Fragility curves for reinforced concrete (RC)/steel vertical hybrid frame structure under mainshock–aftershock sequences

ABSTRACT A reinforced concrete (RC)/steel vertical hybrid frame structure usually consists of a lower concrete structure and an upper steel structure connected in series. This study aims to derive fragility curves for RC/steel vertical hybrid frame structures under mainshock–aftershock sequences. For this purpose, a double incremental dynamic analysis (D-IDA) approach is performed to derive fragility curves for a five-story RC/steel vertical hybrid frame (a three‐story RC frame at the bottom + a two‐story steel frame at the top) under 14 real mainshock– aftershock earthquake ground motions. The fragility curves obtained for RC/steel frame are also compared with fragility curves for a five‐story purely RC frame. Also, residual capacity diagrams are provided for RC/steel and purely RC frames based on the D-IDA results. The results show that RC/steel frame structure has larger collapse capacity than that of the purely RC frame structure, and can diminish collapse probability by 33% compared to purely RC frame structure.