Influence of bond deterioration on the flexural response of FRP strengthened RC beams

Bonding fibre-reinforced polymer (FRP) composites to tensile faces of deficient concrete structures as a means of increase loading capacities and prolonging service life is now common practice. Although FRP application for flexural strengthening is widespread, there is uncertainty surrounding the long-term durability of these strengthening systems. Unlike conventional reinforced concrete flexural members, which are designed to fail in a ductile manner, that is steel yielding followed by concrete crushing, FRP-strengthened member are susceptible to brittle debonding failures. The focus of this study is on intermediate-crack (IC) debonding which is typically isolated by means of shear bond tests. In this paper, a previously developed partial-interaction moment-rotation approach for IC debonding is applied to sets of experimental data in published literature to extract bond characteristics from the FRP-to-concrete interface. The bond characteristics are extracted from deteriorated members to assess the changes at the bond level and are compared with predictions from existing bond-slip models for deteriorated joints. Using the approach, it is found that the environmental loading of FRP-strengthened flexural members generally reduces both the maximum bond stress the slip necessary to initiate IC debonding, thereby compromising the ductility and strength of the member