Behavior of RC T-Beams Strengthened in Shear with CFRP under Cyclic Loading

This study investigated the shear performance of an RC beam strengthened in shear with externally bonded carbon fiber-reinforced polymer (CFRP) strips, subjected to a cyclic loading for 2 million cycles at 1 Hz. The stress level in the stirrups caused by the cyclic loading used in this study was higher than those typically used in fatigue studies, which could have caused the yielding of some stirrups from the beginning of cyclic loading. This was done to reflect the fact that many RC beams in need of shear strengthening do not meet the minimum stirrup requirement for the new and increased shear demand. The experimental results obtained in this study and a comprehensive review of the existing literature showed that RC beams strengthened in shear with externally bonded CFRP could survive 2 million cycles of cyclic loading without failure. Furthermore, the residual shear strength of the FRP-strengthened beam appeared to be greater, albeit slightly, than the static shear strength of the unstrengthened control beam. This study’s results also suggested that limiting the interfacial stress in CFRP strips to less than 1.5 MPa or 25% of its ultimate interfacial strength would increase fatigue life by avoiding debonding of CFRP strips.