Behavior and Effectiveness of FRP Wrap in the Confinement of Large Concrete Cylinders

This paper presents the results of an experimental investigation on the strength and behavior of large 250 mm diameter concentrically loaded unreinforced fiber-reinforced polymer (FRP) confined concrete cylinders. In this study, the effect of the number of layers of the FRP and different overlap locations on the effectiveness of the FRP wrap is determined. Discontinuous versus continuous wrapping configurations to confine the cylinder are also investigated. To quantify the level of strain in the wrap and to aid in developing a deeper understanding of the behavior of these larger sized test specimens, an extensive array of electrical resistance strain gauges is used in addition to electronic speckle pattern interferometry (ESPI) optical measurement at selected locations. The ESPI results prove especially powerful in confirming the existence of strain concentrations at the ends of the overlap region, which may contribute to rupture failure of the wrap. The strain gauges in turn enable the effectiveness of the FRP to be quantified in addition to the distribution of hoop strain in the overlap and nonoverlap regions. Also of interest in these tests is identification of the occurrence of interfacial failure between the FRP and concrete at the FRP rupture failure position. Finally, the test results are found to correlate reasonably well with the ACI 440.2R-08 predictions for FRP-confined concrete columns.