Equivalent uniform moment diagram factor for structural concrete columns

The equivalent uniform bending moment diagram factor ([C.sub.m]) was introduced into design practice to eliminate the need for extensive calculations, based on the solution to a differential equation, to compute the effect of moment gradient, along the column height, caused by unequal column end moments. The expression currently in use in the Canadian Standards Association (CSA) A23.3 standard is a simplified equation based on the elastic behaviour of columns, and does not include the inelastic material behaviour of structural concrete. This study was conducted to investigate the influence of different variables on [C.sub.m] of slender, tied, reinforced concrete columns, and composite steel-concrete columns in which steel sections are encased in concrete, and also to examine existing expressions for [C.sub.m]. Approximately, 38 000 simulated columns, each with a different combination of specified values of variables, were used to generate the [C.sub.m] data. The columns studied were subjected to short-term ultimate loads and unequal end moments causing moment gradient in single curvature and double curvature bending. Two [C.sub.m] design equations are proposed in this paper. One of the proposed equations is a modified version of the current CSA design equation for [C.sub.m].