Experimental assessment of U-Wrap anchorage in reinforced concrete girders strengthened with externally bonded CFRP

Abstract

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 of a strengthened concrete member. 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 girders 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 quantified by the anchorage ratio. 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 57% with a corresponding increase in moment capacity and a change in failure mode. However, varying the ratio of ratio of the areas of U-Wrap anchorage to flexural CFRP had little apparent effect on the flexural capacity of the girder.