Abstract
Intermediate diaphragms are required for box girder bridges in order to keep the shape of cross section and reduce the warping stress due to cross-sectional deformation. The current design guideline of the intermediate diaphragms requires extraordinary stiff diaphragms because of assumptions for the design formula. This study aims at the rationalization of intermediate diaphragm design. FEM analyses with shell elements were carried out in order to grasp the structural behavior of box girders. In the FEM analyses, spacing and stiffness of intermediate diaphragms and curvature of curved girders are considered as parameters. FEA results showed that warping stress is not increased by increment of diaphragm spacing if stiffeners with relative stiffness of 0.02 are installed. Thus, there is no need to follow the required relative stiffness of intermediate diaphragms by the current design guideline. It was also showed that the accuracy of design formula will decrease by increment of the curvature in curved girders, especially if the curvature is greater than 0.01.
