Improved design of intermediate diaphragm spacing in horizontally curved steel box bridges

Eccentric live loading acting on the steel box girders induces cross-sectional distortion in the steel box sections. In particular, the distortional behavior in horizontally curved steel box bridges can be significant compared to that in straight ones; the reason is that the curvature effects of horizontally curved steel box bridges can provide additional distortional behavior due to gravity and live loads even without eccentricity of the applied loadings for every construction sequence (self-weight for non-composite and live loads for composite box sections). Therefore, to control the distortional warping normal stresses induced by the distortional behavior, it is necessary to install intermediate diaphragms in the box sections for straight and horizontally curved box bridges. This study aimed to estimate, using three-dimensional finite element analysis (FEA), the distortional bi-moments and stresses of single-cell horizontally curved rectangular steel box girder bridges with a single span, and to provide an improved design methodology to determine adequate intermediate diaphragm spacing in straight and horizontally curved steel box bridges considering various construction phases. Based on the parametric study, we considered not only various design parameters, such as design live loads, magnitude of the torsional moment, span length, spacing of intermediate diaphragms, subtended angle, and various normal stress ratios but also construction sequences with various loading conditions. Finally, the required intermediate diaphragm spacing for straight and horizontally curved steel box bridges were proposed.