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

by Henry Petroski

  It is certainly true that if the New York Harbor, acknowledged to be the most beautiful in this country, should be defaced by a utility bridge of shabby appearance, it would be an unpardonable offense against the civilization of mankind. A pleasing architectural appearance of the bridge [proposed] was therefore held to be worthy of as much study as the engineering features, and the design aims to combine them in the best manner attainable out of a variety of designs made for the purpose.

  Lindenthal expected his digression to be “pardoned in view of the importance of the project.” Years later, his apparent inability to compromise on any front, functional or aesthetic, was blamed for the great dreamer’s ineffectualness in getting the North River Bridge plans approved. But whereas Lindenthal was talking aesthetics, others were talking politics and economics, each of which was a sine qua non of great bridge building. And perhaps the biggest obstacle of all was the almost strictly technical decision as to whether a suspension bridge of the record span he proposed was indeed practicable. As the great bridge over the Firth of Forth neared completion, the cantilever type was day by day gaining support. In the end, it was Lindenthal himself who publicly raised the issue of a suspension versus a cantilever bridge.

  Proposed cantilever bridge over the Hudson River (photo credit 4.8)

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  The full title of the long paper Lindenthal read before the American Society of Civil Engineers was “The North River Bridge Problem, with a Discussion on Long Span Bridges.” Many pages of Engineering News in the months of January and February 1888 were given over to Lindenthal’s solution of the bridge problem, but many more for the month of March were devoted to his discussion. His definition of a “long span bridge” was one whose structural metal (concrete bridges were not even under consideration) was at least as heavy as the traffic it was designed to carry. There were four types of bridges most suitable for long spans, he asserted: the suspension bridge, which, after Eads, he termed a suspended arch; the erect arch, which was the familiar kind; the continuous girder, of which the Britannia tubular bridge was an example; and the cantilever.

  First discussing the cantilever, Lindenthal pointed out that the type generally lacked rigidity under fast railroad trains, unless it was built with great height and depth, as over the Firth of Forth, at the sacrifice of headroom near the piers, which he thought unacceptable in the Hudson River. In addition to some more technical objections that he raised, he finally condemned cantilever bridges then built for “their general ugliness of appearance.” Such aesthetic concerns, according to Lindenthal, “may not be of much consequence for a railroad bridge off in the woods, but even then it would not be more expensive to build them with an eye to better appearance, if for no other reason than to set a good example in imitative engineers.” Among the things he found objectionable in contemporary cantilever bridges were the “indiscriminate use of eyebars and bulky compression sections in the same chord lines and the irregularity of truss frames,” which he thought to be “as needless as it is ugly looking.” He concluded his diatribe against cantilevers by alluding to two recently built ones in certain unnamed large cities. One of these bridges was the one in Philadelphia over Market Street, whose design was defended in a letter to the editor in a subsequent issue of Engineering News. The writer admitted that “cantilever fever” was prevalent at the time, but that Lindenthal was in fact “entirely ignorant of the special conditions of the case” which led to the bridge that he so criticized. Later in his own career, in fact, Lindenthal would argue precisely that some special conditions caused him to design an unusual bridge in an unusual location, but that continuous girder span was still then far in the future.

  Lindenthal’s discussion of arch bridges was quoted at considerable length from the 1868 report of Eads, including many of his illustrations, and his arguments were presented by Lindenthal as being as true in 1888 “as they were then, and as they always will be.” The discussion of suspended arches, or suspension bridges, was the longest. Whereas Eads had, of course, found the erect arch superior to the suspended, Lindenthal concluded just the opposite—namely, that the suspension bridge presented “the most favorable conditions of stability and rigidity.” Such a diametrically opposed conclusion from one engineer who had just agreed so much with the other with regard to the erect arch is not so much a contradiction as a demonstration of the complexity of the issue. In fact, there are in bridge design, as in all engineering problems, so many competing objectives and contrary constraints that in the final analysis the decision can be purely a question of personal preference and aesthetic taste, taking into account any special conditions at the bridge location. One engineer, because of his prejudices, might choose to design an arch rather than a suspension bridge for a particular site, whereas another might do just the opposite. Both bridge designs might be equally safe and reliable, but they might not have the same functional, aesthetic, and economic qualities.

  In Lindenthal’s case, he was so committed to the suspension concept for bridging the Hudson River that he turned the argument naturally and not unfairly to his use. Lindenthal admitted, for example, that it was “a popular assumption that suspension bridges cannot be well used for railroad purposes,” and further conceded that throughout the world there was only one suspension bridge then carrying railroad tracks, Roebling’s Niagara Gorge Bridge, completed in 1854, over which trains had to move slowly. However, rather than seeing this as scant evidence for his case, Lindenthal held up as a model the “greater moral courage and more abiding faith in the truth of constructive principles” that Roebling needed to build his bridge in the face of contemporary criticism by the “most eminent bridge engineers then living.” In Lindenthal’s time, three decades later, it was not merely a question of moral courage; “nowadays bridges are not built on faith,” and there was “not another field of applied mechanics where results can be predicted with so much precision as in bridges of iron and steel.” He did not promise such precision in the cost of his suspension bridge, however, and concluded his discussion by revealing an estimated cost of “approximately $15,000,000,” which still might have seemed more dreamlike than the bridge itself.

  In the meantime, the legislatures of New York and New Jersey had become involved again. In 1868, the New-York and New-Jersey Bridge Company had been chartered under the laws of New Jersey, which allowed one or two piers in the river as long as there was a thousand-foot clearance between them and a clear height of 130 feet in the center. With the renewed interest in a bridge, there was also renewed interest in getting the New York Legislature to pass a law so that cooperative progress could be made. There was, however, opposition on the New York side among supporters of a bridge farther up the Hudson River, nearer Albany. Early in 1888, a bill was introduced into the New York Legislature, but Engineering News, which by then had become an outspoken proponent of Lindenthal’s plan, if not a downright mouthpiece of his, criticized the proposed legislation:

  It plainly contemplates the erection of a cantilever, and stipulates for the placing of one pier in the river channel, neither of which should be permitted unless found absolutely necessary, even if the cost be considerably increased. If there be one place in the world where a mere “utility structure” should not be permitted, but where dignity and beauty of form should be a controlling feature, it is over the North River at New York, and in that and other respects the suspension type seems to us to have great advantages for the location.

  By midyear, federal legislation was also being proposed that would authorize a bridge company to build, within ten years of the approval of plans by the secretary of war, what was effectively a suspension bridge, for no piers were to be in the river. Among the promoters of the scheme were Lindenthal and Henry Flad, whose reputation, based on the Eads Bridge, was impeccable. As the wheels of Congress turned, there was considerable public discussion of the matter. With at least two bridge proposals competing for government approval, an editorial in The New York Times was optimistic that “we
shall have a bridge across the Hudson into this city ere the century closes.” Though the editorial did not mention Lindenthal by name, he was clearly being paid attention to: “An engineer of Pittsburgh, who makes bridges a specialty, has succeeded in gaining the ear of capitalists, and his calculations meet with respectful consideration from those who ought to know.” The Times seemed to be alluding to the editors of Engineering News, but the newspaper itself had some reservations about his design: “The picture of this greatest of all wonders of bridge making offers much the same beauty of curve in the main span as the East River Bridge and more grace of outline in the towers, though the openwork steel construction of the latter compare unfavorably with the granite piers at Brooklyn.” In fact, the open steel towers recalled unfavorably—to the editorial writer, at least—the Eiffel Tower, then under construction in Paris.

  As The American Architect and Building News emphasized, the problem was not so much the length of Lindenthal’s proposed bridge, for the “much-talked-of bridge over the English Channel would be 20 miles long.” Furthermore, the longest bridge in the world was New York’s elevated railroad, which consisted of a thirty-three mile-long “continuous bridge.” What distinguished Lindenthal’s proposal was the length of its main span, almost three thousand feet between two gigantic towers. Some readers of other publications were not so understanding. In the year following the public explication of the plans, London’s The Engineer carried a critical appraisal by Max Am Emde. Lindenthal responded in a lengthy article in Engineering News, showing the more blunt and acerbic side of his personality, which included a tendency toward ad-hominem argument and sarcasm. Regarding the availability of information about the strength of steel wire for bridge cables, Lindenthal was critical of Am Emde’s lack of knowledge: “Ignorance of it is inexcusable in an engineer, and unpardonable in a critic.” And regarding the weight and number of trains that would be present at any given time, Lindenthal pointed out that “the bridge is not intended for use as a storage yard for loaded freight cars.” This was an especially important point in designing bridges on the scale Lindenthal had proposed, and his argument that such bridges would be heavily loaded over their entire floor only during testing or with “special discipline” enabled him and subsequent American bridge engineers to design relatively light structures for their size, thus making them economically feasible, if potentially structurally unstable.

  Late-nineteenth-century proposal for a railway bridge over the English Channel (photo credit 4.9)

  English engineers, on the other hand, still remembering the Tay and watching the Forth Bridge grow, remained sensitive to the consequences of too light a structure. That there was a rivalry in fact as well as in judgment between engineers on the two sides of the ocean was brought home by Lindenthal’s closing his defense with the assertion that, in building bridges, American contractors had already established that they could hold their own with “contractors from England and other parts of the world.” When the Forth Bridge opened in March 1890, Engineering News would also appeal to national pride: “If English and Scotch railways can afford to bridge the Firth of Forth … the great trunk lines of this country and the City of New York combined should surely afford to bridge the North River.” The Brooklyn Bridge had for too short a time “stood unrivaled among bridge structures for its length of span,” and the North River bridge project was an opportunity for American engineers once again to “eclipse the latest effort of the Old World’s engineers.”

  Lindenthal’s great bridge may have brought him some prominence among railroad executives and readers of Engineering News, but two years after his report he was still a newcomer to New Yorkers generally. This was evident, for example, in a front-page story in The New York Times that described the thirty-five-foot-long model being made to help convince representatives of the federal government to “take hold of the project and build a national bridge,” since private capital seemed impossible to raise and both New York and New Jersey were balking at the price tag. In one place in the story, the “Pittsburgh man” had his first name misspelled “Gustave,” and in another his surname was given as “Lilienthal.” In spite of, or perhaps to overcome, such misnonymity, he seemed to take his case wherever there was an audience, which in 1889 included the meeting of the American Association for the Advancement of Science in Toronto. Lindenthal, furthermore, like Eads and Roebling and Baker before him, and like the builders of the greatest bridges after him, understood that different audiences had to be addressed in different ways. Politicians in Washington might best be swayed with a tangible model, but scientists meeting in Toronto would more likely listen to reason couched in terms of anthropology and natural science and of units of time approaching the scales used in geology.

  “That facility and rapidity of communication is a primary cause of civilization is recognized as an axiomatic truth,” Lindenthal began, and he proceeded to demonstrate that through practice his rhetoric was coming to be as sharp as his science: “The art of bridge building is ancient; the science of bridge building is modern.” He traced the development of bridge types, concluding that the suspension bridge was “as old as mankind itself, perhaps even older,” and he showed himself capable of scientific thinking in the Darwinian mode:

  Zoölogists tell us of the methods employed by apes in crossing streams. Failing to find a fallen tree to act as a beam or truss bridge, or failing to find meeting tree branches forming a sort of cantilever bridge, apes, we are told, form a chain by hanging together hands and tails, and suspended thus over a stream from tree to tree, the rest of the tribe climb along this living bridge from shore to shore. The strength of the chain with its weakest link, was, in this case, the weakest monkey; and there can be little doubt that occasional failures of such living bridges must have engrafted that bit of wisdom early on our anthropological ancestors. Modern bridge engineering, based on mathematical deductions, could not improve it.

  A popular view of a possible stage in the evolution of bridges (photo credit 4.10)

  The address was also full of technical details about strength and economy, demonstrating Lindenthal’s rational approach to bridge design and sound judgment about it that would, decades later, influence favorably the best of those engineers who would work under and learn from him. Engineers who would not heed the lessons of the master, especially with regard to a sense of natural and artifactual history, would find themselves embarrassed.

  Near the end of his address to the scientists, Lindenthal asked rhetorically of his dream, “How long will such a bridge last?” And he answered:

  If well maintained under the most competent engineering superintendence, there is no reason why it should not last as long as the Egyptian pyramids. They were built of more perishable material than steel and iron, provided iron and steel are kept well painted and free from rust. Rust and man are indeed the only destructive agencies for such a structure. No tornado could blow the structure over. No earthquake could shake it down, unless it were so great that the rock would cave and split, and swallow up the North River.

  He also recognized, however, that there was a potentially more destructive force, and Lindenthal began to slip into a political mode that was out of character for this address but would become more and more a part of his rhetoric in his later years. Some of his observations were prophetic; in his desire for aesthetically pleasing bridges he found a silver lining even in the clouds of war.

  Man is more destructive to structures than decay and rust. The necessity of war may bring about the destruction of large bridges in the future as it has in the past. This may not always be an unmixed evil, if inferior structures are destroyed and rebuilt by grander ones. The taste and desire for architectural harmony is growing, though as yet the standpoint of utility, without regard to appearance, is too prominent in most of our bridge structures.

  As Benjamin Baker, near the end of his lecture on the Forth Bridge, had invoked and quoted Thomas Pope, so Lindenthal closed his address by recalling that Pope, �
�an ingenious and ambitious shipwright,” had eighty years earlier designed a gigantic wooden bridge, “partly cantilever, partly arch,” that would have crossed the East River between New York and Brooklyn in one eighteen-hundred-foot span. At the time, Pope had exhibited a model of his bridge, which was never realized. But, rather than see in the story of Pope a fatal paradigm for his own endeavors, Lindenthal saw hope. Pope had also proposed a single-span bridge to cross the North River, which he described, as he did other of his bridge plans, in “quaint verse”:

  Thomas Pope’s early-nineteenth-century proposal for a bridge across the East River between New York and Brooklyn (photo credit 4.11)

  Like half a rainbow rising on yon shore,

  While the twin partner spans the semi o’er,

  And makes a perfect whole that need not part

  Till time has furnished us a nobler art.

  Lindenthal took it upon himself to take over Pope’s dream and to fulfill it in a more modern material and form. He believed that he was indeed a master of the “nobler art” that had evolved into an “exact science” by the end of the nineteenth century, and he was resolute. Determination alone, however, does not build bridges.