Enhancing seismic resilience of non-ductile RC frames with a novel buckling restrained brace system: A nonlinear analysis approach

This paper investigates the nonlinear static and dynamic analysis of seismically deficient reinforced concrete frames retrofitted with a novel buckling restrained brace (BRB). The authors developed the new BRB system through experimental research, featuring a gapless inner stainless-steel bar, enhancing inelastic deformability and energy dissipation. The study aims to develop reliable models for reinforced concrete frames with and without the BRB system using numerical analyses under reversed cyclic loading. Initially, nonlinear static analysis was conducted on two single-story, single-bay, large-scale reinforced concrete test frames: one representing an older building and the other retrofitted with the BRB system. Validation of the numerical results was achieved by comparing them against experimental data. Subsequently, the analysis was extended to a six-story existing frame building in Vancouver, Canada, to evaluate the BRB system's effectiveness through nonlinear dynamic response history analysis. Key performance metrics such as story drift ratios, base shear force, column capacity versus demand, moment-chord rotation response, and ductility were assessed. The retrofitted building showed significant improvements in seismic performance, with the maximum interstory drift ratio reduced to 1.16 % from 2.3 %, achieving the Life Safety performance level per ASCE 41–13 standards. Column shear deficiencies were reduced by 64 %. Additionally, the BRBs demonstrated stable axial force-axial displacement hysteretic behavior, with a maximum displacement ductility demand ratio of 4.1 and a maximum strain of 0.15 %, within the Enhanced Safety performance range. This research confirms the novel gapless BRB system as an effective retrofitting solution for older buildings in seismically active regions.