Seismic plastic design of buckling-restrained braced-RC frame structures based on energy balance

To determine the buckling-restrained brace (BRB) configuration in structures to fully exploit the seismic performance, an integration plastic design method of buckling-restrained braced reinforced concrete frame (BRB-RCF) structures was developed based on energy balance in this paper. The `strong-column weak-beam' global yield mechanism was constructed and the total BRB-RCF system was decomposed into BRB system and RC frame system by using the lateral force ratio, and the bilinear capacity curve was derived. The design base shear was calculated based on an energy balance method to determine the design lateral forces of BRB system and RC frame system, and then the section design of BRBs could be completed. According to the plastic design method and considering the post-yield behavior of BRBs, the internal force demands of beams and columns could be calculated. Using a five-story structure as a prototype, 14 frames with different lateral force ratios were designed, and the design base shears, BRB section areas and reinforcements of RC columns and beams were compared. By performing the nonlinear dynamic analyses under 22 ground motions, the maximum inter-story drift ratio, yield mechanism, story shear ratio, the maximum and cumulative displacement ductility of BRBs and the residual drift ratio were systematically investigated for structures with different lateral force ratios. The analytical results show that the proposed approach can achieve the desired seismic failure modes and meet the performance requirements, and the design lateral force ratio between 0.3-0.5 is suggested.