Abstract：To analyze the influence of the arrangement of inner-span diaphragms on the distortion effect of box girders, an analytical approach applicable to distortion analysis of box girders with inner-span diaphragms was presented. The energy variational method based on the principle of minimum potential energy was applied to establishing the distortion governing differential equation and then the initial parameter solution expressed in terms of Krylov function was derived. The restraint action of inner-span diaphragms on the distortion deformation was replaced by unknown distortion moments which were determined by means of the deformation compatibility relationship and the initial parameter solution. Consequently, the analytical solution for the distortion effect of box girders with inner-span diaphragms was achieved. The distortion effects of the cantilever box girder model and the simply supported box girder example were calculated by applying the present analytical method and the finite element software ANSYS, respectively, so that the influences of the arrangement of the mid-span diaphragm and the variation of cross-section parameters on the distortion effect of the simply supported box girder were analyzed. It is shown that the present analytical solution is in good agreement with the measured value and the numerical solution of ANSYS. Arranging only one diaphragm in the mid-span can reduce the distortion deformation and the transverse bending moment, but it may significantly increase the distortion warping bi-moment. With the increase of the width of cantilever plates, the distortion warping stress at the intersection of the web and top plates reduces rapidly. The variation of the web thickness also affects remarkably the distortion warping stress at the intersection of the web and bottom plates.
