Ductility Analysis of Confined Columns

This paper describes in detail the weakness of the procedure in the American Concrete Institute (ACI) Building Code used for detailing columns for ductility. It also presents an approach for calculating the amount of transverse steel required in confined columns at various load levels by using idealized stress‐strain diagrams for confined concrete and steel, moment‐curvature curves, and a suggested ductility requirement in which the criterion is specified as the attainment of a curvature factor of 12 at a moment capacity of not less than 75% of the maximum moment capacity. The new approach is more realistic than that of the ACI code, which assumes the function of the transverse reinforcement is to compensate for the loss of the cover concrete. This is particularly important in columns acted upon by a combination of axial load, bending, and shear forces. The controversy surrounding this issue is briefly discussed.