Minimum bond length and size effects in FRP-substrate bonded joints

The load transfer mechanism between the fibre-reinforced polymer (FRP) materials and the substrate plays a crucial role in the overall response of retrofitted structural members. The FRP–support material interface can be studied by using pull tests in which a reinforcement plate is bonded to a prism and subjected to a tensile force. The experimental results obtained regard the assembly (FRP strip-support block), then a central problem is how to carry out the interface constitutive laws and the related parameters. The principal objective of the present paper is to contrive a procedure which, for a fixed interface constitutive law, permits to derive the interface mechanical parameters from the pull tests experimental data. This procedure has its basis on the size effect phenomena which the experimental tests evidence. Furthermore, the size effect laws show that the effective or minimum bond length coincides with the internal length of the interface and permits to distinguish small and large specimens in the sense of fracture mechanics.