Strength model for intermediate flexural crack induced debonding in RC beams and slabs

A variety of debonding failure modes have been observed in tests on reinforced concrete (RC) beams strengthened by bonding fibre reinforced polymer (FRP) plates to their tension face. These can be broadly classified into two types: (a) those associated with high interfacial stresses near the ends of the bonded plate; and (b) those induced by a flexural or flexural-shear crack away from the plate ends. The first type of failures has been extensively studied, leading to many strength models. By contrast, the second type of failures has received much less attention, and no strength model appears to have been developed for it. This paper is therefore concerned with the second type of failures induced by a flexural crack, which is referred to as intermediate flexural crack induced debonding. The mechanism of this type of debonding failure is first examined briefly, highlighting the similarity between such debonding failures and those in simple shear tests of FRP-to-concrete bonded joints used for determining bond strengths. A bond strength model based on test results of these joints is then compared with the limited test results of intermediate crack induced debonding failures to develop a suitable debonding strength model.