Spacing of intermediate diaphragms in horizontally curved steel box girder bridges

Horizontally curved box girder bridges inherently exhibit complex torsional and distortional behavior as well as bending due to the initial curvature. Distortional warping and transverse bending normal stresses, two major stress components resulting from distortion, are generally limited to a specific level for efficient use of the cross section by installing adequate intermediate diaphragms. The objectives of the present study are to develop a curved box beam finite element and to propose tentative design charts for adequate maximum spacing of intermediate diaphragms. The validity of the developed box beam element having nine degrees of freedom per node including two distortional degrees of freedom is verified from a series of thorough comparative studies using conventional shell element models. Extensive parametric studies using the box beam elements are performed and the design charts for the maximum spacing of the intermediate diaphragms are presented. Bridges taken into account are single-span, two-span, and three-span continuous horizontally curved box girder bridges. The design parameters considered are the central angle, the number of spans, the span length, the aspect ratio of the box section, the spacing of the intermediate diaphragms, and the desired ratio of the distortional warping normal stress to the bending normal stress. Unlike the current practice where the ratio of the distortional warping normal stress to the bending stress is fixed to a specific value, the proposed design charts facilitate the determination of the maximum spacing of intermediate diaphragm for various desired stress ratios.