Seismic behavior and damage assessment of concrete-filled steel tube columns in diagrid structures

Diagrid structures have become an innovative and attractive choice for high-rise buildings due to their high rigidity and esthetic appearance. Inclined concrete-filled steel tube (CFST) columns, as the main load-carrying members of diagrid structures, are supposed to be subjected to axial tension and compression loads. However, few studies have investigated the seismic behavior and damage assessment of CFST columns under axial cyclic loading. This study presents experimental results for eight circular CFST columns under axial cyclic loading. Based on the observed damage evolution, a damage assessment model for CFST columns subjected to axial cyclic loading was developed using a nonlinear combination of stiffness degradation and hysteretic energy dissipation. The contributions of the maximum response and cyclic loading effects to the damage were specified by introducing combination coefficients, which can be determined from a proposed equation based on the aspect ratio and confinement index of the CFST columns. Finally, the corresponding relationships between the range of the damage index and the degree of damage of CFST columns under different performance levels were established, which can provide the necessary basis for economic loss assessment and repair of earthquake-damaged diagrid structures.