Fatigue Behavior and Prediction of NSM CFRP-Strengthened Reinforced Concrete Beams

Abstract

In this study, a total of 16 reinforced concrete beams (dimensions of 203×305×3,861 mm) strengthened with near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) rods and strips were tested under four-point bending fatigue loading. Monotonic loading was applied to their corresponding control specimens to obtain the static monotonic flexural strength. Fatigue loading with a range of 10% of the corresponding static strength to various upper limits was applied to determine the empirical relationship for each type of specimen. It was found that the dominating failure mode under fatigue was rebar rupture. Mixed failure modes of rebar rupture and unstable cracks in concrete were also observed in specimens with longer fatigue life. As the specimens underwent more fatigue cycles, an increase was observed in their tensile strains of CFRP and deflections due to accumulated damages and the losses of stiffness. A fatigue bond model was developed, which simulated the process of fatigue loading as fatigue crack growth at the NSM-epoxy interface. Based on the comparison with experimental data, the model predicts well the bond behavior and progression of the debonded length for most of the fatigue life.