American Scientist the Magazine of Sigma Xi, the Scientific Research Society

A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society This reprint of a copyrighted article is provided for personal and noncommercial use only. For any other use, including reprinting and reproduction, please contact the author at [email protected]. Engineering Waldo-Hancock Bridge Henry Petroski any people have asked me toric bridges were among the victims. Mhow long a bridge can last. The deterioration of a It was only when they had deteriorated The answer to that question can range to the point of being unsafe that steps from days to months to decades on were taken to catch up on deferred the one extreme and from centuries landmark span offers maintenance, which usually entailed to millennia—and possibly even lon- rather expensive rehabilitation work. ger—on the other, depending on such lessons applicable to diverse and interrelated factors as de- Early and Under Budget sign, construction and maintenance, all bridges everywhere The Waldo-Hancock Bridge is a classic of which are affected by the vagaries case study of a bridge once heralded as of economics, politics, weather and a masterpiece growing obsolete and ne- luck. Examples are legion. London’s glected over time. The bridge is named Millennium Bridge stayed open only for the two Maine counties that it con- three days before it had to be closed building if the bridge is to remain func- nects as it carries the coastal highway, for a major reconsideration of its de- tional. As a result, many old wooden U.S. Route 1, across the Penobscot Riv- sign. The Tacoma Narrows Bridge spans were covered to protect them er. With the completion of the Carlton lasted only four months before it fell from the weather and so extend their Bridge across the Kennebec River in to the wind. Just about everywhere life. Seldom do covered bridges have 1927, the Penobscot crossing was the last we drive, we see interstate highway all of their original fabric in place. major gap in the coast highway. By 1929, bridges built barely 20 years ago being The introduction of iron and, even- there were four bills before the Maine replaced by wider and stronger spans. tually, steel into bridge building gener- legislature: Three would grant conces- Moving toward the opposite extreme, ally resulted in stronger and more du- sions to different companies to construct the world-famous Brooklyn Bridge is rable structures, but steel still corrodes and operate a private bridge, and one well over a century old. In England, and hence must be protected. This is would establish a toll bridge owned and the first iron bridge, completed in 1779, why steel bridges, especially those ex- operated by the state. Until the Waldo- still carries pedestrians over the Severn posed to a corrosive environment such Hancock Bridge was completed in 1931, River. In southern France, the Pont du as salt-water spray or road salt, must motorists had to choose between driving Gard stands as a two-millennium-old be painted regularly. Concrete, which an extra 45 minutes to cross the river via monument to Roman engineering. may be considered the successor to the bridge at Bangor or relying on ferry The thought and care given to the stone construction, is not immune to service. Sometimes, the long detour was initial design of any bridge is a prin- deterioration. It too is susceptible to faster than waiting for the ferry. cipal factor in determining its lifetime. a corrosive environment, in which The engineering firm selected to Among the chief design decisions is cracks can allow moisture to attack re- design a bridge between Waldo and the material of which the bridge will inforcing steel, the rusting of which Hancock counties was Robinson & be made. Historically, timber and stone can result in spalling and subsequent Steinman, based in New York. The as- were used, and the latter is obviously aesthetic and structural deterioration. sociation of the two engineers dated more durable than the former. Who No matter what the material of a from 1920, when senior partner Holton can imagine the Pont du Gard stand- bridge, among the components of a re- Robinson had approached David ing today if the aqueduct had been sponsible design is the specification of Steinman about an international de- made of timber? So why is timber used a regular program of inspection and sign competition for a bridge in Brazil. for any bridge? The answer is, mainly, maintenance. A rule of thumb that has The innovative Florianópolis Bridge, economics. Generally speaking, it is been suggested is that of the order of which incorporated the suspension faster and cheaper to erect a timber 4 percent of the initial cost of a bridge chains into the stiffening truss of the structure. Of course, timber is subject should be budgeted for its annual main- main span, was their first major com- to rot and fire, necessitating regular re- tenance. All too often, however, espe- mission. For the bridge across the Pe- cially during fiscal pinches, budgetary nobscot, David Steinman served as Henry Petroski is Aleksandar S. Vesic Professor politics forces deferral of maintenance, designer, and he produced a bridge of Civil Engineering and a professor of history at such as painting, with disastrous conse- whose main suspension cables were Duke University. Address: Box 90287, Durham, quences. When New York had its fiscal built up of twisted-wire strands that NC 27708-0287 crisis in the early 1970s, the city’s his- were hauled into place fully formed. 498 American Scientist, Volume 94 Copyright © 2006 by Henry Petroski. Requests for permission to reprint or reproduce this article should be directed to the author at [email protected]. Catherine Petroski Catherine Waldo-Hancock Bridge over Maine’s Penobscot River—shown in a merged panorama—was the last link in the coast highway. Finished in 1931 in only 16 months and under budget, it was by 1992 found to be suffering deterioration in its cables. Like many bridges its age, it needed replacement. This was a departure from the system money saved, a replacement bridge Library of Congress. In 2002, it was that John Roebling had promoted and was built between Verona Island, named a National Historic Civil En- that is still employed in most suspen- the eastern terminus of the Waldo- gineering Landmark by the American sion-bridge building today, in which Hancock, and Bucksport, on the main- Society of Civil Engineers. the main cables are built up of paral- land. The rest of the money left over lel steel wires carried back and forth was used to build roads in the vicinity. A Weary Landmark between the anchorages and across the Dedication exercises for the Waldo- Alas, even as the distinguished struc- towers. Steinman defended his design Hancock Bridge took place on June ture was achieving landmark status, as more economical in cost and time 11, 1932, and they included a report on the wires in its cables were corroding for suspension bridges of no more bridge finances by the chief engineer of and snapping. Such deterioration can than about 1,500 feet in total length. the State Highway Commission. David long go unnoticed, since the cables of a The Waldo-Hancock bridge is exactly Steinman—the engineer-of-record rep- suspension bridge are typically covered 1,500 feet between anchorages, with a resenting the firm that was responsible and painted for protection. In the case central span of 800 feet. for all surveys, design and construc- of the Waldo-Hancock, the first signs of The towers of the bridge were also a tion—presented the completed bridge trouble were discovered in 1992, when departure from the usual, which at the to Governor William Tudor Gardiner, time were typically dominated visu- representing the State of Maine. Flags ally by arches or large X’s that served to were raised atop the towers of the stiffen the structure. Steinman felt that bridge, as the assembly at nearby Fort at the Maine location, “the rigor of the Knox stood at attention. The exercises natural rocky setting, the stern lines of ended with the singing of “America adjacent Fort Knox and the background the Beautiful” and benediction, and of colonial architecture in the neighbor- were followed by band music and a ing town called for something simple.” baseball game. He thus employed a predominantly Even before its formal dedication, the vertical and horizontal tower design Waldo-Hancock Bridge had attracted that structurally functioned as what is favorable notice. In 1931, the American known as a Vierendeel truss, which de- Institute of Steel Construction conferred rives its strength and stiffness from the on the structure the annual award of perpendicular rather than the diagonal merit as Most Beautiful Steel Bridge. action of its components. The Golden The first modern suspension bridge in Gate is among other large suspension Maine and still the state’s single lon- Congress of Library bridges built in the 1930s that incorpo- gest span, the Waldo-Hancock has long rated a Vierendeel tower design. presented a striking view to motorists The Waldo-Hancock Bridge was a heading north on U.S. 1 and boaters on model construction project, taking a the Penobscot. The bridge was added to total of only 16 months (from August the National Register of Historic Places 1930 to November 1931) and coming in 1985 and subsequently documented Waldo-Hancock Bridge stretches 1,500 feet al- in at about 70 percent of the original by the Historic American Engineering together, with an 800-foot central span, mak- appropriation of $1.2 million. With the Record, with results deposited in the ing it Maine’s longest.

Load more