Experimental Research on Effects of Debonding on Circular CFST Columns with Different Slenderness Ratios

Concrete filled steel tubular (CFST) structures have a wide range of applications in buildings and bridges due to the high bearing capacity. This beneficial composite action could be weakened even destroyed by debonding. In this paper, the debonding of circular CFST long columns subjected to axial load was investigated experimentally, taking the slenderness ratios and steel ratio as parameters. The simulation method of debonding by using soft PVC sheet was proposed, which can be pulled out after 7-days of concrete curing to avoid the inaccurate pull-out time which may lead to the failure of debonding simulation. The results of non-debonding and debonding CFST long columns were compared. The failure modes of the specimens show that the specimens under axial load are subjected to bending failure. The flexure curvatures of the non-debonding specimens are larger than the corresponding debonding specimens. Compared with the non-debonding specimens, the debonding specimens experience a strong concrete crushing during the loading process. The ultimate load-bearing capacity of debonding specimens is less than that of non-debonding specimens. With the increase of steel ratio or the decrease of slenderness ratio, the ultimate load-bearing capacity of the specimens increases. With the increase of steel ratio or slenderness ratio, the influence of debonding on the ultimate load-bearing capacity decreases. The lateral deflection of debonding specimens is less than that of non-debonding specimens. With the increase of steel ratio or slenderness ratio, the influence of debonding on the lateral deflection increases.