Influences of structural size and confinement effect on the axial compressive behavior of SCFST columns

Abstract

In this study, the mechanical behavior of geometrically similar square concrete filled steel tubular (SCFST) columns under axial compression was investigated using numerical modeling. The effects of the confinement effect and structural size on the axial compressive behavior of the SCFST column were studied. A 3D mesoscale model of the SCFST column under axial compression was established and verified using available test results. The failure mode and the nominal axial stress-axial strain curve were then presented and analyzed. The effects of the steel ratio and section size on the failure mode of the SCFST column were not obvious. As the section size of the SCFST column increases, the peak axial stress and corresponding peak axial strain show a descending trend. Specifically, as the section size changes from 100 mm to 800 mm, the peak axial stress decreases by 46.2% and 23.8% corresponding to the steel ratios of 0.0 and 0.21. With an increase in the steel ratio increases and enhanced confinement effect, the influence of the size effect on the peak axial stress decreases. For the outer steel tube, the vertical stress increases and the hoop stress decreases with the increasing section size, leading to the weakened confinement effect. Subsequently, an empirical formula considering the size effect was proposed to calculate the axial bearing capacity of SCFST columns with different structural sizes and confinement effects. The proposed empirical equation was validated using collected test results. This equation can be applied to predict the axial load bearing capacity of SCFST columns with different structural sizes and steel ratios, especially for large structural sizes.