Collapse safety margin and seismic loss assessment of RC frames with equal material cost

Summary With the premise of equal material cost, a collapse safety margin-based collapse resistance optimization strategy for passively controlled reinforced concrete (RC) frames is proposed based on seismic fragility analysis, collapse safety margin analysis, and seismic hazard loss assessment. The efficiency of introducing buckling restrained braces or lead–rubber bearings on the performance of RC frames is studied by so-called collapse margin ratio (CMR) suggested by FEMA P695 and the modified rigidity-to-gravity ratio (RGR). The proposed strategy is developed from the case study on 4 low-rise and medium-rise RC frames and then verified on a high-rise RC frame. The study indicates that lead–rubber bearings can cause a significant improvement at all damage levels. The contribution of buckling restrained braces to structural stiffness and collapse resistance can be maximized when they are located in potential weak stories determined through inelastic time history analysis. CMR exhibits a better linear relation with the minimum modified RGR. Increasing the equivalent story lateral stiffness and the minimum modified RGR simultaneously can give rise to a significant improvement in seismic capacity, especially CMR. Base isolation is proved to be desirable not only for improving the collapse safety margin of RC frames significantly but also for reducing seismic hazard loss.