Fatigue behavior of notched steel beams reinforced with bonded CFRP plates: Determination of prestressing level for crack arrest

This paper presents the findings of an experimental and theoretical study on the behavior of notched steel beams reinforced by non-prestressed and prestressed bonded CFRP (carbon fiber reinforced polymer) plates under cyclic loading, with specific attention to the effect of crack propagation and FRP-to-steel debonding on the fatigue crack growth (FCG) rate. A fracture mechanics based model is proposed in order to estimate the required prestressing level needed to arrest the crack propagation in the notched beams. Several strengthened beams are tested under different fatigue loading ranges and the experimental results show good agreement with the proposed fracture model. An optical image correlation system (ICS) is used to track the crack tip and observe the crack development pattern as well as to provide information about stress distribution at the vicinity of the crack tip. Experimental results show that the fatigue life of a beam reinforced by the prestressed CFRP plate increases more than five times of that of an identical beam reinforced by non-prestressed CFRP plate. Prestressing also significantly reduces the residual deflection during the FCG process. Furthermore, it is shown that as the stiffness of the FRP-to-steel bond joint reduces the FCG rate increases, while as the crack grows (in steel web) the FCG rate decreases.