Effects of Ground Motion Incidence Angles in a Reinforced Concrete Skewed Bridge Retrofitted with Bucking Restrained Braces

This study evaluates the effect of ground motion incidence angle on the responses of skewed bridges retrofitted with buckling restrained braces (BRBs) in the bents. A three-span skewed bridge with no retrofit is used as a baseline case. The assessment is carried out in OpenSees using a model that accounts for the BRBs between bent columns, abutment and shear keys, as wells as soil-structure interaction effects. The models are subjected to 21 far-field ground motions, and the maximum response under 11 incidence angles is obtained. The two components in each ground motion set are first rotated to their principal directions to minimize correlation among horizontal orthogonal directions. Thereafter, the ground motion components are scaled to the maximum considered earthquake (MCE) level. Nonlinear time history analyses indicate that seismic behavior of skewed bridges can be significantly different from that of straight bridges due to torsional effects caused by the combination of longitudinal and transverse seismic responses. The skew configuration decreases the difference in responses among different angles due to the combinational effects of longitudinal and transverse directions. After the retrofit implementation, the BRBs in column bents can mitigate the influence of incidence angle. Therefore, to predict the maximum bridge response is usually sufficient to apply the minor principal direction ground motion in the bridge longitudinal axis, and the major principal direction orthogonal to the longitudinal axis. The study shows that the use of BRBs as a seismic retrofit increases the seismic performance of the bridge components, reducing transverse drifts, abutment and shear key seismic demands; and reducing strains in bent columns.