Abstract The demand for reinforcement and repair of existing bridges is constantly growing due to the increase of traffic volume and operational load. Near‐surface mounted (NSM) fiber‐reinforced polymer (FRP) method is recognized as a prominent strengthening system, and the bonding capacities of FRP bars in concrete are critical factors affecting their reinforcing efficacy. However, since bridges frequently endure fatigue loads during actual service, the successful application of NSM FRP technology in building construction requires a profound understanding of interface fatigue performance. In this study, the bonding behavior of NSM FRP bars in concrete with epoxy adhesive was evaluated by the parameters of load level, FRP bar type, and cycle number based on pull‐out specimens. In addition, to gain insight into the failure mechanism of the interface, the destroyed surface of the NSM FRP–concrete joint was assessed via scanning electron microscopy (SEM). The results indicated that the failure modes subjected to monotonic and fatigue loads were epoxy adhesive splitting and failure of concrete adjacent to the groove, respectively. With the increase of load level, the fatigue life decreased significantly, and the slip value increased between 14.53% and 59.44% compared to the specimens with a load level of 0.45. A certain load level was beneficial to the interface stiffness, but improving the load level would increase the accumulation of fatigue damage and reduce the bond stiffness. The FRP bar types had no obvious influence on the fatigue life of bonded specimens. However, the slip values of NSM GFRP bars in concrete at load levels of 0.45, 0.55, and 0.65 were 22.22%, 40.38%, and 70.15% higher than those of NSM BFRP bars in concrete, respectively. The number of cycles could eliminate the initial defects, raising the bond stiffness of the interfaces by 17.01% to 30.12%. The failure mechanism of the NSM FRP–concrete interface using epoxy adhesive was uncovered by SEM. Under monotonic loading, the epoxy adhesive splitting was mainly caused by the radial tensile stress along the bond length. Under fatigue load, the specimens were mainly damaged in the concrete adjacent to the groove by the mixture of tension and shear force.
Zhang et al. (Tue,) studied this question.