Flexural resistance of large RC beams retrofitted with anchored prestressed carbon-fibre-reinforced polymer sheets

Strengthening reinforced concrete (RC) structural members with prestressed carbon-fibre-reinforced polymer (CFRP) sheets has become of interest as it results in greater capacity and rigidity in flexure. However, debonding is a serious problem in flexural members reinforced with CFRP sheets, especially when they are prestressed. An effective cure is to anchor CFRP sheets at their ends. In this study, the bending resistance of large-scale RC beams retrofitted with lower-face CFRP sheets anchored at the ends was numerically investigated, focusing on the effects of prestressing levels and anchorage on debonding mitigation. Recently developed attachment techniques, namely externally bonded reinforcement and externally bonded reinforcement on grooves (EBROG), were applied. The model was verified with experimental results, and then applied to assess the effects of end-anchored retrofitting on final capacity, ductility and failure. Retrofitting resulted in a maximum increase of 215% in the yield load, a 246% increase in the cracking load and a 125% increase in stiffness. The ultimate load was improved when increasing the prestressing level of CFRP from 20% to 30% of its nominal strain, which showed effectiveness of the end-anchorage system in harnessing higher prestressing forces. Nevertheless, intermediate crack-induced debonding remained the dominant failure mode at high prestressing levels, especially when using the EBROG technique.