Bond Behavior Between Shear Strengthening FRP And Concrete:an Experimental Study

Fiber Reinforce Polymer (referred to as FRP for simplicity) has been widely used to strengthen existing different types of structures in civil engineering. Shear strengthening of RC structures using externally bonded (EB) FRP is an important application of FRP in structural strengthening reinforced. In an RC beam shear strengthened with EB FRP, FRP debonding is a typical failure mode. In current strength models and design formulae, it is common practice to use the bond strength models deduced based on the experimental data of FRP-to-concrete bonded joint tests (i.e. simple shear test or double shear test) to obtain the shear contribution of shear-strengthening FRP. However, the stress states of the FRP-to-concrete bonded interfaces in FRP shear-strengthened RC beams is quite differently from those in single shear test (or double shear test).Thus the shear strength model, deduced based on the test data of the FRP-to-concrete bonded joints, may overestimate the shear contribution of FRP, leading to unsafe result. Against the above background, in this study have deployed a new test method, namely small beam specimens with a pre-set through-crack and FRP strips bonded to their sides, to study the bond behavior between shear-strengthening FRP and concrete. The research contents presented in this thesis mainly include the following two parts:(1) A total of 20 small beams specimens were tested with four point bending to study the influences of a number of factors incluidng the bond length, strip width, and fiber tensile angle (the angle between fiber orientation and crack opening direction) on the bond behavior between shear-strengthening FRP and concrete. Test results showed that:(a) the failure modes of all beams are FRP debonding, which shows that the small beams test set-up with a pre-set crack is suitable for studying the bond behavior between FRP and concrete; (b) the FRP bond length, width of FRP strips as well as the fiber tensile angle have significant effects on the bond behaviors of FRP-to-concrete bonded interfaces; (3) the distribution of FRP force and FRP strain along the direction perpendicular to the fiber orientation is non-uniform and nonlinear; this is mainly attributed to the progressive debonding of the FRP strips in the width direction, with the FRP strips at the location of larger crack width debonding earlier.(2) Four small beams specimens were tested in which Particle Image Velocimetry (referred as PIV) was used for the further study of the bond behavior between shear-strengthening FRP and concrete. Test results showed that:(a) the digital image of PIV technology can be used to the study of the bond behavior between FRP and concrete, (b) the FRP stress distributions obtained from PIV shows that with the increase of load, the maximum interfacial shear stress is propagated from the mid-line of FRP length to the two free ends; and along the FRP strip width direction, the distribution of shear stresses is non-uniform.