FRP-Concrete behaviour under cyclic debonding force

Strengthening of concrete structures against earthquake actions is one of most important application of FRP; in particular, when strengthening interventions on beams in flexure are designed, effect of cyclic forces inducing very high bond stress regime has to be taken into account in order to avoid premature debonding. This paper presents first results of an experimental campaign on cyclic behavior of FRP-concrete interface. In the present study, a CFRP plate and a CFRP sheet have been bonded to concrete prisms and tested with cyclic loading adopting an experimental setup allowing for stable debonding process. Sequences of cyclic loading, from traction to complete unloading, have been prescribed by controlling the progression of debonding. Both strain gauges along the FRP plate and LVDT transducers have been used. It is shown that debonding force is not affected by cyclic loadings; a small degradation of interface behaviour has been detected after the onset of debonding, with reduction of maximum shear stress. Nevertheless, this reduction remains constant during subsequent phases of debonding and its not modified by further application of high level of cyclic loads.