Investigation of intermediate crack debonding in reinforced concrete beams strengthened with fibre reinforced polymer plates

Abstract

External bonding of fibre reinforced polymer (FRP) composites has become a popular technique for strengthening of concrete structures all over the world. However, the plates are susceptible to debonding prematurely. Intermediate crack (IC) debonding (also known as axial peeling) is one of the mechanisms of debonding leading to failure. The IC debonding may arise at a major flexural crack to the plate end but occasionally it also propagates from the plate end, in the case of diagonal shear cracks. It is the mechanism of debonding that controls the flexural capacity of the beam as well as the sectional ductility. This paper deals with the investigation of IC debonding in tension for face-plated and side-plated reinforced concrete (RC) beams using different types of FRP plate material. The elastic modulus and ultimate tensile strength of the plates of different materials vary between 28-300 GPa and 300-2800 GPa respectively. Tests show that the IC debonding is a gradual process in tension for face-plated beams in comparison to side-plated. The beam bonded with low modulus FRP (i.e., glass ERR) was more ductile than the carbon ERR plated beams. The analytical procedures adopted to draw the moment-curvature relationship in this study are capable of predicting the ultimate flexural capacity (M-peel) of the plated beams with very good accuracy, and are validated with test results from the present study and from the published literature.