Anti-collapse performance of concrete-filled steel tubular composite frame with RC shear walls under middle column removal

In this study, the anti-collapse performance of a 1/4 scaled two-story two-bay concrete-filled steel tubular (CFST) composite frame with RC shear walls was experimentally and numerically studied in the scenario of middle column loss through the quasi-static loading method. Test results show that the main failure modes of the specimen were the fracture and local buckling of steel beams, and the concrete crush in the shear walls and the slabs near the failure column. After the steel beam failed, the internal force was transmitted from the steel beams to the CFST columns and shear walls. Based on the refined finite element models, the effects of the column failure positions, limb lengths, reinforcement ratios, and types of shear walls on the collapse resistance of the models were analyzed. Simulation results indicate that the shear wall significantly contributes to resisting vertical load in the initial loading stage. In the large deformation stage, the collapse resistance of the specimen is mainly provided by the sub-framed structure. After the limb length of the shear wall exceeds 2/3 span, the increase in the bearing capacity is not obvious, while the failure displacement is significantly decreased. The reasonable reinforcement ratio of the RC shear wall in the structure should be designed in the range of 0.2%-5%. The local reinforcement methods for the collapse resistance of CFST composite frame with RC shear walls were proposed. In addition, the simplified dynamic analysis and dynamic increase factor (DIF) for the CFST composite frame with RC shear walls were analytically studied by energy balanced method.