RC Tied Column Axial Capacity (ACI 318-19 22.4)
The column the RC beam tiles never supplied: a concentrically loaded short tied column carries Po = 0.85 f'c (Ag - Ast) + fy Ast, capped at 0.80 phi Po (phi = 0.65) for the accidental eccentricity a concentric load never truly avoids. A 16 in square 4,000 psi column with eight #8 Grade 60 bars gives Po = 1,228 kip and a 639 kip design capacity, with the longitudinal ratio checked against the ACI 1-8% band. No P-M interaction or slenderness - short, tied, concentric only. A design aid, not the engineer of record's stamped design.
Formula and source
Ag = b x h; rho_g = Ast / Ag (flagged outside 0.01..0.08); Po = 0.85 f'c (Ag - Ast) + fy Ast; phi Pn,max = 0.80 x 0.65 x Po.
The ACI 318-19 22.4.2 nominal axial strength of a non-prestressed compression member and the 22.4.2.1 tied-column maximum (0.80 phi Po, phi = 0.65 compression-controlled tied), with the 10.6.1 longitudinal-reinforcement ratio limits, by name.
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