Hysteretic model and seismic energy response of CFST columns in diagrid structure

The mechanical performance of the diagrid concrete filled steel tubular (CFST) columns is significantly different from that of the traditional bending components, and very few research has been conducted on their hysteretic performance. In this study, the axial cyclic test results of eight CFST columns were presented. Based on the experimental results, the degenerate trilinear model was used to establish the dimensionless skeleton curve model, and the calculation formulas for the peak bearing capacity and the corresponding displacement of the CFST columns were proposed. On account of the observed damage characteristics of the CFST columns, different hysteretic rules were selected to establish the unloading stiffness functions in the tension and compression directions. Thus, a hysteretic model suitable for CFST columns under axial cyclic loading was proposed, and the rationality of the hysteretic model was verified by comparison with the test results. Afterwards a refined finite element model of the diagrid structure was established using the proposed hysteretic model of the CFST columns. Through elastic–plastic time history analysis, the energy distribution of the diagrid structure was studied, and the interlayer distribution of the inclined CFST columns under rare earthquakes was analyzed. The results shown that the energy had an obvious mutation at the junction between the bottom module and the secondary node layer, so it is necessary to avoid large stiffness mutations in the design of the diagrid structure.