Fatigue testing of defected steel beams repaired using medium and high modulus CFRP strand sheets

CFRP sheets are extensively used to strengthen defected steel members through a wet layup process. Different techniques were used to control the quality of bonding, such as vacuum bags and rollers. However, air bubbles and excessive epoxy resin might still exist between CFRP layers, causing the reduction in bonding strength. To address this issue, strand CFRP sheets were recently applied in the strengthening of steel elements by some researchers. The advantage of strand CFRP sheets is that CFRP fibre was impregnated with resin to form hardened strands at factory conditions. As a result, the bonding quality during the wet layup can be improved. In this study, two types of strand CFRP sheets, with Young's moduli of 430GPa and 690GPa, were applied on defected steel beams. Eight specimens were tested under four point bending. The failure modes and fatigue life of the specimens were compared with those of specimens strengthened with normal CFRP sheets and CFRP plates. Results showed that the fatigue life of defected steel beams strengthened with high and medium strand CFRP sheets is comparable to that of beams strengthened with CFRP plates and other high modulus CFRP sheets.