Ultimate Axial Load Limit (column and wall:ACI 318)
The strength of a column under truly concentric axial load is
Pn,o = 0.85 * f'c * (Ag - Ast) + fy * Ast
For nonprestressed compression members with tie reinforcement,
φ * Pn,max = 0.80 * φ * [0.85 * f’c * (Ag - Ast) + fy * Ast]