. In the air-chamber of the pier the air-pressure varied from two to four and one-third atmospheres. Under such pressures, not only water and fine sand were forced through the pump, but coarse gravel and stones two or three inches in diameter found their way through without difficulty. The caisson of the East Pier had discharge-pipes for seven sand-pumps, each of them being 5 inches in diameter. One was located near each air-lock, as shown in the plan of the caisson. The pump was readily attached to the pipe just below the roof. These pipes were used alternately for supply and discharge. All trials of the sand-pump up to this time had been made upon one 3 inches in diameter, and either in the open air or immersed entirely in water. Some little experimenting was necessary to determine the best method of working it under the heavy pressure of the air-chamber. It occurred to Mr. Eads that air alone might be used instead of water to drive the pump, inasmuch as there would be great pressure to drive the sand through the pipe. A single trial sufficed to show that the plan was not a good one.
In the first trial of the sand-pump driven by water, the suction-pipe was made long
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enough to reach below the cutting-edge of the caisson to a hole in the sand. At that depth it was supposed that there would be an unfailing supply of water, which, when drawn [forced by the air] into the pipe, should carry the sand with it, as was done when the pump had been immersed in the river. This plan worked successfully for a few minutes, but the water rapidly disappeared from the hole, and, though very wet sand was carried out at first, large quantities of air occasionally escaped. This rapid escape of air appeared to be objectionable in many ways: —1. The loss of air diminished the pressure in the air-chamber, and the expanding air absorbed heat, so that the temperature suddenly fell, causing the formation of vapor so thick that the workmen could with difficulty continue work.
2. The diminished pressure in the air-chamber caused the water against the outer walls of the caisson to force its way down and under the cutting-edge, gradually washing the sand from under the outer sills and causing them to settle, while the sand remained intact under the central walls.
3. Add to the last the very obvious result of diminishing the air-pressure against the roof of the caisson, and we see that the additional weight of the caisson and masonry thrown upon the bearing-timbers would have a tendency to force them down still deeper into the sand, and very unequally, if the sand happened to be of uneven texture and unequally exposed to the influence of moving water.
4. Such an expenditure of air could last but a short time. The action of the pump would be necessarily intermittent.
5. Finally, the rapid passage of gravel and sand through the jet, or iron ring, in the pump and along the exit-pipe was very destructive. The friction was so great that the stream of air and sand issuing from the discharge-pipe often resembled a semi-luminous flame. Mr. Pfeifer records that just before dark the discharge from a sand-pump "looked like a stream of fire. This was so strong that it could be seen from the St. Louis shore."
The next plan was to run the suction-pipe of the pump into a box into which sand should be shovelled, while an independent stream of water should stir up the sand and keep the end of the pipe always covered. This plan worked well.
The main difficulty now was from clogging, and from the rapid destruction of the iron or steel "jet." (See the rings drawn black in Plate XII.) When the pump got clogged inside, sometimes the air was allowed to enter the pipe, and it generally cleared it out. At other times the pump was taken to pieces. If the top of the discharge-pipe was capped, the suction-pipe could be taken off and the pump taken down. When the perforated end of the suction-pipe got clogged, it was necessary to stop the pump for but a moment. It was soon found that with a separate stream of water to keep the sand boiling around the end of the suction-pipe the box was not necessary; a hole in the sand sufficed. So the suction pipe was made long and flexible, with a universal joint. A long handle or lever was attached to it near the end.
The final method of working the sand-pump is shown on Plate XIII. One man held the valve which controlled the main water-supply a second held the lever which regulated the position of the suction-pipe; a third directed the auxiliary stream of water three other men shovelled sand to the pump, while others shovelled to them.
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The "jets," or linings where the currents met, wore off with great rapidity; often one was used up in a run of five or six hours. They were finally made of chilled cast-iron, and put on without any finishing. These wore the best, but it was necessary to get a large supply.
Mr. Eads intended to use 5-inch pumps, but the force-pumps were insufficient to drive them. The water often failed to rise to the top of the discharge-pipe, but fell through the suction-pipe, flooding the sand in the air-chamber.
After several ineffectual attempts to run the large pumps they were abandoned, and small pumps of 3 inches and 3Ë inches diameters were substituted.
Four sand-pumps sufficed for the caisson of the East Pier. These were shifted from place to place as was required. A 4-inch pump was afterwards tried on the "West Pier, and with fair success; but the power was hardly sufficient. Nothing was lacking, however, in the case of the 4 and 5-inch sand-pumps but powerful water-pumps to make them a success. Mr. McComas, the superintendent, in his notes, very highly commends a 3-inch pump with a 3-inch suction and a 4-inch discharge. Col. Mad notes that the 3-inch pump could "discharge 300 cubic yards of sand in twenty-four hours." Mr. McComas records, under date of January 10: "Four men could not supply sand fast enough for one pump." Mr. Eads reports that "one pump of 3Ë-inch bore was found capable of raising 20 cubic yards of sand 120 feet high per hour, the water-pressure required to supply the jet being about 150 pounds pel-square inch."
The simplicity of the sand-pump — it had no working pieces — made any failure on its part impossible. All stones, pieces of coal and brick, too large for the pumps, were laid away on shelves, to be used in the concrete filling of the chamber.
The sand-pumps were always an object of great interest to visitors, and not infrequently did they astonish the workmen. For instance: the jet of a sand-pump being out of order, the water was shut off and the suction-pipe uncoupled, leaving an open pipe 3 feet above the sand. The men supposed that the discharge on the top of the pier had been capped, but for some reason such was not the case, and of course the air blew out with great violence. Says Mr. McComas, who was present: "Quick as thought, Thompson, the foreman, jerked off his hat and clapped it over the open end; but it could not stand the pressure, and it went through a sailing I" No wonder; the air-pressure on it was fully 130 pounds. Thompson, nothing daunted, off with his coat, and, folding it, held it over the pipe till the outer end of the pipe was closed.
By November 25 the caisson was fairly resting on the sand. All the bearing-surfaces were in contact with the bed of the river, and as the supporting screws and chains were no longer of use they were removed. At this time the caisson was immersed about thirty-seven feet. While the experiments with the sand-pump were in progress, the masonry was pushed rapidly forward, and the top of the stone-work was soon several feet above the surface of the river. During the further sinking of the pier the iron walls of the caisson were kept a few feet above the river, and the masonry was kept still higher.
By December 8 the sand-pumps were in successful operation; the piles of sand in the air-chamber were soon cleared away, and the "settling" began. It was a strange sensation to feel the massive pier sinking beneath one's feet, and the descent of an inch gave one
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the impression of a much greater fall. No small anxiety was felt lest the caisson should encounter layers of compact gravel and settle unequally. No trouble was experienced, however. The caisson settled gently and evenly, as the sand was trenched beside the bearing-timbers, thus allowing a slight lateral motion of the sand as it yielded to the pressure. It was soon learned that the admission of water into the air-chamber, consequent upon a loss of a little air, had the effect of increasing the mobility of the sand, so as to bring the caisson down in a very few minutes and with an exceedingly gradual motion. Any inequality in the immersion of the pier was easily corrected by judicious excavation.As the pier descended, it was noticed that the weight, which at first was largely supported by the central "timber girders," was thrown more and more upon the outer walls, where there was great frictional resistance. When the caisson was about ten feet in the sand, it was noticed that some of the brackets along the outer walls were sprung away from the roof of the air-chamber, at their inner angles, and in one case a rivet-head was snapped off. The brackets were sprung most along the west side, where the sand was most compact, and next at the ends where the timber girders intersected the outer walls.
This strain on the brackets had not been expected; on the contrary, cross-timbers had been inserted at the level of the bearing-surfaces, which were to assist the outer walls in sustaining the lateral pressure of the sand. The main cause of the springing out of the walls was soon detected by Mr. Eads. Fig. 32 gives a sketch of one of the brackets, and a section of the outer bearing-sill and the caisson wall. The timber sill was 21 inches wide, and the "cutting-edge" was 2 feet below it. As the edge was forced down, the sand filled the angle D W E under the sill, forming a compact wedge, which, as it was driven deeper into the sand, followed the line of least resistance (indicated by the arrow at E), and consequently sprung the edge out.
The first remedy suggested by Mr. Eads was to trench the sand adjacent to the sills, thus relieving them on the inside till the line of least resistance should be vertical. Accordingly, a trench was dug 9 inches below the sill, along the west side, but it had no immediate effect upon the brackets which had been sprung. Mr. Eads therefore ordered Mr. McComas to remove the cross-timbers — mentioned above, and found to be useless — and to take out the sills one by one, and cut five inches from the side next the wall, as shown at B, Fig. 32. (The sills were short pieces, running only from bracket to bracket.) This opening allowed the sand to escape from the angle formerly closed, and reduced the wedge to a
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symmetrical form which penetrated vertically. The remedy seemed to be efficient, as no further difficulty was encountered. This modification in the size and position of the outer bearing-timbers was adopted for the caisson of the West Pier.It may be well to state that Mr. Pfeifer attributed the springing of the brackets to an excessive load on the inner girders, and, as the brackets were sprung in much the same way at the West Pier, it may be assumed that the distribution of the load was an important element in the problem.
While the caisson was floating or suspended in water, the air escaped under the cutting-edge at its highest point, and the air-pressure could always be accurately calculated from the least immersion of the caisson. When the caisson was but a few feet in the sand, the air forced its way out under its sides in one or two currents of large volume; but as it penetrated more deeply, the passage of the air through the sand evidently became more difficult, and it appeared in small bubbles often sixty or seventy feet distant from the caisson. This retardation of the escapement of air from beneath the caisson caused an increase of air-pressure, by which the water was held at a greater or less depth below the level of the bottom of the air-chamber. The sand enclosed in the air-chamber and forming its floor was usually one or two feet more elevated than the lower edge of the caisson, and was entirely devoid of water. The depth of sand below the edge of the caisson from which the water was expelled did not exceed ten inches, and generally it was not over eight inches. Hence the air-pressure was that due to a depth of water nearly one foot more than the immersion of the caisson. This difficulty of escapement of the air through the sand was afterwards increased by concreting under the edge of the caisson on the rock, and the actual air-pressure could then be no longer accurately determined by the height of the water above. The pressure-gauges usually indicated a pressure of one or two pounds more than was due to the depth of water. It is not probable that the pressure in the air-chamber ever exceeded fifty-one pounds above an atmosphere.
The machinery for handling the masonry, the engines and pumps generally worked well, and the work proceeded as rapidly as the season allowed. The record of nearly every watch was: "The machinery all in order and everything working well." The winter was quite cold, and for about twenty days during the sinking of the pier the masonry was stopped. Another cause of delay was the work of riveting iron plates to the envelope walls and of putting in the timber bracing shown in Plate XIII. The excavation of sand under the pier could have gone on more rapidly had it not been necessary to wait for the masonry. The settling was often eighteen or twenty niches per day. On one day of twenty-four hours the East Pier sank 28 inches.
By December 11, the superintendence of the work by day was left in charge of Mr. McComas, the tireless superintendent of construction. Mr. Eads visited the pier and air-chamber almost daily. Some one of the assistant engineers was there during the night. On December 20, the river was thick with running ice, so that the Hewitt, a lively little tender with twin propellers, which generally made regular trips to and from the pier, transporting men and material, dared not run at night.
On the morning of the 22d, Mr. McComas and a gang of men were carried through the ice to the East Pier by the Little Giant, a small but powerful tug. The same boat
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carried Col. Flad and one "watch" ashore. No boat reached the pier again till noon of the 24th. Consequently Mr. McComas and the off-watch of air-chamber men and masons spent the night at the pier. This emergency had been partly provided for. The Hewitt, with an abundance of good provisions, was tied up at the stern of the caisson, and blankets were furnished to the men. They bunked wherever they could. Mr. McComas says some slept on the boilers, some under them, and some in the kitchen, to the great disgust of the cook. The "Hotel de Hewitt" was not as remarkable for its sleeping-apartments as for its table. The ice-breakers described in Chapter XXI were a most essential protection at this time. The water was deep and the ice was heavy, and all watched with much anxiety the success with which the breakers withstood the current and turned aside the fields of ice.On December 23, as there was no other means of communication with the shore, Mr. McComas placarded the progress made, for the chief engineer to read with a telescope on shore. At 11 o'clock on the night of the 23d, Mr. McComas entered in his log: "I have now been on duty forty hours, and I would remain on for forty more if I thought there was any danger; but everything appears to be in good shape, and the ice is passing by us as quietly as if its course had not been interrupted in the least by our works." Leaving Mr. William Alberts, in whom he had the "utmost confidence," in general charge, the tired superintendent lay down for a few hours. By daybreak he was on duty again, and apparently as ice-bound as ever. About noon, however, Mr. Eads reached the works on the Little Giant, and found all things in "good shape."
By January 7, the men at the pier were ice-bound again. The Little Giant failed in an attempt to reach the pier, and drifted helplessly down the stream with the ice. For several days the weather was cold and the river was thick with moving ice, but it did not gorge. It was too cold to lay masonry, but the sand-pumps were kept in operation and the pier settled regularly. Mr. McComas entered the following in the log of January 11: "I am completely used up; it is as much as I can do to keep from going to sleep standing up. I have had but four hours' sleep in the last eighty-four. I will go home to-night and put in a good one. Temperature, 50°."
It was found to be a very troublesome matter to properly light the air-chamber. Lamps of various patterns, burning various liquids, were tried, with poor success. Glass chimneys, long and short, large and small, were tried, but in vain. They all burned with a very dull flame and emitted an intolerable smoke. The particles of carbon floating in the air were so troublesome at times that it was necessary to precipitate them by water-spray. Some amelioration of the evil was obtained by burning the candle under an inverted funnel or chimney communicating with one of the shafts by a small outlet-pipe, through which the escape of the compressed air was regulated by a cock, thus creating a current above the flame by which the smoke was carried off.
Oil was found to be dangerous, and its use was forbidden. The clothing of two of the men had taken fire from contact with a hand-lamp or candle used in the caisson, and it was found exceedingly difficult to extinguish the flames. One of the men was severely burned, although his garments were almost entirely woollen. Candles were therefore used exclusively.
The consumption of the candles under the action of the compressed air was much more
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rapid than in the normal atmosphere. At the depth of 100 feet they were found to be consumed in about three-fifths of the time required in the open air.At the depth of 80 feet it was found that the flame of a candle would immediately return to the wick after being blown out with the breath. At the depth of 108Ë feet below the surface of the river, Mr. Eads blew a candle out thirteen times in the course of half a minute, the flame making twelve returns to the wick
The brilliantly lighted caisson of the East Abutment, with its pure, clear air, afforded a marked contrast to that of the East Pier.
The laying of a wire by which electric communication was maintained at all times between the air-chamber, the superintendent's office on the "Johnson," and the office of the chief engineer in the city, has already been mentioned. The occasion was quite a festive one. The caisson had penetrated 67Ë feet below the surface of the river, and the air-pressure was 29.3 pounds above the normal pressure of the atmosphere. Nevertheless, five ladies were present, and quite a party of gentlemen, including several representatives of the press. Mr. Eads telegraphed to some of the Directors of the Bridge Company in New York, and others sent greetings to their friends in the "upper air." According to the veracious log, they "had a good time."
The sinking of the pier proceeded with great regularity. The delay was always on account of the masonry and the construction and bracing of the iron coffer-dam around the pier. The removal of the sand below the pier was very rapidly effected. It was desirable, for several reasons, to so regulate the sinking of the pier and the laying of the masonry that the top of the stone-work should always be above the level of the water-surface. Some of these reasons may be briefly given: —
1. First and foremost, the safety of the workmen in the air-chamber. The shafts and circular stairway leading down through the masonry to the air-chamber were to be kept free and secure from all possibility of interruption by flooding. Had their tops been below the surface of the river, the springing of a bad leak in the iron envelope — such as might have been, caused by the crowding of an ice-gorge, had the ice-breaker yielded, or the explosion of a boiler, or the blow of a boat — would have imperilled not only the safety of the pier, but the lives of those at work beneath it.
2. The machinery for handling the stones worked to the greatest advantage when the
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top of the pier was from three to ten feet above the water. If much lower, the stones were lowered by stages.3. The iron envelope required bracing, and it is obvious that this could best be put in after the masonry was permanently laid.
4. Among other minor reasons may be mentioned the importance of additional weight both to the stability of the pier and the facility of settling it against the friction of the sand. The character of the sand was always much the same. Some thin beds of gravel were met, while bits of bituminous coal and limestone and pieces of drift-wood and bark were encountered at all depths.
Col. Roberts found a bone in the sand, within a foot or two of the bed-rock. It was a part of the femur, or thigh-bone, of an animal larger than man, and not petrified. Beneath the West Pier, logs partly charred were met with at the depth of 50 feet below low-water mark. During the last pumping of sand from the air-chamber of the East Pier, 84 feet below low-water mark, particles of charcoal were constantly discharged from the pumps.
On the 12th of January the caisson was 50 feet 6 inches from the rock. On February 1, the distance to the rock was 34 feet. Its progress thenceforward was quite steady. About sunrise on the morning of February 28, one corner of the caisson rested on the rock. Thus in twenty-seven days it had been sunk 34 feet, or an average distance of 15 inches per day.
At 5:40 A. M. on the 28th, Mr. McComas records the immersion as 92 feet, and adds: "We will now commence to settle the caisson for the last time. I hope we shall be successful in landing it level." During the next thirty-five minutes the pier settled uniformly 16 inches, and at 6:15 the exultant superintendent wrote: "East Pier rests on rock! The men are all in high glee and are preparing to fire a salute. There are seven, of them, however, I am sorry to say, that are not enjoying it, on account of their suffering with the cramps."
It has been told elsewhere how the still morning air echoed with the booming of cannon and a chorus of discordant whistles. Col. Roberts presented Mr. McComas with a handsome flag, which was soon flying triumphantly over the East Pier, while smaller flags adorned the Hewitt.
Thus far the only reference I have made to the peculiar sufferings of the "submarines" (as the air-chamber men were often called), on account of the compressed air, is found in this record of the kind-hearted superintendent on the occasion of his landing the pier on the rock. His great joy at the engineering triumph was tempered by a touching sympathy for the sufferings of his most faithful men.
The physiological effect of compressed air was a matter of such importance in the construction of the foundations of the Bridge that I have thought it best to give a full chapter to the subject. (See Chapter XXII.)
Meanwhile, the masonry had not kept pace with the sinking of the pier. The pier was to be faced with granite from 2 feet below extreme low-water upwards. The rock was found to be 85ź feet below low-water, and as the river was about eight feet above low-water, several feet of granite should have been laid while the pier was sinking. Only three courses of granite, amounting to 6 feet in height, had, however, arrived, and the only practicable
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course to pursue was to carry up the iron envelope and let the top of the masonry go below the water-surface. Even after all the granite on hand was laid, the top of the masonry was several feet lower than the surface of the river. Two or three more courses of backing were laid and the envelope securely braced; the shaft linings of wood and brick were carried up for the security of the men. Had the granite been on hand (and the contractors, the Richmond Granite Company of Virginia, had had plenty of time), there could not have been the slightest difficulty in building the entire pier well above high-water. The failure of these contractors to deliver the stone in time led, as will be seen, to serious complications. Meanwhile, a contract was made with Messrs. Joseph Wescott & Son, of Portland, Me., who furnished the greater portion of the granite in the Bridge.The bed-rock was found to be of dark-colored limestone or marble of such close texture as to admit of a moderate degree of polish. Its surface was worn smooth and covered with corrugations of from three to six inches in depth. It had evidently been exposed to the direct and constant action of the current, and at no very remote period.
Mr. Eads reported, as an interesting geological fact, that a piece of the bed-rock was broken off in which was found a considerable amount of white coral. It appeared on the surface of the piece and extended through it, appearing on the lower or fractured side. The walls of the cells were encrusted with quartz, the crystals of which were so minute that they could only be seen through a lens.
No sooner was the caisson resting on the rock than preparations were made to fill the air-chamber with concrete. The stones and coarse gravel which had been screened out of the sand was washed, and all refuse was taken out through the locks. The sand remaining in the chamber was to be used in mixing the concrete. Macadam in boxes was passed into the chamber through the small air-locks. Cement was taken in casks through the central lock.
The filling of the air-chamber began March 7. The space to be filled was about 1,340 cubic yards. The task was executed in fifty-three working-days.
The caisson touched the rock at its south-west corner; at the north-east corner its edge was 16 inches from the rock. It will be seen from this that the rock was, fortunately, very nearly level. The sand beneath the edge of the caisson was removed, the rock laid bare, and the space filled carefully with concrete, the air-pressure being sufficient to prevent the infiltration of more water under the edge of the caisson than could be managed by the pumping arrangements within it. The sand was packed so firmly that no trouble was taken to barricade it out of the space between the rock and the edge of the caisson. When the entire edge of the caisson and the space under its two great interior girders were thus concreted, the rock surface was gradually cleared of sand and the concrete placed directly upon it in layers of nine or ten inches in thickness, the closing courses under the roof of the chamber being stoutly rammed in place. The air-locks were then filled with the same material, and finally the shafts. The concrete was made of broken limestone thoroughly washed, the interstices being filled with mortar made of equal parts of Akron cement and pure sand.
The concrete was mixed and laid under the immediate supervision of Mr. Rud. Wieser, C. E., chief inspector of masonry, and his assistants, Mr. Rich. Richardson and Mr. Fritz Eberley, master-masons, one or the other being constantly on duty. From
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frequent personal inspection, Mr. Eads felt warranted in saying that this part of the work was unsurpassed in excellence by that in any part of the masonry above water.The concreting of the air-chamber was the most tedious and painful part of the construction of the East Pier. Daring the filling, the river rose to a point 26Ë feet above low-water, and the work in the air-chamber was done under an air-pressure that varied from forty-five to fifty pounds per square inch.
The increased pressure resulted in severer and more numerous cases of cramp and paralysis among the men, and the watches were shortened gradually to an hour in length, and finally to forty-five minutes. With such frequent changes, progress was necessarily slow.
Four days were lost by a strike of the "submarines." The men had been receiving $4 for a day consisting of three watches of two hours each. They demanded $5 for two watches of two hours each. Mr. McComas answered by sending them ashore. When the next gang was called, they preferred the same demand, and were likewise sent on shore. By the fourth day most of the men were back at work.
At first the shelter afforded by the ice-breaker, aided by the discharge of the sand-pump, had caused a deposit of sand all around the pier, and at one time below the pier the sand rose to the surface of the water. When, however, the river rose so high, this deposit rapidly disappeared.
On April 3, when the river was 13 feet below the city directrix (21 feet above low-water), Col. Flad took soundings across the river, with the following results. (The West Pier had reached the rock the day before.) The figures indicate feet in depth: —
| 45 | 41 | 48 | 50 | 51Ë | 55 | 54 | 62 | 57 | 50 | 53 | 55 | 50 | 42 | 39 | 35 | 12 |
As the river rose, the envelope walls were of necessity carried up and carefully braced. On the sides, the iron plates, which had thus far been carried up vertically, and were consequently at some distance from the masonry, were at the top sloped in to very nearly the dimensions of the masonry.
This envelope was, however, an expensive and troublesome affair. Its construction had been a constant interference with the masonry; it had been badly pressed out of shape; it had sprung several leaks; and yet so pervious to water were the masonry and the wooden shaft-linings, that its maintenance was thought necessary. But its destruction was near.
On the 13th of April, at 5 A. M., when the river was only 9Ë feet below the city directrix, the envelope which surrounded the East Pier was ruptured, and the top of the pier, which was then 19Ë feet below the surface of the river, was flooded. Only the brick walls of the shafts and their wooden linings appeared above water. An examination of the envelope by the diver proved that the rapid current of the river had scoured out the sand immediately on the east side of the pier, leaving but 35 feet of sand on the bed-rock. Within the envelope the sand had been raised by discharges from the sand-pumps, for the purpose of equalizing the pressure on the envelope. The scour left nothing but water to balance the
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lateral pressure of the sand on the inside. The result was a large break, which let the sand out and the water in. The water leaked into the main shaft so rapidly that it was impassable, and the shaft filled. Under such circumstances, it was deemed unsafe to continue work in the air-chamber. The men were signalled to come up the ladders through the small shafts. One man was in the central air-lock at the time. He came up in quite a shower-bath. All came out without difficulty, and were set at work on the West Pier, which was then on its way to the rock. Work for the time on the East Pier was entirely suspended. For two days the air-pumps were kept at work, till the air-lock doors could be fastened. Mr. Eads was at the time in New York, and Col. Flad was in charge. In their rapid exit the workmen had left one of the blow-off cocks open, and the escape of air required rapid motions of the pumps. At that juncture one of the pumps broke, and Col. Flad thought it best to pump the water from the shafts for a few feet, to prevent the lock-doors from flying open. Finally, Mr. P. Scully, the intrepid diver from St. Charles, descended through the various shafts and closed and fastened the doors, so that at the proper time air might again be used to empty the air-chamber.When the break occurred neither Mr. Eads nor Col. Flad had any anxiety in regard to the pier, provided only the ice-breaker held. Without its protection the scour would doubtless have been greater. Although on the rock, the base of the pier was unfinished; and as it had scarcely more than half its full load, Mr. Eads ordered bracing between the guide-piles, so as to protect the pier. The water was fifty or sixty feet deep on both sides of the ice-breaker, but shallower within it. Col. Flad therefore decided to sink a crib of stone just above the pier. Both the bracing and the crib were taken in hand, but, as the river soon fell, work on both was abandoned.
As soon as the doors of the air-locks were secured the air was allowed to escape, and soon the caisson was full of water. On April 15, the river was at its maximum, only 7 feet 6 inches below the city directrix, or 113 feet 6 inches above the bottom of the caisson. On May 11, the work of filling the air-chamber of the East Pier was resumed. The river had fallen 6 feet, and, though the masonry was still under water, there was no difficulty in emptying the shafts by pumps and forcing the water from the air-chamber. It was found that the caisson was much tighter than formerly, and that much less water leaked into the shafts. The filling of the air-chamber was completed May 27.
The air-locks and shafts were similarly filled, and the pier was a solid mass of masonry.
As the iron envelope was henceforth useless, the plates were removed as far as possible, and a wooden dam was constructed in sections corresponding to the sides and ends of the pier, with cushions along their lower edges which fitted against the fourth joint in the masonry from the top. When these sections were in place and firmly bolted together at the corners they formed an admirable dam, sufficiently tight for practical purposes. This dam was devised and built under the direction of Superintendent McComas. On the 13th of August, 1870, the water was pumped out, and the masonry was carried forward without interruption beyond the reach of the water.
For the items of cost and dimensions of the East Pier, the reader is referred to Chapter XXVIII.
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Chapter XIX. Special Subject No. 2. — The Sinking of the West Pier.
The caisson for the West Pier was launched on the 3d of January, 1870. Its construction was quite similar to that of the East Pier. It was of the same height, 9 feet, but of less length and breadth, being 83 feet long by 48 feet wide. Its iron-work was a little lighter, haying 5/8 andË-inch plates in its walls instead ofž-inch. Instead of seven air-locks, it had but five. Like the other, it was placed within a stockade of ten strong guide-piles, and while floating it was steadied by ten suspension-rods. Its false bottom had been made in three parts, like that of the other caisson, but of pine instead of oak there was, therefore, considerable difficulty in drawing the segments from under the caisson on account of their buoyancy. The bottom was bolted to the caisson on the outside. The pontoon-boats for boilers, derricks, engines, and pumps had received the classical names of "Alpha" and "Omega."
The first stone was laid in the caisson January 15, 1870, at the end of a season of severe cold by January 24, masonry was going on briskly. The water was shallow under the caisson, and on the 24th the sand was reached at the north-east corner the water was, however, five or six feet deep under the south-west corner.
By January 30, the sand had been levelled off so that the caisson rested on the sand, and on the next day, by order of the chief engineer, the suspension-rods were removed. The caisson was then drawing 19 feet. It had been noticed at the East Pier, the caisson being but a foot or two in the sand, that the air escaping under the edge formed a passageway for itself at some readily yielding spot, and continued flowing out there with considerable violence, often carrying sand with it. Col. Flad suggested that a blow-out hole under the west caisson might be used for removing sand. The plan was quite successful for a few days.
A sand-pump was set to work February 2. Col. Roberts was in charge of the work at this pier by day. Mr. J. M. Richardson was in charge at night. Profiting by the experience gained at the East Pier, the chief engineer decided to dispense with the iron envelope at the West Pier as soon as the caisson was well started in the sand. Consequently, the envelope was carried up to a height of only 21 feet above the air-chamber.
Another improvement consisted in stronger and tighter linings to the shafts. The wooden linings, or "tubs," as they were called, of the East Pier were a second thought, suggested by the intolerable leaking of the brick linings and masonry. In the West Pier the wooden linings were 3 inches thick, and carefully put in from the start; accordingly,
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they leaked less, but were still not thick enoughIn the matter of lighting the air-chamber they had better success at the West than at the East Pier, but still there was much to be desired. Gasoline-lamps were used, and the products of combustion were carried in tin pipes to one of the shafts, where there was an escape regulated by a valve. The combustion was still in compressed air. Col. Roberts says "They are much better than anything yet, in the way of lighting the caisson," and he thought they were all that was needed.
Not satisfied with the trials of the large sand-pumps at the East Pier, Mr. Eads put into the air-chamber of the West Pier a sand-pump 4 inches in diameter, with a 5-inch discharge-pipe. Col. Roberts records its performance as "beautiful" on February 11, and again as "grand," five days later.
In my account of the sinking of the East Pier, page 215, I said that the outer sills of the caisson of the West Pier did not fit snugly to the walls of the air-chamber. In point of fact, the space between the sill and the wall was 6 inches, and the sill was only 15 inches wide. This arrangement did not entirely prevent the springing out of the brackets and the opening of the joints at the roof, in the case of several which were placed directly under the cross-girders. The brackets which were not under cross-girders were sprung equally with the others, but the yielding of the plates in the roof saved the rivets from injury. The immersion of the caisson was, at the time, 23 feet, and it had entered the sand only six or seven feet at the point where the strain on the brackets seemed most severe. At one point the sill was turned partly over, which Col. Roberts thought tended to throw the bottom out. Three days later, when four feet deeper, there was no change in the appearance of the brackets, but after a further penetration of two and a half feet Col. Roberts reported the openings as "closed up all right."
Mr. Pfeifer, one of the assistant engineers, was of the opinion that the phenomenon of springing the brackets was due to the deflection of the ends of the iron cross-girders in consequence of the excessive load allowed to fall on the central longitudinal walls. According to him, the proper remedy would have been to throw more load on the outer sills by undermining the central walls.
While it is probable that the central walls carried more than their proportion of the load, when the caisson was but a few feet in the sand, and before much exterior frictional resistance had been developed, it seems impossible that the roof at the sides was deflected enough to produce the results observed.
It has been said that the water was shallow at the site of the West Pier; the caisson had in fact touched the western slope of a sand-bar. The discharge of the sand-pumps, protected by the ice-breaker, raised the sand still higher as the pier went down, and soon it appeared at the water's surface. The friction of the sand on the walls was therefore all the While nearly at a maximum.
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This friction was abnormally great, from the fact that in places the iron envelope bulged somewhat from the pressure of the grouting which had been poured in between it and the masonry. The consequence was that the pier settled with some difficulty. On one occasion, when the immersion was 39 feet, the friction on the walls added to the air-pressure in the air-chamber was enough to support the pier. The sand was removed from under all the bearing-timbers, both central and circumferential, to a depth of four or eight inches, excepting at the south-west comer, where the sills bore for a few feet. Under such circumstances, with full air-pressure the pier was stationary; a lowering of the air-pressure, however, caused the admission of water and a gradual settling. Again, February 26, with 41 feet immersion and masonry about eight feet above water, the sand was removed from under all bearing-surfaces to a depth varying from zero to ten inches. The south-west corner was the deepest, and the effort was to level the caisson. For a few minutes the engineer "stopped the engine, to settle." The air-pressure fell from 18 to 16 pounds, indicating a rise of four or five feet of water in the air-chamber. These diagrams show the effect —
It is obvious that the pier was a little "stubborn," and refused to settle as much as was desired at the north end.
Several diagrams will show the success with which the pier was kept level and the rate of settling (the river remaining nearly stationary): —
Had the granite been on hand, the caisson would have gone to the rock, as the masonry was laid above in the most complete and satisfactory manner. That such was not the case, is in no way chargeable to the officers of the company. The Richmond Granite Company
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was thought to be perfectly trustworthy, and they had contracted to deliver the granite now wanted, during the previous year. Three courses of granite were on hand for this pier, but even after they were laid the sinking of the pier to the rock would have carried the top of the masonry seven or eight feet below the surface of the water.The situation was very annoying, particularly as the West Pier had no protecting envelope. One thing was certain, viz., the caisson must go down to the rock with as little delay as possible. It could have been done without any envelope or dam by building up the shaft-linings and the backing and letting the masonry go under water; but as it was very uncertain when the river would again be down to 5i feet above low-water, such a course did not seem best.
Mr. Eads decided to build a wooden coffer-dam around the three upper courses of masonry, bolting it down and putting pads between it and the pier to make it tight, in all respects quite similar to that already described as made for the East Pier. For three days the sinking of the pier was delayed for the completion of the dam. The coffer-dam, when finished, was very tight, and the water did not rise within it more than an inch an hour; a Cameron pump easily kept it down.
At 2 P. M., March 14, Col. Flad records a settlement of three feet and three inches during twenty-four hours. Two feet of that amount had been effected in a few minutes. The caisson was then five feet from the rock, and very nearly level, the northern end being about one inch deeper than the southern.
On one occasion the air-pressure was reduced four pounds, to facilitate settling. The effect was marked. The water rushed with considerable violence into the chamber from all sides under the cutting-edge of the caisson, and the pier went down suddenly nearly two feet. No great harm was done, however, though three of the brackets on the east side (Nos. 10, 11, and 12, from the north-east corner) actually gave way, and all the brackets on that side were more or less bent. The brackets were designed to sustain not only the lateral pressure of the sand (which had been found by experiment to be about twenty pounds per square foot more than water for each foot of depth in the sand), but they were to assist in carrying the vertical load. It is hardly necessary to add that their strength was not calculated for the momentum of a sudden fall, and the engineer in charge was in future more cautious in settling.
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When the caisson was 1 foot and 4 inches from the rock, and the first course of granite had been laid, the pressure was reduced from 34 pounds to 30 pounds for the purpose of settling. In a short time after the settling began, the water came in very fast from a leak in the south-east part of the dam. At that point the dam was already several feet in the sand. At its lower edge the timbers and casing had met with great resistance, and when some of the bolts gave way the weight of the topmost courses of stone was insufficient to drag the dam down. The result was that the face-stones across nearly the whole south end of the pier were raised from their beds. There was obviously nothing to be gained by trying to pump the dam dry, for the more the water was lowered the greater would be the leak; so the water was allowed to rise nearly to the level of the river. As soon as the shaft-linings were built up the pump was stopped, and the water stood over the pier at the river level.
The remedy adopted for the mishap was to pump away the sand outside the dam and put down a large pad reaching below the two disturbed courses, then pump out the dam and relay the displaced stones. The pad was put down to a depth of 17 feet below the surface of the river. As the water on the pier did not prevent the work in the air-chamber, the shaft being all clear, the dam was not pumped out till the granite arrived, after the base of the pier was finished.
Before sinking the pier the remaining 12 inches, the sand was pumped away from the lower edge of the dam and the internal bracing was well loaded with stones, so that it might not fail to sink with the pier. On April 2 the caisson reached the rock, the immersion being 77 feet and 9 inches. Ninety-nine days had elapsed since the caisson had been launched.
The filling of the air-chamber with concrete began on the 4th of April. This work progressed without interruption till the caisson was filled solid. Gangs of from fifty to one hundred men worked from four to six hours each. The maximum amount of concreting in one day was 100 cubic yards. When work at the East Pier was interrupted, all hands worked at the West Pier, pushing the work very rapidly. At the extreme high-water on April 13-16, some anxiety was felt about the breakwater at the West Pier as well as for that at the East Pier, and Col. Flad, acting for the time for Mr. Eads, considered it hazardous to work in the air-chamber at night; so the night-work was stopped. A man was stationed on the breakwater daring the day to give warning of any evidence of failure, and the workmen were instructed to carefully fasten the inner air-lock doors whenever they came out at night.
The filling of the caisson was completed in the most satisfactory manner May 8, thirty-four
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days having been spent in the work. The amount of concrete put into the air-chamber locks and shafts of the West Pier was 1,339 cubic yards.The air-pressure was generally 40 pounds above the normal.
In a few weeks the long-wished-for granite arrived, the dam was pumped dry, and the pier built above high-water.
Plate XL is a heliotype from a fine photographic negative taken about March 1, 1870, by Mr. Benecke. It shows the top of the masonry of the West Pier, the discharge from the sand-pumps, the guide-piles, the "Alpha" and "Omega" with their chimneys, and six sets of derricks. A few of the timbers and piles of the ice-breaker can be seen in the foreground.
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Chapter XX. Special Subject No. 3. — The Sinking of the East Abutment.
It is with great pleasure that I now proceed to describe more fully than could properly be done in Chapter VI the characteristics of the East Abutment, and briefly narrate the story of its construction. The story is comparatively uneventful, merely because all plans were carefully matured and smoothly executed; still I think it deeply interesting.
The East Abutment is the largest and deepest of the four piers of the Bridge, and in its design and construction we have a faithful realization of the engineer's ideal.
As I have already said, the determination to sink it to the rock was a change of plan. It was known that the sloping bed-rock lay some one hundred and thirty-six feet below extreme high-water, and it was not thought necessary to sink the masonry so far till the success of the plan adopted with the channel piers demonstrated the feasibility of constructing the East Abutment in the same manner. The original plan seemed to offer reasonable security at much less expense; but a foundation of loose sand, guarded never so well by rip-rap and piling, was so inferior to a bed of native limestone that the additional cost of giving this a foundation equally as secure as the other great piers seemed but a trifle in comparison with the importance of giving to the masonry a stability which could not be called in question.
The design of the caisson was completed in March, 1870, and the contract for its construction was made in May. It was built at the "docks" in Carondelet, and launched November 3, 1870, in the presence of a large number of spectators.
The design was so novel, and at the same time so admirable, that I have devoted two entire plates ( XIV and XV) to its full and accurate representation, while Plate XLI gives a bird's-eye view of the top of the caisson, looking west, soon after the laying of the masonry had been begun.
It will be observed from the drawings that the roof and walls of the air-chamber are mainly composed of timber, strongly locked and bolted together. In his Report of October, 1870, Mr. Eads said: "Beneath the masonry piers of suspension and truss bridges, it is quite common to employ a considerable amount of timber. Where the pressure upon the pier is a vertical one, this economical substitute for stone is admissible; but in the piers of an arched bridge, where some one span is at times loaded while the others are unloaded, the thrust of the loaded arch has a tendency to oscillate the piers, and with a few feet in thickness of a material so elastic as wood under their bases, this oscillation would prove a dangerous feature. In the abutment piers, where the thrust is only from one side, and oscillation is prevented by the works on shore, timber may be safely used to a considerable
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extent. To give the desired stiffness to the caisson for this abutment, and avoid the more costly use of iron, the roof of the air-chamber is made of timber 4 feet and 10 inches in thickness. A large amount of timber is also used in constructing and stiffening the sides of the air-chamber, which are 10 feet high, and in forming two horizontal trusses or girders through the air-chamber. These two girders are each 10 feet thick at the top, 3Ë feet at the base, and 9 feet in height. They are about seventy-three feet long, and are interlocked at each end with the sides of the air-chamber. They divide this chamber into three nearly equal compartments, in the direction of the length of the Bridge. Communication is made between these, compartments by means of two openings through each girder. The sides of the chamber are 8Ë feet thick at the top and 18 inches at the bottom, and are composed of timbers, some placed vertically, others horizontally, and some inclined at an angle of about forty-five degrees, and the whole, including roof and girders, thoroughly interlocked together and bolted with large iron bolts. All of the timber is of the very best white-oak. In addition to the iron bolting used, these timbers are thoroughly secured together with large white-oak tree-nails."The wood-work of the caisson was most admirably executed under the superintendence of Mr. John Dunlap, master of ship-carpenters.
Enveloping this entire wooden structure was a cover of plate iron with air-tight joints. This was 3/8 inch thick, and its sides were increased in thickness at the bottom edge to 3 inches by riveting fourž-inch plates together; these extended several feet up the sides. This iron edge extended 10 inches below the wooden sides, and formed the cutting-edge of the caisson. Every two feet the iron sides were strengthened by vertical angle-irons 3 X 7 inches in size, riveted flatwise to the outside of the caisson. Through these angle-bars, bolts 11 inches in diameter were inserted, and by them the iron and wooden sides were strongly held together. This iron covering extended over the wooden top of the air-chamber and formed a floor on which the masonry was laid. The lining of the three shafts sunk through this floor was tightly riveted to the iron flooring.
Across the roof of the caisson, and parallel with its river front, ran two strong plate-iron girders, fully shown in the drawings. They were intended not only to stiffen the roof of the air-chamber, but to secure greater rigidity in the caisson as a whole during the earlier stages of the sinking process.
The iron sides were carried up 15 feet above the roof, and there they stopped. The masonry above that point, therefore, had no exterior envelope.
It was my privilege to visit the caisson a few days before the launch. Built upon ways like a ship, it was a strange-looking craft. A vertical wall of iron, 30 feet high, surrounding a figure of irregular shape, was all that could be seen from without. From the top of the wall, to which ascent was made by a temporary flight of steps, the appearance was equally strange. Nothing but iron was yet visible. The iron girders, 13 feet high, separated what seemed to be an immense iron box into three irregular parts. In the floor of the central part was a large circular opening and shaft leading to the air-chamber. In another were two smaller openings leading to the side shafts. The central shaft was 10 feet in diameter, and communicated with a large air-lock on each side. The openings to the side shafts were 4 feet in diameter, but the shafts themselves below deck were 8 feet in
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diameter. All air-locks were 8 feet in diameter. The details of the central air-locks are fully shown in Plate XV. Numerous small openings in the iron deck showed where air and water were to be supplied, and where the sand was to be pumped out and in. On the occasion of my first visit, just before the launch, I wandered freely into all nooks and corners, candle in hand, and thoroughly inspected the ingenious construction of the caisson. The three compartments below were transverse as compared with those above, as may be seen on Plate XIV, and seemed contracted and small, so much space was occupied by the timber walls and "girders" (as the inner walls were called). Everything seemed exceedingly solid and strong. The carefully squared oak timbers rested smoothly on every support, and the heavy-headed bolts seemed to bind all into a rigid unity. The air-chamber proper was 9 feet deep, and the oaken roof was 5 feet thick above it. The air-locks, though but four in number, were spacious and easily entered at either door. The long air-locks, with outer doors in the upper end, seen in the channel piers, were not found here. I found an unusual supply of 4-inch and 5-inch pipes connecting with the air-chamber, — nineteen in all. Their positions are seen in the engravings. Their careful distribution and their conical mouths were accounted for by the engineer's plan for ultimately filling the air-chamber with sand. The false bottom was in three sections; upon it, previous to the launch, the whole weight rested.The launch was most successful. The ways had been well tallowed, and when the blocks and lashings were removed, nothing but gravity was required to carry the monster into the river. The smoking ways gave evidence of the weight of the caisson, while its momentum was shown by the huge wave its broad front wall raised as it swept into the river. Fortunately the river was high for November; low water would have delayed the launch. After some uncomfortable rockings, the caisson rested with a fairly even keel (?), drawing ten or eleven feet, the smaller end being the deeper. It was towed seven miles in five hours by three steamers, — the "Peter," the "Atlantic," and the "Mary Alice," — and at night was anchored "in position." The river was 16.05 feet below directrix, and the depth of water around the caisson varied from twenty to twenty-nine feet.
On the land side, a platform, standing on piles, supported derricks, boilers, and engines; on the river side was our old friend the "Gerard B. Allen."
Twelve days were spent in completing arrangements for laying masonry; in securing the caisson in position (no guide-piles were used; there was little current, and the caisson could be accurately placed by cables); in stopping leaks in bolting the iron deck down to the wooden one, that the latter might have adequate support while the caisson was floating; in arranging barges, pontoons, trusses, etc., for furnishing power and handling masonry; and in removing the false bottom to the caisson. The last was done by putting in all the air-pressure that the depth of the caisson would allow, and then, after removing all the fastenings, dragging the bottom out by sections, by means of a tug. On the 17th, when the first stone was laid, the river had fallen nearly seven and one-half feet, and one corner of the caisson touched the sand.
On November 22, masons began night-work, using calcium lights, Col. Flad being in immediate charge. Mr. Pfeifer took his turn with Col. Flad in charge of night-work. On
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November 25, as the greater portion of the caisson rested on the sand, a sand-pump was started. "It worked beautifully."All the machinery worked well, and good progress was made. Some trouble was anticipated from rocks, buried timbers, and perhaps steamboat wrecks hidden in the sand, but in this all were happily disappointed. Some rubble-rock was all that was found worthy of mention. When all the sand-pumps were at work, the full complement of men in the air-chamber was: one man in charge, three foremen, and a gang of ten men in each compartment. They worked ten hours per day, and men were plenty. On December 2, the air-chamber men were divided into three watches of working eight hours each.
The caisson settled from one to one and one-half feet daily. On December 3, Mr. McComas writes: "We had quite a blow-out from center chamber to-day, drenching the masons and riveters. Two of them, working on the outside on a scaffold, were thrown by the water up onto the deck of the ‘Allen.’ Two ladies were at the time in the air-chamber, and naturally they were very much frightened. The water rose 14 inches inside in a few seconds."
Mr. McComas attributed the phenomenon to the fact that the sand in the central compartment had been excavated to a depth of several inches below the cutting-edge of the caisson, and that as it was closely packed all round the outside of the caisson, it prevented the free escape of the air under the edges, till the pressure inside was considerably greater than was due to the depth. Whatever water had filtered in had been pumped out by the sand-pumps. Finally the air forced its way up through the sand, making a large passage of escape, through which a large amount of air rushed out at once with comparative violence. The air-pressure remaining was probably less than that due to the depth of the caisson; so that the water rose above the cutting-edge. A similar discharge had occurred once before.
By December 9 the immersion of the caisson was fully thirty feet, or to the top of the iron envelope. By this time, through the deposit of sand and the falling of the river, the sand was above water on all sides but the west, where it was still washed by a gentle current. Observations on its position showed that the caisson had worked its way from the shore about three feet on the north, and about three feet five inches on the south. Mr. Eads at once ordered the superintendent to pump the sand out to a depth of six or eight feet on the east side, and then to settle the western edge twelve or sixteen inches lower than the eastern, before settling it as a whole. The object of this is evident. The action of the water, during the operation of "settling," allowed the caisson to move as in a thick semi-fluid, partially sliding upon its inclined side. An inclination such as is described above, and the removal of the heavy sand-pressure on the eastern side, had the effect of sliding the caisson towards the shore. During the next twenty-four hours, the record shows that the caisson settled 3Ë inches at the eastern edge and 10Ë at the western. On December 15, the western edge was 1 foot and 4 inches lower than the eastern.
On the 18th, the caisson was levelled up again (or rather down). Mr. McComas says: "We have not been very successful in getting the caisson farther east; we have just about held our own." A few days later, it appears from the measurements that six or eight inches
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were gained towards the shore. The effort was continued till, in all, the abutment was moved back 9 inches at the northern end and 10 inches at the southern. Beyond these amounts it would not go. The offsets of some of the upper courses were slightly modified in consequence of this displacement, and the granite courses were placed in correct position.Good progress was made on the masonry and in sinking the caisson during the week ending December 19. Then the weather set in cold, and for eleven days the temperature was too low for the laying of masonry. Meanwhile the ice, which at first ran heavily, gorged and threatened both the ice-breaker and the "Allen." Masonry was resumed December 30, day and night. On January 1, the ice moved some ten or fifteen feet and then stopped. The ice-breaker was injured, and the "Allen" was dragged in spite of her cables. Mr. Eads ordered all hands to throw in rip-rap below the ice-breaker. Struts of timber were put in, and the rock was piled to the surface of the water. On January 11, the ice passed out between the channel piers, while near the East Abutment it held fast, though the immediate danger to the boats was over.
No settlement took place after December 19 till January 14, when the abutment was settled 2 feet and 8 inches. On January 16 and 17 the river fell so rapidly that the "Allen" was aground, and it was necessary to pump the sand out from under her to keep her in proper position. The ice interfered with the transportation of stone, so that even when the weather was mild there was often no stone for the masons.
January 29. — "The twenty-sixth course, containing 240 yards, was laid in ten hours with twelve masons [and a strong force of laborers]. A good day's work." — [Superintendent's Diary.
In the air-chamber each gang worked three two-hour watches. The immersion was 57 feet.
On the night of the 3d of February, 346 cubic yards of stone were laid during twelve hours. As was to be expected from the shape of the caisson, the western end settled more readily than the eastern. The immersion was generally from six to twelve inches greater. This had the effect of slightly moving the pier toward the shore, as already stated.
As the work progressed the value of several new features not yet mentioned was plainly seen. The pier had but three shafts; consequently the masonry was less interfered with. These shafts were lined with stout pine staves 10 inches thick at the bottom. Previous shafts had had weak linings, and it was hoped that 10 inches would be found thick enough; yet, strange to say, the lower course in the central shaft gave considerable trouble by leaking.
The numerous discharge-pipes for the sand-pumps made it possible to locate the pumps more conveniently, and hence the excavation was very rapid. The air-chamber was brilliantly lighted, and at the same time the air was kept pure and clear. The problem of how to light a chamber of compressed air had at last been solved by Mr. Eads in a very simple manner. Fig. 33
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is a complete representation of the lamp employed. G is the chimney-pipe connecting the lamp with one of the discharge-pipes; it has a valve (g) by means of which it may he closed when the lamp is opened. H is a union coupling for connecting the chimney-pipe to the cap of the globe. K is a metallic cylinder for holding the lamp; it is cemented to the globe at J. The lower end is closed by a tight-fitting door hinged at N and caught by a spring at O. The door consists of two metallic disks enclosing a rubber packing. P is a pipe passing through the door, and furnished with a screw-thread on its interior surface; p is a small orifice in the side of P, and R is a thumb-screw by means of which the orifice may be partially or wholly closed. The method of adjustment is obvious. With g wide open, the air within the globe was under only the normal pressure of the atmosphere. The air supply through p could be regulated to the demand of the lamp. All the products of combustion were carried off through G. Either candles or oil could be burned. Several lamps were in constant use, and as they could readily be moved from one discharge-pipe to another, the work in hand was always well lighted. To add to the effect of the lamp, the walls and roof of the air-chamber were thoroughly whitewashed. In consequence of these improvements the air-chamber was cheerful and wholesome to an extent never before realized.The central shaft was not only furnished with winding stairs, but an elevator was put in operation as soon as the depth of the pier was considerable, for the more especial purpose of bringing up the workmen from the air-chamber. The value of this important feature is fully discussed in Chapter XXII.
The result of these several improvements was to make a visit to the air-chamber much more attractive and visitors more frequent. Engineers, both European and American, visited the work, and not infrequently ladies made a trip to the air-chamber. On one occasion, when important legislation was pending before the Missouri Legislature, so large a delegation from Jefferson City visited the air-chamber of the East Abutment that one watch of workmen was forced to be off to afford the visitors room.
On February 7, Mr. McComas adopted a new time-table for the air-chamber men. He formed six gangs, of a foreman and from fifteen to twenty men each, and each gang worked two watches of two hours each. The men rode up from the air-lock in the elevator, and were required to rest in the barracks near the pier the four hours between watches and one hour after the second watch. The immersion of the caisson was 70 feet. The top of the masonry was 6 feet above the water.
On February 9, at the suggestion of Dr. Jaminet, at that time in charge of the hospital-boat, the hours for the "submarines" were changed again: three watches of one hour each, with three hours' rest between watches.
About a week of severe cold prevented the laying of stone, but as the river continued to fall (as is usual in very cold weather) the caisson was sunk so as to keep about six feet of masonry above the water. On February 17, masonry was laid at the rate of 375 cubic yards in ten hours.
Mr. McComas reports, February 18: "Machinery all in good order and working well; no complaint from any one. Everything goes on as regularly and smoothly as clock-work, when not interrupted by the bad weather. River 25.6 feet [below city directrix]; masonry
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21.2 ditto. Immersion, south-west corner, 80.9; north-west, 80.1; south-east, 80.9; north-west, 80.1. From rock, 21.85 feet. Revolutions, [air-pumps] 85 [per minute]; air-pressure, 37.5 pounds [above normal]."At this depth a layer of very coarse gravel was met, which required screening, as only the fine could be pumped out. The screenings were brought out through the air-locks, as there was no convenient storage-room in the caisson.
On the 19th, in consequence of warm rains, the river rose 2Ë feet. This rapid rise suggested the greatest activity in laying the masonry, and led to an estimate of the capacity of the men and apparatus.
February 21. — "Masons have as much as they can do to keep pace with the rising river. Water within four or five feet of the top of masonry, which is as close as I care it to be."
February 26. — Superintendent decides to work "submarines" only during the day, as most of the cases of paralysis ("Grecian bend" he called them) occur in the night-watches. He thinks the men do not rest properly during the day, and some of them even work elsewhere.
February 27. — Masonry stopped by rain and the river rising. "Water 23 inches below the top of stone-work."
Mr. McComas's report for the last day of February is: "River, 14.8 feet; masonry below directrix, 10.1 feet; immersion at all corners, 97.3 feet; from rock, 14.9 feet; revolutions, 85; air, 43 pounds."
During the day the fiftieth course of limestone was laid. The face-stones of the fifty-first course on the river side are granite.
On reaching a depth of 100 feet, by order of the chief engineer the labor of the air-chamber men was reduced to two watches of forty-five minutes each.
On the morning of the 8th of March, Mr. McComas reported as follows: "Everything in good shape and working well. Masonry 8 feet above water; immersion, 101.1 feet; from rock, 10.1 feet; air-pressure, 46 pounds." Four or five days of continuous work would have placed the East Abutment on the rock.
About 3 o'clock P. M., the fearful tornado already described in Chapter VI burst upon the cluster of boats, barges, derricks, platforms, and trusses that surrounded the East Abutment; with what terrific effect has already been told. Mr. McComas's brief record states that "the tornado swept every derrick from the deck of the ‘Allen.’ Fortunately there was but one life lost, that of James Halpin. One mail, named Clark, was seriously injured, and four others slightly. The air-pumps both on the ‘Allen’ and on the platform were rendered entirely useless. A ferry-boat was blown under the platform, carrying away half the piles that supported the boiler. In consequence of which we had to let the air-chamber fill." Mr. McComas does not speak of his own narrow escape.
The air-chamber gang came out leisurely, and while the air was escaping the caisson settled in good shape several inches. All hands were employed in clearing off the wreck and in getting the machinery in order. On Sunday, the 11th, they commenced pumping air. In fifteen hours the chamber was clear. On entering the air-chamber, the superintendent found everything in good order; the sand had not risen any more than it usually did in settling.
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The machinery for lifting stone and pumping water was not ready for work till the 16th. Masonry was resumed March 20. The caisson was then less than nine feet from the rock. The rock was reached at 4:30 P. M. on the 28th of March, 1871. The river stood 17.45 feet; the immersion was 109 feet and 8Ë inches all around; the air-pressure was 49 pounds above the atmosphere. The damaged machinery had been only partly restored; so the progress had been slow, but very satisfactory. It was noticed that after the interruption and the escape of all the air, the air-chamber was much tighter than it had ever been before. Sixty revolutions of the air-pumps were as efficient in maintaining the pressure as ninety-five had been before. This hint should be followed in the execution of similar work.
The surface of the rock was found to be remarkably even, the difference of level being but 10 inches. The caisson was stopped when 1 inch from the rock at the nearest point, — the southern cut-water. The average depth of the rock below the city directrix was 127 feet and 5 inches, and below extreme high-water 135 feet.
Concreting under the exterior sills was begun on the 31st. The broken stone was placed in boxes containing three cubic feet. These boxes were taken through the locks, twelve at a time in each lock, with the necessary amount of cement. Sand was plenty inside. During the night, materials for 30 cubic yards of concrete were taken into the chamber. In spite of the comparatively small amount of concreting to be done, it was a tedious job. The sand was carefully taken out for a short space under a sill, and piled on one side. The concrete was next mixed and placed in position, and firmly rammed, so as to give a good bearing. This was done with men who worked but forty-five minutes at a time, and only twice a day. The head foreman was not present in the air-chamber beyond a few minutes with each gang. Contrary to the original plan, concrete was laid under the central girders and under the locks and shafts. Eighty-two cubic yards of concrete were used. On April 17 the concreting was finished, and the sand remaining in the three compartments was levelled off; it averaged 3 feet 3 inches in depth.
The reader hardly needs to be told that beyond the concrete under the bearing-timbers of the walls it was proposed to fill the air-chamber with sand. In his Report of October, 1870, written while the caisson was being built, Mr. Eads thus explained his plan for
FILLING THE AIR-CHAMBER:
"The most valuable improvement in the design of the caisson will, I think, be found in the method devised for filling the chamber when it has reached the rock. It is a well-established fact that sand constitutes one of the most reliable and durable materials for foundations known, if availed of in positions where it can be securely retained under the structure erected upon it. It is an equally well-established fact that timber, when entirely submerged in fresh-water foundations, is indestructible. These two facts will be relied upon in filling the air-chamber and fixing the foundation of this pier upon the rock. Instead of concrete, sand will be chiefly used for filling the chamber. The sides of the caisson are of great thickness, and are thoroughly interlocked at the corners of the air-chamber and at the ends of the girders. The possibility of the sand surrounding the pier ever being scoured out to the rock, at the site of this abutment, is a very remote one. It is certainly much more improbable than that it may be scoured thus deeply at the sites of the two channel-piers. To avoid all danger from this very remote possibility throughout all time, whatever space there may be existing between the timber walls of the caisson and the bed-rock, after the caisson shall have reached it, will be thoroughly
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concreted, so that these walls will have a substantial bearing upon a solid material, which cannot be affected by any current that may possibly wash the base of the pier. The walls of the air-chamber are so framed as to be sufficiently strong to resist the bursting pressure of the sand within the chamber, caused by the weight of the masonry of the pier and half the side-span upon it, even after all the iron used in it shall have been corroded away. The base of the pier is 5,000 square feet in area, and the weight of the entire pier, including one-half of the span, will be about 46,500 tons. The pressure per square foot on the rock would therefore be 18,600 pounds. The area of the wooden edge of the caisson, including that of the bottom of the girders, air-locks, and shafts, is about 1,250 square feet. This area alone would be capable of sustaining the pier, without any additional support from the sand contained within the air-chamber. Without this sand-filling, the pressure upon the wooden base of the caisson (including the locks and shafts) would be about 74,000 pounds per square foot, or 514 pounds per square inch. This pressure is not beyond the power of good white-oak to resist, nor would it be sufficient to crush the concrete that will be used in filling the small space between the oak and the rock. Tests made with our testing-machine upon a number of blocks of concrete only six weeks old gave an average resistance to crushing equal to 1,200 pounds per square inch. Of course, with the integrity of the exterior of the caisson unimpaired, the escape of sand from the interior would be impossible. With the interior compactly filled, the pressure of the superincumbent mass must necessarily be very nearly equally distributed over every part of the caisson, and hence it cannot exceed about 18,600 pounds per square foot.
The tedious process used in concreting the air-chamber of the channel piers, together with the objections to working men at such great depths, induced me to devise some method by which a smaller amount of manual labor could be made to accomplish equally good results. By the plan determined on in this case I confidently hope to accomplish the necessary work in the air-chamber with a fifth or sixth of the manual labor which was required under the East Pier.
This method is so simple as to be readily explained. So soon as the rock shall have been struck by the iron edge of the caisson, the space then remaining between the wooden walls of the caisson and the rock will be thoroughly concreted. The borings indicate that the rock is quite level, and it is not probable that inequalities of more than eighteen inches will be found in it. It is estimated that 100 cubic yards of concrete will be sufficient to support these walls, forming a bed of an average width of 3 feet 6 inches, by 2 feet 6 inches in height. This concreting being done, all of the pipes passing vertically through various parts of the pier, and used for air, water, and sand-pumps, will be closed at the top, and the pumps, valves, and pipes connected with them in the air-chamber will then be taken off. There are nineteen of these vertical pipes, each either 4 or 6 inches in diameter, the lower ends of which are enlarged conically through 5 feet of their lengths. These pipes being opened at their lower extremities, and one of the inner doors of an air-lock being secured from being clogged by sand, the air from the chamber will be permitted to escape and the chamber will be filled with water. This being done, sand will be introduced through the various vertical pipes mentioned. By means of plummets in these pipes, we shall be able to determine the height of the sand discharged in them; and when it is near the roof of the chamber the air will be again pumped in, and workmen will be sent in to level it off. By repeating this process two or three times, the chamber can be filled neatly to the roof with sand compacted in the water, which will insure its solidity. The remaining space can then be filled with concrete rammed in under the roof of the chamber."
The plan thus minutely laid down was faithfully carried out. Elaborate experiments upon the "angle of repose" of river sand had shown that the angle was independent of the hydrostatic pressure; that is, when the sand has once assumed a certain slope in shallow water, no amount of liquid pressure can diminish the slope. Water currents, however, were very efficient in levelling the sand.
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On the 18th of April, everything being in readiness, Mr. McComas pumped the air-chamber full of water, preparatory to the filling in of the sand. The water was pumped in so as to avoid disturbing the bed of concrete by allowing the water to be forced in from outside. Sand was then put in by hand through all the pipes. When 60 cubic yards had been put in, air was forced in and men were sent in to level the sand. It had formed regular cones below the pipes, and was well packed in many places.
On the 21st of April, air was allowed to escape while the water was pumped in again. Sand was then pumped from the river directly into the caisson through the 6-inch pipes. The pumps worked admirably, throwing immense quantities of sand. The strong currents of water spread the sand very efficiently. While pumping in through one set of pipes, others were used for the overflow, and then the pumps were shifted.
April 23, Mr. McComas writes: "We finished filling all the pipes, with the exception of those adjacent to the main air-lock doors, at 11:30 last night; and I judge from the quantity of sand put in, and from my soundings, that the north and south chambers are well packed, with the exception of the space west of the locks, which I left for entrance. The next filling I will close them entirely, leaving an entrance in center chamber at west lock, which will be the closing-point." An inspection showed that the south chamber was nearly full, the center three-fourths full, and that men could not get into the north chamber. Later, the north chamber was entered after a little cutting with a shovel. All the compartments were packed solid to the roof at the eastern ends. "Bulkheads" were next built from the west air-lock door in the center chamber, so that each compartment could be examined even after another filling. Water and sand were then pumped in, till all pipes were full; Mr. McComas himself entered the chamber, to make certain that every hole and corner was filled solid with sand. The final openings had been so arranged that they would readily fill when the bulkheads were removed. Everything worked most successfully, and on the last day of April, 1871, at 10:52 A. M., Mr. McComas closed the air-lock door for the last time. The final cavities were soon filled, and the great task was finished. Mr. McComas wrote in his "log" that his "conscience was easy and clear, for he knew that every detail of the work was well done."
The air-locks were filled with concrete and timbers firmly wedged in, and the outer doors were taken off. The shafts were filled with concrete, after the wooden linings had been taken out down to below "low water."
Before the end of May all this work was done, and the East Abutment stood like a single block of imperishable limestone upon the unyielding rock, towering up through nearly one hundred feet of sand, ready to receive the massive granite-faced pier which now rises still a hundred feet higher.
During the construction of the East Abutment the chief engineer visited it nearly every day, and the superintendent sent him daily reports. The special duties of Col. Flad and Mr. Pfeifer, in supervision of the work, closed as soon as the caisson was resting squarely on the sand, and immediate charge of the work was left entirely to the superintendent. Mr. Andrews gave his personal attention to the laying of the masonry. Messrs. Morris Wuerpel and Thomas Malvern were the foremen in general charge of the air-chamber gangs, one being on duty by night, the other by day.
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Chapter XXI. Special Subject No. 4. — The Stone Approaches — The Ice-Breakers — A Note on Foundations Built by the Aid of Compressed Air.
The Bridge is flanked on either hand by a graceful facade supported by five piers and arches built entirely of stone. Connected with the fifth pier are the towers, designed to accommodate stair-ways and elevators leading to and from the upper road-ways, and to add to the beauty of the Bridge.
The West Approach is entirely of stone. (See Plate XVII.) Each arch has a span of 26 feet 11 inches, and the crowns are about forty-three feet above the level of the street. The piers rest on the rock underlying the wharf, with foundations 46Ë feet long and 9 feet wide, built of Missouri red granite to the height of the city directrix. Above the granite, the piers, arches, facade, and southern tower (so far as built) are of sandstone from Ste. Genevieve, Mo.
From the towers west to the mouth of the tunnel, at Third Street, the road-ways are carried on piers, arches, and walls of brick or limestone, crossing Main and Second Streets on iron bridges.
The masonry of the East Approach is an exact duplicate of the West with the exception of the foundations of the piers. When the Report of 1870 was made, it was the intention of Mr. Eads to build the five small piers on pile foundations; they were, however, with the exception of No. 5, sunk by the pneumatic process used in sinking the large ones. This was believed to be more certain and economical than coffer-dams, the method used on the West Approach. The result fully confirmed this opinion.
With pier No. 2 a coffer-dam would have proved very expensive, as this pier encountered in its descent the hulk of an old and strongly built ferry-boat. Its planks were 3 inches thick, and the floor-timbers were 4 X 8 inches square. This hulk had to be cut away to permit the descent of the pier, which went directly through it, the caisson cutting the keelson of the wreck in two. This not altogether unexpected difficulty delayed the completion of the pier about three weeks.
It was not deemed necessary to sink the foundations of the first four piers of this approach deeper than 12 feet below extreme low-water mark. The caissons used were made
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wholly of oak timber, excepting only the air-locks and the spikes and bolts used in fastening the timbers together. They were 10 feet high; consequently they are entirely below low-water line. The surface of the wharf is about nineteen feet above the bottom of the foundation of No. 1, and about thirty-two feet above that of No. 4.The main features of the caissons of these piers are shown on Plate XVI. Figs. 1, 2, and 3 show the caisson designed by Mr. Eads, and used for piers 1, 2, and 4. Figs. 4, 5, and 6 show the caisson designed by Col. Flad, and used for pier No. 3. Mr. Eads's design was the more economical, but his caisson was less rigid, and consequently more given to leaks. The caulking was done by means of oakum, cement, and paint.
The towers and pier No. 5 were built on a foundation of concrete 6 feet deep, under which a system of piles was first driven to an average depth of 25 feet. The concrete is based 15 feet above low water mark.
The East Abutment, resting on the rock between these approach piers and the river, together with the pavement covering the river shore, was thought to be amply sufficient to prevent the current of the stream from affecting the foundations of these small piers.
The iron approach east of the towers was designed and constructed by the Baltimore Bridge Company, Col. C. Shaler Smith, president and engineer. Beyond that is a wooden trestle and an embankment. A grade of 68 feet to the mile brings the railroad tracks down to the level of the roads in East St. Louis in a distance of about three thousand feet. (See Plate II .)
The upper road-way for carriages and pedestrians, as it descends from the eastern end of the Bridge, divides at the towers into equal portions, one on each side of the now uncovered railway, and by a grade of four feet to the hundred reaches a broad platform at Fourth Street, whence the two narrow road-ways continue east to the level of Dike Avenue, while from the same platform a road-way beneath the railway tracks runs back to the river wharf directly. (See Plate III for a profile of the Bridge and its approaches.)
All the large foundations were sunk in winter. This arrangement was accidental rather than designed, and was unfortunate for three reasons: In the first place, the cold greatly retarded the laying of the masonry, as work always stopped when the temperature fell to 28° in the second place, the running ice frequently interfered with the transportation of stone; and thirdly, and more than all, it was necessary to construct above each pier an elaborate and expensive bulwark, which should afford adequate shelter from the ice to both sinking pier and floating pontoons. In no case could the ice-breaker have been dispensed with without deferring the work for several months. Incidentally the ice-breakers served another useful purpose, namely, adding to the stability of the piers by increasing the deposit of sediment and preventing scour.
My description of these important adjuncts to the construction of the Bridge foundations is given in very nearly the words of Mr. Eads.
The floating ice frequently attains a thickness of ten or twelve inches, and often covers the entire surface of the river, moving along at the rate of about three or three and a half miles per hour.
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To establish in mid-channel any temporary works to withstand an element so apparently resistless, and of such exhaustless volume, was an untried experiment on the Mississippi that presented several very discouraging features. The two chief difficulties were: First, to place any construction above the pier that would not be quickly scoured out by the current; and, second, to make such construction strong enough to resist the pressure of the ice. The method devised by Mr. Eads for overcoming these difficulties will be fully understood from the following description: —
About two hundred feet above the East Pier, at a point from whence the current would flow to the center of the pier, a pile was driven which formed the apex of a triangular system of piles shaped like the letter A. Prom this pile two lines of other piles were driven at distances of eight feet. These two lines extended down stream a distance of about two hundred feet, and represented the two sides of the letter A. At their lower extremities these two sides were about one hundred and eighty feet distant from each other. The triangle thus formed was filled in with other piles driven in transverse lines from side to side, at distances of about fourteen feet, and the tops of the entire system were then thoroughly braced together with hewn oak timbers 10 X 10 inches square, well bolted to the piles, which were of cypress.
The water was from forty to forty-seven feet deep when this part of the work was executed, and many of the piles were washed up as the work progressed. It was difficult to drive them into the sand more than twenty feet deep, even with a steam pile-driver of 3,500 pounds weight.
About fifty feet above this triangle was placed a clump of nine large piles driven close together, and encased in sheet-iron throughout about twelve feet of their length, to prevent the ice cutting the piles. About one hundred and fifty feet above this clump of piles, a large iron pile made of the shell of an old cylindrical steam-boiler, 28 feet long and 42 inches in diameter, was sunk vertically nearly to its full length into the sand. To the middle of this iron pile, attached before sinking, 12 feet below the river-bed, was a wire cable of If inches in diameter. This cable was led over the clump of piles and firmly secured to it, and from thence it was carried down to the apex of the triangular system below, where it was hauled taut and securely fastened. The object of the cable was to aid in holding the piles steady until the entire protective system was completed, and also to form a cutting-edge on which the large floes of ice could be raised and broken asunder before striking the works below. To the triangular system of piles the floating caisson was secured, and was held by it against the current until it entered the sand.
The iron pile was open through 6 feet of its lower part, to form a sand-chamber, into which one of the sand-pumps was introduced to withdraw the sand and permit it to sink. Above this chamber the pile was filled with ore from the Iron Mountain of Missouri, to insure its sinking in the sand. A central tube 14 inches in diameter, made of an old boiler-flue, enabled the sand-pump to be passed through the pile to the sand-chamber at the bottom, the ore being contained in the annular space surrounding this tube. The water was about thirty-five feet deep at the site of this pile when it was sunk. After its lower end had penetrated to a point about sixty-two feet below the surface of the water, and the cable
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had been tightly stretched, fifty or sixty cubic yards of large rubble-stone were thrown in around the pile to protect it from scour.After this work had progressed thus far, a subsidence of about ten feet in the river made it possible to bolt to each side of the triangle of piles, about ten feet below their tops, longitudinal timbers 10 inches square, running the entire length of the system. These longitudinal timbers, placed near the surface of the water and well secured, constituted hinges by which two enormous ice-aprons were attached, one on each side, to the triangle.
The object of these aprons was two-fold. First, to present an inclined surface on each side of the triangle of piles on which the impact of the ice should be received. Any obstruction opposing a vertical surface to the action of the ice would have been quickly crushed to pieces or ground away, whereas the ice slid up the inclined surface and was broken to pieces. Secondly, to protect the piles from the scouring action of the current, it was necessary to provide some means of keeping the current from them. To do this with broken stone would have been very expensive as well as unreliable, and, besides, would have created an obstruction much larger than the pier, difficult and costly to remove after the masonry was completed. The aprons were planked down their inclined sides to the very bottom of the river.
These aprons were 200 feet long and 60 feet wide. It was necessary to place them beneath the water at an angle of 45°, and with the lower edge or side of each resting on the sand, and to make them of such strength as not only to resist a powerful current, but also to withstand the great pressure of the ice, which might by the fluctuations of the stream be made to impinge as low down as the middle of their surfaces, as well as at twelve or fifteen feet above that point.
The frames of the aprons were made of strong, squared oak timber, placed transversely at intervals of eight feet, so that the upper end of each one of them rested by the side of a pile and on the longitudinal timbers before mentioned. The transverse timbers were each 60 feet long, and were held in place by three equidistant string-pieces, each 200 feet long, bolted beneath them. Two of these skeleton frames were thus constructed on shore, above the works, and were launched with sufficient pine timber beneath to float them. They were then towed, one to each side of the pile structure, and the end of each transverse timber on the side next the piles was placed on the longitudinal timber or hinge before named, and secured temporarily to them by a chain. The outer edges of these frames were then secured to barges placed alongside of them, and the pine floats under the frames were taken out. In this position, as the two frames lay on the water, they were planked with 3-inch oak plank. On that part where the ice was expected to impinge, No. 16 sheet-iron was placed over the planking. A space on each apron about twelve feet wide and extending their entire length was thus covered with iron. Below this iron covering some openings were left through the aprons for the current to pass, to prevent the formation of a bar of sand below the structure which would interfere with the sinking of the pier; a deposit some twelve feet deep was allowed to support the aprons.
When the aprons were both completed, the lines holding up their outside edges at the barges were simultaneously cut away; these edges then quickly disappeared beneath the current and were swept by it to the bottom. Both aprons assumed the desired angle. The
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upper ends of the transverse timbers were then bolted to the piles, and that portion of the pile system extending vertically above the aprons was faced with two or three courses of 10 X 10-inch oak timber at the part nearest the aprons, and above that point with oak plank. At the apex of the breakwater thus formed, about one hundred and fifty cubic yards of rubble-stone was thrown in, to thoroughly close any space left between the upper ends of the two aprons.This structure sufficed to completely turn the ice during the winter, and made a thorough protection to the works and barges about the pier. A deposit of sand rapidly formed behind the aprons, which gave great support to them; whilst they, in turn, protected this deposit, once formed, from the action of the current.
The ice-breaker was duplicated at the West Pier with equally successful results.
The ice-breaker for the East Abutment was smaller and less costly than the others, yet it followed the same general plan. Under the pressure of an ice-gorge it yielded somewhat, and was stayed only by a heavy filling of rip-rap.
The cost of the ice-breakers is given, with other items, in Chapter XXVIII.
It is said
In 1779, Coulomb, best known by his experiments on friction, presented to the Paris Academy of Science a paper detailing a plan for executing all sorts of operations under water by means of compressed air.
The men were to work three or four hours at a shift, and the excavated material was to be placed in pockets on the walls of the air-chamber, so arranged that when the pontoon was floated off into deep water — at the return of high-tide, for instance — the material could readily be dropped. Coulomb thought it possible to work in thirty or forty feet of water without difficulty.
In 1831, Earl Dundonald, then Lord Cochrane, took out a patent for a device for sinking tubular shafts through earth and water, by means of compressed air. His air-lock was much like modern ones, and was to be placed at the top of his main shaft. His invention, though stated in very general terms as an improvement "in the means of, and in the
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apparatus for building and working under water," was made with a view to its use in tunnelling under the Thames, and similar enterprises. He proposed, having sunk to the lower level, to place a second lock in the mouth of the tunnel, provided it proved to be possible to operate the shaft under a diminished pressure.In 1841, Mr. William Bush took out a patent for a plan of sinking foundations, consisting of a caisson with air-chamber, and immediately above it an air-lock, into which excavated material was to be thrown. Above the lock came an open shaft.
A German, by name Gr. Pfaun Muller, made a somewhat similar design for a bridge at Mayence, in 1850; but as his plan was not executed, it was, like the patents of Cochrane and Bush, little known till legal controversies in regard to patent-rights dragged them from obscurity.
In 1841, Mr. Triger, in order to reach a vein of coal on a sandy island in the Loire, opposite to Chalons, sunk an iron tube about forty inches in diameter, some sixty feet, by the blows of heavy weights. The fine sand was removed from the interior by means of a scoop bucket. On reaching a layer of coarse gravel, he could not force the tube
The application of Triger's method was made at Rochester, England, in 1851, where Mr. John "Wright sunk tubular foundations for the bridge over the Medway, working his men to a depth of 61 feet.
In the construction of the central pier of the Royal Albert Bridge at Saltash, England, in 1854-5, Brunei surpassed all similar previous exploits.
In 1859, the foundations of the bridge over the Rhine at Kehl were constructed. The method employed embraced several marked improvements. They were chiefly due to the ingenuity of the engineer, Fleur Saint Dennis, as follows: 1. Brunei's plan of a comparatively small tube, leading to a large air-chamber, appeared in the modified shape of a rectangular iron caisson, entered by two iron shafts carrying air-locks on their upper extremities. 2. The four caissons which were to form the base of a single pier were united into a single caisson with four compartments, upon the entire roof of which the masonry of the pier was to be built. Each compartment was furnished with two shafts. 3. With the
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exception of the filling of the caissons, the masonry was all laid in the open air upon the caisson, either floating or resting upon the bottom of the river. The iron shafts were lengthened as the caisson descended, one being in use while the other was being extended. The descending caisson was partially supported throughout its entire descent by chains and rods with nuts. The nuts were turned by a system of levers worked simultaneously by a capstan. 4. Another great improvement was suggested by the experienced submarine engineer and superintendent, Mr. Castor. It consisted in elevating the excavated material from the air-chamber by a system of chained buckets working in a large central vertical cylinder, which extended somewhat below the bottom of the caisson. It was open at both ends, and was kept full of water. Previously, all excavated materials as well as the filling of the air-chamber and pneumatic tubes had passed through air-locks. The largest of the caissons of the Kehl bridge was 77Ë X 23 feet, and was sunk 65 feet and 9 inches below high water.At Voulte, the caissons of the piers of the bridge over the Rhone consisted of a single compartment each, in other respects resembling the Kehl bridge.
At the Konigsberg bridge, where the Kehl method was used on a small scale, it was found necessary to abandon the chains after the caisson had penetrated a few feet into the river-bed. The air-pumps broke down, and as the platforms were not strong enough to support the descending pier, nothing could be done but take off the chains.
In 1869, Mr. Eads found Mr. Audernt sinking small piers without suspension-rods, and discharging the excavated sand at the upper air-lock by means of a "receiver," an ingenious arrangement devised by the engineer, Mr. Moreaux.
By the year 1860, the method used at Kehl, with slight modifications, was in general use throughout Europe.
The construction of the foundations of the St. Louis Bridge marked another era in the history of deep foundations, and to Mr. Eads belongs the credit of introducing several features of prime importance.
1. He placed the air-locks permanently within the air-chamber at the bottom of open-air shafts. Thus he was spared the great labor and annoyance of constantly removing the air-locks as the air-shafts were lengthened; while the introduction of an open-air elevator gave great relief to the workmen and great convenience in the transfer of materials and tools. Again, this improvement avoided the expense of iron shafts, and the large leakage of air which the numerous shafts would have involved in spite of all precaution.
2. The sinking of a massive pier not only without suspension-rods, but without any exterior shell or dam to protect the masonry, beyond the few feet necessary either to stiffen the caisson or to float it until the bed of the stream was reached.
3. The construction of a pneumatic caisson mainly of wood, covered with a single thickness of plate iron.
4. The invention of the sand-pump. Malezieux characterized the sand-pump as an invention "perfected with great ingenuity."
It is not sufficient, however, to stop with an enumeration of the new features introduced at the St. Louis Bridge. We should not fail to add that old methods were applied on a
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scale never before attempted. The foundations of the St. Louis Bridge are very much larger and deeper than any previously built.The East Abutment extends 135 feet and 6 inches below high water, and 40 feet deeper than does the Saltash pier; and it contains at least five times as much masonry below high water.
NOTE TO PAGE 248. — After reading Chapter XXII Mr. Eads wrote me as follows: —
"It should be stated that I fixed the length of time of the watches in the caisson in every instance, and not Dr. Jaminet nor Mr. McComas. This I did because of my experience in the diving-bell, and my long talk with Mr. Brereton about the Saltash pier. I came to the conclusion set forth by yon in your second proposition, on page 262, viz., that the time of work should diminish as the pressure increased; and my recollection is quite distinct that I had limited the watches to one hour each on reaching 100 feet of depth. Some eight or ten days before the rupture of the East Pier envelope I left St. Louis for New York, and only an hour or two before starting Mr. McComas urged me to allow him to work the men in the East Pier two hours instead of one, and referred to the great delay caused by changing gangs of men so frequently through the small air-lock of that pier. He was full of energy, very zealous, trusty, and capable, and pressed this request with unusual earnestness. I refused to permit the change, however, on the ground that I feared its effect upon the men. To this he replied that he had consulted Dr. Jaminet on the subject, and that the doctor was firm in the belief that if he doubled the period of rest between the watches as fixed by me, the men could work two hours at a time in the caisson with greater safety than they were then doing. They were then working one hour, with intervals of two hours for rest. He proposed to work two hours, with intervals of four hours to rest. I finally consented to the change, on condition that the doctor should first give him a written certificate approving of it. This certificate I have no doubt he received (although I never asked to see it), as he would not have made the change without it. Fortunately, the rupture of the envelope suspended work in the East Pier a few days later, and thus, as I firmly believe, prevented a greater loss of life by such long watches. The rise in the river which caused the suspension of the work increased the depth greatly over one hundred feet, and thus enhanced the danger to the men by the increased pressure."
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Chapter XXII. Special Subject No. 5. — The Physiological Effects of Compressed Air.
Very little was known of the peculiar effects of compressed air upon men, when the sinking of the East Pier of the St. Louis Bridge began. The observations of European engineers where it had been used were generally limited to the effect upon the human ear. In 1852, Mr. J. Hughes, assistant engineer at the Rochester bridge, England, noted that men at work in compressed air had "a remarkable increase of appetite for food." Respiration, he says, was "slightly affected," and when the transit of the air-lock was rapidly made, there was some complaint of headache. The greatest depth under water was 61 feet.
In 1861, Mr. Robert P. Brereton, one of the assistants of Mr. Brunel at the construction of the center pier of the Royal Albert Bridge at Saltash, England, stated before the Institution of Civil Engineers some of their experiences. The maximum air-pressure was 40 pounds above the normal usually the pressure was much less, as the water in the main cylinder was kept down by pumps. Mr. Brereton said that at first his men worked too long at a time, and on coming out they were slightly paralyzed, but in two or three days they quite recovered. With three-hour shifts the men could remain at work for several months consecutively. (Brunel was about two years in establishing his pier.)
The eminent engineer John Hawkshaw said that at the Londonderry bridge, "where 75 feet pressure was experienced, there had been some casualties." One of the effects produced by the air-pressure was that the joints of some of the less robust men began to swell.
In 1865, Dr. A. Magnus, of Konigsberg, published the result of his observation upon the effects of compressed air in the caisson of the bridge pier at that point.
"It has been shown in former works of this kind (at the mines of Douchy, for example) that the human organism may endure a pressure of four atmospheres without harm, but that it frequently happens that sickness is caused by a rapid diminution of pressure. So far as I know," he continues, "there are no German publications about this matter, though certain Frenchmen speak of them." The rules he gives have reference only to the ear, when entering the air-chamber.
In like manner, all who had written on the subject had assumed, from the comparative immunity with which men worked under two, and even three atmospheres, that no harm could arise from four or five atmospheres.
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Reference has been made in a previous chapter (see p. 59) to the visit of Mr. Eads to the bridge building at Yichy, in 1869. Mr. Audernt, the resident engineer, had put down forty piers by the method of compressed air, but his deepest had been only 75 feet below the surface of the river (the Po at Placenza); but neither he nor Mr. Moreaux (the "builder of a thousand bridges") could give any definite opinion as to the practicability of working men at a depth such as the East Pier of the St. Louis Bridge would reach. In England, Mr. Eads conferred very fully with Mr. Brereton. It is probable, however, that his own diving-bell experience made him the best judge of the effects of air-pressure, and yet even he had no adequate idea of the peculiar results actually experienced. As he himself said, no similar work having penetrated to so great a depth, he was left without any benefit from the experience of others, either in guarding against any injurious effects of the great pressure upon the workmen and engineers subjected to it, or in relieving those affected by it.
With this brief introduction, I proceed to give as full account of all matters relating to compressed air during the building of the St. Louis Bridge as my space will permit.
Until the cutting-edge of the caisson of the East Pier was nearly sixty feet below the surface of the river, there was no serious drawback to working four, or even six consecutive hours in the air-chamber. The men worked eight hours consecutively, coming up, however, to lunch at the end of four hours, till the caisson was down 42Ë feet. Then, one of the foremen being sick, it seemed best to change the day's work to two watches of four hours each, with a rest of eight hours between. This scheme was followed till February 5, when, the immersion being 65 feet, a day's work was changed to six hours, consisting of three watches of two hours each, with two-hour rests.
The first effect noted upon the men was an occasional muscular paralysis of the lower limbs. This was rarely accompanied with pain, and usually passed off in a day or two. As the depth of the caisson increased beyond 60 feet, the paralysis became more difficult to subdue. In some cases the arms were involved, and in some the sphincter muscles and bowels. In the severer cases the patients also suffered much pain in the joints and in the region of the stomach. Many of those affected suffered no pain whatever.
So long as the affection was painless, it was not regarded as a very serious matter. A workman walking about with difficult step and a slight stoop was at first regarded as a fit object for jokes, and cases of paralysis and cramp soon became popularly known by the name of "Grecian bend." In some cases there was paralysis of the nerves of sensation alone. The numbness generally extended over one or both legs, although it occasionally applied to the arms and face.
The common remedy was the rubbing of the affected parts with oil or liniment of some kind. A certain "Abolition Oil" gained great popularity; according to Col. Roberts, it "worked like a charm."
In cases of entire or partial paralysis of the limbs, a battery was frequently used, but the records show that the remedy was thought of little value. A more efficient means for relieving pain was the warm bath, and it was repeatedly used for the earlier severe cases. Subsequently, Dr. Jaminet forbade its use, though it was a first remedy at the City Hospital.
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A fancied safeguard was the use of galvanic bands or armor. At first, in the opinion of the superintendent, the foremen, and the men, the armor gave remarkable immunity, and all the air-chamber men of the East Pier were provided with it at the Company's expense. The bands were made of alternate scales of zinc and silver, and were worn around the wrists, arms, ankles, waist, and also under the soles of the feet.
As the pier descended into the sand, the distance from the top of the pier down the winding stairs to the air-lock increased as well. A depth of 70 feet made it necessary for each watch on its exit from the air-chamber to climb about one hundred and forty steps. The men were instructed to rest frequently on their way, but the request was generally disregarded. The fatigue of the ascent added not a little to the distress and prostration of those affected with cramp.
It was noticed that to one with cramps it was often a relief to return to the air-chamber.
When the immersion was 65 feet, a man just leaving the air-lock became unable to ascend the stairs. On the 15th of February, immersion 76 feet, a man suffering greatly in his limbs and back was sent to the City Hospital. From this time forward severe cases of cramps and paralysis were frequent, and several cases were sent to the hospital. The superintendent noted the fact that the sick were often thinly clad and poorly fed. One man became unconscious, and did not speak for three hours. All that they could do for him was done. He was stripped, rubbed, and wrapped in warm blankets. Mr. McComas says (in his diary) that the poor fellow came to his work with no stockings (the weather was cold), and that his clothing was very thin.
A great majority of the cases were among the new hands. In marked contrast with the number of men who were attacked at the end of their first trial was Keith, a sub-foreman. On February 20, when the immersion was 81 feet, the foreman of his relief being sick, Keith remained in the air-chamber ten hours out of twelve, and suffered no harm. Occasionally the old hands suffered, but the severe cases were new men. On February 26, nine men were attacked at once, one an old hand; none, however, seriously.
On the 28th of February the caisson reached the rock. Immersion, 93 1/3 feet; pressure in the air-chamber, 44 pounds above the normal. The two foremen had been very active for a day or two, in their zeal to "land the caisson," and, as a consequence, while all others were rejoicing over the triumph they were groaning with aches, which did not yield to the ordinary applications. "All remedies fail," wrote the superintendent, at 5:40; "Shrieves is suffering severely." At 6:40 Tie was well and out.
For a few days the force in the air-chamber was small. Most of the workmen were affected. "It seems impossible," wrote Mr. McComas, "to keep a force up." He determined to shorten his watches to one hour. The next day the gangs were relieved every hour. There was no complaint, but the men evidently disliked being called up so often, and dreaded so many ascents of those winding stairs 100 feet high. The following day they resumed the two-hour watches.
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night gangs had suffered most, the explanation being that the men did not rest properly by day.There were only a few cases from then till March 19 then they were startled. This "log" entry of Mr. McComas tells the whole story: "James Riley died to-day at 10:15 A. M. Verdict of the jury, ‘apoplexy.’ He had worked only two hours in the air-chamber. Came up feeling very well, as he said to one of his friends. In fifteen minutes afterwards he gasped and fell over, and was dead in a few minutes. I was fearful it would have a bad influence on the men, but they did not appear to mind it in the least." This was the first death, but another of the men died at the hospital the same day. During the next few days several very severe cases were sent to the hospital and three more deaths occurred, — two on one day. On March 28, a man applied for work in the air-chamber, whom the superintendent at first, for some reason, refused to take. A little urging resulted in the man's putting on the armor and working two hours. Fifteen minutes after coming out he was dead. Verdict, "apoplexy," as before.
It was evident that more stringent regulations were necessary to check both the number and the severity of the cases. Dr. A. Jaminet, a regular practitioner in the city, and Mr. Eads's family physician, was employed to take charge of all the men at work in the air-chamber, and to establish such regulations as in his judgment the well-being of the men demanded. Dr. Jaminet took charge March 31. A floating hospital was at once fitted up on a boat lying just below the pier. Besides ordinary accommodations, berths were fitted up in which workmen could lie down during their hours of rest.
Dr. Jaminet had been a frequent visitor to the air-chamber, and had himself felt the peculiar effects of compressed air.
Dr. Jaminet had noted the men as they came from the air-chamber. Their appearance was pallid and cold. In some the pulse was quick, varying from ninety-five to one hundred and ten, but somewhat weak; with others it was as low as sixty. Without exception, the workmen complained of fatigue.
Dr. Jaminet observed that the pulse always quickened on entering the air-chamber, though it soon fell to the normal pitch, and even lower, in the course of a watch.
On one occasion, the pressure being 32Ë pounds more than an atmosphere, he recorded the pulse of himself and five other visitors as follows: Before entering, 81, 78, 78, 79, 79, 80. Temperature, 56° of external air. They were ten minutes in the air-lock. At the end of six minutes their pulses were 100, 88, 98, 86, 95, 90. Thermometer, 62°. Temperature in air-chamber, 48°. In twenty minutes all felt a marked exhilaration. At the end of two hours their pulses were 68, 70, 71, 69, 70, 72. Their chests expanded during inspiration normally. They spent five and a half minutes in the air-lock on their return, and they felt very cold. Thermometer fell to 37° in four minutes. Before ascending stairs, pulses stood 69, 70, 69, 71, 68, 72, after climbing the stairs, 106, 104, 92, 94, 102, 99.
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On another occasion, Dr. Jaminet, three strangers, and two workmen entered together. Pressure, 37Ë pounds. Depth, 81 feet. The pulse record was as follows: —
Before entering 81 75 76 80 76 82
On entering chamber 97 77 77 92 88 90
At end of two hours 64 70 67 69 68 68
On reaching top of pier 104 90 90 100 94 96
In the air-chamber the number of respirations increased from eighteen to twenty-one per minute, and for a time at least there was a feeling of exhilaration. The workmen, without exception, sweat profusely throughout their stay in the air-chamber, though the thermometer was often below 60°.
The air-lock was, as a rule, excessively warm when the pressure was increasing, and exceedingly cold when the pressure was diminishing.
Dr. Jaminet always complained of cold in the air-lock, returning, and severe epigastric pain about ten minutes after coming out. On the day the caisson touched the rock, — pressure, 45 pounds, — he remained in the air-chamber two hours and three-quarters. While in the air-chamber he felt well. In the air-lock, on his way out, he was conscious of a great loss of heat, and a violent pain in his head. The air was escaping very rapidly. (The chief engineer was with him in the lock, and, as was usual with him, the discharge-cock was wide open.) At Dr. Jaminet's request, the escape of air was stopped a moment; the time spent in the lock was, however, but three and one-half minutes.
With difficulty the doctor climbed the stairs. His pulse was 110; he was suffering severe epigastric pain, and his strength was nearly gone. He went directly ashore on the first boat. With great exertion he managed to walk from the boat to his buggy, not one hundred yards away, and clamber in. He was able to drive to his house, half a mile distant, and stagger into his office, where in a few minutes he became paralyzed. For some time he could not speak, but he retained his consciousness. Gradually he gained command of himself, but his sufferings were intense, and for three or four hours he considered his life in extreme danger. It was over twelve hours before he began to move his legs. A little later he was able to walk, but he was feeble for some days.
Dr. Jaminet made several careful investigations upon the amount and character of the waste of the human system while in the air-chamber. He found that, invariably, an abnormally large amount of urine was secreted, and that it contained unusually large amounts of urea.
Prior to March 31, the men had been at liberty to spend their "off" hours as they
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pleased, provided they promptly answered the whistle-call for their watch. The doctor now required them to lie down in the berths provided for that purpose, for at least one hour, immediately on corning up. The intervals for rest and food between the working watches (which last had been three in number and two hours each) were increased to three hours. Each man was also subject to a rigid physical examination; all old hands deemed unsuited to the work were discharged and unpromising applicants were rejected.Under the new regime things promised well. At first the men were on a strike, demanding $5 a day and only four hours' work (they had been receiving $4 for a day of six hours); so there was little work in the air-chamber for some days. April 4, a new man was slightly affected; he was at work again in two days. The next day a sub-foreman (Lyon) was taken seriously ill.
This did not appear to mend matters much. The doctor reports that the men refused to obey orders as to the hours of rest. As soon as their second watch was over they hurried ashore, "and instead of going home to keep quiet and rest, the most of them were wasting their time in bar-rooms or other places unfit for any man employed in such exhausting work." This strong statement shows that at times his patience was sorely tried.
On the 8th, a man whom the doctor had once rejected came with a friend, and entered the air-chamber without the doctor's knowledge. At the end of the second watch he was taken very badly with cramps and paralysis, and it was months before he fully recovered. Five more cases occurred at the East Pier up to the morning of the 13th of April, when, owing to the flooding of the top of the pier, the concreting in the air-chamber was discontinued. Only one of these cases was serious. The man was badly paralyzed and broken down. After lingering about a year, he died.
The pressure at the East Pier for several days had been 50 pounds. At the West Pier, which was now on the rock, concreting was also going on under an air-pressure of 40 pounds. A very bad case had occurred at the latter pier on the 12th. The pressure being less than at the East Pier, there was thought to be little danger, and the doctor had confined his attention chiefly to the deeper pier. The men had been working six hours per day, in three watches. A few cases had been sent to the floating hospital, but they were slight. The case on the 12th, however, resulted in death. The man was really unfit to be there. He had been a hard drinker for the last year, though he declared he was sober the day he went into the air-chamber. He worked but two hours. This was the only death resulting from work at the West Pier.
After the 13th, the number of men at work in the caisson of the West Pier was about one hundred. The day's work was reduced to two watches of two hours each. During the next fifteen days there were fourteen cases of cramps and paralysis. Two or three only were serious, and all recovered. Dr. Jaminet asserts that none of these men had been examined by him, having been employed before he gave his special attention to the West Pier.
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A boy had been smuggled in by a friend, and was taken sick the first day. The next day the doctor sent him home, with the injunction not to return; but he came back two days after and entered the caisson again. After the first watch he was attacked again, and did not recover for a month. On each occasion he was insensible when carried to the hospital. He was twenty years old, and very slightly built.
The air pumped into the caisson was of course very much heated by the work of compression, and the cylinders of the air-pumps and the pipes were kept covered with water as much as possible in order to keep the temperature down. For some reason, perhaps the temperature of the external air, the air in the caisson of the West Pier during two days in April was warmer by some 16° than usual. A corresponding increase of course took place in the temperature within the air-lock, where the thermometer reached as high as 90°.
The doctor was greatly concerned about the effect of this temperature, and in order to keep it down he had an ice-box placed over the supply-pipe.
Notwithstanding the doctor's vigilance and care, cases of cramps and paralysis were of almost daily occurrence. Satisfactory results were obtained only when the following rules were rigidly enforced: 1. The watches were reduced to one hour each, three in number, alternating with long rests of three hours. 2. The men were kept at the pier all day; were required to bring their dinner, and whenever absent for a day they were re-examined before returning to the air-chamber. 3. The men were required to lie down and keep quiet for at least thirty minutes after each watch. Some hot beef-tea was given to each man at dinner.
No new cases occurred for ten days. Meanwhile the submarine work of the West Pier was finished.
On the 11th of May, work was resumed at the East Pier. Men worked three watches of one hour each, distributed over twelve hours. Pressure, 49 pounds. On the first day there was one case, which resulted in speedy death. The victim had worked three months at the other pier, and had suffered no inconvenience. He was on duty from 8 till 9 o'clock, and felt well after coming up. As he had neglected to bring his dinner, he was allowed to go ashore at 11:30 to get a meal. He, however, got nothing to eat, but drank in a saloon. He returned just before 1 o'clock, and worked from 1 till 2. On leaving the air-chamber he, in common with the rest of his gang, came through the air-lock in "less than four minutes." He was taken sick in the air-lock, and was unable to climb the stairs. He became unconscious while being brought up, and died two hours afterwards. The post-mortem examination showed that he had had no dinner, and only a light breakfast.
It appears that the temperature in the air-chamber was unsually high. The external air was 66°, and as no adequate cooling-apparatus was in use, the air from the pumps must have entered the caisson very much heated. On the following day, by noon, the air-supply came through a coil of 150 feet of copper pipe immersed in the river. The temperature in the air-chamber fell to between 66° and 70°.
The doctor at once transferred the ice-box to the air-lock, and enforced his rules strictly. Fourteen cases occurred between the llth and 27th, when the filling was completed. Only one was serious. This patient had not only paralysis of the legs, but fever and
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hemorrhage of the lungs. He had evidently been unfit for the work. He recovered in two weeks.During the last few days there was room for only three or four men to work at once, and they changed gangs every half-hour. Moreover, the doctor was present and examined every man once in six hours.
In spite of the efforts to keep down the temperature, the men complained of the heat, and of being very tired on coming out, and not infrequently of having headache. As soon as a man complained of pain or numbness, he was required to rest over one watch.
To prevent the men reckless of danger from passing through the air-lock too rapidly, the size of the inlet and discharge-pipes was changed, so that though the valve was wide open, the stipulated time could not be curtailed. One can imagine the imprecations bestowed on the "slow coach" by men in haste to get out.
| CASES. | |
| At the City Hospital, reported by Dr. E. A. Clark | 35 |
| Reported by Dr. Paul P. Eve (other hospitals and elsewhere) | 3 |
| Reported by Dr. A. Jaminet | 49 |
| Not reported by physicians | 4 |
| Total | 91 |
| Number of serious cases | 30 |
| Number crippled for life (apparently) | 2 |
| Number of deaths |
13 |
The whole number of men who worked in the air-chamber of the East Pier was three hundred and fifty-two. This number includes many of those who worked at the West Pier, but many, probably one hundred and fifty others, who worked only at the West Pier, are not included. The ninety-one cases given above include only the deaths or those requiring medical treatment. There were probably a full hundred others slightly attacked, eliciting a few groans, but more jokes.
In his Report of October, 1870, Mr. Eads gives the names of forty-eight men "who were employed in the caisson of the East Pier from the time it entered the bed of the river until it was filled with concrete."
Three important changes had been made in the East Abutment, intended to subserve the comfort and health of the men: First. The air-locks were 8 feet in diameter instead of 6. Second. The candles lighting the air-chamber burned in globes which discharged the products of combustion into the open air. Third. An elevator in the central shaft was used to bring up the men at the expiration of their watches.
The first change arose from a desire to give the men more air to breathe while waiting
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in the lock. The second contributed certainly to the comfort and cleanliness of the men, and hence to their health. (See p. 216.) The elevator seemed indispensable, and justified itself a thousand-fold. The winding, stairs numbered one hundred and ninety steps. What a torture to weary "submarines"! The eminent French engineer, Malezieux, after visiting St. Louis to see the work in progress, spoke enthusiastically of this improvement.The success of the regulations finally adopted at the channel piers on the suggestion of Dr. Jaminet led the chief engineer to place him in charge of all sanitary measures at the East Abutment. He entered on his duties when the caisson was 56 feet below the surface of the river; pressure, 27 pounds (above the normal). He found seventy-six men at work in the air-chamber. They were in four gangs: two by day and two by night, working six hours each: two hours on and two off. All of them had worked in the air-chambers of the East or West Piers.
During the month the number of men was increased to one hundred and forty. Of one hundred and thirty-three applicants examined, sixty-seven were rejected as unfit for the work. The most common cause was "general debility, caused by intemperance." No men were received older than forty-five years.
A building with berths, mattresses and blankets, and a hospital, were provided. The men were required to lunch at the abutment. Beef-tea was furnished to every man at his meal. No one was allowed to leave the works till one hour after his work for the day (or night) was over. The men were examined daily, and no one was permitted to enter the air-chamber unless in good working condition.
When the pressure reached 32 pounds, a day's work was reduced to two watches of two hours each, with rests of four hours between them, and perfect rest lying down for one hour after the second watch. The doctor had two slight cases of paralysis, but in each case the patient recovered in twelve hours so as to go home alone.
When the pressure reached 34Ë pounds, the work was reduced to three watches of one hour each, with intervals of rest three hours long. Two men were taken sick, who recovered in twelve hours.
When the pressure was 40 pounds, the elevator was stopped for about twenty-four hours (in consequence of a leak in the wall of the main shaft), and the men had to climb one hundred and seventy steps after each watch. Four men were taken sick with pains and paralysis about twenty-five minutes after coming up the stairs. They all recovered in about twelve hours. After the elevator came in use again, no case occurred for four days, when, the pressure being 42J pounds, six men were taken, though within twelve hours all were discharged from the hospital. The doctor asserts that the men fell sick partly through their not resting as ordered. On reaching a depth of 100 feet, by order of Mr. Eads a day's labor of the air-chamber men was reduced to two watches of forty-five minutes each. No more cases of sickness for ten days.
During the next ten days the air-chamber was full of water, in consequence of the tornado of March 8, 1871. (See Chapter VI.)
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Two cases happened on the 18th, while the elevator was still out of repair. Both cases were light. Pressure, 46 pounds.
The comparative immunity enjoyed thus far at the abutment seems to have made the men reckless, and the doctor complains that they would not obey orders as to lying down after coming from the air-chamber, and as to not drinking water for thirty minutes after coming up. (No reason is given for the rule last referred to.)
One man worked two hours instead of forty-five minutes, and then did not lie down on coming out. He was taken in the usual way. Some half-dozen light cases, easily disposed of, occurred previously to April 14, when the pressure was 49 pounds. On that day a man was taken, who died two weeks later. This was the only death by compressed air at the East Abutment; and it would appear from the report of the doctor and of Superintendent McComas that the man brought his fate upon himself. He had failed to bring his dinner, so went home to eat it, contrary to orders. Then, on his way back, he "filled himself" with beer. Moreover, on coming up from his second watch, he left the works before his hour of rest was up. These facts were duly recorded by the superintendent on the day of their occurrence. On reaching home in the afternoon, the man was taken sick with vomiting. His dinner had evidently been eaten with great haste, and was still undigested. In a few minutes general paralysis supervened. The history of his case up to his death shows that the man's blood was in a bad state. He had worked in the air-chamber over three months.
Two slight cases close the list; one was that of a man who walked up the stairs instead of taking the elevator, and was taken sick on reaching the top.
| Number of cases | 28 |
| Died | 1 |
| Completely recovered | 27 |
Of all those that died from the effect of compressed air, eight were examined post mortem. In all cases the brain and spinal cord were congested. As a rule, the interior organs of the body were excessively congested. There was no doubt that the immediate cause of death lay in the influence to which the men had been exposed in connection with their work in compressed air, though in nearly every instance the post mortem revealed weaknesses and susceptibilities which, could they have been known earlier, would have caused the rejection of the men by the medical examiner. When death did not intervene for some weeks, the developments were much confused. Four of the reports are given below, in the belief that the importance of giving full information justifies their insertion.
Theodore Louis Baum was a German, twenty-one years old. He was admitted to the hospital March 22, 1870; he died the next day. The coroner reported: —
"On examining the contents of the cranium, the substance of the brain was found overcharged with blood, ooziug freely from minute points on section. The meninges were also highly congested, and considerable serous effusion between them, most marked under the arachnoid. The spinal canal was also opened and examined, and about the same condition existed here as in the brain. The effusion under the dura mater was well marked. There was also found in the inside of the dura mater, at several points, small clots of extravasated blood. In examining the thorax, the small capillaries of the
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pleura and pericardium were found highly injected. The lungs very highly congested, but much less than the other organs. All the abdominal viscera were entirely congested; clots of extravasated blood were found in the kidneys, and small dark patches on the mucous membrane of the bladder, resembling ecchymosis."
John Sayers, twenty-two years old, was admitted to the hospital after his first watch of two hours. He died in twelve days. The coroner reported as follows: —
"The brain and spinal cord were found highly congested, the latter being softened in many places to pulpy consistency. There was evident subarachnoid effusion, and probably more than a normal quantity of fluid in the dura mater of the cord. Small clots of extravasated blood were found at different points on the external surface of the latter membrane. All the abdominal viscera were surcharged with blood, the lungs suffering less in this respect than any of the other organs. There were clots of blood found in both kidneys; one of the ureters was very much enlarged."
Henry Krausman, age twenty-seven years, a German, was taken sick March 21. He died in the hospital two days afterward. The post mortem was recorded as follows: —
"The whole contents of the cranium were found highly congested, with effusion beneath the arachnoid, the vessels of the latter membrane being highly injected. Blood oozed freely from the substance of the brain on section. The spinal cord presented pathological conditions precisely like those of the brain, with the addition of the existence of clots of extravasated blood at different points inside the dura mater; there was also a congested condition of the thoracic content, less marked probably in the lungs than in the other organs. The abdominal viscera were very highly congested, with extravasation of blood in the kidneys. The mucous membrane of the bladder was healthy, and a small quantity of bloody urine was in the bladder."
William Sayler was a German, thirty years old, of medium stature, and well built. He worked three months at the West Pier, where the pressure was for two weeks 40 pounds to the square inch, from which he suffered no inconvenience.
On May 11 he began work at the East Pier, where the pressure was 49 pounds above the atmosphere. He worked from 8 to 9 o'clock A. M., and felt well after coming up. He went ashore at 11:30. At 1 P. M. he resumed work, and finished his watch without complaint. While in the air-lock, at 2 o'clock, he felt sick, and was unable to ascend the stairs. He became insensible while being carried to the hospital, where he remained insensible till 4:20 P. M., when he died.
A post-mortem examination was held sixteen hours after death, by Dr. Jaminet, which elicited the following facts: —
"Cranium. — All the blood-vessels of the scalp, as also all the membranes covering the brain, were highly congested, and about two ounces of serum escaped from the vertebral canal when the brain was removed. The brain was congested, and two ounces of serum found in the ventricles.
The heart was of normal size; the right ventricle, as also the left, were normal. The lungs were inflated and of normal appearance, but there were large adherences around the base of the right, which seemed to be of long standing. The liver was normal as well as the spleen. The kidneys were normal, as was also the bladder, but empty. The stomach normal and entirely empty; no traces of food were found, which confirmed my opinion that this man had not taken any dinner, and probably a very light breakfast, but had been drinking beer and whiskey quite freely, as it was afterwards ascertained."
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| Total number of men engaged in the air-chambers of the East and West Piers and East Abutment, about | 600 |
| Cases reported by Dr. Clark | 35 |
| Cases reported by Dr. Eve | 3 |
| Cases reported by Dr. Jaminet | 77 |
| Cases not reported | 4 |
| Total | 119 |
| Number of deaths | 14 |
| Number of post-mortem examinations | 8 |
| Number known to be crippled | 2 |
A majority of all cases, including at least three-fourths of those that died, worked in the air-chamber only one day, and generally but a single watch of two hours.
Two-thirds of those taken sick at the East Pier were attacked immediately on coming out, either on the stairs or as soon as the top was reached. In other cases the men were generally attacked within half an hour.
At the East Abutment, with the exception of the man who died, as already detailed, there were no serious cases. Of these twenty-eight cases there were —
| Attacked immediately after leaving the air-lock | 4 |
| Attacked 15 minutes after leaving the air-lock | 4 |
| Attacked 20 minutes after leaving the air-lock | 12 |
| Attacked 25 minutes after leaving the air-lock | 2 |
| Attacked 30 minutes after leaving the air-lock | 6 |
| Attacked later than 30 minutes after leaving the air-lock | 0 |
| Total | 28 |
I have now given a statement of facts and personal observations sufficiently full for an intelligent discussion of the whole matter. I frequently visited the air-chamber of the East Pier, but my visits were short, and I felt no special inconvenience. Neither Mr. Eads nor his assistants, nor even the superintendent, though almost daily in the air-chamber, can add much to our stock of information. None of them suffered beyond an occasional numbness, or a slight pain in the joints. As a rule, chance visitors had no personal sufferings to report beyond a "frightful pain" in their ears while making the first passage of the air-lock. I have no record that any of the ladies who visited the air-chambers ever suffered at all. Sometimes they bravely made the passage of the air-lock while the gentlemen attending them were forced to withdraw.
I now propose to discuss at some length these very important facts, giving first the views of others expressed at the time, and finally, the conclusions to which I have been led by a very careful examination of all points.
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The "Bridge cases" excited great interest and discussion in medical and scientific circles, but the physicians were not at all agreed as to the manner in which the compressed air acted so as to produce the symptoms exhibited.
Dr. E. A. Clark,
Another eminent physician thought that the men were poisoned by carbonic acid, which had been abnormally retained within the system while in the air-chamber, but which was set free as soon as the pressure was removed.
Dr. Jaminet, the physician in the employ of the Bridge Company, thought that the men were sick from physical exhaustion, caused mainly by the rapid waste of the system, which, in his opinion, went on four times as fast under a pressure of four atmospheres as when under the normal pressure. Exhaustion was hastened also by labor in the air-chamber, and the effort of climbing a long flight of stairs on coming out. He refers, in support of his theory, to the following well-established facts: That in the air-chamber, under four atmospheres, four times the usual amount of oxygen was inhaled at each inspiration; that the breathing was more rapid; that the men sweat profusely all the time they were in the air-chamber; that the amount of urine secreted was larger than usual, and of greater specific gravity; that men whose vital energies were at a low ebb, and men with empty stomachs, were struck down first; that the muscular effort of walking up stairs increased the chances of sickness; and that long watches were more dangerous than short ones.
Dr. Jaminet's argument is founded on strong premises. If he does not reach the whole truth, he does a part of it. Certainly he was led to the adoption of measures, some of which worked admirably and went far to confirm his conclusions.
It is not so much my purpose to show that the views of others are wrong or inadequate, as to present an explanation which, so far as I know, is entirely new. While I award to Dr. Jaminet great credit for his professional zeal and considerable success in his efforts to account for and guard against the evils noticed, I insist that the theory of ordinary physical exhaustion fails to account for the phenomena observed.
My opinion is that the vital energies of the men taken sick were to a great extent paralyzed by loss of heat. This loss was due —
1. To the expansion of the air in the lock, while coming out.
2. To the expansion of the free gases and vapors within the body, when relieved of the abnormal pressure.
3. To the liberation of the gases held in solution by the liquids of the body.
4. To the severe physical effort of climbing the stairs.
I think that the chief loss of heat was suffered in the air-lock when coming out of the air-chamber, but that the loss continued, though more slowly, during the succeeding few minutes, while the men were ascending the stairs and the liberation of gases was going on.
The great loss of heat which necessarily attended every exit from the chamber, though
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incidentally noticed, seems not to have received proper consideration. A few words are necessary to show the importance of considering this point carefully.The central air-lock of the East Pier contained about two hundred cubic feet. It would hold thus ten men and 175 cubic feet of air. One hundred and seventy-five cubic feet of air under a pressure of four atmospheres would occupy, under the normal pressure of one atmosphere, 700 cubic feet, the temperature remaining the same. Now the loss of heat resulting from the expansion of this air, as a part of it is allowed to escape, is easily found by the rules of thermodynamics. Air at 70° expanding against a pressure diminishing from four atmospheres to one, without receiving heat from surrounding objects, is reduced in temperature to 106° below zero!
It was noticed that the escape-cock was often covered with frost, and that the temperature, as indicated by a thermometer in the air-lock, sometimes fell to 32°.
But the absorption of heat through expansion takes place within the human body as well as without it. All the liquids of the body are surrounded by a certain amount of their own vapor; and gases, such as air, carbonic acid, etc., exist in cavities and pores all through the body, notably in the abdomen. Just how much this gaseous volume is, it is impossible to tell; but there can be no doubt that it exists in considerable quantities, and that gases pass by insensible degrees through all animal tissues. Now, in coming from a pressure of four atmospheres, there would be four times the normal amount of such gases in one's body. In passing through the air-lock, three-fourths of this must imperceptibly escape by expansion, and during the expansion they must absorb and carry off heat from the interior of every organ of the body. Where the gases were most abundant, the loss of heat would be the greatest, viz., in the abdomen.
Very closely connected with this was the loss of internal heat through evaporation and the liberation of gases. The amount of gas which a liquid can hold in solution is proportional to the pressure. All the liquids of the body probably contain air and various gases in solution. After an hour's stay in an air-chamber under a pressure of four atmospheres, the amount of gases held in solution in the liquids of the body was probably very nearly four times the normal amount. The absorption of the gases was attended by the evolution of heat and a feeling of exhilaration. This feeling every visitor noticed on entering the air-chamber. Now, on return to the air-lock, and to a reduced pressure, this extra amount of gas began to escape, and one felt the effect of processes just the reverse of those previously experienced. The evaporation was attended by a loss of heat and a depression of the spirits. The increased vital energy gave place to a very low ebb of vitality and an all-pervading sense of frigid helplessness. It will be remembered that
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Faraday produced the most intense cold — 166° below zero — by allowing very volatile substances to evaporate under a greatly diminished pressure.These losses of heat can be considered only qualitatively; quantitative results are hard to reach, but an admirable and perfectly analogous experiment could easily have been tried, illustrating the heat absorbed by evaporation. Had Dr. Jaminet, after boiling water in the air-chamber, taken a gallon of the water, every atom of which had a temperature of 297°, into the air-lock with him, on his return to the upper air he would have found, when he came out of the lock, no matter how quick his passage, that the water remaining in his pail had a temperature of exactly 212°, and that considerable of the water had evidently boiled away in the lock. This experiment was not tried, but every physicist knows that I am right in my statement of the result.
Now, how can we account for the loss of 85° of heat in the water? The answer is easy: A part of the water formerly confined by the pressure of four atmospheres has escaped from under a less restraint, and, while transforming itself into a gas, has robbed the water remaining of a portion of its heat. Any liquid saturated with any gas would, under a diminished pressure, part with its heat in precisely the same manner.
It is obvious that the liberation of gases held in solution by the fluids of the human body is a dangerous process. In escaping from the corpuscles of every liquid, and from within every tube and duct, there are two possibilities: First, the escape may be so rapid and violent as to rupture the minute tissues; and, secondly, the absorption of heat may be so great that the vital fluids may lose their vitality.
There is another point: The escape of gases held in solution by increased pressure is not instantaneous when the pressure is reduced; it requires time, even if the pressure is suddenly removed. Hence the internal loss or heat did not end with the exit from the airlock; it went on for some minutes, during which the vitality of the system was being reduced to a minimum.
There was yet one more demand made upon the vital heat and energy of the air-chamber men when they emerged, half-frozen, from the air-lock of the East Pier, namely: the mechanical effort of climbing 110 feet vertically before physical reaction had had time to set in, and while the loss of heat from evaporation and the liberation of gas was still going on. This effort alone, as has been found by experiments, reduces the temperature of the body. To raise 150 pounds 110 feet is equivalent to raising the temperature of one pound of water twenty-two degrees. Hence twenty-two thermal units would be lost in the ascent by every man.
When we consider the combined effect of the four causes of loss of internal heat and vitality, taken in connection with the necessarily exhausted condition of men who had been laboring hard, secreting excessively, and sweating profusely, we cannot be surprised that they were chilled to their vitals, and that many of them failed to pass the minimum point without cramps and paralysis; we are rather surprised that so many escaped. We know that the temperature of the vital organs varies between very narrow limits. We know that sudden cold (as in the case of a man swimming in cold water) produces cramps in the legs, and sometimes intense headache. The almost invariable symptom in the Bridge cases was the paralysis of the bladder and the splinter and both caused doubtless by loss of
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This brings me to the consideration of a very suggestive remark of Dr. Jaminet. Feeling, most certainly, that his theory of exhaustion did not fully account for the symptoms, he adds, with less regard for his theory than for a truthful statement of facts as he observed them: "The paresis [weakness] or paralysis is but the result of reflex action caused by the spontaneous refrigeration of the whole system, but principally of all the abdominal organs" (p. 114). No more satisfactory confirmation of the truth of the explanation I have given could be asked than this observation of Dr. Jaminet.One remark in reference to the time when the men were attacked. None were ever attacked on entering the caisson; none were ever sick when in the air-chamber, no matter how long the watch.
One word as to the pressure upon nerves, blood-vessels, and the brain. In nearly every post-mortem examination, an increased amount of serum was found in the vertebral canal or within the cavity of the skull. I may not be physiologist enough to explain why this was the case, but I do not feel, as many do, that it furnishes a satisfactory explanation of the phenomena of sickness and death. It would appear that some yielded suddenly, and died in a few minutes others were so prostrated, their energies were so far overcome and destroyed, that restoration was impossible, though sufficient vitality remained to prolong life for a few weeks; with others the struggle was long and severe, and the battle finally drawn, leaving the unfortunate victims with certain organs permanently impaired.
It must not be forgotten that no one was attacked while under pressure, nor while pressure was being applied; the fatal moment was when the pressure was removed, or within half an hour from leaving the air-chamber. Now, there can be no doubt but that the aerostatic and hydrostatic pressure throughout every part of the human body corresponded closely to the external pressure. In so far as there were cavities in the skull and spine containing gas and air, compression took place and additional air or liquid was forced into them. The internal pressure was sensibly equal to the external; any momentary difference produced acute pain, and no tissue was strong enough to withstand any great inequality. The pressure upon the spinal cord, upon the blood-vessels and the brain, applied alike to every man, whether he fell sick on coming out or not. If serum, or blood, or air was forced into a cavity, it was generally absorbed, or returned without injury. A too rapid change of pressure would, of course (neglecting any question of heat), tend to cause headache, and do harm in the sockets of the joints.
As to the waste of the system while in the air-chamber, I think that Dr. Jaminet has greatly overrated it. Unquestionably, the waste was abnormally rapid. Men took
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one full inspirations per minute, instead of eighteen. It is true, a man inhaled four times as much oxygen as usual at a breath; but so he did of nitrogen, and, as usual, the amount of oxygen consumed was largely regulated by the amount of nitrogen mixed with it. Candles burned about sixty-seven per cent faster under four atmospheres than under one. It is possible that the vital processes in the human body were accelerated in about the same ratio. Exact information as to the rate of waste and the influences of long watches is wanting. It is to be regretted that some one did not think to try experiments upon animals. Dogs, well fed, would doubtless have lived some days in the air-chamber, and, if carefully brought out, might have survived unharmed.In conclusion, I agree with Dr. Jaminet, that only sound men should be employed; that they should not be exhausted by long terms of labor; that they should be well fed; that they should not pass in or out too rapidly; that they should, on coming out, be spared immediate hard work. For some unaccountable reason, Dr. Jaminet allowed twice as much time for entering the air-chamber as for coming out, though he saw that the coming out was the critical thing. His rule should be reversed: say eight minutes for going in and twelve for coming out, the pressure being 48 pounds above the normal.
But I would add to the above requirements one other, and the most important of all, namely: that such a supply of heat should be given every man that he could lose a large amount and still have plenty left. This could readily be done in various ways.
My conclusions may be stated in the form of —
1. Men must be sound and well fed. They should eat a hearty meal about one hour before entering the air-chamber.
2. The periods of labor should be diminished as the pressure increases: say, to two watches of two hours each per day under a total pressure of four atmospheres.
3. Men should have perfect rest and warmth for half an hour after coming out. This includes the use of an elevator.
4. The pressure in the air-lock should not be increased more than six pounds per minute, nor diminished more than four pounds per minute. If, when the pressure is increasing, any one has pain in his ears which cannot be removed by blowing his nose, or by swallowing water, the inlet of air should be stopped and the man sent out.
5. Every man, just before leaning the air-chamber, should be required to swallow about a pint of hot coffee, tea, or soup.
6. There should be separate air-locks for entrance and for exit. The exit air-lock should be provided with heating apparatus, which should maintain a proper temperature and furnish direct heat to the bodies of the men.
Carefully observing these rules, it is probable that men can safely work under a pressure of five atmospheres.
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Chapter XXIII. Special Subject No. 6 — The Investigation and Reports of the Board of Engineers of the United States Army.
Simultaneously with the greatest activity in the erection of the St. Louis Bridge, in the latter part of 1873, and in January, 1874, a drama was acted exhibiting on the one hand the inevitable conflict between river and railway interests, and on the other the open hostility of military towards civil engineers. The performers were certain prominent steamboatmen of St. Louis, a board of engineers from the army, the Chief of Engineers, and officers of the Bridge Company.
Although without influence upon either the design or the construction of the Bridge, this episode, which I have very properly styled "a drama," constitutes an interesting chapter in the history of the Bridge. I proceed to give the main points in as condensed form as possible.
In spite of the fact that the plans of the Bridge had been published and discussed for five years; in spite of the fact that a scale-drawing of the arches was all the while hanging in the Merchants' Exchange of St. Louis, certain steamboatmen seem to have been greatly surprised when they saw the arches spring out from the masonry, and gradually stretch themselves over the wide expanse of water between the piers. There can be no doubt that the arches looked extremely low. A span of over five hundred feet dwarfs an ordinary height to such an extent that the eye is greatly deceived. Had the superstructure over the center span been built with a horizontal lower chord 50 feet above the city directrix (5 feet lower than the crown of the arch), the appearance would have been much worse than now. The height of the truss or girder above high water would have been less than the depth of the structure at the center of the span.
Consequently, a few men closely identified with steamboat interests, who had regarded the progress of the Bridge for five years with apparent indifference, formally protested against its erection to the Secretary of War. The result was the issue of an order (sect. 10, Special Orders No. 169), August 20, 1873, convening at St. Louis a board of engineers, "to examine the construction of the St. Louis and Illinois Bridge across the Mississippi River at St. Louis, and report whether the bridge will prove a serious obstruction to the navigation of said river, and if so, in what manner its construction can be modified." The board consisted of Col. J. H. Simpson, Maj. Gr. K. Warren, Maj. G. Weitzel, Maj. William E. Merrill, and Maj. Charles E. Suter. Col. Simpson, the senior member of the board, had at that time his headquarters in the city of St. Louis.
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The date named for the meeting of the board was September 2, or as soon thereafter as convenient. Preparatory to the meeting of the board, Col. Simpson applied to Capt. John S. McCune, the president of the Keokuk Northern Line Packet Company (who at the time prominently represented the hostility to the Bridge), for names and dimensions of the largest boats plying to and from St. Louis. From Col. Flad the board procured tracings showing profiles of the Bridge, dimensions, etc. Mr. Eads was at the time in Europe.
At the request of Dr. Taussig, a copy of the order convening the board was sent to the Bridge Company; but no information was given as to the nature of the complaints made against the Bridge. It was not known, therefore, whether it was objected that the Bridge did not conform to the acts of Congress, or whether objection was made to the acts of Congress themselves, on the ground that the Bridge, as authorized, would seriously obstruct navigation.
On the 2d of September, the following communication was addressed to the board of engineers: —
"OFFICE ILLINOIS AND ST. LOUIS BRIDGE COMPANY,
ST. LOUIS, Mo., September 2, 1873.
Col. James H. Simpson, Maj. Governeur K. Warren, Maj. Godfrey Weitzel, Maj. William E. Merrill, Maj. Charles R. Suter, Board of Engineers under Special Order No. 169, War Department, August 20, 1873:
The undersigned, the Illinois and St. Louis Bridge Company, having learned from a copy of Special Order No. 169, issued by the War Department, and obtained from you on Saturday, the 30th ultimo, by personal request, that your honorable board is convened in this city for the purpose of examining the construction of this Company's Bridge, and reporting whether it will prove a serious obstruction to the navigation of the Mississippi River, and if so, in what manner its construction can be modified, begs leave to represent that this Company has received no notice, and is possessed of no information as to the grounds for or character of the complaint, if any, on which your special order is based, and that, being largely interested in your proceedings and final actions, it feels authorized to respectfully request that you permit it to be represented at your several meetings by counsel.
This company has been in existence and practically at work, carrying out the objects of its charters, for over five years; it has expended and become liable for about $9,000,000; its plans for the Bridge have been published and circulated widely, and have been thoroughly known to the public during the whole time above spoken of; the business of this city has been largely affected by the expected completion of the Bridge, and the railroad grade of the Bridge has been established and fixed in accordance with and for the accommodation of the grade of more than twenty leading trunk railroad lines, all converging at the Bridge, which railroad lines carried to and from the city of St. Louis in the past year over 5,000,000 tons of merchandise.
During the whole of this long period no complaints have been made by either the government or the people; the citizens of St. Louis, all of whom are, directly or indirectly, largely interested in the commerce of both river and railroads, looked on with the utmost favor and approval, giving every aid and encouragement that would hasten the final completion of this great undertaking; whilst it is safe to say that its size, location, and importance render this structure one of national concern.
If, therefore, under these circumstances, this Company learns for the first time that, just as its work is on the eve of completion, your honorable board is convened for the purpose of examining the
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construction of a Bridge the plans of which were well known all over the country, it cannot but be somewhat startled at the intelligence.
Entertaining a profound respect for the scientific attainments and honorable reputation of the members of your board, and fully satisfied that you will discharge your duties impartially, this Company, being desirous on the one hand of rendering all the assistance it can in your investigation, and on the other asking to be heard on its own behalf, would most respectfully request: —
First. To allow this Corporation to appear and be represented before you by its officers and counsel, to assist in obtaining, arranging, and eliciting testimony.
Second. To have your proceedings and all testimony adduced reduced to writing by a short-hand reporter.
Third. And to order your sittings so that the Company may be represented thereat. In all these matters it is expected that your board shall of course have unlimited control; nor is any more asked than that the Company shall be allowed to protect itself from any misapprehensions under which it might suffer by being excluded from participating, to an ordinary degree, in proceedings so directly pertaining to a business in which its own interest, as well as that of the public at large, is so greatly involved.
Yours very respectfully,
GERARD B. ALLEN, President.
WILLIAM TAUSSIG,
Chairman Executive Committee."
The board of engineers did not organize till September 4, on which day the president of the board, Col. Simpson, replied as follows: —
"ENGINEER'S OFFICE, U. S. ARMY, 1122 PINE STREET,
ST. LOUIS, Mo., September 4, 1873.
Gerard B. Allen, Esq., President Illinois and St. Louis Bridge Company, St. Louis, Mo.
SIR: Your communication of September 2, 1873, has been received. Our board is directed to consider but two questions, viz.: Whether the Bridge, as constructed, will prove a serious obstruction to navigation; and if so, in what manner its construction can be modified.
In doing this, we are desirous of having your Company represented by its chief engineer, and by any other executive officers of the Company you may think best; but we do not desire to have legal counsel, as we are not directed to consider questions of law.
We are not authorized to take sworn testimony, but only such as persons interested may choose to give.
We do not, therefore, consider it worthy of being recorded in the manner you propose. Such serious obstructions to navigation as we may find, if any, and such modifications, if any, as we may propose, will be based on our own determinations of facts.
I am, sir, very respectfully,
Your obed't serv't,
J. H. SIMPSON,
Col. Engineers, U. S. A., President of Board."
The sessions of the board continued through the 4th and 5th of September (Thursday and Friday). The attention of the board up to 2 o'clock P. M. of the second day was given to hearing complaints and charges against the Bridge.
Capt. McCune, Capt. Silvers, Capt. B. W. Gould, Capt. J. E. Pegram, Mr. James Collins, and others, preferred complaints against the Bridge. They were represented by Col. Bryson, a lawyer. They presented carefully prepared tables of measurements and
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statistics, and testified concerning the heights of boats, their chimneys, the character of the St. Louis harbor, the necessity for high pilot-houses and tall chimneys; they discussed the questions: whether chimneys could be lowered and raised; whether artificial draft could be used the expenses that would be incurred by preparing chimneys for lowering; and the difficulties of piloting boats under the Bridge. "When it appeared that these witnesses were in harmony on all points, Maj. Warren — with a view, as he said, to save time — drew up a paper, which the opponents of the Bridge assented to and signed, as follows: —"To THE BOARD: The river interests, represented by those present, hold that the lowering of the pipes and pilot-houses is impracticable, and any bridge requiring it to be done for any considerable portion of the season is a serious obstruction to navigation."
Dr. Taussig, Col. Flad, and John W. Noble, Esq., had been present all this while, but they were allowed no part in the proceedings till the witnesses against the Bridge should be through. As soon as the line of complaint was made known by the testimony of Capt. McCune and his coadjutors, the Bridge Company promptly secured the attendance of other steamboatmen, holding views directly opposed to those presented to the board. For instance, they were prepared to show by river-men of large experience: —
1. That it was entirely practicable to lower the largest steamboat-chimney.
2. That pilot-houses were often unnecessarily high.
3. That the simpler solution of the difficulty, so far as it existed, lay in modifying the steamboats rather than the Bridge.
4. That the difficulties claimed for piloting boats under the crown of the arch did not exist.
Not till the afternoon of Friday was the Bridge Company at liberty to place witnesses on the stand. Two only were then present, Capt. Bart. Able and Capt. George W. Ford they, however, testified that in their opinion steamboat-chimneys were often one-third higher than was necessary.
Dr. Taussig then requested that the board would adjourn till the following day, or till Monday, that the other witnesses might be presented. This was refused by the board. In fact, Maj. Warren said: "If a thousand steamboatmen should come and say that this Bridge was no obstruction, it could not change my opinion." The Bridge Company then asked to be allowed to present a paper signed by steamboatmen and experts, expressing their views on the questions raised. This was also refused, on the ground that the board did not want the opinion of irresponsible parties who were not present to answer their questions. The board only requested that Col. Flad should answer a few questions which they would put to him.
Dr. Taussig asserted that if the board would give them opportunity ("as many hours as their opponents had had days"), the Bridge Company would effectually disprove every serious objection against the Bridge.
As, however, opportunity was refused, the officers of the Company protested against the investigation as unfair, and withdrew. Later, Dr. Taussig, and Gen. Noble, filed affidavits with the honorable Secretary of War, stating the facts substantially as given above.
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The Report of the board, with several accompanying papers, was presented to Gen. Humphreys, the chief of engineers, September 12, 1873. It was as follows: —
ENGINEER'S OFFICE, UNITED STATES ARMY,
ST. LOUIS, Mo., September 11, 1873.
GENERAL: The board of engineer officers convened by Special Orders No. 169, War Department, Adjutant General's office, Washington, August 20, 1873, "to examine the construction of the Illinois and St. Louis Bridge across the Mississippi River at St. Louis, and report whether the Bridge will prove a serious obstruction to the navigation of said river; and if so, in what manner its construction can be modified," have the honor to submit the following report: —
In considering the subject laid before them, the board have confined themselves strictly to their instructions, which direct them to ascertain whether the Bridge, as being built, will be a serious obstruction to the navigation of the Mississippi River; and if so, what modifications can be made in its construction.
They have not undertaken to decide whether the Bridge is or is not being built in conformity to the acts of Congress authorizing its construction, although this question will be of importance when it becomes necessary to decide who shall pay for such modifications as may be determined on.
The board have obtained from the steamboatmen who complain of the present structure a statement of their objections and the reasons therefor.
They have obtained from the officers of the Bridge Company such drawings and statistics as were needed for a clear comprehension of the nature of the structure, and have caused a sufficient number of measurements to be taken to assure them that the drawings herewith submitted are substantially correct.
Appended to this report are the following documents and drawings: —
A. Copy of special order convening the board.
B and C. Copies of acts of Congress authorizing the construction of the Bridge.
D. Tracing giving profile of Bridge and approaches. (Furnished by the Bridge Company.)
E. Tracing showing elevation of center and west span of Bridge and portion of Western Approach. (Furnished by the Bridge Company.)
F. Tracing showing the outline of the lower part of the superstructure, as originally designed and as now being constructed. (Furnished by the Bridge Company.)
G. Water-record of the port of St. Louis for the last thirteen years last giving the duration of various stages for each month of each year, and also some special observations taken previous to the continuous records. (Compiled by the board from the official records.)
H. Tabular recapitulation of the above, giving the duration of various stages for each year, the average yearly duration of each stage, with the corresponding heights under the center of the middle span, and the heights available for a width of 174 feet, or 87 feet on each side of the center of the arch.
I. Drawing showing outline of center arch, with lines of extreme high and low water, and also the width of clear headway available at different heights above extreme low-water. (Prepared by the board.)
K. Tabular statement giving the most important dimensions of some of the principal steamboats plying to and from the port of St. Louis. (Furnished by the Boatmen's Association of St. Louis.)
L. Diagram giving graphically the heights of chimneys and pilot-houses of steamboats enumerated in the preceding list, and showing the relative height of chord of the center arch, which is 174 feet long and 5 feet below the crown of the arch, for different stages from extreme low-water of 1863 to extreme high-water of 1844. (Prepared by the board.)
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These drawings, etc., present the general features of the structure so clearly that a detailed description seems unnecessary.
The objections made to the Bridge are as follows, viz.: —
1. The height under the lower arch is so small that a large proportion of the boats which will have occasion to pass under it must lower their smoke-stacks at all, or nearly all, stages of the river, while many of the larger boats will not be able to pass under it during the higher stages, even with their smoke-stacks down.
2. The small height afforded is only available for a portion of the whole span, owing to the arch-form of the lower part of the superstructure. Moreover, the difficulty of passing under the exact center of the arch will be very great, especially in foggy or windy weather, and any considerable deviation to either side may bring the boat's upper works in contact with the Bridge.
3. These difficulties would probably deter most boats from ever passing the Bridge, thereby preventing the ready transfer of freight from one boat to another, or its delivery and shipment at different parts of the city, without resorting to costly transfers by drays or barges. This, it is claimed, would practically cut the Mississippi River in two at this place.
An examination of appendices K and L will show that the first point is well sustained. The list of boats enumerated therein comprises only those which happened to be in port at the time the board was in session, or whose dimensions were attainable. It might have been increased considerably had time been available.
The apparently unreasonable height and size of the chimneys in general use on these steamboats are really essential to secure a good draught to the furnaces and economical combustion of fuel. Artificial means to produce the same end are generally very expensive and often ineffective.
Although it is a comparatively easy task to lower small chimneys, dealing with those of large size is a very serious matter indeed. Their weight is so utterly disproportionate to their strength, even when new, that no machinery yet devised will enable large chimneys to be lowered, either wholly or in part, without very great labor and danger.
The elevated position of the pilot-house is necessary to enable the pilot to have an unobstructed view of the river ahead and astern of his boat. Experience has decided this point most clearly.
The second objection is mainly owing to the peculiar system of superstructure employed, and which we understand was adopted principally on the ground of economy. Appendix I gives the widths which are available under the center span at different heights above extreme low-water. The side spans have not been considered, as they are 4 feet lower than the central one.
Appendix F shows the lower line of the superstructure as originally designed, with the railroad tracks below the arch for a portion of the width (226 feet). By a subsequent modification, the lower arched tube was lowered 4 feet at the crown, while the railroad tracks were raised through a similar distance. This brings the road-way entirely above the arch, and increases the height at the center of the arch about four feet. The practical conditions are, however, but little altered by this modification. The full height is only given at the exact center of the arch, and in order to consider the matter in its practical bearing it is necessary to assume that some definite width will be required for the safe passage of a boat.
The width of draw-spans required by Congressional legislation up to this date varies from one hundred and sixty to two hundred feet. The former width would be too small for the large boats used on the Lower Mississippi, and an approximation to the greater width would probably be necessary. The horizontal chord of the center span, which lies 5 feet below the crown of the arch, is 174 feet long, and gives the least width of water-way which seems compatible with safe navigation. The height of this chord is 50 feet above the city directrix. It may therefore be assumed that a boat, no portion of whose structure extended above this limiting height, might pass safely under the Bridge, provided that
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the pilot was enabled to keep her within the space mentioned, viz., 87 feet on each side of the center of the span. The position of this chord with reference to different stages of water is given in appendix L, which also shows the relative height of the chimneys and pilot-houses of a large number of the boats which will wish to pass under the Bridge when it is completed.
There remains still to be considered the practical difficulty of keeping a boat within the limited width necessary for safety.
It is the opinion of the board that this will be a matter of very great uncertainty, and this is also the view taken by intelligent pilots who were questioned on this point. They maintain that the same width of water-way between piers, with clear head-way above, would be far preferable. The reason given for this is that the piers would define the available width with exactness; they are easily seen and can be avoided. In case of wind, a boat can be dropped through the opening by lines made fast to ring-bolts on the pier itself.In case of striking them under head-way, the damage done is to the hull alone; and even if so great as eventually to sink the boat, time will generally be afforded to save the lives of the crew and passengers.
In the case of a wide arch, however, the case is different. The piers are too far apart to be of service as guides, and lights placed on the structure will be so nearly overhead as to be of no great assistance. If range-lights could be placed at some distance above and below the Bridge, the difficulty might be mitigated; but in a crowded harbor like that of St. Louis it would be almost, if not quite, impossible to give the lights sufficient individuality to avoid the chance of mistakes. Moreover, in foggy weather the lights could not be seen. In case of wind, there would be great danger of a boat sheering or making so much leeway as to come in contact with the Bridge. In this case the shock would come upon the light upper-works, which would probably be destroyed. As the passengers are carried on the upper decks, such an accident would probably be attended with great loss of life.
The chance of dropping through the pier is not available in this case, as the arch of the center span springs from a point about at the level of high water of 1844.
The third objection seems fairly sustained by the facts already cited, especially when it is remembered that the principal part of the river business is done during the higher stages of water. The large New Orleans boats, for instance, rarely attempt to do business after the river gets to a lower stage than 20 feet above extreme low-water.
A large part of the St. Louis river-front is above the Bridge, and several elevators, a sugar refinery, and other similar buildings are already located above it. These could not safely be reached during high stages by the large boats navigating the lower river, and much inconvenience and expense would thus be entailed; but the board consider these interests in a measure local, and of infinitely less importance than the national interests involved in the question. The government has expended, and is still expending, large sums of money in improving the navigation of the Upper Mississippi, Missouri, Illinois, and other rivers, for the express purpose of allowing the largest steamers to navigate them. It would therefore seem entirely out of keeping with this general policy to allow, at the very threshold of these improvements, a structure which would practically debar a large proportion of existing steamboats from using them.
The board are therefore unanimously of the opinion that the Bridge, as at present designed, will prove a very serious obstruction to the free navigation of the Mississippi River.
They would, moreover, state that arched trusses like those under consideration present so many difficulties to free navigation that in future their use should be prohibited in plans for bridges over navigable streams.
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The board have very carefully considered the various plans proposed for changing the present structure, but find none of them satisfactory.
The piers being only made strong enough to withstand the thrust of the unloaded arches, it will be impossible to raise separately either of the spans, or to substitute for one of them a straight truss or a suspended road-way. The practical difficulty of raising the entire structure would be very great, as well as enormously costly.
Moreover, in any such plan, the present approaches, including the costly tunnel under a portion of the city of St. Louis, could not be used without considerable modification, as the steamboatmen deem a clear height of 75 feet above high water the least admissible.
Under these circumstances, the board do not feel justified in recommending any change which would involve a complete remodelling of this magnificent structure, now so nearly completed. At the same time, as already stated, they deem it absolutely necessary that some provision should be made for allowing large boats to pass the bridge with safety whenever they find it necessary to do so.
They would therefore recommend, as the most feasible modification, a plan which has been already tried and found efficient at the railroad bridge over the Ohio River at Louisville, Ky.
Let a canal, or rather an open cut, be formed behind the East Abutment of the Bridge, giving at the abutment a clear width of water-way of 120 feet. The shore-side of this cut should be laid out on an easy curve, joining the general shore-line about five hundred feet above the Bridge and about three hundred feet below it. The river side may be entirely open, but the shore side should be revetted vertically with stone or crib-work to a height of about five feet above extreme high-water. This wall should be provided with ring-bolts and posts, to enable boats to work through the cut with lines.
Let this opening be spanned by a drawbridge giving a clear span of 120 feet in width.
By this plan, boats as large as any now built would be able to get through the Bridge, in any weather and at any stage of water, and only at the cost of some little delay.
The steamboatmen have stated to the board that they would be satisfied with this modification, and the engineers of the Bridge Company only raise as an objection the delay to trains caused by opening and shutting the draw. While recognizing the validity of this objection, the board deem that the difficulty can be mitigated, if not entirely overcome, by providing machinery capable of opening and closing the draw with any desired rapidity. The use of this draw by the boats will be only in cases of necessity, and the inconvenience which this use may occasion to travel on the Bridge there seems no course but to submit to.
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Detailed estimates of the cost of this proposed modification can only be made after a special survey and study of the locality. Owing to the pressure of their other official duties, the board deem that it would be impossible for them to remain in session while these surveys and calculations are being made, and would therefore recommend that it be made a special duty of the local engineer officer to prepare and submit the estimate.
Whether this modification be carried out or not, the board deem it very important that such lights and marks be displayed by the Bridge as will enable boats not only to distinguish the position of the piers and arches with certainty, but also to be able to tell the clear head-way available under the Bridge.
The modification proposed by the board will not require the present work of constructing the Bridge to be interrupted, and the only action which seems necessary is to submit this matter to Congress at its next session, with the recommendation that action be taken to enforce the modification, and at the same time to determine by whom it shall be carried out.
Respectfully submitted.
J. H. SIMPSON,
Colonel of Engineers and Brevet Brigadier-General, U. S. A.
G. K. WARREN,
Major of Engineers and Brevet Major-General, U. S. A.
G. WEITZEL,
Major of Engineers and Brevet Major-General.
WILLIAM E. MERRILL,
Major of Engineers and Brevet Colonel.
CHARLES R. SUTER,
Major of Engineers, U. S. A.
Brig. Gen. A. A. HUMPHREYS,
Chief of Engineers, U. S. A., Washington, D. C.
In transmitting the Report to the Secretary of War, Gen. Humphreys had said: —
"The views and recommendations of the board are concurred in by me, and it is recommended that the matter be submitted to Congress at its next session, for such action as in their judgment may seem to be necessary.
It is further suggested that the chief of engineers be authorized to furnish the Bridge Company with a copy of this communication and the Report of the board."
The Bridge Company was notified October 15 that Gen. Humphreys concurred with the board in their Report, and that the views and recommendations of the board had been approved by the Secretary of War. Mr. Eads had but just returned from Europe. The Bridge Company had been inclined to regard the Report as a harmless bit of spite, too extravagant to injure the Bridge, but sure to rebound with great discredit upon the heads of those who made it. When, however, it was reported that the Secretary of War had approved the recommendations of the board, some anxiety was felt lest the credit of the Company might suffer. The next phase of the story is best told in the words of Mr. Eads.
REVIEW OF THE REPORT BY MR. EADS.
ENGINEER'S OFFICE, ILLINOIS AND ST. LOUIS BRIDGE COMPANY, October, 1873.
To the President and Directors.
GENTLEMEN: The Report of a board of United States engineer officers, dated September 11, 1873, approved by the chief of engineers, U. S. A., having been referred to me, I respectfully submit on these important papers the following review: —
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Owing to an inadvertence which occurred in the United States bureau of engineers when transmitting to this Company the above papers, it was stated that the Report had been approved by the honorable Secretary of War. Fearing such high official sanction might possibly affect the credit of the Company, the chairman of your Executive Committee and myself immediately visited Washington to obtain a recall of this approval until a review of the Report could be laid before the department.
We learned from the honorable Secretary that he had not approved the Report, and had taken no action on it; and a letter from the chief of engineers, addressed to the president of the Company, explained and corrected the inadvertence above mentioned.
The order convening the board directs it to "examine the construction of the St. Louis and Illinois Bridge across the Mississippi River at St. Louis, and report whether the Bridge will prove a serious obstruction to the navigation of the river; and if so, in what manner its obstruction can be modified." The Report declares that the Bridge will be a very serious obstruction to navigation when completed.
The correctness of this decision rests wholly upon the reliability of the testimony received by the board and the qualifications of its own members as experts in river navigation. For, manifestly, if the evidence relied upon be untrustworthy, and the members themselves not qualified to act as experts, their opinions, although unanimous, and strengthened by the indorsement of the chief officer of their corps, can be of no value whatever. The views of the steamboatmen referred to in the Report are shown by the accompanying letters to be wholly incorrect. The first one of these letters is from the mayor of St. Louis, Capt. Joseph Brown, who commanded several of the largest steamers on the river, and the second one is from a number of other well known, highly respected, and skilful commanders, who have also navigated some of the largest steamers afloat. Several of these gentlemen are to-day deeply interested in the largest ones; hence they would be peculiarly injured if the Bridge were really a serious obstruction. Not one of these gentlemen has a dollar of Interest in the Bridge.
The height necessary for the pilot and the difficulty of steering through the central part of the arch are the only two questions on which the board seemed to think it necessary, to support its own views by reference to the assertions of steamboatmen. It will be hereafter seen by quotations from these letters that on these two points their statements were wholly unreliable. This fact established, it remains to examine what value should attach to the opinions of the distinguished experts themselves. The Report declares: —
"The apparently unreasonable height and size of the chimneys in general use on these steamboats are really essential to secure a good draught to the furnaces and economical combustion of fuel. Artificial means to procure the same end are generally very expensive, and often ineffective."
Nowhere has the economy of fuel been so closely studied as in the construction of ocean steamers. Artificial means are seldom used on them to produce a draught, and although the largest ones consume much more fuel per day than any Mississippi steamer, none of their chimneys approach the height of some of those on the river. The great development of power witnessed every day in locomotives, whose chimneys never exceed ten or twelve feet in length, is obtained without any artificial means to procure draught, except by the escapement of their waste steam. These facts completely disprove this first statement of the board.
The Report says: "Although it is a comparatively easy task to lower small chimneys, dealing with those of a large size is a very serious matter indeed. Their weight is so utterly disproportionate to their strength, even when new, that no machinery yet devised will enable large chimneys to be lowered either wholly or in part without very great labor and danger."
As it is well known to every sue that it is more difficult to raise a thing than to lower it, the reader will wonder by what extraordinary means these formidable chimneys were ever erected, when it is so very difficult to let them down. The second letter referred to above says: "We have often raised and
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lowered them, and do not think, with such appliances (falls and derricks), that it is either dangerous or a very great labor. We believe $1,000 or $1,500 would pay for hinging the chimneys and providing improved appliances by which the largest chimneys in use could be readily lowered and raised." This is the testimony of thirteen experienced steamboat-captains, and it is sufficient to refute this second statement of the board.
The entire weight of that part of the largest chimney which would require to be lowered is only three or four tons. If we assume the length of this part to be 70 feet above the hurricane-deck, and 7 feet in diameter, and made of No. 12 sheet-iron of a strength equal to 50,000 pounds per square inch, a little calculation will show that such a cylinder, if well riveted, will, even after discounting forty per cent of its strength for the riveted joints, require over 300 tons to pull it asunder. Standing erect, it will sustain 60 tons with safety. If each end of such a chimney be provided with a strong angle-iron flange sufficient to preserve its circular form, and it be placed horizontally on rests at its ends, it will support a distributed load over its length equal to half a dozen such chimneys. The size of chimney named is an extreme one, whilst the thickness is not unusual, nor is the tensile strength beyond that of good iron. A few of the simplest calculations that are made in the office of an engineer will suffice to disprove completely the third statement of the board, to the effect that "their weight is so utterly disproportionate to their strength, even when new."
The board enforces its opinion respecting the necessity of very high pilot-houses by declaring that "experience has decided this point most clearly." This declaration loses all of its force when compared with the following simple statement made by the gentlemen just referred to, one of whom is the captain and part-owner of the Richmond, which probably carries the highest pilot-house afloat: "In no case is it absolutely necessary for safety [in navigating the largest boats] for the pilot to be more than thirty-five or forty feet above the water-line." The fourth statement of the board is thus shown to be fallacious.
On the assumption that a clear height of 50 feet above directrix is requisite for safe navigation, the Report says: "The horizontal chord of the center span, which lies 5 feet below the crown of the arch, is 174 feet long, and gives the least width of water-way which seems compatible with safe navigation." On this assumption it will be evident, presently, that the board has understated the safe width at least fifty per centum.
The highest part of the boat remaining, when the chimneys are lowered, is the pilot-house. This, on large steamers, is usually surmounted with a pyramidal canopy or roof, the apex of which is, of course, safe anywhere within the 174 feet. As it is much higher than any other portion of the boat, it follows that when it is at either end of this distance, one-half the width of the steamer must be outside of this 174 feet, and yet in safety under the descending part of the arch, — for the apex of this canopy is immediately over the keel of the boat. As the largest steamers are from eighty-five to ninety feet wide, it is evident that that much more should have been added by the board to this 174 feet. Therefore, on its own data, this fifth statement — to wit, that the least width compatible with safe navigation is only 174 feet — is also an error. It should have been stated at about two hundred and sixty feet. The board, having arbitrarily assumed 174 feet as the only width of water-way compatible with safe navigation afforded by an archway 520 feet wide and 55 feet high, then endeavors to support the remarkable proposition that if the piers were placed at no greater distance than 174 feet apart they would be "far preferable," if there were clear head-way above. The arguments advanced in support of this novel opinion are equally as notable as the proposition itself. The Report says: "The reason given for this is, that the piers would define the available width with exactness; they are easily seen and avoided." "In the case of a wide change, however, the case is different. The piers are too far apart to be of service as guides, and lights placed on the structure will be so nearly overhead as to be of no great assistance." Even the possibility of hitting the piers when so close together does not lessen the
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superiority of the narrow gauge. In this event the board offers the following consolation: "In case of striking the piers under head-way, the damage done is to the hull alone; and even if so great as eventually to sink the boat, time will generally be afforded to save the lives of the crew and passengers;" whereas, in case of a collision with the arch, the board assumes that the upper works of the boat would be destroyed, and, "as the passengers are carried on the upper decks, such an accident would probably be attended with great loss of life." Further on we are told that "the steamboatmen deem a clear height of 75 feet above high water the least admissible" — a concurrence in which opinion doubtless actuated the board in recommending the canal.
In these last few extracts there are three distinct assumptions, and these constitute the seventh, eighth, and ninth errors on which the decision of the board rests. These are as follows: —
1. Lights placed on an arch 50 feet above high water are of no great assistance.
2. Greater head-room for passing boats is indispensable.
3. Piers 520 feet apart are too wide to serve as guides.
From these three postulates, drawbridges and narrow piers are absolutely necessary for safe navigation. If lights 50 feet high are "of no great assistance," surely they will be of no use at all 75 feet high; and if piers 520 feet apart are too wide to serve as guides, there would be no means left the bewildered navigator, in approaching an opening 520 by 75 feet, but to run it by the compass or by buoys placed in the channel.
The absurdity of this corollary proves that the three premises of which it is a logical sequence are incorrect.
The fact that all three of these assumptions are errors is fully established by the counter-statements in the letters referred to. In addition to this disproof, the following extract from the Report will show the fallacy of two of them, and prove conclusively that the board itself believed it quite practicable for an arch 55 feet high to be effectively lighted, and its wide piers distinguished with certainty. The Report says: "Whether this modification [the canal] be carried out or not, the board deem it very important that such lights and marks should be displayed by the Bridge as will enable boats not only to distinguish the position of the piers and arches with certainty, but also to be able to tell the clear head-way available under the Bridge."
Reasonable gentlemen would hardly wish to compel the Company to display lights to enable boats "to distinguish the position of the piers and arches with certainty," if they really believe that "the piers are too far apart to be of service as guides, and lights on the structure will be so far overhead as to be of no great assistance." As the latter statement is completely refuted by the former one, I think its insertion in the Report must have escaped the notice of the board.
Another proof that the board was not justified in declaring that the arch is too low, is shown by the following facts, which the Bridge Company was prevented from laying before the board. In the spring of 1866, several large meetings were held on 'Change in this city by gentlemen interested in protecting the navigation of these rivers. Much discussion ensued as to the proper conditions to be imposed by law in bridging them. A memorial to Congress presented at one of the meetings was referred to a committee of the following fifteen gentlemen: J. S. McCune, J. F. Griffith, Barton Able, Joseph Brown, H. C. Moore, David White, J. H. Alexander, Wm. M. McPherson, A. W. Fagin, Geo. Pegram, Adolphus Meier, Felix Coste, James Ward, N. Stevens, and J. B. Eads.
On the 18th of April, 1866, this committee unanimously reported a series of resolutions, and from their report I quote the following: —
"Your committee have carefully examined the subject with reference to ascertaining what restrictions are really demanded by the marine interests involved, and what can be conceded by those interests to such an extent as to leave no serious difficulties in the way of the requirements of the land
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transportation in crossing the river, and yet preserve a comparatively uninterrupted navigation on the Mississippi.
The views of your committee are embodied in the following resolutions, the adoption of which they respectfully recommend: —
Resolved, That the delegation in Congress from Missouri be requested to procure at an early day the passage of a law to regulate the construction of bridges over the Mississippi River, and that they earnestly endeavor to incorporate the following provisions in said law: —
1. That all bridges crossing the Mississippi River shall have a clear height of 50 feet over the main channel, between the lower part of the bridge and high-water mark, measured in the center of the greatest span.
2. If below the mouth of the Missouri, they shall have one span 600 feet, or two spans of 450 feet each, in the clear of abutments. * * *
4. No drawbridge, with a pivot or other form of draw, shall be permitted.
Resolved, That a copy of this report and resolutions be sent to each member of the Senate and House of Representatives from Missouri at Washington."
These resolutions were unanimously adopted by the Exchange, and may, therefore, be taken as the authoritative expression of the largest and most influential body of merchants, shippers, and steamboatmen in the valley of the Mississippi. Among the fifteen names are those of ten gentlemen directly interested in river navigation, and, with very few exceptions, these were all representative men in that interest.
In recommending such unusually long spans, the committee was informed at the time by me that arches of such great length were entirely practicable, but that trusses increased in weight so rapidly in proportion to the span, that their great cost made them virtually impracticable. It was for this reason, and with a full knowledge of the fact, that, in denning the height, the words "measured in the center of the span" were inserted by this committee.
These resolutions were published in the papers at the time, and every one had, therefore, full notice of the height agreed upon, and that that height referred expressly to the center of the greatest span over the channel. After a company has, during the last five years, expended millions of dollars in constructing a bridge with spans greater and higher than those required in these resolutions, and with its plans publicly exposed on 'Change all the time, it is a remarkable fact that some of the gentlemen who were most influential in shaping the report of the committee in 1866 have been the most active in 1873 in obtaining from six eminent United States engineers an official declaration that the Bridge, whose dimensions they were chiefly instrumental in fixing, will, when completed, prove "a very serious obstruction to navigation." And this, too, after being prominently active in securing an official declaration from the Merchants' Exchange of St. Louis that these dimensions will "preserve a comparatively uninterrupted navigation on the Mississippi." This Exchange is composed of more than one thousand members, a large number of whom are owners and captains of steamboats, while almost every one in it is more or less directly interested in preserving the navigation of the river. On such questions it can speak more intelligently than any other body in this valley.
It is no justification for the bad faith of these recalcitrant committeemen to say that the Exchange declared in 1873 that 75 feet in height was requisite for the safe navigation of the Mississippi. The Exchange did not, like them, ignore and repudiate in 1873 what it said in 1866. The height of 75 feet, as will be seen by the resolution of last May, applied only to bridges that maybe built below St. Louis. It will, on these facts, be conceded that it was an error of the board to assume that greater height than is given by the center arch of this Bridge is really necessary.
The tenth objection to the Bridge is because its arches make the following method of navigating bridge-openings impracticable when descending the stream: —
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"In case of wind, a boat can be dropped through the opening by lines made fast to ring-bolts in the pier itself." "The chance of dropping through along the pier is not available in this case, as the arch of the center span springs from a point about at the level of high water of 1844."
This method of navigating bridge-openings, I think, originated with the board, as it is not credited to any of the steamboatmen examined, and has not yet, I believe, been used on these rivers. I have never seen a steamboat, or other vessel, dropped down in a current by a line attached to a ring-bolt below her, and I think the laws of gravity would prevent the success of the system, even if this Bridge had unlimited head-roo