Engineers of Dreams: Great Bridge Builders and the Spanning of America

by Henry Petroski

  In time, the physiological condition of the bends began to be understood and guarded against, but other aspects of work on large construction also imperiled the health and safety of workers and engineers alike. A bridge from New York to Brooklyn was John Roebling’s dream, but while he was involved in surveying to fix the location of the Brooklyn tower, in final preparation for beginning work on the pier, his toes were crushed when a ferryboat bumped into some piles of the slip on which he was standing. The symbolic significance and irony of the accident were probably not lost on the senior Roebling, who had had to fight for years the opposition of the ferryboat interests. He soon developed lockjaw, or tetanus, of which he died on July 22, 1869, a little more than three weeks after the accident.

  John Roebling’s bridge did not die with him, of course, and it was under construction contemporaneously with that of Eads. The chief engineer was Roebling’s son Washington, who was born in 1837 and graduated from Rensselaer Institute in the Class of 1857. He gained practical experience in the family’s wire-rope mill, and in assisting his father in building the suspension bridge across the Allegheny at Pittsburgh, just before the Civil War. It had been said that the elder Roebling was upset when Washington enlisted in the Union Army, first in the New Jersey militia and later in a more active New York artillery regiment, for which he would build bridges and ascend in balloons to observe enemy movements. He was to become a veteran of such battles as Second Bull Run, Antietam, Chancellorsville, and Gettysburg, and attained the rank of lieutenant colonel, by brevet, before resigning in 1865 to assist his father with the completion of the Cincinnati and Covington Bridge across the Ohio River, now known as the Roebling Bridge.

  While Washington was still in the army, he had met Emily Warren, sister of his general, at an officers’ ball. She captured his heart at first sight, and the two were married early in 1865. At his father’s request, the young Roebling couple went to Europe to make a study of pneumatic caissons, in preparation for the construction of the Brooklyn Bridge. They also visited such then famous suspension bridges as Telford’s across the Menai Strait and the Clifton Suspension Bridge erected across the Avon Gorge, near Bristol, as a memorial to Isambard Kingdom Brunel. Roebling was critical of the towers of each, mostly on aesthetic grounds, and found the deck of the Menai bridge to be very light and subject to vibrations. On the Continent, he received a grand tour of the Krupp ironworks in Essen, Germany, where he was shown an eyebar that had been made up especially for the occasion of the American engineer’s visit. Such eyebars were essential links in tying the steel strands of wire that make up suspension-bridge cables into the anchorage.

  Throughout his travels, Washington Roebling wrote of what he was learning to his father, who was back in Trenton thinking about the great East River bridge and how it would be designed and constructed. The clear necessity of deep foundations for the towers, in particular, was of prime concern, and Washington’s information about caissons, which he spelled “cassoons,” was invaluable. Colonel Roebling, as he came to be known, also visited St. Louis, early in 1870; he and Captain Eads, who had become so designated in recognition of his exploits on the river, discussed caisson design. Subsequently, the roughly contemporaneous design of caissons to establish foundations for the St. Louis and Brooklyn bridges resulted in some conflicting claims, and in 1871 Eads sued Roebling for patent infringement. The rivalry led to a series of letters in the English trade journal Engineering, to which Eads first wrote in April 1873 to “correct some statements” made by Roebling in a pamphlet on pneumatic-tower foundations that he had recently published.

  The crux of the matter concerned the location of the air lock, which Eads had put within the caisson’s chamber, thus making ingress and egress relatively convenient and obviating the need to pressurize the vertical access shaft, or even to make it airtight. What irritated Eads was Roebling’s statement that the idea was not new with Eads but had been used earlier in Europe, although admitting that “the first practical application … on a really large scale in this country” was in the St. Louis Bridge. Eads contended that Roebling had neglected to distinguish between iron caissons and those upon which masonry was piled, and that he had thus not given sufficient credit to the American innovation. Eads’s second letter to Engineering on the subject included drawings of Roebling’s Brooklyn caisson, which had the air lock outside the air chamber, and his New York caisson, launched about a year later, in May 1871, which had its air lock inside the air chamber and was clearly similar to Eads’s design. Eads explained his interest in carrying on about the matter, while incidentally getting in some digs against Colonel Roebling and providing some insight into the nature of what constituted engineering practice, then as now:

  I trust I shall not be understood as finding fault with Colonel Roebling for copying my plans in his New York caisson. On the contrary, I hold it to be the duty of an engineer to use the surest and most economic methods which are known in accomplishing his work, and, if possible, to improve upon those methods. Nor is the lack of inventive talent, whereby it is frequently possible to improve on the plans of others, or to devise new ones, at all necessary to constitute an able engineer, or to insure professional success. It is of much greater importance that the engineer, on whom rests the responsibility of a work, should be competent to select the best devices proposed by his assistants, or used by others, than to be able to invent novel ones himself. The obligation to adopt the best is, however, not incompatible with a generous regard for the rights or merits of others, and his professional reputation will never suffer by giving such credit to them as may be justly due.

  The exchange between Eads and Roebling may have been especially emotional because of the bad experiences both men had had personally, and because of their workmen’s suffering from the bends and other complications in the pressurized caissons. Late in 1870, a fire had broken out in the Brooklyn caisson, and Roebling worked himself to near-exhaustion directing operations to extinguish it. Spending so much time in the compressed and smoke-filled air caused him to suffer an attack of the bends and remain paralyzed for some hours. He recovered, only to suffer a much more serious attack in the New York caisson in 1872, when he appeared to be close to death. He recovered again, however, or appeared to, and went back to active work on the bridge. But by the end of the year, he was in extreme pain and frequently sick to his stomach, and he and Emily went to Europe for his health. He never did fully regain his strength, and was to spend three years in Trenton while the bridge towers were completed. Eventually, he became bedridden, in a room that overlooked the bridge under construction, with Emily effectively serving as assistant engineer and intermediary between the incapacitated chief engineer and his lieutenants on the construction site.

  Though an engineer like Eads or Roebling dominates the story of a given bridge at a given time, that engineer is typically not only one among many working on similar problems contemporaneously, but also constantly dependent upon the assistant engineers responsible for the various parts of each larger project. Among the young men Washington Roebling had hired as assistants shortly after his father’s death was Francis Collingwood, Jr., who in 1855 had graduated first in his class from Rensselaer Institute, where the younger Roebling had met him. Collingwood had worked as a city engineer in his hometown of Elmira, New York, and in the family jewelry business before being asked by Roebling to help the self-taught engineer William Paine on the Brooklyn caisson. Though Collingwood agreed only to a short engagement, he became so involved that he was among those engineers believed to have been capable of taking charge of the work in the event of Roebling’s death, and remained associated with the work until its completion in 1883. Collingwood’s distinguished career on the Brooklyn Bridge project, and later as a consulting engineer, is remembered today in the American Society of Civil Engineers’ Collingwood Prize, which he instituted and endowed in 1894 to recognize young engineers who publish technical papers of exceptional practical merit. The subjects of prize-winning paper
s can range from the foundation of piers to the capacity of the superstructure they support. Whether engineers write such papers or not, the problems they deal with, as Eads and his colleagues knew, must be addressed in designing and building the artifacts.

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  As papers alone do not make a design, so piers alone, difficult as they may be to construct, do not make a bridge. Eads wanted the superstructure between and over the piers to be as solid as the masonry it would bear against, and in his report he wrote as follows about the strength of the bridge under the heaviest load that he could conceive its ever having to carry: “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.”

  In addition to all the people and locomotives it might have to carry, Eads’s bridge would have to carry its own weight, of course. For many a bridge, in Eads’s time as well as before and since, the weight of the structure itself can be so many times greater than what could physically be crowded onto it that a considerable proportion of its strength must go toward just holding itself up. The weight of a structure is also a principal determinant of its cost, and so there are clear advantages to using material that is strong relative to its weight. Before the 1860s, steel was not generally available in sufficiently large amounts or pieces to be incorporated in bridge structures, but Eads believed that the most economical arch would be made up of cast-steel tubular segments. He thus specified steel for the major structural elements, making his bridge the first to incorporate so much of the high-strength material.

  The Keystone Bridge Company of Pittsburgh was given the contract to build the superstructure. Keystone grew out of what Andrew Carnegie called the first iron-bridge company, the firm of Piper & Schiffler, which he organized in 1863 with the help of the engineer Jacob Linville, the “hustling, active mechanic” John L. Piper, and “a sure and steady” Mr. Schiffler, whose first name Carnegie seemed to have forgotten in writing his autobiography. In 1865, the Piper & Schiffler firm was absorbed into Keystone, a name Carnegie was “proud of having thought of as being most appropriate for a bridge-building concern in the State of Pennsylvannia, the Keystone State.” Among the first major contracts of what came to be Keystone was the enormous 320-foot-span truss bridge over the Ohio at Steubenville. By the time Eads approached them, the very successful company had an established reputation but a “bad credit” rating, according to Bradstreet’s, because they never borrowed any money.

  Andrew Carnegie and James Eads were perhaps more alike than either of them might have wanted to admit. Like Eads, Carnegie finished his formal education at age thirteen, when his family sailed from Scotland to America to seek better opportunities. They settled in Pittsburgh, where young Andrew began working as a messenger boy. He had to stay on in the office every other night, thus getting home as late as eleven o’clock, and that “did not leave much time for self-improvement, nor did the wants of the family leave any money to spend on books.” It so happened, however, that a Colonel James Anderson “announced that he would open his library of four hundred volumes to boys, so that any young man could take out, each Saturday afternoon, a book which could be exchanged for another on the succeeding Saturday.” Andrew found that Colonel Anderson’s largess extended only to “working boys,” however, “and the question arose whether messenger boys, clerks, and others, who did not work with their hands, were entitled to books.” Not to be deterred, Andrew wrote a letter to the Pittsburgh Dispatch, arguing for a more inclusive policy, and his persistence paid off: he was allowed to check out a book a week. The memory of this experience no doubt prompted an older and more affluent Carnegie to give so many libraries to communities.

  As youths, Carnegie and Eads read in different subjects, the former reveling in history and essays, the latter in science and mechanics. Yet great engineering projects tend to bring such disparate traditions and personalities together, and by the time the two men met over the plans for the St. Louis Bridge, they were equally headstrong, albeit each in his different sphere of endeavor. Carnegie remembered Eads as an “unusual character,” whom he characterized as “an original genius minus scientific knowledge to guide his erratic ideas of things mechanical,” but Eads’s own reports and achievements belie this assessment. Carnegie’s point of view was no doubt influenced by Linville, who advocated trusses, like the one at Steubenville, over arches for large bridges. Linville told Carnegie that if the St. Louis bridge were built on Eads’s plans, it would “not stand up; it will not carry its own weight.” Keystone could not sell a truss bridge to the customer Eads, however, for, according to Carnegie, he “was seemingly one of those who wished to have everything done upon his own original plans. That a thing had been done in one way before was sufficient to cause its rejection.” Eads’s response to such criticism was reflected in his report, where he wrote, “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?”

  Eads wanted a steel arch, not unlike the one in Koblenz, and Keystone did agree to construct it for him, but this was not to be easy. After approval of the plans, the next step lay in raising the money. This obstacle was overcome thanks to Carnegie’s “first large financial transaction,” the sale of some bridge mortgage bonds to Junius S. Morgan, the American financier in London and father of J. Pierpont Morgan. Getting the steel parts fabricated and assembled into the bridge was another matter. John Piper, who began addressing Eads not just as “Captain” but also as “Colonel,” came to refer to him in succession as “Mr. Eads,” “Jim Eads,” and occasionally “Damn Jim.” When Eads insisted on steel over iron parts, it took considerable time and money to get them made to meet the specifications. The joke that had been current when the bridge was still a proposal could thus continue to be told:

  First gentleman: “How much would the bridge cost?”

  Second gentleman: “Seven million dollars!”

  First gentleman: “How long will it take?”

  Second gentleman: “Seven million years!”

  Once the steel parts were made and shipped to St. Louis, they were erected without interfering with traffic on the river. The method employed had been suggested over a half-century earlier by Telford as a means of constructing a five-hundred-foot cast-iron arch across the Menai Strait without the use of any scaffolding in the water, and in St. Louis it was implemented by extending the halves of each arch—part by part—equally on either side of the central piers, supporting the heavy mass by guy wires that passed over temporary towers erected atop the piers—until the arch was completed and could support itself. Eads had at one point urged the use of catenary cables, slung over towers much like a suspension bridge, to support the partial arch, but the steadily changing weight of the arch as it progressed out from each tower would have called for constant readjustment of the curve. Early in 1871, Linville proposed to Walter Katté, engineer in charge of Keystone’s western office, in St. Louis, that direct guys to the towers and backstays be used, along with Henry Flad’s scheme of using hydraulic rams to adjust cable tensions, thus effectively employing the cantilever principle to support balanced back-to-back arch sections until the completed arches could support themselves. Original estimates were that the arches could be completed in a few months, but delays in receiving parts slowed the work considerably. Since financial assumptions had been based on projected revenue once the bridge was completed, it was imperative that steady progress be made toward that end. Incentives were offered to Keystone to close the arches by January 1, 1874, and to have the bridge ready for traffic by March.

  The St. Louis Bridge under construction, showing the cantilever principle employed (photo credit 2.10)

  By the end of the summer of 1873, the halves of the arches were approaching each other, but the critical operation of putting the last piece
of steel in place was thwarted by the exceedingly high seasonal temperatures, which had so expanded the metal that the gap was too small for what might be called the steel keystone. Eads was in Europe at the time, recuperating from a condition characterized by chronic coughing and hemorrhaging lungs, and the task fell mainly to Henry Flad and a young engineer named Theodore Cooper, who earlier had been responsible for making sure that the steel mills were producing the proper material for the bridge parts. When the late-summer heat showed no signs of letting up, a wooden trough was constructed along the entire length of the arch, so that ice might be packed in and cool the steel enough to contract it—and thus open the gap wide enough for the last piece to be inserted. This scheme did not succeed, however, and it was necessary to resort to an alternative plan that had been devised by Eads.

  Earlier in the year, he had applied for a patent involving the erection of arches that incorporated a screw mechanism capable of raising the completed arch a few inches, so that the supporting cables would be slackened and could be removed. By cutting the ends off the too-long arch ribs, threading them, and inserting the screw mechanism into the sprung arch, it was possible to close the arch on September 17. After that, work went relatively smoothly and quickly, and in January all the cables were removed and the arches became self-supporting. The Keystone Bridge Company announced that the bridge was to be available for pedestrian use in late April, but then Carnegie reconsidered allowing any traffic on the bridge until his company had been paid. It was another month before the upper roadway was opened to pedestrians and fifteen thousand people paid a nickel apiece for the privilege of being among the first to walk across the Mississippi at St. Louis. By July 2, the rails had been completed on the lower deck, and fourteen heavy locomotives, in two sets of seven, were driven back and forth for five hours, first on both sets of tracks and then in one long line. Such a procedure, during which engineers monitor the structure’s behavior, constituted what is known as a proof test.