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 because of their high strength-to-weight ratio, corrosion resistance, rapid and easy installation, and reduced cost compared to complete or partial component replacement. However, a governing failure mode in most externally bonded CFRP applications is debonding from the concrete substrate, which limits the composite strength utilization and deformability. Improved performance, in terms of both deformability and ultimate strength, may be achieved with the addition of transverse U-wrap anchorage for longitudinally oriented CFRP tension reinforcement. Design guidance for U-wrap anchorage is, however, lacking due to the limited experimental data. This work reports on flexural test results from structural-scale reinforced concrete beams strengthened in flexure with externally bonded CFRP anchored with U-wraps. The parameter of interest is the ratio of the areas of U-wrap anchorage to flexural CFRP, which is varied between 3.2 and 9.6. Experiments employ a 3D digital image correlation (DIC) system to collect full-field displacement data that can accurately characterize the effects of U-wrap anchorage on the strain in the flexural CFRP as well as the failure origin and progression. U-wrap anchorage resulted in an increase in CFRP strain at ultimate flexural capacity of up to 68% with a corresponding increase in moment capacity and a change in failure mode. However, varying the ratio of the areas of U-wrap anchorage to flexural CFRP from 3.2 to 9.6 had little apparent effect on the flexural capacity of the beam.