Investigation of bond slip effect on the P-M interaction surface of RC columns under biaxial bending

The nonlinear behavior of reinforced concrete columns subject to biaxial bending and consideration of bond-slip at the steel-concrete interface are investigated. Separate degrees of freedom are used for the steel and concrete parts to allow for the dierence in displacement between the reinforcing bars and the surrounding concrete. The eect of bond-slip is investigated on the numerical bearing capacity of a reinforced concrete column subject to axial and biaxial bending forces. The axial force-bending moment (PM) interaction surface of the reinforced concrete column under two conditions (with and without bar slip) is calculated, and compared also with ACI criteria. The results show that although ACI criteria is based on perfect bond assumption, the results are conservative anyway, due to the fact that the benecial eect of stirrup connement on concrete compressive strength is neglected, and the use of reduction factor ʹ does not make any modication necessary for considering the bond-slip eect on the ultimate capacity of the RC section.