Stress–cycle curves for concrete beams with fibre-reinforced polymer using runout data

The use of externally bonded fibre-reinforced polymer (FRP) increases the fatigue life of reinforced-concrete beams due to a reduction in the steel stress level when compared with unstrengthened beams. For steel stresses up to 80% of the yield stress, fatigue failure is normally marked by the gradual deterioration of the steel reinforcement, which leads to a stress transfer to the FRP, until failure. Higher steel stresses are associated with FRP debonding, while steel stresses below the fatigue limit will never lead to fatigue failure. In this work, the maximum likelihood estimation method was used to determine stress–cycle curves and confidence intervals. Experimental data with runouts of fatigue tests found in the literature and generated through an experimental programme were used to adjust the fatigue model. The aim was to characterise the large scatter between the results of fatigue tests from different sources. The proposed fatigue model was found to represent accurately the slope of the fatigue curve for FRP-strengthened beams.