Seismic response of regular multi-span bridges having buckling-restrained braces in their longitudinal direction

Abstract

Buckling Restrained Braces (BRBs) have been used widely in building seismic resisting systems, and have much potential for applications in bridges. One such application is in ductile end diaphragms, a design concept that aims to protect bridge substructures and limit displacement demands by the use of fuse elements, and that can achieve these goals using BRBs. Here, regular, straight, simply-supported, multi-span bridges with BRBs in bidirectional ductile end diaphragms are studied in the longitudinal direction to better understand the behavior of such bridges and correspondingly provide design recommendations (to complement the existing AASHTO design provisions that already address response in the transverse direction for that structural system). Two different layouts of implementation were studied, and designed using the multimode spectral method to identify their respective benefits. A parametric study was conducted on the preferred configuration in which BRBs were used to connect spans to piers, using nonlinear response history analysis to understand the influence of pier stiffness, BRB yield displacement, target BRB ductility demand, and other factors on overall inelastic response. Overall, the use of BRBs was found to effectively limit the displacement demands in columns and expansion joint opening, achieving the structural fuse objective. These dynamic analyses allowed to understand the impact of many parameters on longitudinal response and behavior of the type of bridges considered, which led to a proposed design procedure for BRBs used in this configuration.