Fatigue behavior of reinforced concrete beams strengthened with externally bonded prestressed CFRP sheets.

An experimental study was conducted to investigate the fatigue behavior of RC beams strengthened with posttensioned prestressed carbon fiber-reinforced polymer (CFRP) sheets. The experimental program consisted of nine rectangular-section simply supported RC beams: four beams were statically tested to failure to determine the values of the fatigue loads to apply, and the remaining five beams were tested under fatigue load. The main purpose of the fatigue tests was to gain a better understanding of the fatigue performance and failure modes of RC beams strengthened with posttensioned prestressed CFRP sheets. The experimental results indicated that the fatigue failure mode of the prestressed CFRP sheet-strengthened RC beams was the tensile steel reinforcement rupture at the main cracked section. Moreover, the fatigue performance of the prestressed CFRP sheet-strengthened RC beams was significantly better than that of both unstrengthened and nonprestressed CFRP sheet-strengthened beams. Finally, a fatigue life prediction model that considers the gradual deterioration of performance of the component materials and partial debonding of the FRP was presented and applied to predict the fatigue life of 28 tested beams with two extreme FRP-to-concrete interfacial states. The results showed that the predicted fatigue life was close to the experimentally measured fatigue life for the fully bonded state. Thus, the effectiveness of the proposed model was verified, and the effect of fatigue load-induced FRP debonding along the beam substrate on fatigue life prediction was found to be insignificant