Shear lag in box girder bridges

A finite-segment method for analyzing shear-lag effects in box girders is presented in this paper, with an assumption that the spanwise displacements of the flange plates are described by a third-power parabolic function. The governing differential equations for two generalized displacements are established according to the principle of minimum potential energy. In order to obtain the longitudinal stresses under the shear-lag effect, the element stiffness equations are developed based on the variational principle by taking the homogeneous solutions of the differential equations as the displacement functions of the finite segment. The effect of two major parameters on shear lag is investigated for cantilever and continuous box girders with varying depth under three kinds of loads. It is shown that the height ratio, in addition to the flange width to span length ratio, has a significant influence on the shear lag. The solutions based on the present method are compared with the results of model testing and the finite strip method. The accuracy of the present method is proved to be satisfactory.