In Rockingham, Vt., there were two bridges over the Williams River that were falling into disrepair. They were built in the 1960s and were not designed to withstand the increasing flow of traffic in the region. The state of Vermont ultimately chose an innovative precast concrete design using pretensioned bulb-tee beam segments that are post-tensioned together.
The final design features two distinct bridges with individual substructures and continuous girders. The new bridges are wider than the existing structure, with two 12-ft travel lanes, a 4-ft left side shoulder, and a 10-ft breakdown lane. Both bridges 24N and 24S have abutments and pier substructures supported by footings on piles, with the exception of one pier on the southbound bridge bearing on bedrock.
The main prestressed concrete beam segments range in weight from 144,920 lbs to as much as 186,920 lbs. “The final design was based on J. P. Carrara’s capacity to fabricate and ship the elements to the job-site,” French says. The girders maxed out the lifting capacity at the Middlebury, Vt., plant, and Carrara used professional drivers and trucks with steerable trailers to safely transport the girders along the winding roads that led to the job-site.
Precast concrete girders weigh up to 186,920 lb.
The girders have a lifecycle of more than 100 years—25 years more than the standard service life of bridges in this region.
The certified PCI Producer used specialized trucks with steerable trailers to transport the massive girders on Vermont’s winding roads.
Build two 863-ft precast concrete bridges over Williams River in Vermont.
The project included 70 precast concrete girder segments ranging from 96 to 147.5 ft.
Girder installation was completed in six weeks for the northbound bridge, and 10 weeks for the southbound bridge.