Impact of reserve strength on buckling-restrained braced frame performance

Buckling-restrained braced frame (BRBF) systems exhibit robust performance when subjected to seismic loading. However, the low post-yield stiffness of buckling-restrained braces (BRBs) may cause BRBFs to develop large maximum and residual drifts and allow the formation of soft stories. Thus, reserve strength provided by other elements in the structural system is critical to improving seismic performance of BRBFs. 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. These two approaches to providing reserve strength can be used together or separately, leading to a variety of potential configurations. In addition, special attention must be given to beam-column 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.