Realistic Bond Strength of FRP Rebars in NSC from Beam Specimens

摘要

This study concerns the interfacial bond strength between FRP rebar and normal strength concrete (NSC). Three different types of rebars were tested using the beam specimens carbon (CFRP); glass (GFRP), and steel. This involved a total of 26 beam specimens containing 10-, 16-, and 19-mm rebars. The test embedment lengths were 10, 15 and 20 times the rebar diameter (d{sub}b). For each rebar tested, the results concern load deflection curves, bond stress-slip constitutive relationships and the mode of failure. For evaluation purposes, the test results from a previous study on pullout specimens by the authors are also included. Based on these results, a proposal for the average bond strength of straight FRP rebars under tension in NSC is made. Introduction The investigation of the bond strength of reinforcing bars in concrete is usually carried out using the pullout specimen because it is economically feasible. Moreover, many of the influencing parameters on the bond behavior can be considered in such a test program. However, some researchers have noted the fact that, the results of pullout tests give an upper bond value for the bond-slip performance of a reinforcing bar (Benmokrane et al. 1996). This is because, in the pullout test, splitting of the concrete is avoided by the thickness of the concrete cover and by the confining action of the reaction plate on the concrete specimen. The eccentric pullout test (splitting test) Okelo (2002) is thought to be a more realistic representation of what happens in a beam, but Lutz and Gergely (1967) found that it does not allow diagonal tension cracks common in beams to form. In beam tests the concrete surrounding the reinforcing bar is under tension, causing eventually, diagonal tension cracking at low stresses and hence reducing bond.