Case Study of Burr Truss Covered Bridge

Abstract

Despite considerable popular interest, an understanding of the structural behavior of such bridges is singularly lacking. Such an evaluation is attempted in this paper for the Burr Truss using the Barrackville Bridge as an outstanding example of this system. From the analysis it is clear that the most important structural characteristic of the Burr arch-truss system compared to a multiple King post truss is the stiffness and associated deflections. For long-span timber bridges, such as the Barrackville Bridge, the arch provides a necessary stiffening of the truss so that deflections resulting from live and dead loads and the effects of creep and shrinkage would be controlled to acceptable limits. This additional stiffening is achieved economically with only a 12% increase in dead load. The analytical results confirm the engineering merits of the Barrackville Bridge, whereas the structure itself testifies to the superb craftmanship employed in its construction. The bridge is an outstanding monument to both Theodore Burr and Lemuel Chenoweth, its builders.