A simple and rational beam segment model for analyzing intermediate crack-induced debonding in FRP-strengthened beams

Intermediate crack (IC) induced debonding failure of fibre reinforced polymer (FRP) plate strengthened reinforced concrete (RC) beams is one of the common debonding modes, in which debonding initiates at a major flexural crack and then propagates toward a plate end. Finite element (FE) method has been used to analyze the IC debonding failure and a whole strengthened beam has been taken as a mechanical model in existed researches. In view of that it is difficult to appropriately simulate all the cracks in an entire strengthened beam and consequently to carry out a parameter study, a beam segment between two major adjacent flexural cracks in a flexural-shear zone of a strengthened beam was taken as a new simple mechanical model. The new simple “beam segment model” was validated to be rational by using Saint–Venant Principle and a numerical study. In the light of this, a parameter study was performed through a three dimensional nonlinear FE analysis of the proposed beam segment model. The influences of the load level, the bond-slip (δ–τ) relationship of FRP-to-concrete interface, and the geometry of the beam segment on the IC induced debonding were investigated. The numerical analysis shows that the influence of δ–τ relationship of FRP-to-concrete interface on debonding is fairly more significant than that of crack spacing of strengthened beams. Comparisons between analytical and experimental results show that the proposed beam segment model is appropriate for estimating the IC induced debonding.