Experimental investigation of FRP-confined concrete-filled stainless steel tube stub columns under axial compression

This paper presents the behavior of fiber-reinforced polymer (FRP)-confined concrete-filled stainless steel tube (CFSST) stub columns under axial loading. Six CFSST stub columns and 18 FRP-confined CFSST stub columns were tested. Typical failure modes and load-displacement curve were obtained. The effects of the number of carbon FRP (CFRP) wrapping layers and the thickness of the stainless steel tube were analyzed. In contrast to the uniform outer buckling of CFSST specimens, all FRP-confined CFSST specimens were found with the first explosive rupture of the CFRP wrap in the midheight region. Typical axial load-displacement curve exhibited four stages, namely, elastic, secondary ascending, repeated fracture, and post-fracture stages. All CFSST and FRP-confined CFSST specimens underwent substantial hardening after the yielding of composite sections. With the confinement of wrapped CFRP, the load-bearing capacity of FRP-confined CFSST specimens was increased by up to 71.35%, and the energy absorption capacity was also enhanced considerably. Test results indicated that the improvement in the load-bearing capacity approximately increased linearly with the number of CFRP wrapping layers, and the load-bearing capacity increased with confinement ratio (xi(frp)/xi(ss)). Based on the trend line of the increase in load-carrying capacity versus confinement ratio (xi(frp)/xi(ss)), a simplified method was proposed to predict the capacity of FRP-confined CFSST stub columns. This simplified method conservatively predicted the experimental results, warranting its further application in the field of engineering.