Externally bonded FRP systems offer an attractive method to improve the fatigue life of steel beams. The fatigue performance of such a strengthened beam can be further enhanced by prestressing the bonded FRP reinforcement. While a number of studies have been conducted on the fatigue strengthening of steel beams using FRP, they have generally been concerned with the overall performance of the strengthened beam, with limited attention to the behaviour of the FRP-to-steel interface and its effects. Against this background, this paper presents the preliminary results of an ongoing experimental program aiming at investigating the behaviour and fatigue failure mechanism of FRP-strengthened cracked steel beams under fatigue cyclic loading, with particular emphasis on the debonding process of the FRP reinforcement and the effect of debonding on crack propagation. The effects of prestressing and debonding on the fatigue performance of the strengthened beam are clearly demonstrated by the test results.
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