Design of steel-strapped, high-strength concrete columns subject to unequal end moments

Abstract

A new equation is proposed for practical flexural design of high-strength concrete columns confined externally with tensioned steel straps. The proposed equation is based on the simplified approach of the equivalent moment factor adopted by existing design codes. It also accounts for non-linear behaviour of the materials, which is usually neglected in the codes. The equation was derived using results from rigorous theoretical analyses of 120 simulated strap-confined columns subjected to short-term ultimate loads and unequal flexural moments at the column ends. The theoretical simulations accounted for parameters shown to influence the design of strap-confined columns, such as load eccentricity, longitudinal reinforcement ratio, free concrete cover and volumetric confinement ratio. The proposed equation was found to predict the strength of strap-confined columns with sufficient accuracy, making it suitable for practical design and rapid assessment of such structures.