Fatigue retrofitting of cracked steel beams with CFRP laminates

In recent years, carbon fiber-reinforced polymer (CFRP) externally bonded to steel members has been considered an effective technique for fatigue crack repair of steel components. This paper investigated the fatigue behavior of six cracked steel beams strengthened using CFRP laminates via two approaches, i.e., sole adhesive bonding and adhesive bonding together with mechanical anchorage. Two types of epoxies were selected to compare the effectiveness. The tensile flange of the steel beam was artificially cut to simulate an initial crack. A digital image correlation (DIC) system was adopted to detect strain distribution along the retrofitting patches. Different failure modes were observed for specimens with different retrofitting schemes. Test results showed that, in comparison with control specimens with sole adhesive bonding, application of mechanical anchorage significantly retarded crack propagation and extended fatigue life of the steel beams attributed to the pronounced frictional bond. The crack mouth opening displacement (CMOD) was also considerably reduced. The displacement fields obtained from the DIC recorded at specific crack lengths were analyzed to provide information on strain distribution along the CFRP laminates and corresponding bond-slip relationship. This study extends the understanding of fatigue repair for steel beams and provides useful suggestions for the strengthening method.