Constitutive Model for Buckling of Transversally Restrained Longitudinal Bars in Reinforced Concrete Columns

July 30, 2010
Publication: Proceedings of the 9th US National and 10th Canadian Conference on Earthquake Engineering|Toronto, Ontario n 831
Author(s): Mohamed Talaat K.M. Mosalam

This paper introduces a constitutive material model of reinforcing steel bars in reinforced concrete (RC) columns. The model accounts for the restraining effect of transverse reinforcement on the bar buckling length and the stress at the onset of buckling. Once the bar buckles, the material model uses a strain decomposition approach to condense the bar rotational and transversal degrees of freedom and model the post-buckling softening behavior in terms of convenient axial stress and strain quantities. The model incorporates stiffness reduction upon strain reversal from a compression cycle in which bar buckling occurred, and a plastic strain-dependent damage index calibrated to impose hysteretic stress reduction and predict bar fracture. Due to the strain decomposition approach used, the bar buckling model has the advantage of flexibility to use an existing library of steel uniaxial material models as base. The model-predicted monotonic and cyclic axial responses of individual reinforcing steel bars compare well with published experiments. Finally, the proposed model is used successfully to model buckling in the longitudinal reinforcement of two RC bridge column models experimentally tested under combined axial and lateral loading.