ROUTE 3A OVER MTBA (CONRAIL)
Hingham, Massachusetts
The Route 3A Bridge over the MBTA Greenbush Line was constructed in 1932 with a reinforced concrete deck on steel stringers. The bridge is notable for its 52 degree skew. When C&C was assigned to provide engineering for the rehabilitation of this structure, there was concern for the condition of the concrete in the wing walls and abutments, as some surface spalling had begun to take place.
During our pre-design inspection, we ordered concrete testing, including compressive strength and chloride ion content sampling to verify the condition of both the deck and the abutments. It was discovered that while the deck was beyond repair, the abutments and wing walls were generally salvageable. However, our inspection also identified decay in the steel stringers that suggested total replacement as the only suitable alternative for rehabilitation.
When the MBTA recently decided to restore passenger service on the rail line, the Massachusetts Highway Department directed us to meet new minimum clearance standards under the bridge. To do this, we designed a system with oversized, but shorter height stringers to replace the existing steel. The bridge seats would have to be raised about six inches to make the new rails clear the passage envelope specified by the MBTA.
Traffic Management during construction presented a challenge in that pedestrian traffic had to be maintained at all times. To meet this challenge, we designed a three-span pedestrian bridge to be located on the north side of the construction zone. The walkway was connected to existing sidewalks on both approaches. Vehicular traffic was accommodated in a three-phased management plan using traffic barriers bolted to the existing deck. Because of the poor quality of the concrete deck, the barriers had to be through-drilled and bolted to the stringers as well as the concrete deck.
During construction, we were called upon to coordinate the reconstruction of the abutments with Verizon, who maintained a bank of communications ducts across the bridge. Minor changes in the plans for the ducts allowed a bank of nine ducts to fit snugly between the new stringers, and the work was accomplished without interruption of service to Verizon customers.
Client: Massachusetts Highway Department
