Evaluation of buckling-restrained braced frame seismic performance considering reserve strength

Buckling-restrained braced frame (BRBF) systems are used extensively for resisting lateral forces in high seismic regions of the United States. Numerical and large-scale experimental studies of BRBFs have shown predictable seismic performance with robust ductility and energy dissipation capacity. However, the low post-yield stiffness of buckling-restrained braces (BRBs) may cause BRBFs to exhibit large maximum and residual drifts and allow the formation of soft stories. Thus, reserve strength provided by other elements in the lateral-force-resisting system is critical to improving seismic performance of BRBFs. This reserve strength can be provided in two primary ways: (1) moment-resisting connections within the BRBF and (2) a steel special moment-resisting frame (SMRF) in parallel with the BRBF to create a dual system configuration. These two approaches to providing reserve strength can be used together or separately, leading to a variety of potential system configurations. In addition, special attention must be given to the connections within the BRBF since moment-resisting connections have been observed experimentally to limit drift capacity due to undesirable connection-related failure modes. This paper presents nonlinear dynamic analysis results and evaluates performance of BRBF and BRBF-SMRF systems using moment-resisting and non-moment-resisting beam-column connections within the BRBF. Reserve strength is shown to play a critical role in seismic behavior and performance of BRBFs.