PREDICTIONS OF ULTIMATE BEHAVIOR OF CONFINED COLUMNS SUBJECTED TO LARGE DEFORMATIONS.

A stress-strain relationship for unconfined and confined concrete is proposed. Based on this relationship, the behavior of reinforced concrete columns subject to axial and lateral loading is predicted and compared with experimental data on round and square columns. A parametric study was conducted to assess the influence of the concrete strength, the degree of confinement, the level of axial load, and the shape of the section on the capacity of columns subjected to large deformations. It was found that under constant axial load, the moment resistance of the column may exhibit a peak followed by a drop (the predicted values according to the ACI procedure are close to this first peak); the extent in drop in moment depends on compressive strength of concrete, axial load level, shape of the section, and confinement. Additional study results are discussed in the paper.