When construction crews are finished working on the Congress Street Bridge in Boston, the people who regularly cross it may not recognize it.
The bridge may still look like a bridge, but when it reopens in the fall of 2006, it will be a very different span.
It is actually not the first time the bridge has undergone a major overhaul, according to Brian McKenney, resident engineer of the Massachusetts Department of Highways. Years ago it was a moveable bridge designed to let water traffic move smoothly underneath it. Back in 1959, though, the structure was locked in place.
More than 40 years later the work is much more substantial. Most parts of the bridge are being replaced or at least reconditioned.
“The work is long overdue,” McKenney said.
Perhaps the most interesting part of the $16.3-million project is that new fenders are being installed on most of the piers at water level. Few, if any, boats travel the Fort Point Channel anymore, but the Coast Guard still requires that bridges be protected from vessels that may bump and subsequently damage the substructure. As much as 80 percent of the existing fender system, which was constructed of wood timbers, is being removed.
The new fiberglass fenders measure 12 by 12 in. (30.5 by 30.5 cm) and are being installed with the help of plastic piles that measure 16 in. (40.6 cm) in diameter. When they are driven into the soil beneath the channel, workers must be careful not to drive the piles too deep to avoid a tunnel carrying electrical cables located farther down.
McKenney said that so far the workers have been successful avoiding the tunnel.
As for the rest of the bridge, which is 549 ft. (1,499 m) long, there is still a great deal of work to be done. Remaining construction includes: removal of an existing counterweight remaining from the days when the bridge was moveable; relocation of a water main inside the utility bay (so there will be a new framework beneath the south sidewalk); replacement of the reinforced concrete deck on four of the spans; construction of a new sidewalk; and the replacement of most of the bearings.
In general, the work will include the demolition of the superstructure and reconstruction of the substructure, according to McKenney.
Nine new telecommunications conduits for Verizon and AT&T also are being added on the bottom side of the decks. As far as the surface of the structure is concerned, the entire bridge will have its lead paint removed. The new paint will be gray instead of the rust color that it has been in the past.
Part of the work will include installation of a new traffic signal at the intersection of Congress and Dorchester streets and navigational lighting placed atop the piers. Finally, new expansion joints will “beef up the trusses,” according to McKenney.
Temporary supports were needed at the east end of the bridge to brace it while piers 7 through 9 were being rebuilt. That involved lifting the bridge to allow the new piers to be built.
“That was difficult,” McKenney said. The piers are constructed of a granite block facia. Contractors reused the existing granite on the outside and poured a new concrete core on the inside. Piers 1 through 6 are still in good shape and will not be replaced.
Several things will remain in place, such as the steel framework, pedestrian gates, trusses for the counterweight and the old arm once needed when the bridge was moveable.
“Some of the historical pieces will remain for decorative reasons,” McKenney said.
Very little dirt will be moved in the project other than where new approaches are being built.
The bridge was originally built in 1930. Because of its location near historic downtown Boston, it has always carried a great deal of traffic, whether vehicular or pedestrian.
Within walking distance is the site of the Boston Tea Party and the Children’s Museum of Boston. Traffic has been redirected to two neighboring bridges: Summer Street to the southwest and the Joe Moakley Bridge on Seaport Boulevard to the northeast.
Most of the construction has gone without a hitch, but there was a slight problem when it was discovered that the design of the new bridge called for work to be done on a slightly different plane than the actual bridge. That meant that there was a difference of a couple inches between the two planes.
“It was definitely correctable, but it did involve corrective action,” McKenney said.
The primary contractor of the project is Walsh Construction, of Sharon, MA. Workers are using Caterpillar and Hyundai excavators and 50-ton (45 t) RTC850 cranes from Link-Belt, as well as Grove RT750 cranes. The subcontractor doing the concrete work on the decks, Independent Concrete Pumping, of Wakefield, MA, used barges on the water during its part of the project to support its machinery. The project was originally scheduled to be finished by May 2006 but it may take until that fall to finish, according to McKenney. CEG