Modified confinement model for monotonic axial behavior of concrete-filled tubular columns

Abstract

Concrete-filled tubular (CFT) columns exhibit higher axial resistance and better displacement ductility as compared to the conventional reinforced concrete members. The performance of CFT members may be influenced by many geometric and material parameters. This study presents an experimental study on twenty-two CFT column specimens subjected to monotonic axial compressive loading until their failure. The main parameters varied in the test specimens were the grade of concrete, slenderness i.e., length-to-depth (L/D) ratios, and tube compactness i.e., depth-to-thickness (D/t) ratios. The L/D ratios were varied in the range of 3–10 for two different values of D/t ratios (i.e., 13 and 26). The performance of CFT columns was evaluated in terms of the peak axial strength, ductility, and post-peak resistance. Test results showed that as the grade of concrete was increased, the peak axial resistance was improved. Further, the increase in the L/D ratios resulted in a steeper degradation in the post-peak stiffness of the CFT columns. An analytical investigation was also conducted to predict the axial strengths using the available confinement models and various design codes. The D/t ratios were varied in the range of 10–120, whereas the L/D ratio was varied between 3 and 48 in the analytical study. Based on both experimental and analytical investigations, a modified confinement model has been proposed to predict the peak axial strength as well as the post-peak axial resistance of CFT columns. The proposed model includes the effects of material grades, tube compactness ratio, and column slenderness ratio.