Investigation of Bond Slip Effect on the P-M Interaction Surface of RC Columns under Biaxial Bending

The nonlinear behavior of reinforced concrete columns subjected to biaxial bending with consideration of bond-slip at the steel-concrete interface is investigated. Separate degrees of freedom are used for the steel and concrete parts to allow for the difference in displacement between the reinforcing bars and the surrounding concrete. The effect of bond-slip is investigated on the numerical bearing capacity of reinforced concrete column subjected to axial and biaxial bending forces. The axial force–bending moment (P-M) interaction surface of the reinforced concrete column for the two conditions of (with and without bar slip) is calculated and compared also with ACI criteria. The results show that, although the ACI criteria is based on the perfect bond assumption, the results are conservative anyway due to the fact that the beneficial effect of stirrups confinement on the concrete compressive strength is neglected, and the use of the reduction factor φ, does not make any modification necessary for considering bond-slip effect on the ultimate capacity of RC section.