Cyclic behaviour of FRP-to-concrete bonded joints: An experimental study

Flexural strengthening of reinforced concrete structures using externally bonded FRP laminates has gain wide acceptance among design professionals as an effective strengthening and retrofitting technique. Effectiveness of such strengthening systems relies heavily upon the interfacial shear stress transfer mechanism of the bonded interface. Extensive research has been carried out to better understand and model the behaviour of FRP-to-concrete bonded interfaces under quasi-static monotonic loading. On the contrary, much less work has been done so far on understanding the behaviour of FRP-to-concrete bonded joints under cyclic loading. Ability to understand and model the behaviour of FRP-to-concrete bonded interfaces is essential in predicting the long-term performance of FRP-to-concrete bonded joints. This paper presents the results from a series of single-shear pull off tests aimed at investigating the behaviour of FRP-to-concrete bonded joints under quasi-static cyclic loading. Load-displacement, strain distribution along the bond-length at different loads, interfacial shear stress distribution along the bond length at different loads, and bond-slip curves at different locations along the bond length are presented and discussed. Test results are used to verify the accuracy of several assumptions made in existing theoretical bond-slip models under cyclic loading. Some of the assumptions made in developing the existing theoretical solutions were found to be not in agreement with the test observations.