Slenderness effects on concrete-filled steel tube columns confined with CFRP

The inelastic outward local buckling of steel tubes is common in concrete-filled steel tube (CFST) columns. The use of fiber-reinforced polymer (FRP) to suppress outward local buckling has been proposed and proven to have potential in both strengthening and new construction. This paper presents the results of an experimental program performed to study the effect of slenderness ratio on the behavior of CFRP-confined CFST columns. Eight specimens with heights ranging between 588 and 2688 mm were tested under axial compression. The effect of the number of CFRP layers was also studied. The results showed that the CFRP hoop wraps provided confinement to the concrete and the steel tube, and thus effectively improved the behavior of the CFST columns. The strengthening effect of the CFRP hoop wraps decreased when the slenderness ratio increased. The existing AISC expression of stability coefficient for CFST columns was extended to propose a formula for the stability coefficient of CFRP-confined CFST columns, and the predictions showed good agreement with the experimental results.