Strength of Spandrel Walls in Masonry Arch Bridges

Previous research on the strength of masonry arch bridges has focused on the carrying capacity of the arch barrel in the span direction. Although the results of a spandrel wall collapse may be very serious, the transverse strength of masonry arch bridges has not been widely addressed. Recent experience, however, has shown that the transverse behavior and the strength of the spandrel walls are at least as important as the behavior in the span direction. Although complex computer analysis methods have been proposed for examining the masonry arch bridge as a three-dimensional structure, these methods are not suitable for everyday practical application. An approximate analytical method for the prediction of the strength of masonry spandrel walls is developed based on the conventional analysis of fills supported by retaining walls. The method is based on the determination of loads by Coulomb-Rankine analysis and the determination of resistance by the fracture line method, similar to the yield line method for reinforced concrete slabs. A table that further increases the simplicity and speed of the method is also provided. The proposed method allows the practicing engineer to calculate a factor of safety for the transverse strength of a spandrel wall for different situations, such as moist soil, cracked wall, effect of live load for shallow fill bridges, or existence of parapet walls. Results of these conventional, simplified analyses compare favorably with observed bridge distress and results of a previously validated finite element analysis method.