Improving fatigue performance of CFRP strengthened steel beams by applying vacuum pressure in the wet layup of CFRP woven sheets

Multiple layers of CFRP woven sheets are generally laminated through a wet layup process with epoxies being evenly distributed in each layer of CFRP sheets. Although attempts were made by researchers to evenly distribute epoxy resin in CFRP layers, the bonding quality is not easily controlled. Air bubbles or excessive epoxy resin may exist in hardened CFRP composites. As a result, the bonding strength may be affected. For the two types of CFRP materials that are commonly used in the strengthening of defected steel structures, CFRP woven sheets are required for curved sections, such as truck chassis and circular sections. The difference in the layup process of CFRP plates and CFRP sheets may contribute to the difference in fatigue life of repaired steel members. In this study, a vacuum bag was used to provide a negative pressure to suck out excessive epoxy resins and air bubbles during the wet layup process. The failure modes and fatigue life of steel beams strengthened with and without vacuum bags were compared. An increase in fatigue life was found to be ranging from 50 to nearly 4 times.