The Father of Modern Bridges

Perhaps no twentieth-century engineer has left a more visible mark on a major city than has Othmar Ammann on New York. His five major bridges there bear much of the enormous traffic flow to and from the city while requiring remarkably little maintenance. They are beautiful and efficient structures, for Ammann achieved an uncommon harmony of visual elegance, simplicity, and power with practical design. But that harmony developed slowly. From the powerful early arch at Hell Gate and the later world-famous George Washington Bridge to his ultimate achievement, the Verrazano-Narrows Bridge, across the entrance to New York Harbor, Ammann showed the way to a new approach to bridge architecture—an approach based on the idea that an unornamented, inexpensive solution can be in all respects the best solution. Civil engineers speak of Ammann with a certain reverence in this regard, for he almost singlehandedly led the way to this aesthetic.

Before the work of Ammann and his contemporaries, engineers paid little direct attention to the artistic possibilities inherent in construction. Instead they kept largely to themselves, producing designs that were sometimes passed along to architects for “ornamentation.” A few engineers—Thomas Telford in England, John Augustus Roebling in the United States—managed to design bridges that were at once beautiful and structurally expressive. But they were normally built at least partially of stone, and the aesthetic of masonry construction is thousands of years old. Roebling’s and Telford’s aesthetic approaches to their construction materials were hardly new.

Alexandre Gustave Eiffel made great strides in developing an artistic approach to iron construction. His most famous structures, including the Paris tower that bears his name and a great arch-supported viaduct in France’s Garabit Valley, at once express strength and beauty. Benjamin Baker, with his monstrous Forth Bridge in Scotland, and others followed Eiffel’s lead.

Eiffel, however, worked before the twentieth-century heyday of the long-span bridge. He also worked primarily in iron, the material of the great Victorian engineering works, and iron is neither as strong nor as versatile as steel. An approach that reflected the new material’s properties and strengths became necessary early in this century, and Ammann, a talented engineer with an eye for design, led the way.

Born in Schaffhausen, Switzerland, to a German-speaking household, Othmar Hermann Ammann attended the Federal Polytechnic Institute of Zurich and earned an engineering degree in 1902. His talent for drawing had been evident from youth, and he had considered studying architecture but discovered both an interest in and an aptitude for mathematics and physics. The Swiss have a strong tradition of combining efficiency with elegance in engineering. Their designs tend to bring together the thorough engineering associated with Germany and the lightness and artistry of French techniques. Ammann was schooled in this tradition by one of the giants of European structural engineering, Wilhelm Ritter.

Upon his arrival in the United States in 1904, when he was twentyfive, Ammann was immediately hired by Joseph Mayer, a New York engineer who specialized in bridges. Mayer was then developing a plan with Gustav Lindenthal, the most famous bridge engineer of his generation, for a span of unmatched length across the Hudson River. The project wasdropped, but Ammann would keep the idea in mind for many years. Shortly afterward he was hired by Frederic C. Kunz, of the Pennsylvania Steel Company, to work on the engineering calculations for the Queensboro (Fifty-ninth Street) Bridge in New York and to write most of a civilengineering text, which became the standard work in its field. Titled Design of Steel Bridges , it is credited solely to Kunz; a single sentence of acknowledgment—“I also wish to mention Mr. O. H. Ammann”—appears at the end of the preface. Not surprisingly, Ammann left Kunz some time before the book’s publication in 1915.

In August of 1907 the Quebec Bridge over the St. Lawrence River in Canada collapsed while under construction. (See “A Disaster in the Making,” Invention & Technology , Spring 1986.) Ammann went to C. C. Schneider, the chief engineer of the American Bridge Company, who had been appointed to investigate the collapse, and offered to assist in his analysis of the accident. Schneider agreed, and Ammann’s well-written report on the disaster earned him a measure of fame and respect in his profession.

In 1912 Ammann took a job as chief assistant to Gustav Lindenthal, who was preparing what would become his most famous work—the great railroad bridge between Queens and Wards Island at the confluence of the East and Harlem rivers, known as Hell Gate. The engineers faced several challenges. The span was large; the ultimate design would be the longest arch-type bridge in the world. More significantly, the rapid tidal currents that gave Hell Gate its name made impossible the erection of scaffolding in the river. Any support for the developing span would have to come from backstays or counterbalancing systems on the shore. Furthermore, geological conditions on the banks of the East River necessitated unusually deep foundations for anchorages or piers.

The engineers considered a number of options. The conventional choice would have been a cantilever bridge, since suspension spans were considered unsuitable for railroad spans except those of great length. Ammann did not agree; his report on the Hell Gate project suggests that all three types—cantilever, suspension, and arch—could have been built for approximately the same cost, depending upon “the individual judgment of the designer in the selection of the truss system, material, permissible unit stresses, foundations, and architectural features.” He then elaborated on this last aspect, remarking on the role of aesthetics in such a project: “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 [which] 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.” Even at this early stage of his career, Ammann gave a great deal of thought to aesthetic considerations.

Further investigation suggested that the arch type might in fact be somewhat cheaper because it would use less steel, and thus a preliminary selection was made. However, two types of arch had been suggested. Lindenthal had designed a crescent arch similar to Eiffel’s Garabit Valley viaduct, in which the two chords—the top and bottom edges of the arch structures—join at the ends, at the abutments; but he had also designed a spandrel arch, in which the chords are closest at the peak and diverge toward the ends. The costs were comparable; while the crescent type used slightly less steel, the spandrel arch would be cheaper to construct without the temporary support known as falsework. The decision was finally made almost completely on aesthetic grounds: “Although both designs are pleasing in appearance,” Ammann wrote, “the spandrel arch, owing to its height increasing from the center toward the ends, is 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.”

The Hell Gate Bridge opened in 1917. The final design communicates rigidity, but it is far from honest in its structural form. Nearly all of the weight and outward thrust of the span is carried by the lower of the two steel arches. The upper chord and intervening members primarily serve as stiffening. Some photographs of the bridge under construction, in fact, show the top chord assembled before the tower tops; its steelwork ends, unsupported, in thin air. David Billington, a Princeton University professor of civil engineering, has criticized the design, calling it “defective as structural art” and generally inexpressive of the way the load is carried, a shape governed by classical principles appropriate to wood and concrete rather than steel. A traditional arch must be heavier toward its ends in order to support its own weight; a steel arch need not.

It must be remembered, though, that a late-twentieth-century viewpoint separates us from Lindenthal and the young Ammann. The Hell Gate Bridge was designed in an age of Edwardian, beauxarts taste, an age in which ornament, gravity, and solidity tended to be equated with dignity. Charles Evan Fowler, a well-known structural engineer, voiced a typical sentiment in 1918 when he wrote of the rebuilt Quebec Bridge that “the design of the present structure … is strictly utilitarian, although it is to be hoped that great pylons will be added at each end, and proper finials over the tower posts.” He also praised the ornament of the Hell Gate’s two towers and expressed the hope that the New York City government would finally add to the Brooklyn Bridge the parapets that had originally been designed for its towers. As for the Hell Gate arch itself, Fowler wrote: “The outline of the structure is most pleasing. This is due not only to the smooth curve of the arch proper, but mostly to the reverse curve of the top chords near the towers”—the specific feature Billington and most modern critics fault. In such a light it is difficult to criticize Ammann. The techniques of his era can seem dated or undeveloped today, but Ammann and Lindenthal were simply trying to produce a powerful and uncluttered form within the aesthetic of their age. Ammann proved with this, his first major project, that his sense of power in form was already highly attuned, if not as refined as it would later become.

Not long after the Hell Gate project, Lindenthal tried to revive his plan to bridge the Hudson. The problem had long intrigued engineers, for it was clear that such a span would be necessary for the development of the New Jersey suburbs. In the text he ghostwrote for Kunz, Ammann closes his discussion of long-span bridges with a review of four proposals for a Hudson River bridge, including those of Lindenthal and Mayer. Lindenthal had drawn up plans independently as early as 1887; his latest design was for a huge twenty-lane rail and automobile bridge at Fifty-seventh Street. Ammann argued against this, saying that the midtown area, already congested by 1920, could not handle the added traffic flow. Lindenthal insisted that he was planning “for a thousand years” and would not accept Ammann’s suggestion to scale the project back and move the crossing northward. From their first work together, the two men had never been well matched; Ammann’s quiet temperament contrasted with Lindenthal’s fiery spirit. Further disagreements ensued, and ultimately they could no longer work together. The two men parted in 1923.

Over the next several months, supported by family and friends, Ammann worked out the details of his own proposal for the Hudson River bridge. Largely alone, in borrowed office space in Manhattan’s garment district (the cutting-room tables were used for drafting), he developed his plan with no firm guarantee that it would be accepted. The final design called for a 3,500-foot main suspended span—twice the length of any existing bridge—between Fort Lee in New Jersey and 179th Street in Manhattan.

Ammann chose this site for a number of reasons. Most important, the Hudson narrows significantly at this point. Also, both ends of the bridge would fall in relatively undeveloped areas; land for anchorages, towers, and approach roads could be acquired cheaply. In addition, the site was far enough from midtown Manhattan toavoid compounding already troublesome rush-hour snarls. And both sides of the river held outcroppings of solid rock, ideal for foundations or cable anchorages.

Previous proposals had included cantilever and arch designs, but as Ammann explained in a 1943 speech, “it is well recognized that for very long spans … the suspension type, when properly designed, offers such outstanding merits that its superiority, both economic and aesthetic, is obvious.” The English engineer Max am Ende had proposed an immense 2,850-foot arch, which Ammann described in 1933 as “remarkably bold and very creditable,” but far more expensive and difficult to construct. Ammann remarked that “a great mass of steel [in the arch] at a height of about 600 ft. above water level would not be as attractive in appearance as a graceful suspension bridge, provided the latter is without clumsy stiffening trusses, such as were embodied in several of the early designs for a Hudson River bridge.” Here, as throughout his career, Ammann reveals what may be the most striking single visual characteristic of his suspension bridge designs: his taste for thin, delicate-looking decks set against massive towers of simple outline.

This taste apparently provoked controversy. Ammann’s original drawings showed bulky steel-and-concrete towers faced with granite. Both the steel and the concrete were to bear structural load. This was unconventional; most suspension bridges of the day had slender steel towers that appeared nearly flat in profile.

Ammann vigorously defended his choice. “There are existing towers of this kind,” he wrote, “which are manifestly too slender.… no matter how well designed such slender steel towers may be, and how much they may be justified in certain cases, they can not compare in their monumental effect upon the entire structure with the massive towers so admirably exemplified in the Brooklyn Bridge.” Cass Gilbert, the project’s consulting architect, made studies for both styles of towers.

Ammann was quite aware of the complaint that unnecessarily heavy, sheathed towers are aesthetically dishonest, and he wrote that he was “not impressed by the criticism. … The covering of the steel frames does not alter or deny their purpose any more than the exterior walls and architectural trimmings destroy the function of the hidden steel skeleton of a modern skyscraper, except to the uninitiated.”

This defense seems curiously weak, and is obviously flawed. Skyscraper walls are necessary to the function of a building, while the concrete shells on Ammann’s towers were hardly more than cosmetic. Moreover, it may be enough for an architect to design a facade demonstrating his own concept of beauty, but one might expect Ammann, the consummate structural engineer, to create a structure that functioned as art without ornament—as he later would.

Whatever Ammann said, the ultimate decision was made on financial rather than aesthetic grounds. The George Washington Bridge, proposed durine the building boom of the 1920s, was completed in 1931, nearly two years after the stock market crash and well into the Great Depression. The bridge was built substantially under budget (like most of Ammann’s structures), but the Port Authority could hardly afford the concrete and stone planned for the towers.

Ammann had clearly expected this decision for some time. The original towers, in which steel and concrete formed the load-bearing structure, were replaced early in the project with steel frames designed to carry both the concrete and the stone facing. The stated reason was uncertainty regarding the interaction of the different structural materials, but the towers were also designed to present a “neat appearance” in their skeletal form. Adding the shells became “essentially an aesthetic and architectural question,” in Ammann’s words, rather than one of structural necessity.

There has, over the years, been some question about Ammann’s personal feelings about the towers. A 1934 New Yorker profile quoted Ammann as having said, in reaction to Gilbert’s plan to put masonry facing on the towers, that he “hoped he would never be permitted to add it.” Several comments he made later in life also suggest that he preferred the uncovered towers. Edward Cohen, Ammann’s assistant in the 1950s and early 1960s, tells of a young engineer (perhaps Cohen himself) who asked him this very question; the old engineer “would only smile and remark that time had proven the decision to leave the towers bare the right one.”

It may be that Ammann deliberately tried to create a bit of mystery about his original ideas and that he felt slightly ashamed about the clumsiness of his original design and its failure to express structural integrity. He may simply have been trying to please everyone, playing artist to the architects and technocrat to his fellow engineers. Whatever his motive, Ammann seems to have undergone a metamorphosis.

The change is reflected in his writings. In 1931 he declared that “it is often essential, in order to improve the general appearance of a structure, to mask or supplement certain crude engineering features by architectural embellishments, the design of which must be left to the architect.” Twelve years later he said that “engineers in particular are much to blame for the truly unattractive or even atrocious appearance of some of our bridges. This situation has changed in the last 25 years. Under pressure of public opinion, bridge engineers have been forced to give serious attention to aesthetic design.” Ammann now believed that a bridge’s beauty must arise from the engineer’s structured design, not from an architect’s adornment, and there can be little doubt that his attitude had been affected by the George Washington experience.

In 1930, as the George Washington Bridge was being built, Ammann was named chief engineer of the Port of New York Authority (later called the Port Authority of New York and New Jersey! One of his responsibilities included the design of a bridge across the Kill Van KuIl, the waterway between New Jersey arid Staten Island. Just as the George Washington pushed the suspension bridge to new limits of size, the Kill Van KuIl span, eventually named the Bayonne Bridge, was by far the largest steel arch yet built. Cues for the design were obviously taken from the Hell Gate Bridge. The Bayonne Bridge is also a spandrel arch, albeit less dramatically flared than the older structure. The top chord is again largely nonstructural, serving primarily as wind bracing. Moreover, Ammann once again designed masonrycovered abutments at the bases of the arch, although they were plainer and far less prominent than those at Hell Gate. At Bayonne the abutments were completely decorative; at Hell Gate they had in fact played a modest structural role.

Ammann’s peers scarcely criticized him when he unveiled his Bayonne plan. Fowler again exhibited his aesthetic preferences when he expressed regret “that money was not available to construct the Kill Van KuIl Bridge with the beautiful arched approaches and with adequate towers such as are a very great artistic asset to the Hell Gate Arch.” The only real complaint came from Lindenthal—who by this time was barely on speaking terms with Ammann—suggesting that a different steel arch might have proved sturdier and more pleasing to the eye. Despite these remarks, the typical engineer of the day was hardly concerned with aesthetic design at all; Ammann’s approach, flawed as it was in this case, still represented an unusual interest in architectural and structural appearance.

Just as at the George Washington Bridge, however, the steelwork of the Bayonne Bridge was ultimately left uncovered. Thus the overall visual effect is not what the engineer had planned; although a bit strange, the bridge projects a powerful image, especially from afar. Each end of the top chord of the arch disappears into a tangle of steel that obviously bears no structural load—the framework was meant to carry the tower abutments—and the foreshortened views from the bases of the arch are therefore odd. From a distance, however, the entire arch shows a lightness unlike many structures of the time. It is especially dramatic by night, when the arch is delineated with a line of small white lights, and the bridge’s “rainbow” curve rises dramatically from its glowing surroundings, visible for miles.

If Ammann was disappointed to see his George Washington Bridge design modified so drastically, it does not come through in his writing: “The steel towers as they stand … represent as good a design as may be produced by a slender steel bent, and … they lend the entire structure a much more satisfactory appearance than [I] (and perhaps any one connected with the design), had anticipated.”

The fact that both the Bayonne and George Washington bridges looked good despite their uncovered steelwork seems to have surprised Ammann and his team of engineers and must have given them reason to reflect: if naked steel demonstrated a pleasing appearance in this accidental view, how much better it might appear in a properly designed setting. Ammann never again specified architectural treatments on his structures. From the changed plans of the George Washington and Bayonne bridges came Ammann’s greatest development as a designer of public structures and as a structural artist—the understanding that necessary materials need not be hidden, nor need they be ugly.

Just as the towers of the George Washington Bridge aroused controversy among artists and urban planners, so the design of the suspended spans themselves excited engineers. From the earliest days of suspension-bridge design, critics had maintained that the structures lacked rigidity. In many cases this was true, for these primitive designs were often poorly executed and badly built, with uneven stresses in their cables and weak anchorages. The Brighton Bridge collapse in England in 1836 did little to improve their reputation. Engineers were especially uneasy about the strength of suspension bridges under the heavy loads of rail traffic, and most railroads stayed with expensive, unattractive truss designs even into the twentieth century, despite growing knowledge that they weren’t necessary.

Many suspension bridges were given grotesquely ugly and very expensive stiffening trusses. In 1943 Ammann singled out the Williamsburg Bridge over the East River in New York for particular criticism: “Aesthetically it is the one bridge which New York can be least proud of. Apparently little or no attention was given to its appearance. Technically and economically also it is contrary to modern conceptions of design in almost every major respect.” Even the Brooklyn Bridge, rarely criticized on aesthetic grounds, has rather a deep deck structure for today’s eyes. Around the turn of the century, the emergence of modern deflection theory gave engineers a way to calculate stresses in a structure deformed under a realistic load rather than as if it were inflexible, and this allowed a much more accurate understanding of a design’s capabilities. One result was Leon Moisseiff’s Manhattan Bridge, which—while no great beauty—has a far thinner deck and lighter suspended structure than its contemporaries.

While designing the George Washington Bridge, Ammann realized that the weight of the deck was so great—five times the maximum live load—that no stiffening system would be necessary. No engineer had considered the effect of dynamic wind action on a bridge structure; only static wind loading was taken into account, and the dead weight of the deck was great enough that Ammann was hardly concerned with such loading. “I must confess,” he said in 1953, “that there was no doubt in my mind that a span of 3,500 feet, with an ultimate suspended dead weight of 63,000 tons, 15 to 20 times the maximum wind force which could possibly be exerted vertically on its floor structure, could [not] be moved by wind.”

Few structural engineers disagreed, and when Ammann s design proved safe, inexpensive, and attractive, similar bridges appeared throughout the country. The great French architect Le Corbusier called the George Washington “the most beautiful bridge in the world”; similar praise abounded. The strikingly thin deck of the George Washington provided a distinctive appearance against the massive towers, appealing to architects and engineers alike. That appearance was hardly marred when a second deck was added to carry increased traffic in 1962; the addition had been planned for in the original design, and Ammann himself was hired to implement it.

In 1939 Ammann completed another bridge, this time between Queens and the Bronx. Called the Bronx-Whitestone Bridge, this more than any structure showed the engineer’s ultimate aesthetic development. He worked with a new architect on the project, Aymar Embury II, who had trained as a civil engineer and whose approach, far more utilitarian than Gilbert’s, is evident throughout the design. The towers of the Bronx-Whitestone Bridge are flat, smooth rectangles with open arch portals and similar arches supporting the roadway. The towers do not taper, and no ornamentation has been applied. The anchorages and tower foundations are simple concrete blocks. The suspended deck was to have no stiffening trusses.

The total effect is of strength unparalleled in any steel structure of its time. Critics found the design nothing short of artistically flawless. Talbot Hamlin, writing in 1941, considered it among the nation’s greatest architectural achievements in the five years before World War II. Perhaps the editor’s note attached to one of Ammann’s articles about the design best sums up the general feeling: “The new structure breaks no records for length of span but it embodies a number of departures in design that emphasize, more strongly perhaps than mere increase in size, the rapid progress that is taking place in the bridge-builder’s art.”

One distinctive aspect of the Bronx-Whitestone span was its stiffening system. Since the success of the George Washington Bridge, many designers had begun to specify suspended decks that were stiffened purely by the plate girders that made up the floor. This made for an inexpensive and attractively thin deck. The Bronx-Whitestone’s 2,300-foot center span had plate girders only 11 feet deep. No problems with rigidity were expected, especially after the George Washington Bridge had proved amply stable. What no engineer took into account was the effect of dynamic wind action on the hanging structure: the plate girders making up the deck acted like an airfoil, and they presented far more surface area to the side than would open trusses. The smooth side of the deck behaved like a sail.

Ammann described the result in 1946: “Oscillations under the action of wind developed first in March 1939, during construction.… The vertical motions … [were] between 2 and 3 ft. They were accompanied by longitudinal motions of the floor. … it was expected that the increased dead weight due to the placing of the floor concrete would dampen them, but this proved to have little effect. Immediate steps were taken to check the motions, and during the following two years a number of devices were successively installed and improved upon to stiffen the structure. … In their effect upon the structure, the most severe observed amplitudes are entirely harmless, and would be so even if they occurred very frequently. As they have actually occurred only at long intervals, there has been occasion for very little adverse comment by the public. Nevertheless it was concluded that they should be eliminated.”

Similar oscillations had been noted in bridges across the country designed on the George Washington model. None of them, however, prepared the engineering community for the disaster that was brewing. In July 1940 Leon Moisseiff’s Tacoma Narrows Bridge over Puget Sound in Washington opened. Almost immediately the span gained notoriety for its tendency to oscillate even in light winds, and it soon acquired the nickname Galloping Gertie. On the morning of November 7, the motion became strong enough—with oscillations reaching heights of more than six feet—that the bridge had to be closed to traffic. At about eleven-fifteen, a six-hundred-foot-long slab of the center span broke free in a forty mile-per-hour wind and fell into the sound. Civil engineers were shocked; professional journals for months after published dozens of articles about dynamic wind action on structures of all kinds. The Federal Works Administration, which had sponsored the project, called an inquiry and assigned a team of engineers to analyze the disaster: Glenn B. Woodruff, who had designed the Golden Gate Bridge; Theodor von Karman, the great aerodynamicist at the California Institute of Technology; and Othmar Ammann.

Their report attributed the failure to several factors. The Tacoma Narrows Bridge had an especially thin deck, of the type pioneered over the Hudson by Ammann. But the Tacoma span’s roadway was only thirtynine feet wide, carrying only one lane of traffic in each direction. The deck was simply not heavy enough to resist what became known as the von Karman effect—the backand-forth motion exhibited by a thin, solid object in a moving column of air. (The typical example is that of a reed in a gust of wind: the stem shudders with increasing amplitude.) The deck of the Tacoma Narrows Bridge demonstrated both that type of motion and a longitudinal twisting movement. Such “torsional oscillation” was unforeseen and unendurable: the bridge deck’s own weight was enough, under such severe and varied stresses, to tear it apart.

With the standard conception of wind loading utterly overturned, engineers were forced to analyze the poorly understood matter of dynamic fluid flow around a suspended structure. Meanwhile, bridges throughout the country sprouted cable stays, stiffening trusses, and extra steelwork. Stiffening trusses were added to the Bronx-Whitestone Bridge in 1946, as soon as postwar steel was available. Even today questions about wind action on bridges intrigue academic engineers, and the primary factor in their calculations remains a figure Ammann himself developed in the Tacoma Narrows report. Called the stiffness index, it allows engineers to calculate the overall resistance to oscillation in any suspended structure. Years later Ammann was asked to comment on the fact that none of his structures had ever collapsed. His answer, doubtless made with the Tacoma Narrows in mind, was that he had been “lucky.”

The new science of aerodynamics allowed Ammann to apply his aesthetic principles to his final, greatest achievement. Since the early 1920s the need had been recognized for a crossing at the Narrows, the mile-wide entrance to New York Harbor, and various proposals for it had been submitted over the years. It was only in the late 1950s that serious planning began for what would become the Verrazano-Narrows Bridge.

Between then and his death in 1965 at the age of eightysix, Ammann directed three major construction projects—an immense amount of work for any engineer, let alone one of his years. Within that time Ammann was responsible for planning the Verrazano-Narrows Bridge, for adding the second deck to the George Washington Bridge, and for building the Throgs Neck Bridge over the East River. Less than two miles from the Bronx-Whitestone Bridge, the Throgs Neck is similar in size, capacity, and appearance; it first carried traffic in 1961.

By this time Ammann had long since retired from the Port Authority to set up his own practice. He and Charles S. Whitney, a colleague who had worked for him during vacations from engineering school, founded Ammann & Whitney, Consulting Engineers, in 1946. Abba Tor, an engineer who worked there from 1957 to 1964, recalls that Ammann was still very much the spirit of his firm, even in his eighties. The old engineer continued to put in a full week, coming to the office and visiting job sites as necessary. While working on projects that required him to stay in New York, he retained an apartment at the Carlyle Hotel that allowed him a view of every one of his bridges. In an office where informality and first names were commonplace, he was unfailingly called Mr. Ammann, and he used the same form of address with his employees. In the 1970s, after Ammann had died, Ammann & Whitney, Consulting Engineers, was hired to renovate the Northeast corridor’s aging truss railroad bridges. A number of turn-of-the-century plans bore a young draftsman’s initials: “O.H.A.”

Most of the advances embodied in the Verrazano-Narrows Bridge are technical improvements rather than sweeping aesthetic changes. The towers are modeled largely on those of the Bronx-Whitestone but are more deeply buttressed because of their greater size and dead loading. Their proportions differ as well, the Verrazano-Narrows towers being taller and thinner in elevation and deeper in profile. These modifications were dictated more by technical necessity than by any desire to mold the tower forms, although Ammann once again “considered it important to give due consideration to their aesthetic treatment. Simplicity of form and structural arrangement, as well as clear expression of the function of towers, were the guiding motives.”

The Verrazano towers were also sophisticated from an engineering standpoint by virtue of their complex cellular structure. The hollow tower shells are subdivided into compartments to resist torsion and to carry loads more evenly. Each interior cell is accessible for painting and maintenance. Perhaps nothing better emphasizes the sheer size of the bridge—or Ammann’s thoroughness—than one often-quoted figure that Ammann took into account in his design: The two towers are one and fiveeighths inches farther apart at their tops than at their foundations, allowing for the curvature of the earth.

Ammann’s great achievement here, however, lies in the design of the deck structure. After the Tacoma Narrows disaster, concerned engineers returned to heavy, expensive wind trusses on suspended structures. The desire for thin decks remained, however, and some engineers (especially in Britain) developed what became known as the wingedbox structure. This deck is much deeper at the center than at the edges; the thin edge presents little surface toward the wind, which passes over and under the deck rather than building up pressure. The winged-box deck has the advantages of being lightweight and inexpensive to build. It cannot, however, be modified to carry extra traffic loading.

Ammann recognized the need for expansion capability in the new structure and was not satisfied that a thin deck with expansion framing to be added later (as on the George Washington) would be aerodynamically stable. This feeling may have resulted from a report that the George Washington span had oscillated to dangerous amplitudes during a 1955 hurricane. Although the winged-box type of deck is aerodynamically sound, the design sometimes tends to divert wind currents across the roadway, making the bridge difficult to cross on windy days. Ammann therefore developed a completely new structure. Two levels of roadway were specified, each allowing six lanes of traffic flow. In place of the standard practice of adding the roadway as a direct part of the deck structure, Ammann designed a separate concrete-filled steel-grid roadway. Since it is largely independent of the suspended floor structure, it suffers less wear and tear as the bridge flexes. It is also easy to replace at the end of its lifetime. (Typical suspension bridges must be resurfaced every five to twenty-five years.)

The deck itself was designed so that all the structural members would work together to create a stiff, lightweight whole. The longitudinal members—the floor beams running the length of the roadway—were all locked into a single structural unit. These in turn were bound to the other structural members of the deck to create a “tube,” rectangular in cross section and open enough to keep wind pressure low. The strength of a tubular bridge structure has been well known since Robert Stephenson’s 1850 Britannia Bridge. At the Narrows, however, Ammann applied that structural concept to modern materials and aesthetic forms, using computers for the first time in any large suspension bridge. In doing so, he vastly improved on the older idea. A solid-steel tube would hardly be costefficient, aesthetically pleasing, or aerodynamically stable; Ammann’s more open design was all three.

This final triumph confirmed Ammann’s status among his colleagues as the greatest steel-bridge designer in the world. The revolutionary deck of the Verrazano-Narrows Bridge was described in a 1980 symposium as “a radical departure from previous norms” that “may, in retrospect, have been one of the most significant and least publicized contributions of American suspension bridge engineering.” Awards were heaped on Ammann as his design neared completion; in 1964 alone, he received no fewer than nine from various engineering societies and civic groups, including an honorary doctorate of science from Fordham University. He was also presented with the National Medal of Science by President Johnson, making him the first civil engineer so honored. Gay Talese wrote a profile of Ammann for The New York Times and subsequently published a book about the construction of the Verrazano-Narrows Bridge. Othmar Ammann was instrumental in changing structural art from a point of contention between engineers and architects to a primary design consideration. Today engineers of public structures consider visual elegance a necessity. Contemporaries of Ammann, such as the Europeans Robert Maillart and Pier Luigi Nervi, applied similar principles of structural art to new materials and different kinds of structures, but Ammann’s progression toward an artistic engineering approach was especially influential among engineers of all disciplines because of the monumental nature of his works. No engineer who commutes between New York and New Jersey can fail to be impressed by the George Washington Bridge; no civil-engineering student who sees a film of the Tacoma Narrows collapse can ignore the importance of the thorough application of engineering principles within an aesthetic approach.

Ammann’s effect on his immediate colleagues was likewise unmistakable. Although few engineers designed bridges that physically mirrored his, the ideas he brought to structural engineering can be seen in virtually every large American bridge constructed since the Bronx-Whitestone. Unornamented, plain steel towers have become legion; structure is expressed without shame. Even the bridge engineer David Steinman, long a rival of Ammann and a vocal critic of his style, demonstrated a parallel development. The comparison of Steinman’s 1929 Liberty Bridge proposal for the site of today’s Verrazano-Narrows, awash in Gothic arch forms and superfluous turrets, with his 1957 Mackinac Straits Bridge in Michigan, with its simple towers of diagonal cross-bracing, shows a development that clearly drew on Ammann’s ideas. Other structural engineers show similar stylistic changes.

As for the future of bridge engineering, Ammann held some definite ideas as well. In the early 1960s he repeatedly stated that modern specifications and steelwork would be sufficient to build an economical suspension bridge with a 10,000-foot span. A few years before his death, in fact, he discussed preliminary plans for a bridge over the Messina Strait between Sicily and the Italian mainland. And about the future of his own bridges? In 1958 a reporter asked him how long his structures were meant to last. “Well, you never know what men or civilizations will do with themselves,” Ammann replied. “But barring catastrophes—that none of us like to foresee … How long? Why, forever, of course.”