Model for Behavior of Slender Reinforced Concrete Columns Under Biaxial Bending

Derivation of an exact mathematical formula to predict strength behavior of slender columns under biaxial bending is not practical due to the large number of influencing parameters. In this paper, a computerized nonlinear model for predicting strength and behavior of slender columns subjected to combined compression and biaxial bending is developed. The model, developed for short-term loading, utilizes realistic stress-strain relationships of the materials, i.e., concrete and reinforcing steel, and the usual assumption in flexural mechanics. The effect of confinement due to ties or spirals on the stress-strain relationship of concrete in compression and tension stiffening of concrete are considered in the model. The model is capable of predicting sectional behavior by computing the ultimate moment strength and moment-curvature relationship of a section under given axial load and angle of eccentricity. When length, boundary conditions, end moments, and thrust are given, the model predicts member behavior and provides such information as magnified moments, deflections, deflected shape, and eventual mode of failure (material or stability). Predicted results of sectional and mamber behavior are compared with the limited test data available, and the comparison is judged good