String debonding effect of curved RC member reinforced by bonding FRP in intrados

The bonding tests of FRP (fiber reinforced polymer/plastic)-concrete interfaces of 26 curved surface specimens were executed, and the influences of concrete strength, FRP bonding layer numbers, FRP bonding length, and component curvatures on the adhesive strength, interface strain and failure mechanism were investigated. Research result shows that there are three kinds of failure modes in curved concrete members, including the string peeling, FRP fracture at the crack, FRP peeling on the crack side. The greater the curvature of the component, the more likely the string peeling will occur. FRP tensile failure often occurs in small curvature members. With the increase of external load, the peak value of FRP strain has a backward transfer process. It is shown that the FRP along the fiber length is not all involved in the work, and there is an effective working (bonding) length. The analysis result of the test data by the virtual zero point method shows that the effective length of FRP pasted on curved concrete members is about 14 cm. The curvature has a significant effect on the adhesive strength. With the increase of the curvature, the changing gradient of the fiber strain increases, the effective adhesive length becomes shorter, and the adhesive strength decreases. When the curvature is the same, the more the number of fiber layers, the more uniform the strain distribution along the fiber direction and the higher the adhesive strength. But this increase is not linear with the number of FRP layers, and the adhesive strength with two layers of fiber is about 1.5 times of that with one layer. When the number of fiber layers increases, the normal stress of the adhesive layer increases rapidly, and the specimens are more prone to string-debonding failure. This failure is caused by the coupling effect between the normal bonding stress and in-plane shear stress. The stress function of the pasting layer can be expressed by the cosine function of the center angle of internal arc curvature. When the vector height is 30, 60, and 90 mm, the average error of the component is 7.7%, 2.4%, and 8.8%, therefore, the function has higher accuracy.