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

by Henry Petroski

  Under Lindenthal’s direction, three comparative designs for a bridge with an 850-foot main span were considered: a stiffened suspension bridge with eyebar chains, a smaller version of his Manhattan Bridge, which in turn was a smaller version of his North River Bridge; a three-span continuous truss of unremarkable profile; and a three-span cantilever, more graceful than Boller’s design and bearing some resemblance to Lindenthal’s plans for the Queensboro Bridge. The bridge architect would no doubt have preferred the suspension design, for the truss would have the appearance of “a utilitarian structure,” a fault also common to cantilevers, which provide “no opportunity for monumental towers or abutments at the ends, because the absence of a large horizontal thrust or pull does not justify a large mass of masonry at those points, as in the case of an arch or a suspension bridge.” Although the words are Ammann’s, in his definitive report on the Hell Gate Bridge, they can be assumed to have been approved of if not inspired by Lindenthal. An arch design would also have satisfied the requirements of having no piers in the water and of being erectable without falsework to obstruct the waterway, in the manner of the Eads Bridge, but the arch was not considered at first, because there were no natural abutments to take the thrust. The suspension bridge would not normally be economically competitive with the other designs for an 850-foot span; according to Ammann, however, “whatever differences in cost may be found by comparative designs are largely due to the individual judgment of the designer in the selection of the truss system, material, permissible unit stresses, foundations, and architectural features.”

  Ammann’s list of factors to be weighed by a designer did not include the one that ultimately had the most effect on the bridge type chosen. Among the existing structures on Ward’s Island were state-hospital buildings, and in 1905 the line of the railroad had to be moved farther north to increase its distance from them. In order to fit the approaches to a suspension or cantilever design onto the island, a tight curve in the railroad would have been necessary, and this was undesirable in conjunction with the heavy grade that was needed to provide the proper clearance for ships to pass under the bridge. An arch bridge was considered, and it was found that one could be built with less steel than the alternative designs required; even with its more costly foundations, it was a competitive choice. In the final analysis, the favorable appearance of the arch led to its adoption.

  Two arch designs for the Hell Gate Bridge (photo credit 4.25)

  Lindenthal’s first arch designs were modeled after Eiffel’s Garabit Viaduct, a crescent-type arch over the Truyère River in France, as well as some German spandrel-arch bridges over the Rhine. The latter arch type was selected, in part because it was “more expressive of rigidity than the crescent arch, the ends of which appear to be unnaturally slim in comparison with the great height at the center.” David Billington, the premier structural critic of the later twentieth century, has interpreted this as indicative of Lindenthal’s predilection for “massiveness over lightness: the German over the French.” Before detailed design work began, however, the top chord of the arch was given “a slight reversal of curve toward the ends,” partly to provide some wind bracing, but also to “improve the silhouette of the arch.” This structural fillip would ultimately contribute much to the characteristic profile of the Hell Gate Bridge, as well as to the feature of the design that has been most questioned.

  Whereas Ammann wrote that “the artistic outlines of the steel superstructure are the result of the proper interpretation of the economic and engineering requirements of the structure,” Billington sees the stone towers above their base as structurally unnecessary to take the loads from the steel, and thus he sees the towers as nonfunctional and “rather a massive frill.” It is not clear how much of a role, if any, the consulting architect Hornbostels opinion played in the choice of arch type and its final recurved shape, but he certainly influenced the design of the towers, which from the beginning were also a point of some discussion and have continued to be the focus of structural criticism of the bridge. When the original design was presented in 1907, the Art Commission, “although not objecting to the design as a whole, disapproved of the decorative features of the towers and their bases.” This must have disappointed Lindenthal, the bridge architect of record, for he unquestionably wanted to produce an attractive structure and bring American bridge building up to what he considered European standards of aesthetics. He was not alone in his concerns. The never-to-be-built Lindenthal-Hornbostel towers dominated the frontispiece of Henry G. Tyrrell’s 1912 “systematic treatise,” Artistic Bridge Design, and as the existence of numerous contemporary municipal art commissions attests, there was rising sensitivity about the appearance of large urban structures.

  The towers of the Hell Gate Bridge clearly had to be modified before final approval was sought and construction begun, and one detail, where steel arch and stone tower came together, had to be addressed. As shown so clearly in the 1906 architectural rendering reproduced in Ammann’s report, the original tower design left a gap of about fifteen feet between the masonry and the steel, an arrangement that might have precluded Billington’s criticism of the final design three-quarters of a century later. As described in a recent account, Lindenthal was aware that this represented the “correct engineering solution,” clearly showing all the thrust transmitted through the lower chord to the abutment:

  Lindenthal feared, however, that the public, supposing that the towers supported the bridge, might think he had forgotten something. To deal with this possible psychological hazard, he grafted stubs of girders to the ends of the upper chords and placed T-shaped forms of concrete within the side openings of the towers. At a distance, they appear to be connected, but in fact a space of about six inches separates them.

  Whether he really feared the public’s perception or the art commission’s, the towers themselves were modified, but there appears to be no official record of approval of their final design. As he did in Pittsburgh in concealing the slender end posts of the Smithfield Street Bridge with ornate portals, so Lindenthal appears also to have employed an architectural treatment to conceal the potentially confusing structural detail of the recurved top chord of the Hell Gate arch. Perhaps he did not really want to or know how to end his masterpieces. There seems little doubt, however, that appearance was important to Lindenthal, who also envisaged extra-technical and extra-utilitarian functions for the Hell Gate Bridge. According to Ammann:

  A 1906 design detail for the Hell Gate Bridge tower and arch (photo credit 4.26)

  Mr. Lindenthal conceived the bridge as a monumental portal for the steamers which enter New York Harbor from Long Island Sound. He also realized that this bridge, forming a conspicuous object which can be seen from both shores of the river and from almost every elevated point of the city, and will be observed daily by thousands of passengers, should be an impressive structure. The arch, flanked by massive masonry towers, was most favorably adapted to that purpose.

  Completed Hell Gate Bridge, showing the steelwork of the upper chord carried into the towers and the long curving viaduct over Ward’s Island (photo credit 4.27)

  The visual appearance of his bridges was thus of considerable importance to Lindenthal, and now that he was in charge of a privately financed project rather than a municipal one, with its many constituencies, the bridge architect not only could but had an obligation to consider the important factor of aesthetics. As Ammann explained his mentor’s method, or perhaps echoed him:

  A great work of art evolves from an idea in the mind of its creator. It is brought on paper or into a more contemplative form and then changed and remodeled. Not until the plans have passed through changes and corrections, and have been submitted to an almost endless series of finishing touches, does the great work attain its perfection.

  A great bridge in a great city, although primarily utilitarian in its purpose, should nevertheless be a work of art to which Science lends its aid. An elaborate stress sheet, worked out on a purely econ
omic and scientific basis, does not make a great bridge. It is only with a broad sense for beauty and harmony, coupled with wide experience in the scientific and technical field, that a monumental bridge can be created. Fortunately, the Hell Gate Bridge was evolved under such conditions, and therefore may well be said to be one of the finest creations of engineering art of great size which this century has produced.

  Questions of aesthetics and symbolism aside, a great engineering project still needs a great engineering staff, and there were many more details than towers and recurved chords to be considered and calculated. How would the individual steel members, some to be twice as heavy as the largest previously used in construction, be made and joined? How would the weight of locomotives and railroad cars be borne by the various parts of the bridge, individually and acting in concert? To answer such questions required detailed thought and calculation, of such depth and magnitude that they were beyond the mental or physical capacity of one engineer. As chief engineer and bridge architect, Lindenthal directed his staff to explore various options and to consider and compare alternatives. Though he could indeed direct that this or that tower design be chosen, someone else would be expected to calculate the volume of masonry or concrete it would require, to estimate the time needed to construct it, and to prepare whatever detailed drawings were needed to make sure the abutments were located and aligned to meet and match the steelwork that someone else was thinking about in equally precise detail. Other engineers would later have the responsibility for overseeing and inspecting the construction to make sure that the plans were being followed so that things did meet as they were designed to. During the construction phase, Lindenthal was assisted by an engineering staff of ninety-five, and Ammann, as assistant chief engineer, “had general charge of the office, field, and inspection work.”

  In early 1914, Engineering News reported that the Hell Gate Bridge was then actively under construction, “with minor architectural changes in the terminal towers,” but other details began to attract the attention of some ever-critical readers. In a letter to the editor, “an admirer of the central span” wondered why the drawings showed a steel-viaduct approach to the bridge, and why the Art Commission did not object to it. The reader knew “the deteriorating and nerve-racking noise which is likely to accrue from trains passing over such a structure.” He suggested that concrete arches would have been just as economical. Furthermore,

  The arches could be built with fine architectural effect, and in such a way that screen walls could be carried up on both sides to, say, 15 ft. above base of rail, with the result that noise of traffic would be almost entirely eliminated. Such a structure would be almost as silent and picturesque as one of the beautiful old aqueducts still to be seen in the older countries.

  Lindenthal responded almost by return mail, explaining the choice of steel over concrete viaduct spans. The weight of a large masonry viaduct could not be supported easily or economically by the ground conditions on Ward’s or Long Island. He pointed out that with development and the introduction of sewer lines, the ground would be drained, and the piers would settle. Steel girders could be adjusted under such circumstances, but masonry arches would develop unsightly and possibly threatening cracks. Whether this was part of the design logic or a subsequent rationalization, Lindenthal had taken all such criticism seriously and responded accordingly. With regard to noise, he pointed out that the rails would be embedded in broken-stone ballast fourteen inches deep, carried in troughs of reinforced concrete, thus deadening much of the sound.

  He also took the opportunity to explain that the towers “were necessary parts of the structure, and not mere ornamental parts.” For the thrust of the arch to be properly resisted, the towers had to provide a certain weight to the foundation, and Lindenthal chose to accomplish this by building tall rather than squat towers, which “would have been unsightly.” His solution, in other words, was much like erecting the buttresses of a Gothic cathedral higher than appearances demand in order to add weight and maintain slenderness. Since the weight was needed in the towers for structural reasons, Lindenthal chose to provide it without sacrificing proportion. In the case of the viaducts, the additional costs would have been prohibitive.

  In fact, there eventually was a change in the design of the viaduct from the original to the revised drawings, published seven years apart, in Engineering News. In 1907, the viaduct over Ward’s Island was shown to be steel girders resting on steel piers, but in 1914 sketches, though the steel girders remained, the piers were shown as concrete. The decidedly social rather than technical reason for the change was mentioned in passing by Lindenthal during the discussion appended to Ammann’s paper. According to Lindenthal, an “objection was made by the authorities of Ward’s and Randall’s Islands to the steel columns, because they feared that inmates of the municipal institutions on those islands would climb them and make their escape. It was insisted that the design adopted should prevent this.” Ward’s Island held the state mental hospital, of course, and Randall’s Island, over which the viaduct also passed, was the location of a correctional institution. Presumably, a technical answer was found to the prior objections to heavy concrete piers, or more money was simply spent on them.

  By the end of the year, when the foundations were complete and the steel had begun to be erected, a small item headed “Hell Gate Arch Bridge Not a New Thing” appeared in Engineering News. In spite of its headline, the item signaled that all was once again well between the bridge builder and the journal. It proudly quoted this passage from Carlyle’s Sartor Resartus: “Never perhaps since our first Bridge-Builders, Sin and Death, built that stupendous Arch from Hell-gate to the Earth, did any Pontifex, or Pontiff, undertake such a task.” Engineering News thereupon christened Gustav Lindenthal “pontifex” of the modern Hell Gate arch.

  Construction progressed; the two trajectories of steel met over the unobstructed water in the fall of 1915, and the arch bridge and viaducts were completed a year later. The first passenger train to cross the bridge was the Federal Express, the previously established night train between Boston and Washington, D.C. The Federal Express route had for a long time included a fourteen-mile car-ferry transit through the crowded waters of the East River, which in winter was subject to delays caused by ice. When the car ferry was discontinued in 1912, the Express was operated over the Poughkeepsie Bridge until early 1916; at that point, regular service was discontinued. A weekly ferried Express was reinstituted briefly during the summer of 1916, so that travelers could bypass New York City during an infantile-paralysis epidemic. The completion of Hell Gate Bridge and the New York Connecting Railroad allowed the restoration of regular Federal Express service in 1917.

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  Though the Hell Gate Bridge would be mentioned in Lindenthal’s obituary as his “chief memorial,” even with its completion his career was far from over. Before the Hell Gate was finished, Lindenthal became consulting and chief engineer for a railroad bridge on the road between Sciotoville, Ohio, and Fullerton, Kentucky, across the Ohio River, about 120 miles above Cincinnati. The bridge was to carry heavy freight traffic, mostly coal trains, on a new branch of the Chesapeake & Ohio Railroad. The Sciotoville was the first large continuous truss bridge, which means that it consisted of truss elements rigidly connected across piers rather than of separate elements between them, and the longest and heaviest fully riveted one then erected in America. With two 775-foot river spans, it has been called “perhaps the boldest continuous bridge in existence” and “the ultimate expression of mass and power among American truss bridges.” J. E. Greiner, a Baltimore consulting engineer, in a written discussion of Lindenthal’s paper on it, called the completed bridge a “daring and handsome structure, decidedly ‘Lindenthalic’ in all its features,” and declared it to be another of the master’s structures evidencing, in Lindenthal’s own words, the “genius that originates as distinguished from routine which merely imitates.” Another discussion was submitted by Charles Evan Fowler, the New York c
onsulting engineer who had published in 1914 plans for a cantilever bridge between San Francisco and Oakland that would have surpassed the Quebec in span. One structural critic called Fowler’s “the boldest bridge plan ever made” but did not think the tolls from wagon and automobile traffic using it would pay for the upkeep of the roadway. Nevertheless, Fowler seemed to be more interested in size than suitability, in giantism than genius, and his discussion of Lindenthal’s paper revealed, however subtly, that a massive cantilever across San Francisco Bay would bring the record for that kind of span below the Canadian border to the United States, the home of all other great spans: