Experimental determination of FRP–concrete cohesive interface properties under fatigue loading

An experimental investigation of the fatigue behavior of externally strengthened concrete with fiber-reinforced polymers (FRP) is conducted. In the experimental program, strain patterns along the bonded length and the surrounding concrete are determined using digital image correlation. The results herein presented indicate that debonding occurs during fatigue and it is related to the load range. The post-fatigue bond capacity of the interface is not affected by the previous cyclic loading if the remaining bonded part is enough to fully establish the stress transfer zone associated with quasi-static crack growth. Although further research is needed, this work points out several new and interesting aspects of the fatigue behavior of the FRP–concrete interface: (1) during fatigue loading the length of stress transfer zone is smaller than the stress transfer zone associated with the cohesive crack under quasi-static loading; (2) post-fatigue results suggest the possibility of a different debonding mechanism during fatigue loading; (3) fatigue life is dominated by crack initiation for fatigue loading with high amplitude and by crack propagation on decreasing the amplitude of fatigue load cycle.