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

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- Library of Congress 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. www.americanscientist.org Copyright © 2006 by Henry Petroski. Requests for permission to reprint or 2006 November–December reproduce this article should be directed to the author at [email protected]. haps as few as four to six years. Since that was also the time it might take to design and build a new bridge, it was clear that decisions had to be made and actions taken very quickly if the region was to continue to have a convenient Penobscot crossing. By putting the project on a fast track, it was thought, the new bridge might be ready for traffic in perhaps three years. Among the most important decisions in designing a new bridge are where to locate it and what kind to build. Ob- viously, the original Waldo-Hancock was already in place and carrying traffic, and so its exact location was not available for a new bridge. Locating a new bridge right next to the old makes sense, since then there only has to be minimal realignment of existing roads. Rodd M. Halstead M. Rodd However, the existing approach from Waldo-Hancock’s cable-stayed replacement (foreground), formally known as Penobscot Nar- the west hugs the high riverbank and rows Bridge and Observatory, is scheduled to open about the time this article appears. so necessitates a sharp right-angle turn on entering or exiting the bridge. Lo- a limited section of one of the cables traffic crossing the bridge, tiny cracks cating a new bridge a bit downriver was unwrapped—a low section near grow and reduce the residual strength from the old and blasting a new stretch mid-span, where intrusive water would of the wire. Eventually, when the force of road out of nearby rock presented naturally collect to promote corrosion— exceeds the strength, the wire snaps. an opportunity to incorporate a more and 13 wires inside were found broken. Large-truck traffic accelerates the pro- gradual approach curve. As for the Since each cable has a total of 1,369 in- cess of fatigue, and there were concerns kind of bridge to build, the lay of the dividual wires, the number of broken that all trucks might have to be banned land and navigation requirements im- ones was relatively small. The load that from the bridge. Probably because of mediately called to mind three obvious had been carried by the broken wires pressure from truckers whose livelihood choices: another suspension bridge, an was assumed to be redistributed among depends on access to the bridge, how- arch bridge or a cable-stayed bridge. the remaining intact wires. Every bridge ever, truck traffic was restricted rather The citizens of the adjacent counties is built with a factor of safety, which is than banned outright. In the fall of 2002 naturally had strong feelings about the the ratio of the load it can theoretically the state posted signs ordering heavy familiar Waldo-Hancock Bridge and carry divided by the actual load it bears. trucks to maintain a minimum distance how a new span would affect traf- The Waldo-Hancock Bridge was built of 500 feet between one another. This fic patterns and the aesthetics of the with a safety factor of about 3, and the would minimize the likelihood that the area. County commissioners, environ- loss of the holding power of a few wires bridge would experience more than a mental activists, preservationists and did not diminish that appreciably. single truck in each direction at a time. other interested citizens wanted to be In 2002, in conjunction with reha- Eventually the minimum distance al- informed about, watchful of and par- bilitation work that was ongoing, the lowed was to be extended to 800 feet, ticipants in decisions that would af- entire north cable of the bridge was thus reducing further the chance of the fect the quality of life in the vicinity. unwrapped and a considerably larger bridge being overloaded. The Maine Many of them expected or wanted to number of wires was found to be bro- Department of Transportation was also see the historically significant bridge ken. A portion of the south cable was considering cracking down on over- remain in place, and they expressed also inspected, and by comparing its weight trucks. It was bad enough that concerns about the new ruining the fa- condition to that of 10 years earlier, the the bridge had been designed when a mous scene by upstaging the old. They speed with which the wires were dete- 10-ton truck was considered large. Now, were also concerned about the kind of riorating could be assessed. (In contrast however, trucks weighing as much as 50 bridge that would be built, desiring it to the 13 broken wires found in 1992, tons are allowed on the highways, and to be compatible with the existing one. there were 87 found in 2002.) According in reality some trucks weigh more than Then there was the issue of the com- to calculations, in parts of the cable the that. Repeatedly loading the bridge so bined cost of building the new bridge safety factor had dropped to as low as far over design expectations had accel- and restoring the old one. If such con- 2.4, and projections indicated that the erated its deterioration. cerns were to rise to objections and rise safety factor could drop to the danger- again to legal obstructions, not only ously low level of 2.2 in four to six years. A Suitable Replacement would the new bridge be delayed, but Among the causes for wires continuing By the summer of 2003, it was clear also traffic on the old might have to be to break is the phenomenon known as that, even with restrictions on truck restricted even more. Thus, a bridge metal fatigue. Every time the force in traffic, the Waldo-Hancock Bridge had project advisory committee was es- a wire is cycled, as it is in the course of a limited useful-life expectancy, per- tablished to facilitate communication

500 American Scientist, Volume Copyright © 2006 by Henry Petroski. Requests for permission to reprint or reproduce this article should be directed to the author at [email protected]. between citizens and the state, espe- When the latter was chosen, design the disruption caused by the deteriora- cially as embodied in the Department arguments continued, including over tion of its cables. of Transportation. whether the bridge should have one The story of the Waldo-Hancock When it became clear that accelerat- or two planes of cables, how it should Bridge is being repeated across the ing deterioration in the cables of the old be lit and so forth. It is seldom easy country. Aging bridges, expensive to bridge might force it to be closed for to come to a final agreement among maintain, are not being kept up. Hav- safety reasons long before the new was participants whose principal concerns ing been built when traffic was lighter completed, the DOT came forth with a range from aesthetics to economics. and vehicles smaller, they are also func- plan to prevent that. In order to avoid Groundbreaking for the new bridge tionally obsolete, in that many of them a total ban on truck traffic for the dura- took place in December 2003. At the have only a single lane in each direction tion of construction of the new bridge, it time, it was expected to be completed and have no shoulders. Furthermore, proposed to add supplementary cables in two years at an estimated cost of when they remain in use at all, they to the old, thereby enabling some of the about $50 million. By the fall of 2005, the are unable to carry safely the added weight of the existing structure and its completion date had slipped by about a weight and volume of traffic that is ac- traffic to be taken off the original cables. year and the cost had risen to $84 mil- celerating their deterioration. Thus, it This unusual measure—a unique pro- lion, 100 times the cost of the original is a common sight to see a new bridge cedure in the United States—naturally bridge. Among the reasons given for being constructed beside an old one, added to the cost of the entire project, the increased cost were higher prices or to look over from a new one to see but it also allayed the concerns of lo- of construction materials. In early 2006, an abandoned old bridge with weeds cal truck operators and bought time to it was announced that the name of the growing through its cracked roadway allow for any unforeseen delays in the new structure would be the Downeast or rust-stained concrete crumbling from construction of the new bridge. The add- Gateway Bridge, but local and regional its parapet. What has happened at the ed cables were expected to carry about politics led to a reconsideration, and the site of the Waldo-Hancock Bridge in 50 percent of the dead load of the struc- name finally approved by the legislature Maine provides a model to learn from ture and increase the safety factor from was Penobscot Narrows Bridge and Ob- for departments of transportation and a low of 1.8 to 3.2, thus allowing trucks servatory—the latter term referring to interested citizens elsewhere. weighing up to 40 tons to use the cross- the 400-foot-high observation deck that ing. In late 2005, after the supplementary will be located on one of the towers. Acknowledgments cables had proved themselves over two One state senator did not think all the I am grateful to many people in Maine winters and the completion of the new fuss over the name was worth it. She and elsewhere who brought the plight of bridge was in sight, trucks weighing as believed that local people would refer to the Waldo-Hancock Bridge to my atten- much as 50 tons were allowed to cross it as the “new bridge” or as the “Buck- tion and kept me informed about its status the existing bridge once again. sport bridge,” as they had called the and replacement. Among those who pro- Waldo-Hancock. The two halves of the vided clippings and other information are In with the New cable-stayed deck were expected to meet Tom Doe, Richard Dudman, John Hyk, C. In the meantime, a contract to design well before October, when the roadway Newcom and Carl Osgood. David Milan and construct the new bridge had been was to be open only to pedestrians for and Pam Person were kind enough to copy let to the Figg Engineering Group, of a day of celebration. The new bridge, me on e-mails regarding the selection pro- Tallahassee, Florida. Figg was known which dwarfs the old, was expected to cess for the new bridge. I am also indebted to Mainers for the recently completed open for traffic shortly thereafter. to the History and Heritage Committee of Sagadahoc Bridge that now carries Meanwhile, as local and region- the Maine Section of the American Soci- Route 1 easily across the Kennebec al newspapers carried stories of the ety of Civil Engineers, whose nomination River at Bath, thus relieving a historic progress on the new bridge, the old package for making the original bridge a bottleneck at the old Carlton Bridge. one continued to carry traffic with the National Historic Civil Engineering Land- The firm is also noted for other dis- help of the supplementary cables. The mark provided a comprehensive collection tinctive bridge projects, including the once-clean lines of Steinman’s Waldo- of background material. This package was stunningly high arch that carries the Hancock Bridge are cluttered by its submitted to ASCE’s History and Heritage Natchez Trace Parkway across a broad life-support systems, and comments Committee, which I chair. valley in Tennessee, and the Clark ca- on the status of the landmark have ble-stayed bridge across the Mississip- generally been relegated to all but foot- Bibliography pi at Alton, Illinois, whose construction notes to the celebratory news of the Angelo, William J. 2003. Maine cables get ex- was the subject of a widely acclaimed new. The new bridge is expected to be tra support in rare procedure. Engineering PBS documentary. Figg and the Maine a signature structure for the area, and News-Record, November 10, pp. 24, 27. DOT were the principal technical where once there was talk of costly Maine Department of Transportation. 2006. players in determining the type of rehabilitation of the old bridge to make Waldo-Hancock Bridge Replacement Project. bridge that would cross the Penob- it into a pedestrian way, increasingly http://www.waldohancockbridge.com/ waldo-county-bridge/news.php. scot, in consultation with the project there seems to be resignation to its advisory committee. Not surprisingly, more likely fate—demolition. Even the Steinman, D. B., and C. H. Gronquist. 1932. Building first long-span suspension bridge there were many points of view and cost of that has been estimated to be as in Maine. Engineering News-Record, March differences of opinion among the par- much of $15 million. This would be a 17, pp. 386–389. ticipants. The decision ultimately cen- sad fate for a National Historic Civil Taber, Peter. 2003. DOT makes urgent call for tered on the choice between a suspen- Engineering Landmark whose plaque new bridge. Waldo (Maine) Independent, July sion bridge and a cable-stayed bridge. has not even been mounted because of 3, pp. 1, 9. www.americanscientist.org Copyright © 2006 by Henry Petroski. Requests for permission to reprint or 2006 November–December reproduce this article should be directed to the author at [email protected].