Experimental study on the fatigue bond behavior of concrete beams reinforced with hybrid fiber-reinforced polymer and steel bars

This paper presents an experimental program of the bond behavior of concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars, and the bond behavior between flexural cracks is investigated. Under the static loading, both the slip of steel and glass FRP (GFRP) bars increased significantly after steel yielding, while the slip of steel bars presented a faster increase rate. A method of calculating the bond stress based on test data was proposed, and this method overcame the disadvantage of histogram distribution of the conventional method. An analytical model of calculating the bond stress was proposed, and was verified with the test results. Under the fatigue loading, the bond stress deteriorated more seriously with a higher upper limit of fatigue load. The slip increased rapidly at the initial stage, and remained approximately unchanged with the increase of fatigue cycles, and the slip increased dramatically when the beam was subjected to fatigue failure. After fatigue loading, the yielding strength and ultimate strength of steel bars showed an increase rate less than 5%, while the hardening phase decreased significantly. The ultimate tensile strength of GFRP bars after fatigue decreased in the range of 4.5%-32.3%, and the modulus for elasticity remained unchanged.