Structural Analyses of Two Historic Covered Wooden Bridges

Abstract

Structural analyses were conducted of two covered wooden bridges still in use in the Summer of 2002. The Pine Grove Bridge and Brown Bridge represent the 19th century truss forms of the Burr-arch truss and the Town-lattice truss, respectively. In the Burr-arch truss, the arch is shown to be dominant in carrying the dead load of the bridge, while the truss, following simple beam behavior, primarily provides resistance against concentrated live loads. The use of camber and a common retrofit of steel ties are found to have varied effects. The Town-lattice truss is found to follow simple beam behavior with stress concentrations at the supports. Studies are conducted to highlight the sizing and placement of the chords, the behavior and advantages of bolster beams, and the sizing and placement of the lattice members. It is hoped that this study may aid those wishing to better understand these bridges’ historic significance and demonstrate how modern engineering analysis may aid our understanding of historic bridges.