Load rating of masonry arch bridges

A masonry arch bridge can be analyzed by frame analysis methods by considering a unit width of the arch ring and the overlying fill. The arch ring is divided into at least 10 segments, each of which is given cross-sectional properties corresponding to the properties of the material in the arch ring. The dead load of the arch ring and the overlying fill are considered as nodal loads, and the axle loads are applied to the frame as linearly varying pressures, based on a simplified distribution of pressures through the fill. The supports are considered to be rigid in the vertical direction and elastic springs in the horizontal direction. The elastic spring constant varies depending on the type of foundation and the condition of the springings. Based on this application of dead and live loads to the structure, the axial thrust and moment can be found throughout the arch ring, and compared to an estimate of the capacity of the arch ring. This procedure can be used to find an appropriate load rating for the structure service level. An example rating of a bridge in Adams County, Pa., is provided, along with the results of a validation field test of the structure.