Hoop strains in FRP-confined concrete columns: experimental observations

It is now well understood that the hoop rupture strain of fiber reinforced polymer (FRP) jackets confining concrete is often lower than the ultimate tensile strain of the component fibers. This paper presents the results of an experimental study designed specifically to investigate the two newly identified material dependent factors influencing the hoop strain efficiency of FRP jackets. 36 circular FRP-confined normal and high-strength concrete (normal-strength concrete and High-strength concrete) specimens were tested under axial compression. The results indicate that the hoop rupture strains of FRP jackets decrease with either an increase in the strength of the unconfined concrete or the elastic modulus of the fiber material. These observations were verified by additional results from a large FRP-confined concrete test database assembled from the published literature. In addition, the hoop strain-axial strain relationship of FRP-confined concrete was studied and the influence of the test parameters on the behavior was established. The findings from these investigations are presented together with an expression for the prediction of the strain reduction factor and a model to describe the hoop strain-axial strain relationship.