Interface Fatigue Test of Hybrid-Bonded Fiber-Reinforced Plastic-Reinforced Concrete Specimen

This research produced five hybrid-bonded fiber-reinforced plastic (HB-FRP)-reinforced beam specimens, and different fatigue load amplitudes were used as parameter variables for the fatigue performance tests of the FRP–concrete interface. The results show that FRP sliding with the number of cycles can be roughly divided into fatigue initiation stage, fatigue development stage, and fatigue damage stage, and finally, because the load is too large and friction, pin, and bonding cannot provide a greater inhibition effect, FRP adhesive length is not enough to withstand the stripping load and failure. FRP slip increases with increasing fatigue load amplitude for the same number of fatigue cycles; for the specimens with fatigue damage, the interfacial stiffness of FRP–concrete decreases with the increase in the number of cyclic, and the rate of stiffness damage at the FRP–concrete interface accelerates with increasing fatigue load amplitude. For fatigue load magnitudes higher than 0.6, the slopes of fatigue bond–slip curves decrease with the increase in the number of cycles. When the fatigue load magnitude is lower than 0.4, the slope of the fatigue bond–slip curve increases with the number of cycles and is close to the slope of the monotonically loaded curve. Due to the difference in load class, the bond strength of HB-F-1 continues to decrease with the increase in fatigue times, decreasing by 26% after 100 fatigue cycles and decreasing to 7.33 MPa after 5000 fatigue cycles. The bond strength of the sample HB-F-2 first increased and then decreased with the increase in fatigue times. After 10,000 fatigue cycles, the bond strength decreased by 8%, and at 11,133,300 fatigue breaks, the bond strength of the sample HB-F-3 continued to increase with the increase in fatigue times. At 2 million fatigue load cycles, the bond strength increased to 7 MPa, far from reaching the peak strength. The empirical formulas for the fatigue life curve of HB-FRP-reinforced specimens under single steel fasteners are proposed.