A comparative study on fatigue behaviour of steel beams retrofitted with welding, pultruded CFRP plates and wet layup CFRP sheets

This paper investigates the fatigue behaviour of defected steel beams retrofitted with three different methods, i.e., welding, welding and bonding with CFRP plates or CFRP woven sheets laminated via a wet lay-up process. Two different types of CFRP materials and two types of epoxies were selected in this study. An initial cut was made on the tensile flange in the mid span of each beam. Different failure modes were observed for beams retrofitted with CFRP plates and CFRP sheets. It was found that one layer of CFRP plate and epoxy strengthening system can extend the fatigue life of steel beams about 7 times comparing with beams repaired with solely welding method, while the fatigue life was extended abound 3 times for beams strengthened with 4 layers of CFRP woven sheets. Mean S–N curves were obtained based on the test data, that can be used to predict the fatigue life of steel beams retrofitted with similar CFRP materials. The crack propagation rate was measured using strip strain gauges. The CFRP plates showed better performance in resisting crack propagation than CFRP sheets under fatigue loading conditions. The relationship between the maximum stress and the crack propagation rate could be used to predict the crack length of beams retrofitted with similar CFRP strengthening systems.