Fatigue Crack Growth in Cracked Steel Beams Strengthened Using CFRP Strips

Carbon Fibre Reinforced Polymer (CFRP) repair of damaged steel beams has been proven to be effective under monotonic loads as well as under fatigue loading. In this paper, the behaviour of CFRP repaired cracked steel beams under fatigue loading is considered and the fatigue crack growth of damaged steel beams reinforced by using CFRP strips is analysed. Experimental fatigue tests were performed on nine cracked steel beams. Eight beams were reinforced with CFRP strips and then tested, while one un-reinforced beam was used as a reference specimen. The initial crack was created by notching the tension flange and part of the web in the beam for an initial crack length of 20 mm. Then fatigue tests were performed up to a final crack length of about 60 mm. The results in term of fatigue crack propagation curves showed that bonding CFRP strips at the tip zone reduces the fatigue crack growth and increases the fatigue life. Strain gauge measurements along the CFRP reinforcement also showed the existence of a debonded area at the crack location between the reinforcement and the steel substrate. Analytical models accounting for debonding effects were also performed to evaluate the stress intensity factor and to predict the fatigue crack growth curves.