Curvature limits for composite steel box girder bridges

Composite concrete deck over steel box girder bridges are used in curved alignments as an economical solution because of their high flexural and torsional strength. Curvature effects on bending, shear and deflection may be ignored for bridges with light curvature. The Canadian highway bridge design code (CHBDC), the American Association for State Highway and Transportation Officials (Aashto) guide specifications for horizontally curved bridges and Aashto LRFD bridge design specifications specify limitations to treat a horizontally curved bridge as a straight one in structural design for only girder bending moment. Also, CHBDC curvature limitation does not differentiate between open and closed bridge cross-sections. The curvature limitation of the Aashto guide does not consider the effect of bridge width, leading to an inaccurate estimate of the structural response. To investigate the accuracy of these curvature limitations, a series of horizontally curved composite steel box girder bridges were analysed using finite-element modelling. The key parameters considered in this study were the degree of curvature and bridge span, width and continuity. Longitudinal bending stresses, support reactions, deflections and frequencies were determined and compared with those obtained for straight bridges of identical configurations. Results showed that code curvature limits were unsafe and needed to be updated. Empirical expressions were developed to determine curvature limits more accurately and reliably.