Equivalent Lateral Force Design Method for Longitudinal Buckling-Restrained Braces in Bidirectional Ductile Diaphragms

Abstract

Bridge design specifications include design provisions for ductile diaphragms to resist seismic excitations perpendicular to a bridge’s axis. Buckling restrained braces (BRBs) can conveniently be used for this purpose. Bidirectional ductile diaphragms expand the concept to resist all-direction seismic forces, and nonlinear inelastic response history analyses (NL-RHAs) can be used to show that satisfactory seismic performance objectives can be obtained using this concept. However, a simple design procedure is needed to address the design of the BRBs in the bridge longitudinal direction. As a first step, to fill that need for common multispan simply-supported bridges, a relatively simple-to-use equivalent lateral force (ELF) procedure has been developed on the basis of results from “optimal designs” obtained using NL-RHAs. Findings indicate that the proposed ELF design procedure leads to design that meet the target design objectives.