ENGINEERS OF DREAMS Great Bridge Builders and the Spanning of America By Henry Petroski Knopf. 479 pp. $30
“We may lack glamour and sparkle. We might even be considered dull by many people,” the bridge designer Othmar Ammann once remarked of himself and other largely unsung titans of structural engineering. Though he may have lacked popular acclaim, at the end of his career Ammann could nonetheless take pride in the view from his apartment atop Manhattan’s Carlyle Hotel. For he played a key role in creating more than half a dozen spectacular bridges dotting the skyline around New York City.
Structures like Ammann’s soaring George Washington and Verrazano-Narrows bridges were once thought beyond any man’s reach. Nowadays, Henry Petroski writes in “Engineers of Dreams,” we tend to take these colossal achievements for granted. Bridges are boons to transport and communication, but we traverse them not so much marveling at their visual lyricism as distractedly hunting signs for the appropriate highway turnoff. Petroski’s book, a paean to the delicate balance of art and science that the best bridges represent, heightens our appreciation of these most utilitarian of monuments.
Amply illustrated with black-and-white period drawings and photographs, Petroski’s latest volume explains how major U.S. bridges came into being and why they look the way they do. Petroski, a professor of civil engineering at Duke University and author of “The Pencil” and “The Evolution of Useful Things,” uses a skillful blend of biography, historical anecdote and technological illumination to convey a sense of passion and drama not readily associated with the minute calculations of load-bearing and stress that are the engineers’ daily task.
Focusing on the careers of five 19th- and 20th-century figures who responded to demand first from the expanding railroads and then from the American infatuation with the automobile — Ammann, James Buchanan Eads, Theodore Cooper, Gustav Lindenthal and David Steinman — Petroski demonstrates how successive generations of engineers were spurred on to ever greater feats of daring. Yet this chronicle of the drive to create longer and larger bridges is no saga of unalloyed progress. Dreams, Petroski reminds us, can spiral into nightmares.
One such blow came when the south arm of the cantilevered Quebec Bridge collapsed while under construction over the St. Lawrence River in 1907 after Theodore Cooper miscalculated the weight of the steel the finished bridge would contain, leaving its lower portions unable to bear the load. With it collapsed much trust in cantilevered structures. The disaster reverberated throughout the profession, prompting an alteration of the load of the Queensboro Bridge linking Manhattan and Queens, then under construction. Failures of other bridges brought more redesign and retrofitting.
Technological innovation further transformed bridge appearance, and the tension between structural principles and aesthetics is a leitmotif of Petroski’s narrative. A fundamental shift occurred after a consultant to Ammann, Leon Moisseiff, who later co-designed the Golden Gate Bridge, developed the so-called deflection theory, which showed that longer bridges could take more slender and flexible forms because their composite weight exceeded that of smaller, comparably cumbersome earlier structures. This permitted Ammann to build the strikingly slender single deck used in the George Washington Bridge (a second, lower deck was completed in 1962 and dubbed by some the Martha Washington Bridge).
When economic constraints led to the scrapping of plans to clad in stone the towers of the link over the Hudson between upper Manhattan and New Jersey, there was no looking back. The suspension span became a celebration of the new. Le Corbusier proclaimed it the “the most beautiful bridge in the world,” whose “steel structure seems to laugh.”
But the ensuing predilection for the more streamlined silhouette could not be indulged ad infinitum because of limits to just how much wind a ribbonlike bridge deck can withstand. This became clear when the Tacoma Narrows Bridge near Seattle oscillated so in the weeks after it opened in July 1940 that throngs of thrill-seeking motorists were drawn by the wavelike motion of a roadway they called Galloping Gertie. The unintended amusement ride ended abruptly a few months later when the bridge wrenched apart and fell into the water. Film footage of the undulating span is standard fare in today’s engineering courses — the structural engineering world’s equivalent of the Zapruder film of the Kennedy assassination.
The educational use of this footage fulfills, at least in part, Petroski’s wish for greater communication between generations of engineers, who, he warns, ignore the past at their peril. Even if today’s engineers gain in confidence as new building materials and computer design tools are introduced, he insists that their work be coupled with a sense of history, since he justly believes that the finest bridges fuse engineering know-how with artistic vision in equal measure. Petroski concludes by pleading for proper bridge maintenance, citing a 1992 Transportation Department report that says 20 percent of America’s half-million bridges are in a deficient state. By refocusing our view of a valuable part of the U.S. industrial heritage, this book should serve as potent ammunition for those seeking to prevent decay of the national infrastructure.