Seismic Performance Evaluation of Two- and Three-Story Steel Frames with an Upgraded Hybrid Buckling-Restrained Brace

A novel hybrid buckling-restrained brace (HBRB) configuration is introduced in this study to address the inherent limitations of conventional buckling-restrained braced frames (BRBFs). The HBRB comprised parallel steel plates with different yield strengths, featuring a low yield point (LYP160) and high strength (SA440B). A staged yielding mechanism is intended to be achieved, whereby the LYP160 cores yield initially during minor seismic excitations while the SA440B core remains elastic, providing requisite re-centering force. The hysteretic behavior of the proposed brace was scrutinized through cyclic loading. Subsequently, pushover and incremental dynamic analyses were conducted on two- and three-story frame models incorporating various bracing configurations to assess seismic performance factors. Furthermore, Nonlinear time history analysis was employed to evaluate the efficacy of HBRBs in mitigating residual displacements. Results indicate that the HBRB exhibits enhanced post-yield stiffness and partial re-centering capacity due to its staged yielding behavior. Comparative pushover and incremental dynamic analysis revealed lower average overstrength and response modification factors for HBRB models obtained from pushover analysis (3.4 and 9.3, respectively) than the incremental dynamic analysis (4.9 and 12.1, respectively). Conversely, a slightly higher ductility reduction factor was observed in the pushover analysis (2.8) relative to incremental dynamic analysis (2.5). Eventually, nonlinear time history analysis demonstrated an average reduction of 18% and 43% in maximum and residual drift ratios for HBRB models compared to BRB models.