Computational study of self-centering buckling-restrained braced frame seismic performance

SUMMARY: Recent research developed and experimentally validated a self-centering buckling-restrained brace (SC-BRB) that employs a restoring mechanism created using concentric tubes held flush with pretensioned shape memory alloy rods, in conjunction with a buckling-restrained brace (BRB) that dissipates seismic energy. The present computational study investigated how the SC-BRB can be implemented in real buildings to improve seismic performance. First, a computational brace model was developed and calibrated against experimental data, including the definition of a new cyclic material model for superelastic NiTi shape memory alloy. A parametric study were then conducted to explore the design space for SC-BRBs. Finally, a set of prototype buildings was designed and computationally subjected to a suite of ground motions. The effect of the lateral resistance of gravity framing on self-centering was also examined. From the component study, the SC-BRB was found to dissipate sufficient energy even with large self-centering ratios (as large as 4) based on criteria found in the literature for limiting peak drifts. From the prototype building study, a SC-BRB self-centering ratio of 0.5 was capable of reliably limiting residual drifts to negligible values, which is consistent with a dynamic form of self-centering discussed in the literature. Because large self-centering ratios can create significant overstrength, the most efficient SC-BRB frame designs had a self-centering ratio in the range of 0.5-1.5. Ambient building resistance (e.g., gravity framing) was found to reduce peak drifts, but had a negligible effect on residual drifts.