Analytical modeling of bond behavior between FRP plate and concrete

The bonding of FRP plate on the tensile side of concrete members has been accepted as an effective and efficient technology for improving the strength and stiffness of concrete structures. Intermediate crack induced debonding is a common failure mode for FRP strengthened concrete beams. This kind of failure mode can be studied with direct shear test, which involves a FRP plate bonded on a concrete prism with a stretching force acting on one end of the plate. To investigate the failure mechanism of the plate-to-concrete joint, a simplified bond slip model with a linear ascending segment and an exponential softening segment is proposed for the plate-to-concrete interface. With the bond–slip model, the closed-form solutions for the tensile stress in FRP plate, interfacial shear stress and displacement of the FRP plate are derived and verified with experimental results. With the analytical model, a theoretical model is proposed for calculating the effective bond length of a plate-to-concrete joint. Effect of different parameters including stiffness of FRP plate, interfacial fracture energy and interfacial shear strength on the effective bond length are comprehensively studied. Finally, a simple analytical solution of the bond strength for the cases with bond length smaller than the effective bond length is derived and compared with the complicated closed-form solution reported in the literature.