Fatigue performance of tensile steel members strengthened with CFRP plates

In this paper the fatigue behaviour of steel structures retrofitted by using FRP materials is investigated. Preliminary tests were performed at different loading conditions to assess the fatigue performance of unconditioned double sided reinforcement specimens. The stiffness degradation of the reinforced member due to progressive debonding of the adhesive was selected as an index for a subsequent and progressive global failure. Failure mechanisms were observed to start with initial debonding at the plate end and then failure propagated along the element in the interfaces. Visual inspection of the bonds after failure revealed that the adhesive/metal interface represents the weakest point of the reinforcing system. S–N curves were defined and the fatigue behaviour of the specimens was compared to the fatigue resistance of welded detail categories described in the Eurocode 3. The results showed that fatigue resistance of the bond between the steel plate and the CFRP plate is remarkably superior to that of welded cover plates (Eurocode 3 categories 36*–56*).