Axial resistant behavior of bolt-connected CFST columns: Experimental and numerical studies

Abstract

In recent years, the concrete-filled steel tubular (CFST) columns with large cross-sectional aspect ratios have been paid much attention for practical engineering applications. By installing bolts to connect opposite surfaces of the steel tubes in bolt-connected CFST columns, the axial resistant behavior of CFSTs with large cross-sectional aspect ratios can be significantly improved. This paper presented experimental and numerical studies on axial resistant behavior of the bolt-connected rectangular CFST stub columns. In this study, 19 bolt-connected CFST columns were designed and tested under axial compression, and an ordinary CFST column was also tested for comparison. The failure modes, ultimate resistance, residual resistance, and ductile performance of the bolt-connected CFST columns were investigated concerning the effects of key parameters including: (1) cross-sectional parameters, (2) connecting bolts parameters, (3) confining factor of cross sections ξ. The test results indicated that the generation and development of local buckling deformation on the wider side of the steel tube could be delayed by installing bolts, thus the confinement effect of steel tube on the core concrete was improved to achieve better axial resistant and ductile performance. In addition, a refined finite element (FE) model was established using Abaqus, and its validity was verified against tests for conducting an extensive parametric study. According to the experimental and numerical results, it was found that the spacing-to-width ratio, cross-sectional aspect ratio and width-to-thickness ratio of steel tube had significant effects on axial resistant and ductile performance of bolt-connected CFSTs. In addition, a bolt spacing corresponding to s/D ≤ 0.5 was recommended to achieve a satisfactory ductile performance in engineering practice.