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

by Henry Petroski

  Comparison with Hell Gate Bridge of pylon-design details of the Sydney Harbour arch as proposed and as built (photo credit 5.9)

  Formal ground-breaking occurred in September 1927, simultaneous ceremonies taking place on each side of the river as speeches were delivered from the steamer De Witt Clinton anchored midstream. Silzer, no longer governor of New Jersey but now chairman of the Port Authority, waited patiently, while a telephone cable was repaired, for the ceremonies to begin. This cable, which had been cut by a passing ship, was to carry the speeches from the steamer’s saloon to WOR in Newark for broadcasting to those on the shore. After the forty-five-minute delay, the chairman began the proceedings and announced that “there are compensations for everything, and I made up my mind when this delay occurred that for every minute of it I would deduct a minute from my speech, and the result is that there is nothing left of the speech.” Silzer, the consummate politician, had made a deal with himself that could please everyone.

  Shortly after the ground-breaking ceremonies, the issue of how to suspend the deck was settled: the Trenton, New Jersey, firm of John A. Roebling’s Sons submitted a wire-cable bid lower by about 10 percent than that for an eyebar design. Matters of price were not expected to be the only determining factors for securing engineers’ professional services, but that was certainly not the case when it came to choosing one form of construction over another. As for the towers that would support the cables, their final appearance was to undergo a much more prolonged discussion, and how important a role economic considerations played in that decision is still debated. In the meantime, the contract for the steel superstructure for the bridge, with a single deck, was let to the McClintic-Marshall Company.

  The design of the bridge was described in an August 1927 issue of Engineering News-Record, with bare steel towers shown in the construction drawings and masonry-clad towers in a perspective drawing of a completed bridge. The discussion began with the declaration that “esthetic considerations played a large part in the determination of all the general features of this bridge,” and such considerations were “most commanding, perhaps, in relation to the towers.” The architect Cass Gilbert, whose Gothic-style Woolworth Building was still, in the late 1920s, the world’s tallest skyscraper, had been consulted by the Port Authority on the Hudson River Bridge “from the earliest stages,” and his treatment of the towers was expected to prevail. The steelwork had to be designed and erected first, however, and thus Leon Moisseiff, as advisory engineer of design, would have a great deal to say about what was to support the architectural façade of the towers.

  The structural design of the towers as a composite of steel and concrete to be clad in stone came in for considerable criticism of the kind R. S. Buck had raised; an early modification was to increase the capacity of the steel framework so that it could support the ultimate weight of the bridge and its traffic without any help from the concrete. Even then, the nature of the steel design was not simple, in that it resulted in what is known as a “statically indeterminate structure.” As with the Queensboro cantilever, this, of course, meant that the distribution of forces among the various steel members was not just a function of applied loads and geometry, but depended upon the stiffness of the steel and how the structure was assembled and how it moved under the load. Because of possible uncertainties in construction and analysis, it was widely held that indeterminate structures were to be avoided, but Moisseiff supplemented intricate analysis with model tests and allowed for variations in the completed design.

  Moisseiff’s interest in the bridge towers went beyond his elegant structural analysis, however, as he revealed in a book review that appeared in Engineering News-Record late in 1928. “Esthetics of bridges has come to be so live a topic that the publication of a work on the subject by an engineer of standing and culture is timely,” Moissieff began this review, of a new book by Friedrich Hartmann, professor at the Technische Hochschule in Vienna, and approvingly reported on its author’s viewpoint:

  He fully realizes the difficulty of expressing the achievements of modern engineering in the esthetic habits of the past. He therefore believes that architects, as a rule, are distant from the conception of steel bridges. Structures which fitted in the landscapes of medieval towns do not meet modern requirements. Dogmas and slogans on the relation of the useful to the beautiful have lost their value. “Neither is the necessary always beautiful nor the beautiful always necessary. The reverse may be true in both cases.” Engineers themselves should endeavor to develop the beauty of their structures.

  Moisseiff explained that the modern “designer of bridges cannot always make use of stone and its substitute, concrete, to the continuous and solid texture of which man has been accustomed by ages. He is generally compelled by the demands of feasibility and economy to make use of the high resistance of steel.” Moisseiff reported how Hartmann, “with a malicious pleasure … quotes diametrically opposed opinions of architects on the appearance of the Forth bridge,” that great steel cantilever. Most important for Moisseiff, however, was that Hartmann had opinions about American bridges, both standing and under construction: “Naturally he is against masonry towers and prays for their omission in the Hudson River bridge.”

  The basic idea for the towers appears to have come from Ammann himself, even before he became associated with the Port Authority. One of his first open discussions of the plans he had sent to Silzer occurred at a meeting of the Connecticut Society of Civil Engineers in early 1924. After spending over half of his time making a case for a bridge based on developing traffic patterns, Ammann discussed various aspects of the proposed design. In the concluding section of the paper, he dealt with the towers, “another important part of a suspension bridge.” While the Brooklyn Bridge towers were “a magnificent example of the old massive masonry type, unquestionably the one most pleasing to the eye,” cost had become prohibitive for the great weight of stone needed just to support towers projected to be as high as forty-five-story buildings. Ammann continued by contrasting steel towers:

  The opposite extreme is represented by the slender flexible steel towers. With proper architectural treatment, as in the case of the Manhattan Bridge, this type may be rendered very pleasing to the eye, but often its construction suggests crude utility. This type is, in most cases, the cheapest in first cost.

  The “braced steel towers,” as represented in the Williamsburg bridge, have a more massive appearance and certain advantages in erection but, unless well proportioned, look clumsy. They may be covered by a decorative shell of masonry as proposed in Mr. Lindenthal’s design for the 57th Street bridge, but such shells involve a heavy additional expense.

  Ammann’s innovative compromise for the 179th Street bridge was to resort to “the combination and utilization, to the full extent of their strength, of the two modern materials available for structural parts in compression, namely steel and concrete, the former completely embedded in the latter.” He was, in effect, proposing a sort of reinforced-concrete tower, something that would not be fully realized on such a scale until the Humber Bridge was built many decades later in England. In order to facilitate the construction of such a unique tower, Ammann proposed that the steel skeleton be designed to carry most of the load of the bridge itself, with the concrete and the steel sharing in carrying the added load of the traffic. Furthermore, the concrete would protect the steel from corrosion, thus reducing maintenance cost, and would provide a “more monumental appearance” than bare steel for a small additional cost. Finally, “the architecture of the towers has purposely been kept plain so as to be in harmony with the simple construction of the steel work. The monumental effect must be produced by harmony of mass and lines, and not by ornamentation.”

  The sketches accompanying the paper are captioned “Copyright by O. H. Ammann,” but they may very well have represented the work of the architect R. A. Ruegg, whose “valuable assistance” the engineer acknowledged in closing his paper. The architectural argument may also have been Rue
gg’s, for Ammann seemed to be having some difficulty in establishing his own structural aesthetic at the time, or at least seemed willing to be swayed more by the weight of opinion than the towers themselves would be by the weight of the bridge. Whereas his later bridge towers would resemble visually the open portal design in this paper, albeit more slender and in steel rather than in massive concrete or stone, the 179th Street bridge would not.

  In the tradition of large engineering projects, even after it was completed the final design of Ammann’s Hudson River bridge remained to be described in considerable detail, in words and pictures. Such final reports were typically prepared for limited distribution, and thus were a relatively expensive undertaking. In the case of this great suspension bridge, the Port Authority chose not to print the report itself but, rather, appropriated funds for the estimated cost to the American Society of Civil Engineers; this organization issued a series of eight papers on the bridge as a volume of its Transactions for 1933, giving the Port Authority enough reprints to distribute as it saw fit. The society bragged about this publishing coup: “Not since December 1911, when Vol. 74 was mailed to the Membership, has TRANSACTIONS appeared on other than a very thin and transparent grade of Bible paper. In order to present the numerous photographs … to the best advantage, Vol. 97 is published on a good grade of English finish paper.” However, since this was happening at the nadir of the Depression, the society found itself in the curious position of also having to justify such extravagance “in a year of unusual financial stringency.” The explanation was that, “with the expenditure of relatively little more” than was given by the Port Authority, the society could “furnish all its members with a technical record of this milestone of engineering progress.” The society also thus associated itself with the project in a distinctive way, and hence gave an extraordinary imprimatur to the project and its engineers.

  Four versions of Ammann’s proposed Hudson River bridge (left to right, top to bottom): the original 1923 proposal; a version with slender steel towers; a version with granite-faced towers and eyebar chains; and the bridge essentially as completed in 1931, with a single deck suspended from four wire cables and bare steel towers, but topped by observation platforms that were never added (photo credit 5.10)

  The debate over whether the towers should or should not be encased in concrete and stone had continued throughout the construction of the bridge and remained an issue even in the final report. When his status changed from independent engineer to bridge engineer for the Port Authority, Ammann’s association with architects seems also to have altered, and it was not Ruegg’s but Cass Gilbert’s architectural sketches, dominated by even more massive stone-faced towers (and approach viaducts on the Manhattan side), that then appeared to be the dominant feature of the bridge. In early Port Authority plans, the Gilbert stonework even overwhelmed the heavy eyebar chains that were chosen by the artist over wire cables. In his final report on the bridge, however, which dealt with its general conception and the development of the design, Ammann could not ignore the story behind the towers, which at the time remained the bare steel that Moisseiff had designed and had subsequently redesigned to be able to support even the double-decked bridge without the aid of concrete:

  There is no part of the design … which has called forth as much comment, favorable and unfavorable, on the part of engineers, architects, and laymen, as the towers. Indeed, as the writer has endeavored to show, the design of the suspended structure, the floor, and the cables, resolved itself largely in the application of natural and most simple structural forms which neither required nor permitted architectural treatment to satisfy aesthetics.

  The design of the towers, however, is not so well defined. There are widely different meritorious forms and the effect of the towers on the appearance of the entire structure is perhaps more pronounced than that of any other part. They may enhance or destroy the natural beauty of a graceful suspended structure. There are existing examples which illustrate both effects.

  It is futile to theorize about this question—it is largely a matter of aesthetic conception, which is intensely individual and changeable—nor can it be dealt with on general principles without regard to the local scenery or landscape. Moreover, the aesthetic treatment of a bridge, as that of any other engineering structure, is not always satisfactorily solved even by correct and honest application of engineering principles. The appearance of a structure so conceived may sometimes be materially enhanced by the addition or the architectural embellishment of certain structural parts, whether structurally required or not. The flanking abutments of an arch bridge, and the towers and the anchorages of a suspension bridge, offer opportunity for such enhancement.…

  The writer, who has conceived and is primarily responsible for the type and general form of the design, considers the steel towers as they stand to represent as good a design as may be produced by a slender steel bent, and that they lend the entire structure a much more satisfactory appearance than he (and perhaps any one connected with the design), had anticipated. Nevertheless, he believes that the appearance of the towers would be materially enhanced by an encasement with an architectural treatment, such as that developed by the architect, Mr. Cass Gilbert.…

  The writer is not impressed by the criticism, based solely on theoretical and utilitarian grounds, that the encasement would constitute a camouflage which would hide the true structure and its function.

  Ammann may still have been unsatisfied with the bare towers, but not Moisseiff, who wrote an entire paper on the design of the towers for the special Transactions volume. Though he pointed out that “the fact that the towers were conceived to be ultimately encased in masory is important to the understanding of their design and their articulation,” he spent few words on the controversy, other than to express his opinion that the towers “would probably remain without enclosure.” The engineer was not to be alone in his view; the architect Le Corbusier would call the structure “the most beautiful bridge in the world,” and “blessed.” He would also write: “When your car moves up the ramp the two towers rise so high that it brings you happiness; their structure is so pure, so resolute, so regular that here, finally, steel architecture seems to laugh.”

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  For all the debate over appearances, actual construction of the 179th Street Bridge had progressed very deliberately, and the bridge was finished six months earlier than had been thought possible. Yet final details of the towers remained uncertain even as the bridge was being dedicated, on October 24, 1931; the program for that event shows an observation platform that was never built. The program also contains a very brief popularized history of Hudson River crossings, and a description of the gigantic nature of the endeavor and enterprise. Not uncharacteristically, there is no mention of the role that engineers like Ammann played, either in the technical design or in the political and financial machinations that were so necessary in the preliminary stages. The short program did, however, include a justification for the name of the structure, which, also not uncharacteristically, had been a matter of some controversy.

  Photograph of the George Washington Bridge as completed in 1931, showing the extreme slenderness of its single deck (photo credit 5.11)

  The site of the bridge, the program explained, was of historic interest: during the American Revolution, George Washington had led patriots against the British at this location. Thus it was fitting to bestow George Washington’s name on the monumental structure. The name “George Washington Memorial Bridge” had actually been announced nine months earlier by the Port Authority, which had appointed a committee to select a name from the many suggestions that had been made. Though there was strong feeling that the simple title “Hudson River Bridge” was sufficient, the committee acceded to custom by agreeing that “something more historically significant was desirable.” There was quick opposition to the “ridiculous name” that had been “born in a vacuum, warmed by patriotism but chilled by an utter absence of common sense.” Since there
was already a Washington Bridge over the Harlem River, barely a mile to the east, some argued that there could be confusion, but even the chairman of the Port Authority, John F. Galvin, admitted that people would continue to call the new bridge the “Hudson River Bridge,” no matter what its official name. There were, naturally, alternatives suggested, including “Palisades Bridge,” after the New Jersey cliffs that also served as the west abutment, and “Cleveland Bridge,” after the U.S. president, who had been born in New Jersey and been a governor of New York. Within barely a week, the Port Authority commissioners, who wanted the bridge “named to suit the public,” agreed to refer the matter back to the special committee that had recommended the name in the first place. It had become known that the George Washington Bicentennial Commission, which had been requesting public entities to take the occasion of the bicentennial of the birth of Washington to name “bridges, highways and other public monuments” after him, was a strong proponent of the name originally chosen. The public was now invited by the Port Authority to submit more names.