End debonding of CFRP wraps and strips for the strengthening of concrete structures

In strengthening RC elements by means of FRP wraps or strips, bonding between the FRP reinforcement and the concrete substrate is a very relevant aspect. Bonding is influenced by the mechanical and physical properties of concrete, composite and adhesive, as well as by the surface treatment of the concrete substrate. Several relationships are proposed in design recommendations in order to estimate the fracture energy and then the debonding load of the FRP reinforcement from the concrete substrate. These relationships generally include parameters calibrated from experimental push-pull tests. In this work an enlarged experimental database is considered combining results selected in the literature and push-pull debonding tests performed by the authors. Authors' tests were performed with both wraps (13) and strips (17) of different lengths. The debonding load is theoretically evaluated on the basis of the fracture energy concept. The enlarged experimental database is used to achieve a refined calibration of the involved experimental parameters. As a refinement to current bond strength and fracture energy models, calibrations are performed separately for wraps and strips by two different statistical models in order to appreciate the influence of the reinforcement type and model assumption on the debonding load.