Experimental investigation on axial compressive behavior of fiber reinforced polymer-reinforced concrete columns confined with external fiber reinforced polymer jackets

An innovative glass fiber reinforced polymer (GFRP) closed-type winding (GFRP-CW) tie was developed to eliminate the bond slip failure and make full use of the tensile strength of ties compared with conventional pultruded fiber reinforced polymer (FRP) rod ties. Although better confinement effect of GFRP-CW ties, however after spalling of concrete cover, the compressive longitudinal FRP bars in the plastic hinge regions of columns are most likely to crush or buckle. External FRP jackets can effectively restraint damage to concrete cover. Against this background, a novel FRP-reinforced concrete column confined with external FRP jackets and the internal GFRP-CW ties were proposed to prevent the FRP bars from premature buckling or crushing. In this article, twelve square new columns were constructed and tested to characterize the axial compressive behavior. The test parameters included FRP wrapping type (GFRP or carbon fiber reinforced polymer (CFRP)), FRP wrapping layers, and spacing of ties. Test results confirmed that FRP-reinforced concrete columns with external FRP jackets had significantly larger ductile behavior and exhibited higher load-carrying capacity than their counterparts FRP-reinforced concrete columns due to the contribution of longitudinal GFRP bars and the concrete cover. The test results also suggested reasonable spacing of ties and layers of GFRP jackets for an expected moderate confinement behavior.