RC Tied Column Axial Capacity (ACI 318-19 22.4)
The axial capacity of a concentrically loaded short tied column.
Example
You enter
- Column width b (in) 16
- Column depth h (in) 16
- Concrete strength f'c (psi) 4000
- Steel yield fy (psi) 60000
- Total longitudinal steel Ast (in²) 6.32
You get
- Gross area Ag 256 in^2
- Rho g 0.0247
- Nominal Po 1,228 kip
- Design phi Pn,max (0.80 x 0.65 x Po) 639 kip
Checked against published worked examples from: StructurePoint.
Details, formula, and sources
ScopePo = 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 or tableAg = b x h; rho_g = Ast / Ag (flagged outside 0.01..0.08); Po = 0.85 f'c (Ag - Ast) + fy Ast with fy not more than 80,000 psi (22.4.2.1); phi Pn,max = 0.80 x 0.65 x Po.
Source and editionThe 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.
Free accessACI 318 is readable free through the ACI online reading room at concrete.org; the 22.4 axial provisions and 10.6.1 limits are in the published code.
What governsEstimate. AHJ and licensed professional govern.
API field namesb_in, h_in, fc_psi, fy_psi, ast_in2, ag_in2, rho_g, po_kip, phi_pn_kip
- Nominal strength Po = 0.85 f'c on the net concrete plus fy on the longitudinal steelACI 318-19 22.4.2.2
- Tied cap phi Pn,max = 0.80 phi Po (phi = 0.65) for the accidental eccentricity a concentric load never truly avoidsACI 318-19 22.4.2.1 / 21.2
- Steel ratio longitudinal rho_g flagged against the 1% minimum and 8% maximumACI 318-19 10.6.1.1