Equivalent uniform moment diagram factor for reinforced concrete columns

The ACI Building Code, ACI 318-02, permits the use of the equivalent uniform moment diagram factor C-m for computing the effect of moment gradient, along the column height, caused by unequal column end moments. The concept of equivalent uniform moment diagram was introduced into design practice to eliminate the need for extensive calculations based on the solution to a differential equation. The expression currently in use by the ACI code is a simplified equation based on the elastic behavior of columns and does not include the inelastic material behavior of reinforced concrete columns. This study was conducted to investigate the influence of different variables on C-m of slender tied, reinforced concrete columns and to examine the existing expressions for C-m. Approximately 17,000 square reinforced concrete columns, each with a different combination of specified variables, were simulated. 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-m expressions are proposed for use in slender reinforced column designs.