Energy release rate of interface crack in RC beams strengthened with fiber reinforced polymer under four point bending

A popular method for strengthening reinforced concrete (RC) beams is to bond fiber reinforced polymer (FRP) plates to the soffit. An important failure mode for such retrofitted members is debonding of the FRP plates from the member due to high interfacial stresses near the intermediate crack. Accurate prediction of the energy release rate of interface crack between FRP and concrete is a prerequisite for designing against debonding failure. In this paper, a theoretical analysis was conducted to investigate the energy release rate of interface crack embedded in the FRP-plated RC beam subjected to four point bending. A mechanical analysis model including the consideration of the major flexural crack and tension steel reinforcement was established for the interface crack tip of plated RC beam. The deflection of the FRP-plated RC beam and the axial force in the plates were analyzed on the basis of the classical beam theory. The compliance of plated RC beam was derived before the tension steel yielding, and a theoretical solution of the energy release rate was then proposed. Moreover, numerical results based on the proposed theoretical model were presented to illustrate the effects of various parameters on the energy release rate of interface crack in the plated RC beam. © Smithers Information Ltd., 2014.