Bond Stress-Slip Model for Steel Bars in Unconfined or Steel, FRC, or FRP Confined Concrete under Cyclic Loading

An experimentally based relationship of the cyclic local bond stress-slip response of steel bars corresponding to splitting mode of bond failure is developed. The relationship is composed of a monotonic envelope response and cyclic bond degrading response. The model accounts for both unconfined and moderately confined concrete and incorporates the effect of several critical bond parameters such as the diameter of steel bars, the ratio of concrete cover to bar diameter, the concrete compressive strength, the type of confinement such as steel ties, fiber-reinforced concrete (FRC), and fiber-reinforced polymer jackets, and the area or content of confining reinforcement. Results predicted by the model showed very good agreement with the test data. The bond-slip relationship can be utilized for evaluating the seismic behavior and bond degradation response of bond-critical regions in reinforced concrete members when confined internally with steel ties or fiber reinforced concrete or retrofitted using external FRP jackets.