Fatigue testing of defected steel beams retrofitted using sandwich-layered high and normal modulus CFRP sheets

CFRP sheets are extensively used to strengthen defected steel members due to the advantages of high strength and light weight of CFRP. Among different types of CFRP sheets, high modulus sheets showed better performance in extending the fatigue life of defected steel elements. It was found that fibre breakage was the main failure mode for specimens reinforced with high modulus CFRP sheets comparing to debonding failure in the interface between CFRP and steel for specimens repaired with normal modulus CFRP. It is generally believed that failure should occur within the adhesive layer in the form of cohesion failure so that the FRP material can be better utilised. In this study, CFRP sheets with high and normal modulus were applied in a sandwich layered manner. Fatigue tests were conducted with fatigue life being compared with those obtained from previous tests. Results showed that failure happened consistently in the interface of steel and epoxy resin with a fatigue life of around 80% of that strengthened with high modulus CFRP sheets only.