Axial compressive behavior of high-strength spiral-confined high-strength concrete-filled high-strength square steel-tube columns

To enhance the axial compression capacity and ductility of high-strength concrete-filled high-strength square steel tubes (HCFHSSTs), the imbedding of high-strength spirals (HSS) within HCFHSSTs is proposed. By varying the thickness and yield strength of the steel tubes, spacing and yield strength of the spirals, and diameter of the spiral confinement, high-strength spiral-confined high-strength concrete-filled high-strength square steel tube (HSS-CHCFHSST) stub columns under axial compression were tested. The experimental results demonstrated that compared with a normal-strength spiral (NSS), the application of a HSS significantly enhances the load-bearing capacity and ductility of HCFHSST stub columns under axial compressive loads. In the testing phase, the HSS exhibited yielding behavior subsequent to the HSS-CHCFHSST stub columns achieving their peak load; this was followed by multiple instances of fracturing. The working mechanism and parameters of the HSS-CHCFHSST stub columns were analyzed numerically. After the peak load, the HSS effectively confined the core concrete, increasing its stress. The HSS-CHCFHSST column exhibited a higher axial compressive capacity and ductility than an equivalent HCFHSST column using a thick tube. Considering the significant contribution of the core concrete confined by HSS to the load-bearing capacity of HSS-CHCFHSST stub columns under axial compressive conditions, a comprehensive equation was formulated for the precise calculation of their axial compression capacity.