Interface Crack Propagation in Fiber Reinforced Polymer-Strengthened Concrete Structures Using Nonlinear Fracture Mechanics

In this paper, the crack propagation along FRP -concrete interface of FRP-strengthened concrete structures is analyzed by using nonlinear fracture mechanics, in which the concept of mode II fracture is applied to describe the interfacial slip relationship. Two types of the shear stress-slip relationship were proposed, and have been implemented with the mixed finite element methods to perform numerical simulations. A simulation for a simple shear test is carried out to verify the interface crack model. It is found that the interfacial fracture energy is the most important parameter for the bond behavior and the ultimate load can be expressed in terms of the fracture energy. Choosing different bond strength and shear stress-slip relation ship may influence the effective bond length between FRP sheets and concrete. In addition, an example of a FRP-strengthened concrete beam is also analyzed, in which the composite behavior is significantly dependent on the bond strength of strengthened beam, and the debonding propagation and the failure load due to debonding may also be expressed with fracture energy. The fact that cracks are localized or distributed, for plain concrete beams without reinforcing steel bars, is regarded to be affected by bond strength, interfacial fracture energy, concrete tensile strength and mode I fracture energy of concrete.