Seismic Stability of Buckling-Restrained Braced Frames

Buckling Restrained Braced Frames (BRBFs) are widely used as seismic force resisting systems due to their ductility and energy dissipation. However, because of the modest overstrength and relatively low post-yielding stiffness, BRBFs subjected to seismic loading may be susceptible to concentrations of story drift and global instability triggered by P-∆ effects. Due to the use of simplistic methods that are based on elastic stability, current code design provisions do not address seismic stability rigorously and do not consider the particular inelastic response of a system. Design strategies are needed to prevent undesirable seismic response in BRBFs, such as drift concentration and large residual drift. This study used the FEMA P-695 Methodology to evaluate the response of current U.S. code-based BRBF designs and to study the effect on seismic stability of three potential enhancements: strong-axis orientation for BRBF columns, gravity column contribution, and a BRBF-SMRF dual system. Results from nonlinear static and dynamic analyses allowed assessment of seismic behavior. Results from collapse performance evaluation quantify the improvement that is achieved with each alternative and provide a means of comparison.