FRP-Concrete Bond Behaviour Under Cyclic Debonding Force

The strengthening of concrete structures against earthquake actions is one of the most important application of FRP; nevertheless, the effect of cyclic forces on FRP - concrete bonding has been scarcely experimentally investigated. This paper presents the results of an experimental campaign on FRP-concrete specimens subject to shear cycles at very high force levels, typical of earthquake excitation. Both CFRP plate and CFRP sheet have been tested. An experimental set-up (single shear test) allowing for stable debonding process has been adopted and both strain gauges along the FRP plate and LVDT transducers have been used. The sequences of the cyclic loadings under traction have been prescribed by controlling the progression of the debonding. It is shown that the debonding force is not affected by cyclic loadings; a small degradation of the interface behaviour, with the reduction of the maximum shear stress, has been detected only after the onset of debonding. Nevertheless, this reduction, analogous to that showed by monotonic loading tests, remains constant during the development of the debonding and is not modified by further application of cyclic loads at very high force level.