Concrete DIF and its application in modelling the behaviour of FRP-concrete bond

Debonding at the FRP-concrete interface is one of the main failure modes in RC structures strengthened with externally bonded FRP under dynamic loading. Most debonding failures occur in the concrete adjacent to the FRP under static loading. Similar failure occurs in many cases under dynamic loading, although the mode shift phenomenon exists where failure may occur in the adhesive layer or at the concrete-adhesive or adhesive-FRP interfaces. This paper is concerned with the FRP debonding failure where failure occurs in the concrete adjacent to the adhesive-concrete interface, as in most static loading cases. It is well known that the strength of concrete-like materials under high strain rate events is higher than that under static loading, and this increase of strength is described commonly using the Dynamic Increase Factor (DIF). This paper presents a numerical study on the uniaxial tension DIF, with a particular focus on how the DIF may be included in an appropriate manner in the FE modelling using a local concrete model. The inevitable mesh-dependency issue due to numerical localization and its implications on the rate effect in meso-scale modelling of FRP-concrete bond behaviour are discussed.