Development and seismic evaluation of double-stage Yield BRBs for precast reinforced concrete column–steel beam structures

This study proposes and numerically evaluates a double-stage yielding buckling-restrained brace (BRB) system for precast reinforced concrete column–steel beam (PRCS) structures. The proposed system incorporates a staged activation mechanism consisting of a no-gap first-stage connection and a gap-controlled second-stage connection, enabling effective energy dissipation over a wide range of seismic intensities. Closed-form force–rotation relationships are derived to characterize the two-stage response, and an OpenSees-based numerical modeling framework is established and validated against the theoretical predictions. Parametric analyses are conducted to investigate the effects of gap size and other key design parameters, followed by structural-level evaluations of PRCS structures, including optimal damper layout selection, nonlinear time-history analysis, incremental dynamic analysis, and fragility assessment under far-field, near-field no-pulse, and near-field pulse-like ground motions. The results demonstrate that PRCS structures equipped with double-stage yielding BRBs with nonzero gap values exhibit significantly reduced peak interstory drift ratios compared with zero-gap configurations, with more pronounced benefits observed under strong seismic excitations. Gap sizes of 2–3 mm provide a favorable balance between deformation control and energy dissipation, and mid-height BRB layouts yield optimal seismic performance. Fragility analyses further confirm reduced damage exceedance probabilities. Overall, the findings provide fundamental support for the practical application of double-stage yielding BRBs in PRCS structures.