Hybrid test and numerical study of beam-through frame enhanced by friction spring-based self-centering rocking core

Beam-through frames (BTFs) are gradually becoming popular as low-to-medium rise buildings in China because of their economic benefits and fast construction. However, BTFs are prone to soft-story failure mechanisms, especially under the ultimate stage. The self-centering rocking core (SRC), composed of a steel truss rocking core and a friction spring-based self-centering (SC) device, is introduced to improve the resilience of the BTF. Quasi -static tests and hybrid tests were conducted to investigate the seismic performance of the SC device and the SRC, respectively. Quasi-static tests demonstrate that the SC device has highly stable flag-shaped hysteretic behavior under two different loading protocols. Hybrid tests reveal that the system could realize the target seismic per-formance with an effectively controlled deformation pattern under both far-field (FF) and near-fault (NF) pulse -like ground motions. Based on the experimental results, the uniaxial material model of the SC device and the numerical model of the system were verified. Subsequently, a parametric study was performed to investigate the influence of two stiffness parameters (i.e., the ratio of the initial actual (experimental) compression stiffness to the initial theoretical compression stiffness (IC) and the ratio of the initial actual tension stiffness to the initial actual compression stiffness (p)) of the SC device on the seismic performance of the system. The incremental dynamic analysis (IDA) results show that the collapse capacity of the system increases first and then decreases with the increase in IC values and a larger p leads to a larger collapse capacity of the system. Besides, the influence of such stiffness parameters on the peak responses of the system under various seismic hazard levels was also investigated. The strategy employing the SRC could realize a uniform peak inter-story drift (PID) distribution of BTFs while the peak floor acceleration (PFA) tends to be concentrated on the upper floors.