Cianbro Corp. of Pittsfield, Maine was recently awarded a $60 Million project to replace a 90-year-old Strauss heel trunnion bascule bridge in New London, Connecticut. Opening and closing up to 1,600 times per year and with 36 trains crossing daily, the span over the Thames River is used by Amtrak for its Northeast Corridor line between Boston and Washington D.C. In order to quickly reopen the route to passenger trains, Cianbro was tasked with removing the old 650-ton tilting span and installing the new 1,400-ton vertical-lift span within 96 hours or face $500,000 per day in penalties.

Cianbro wanted to use previously purchased Flexifloat barges to float the new 188-foot span between the existing piers and elevate it into place using an on-board jacking system. In addition to the weight of the span, the barge needed to accommodate the necessary substructure as well as jacking system. Finally, as the existing piers were being used to support the new span, Cianbro needed a barge that would both fit between the 150-foot gap between the pier fenders and also allow the contractor to safely perform the work.

Working with application engineers at Robishaw Engineering, Cianbro was able to configure their Flexifloats into a 140-foot-wide, 15,600-square-foot assembly to support the 3.2-million-pound deck load. A combination of timber mats and W36 beams was used to help distribute the load, keeping the deck bearing pressure within the rated 5,000 psf.

After the replacement span was erected on the Flexifloat barge, it was lifted approximately 35 feet above the water using strand jacks. The assembly was then positioned between the piers and the span was lowered onto the abutments. Despite several unprecedented operational challenges, Cianbro and Amtrak worked together to resolve these issues and restore full service as quickly as possible.