Behavior of multi-cell concrete-filled steel tube columns under axial load: Experimental study and calculation method analysis

Abstract

Multi-cell concrete-filled steel tube (MCFST) columns are widely used in super high-rise buildings. However, related studies on their axial compression behavior are limited. In order to propose calculation model and design advice, three concrete-filled steel tube column samples were designed and constructed for testing. The samples varied in their cross-sections (i.e., basic type with reinforcement cage, simplified type without reinforcement cage, and reinforced type with circular steel tube). Damage evolution, load-bearing capacity, stiffness degradation, ductility, and restoration capacity were analyzed to investigate the effect of different sections. Experimental results showed that the reinforcement cage effectively improved the bearing capacity. Due to the excellent mechanical behavior of the concrete-filled circular steel tube, the comprehensive behaviors including the bearing capacity, ductility, and restoration capacity of the samples improved. The confinement mechanism of MCFST was analyzed based on the test results. A “separation model” was proposed, followed by calculating the load–deformation curves of 12 samples with various shapes and structures, which considered that the MCFST was composed of several single cells, and calculating the constitutive relationship of concrete in every cell individually. Bearing capacity errors were approximately ± 5%, and errors of ultimate deformation were approximately ± 15%, showing good agreement with the test results. This data indicates that the constitutive relationship of concrete based on the “separation model” is reasonable. Furthermore, the ultimate state of every individual MCFST cell was calculated based on the “separation model,” indicating that the model can be used to assist in MCFST design.