Experimental study and practical constitutive model of bond performance between engineering cementitious composites concrete and reinforcement considering constraint effect under cyclic loading

To study the bond performance between steel bars and engineering cementitious composites (ECC) concrete, 30 groups of ECC concrete eccentric pull-out specimens considering constraint effect were designed and subjected to cyclic loading tests. Subsequently, the effects of cover thickness, stirrup spacing, concrete strength and longitudinal rebar diameter on bond performance were investigated. The bond performance between rebars and ECC concrete was examined from the perspectives of failure mode, bond strength, energy dissipation capacity, and the degradation of stiffness and strength. The experimental results show that as the stirrup restraint degree increased, the bond strength degradation weakened obviously, and the energy dissipation capacity improved significantly. With the rising of the cover thickness, the bond strength degradation diminished slightly, and the energy dissipation capacity increased slightly. The enhancement effect of increasing the cover thickness on the bond strength was less than that of increasing stirrup ratio. With the increase of concrete strength, the bond strength and energy dissipation capacity of the specimen grew continuously, and the strength degradation coefficient was almost unchanged. Specimens with smaller steel bar diameters exhibited higher bond strengths, a slower decline in the curve after the peak, and an increased capacity for energy dissipation. Finally, on basis of the test data, calculation formulas for bond force and slip at the characteristic points were established. By altering the Pinch4 material parameters in OpenSees, a practical hysteresis constitutive model of ECC concrete bond-slip was created, and the accuracy of the model was confirmed using test data.