STORIES FROM 'THE CHRONICLE'
At Work on the Living Bridges
By Lawrence Biemiller|
New York -- Cosmas Tzavelis is squinting at the underside of the Williamsburg Bridge, the least lovely and most troublesome of New York's big East River crossings. Against the bright background of afternoon it's hard to see into the shadows beneath the bridge's deck, but even so he has no trouble finding corroded steel high in the Delancey Street approach, along with buckled beams, a broken column, and stonework that has been pulled apart. "The bridges were neglected for years and nobody was responsible," says Mr. Tzavelis, an associate professor of civil engineering at Cooper Union who has been a consultant on some of the city's biggest bridge-rehabilitation projects. "A bridge is like a living organism -- it suffers when you don't maintain it."
For all its problems, the Williamsburg Bridge is in no immediate danger, and Mr. Tzavelis doesn't flinch when a Brooklyn-bound subway train thunders up the long approach and passes directly overhead. Bridges have a knack for redistributing load away from weakened members, he says when he can make himself heard again. And renovation of the bridge is progressing nicely. Its two steel towers are currently wrapped, Christo-like, for sandblasting and repainting. Here beneath the Manhattan approach, crews are excavating for an entirely new support system to replace the corroded original structure of steel columns and X-braces.
The Williamsburg Bridge, designed by Leffert Lefferts Buck and named after the neighborhood at its Brooklyn end, was the second suspension bridge built across the East River, opening in 1903 -- 20 years after John and Washington Roebling's Brooklyn Bridge. Unlike the Roeblings' graceful span, celebrated in paintings and poems, Buck's carries its traffic within a bulky lattice truss that almost no one thinks beautiful. The Williamsburg Bridge, Mr. Tzavelis notes, was built more quickly and more cheaply than its predecessor. "Now this fact is haunting the bridge," he says. To economize, he says, "in the cables they didn't use galvanized wire." The outermost cables have corroded and are being replaced -- an extraordinary and expensive undertaking.
In many other respects, though, the Williamsburg Bridge has quite ordinary problems -- ordinary for big-city bridges, at least. Because they weren't cleaned or lubricated, its expansion joints corroded and froze. The structure, designed to expand and contract as the temperature changed, began instead to wrench itself apart. Because repaintings were rare, corrosion attacked other parts of the bridge, too -- attacked wherever accumulations of dirt and pigeon droppings caused water to pool or drip. In winter, road salt coated the metalwork. Mr. Tzavelis says the most effective way to extend a bridge's life is to wash it once a year. "Have a fire truck come hose it down, especially the salt-splash zone -- it's cheap compared with a major renovation." He also recommends regular cleaning of expansion joints, drains, and surfaces that collect dirt.
None of which is easy to accomplish in New York in the 1990s. When the Brooklyn Bridge opened, he says, it had a staff of about 200. Now the city's biggest bridges are lucky if they have a single crew assigned.
One problem that maintenance can't counter is that some truckers overload their vehicles, stressing the bridge deck and the smaller members that support it. "Deterioration of the deck is the most common problem -- we see it every day," Mr. Tzavelis says. Decks can also deteriorate if a paving contractor added too much water when mixing the concrete. Initially, the extra water makes the concrete easier to work with, but "the water leaves very small voids and in winter moisture can get in and freeze and expand, or attack steel rebars, which corrode and expand," he says. Other common ailments include rivet corrosion: "Rivets are among the first things to go."
The Williamsburg Bridge has suffered all of these indignities and more. Even so, it may end up in better shape than the third of New York's suspension spans, the 1909 Manhattan Bridge. "In the Manhattan Bridge, we have torsional problems," Mr. Tzavelis says. Its designer, Othneil F. Nichols, inexplicably put its subway tracks on the outer edges of the bridge, rather than in the middle, where Buck had located the tracks on the Williamsburg Bridge. When a loaded train crosses the Manhattan Bridge, Mr. Tzavelis says, the deck structure twists out of true -- or deflects, to use the engineering term. The bridge reopened to subway traffic last year after being strengthened, but the problem persists. On the whole, the city's bridge-rehabilitation efforts are paying off, although the task is Herculean: To replace a column on one bridge, he recalls, contractors "designed a temporary column to support two million pounds, and used hydraulic jacks to lift the bridge half an inch to put it in -- while traffic was moving."
Indignities and all, New York is still a fine town for a bridge enthusiast like Mr. Tzavelis. The five boroughs offer more than 2,000 bridges of every size and description. The Civil War-era pedestrian bridges in Central Park are counted among the handsomest in the nation. The 1964 Verrazano Narrows Bridge is the world's second-longest suspension span, after the Humber River Bridge in Great Britain. "The whole city is like a bridge experiment," says Mr. Tzavelis, who takes a particular interest in how bridges look. At Cooper Union he has worked with students and faculty members from both the architecture and art schools, hoping to come up with designs that are both attractive and inexpensive -- cost being often the determining factor in the choice of bridge designs. When he's not teaching structural engineering or consulting about bridges or working on new software for designers, he sometimes collaborates with his sister, Maria Tzavelis, an architect in Greece, where they grew up. "When I was a little kid I liked to build things," he says. "In the summers I built structures for me and my sister to sleep in during the afternoon siesta."
Now, he says, "I'm interested in aesthetics and how structural analysis and design can benefit from the principles of aesthetics." In structural analysis, engineers "mostly look at economical design -- we don't look at aesthetics." The consequences are not always happy ones, he says: The truss "seems to be the most economical design, but it's not the most beautiful." He's quick to add, though, that preferences in bridges are as personal as preferences in anything else. Pressed to pick favorites, he ranks the Brooklyn Bridge as No. 1 and the Verrazano as No. 2.
He doesn't rank another bridge he's worked on as a consultant -- the Queensboro Bridge, at 59th Street. Unlike the other East River automobile crossings, which are suspension spans, the Queensboro Bridge is a cantilever truss bridge. A dense, lacy superstructure of rods, pins, plates, box-girders, and cross-braces supports the two-level deck, essentially hanging it from four steel towers -- one on each side of the river and two close together on Roosevelt Island. Designed by Gustav Lindenthal and opened in 1909, the bridge is constructed in such a way that what hangs on one side of each tower counterbalances what hangs on the other side. Because the towers are not evenly spaced, the bridge ends up having an assertive, asymmetrical profile -- and a uniquely New Yorker- like character.
To be sure, Mr. Tzavelis calls the Queensboro Bridge "overdesigned" and says it devotes a disproportionate amount of effort simply to holding up its own considerable weight. But it does a fine job nevertheless of showing off what civil engineers do. Unlike modern highway bridges, which support themselves on thick, straight girders and inspire no poetry, the Queensboro Bridge is a sonnet to slide rules and drafting tables, to calculations and drawings as intricate as the bridge they produced. Walking along its pedestrian lane, high above the river on the south side of the great trusses, you can put your hand up against any box-girder and feel the bridge vibrating. What you sense is really only a complicated structure responding as hundreds of cars and trucks race across it -- as the weight of every car and every passenger and every bag of groceries shifts through the rods and girders of each huge cantilever. But still the bridge feels like a living organism -- one too big to notice you, or too slow, perhaps, but one throbbing with its own life nonetheless.
Copyright (c) 1996 by The Chronicle of Higher Education, Inc. http://chronicle.com Title: At Work on the Living Bridges of New York City Published: 96/05/17