USDA Forest Service Silver Bridge Reconstruction

Mount Tabor, Vermont

DuBois & King conducted planning, permitting, and engineering services for this 90-ft-long truss bridge placed on new cast-in-place concrete abutments. D&K evaluated and developed repairs to this two-span bridge, including the 90 ft main steel truss span and the 35-ft-long concrete beam approach span. Reviewed as-built plans and previous inspection records, and conducted a detailed visual inspection of the site, including bridge and roadway approaches.

The Forest Service’s initial intention was to limit repairs to repainting the steel truss and making surface repairs to the concrete abutments and pier. However, the concrete abutments and pier had significant deterioration, putting the feasibility of surface repairs into question. It was recommended to conduct an abutments investigation. D&K obtained twelve concrete cores through the abutments and the pier and performed several structural capacity tests. Results confirmed that concrete was in an advanced state of deterioration.

D&K conducted an alternatives analysis, including the construction of new abutments and rehabilitation of the pier, or elimination of the pier and construction of a single span structure, either by rehabilitation of the existing truss or by the installation of a new, pre-engineered, pre-fabricated truss bridge. The Forest Service selected a pre-fabricated steel truss bridge, with new abutments. The trusses were finished silver to match the pre-existing historic bridge.