Effect of U-Wrap Anchors on Flexural Behavior of Reinforced Concrete Beams Flexurally Strengthened with Externally Bonded CFRP Sheets

Externally bonded carbon fiber-reinforced polymer (CFRP) composites have been instrumental in the flexural strengthening of concrete structures. However, intermediate crack debonding from the concrete substrate is a governing failure mode in most externally bonded CFRP applications, limiting the composite strength utilization and deformability of a strengthened member. The addition of transverse U-wrap anchorage for longitudinally oriented CFRP sheet tension reinforcement can improve performance in terms of both deformability and ultimate strength. Due to the scarcity of experimental data, design guidance for U-wrap anchorage to mitigate intermediate crack debonding is lacking. The results of flexural tests on large-scale reinforced concrete beams strengthened in flexure with externally bonded CFRP anchored with U-wraps are reported in this paper. Test results indicate that U-wraps can increase the strain utilization of longitudinal CFRP between 40% and 57%, while also mitigating the intermediate crack debonding failure mode. Varying the ratio of the area of U-wrap anchorage to area of flexural CFRP had little effect on the beams' flexural capacity.