Peeling behaviour of reinforced concrete beams strengthened with CFRP plates under various end restraint conditions

Reinforced concrete (RC) beams strengthened with externally bonded fibre-reinforced polymer (FRP) are shown to have higher flexural capacity compared to unstrengthened specimens. However, concrete cover or FRP peeling may occur before the beam can achieve enhanced capacity. Thus, the FRP efficiency can be greatly reduced due to this premature failure. This research presents an experiment programme conducted to examine the peeling behaviour of strengthened beams under various end restraint conditions. In the experiment, carbon fibre-reinforced polymer (CFRP) plates were applied to strengthen RC beams and carbon fibre-reinforced sheets were used as end wrapping material. Three different wrapping schemes, namely, U-, L- and X-wrappings were examined. Without wrapping, the FRP-strengthened beams showed little strength improvement over unstrengthened ones. For U-wrapped strengthened beams, end peeling could be prevented but shear-flexural peeling followed by premature concrete crushing took place instead. For L- and X-wrapped beams, neither end peeling nor shear-flexural peeling was observed and the beam failed in flexural concrete crushing mode.