Moment and Shear Load Distribution Factors for Multigirder Bridges Subjected to Overloads

Abstract

Movement of industrial freight infrequently requires special overload vehicles weighing 5 to 6 times the normal legal truck weights. The gross vehicle weight of the vehicles frequently exceeds 1800 kN whereas, the normal interstate legal limit in the United States is 356 kN. Because of the unusual configuration of the vehicles, it is difficult to analyze the effect of these loads on highway bridges by using current simplified analysis methods. This report aims to provide modified moment and shear load distribution factor equations for the vehicles to quickly determine their effects on multigirder bridges. Finite element analyses of 118 multigirder bridges and 16 load cases of overload vehicles for each multigirder bridge were performed, and the load distribution factor equations for the multigirder bridges were proposed on the basis of the analysis results. Various configurations of the vehicles, number of bridge spans, skew angles of the bridge and diaphragms were considered in developing the equations. The developed equations were found to be capable of replacing a time-consuming 3D finite element analysis rationally and conservatively.