Seismic performance of existing skewed bridge bents retrofitted with buckling restrained braces

With the continuous update to international seismic codes and provisions, there is a growing need to enhance the performance of existing bridges under the action of earthquake loads. This research focuses on analytically evaluating the effectiveness of buckling restrained braces (BRB) in retrofitting existing skew bridges by adding a replaceable structural steel element between the piers of the existing bridge bents. The concerned bridges studied in this research are designed to fulfill the requirement of an older seismic code of practice that has since been replaced by a new version with more stringent seismic requirements. In this paper, a nonlinear 3D finite-element (FE) model is developed to predict the lateral response of skewed reinforced concrete (RC) bridges under seismic loading. The FE model is initially validated by comparing its outcomes to previously published results. Subsequently, the model is employed to conduct a numerical investigation, considering various bridge design parameters such as skew angles and bridge heights. Fragility curves are developed and utilized herein to measure the effectiveness of BRB. It is observed that BRB is an effective retrofit technique, providing significant additional lateral strength to the existing structure. For instance, retrofitting skewed bridges with BRB may reduce seismic forces and lateral drifts by up to 35% and 45%, respectively, compared to the corresponding values of the original structures. Moreover, utilizing such a retrofit method leads to less expected damage in terms of concrete and reinforcement strains, resulting in a lower probability of collapse under seismic threats. The proposed rehabilitation procedure using BRB as a retrofit technique establishes a sufficiently reliable system that ensures satisfactory seismic performance.