The historic Boston University bridge is receiving a sorely needed $20-million total body makeover while still remaining open to a steady stream of cars, cyclists and pedestrians.
Crossing over the Charles River, the 80-year-old Boston-Cambridge link, which provides spectacular views of Boston’s skyline, had aged to the point where the sidewalks were crumbling, the railing had rusted, and concrete was spalling. The old drainage system was so corroded that stormwater went through the bridge and into the river.
The project received a boost from 2008 Massachusetts legislation that created the $3-billion, eight-year Accelerated Bridge Program. Pihl Inc., the U.S. branch of Denmark contractor E. Pihl and Son, holds an $18-million contract to refurbish the multiple-span crossing. The central span is a steel truss with a suspended deck 170 ft long and 40 ft wide. Two 100-ft-long concrete spandrel arches featuring decorative stonework flank the main arch. A freight railroad line runs below the bridge with little clearance.
Former owner Massachusetts State Dept. of Conservation and Recreation awarded a $2.3- million contract in 2008 to repair the 8-ft, 7-in.-wide sidewalks so that users would have a comfortable experience during the larger $20-million planned renovation, says Mark Gravallese, project manager with the Massachusetts Dept. of Transportation.
But during the course of the contract, crews found corroded utility duct banks and severe steel damage. “Thing is spiraled beyond the contractor’s control,” says Gravallese.
The contract was terminated, and the rest of the sidewalk work rolled into the current two-year contract, scheduled for completion in December 2011. The state Dept. of Transportation took over management of the bridge in 2009 as part of a statewide reorganization.
To keep traffic flowing, the repairs are scheduled in three phases of six- to nine- months each. The downstream portion will be repaired first, then the middle traffic lanes and finally the upstream portion. Each phase consists of removing and replacing the existing concrete deck, replacing steel stringers and installing a new drainage system, says Henrik Due Pedersen, Pihl project manager.
Demolition is performed at night, with access restricted to emergency vehicles. During the day, a work zone squeezes in next to two travel lanes. The four-lane bridge carries 40,000 vehicles over the river daily.
“There’s a lot of character to this bridge,” says Jerry MacKenzie, project manager for consulting engineer STV Inc.’s Boston office. “Even the paint colors have to be approved” by preservationists. Crews are patching cracks on the concrete walls and “cleaning graffiti and 80 years of grime,” adds MacKenzie. Light fixtures, granite blocks and iron stairwells leading up to the bridge all are being refurbished. “There are 18 layers of paint, all lead-based,” notes MacKenzie.
Despite the rust and grime, the substructure is in fairly good shape. For example, only one abutment had to be replaced. The new abutment sits on new, 40-ft-deep steel piles, says MacKenzie. The replacement eased access to the interior through the 2.5-ft-thick walls. Interior arches are receiving a new waterproofing membrane.