Collapse capacity of reinforced concrete skewed bridges retrofitted with buckling-restrained braces

Abstract

This study assesses the collapse capacity and failure modes of skewed bridges retrofitted with buckling-restrained braces (BRBs) at the column bent. The asymmetric configuration of these bridges requires a three-dimensional numerical model that considers uncertainties in the seismic ground motions. The factors controlling the seismic performance of these bridges are obtained from a case study of a three-span reinforced concrete box girder skewed bridge with varying skew angles of 0°, 18°, 36°, and 54°. Numerical models with distributed plasticity and concentrated plasticity are created considering material deterioration and plastic deformation properties. A numerical distributed plasticity model with strength and stiffness deterioration is calibrated with a concentrated plasticity model by performing two-dimensional incremental dynamic analyses (IDAs) on the straight bridges (i.e., 0° skew angle), using 21 far-field ground motions. Then, the collapse capacity of original and retrofitted skewed bridges is obtained from three-dimensional IDAs using the distributed plasticity model. The collapse capacity and failure modes of BRB components are summarized based on investigations from experimental data. Nonlinear time history analyses indicate that the BRB retrofit greatly improves the seismic performance of skewed bridges, but it has negligible effects on the bridge’s collapse capacity after BRB failure. However, the use of BRB greatly reduces the bridge’s probability of failure, and the mean annual frequency of global collapse, since the BRB components dissipate seismic energy as structural fuses. The proposed method of parameter calibration, including BRB failure, is found to be sufficiently reliable to perform satisfactory results.