Checkered House Bridge Truss Widening Project, Richmond, Vt.
The longest of Vermont's three remaining Pennsylvania through trusses, the 350-ft, 85-year-old steel span over the Winooski River, was too narrow and in need of a significant structural upgrade. The project team had to keep the original superstructure intact and widen the entire bridge by 12.6 ft. In addition, work had to comply with National Historic Preservation Act and U.S. Dept. of Transportation standards.
Despite an earthquake, two 100-year-flood events and a tropical storm during construction, the $13.9-million project was completed on time and within budget.
The project had to be designed swiftly so that it could be reviewed and approved in a timely manner and allow construction to continue with minimal impact to the public. The owner used a design-build contract, the second one in its history.
The team first replaced the bridge's abutments and removed its floor system. It unbolted and separated the southern truss from the northern truss, which was held in place by a falsework system.
To limit potential distortion and twisting, 10 side-launch hydraulic jacks were used for the widening project, which took one-and-a-half days and was unusual for such a large structure.
Before the move, the team planned and predicted how the truss might react when moved. Since it had to be moved at an even pace, constant communication was critical as was monitoring the truss for any irregular movement.
Steel retrofits were made to strengthen the existing trusses, nearly 80% of which were retained. The team replaced the bridge's floor beams and stringers and installed a lightweight concrete deck.
Because the bridge remained closed during construction, the project also included constructing the longest U.S. temporary span at the time, a 267-ft-long, single-span structure over the river for the redirected traffic.
Work included blasting adjacent to a major roadway to remove a substantial amount of rock ledge on the river's western side. The team also reconfigured adjacent roadways to improve traffic flow near the structure.
The judges praised the team's "well-executed" approach and its ability to perform such a significant renovation while maintaining the structure's historic-registry status.
Owner Vermont Agency of Transportation
General Contractor/Construction Manager Harrison and Burrowes Bridge Constructors Inc.
Lead Design Firm/Structural Engineer Clough Harbour & Associates LLP
Civil Engineer FINLEY Engineeering Group Inc.
MEP Engineer Mabey Bridge and Shore Inc.
Steel Subcontractor STS Steel Inc.