Shaking Table Test and Numerical Analysis on Seismic Performance of Step‐Back Reinforced Concrete Frame Structures

Step‐back buildings, characterized by a stilted story with columns of varying lengths, are prevalent in mountainous regions. These different vertical components often result in uneven structural stiffness, both vertically and laterally, which affects the seismic performance of these structures. This study investigates the seismic performance of step‐back reinforced concrete (RC) frame structures through experimental tests and numerical simulations. Shaking table tests were conducted on two 1/8‐scale models: one representing a step‐back RC frame and the other a conventional structure. The comparison focused on failure patterns, dynamic properties, and structural responses, including acceleration, deformation, torsional effects, and story shear. The results show that the superstructure of the step‐back structure model suffers more severe damage with a partial column hinge failure mechanism. The damage to columns in the stilted story and the first story of the superstructure is uneven. In particular, the torsional response of the stilted story is particularly significant. The shear force in the stilted story increases significantly, indicating an apparent redistribution of internal forces. Moreover, a 3D numerical simulation model of the tested step‐back structure was established and validated. The influence of lateral stiffness in the stilted story on the seismic response was investigated. The results show that the reduced lateral stiffness in the stilted story leads to a reduced internal force redistribution of columns in the stilted story, with seismic damage being shifted downwards and concentrated in the shortest column. The torsional effect tends to increase, which may be due to the reduced torsional stiffness of the stilted story. More research is needed on the effect of torsional stiffness or related indicators on the torsional effect of step‐back structures.