Studies On FRP-Concrete Interface With Tri-linear Bond-Slip Law

External bonding of fiber reinforced polymer (FRP) plates or sheets has emerged as a popular method for the strengthening of reinforced concrete (RC) structures. In this strengthening method, the performance of the FRP-to-concrete interface in providing an effective stress transfer is of crucial importance. Therefore, for the safe and economic design of externally bonded FRP systems, a sound understanding of the behavior of the FRP-to-concrete interface needs to be developed.This paper presents a close-form analytical solution of both interfacial shear stress distribution and load-displacement response, which is capable of predicting the entire debonding propagation process including elastic, elastic-flow, elastic-flow-softening, elastic-flow-softening-debonding, flow-softening-debonding, and softening-debonding stages. Based on experimental result of high Young's modulus type of CFRP-to-concrete bonded joints, a nonlinear fracture mechanics method, in which the trilinear local bond slip law is employed, is used to understand the stress transfer mechanism, interfacial crack propagation and ductility behavior in adhesive bonded joint. It is also shown how experimental load-displacement response of bonded joints can be used to identify interfacial properties, including the interfacial fracture energy and parameters of the local bond-slip relationship. The concept of serviceability limit state and ultimate limit state is considered.The major contributions of the work presented in the thesis are listed as follows:(1) First, based on the trilinear local bond-slip model, a nonlinear fracture mechanics method is used to get a close-form analytical solution of the full-range debonding behavior along FRP-to-concrete interface, including the interfacial shear stress distribution and load-displacement response. Then, its load-carrying capacity, effective bond length and debonding propagation behavior are obtained.(2) Comparing with the closed-form analytical solution, experimental load-displacement response of bonded joints can be used to identify interfacial properties, including the interfacial fracture energy and parameters of the local bond-slip relationship.(3)With the identified interfacial properties, numerical simulations are conducted to study the influence of parameter of FRP-to-concrete interface, including the effective bond length and FRP plate stiffness, load-displacement response, ultimate load and effective bond length.(4) Based on the fully understanding the debonding behavior of FRP-to-concrete interface, comparison of experimental and theoretical analysis, including load-displacement response, the effective bond length, interfacial shear stress and axial stress distribution, is used to better understand the full range behavior and the parameter of FRP-concrete interface. It tries to provide a reliable theoretical basis for FRP-strengthened concrete technology.