Tallahassee, Fla. — Built in 1929, the Checkered House Bridge, located in Richmond, Vt., is a 350-foot-long steel truss bridge placed on the National Register of Historic Places in 1990. This bridge needed to be widened 12 feet., 6 inches to allow for two vehicles to safely cross the bridge simultaneously in opposite directions and to accommodate modern traffic loads.
This project is only the second design-build project undertaken by the Vermont Agency of Transportation and this rehabilitation widening project had to satisfy Section 106 of the National Historic Preservation Act of 1996 and Section 4(f) of the U.S. Department of Transportation requirements.
The design-build of Harrison & Burrowes Bridge Constructors, Inc. and CHA Consulting, Inc. brought in the Finley Engineering Group, Inc. (FINLEY) early in the bid process to do the conceptual design. FINLEY realized that traditional construction methods could not be used on this project so the incremental launch method was selected. FINLEY developed an extensive and detailed launch analysis to include all critical load cases and conditions (ice flows, wind loading-30-mph average gusts/daily wind speeds, aesthetics, preservation requirements and environmental protection) and designed a unique jack and roller side-launching system allowing the team to save 80 percent of the original truss, preserving the bridge as much as possible. Innovative materials were used to reduce dead load while providing a lightweight, strong and durable deck.
FINLEY designed the falsework and jacking system which enabled the north truss to be moved with lateral support provided from the south truss system. Ten specially designed 18-inch stroke capacity hydraulic ram systems were placed on the top/bottom chords and at each abutment, and provided carefully monitored constant pressure to nudge the 65-ton north truss on the rollers to its new location. Movement had to be carefully orchestrated, and the team had to advance the support brackets for the jacks with every 12 inches of movement. FINLEY’s Engineer was on-site during the launch to monitor 10 critical connection points that, when cut free, would expose the truss to potential distortion and twisting.
The project was completed on-budget and on-schedule. The design-build team worked closely together to provide an innovative engineering preservation solution to widen the bridge, meet the owner’s needs in the most effective and safest manner, and provide the optimum financial and historic value to the traveling public.