Experimental study on restoring force model for outer shell beam-column joints of steel structure

Restoring force model is the foundation of the elasto-plastic time history analysis of the steel structure or the member. However, the restoring force curves obtained from the experiments are complex and difficult to be directly used for the seismic calculation of the structure. In order to simplify the restoring force characteristics of the outer shell beam-column joints of a steel structure, a computational model based on the properties of the test curves and described by a mathematical method was presented. Through the quasi-static test method, the seismic performance of four outer shell joints under cyclic loading was studied, and the stress stage and failure mode were analyzed. Then, a tri-linear restoring force model accorded with the skeleton curve characteristics was established. Based on this model, the stiffness degradation rules of the specimens under reciprocating load were deduced by regression statistical method. In addition, the hysteresis curve models of the joints were calculated and compared with the experimental results. The results show that the stress process of the specimen is divided into three stages: Elasticity, yield, and plasticity. Moreover, the tri-linear skeleton curve models are in good agreement with the experimental results, which reflect the stress properties of the joints at different stages. Meanwhile, the hysteresis models considering stiffness degradation describe the hysteresis rules, these rules are approximately the same as the hysteresis curves obtained from the tests. The proposed restoring force model can accurately reflect the moment-rotation relationships of the specimens, providing theoretical references for the nonlinear seismic response analysis of the outer shell joints. © 2017. Eastern Macedonia and Thrace Institute of Technology.