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

by Henry Petroski

  The book that Steinman wrote with Sara Ruth Watson, Bridges and Their Builders, had its origins when Steinman, the very visible engineer and promoter of his profession, was approached by the publisher G. P. Putnam’s Sons to write a book for the general reader on the history of bridges. After entering into a contract to do so, he had not been finding time to complete the ambitious project when, early in 1941, in Tampa, Florida, he met Watson, who taught at Fenn College in Cleveland, at a meeting of the American Toll Bridge Association, an organization Steinman had founded about a decade earlier. He was at the meeting to give his classic demonstration of bridge-deck instability, using (like von Kármán) a crude model and an electric fan, in his lecture, “Bridges and Aerodynamics,” and Watson was there to lecture on “Bridges in Poetry and Legend.”

  When Steinman checked in at the meeting and met Watson, she “struck him as so charming” that he offered on the spot to turn the book contract over to her, according to his biographer Ratigan. However, Steinman and Watson agreed to write the book jointly, and it was immensely successful. The chapter on the Roeblings and the Brooklyn Bridge so captivated Irene Steinman that she suggested it be made into a movie. To his response, “I can’t write a movie,” Irene retorted, “David, you can do anything.” Since this was no doubt what the egoist Steinman wanted to hear, he set out first to write an entire book on the Roeblings and their bridge, seeing this as a necessary first step toward writing a screenplay. This new book project was to take five years to complete, during which time the movie notion seems to have been forgotten, but not other ones.

  David Steinman, with simple model and electric fan, giving one of his many lectures on the aerodynamics of suspension bridges (photo credit 6.14)

  In his early sixties, Steinman began to write poetry, some of it bordering on the devotional but much of it about bridges and bridge building, and the verse was eventually collected in several volumes, including I Built a Bridge and Songs of a Bridgebuilder. His poetry, like almost everything else he did, brought him recognition and awards, and he must have relished the attention that poetry societies gave an engineer who advocated the liberal education of his colleagues so that they might be more readily perceived also, as a group, to be citizens of culture and stature. In one of his poems, Steinman praised the life of the mind, as nurtured in college, where eager young students go

  To spark the things of spirit that transcend

  The shibboleths of ancestry and creed.

  Such ideas must have consoled Steinman, who had repudiated his ethnic origins, even before he committed the thoughts to verse. His major prose-writing project of the time gave him, in addition, a surrogate family to research—the Roeblings and their Brooklyn Bridge. In the preface to his finished work, Steinman perpetuated the myth of his own life story, making himself a child of the bridge rather than of an immigrant family that lived in the squalor and hunger that surrounded it:

  A boy grew up in the shadows of the Bridge. He loved to walk over the span and to explore its marvels. He was awed by its vastness, by the majesty of the towers and by the power of the cables; and he was fascinated by all the details of the construction—the anchorages and the cables, the trussing and the beams, the slip-joint at mid-span, the machinery of the cable railway, the stone work of the towers, and the magic of the radiating stays. When he returned from these pilgrimages he would recount to his playmates and to his elders the wonders he had seen. To him it was truly a “miracle bridge”; and, as he wondered how so marvelous a work could have been created, he was fired with the ambition to become a builder of suspension bridges. In a background of poverty, this far-flung ambition seemed beyond the boy’s reach; but the spirit of the Bridge, and later the story of its builders, had entered his heart—and the dream came true.

  It was, Steinman continued, “in partial discharge of that debt of inspiration” that he undertook to write his book on the Roeblings, perhaps imagining them to be his professional progenitors. Gleaning information from “thousands of sources—original manuscripts, family letters, diaries, memoirs, notes, reports, periodicals, newspaper files, biographical works, scrapbooks, technical literature, records of historical societies, and correspondence,” Steinman cobbled together a gripping story, if in a ponderous book. The first edition of The Builders of the Bridge appeared in 1945, the same year that his longtime partner, Holton Robinson, died. Soon afterward, as if released from some constraint by the event, Steinman dropped his elder’s name from the firm’s, as he had omitted his parents from his biography. In 1948, the firm of D. B. Steinman received a contract for modernizing the Brooklyn Bridge by eliminating the trolley tracks so that it could carry six lanes of vehicular traffic. Steinman assumed, as a further labor of love, this responsibility to modify yet preserve the bridge that had inspired him as a youth.

  A second edition of Steinman’s story of the Roeblings appeared in 1950, and it differed from the first mainly in its acknowledgment of a woman’s contribution to the Brooklyn Bridge enterprise. When Colonel Washington Roebling was struck with caisson disease in 1872, at the age of thirty-five, and became bedridden in a room overlooking the construction site of the Brooklyn Bridge, where three years earlier his father had suffered the accident that was to claim his life, control of the bridge project might have passed on to another engineer had it not been for Washington’s wife, Emily Warren Roebling. According to Steinman, writing elsewhere,

  She grasped her husband’s ideas and she learned to speak the language of the engineers. She made daily visits to the bridge to inspect the work for the Colonel and to carry his instructions to the staff. She became his coworker and his principal assistant—his inspector, messenger, ambassador, and spokesman—his sole contact with the outside world.

  Emily Roebling in fact functioned as assistant to the chief engineer. In a speech on the occasion of unveiling a tablet memorializing her, Steinman related how, upon the day the bridge was dedicated in 1883, Washington Roebling turned to Emily and told her, as a more generous Lindenthal might have told his assistant Ammann or Steinman upon the completion of the Hell Gate Bridge, “I want the world to know that you, too, are one of the Builders of the Bridge.” In an epilogue added to the second edition of his book, Steinman claimed as one of its accomplishments the attention that the book had directed “to the heroic contribution of a woman in the building of the Bridge.” He was, in part, atoning for the fact that he had forgotten her in giving his story of the builders of the bridge the subtitle The Story of John Roebling and His Son, and that he had seemed to dedicate it to the great men alone. Perhaps Steinman was coming to realize, no matter how subliminally, the debt he owed his own father and mother.

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  Steinman was able to devote time to literary pursuits in the 1940s in part because it had been a slow decade for new bridge building. This was caused not so much by the collapse of the Tacoma Narrows—that should only have affected the genre of suspension bridges, the way the fall of the Quebec had adversely affected only cantilever bridges a few decades earlier—as by World War II, which had focused so much attention on the destruction of existing bridges rather than on the erection of new ones, both literally and metaphorically. Writing after the war, Steinman noted that, “compared to the 1930s, when nearly every year witnessed a new bridge triumph, this slowing down of an accelerated tempo is an unusual situation.” This article in Engineering News-Record presented a series of tables giving such information as the world’s longest spans in various categories and recording “progress in bridge building as recorded in successive record span lengths.” Suspension bridges had dominated that progress for the previous century, with only rare anomalies, such as the Firth of Forth and Quebec steel cantilevers or the Hell Gate and Bayonne arches. Steinman, and others who had dreamed of designing and constructing even greater suspension bridges, must have worried, especially when they looked at the historic record, that in the wake of the Tacoma Narrows disaster their bridges of choice might become as unpopular as cantilevers had
earlier in the century.

  Steinman still wanted to build the record-setting Liberty Bridge, which was on his drawing board, on the cover of his firm’s brochure, and in the frontispiece of his book with Sara Watson. When Bridges and Their Builders was issued in a revised edition by Dover Publications in the mid-1950s, however, Liberty Bridge no longer occupied a position of honor; by then it was clear that his dream bridge was not to be in Steinman’s trophy case. In the meantime, he had begun to dream of other great spans, such as those crossing the straits of Mackinac, in Michigan, and Messina, in Italy, which awaited the design of exceptional bridges. Yet, if suspension structures were to make credible bridge proposals for such crossings, the matter of aerodynamic stability would have to be addressed. One approach was to test bridge models in wind tunnels, the way airplane-wing designs had then been studied for some years. Such an approach was, however, open to the limitations of experimental work generally, which meant that it gave only specific information on a specific test of a specific model of a specific design. A cleverly selected array of experiments could provide rather conclusive evidence about the phenomena and design under consideration, but there would always remain uncertainty as to whether the critical conditions had been tested or whether the model gave a true representation of the behavior of the full-scale bridge.

  Theoretical studies, on the other hand, could encompass general conditions and thereby deal, in principle, with every conceivable combination of wind and resistance, for example. Whereas Ammann was able to dismiss Steinman’s “guesswork expressed in impressive sounding scientific words” during their letter exchange on cable stays, a more mathematically based description of the rigidity and aerodynamic stability of suspension bridges was more difficult to refute. Steinman, with his theoretical background and experience translating the mathematical Melan, was recognized to be capable of producing such a description, and he published it in the November 1943 issue of the Transactions of the American Society of Civil Engineers, exactly three years after the Tacoma Narrows collapse. He modeled with mathematical formulas of considerable generality the cables and stiffening girders of a suspension bridge, and proceeded to pursue their mathematical and physical implications for the engineering of such bridges. He was able to conclude from his formulas that by “increasing weight, depth, rigidity, and bracing,” or adding stays and devices of various kinds, much as John Roebling had written about and done in the previous century, engineers could make suspension bridges stable in the wind. However, Steinman also pointed out that “these methods resist or check the effects, but do not eliminate the cause.” He was also able to conclude from his theoretical analysis that modifications to the cross section of a bridge, such as “using open spaces in the floor or by adding horizontal fins or other wind-deflecting elements” could eliminate the cause of instability. He found it “more scientific to eliminate the cause than to build up the structure to resist the effect,” a point of view with which von Kármán would no doubt have concurred. The idea of cutting slots in a bridge deck to obviate its oscillation was, in fact, one of the recommendations that emanated from the board of engineers appointed to investigate the Tacoma Narrows collapse, and the rebuilt bridge across the Narrows did incorporate the idea.

  Finally, Steinman concluded his Transactions article with a more personal request, that readers “share with him his faith and conviction that suspension bridges of all span lengths can be designed economically to any desired degree of rigidity and with assured aerodynamic stability.” Not surprisingly, given the interest in the subject in the wake of the Tacoma Narrows collapse, Steinman’s work attracted discussions that occupied more pages than did his paper, as did his responses to these discussions. In general, however, the reactions of readers, especially to his conclusions, were favorable.

  In the 1950s, after a decade in which literary and historical pursuits competed for his time as a theoretician and a designer, Steinman rededicated himself with rejuvenated interest to promoting bold new suspension bridges. In part because of theoretical work like his on aerodynamic stability—which provided guidance to wind-tunnel tests of new deck designs, which in turn confirmed theoretical predictions—there was renewed interest and confidence worldwide in building long-span suspension bridges. One project that had been shelved during the 1940s was the crossing of the Straits of Mackinac, which had so separated the Upper from the Lower Peninsula of Michigan that the Upper Peninsula was for all practical and economic purposes more a part of Wisconsin than of Michigan. Thousands of cars would wait sometimes almost a full day to get ferry service across the straits during summer-vacation time. At least as far back as 1888, when Cornelius Vanderbilt was attending a directors’ meeting at the Grand Hotel on Mackinac Island and said, “What this area needs is a bridge across the Straits,” an obvious advantage had been seen in such a structure. In one of his later poems, “The Bridge at Mackinac,” Steinman would not only set the scene but also use rhyme to clarify the pronunciation of the place name. Whereas the island’s name is pronounced as it is spelled, this is not so for the waters in which it stands:

  In the land of Hiawatha,

  Where the white man gazed with awe

  At a paradise divided

  By the straits of Mackinac—

  Regardless, however, of how the place names were pronounced, it had not been until the 1930s that legislation encouraged the serious consideration of a bridge across the straits. Even then, although the technological climate was right, the financial promise of a self-supporting toll bridge for seasonal traffic in the upper Midwest was not so bright as it was in the traffic-growth areas on the East and West Coasts.

  By 1950, the sight of thousands of cars waiting for ferries had renewed interest in a bridge. An Inter-Peninsula Communications Commission appointed by Governor G. Mennen Williams promoted a resurrection, with an influential membership, of the Bridge Authority that had been abolished during the war. Though there was some question as to whether the Authority could actually finance or build a bridge, they could certainly gather technical and financial information. The engineering questions were to be addressed first by a board of three consulting engineers, to be recommended by Dean Ivan C. Crawford of the University of Michigan.

  A major suspension span would likely be among the bridges of choice for the Mackinac crossing, and so the appointment of a credible consulting board was saddled with the decade-old legacy of the Tacoma Narrows disaster. Whereas Ammann had been a member of the expert committee that reported on that accident, Steinman had subsequently been a much more visible theorist as to how such an event could have happened and be prevented in future bridge designs. The naming of consulting engineers was further complicated by the debate that had ensued between Ammann and Steinman as to how to deal with their own flexible bridges. In the end, Dean Crawford extricated himself from the dilemma by recommending both Ammann and Steinman for appointment as consulting engineers for the project, along with Glenn Woodruff, the San Francisco engineer who had sat on the Tacoma Narrows investigatory panel with Ammann and with the aerodynamicist von Kármán.

  The board of engineers reported in January 1951, after six months of study, that a “perfectly safe suspension bridge” could be built across the straits, for a cost of approximately $75 million. An independent report on traffic and financing matters supported the economic feasibility of such a project. A final decision was delayed for various reasons, including: questions of steel availability during the Korean War; suggestions that there were unsuitable foundation conditions beneath the straits; and a stipulation that none of the preliminary consulting engineers could be picked for the actual construction project. This last was a frustrating obstacle, for Ammann and Steinman were the two most logical builders. In the end, the Michigan Legislature granted the Bridge Authority the right to engage the engineer of its choice.

  In the meantime, the federal Advisory Board on the Investigation of Suspension Bridges, which had been appointed by the commissioner of public roads in
1942 to coordinate research relevant to suspension-bridge design, especially with regard to aerodynamic stability, had issued its preliminary report of tentative findings, which was published in 1952 by the American Society of Civil Engineers. The authors of the 1941 failure report—Ammann, von Kármán, and Woodruff—were members of the Advisory Board, but the “competitor” Steinman was not. Steinman’s articles were, however, prominently referenced in the new report. The behavior of some particular bridges, including the Bronx-Whitestone, was discussed, and an unpublished report by Ammann to the Triborough Bridge Authority was quoted as admitting that the effect of the stay cables had “not been sufficient to prevent nor apparently reduce the exceptional oscillations of larger amplitude.” Such disappointing behavior had led to the addition of the present stiffening truss to the bridge, and it gave Steinman a victory of sorts.

  Financing for a Mackinac Bridge was not easy to come by, and the Michigan Bridge Authority had no funds to engage an engineer to produce a design. Only Steinman would agree to undertake the job on speculation. Thus, in January 1953, he was selected as designing engineer of the Mackinac Bridge; Woodruff was later named as his associate. Preliminary plans and estimates were ready within two months, and construction contracts were negotiated, as required, before the bonds could be issued in late 1953. Steinman’s design incorporated features endorsed by the Advisory Board, including space between the deep stiffening trusses and the outer edge of the roadway. This was to raise the critical wind velocity, at which oscillations of the deck could start, from the forty-two miles per hour that had become associated with the failed Tacoma Narrows Bridge to a calculated value of 642 miles per hour. An additional feature—namely, an open-grid roadway under the two center traffic lanes—raised the critical wind velocity to “infinity.”