A novel numerical approach for modelling the monotonic and cyclic response of FRP strips glued to concrete

The mechanical behaviour of the adhesive interface between the FRP strips and the concrete substrate often controls the response of FRP-strengthened RC members. Plenty of studies devoted to understanding the mechanical behaviour of FRP strips glued to concrete mainly focused on their response under monotonic actions, which are certainly relevant in a wide class of practical applications. On the contrary, few contributions are currently available to better understand the response of FRP-to-concrete interfaces under cyclic actions, such as those deriving by either seismic excitations or traffic loads. This paper presents a novel numerical approach to simulate such a response. Particularly, a damage-based approach is formulated to simulate the fracture behaviour of FRP-to-concrete joints under loading/unloading cycling tests. The model is formulated within the general framework of Fracture Mechanics and is based on assuming that fracture at the FRP-to-concrete interface develops in (pure shear) mode II, as widely accepted in similar problems. Two alternative expressions of the bod-slip behaviour are considered herein and a preliminary validation is finally proposed