Simplified Method of Lateral Distribution of Live Load Moment

Abstract

This paper introduces a simplified method, known as Henry’s method, for the calculation of distribution factors of the live load moment. Using the simplified method, the live load effects are equally distributed in all beams, including interior and exterior beams. This method has been used in Tennessee for nearly four decades. It offers advantages in simplicity of calculation and flexibility in application. To carefully examine the simplified method, 24 actual bridges of six different types of superstructures were selected for the study. The distribution factors of actual bridges using Henry’s method were compared with the ones from the AASHTO LRFD, the AASHTO standard, and finite-element analysis. In the comparison study, the effects of bridge superstructure types and key parameters that significantly affected the calculation of distribution factors are discussed. Based on the results of the comparison and evaluation, a modified Henry’s method was proposed by introducing modification factors to Henry’s method. With proper modification, the simplified method can be used to determine reasonable and reliable distribution factors of the live load moment.