Crcak-induced Interficial Debondinganalysis In FRP Strengthened Concrete Beams

In recent decades, given such adwantages as low weight compared to strength,immunity to corrosion, low creep, ease of application on site and so on, Fiber ReinforcedPloymer(FRP) has became increasingly polular in structural retrofit industries. TheInterface between the FRP plate and concrete plays a critical role in this strengtheningmethod by providing effective stress transfer from the existing structures to externallybonded FRP plates and keeping integrity and durability of the composite performance ofFRP-concrete structures.The bonding of FRP plate on the tensile surface has been proved to be an effectivemethod to increase both the strength and stiffness of concrete members. However,debonding along the FRP-concrete interface can lead to premature failure of the structureThereforce, it has underlined the need to understand the debonding mechanism ofFRP-Concrete Interface under different fracture modes.In this thesis, theoretical analysis and numerical simulation method are adopted tocharacterize the debonding performance of FRP-Concrete Interface under two differentfracture modes, which is based on experimental data. Different problems related tocrack-induced debonding of the FRP plate in the flexural strengthened concrete beamshave been investigated.(1) Based on the results in direct shear test, the investigation focuses on the effect ofconcrete composition on the bond behavior between FRP and concrete. The results showsthat the bond capacity of the specimen is found to be governed by the concrete surfacetensile strength, aggregate size and aggregate content. Then, adopting the three parametersmodel, an analytical model has been developed to study the debonding behavior in thedirect shear test, and a Linear Frcature Mechanics Approach is employed to study ultimatebearing capacity at the FRP-concrete interface, the expression for bearing capacity ofFRP-concrete interface under Mode II is derived. Besides, good agreement between thetheoretical and experimental results can be achieved. Last, through the numerical analysis,parameters study is carried out to study the influence of different factors on debondingfailure.(2) Based on the results in four-point bending test, considering the influence of the verticaldisplacement on the debonding behavior, a four parameters shear-slip model have beendeveloped to study a flexural/shear crack-induced debonding behavior under mixed mode. The simulated results and experimental results can achieved good agreement. Comparisonis carried out between a flexural/shear crack-induced debonding and a flexuralcrack-induced debonding. The results shows the vertical displacement can rapid the FRPdebonding from concrete beams.(3) The debonding behavior of FRP-concrete interface is simulated through the techniqueof ABAQUS under four-point bending test. The simulated results and experimental resultscan achieved good agreement. Besides, the results shows FRP can slow the propagation ofcrack, reduce the deformation of the beams, increase both the strength and stiffness ofconcrete members.