Characterization of FRP Uwrap Anchors for Externally Bonded FRP-Reinforced Concrete Elements: An Experimental Study

Abstract

While the majority of U-shape wrapping (Uwrap) studies have focused on the mechanism of the shear-strengthening effect, very few studies have been devoted to the use of Uwraps as anchorage for longitudinal fiber-reinforced polymer (FRP) sheets or plates. This investigation therefore focuses on the anchor effect of the carbon-fiber-reinforced polymer (CFRP) Uwrap on externally bonded FRP-reinforced concrete elements. Based on selected parameters from the preliminary study, a parametric study was conducted on concrete blocks with an attached FRP sheet with and without Uwraps. Pull-out tests were conducted on these specimens. Slips along the length of the FRP sheet and debonding propagation in the region under the Uwrap were observed using a linear variable differential transformer (LVDT) and strain gauges. Among the tested specimens, the FRP Uwraps with a 45° angle without an edge distance maximizes the benefit of the anchoring effect. Two factors were found to control the Uwrap performance: the stress concentration at the corner region of the Uwrap, and the frictional behavior between the debonded surfaces of the concrete and the FRP sheet to determine the behavior of the Uwrap and its anchor capacity.