Numerical study of high-strength spiral stirrup confined high-strength concrete filled high-strength square steel tubular short columns under axial compression

In order to improve the ductility of high-strength concrete filled high-strength square steel tube (HCFHSST), high-strength spiral stirrup (HSS) can be embedded in high-strength concrete filled high-strength square steel tubes to form composite confinement on the core concrete. Considering the confining effect of square steel tube and HSS on concrete, a compressive constitutive model for core concrete of high-strength spiral stirrup confined high-strength concrete filled high-strength square steel tube (HSS-CHCFHSST) was established. The force mechanism of a typical axial compression short column and parameters analysis was presented. The findings suggest that, due to the confinement effect of high-strength steel tube and HSS on the concrete, the loadlongitudinal displacement curve of HSS-CHCFHSST declines gently. unlike normal-strength spiral stirrup (NSS), HSS have a negligible impact on bearing capacity but significantly enhance displacement corresponding to peak load. Even with larger stirrup spacing (60 mm) and smaller diameter (5 mm), the HSS effectively improve the bearing capacity and particularly the displacement corresponding to peak load of HCFHSST short columns. To optimize confinement efficiency, the diameter-to-width ratio should not fall below 0.8. The current design models' calculations for the axial bearing capacity of HSS-CHCFHSST short columns were found to be conservative, not fully leveraging the superior mechanical properties of high-strength concrete under the composite confinement of square steel tube and HSS. Consequently, a more precise equation for calculating the axial bearing capacity of these columns was proposed and well verified.