Evaluation of the effects of stirrup spacing and buckling of steel reinforcing bars on the capacity of RC columns

The capacity of reinforced concrete sections highly depends on the interaction between reinforcing bars and surrounding concrete. The buckling of longitudinal steel bars has an important role in the nonlinear behavior of RC sections. In order to perform nonlinear analysis on the buckling of the bar in RC columns, two types of column and joint elements are modeled and separate degrees of freedom are used for the reinforcing bars and concrete. Buckling eect is considered in the numerical modeling of bars, and ability and reliability of the numerical method are assessed through verication of the numerical and experimental results. The eect of stirrup spacing on the Axial-Force-Moment (P-M) interaction curve of the RC column is calculated using the nonlinear model for the buckling of bar and compared with the ACI criterion. Results show that numerical capacity in an RC section subject to pure axial compressive load and pure bending moment, with buckling eect of the bar, is only about 6% and 9% lower than that obtained without buckling eect, respectively. Also, although ACI criterion does not take buckling eect of the bar into account in the estimation of ultimate strength capacity of RC section, the ultimate capacity recommended by ACI code is acceptable and conservatively enough.