Ultimate condition of fiber reinforced polymer-confined concrete: Fid-Bau Portal

Ultimate condition of fiber reinforced polymer-confined concrete

Lam, L. / Teng, J.G.

One important application of fiber reinforced polymer (FRP) composites is as a confining material for concrete in the retrofit of existing concrete columns by the provision of FRP jackets. Such jackets are commonly formed in a wet layup process, with the fibers being present only or predominantly in the hoop direction. This paper presents the results of the first study involving comparative experiments in an attempt to clarify the causes for the reduced strain capacity of FRP when used to confine concrete. To this end, test results obtained from three types of tests - namely, flat coupon tensile tests, ring splitting tests, and FRP-confined concrete cylinder tests - are compared for two tapes of FRP (carbon FRP (CFRP) and glass FRP (GFRP)) and carefully interpreted. The following conclusions can be drawn: The average hoop rupture strains measured in the FRP-confined concrete cylinders are affected by at least three factors 1. the curvature of the FRP jacket; 2. the deformation nonuniformity of cracked concrete; and 3. the existence of an overlapping zone in which the measured strains are much lower than strains measured elsewhere. These three factors combine to produce an average FRP hoop rupture strain in confined cylinders that is much lower than that from flat coupon tests. The lower FRP strains in the overlapping zone reduce the average hoop strain, but do not result in a lower confining pressure in this zone because the FRP jacket is thicker here.