Debonding along the FRP–concrete interface under combined pulling/peeling effects

The bonding of fiber reinforced plastics (FRP) plates or sheets to the concrete beams has been found to be an effective technique for flexural strengthening. In a reinforced concrete beam, debonding may be induced by a major flexural/shear crack in the span. Under such condition, there is relative vertical displacement on the two sides of the major crack. The FRP is then under both pulling and peeling forces, resulting in a combination of shear sliding and opening displacement along the FRP/concrete interface. In this investigation, using a novel experimental set-up, the effect of combined pulling/peeling on FRP debonding is studied. A new theoretical model for debonding analysis under such a situation is developed. In the model, the interfacial behavior is described by four parameters, with one of them, the interfacial shear strength, affected by the maximum interfacial normal stress. With a set of parameters obtained from two of the specimens, the model is able to describe the debonding behavior of FRP for various specimens with different thickness and under various degrees of peeling effect. The applicability of the proposed analytical approach to the analysis of interfacial debonding under combined pulling/peeling effects in real material systems is hence demonstrated.