A partial-interaction approach for extracting FRP-to-concrete bond characteristics from environmentally loaded flexural tests

Bonding fibre-reinforced polymers (FRP) to reinforced concrete (RC) members has become a popular means for enhancing load-carrying capacity and extending service life. However, the long-term durability of flexurally strengthened members remains uncertain. In this paper, a numerical solution to a previously developed partial-interaction (PI) moment-rotation approach for intermediate crack (IC) debonding in FRP-strengthened RC flexural members is applied to a set of test results in published literature to extract bond characteristics. This is significant in four respects: (1) the model is based on fundamental PI theory, which directly simulates the formation and widening of cracks associated with the tension-stiffening mechanism, and explicitly allows for any changes at bond interfaces due to environmental loading or corrosion of the steel reinforcement. (2) The model also simulates the mechanism of compressive concrete softening should it occur prior to the complete debonding of FRP laminates. (3) Changes to local bond characteristics at the FRP-to-concrete interface due to environmental loading can be quantified by matching the experimental load-deflection response of deteriorated members. (4) The approach can be applied to a wide range of flexural test data, so as to broaden the bounds of bond-slip models, which are otherwise limited to the bounds of shear bond tests. Using the approach, a set of bond characteristic deterioration factors, derived from full-range load-deflection responses of environmental loaded flexural members, indicate that bond deterioration at the FRP-to-concrete interface generally compromises the ductility and strength of flexural members.