Axial compressive behavior of UHPC confined by FRP

To improve the negative influence on the structural members from the failure brittleness of the ultra-high performance concrete (UHPC) and enhance the load-bearing capacity and deformability of the structural members, the fiber-reinforced polymer (FRP) confined UHPC columns have been proposed and are attractive in practical engineering. The performance of the unconfined and FRP-confined UHPC cylinders under axial compressive load was investigated experimentally. The following conclusions can be drawn from this study. For the FRP-confined UHPC cylinders with low, medium or high confinement levels, the stress-strain relations showed three kinds of behavior. Based on the analysis of the lateral strains of FRP and the shear-slip deformation patterns of UHPC cylinder, a three-stage failure mechanism for the FRP-confined UHPC cylinders under compression was proposed in this paper, including: (I) the formation of microcracks, (II) the formation of shear cracks, and (III) the formation and propagation of major shear cracks. Besides, design-oriented equations for predicting the ultimate compressive strength and ultimate axial strain were proposed, in which the confinement stiffness ratio and the strain ratio were considered as essential parameters.