Isolated Column Footing Design

Biaxial soil pressure with lift-off, overturning and sliding, one-way shear, punching shear with moment transfer about both axes on an edge-aware perimeter, flexure with the short-direction band, anchorage, and the column's bearing on the footing — for a single rectangular spread footing, by ACI 318-08 or ACI 318-19. Designs for your own load cases, combined by BNBC 2020, ASCE 7-05 or ASCE 7-16 (wind, orthogonal earthquake), for ETABS combinations, or both.

ACI 318-08ACI 318-19BNBC 2020ASCE 7-05ASCE 7-16

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Design basis

Design code

Design for

D, L and E per column below; the code's strength and service combinations are built from them.

Loads from ETABS

An ETABS Joint Reactions table or the EtabsWebBridge: assign one joint per column, then take D/L/E from its cases or bring its combinations in as they are.

Your loads → code combinations

base shears

Enter your own service loads for each case, or bring them from ETABS. The BNBC 2020 combinations are made from them, and the footing is designed for every one.

Case	Pkip	Mxkip·ft	Mykip·ft
D
L
Ex
Ey
Wx
Wy

Service (unfactored) loads at the column, compression +. Mx pushes the +L end down, My the +B side; V is the base shear acting in +x, +y at the load height. Ex, Ey, Wx and Wy are taken both ways; leave a row at 0 if it doesn't apply.

Combinations byVertical seismic Ev/Dkv

L in 1.2D + L and the strength combinations with W or E

Ex and Ey together: 100 % of one + 30 % of the otherBNBC 2020 Sec 2.5.13.1(b): SDC D, or SDC C with plan irregularity type V.

W is service level (Sec 2.4), factored 1.6 for strength: enter the wind case that code defines. 0.5 L is permitted where the live load is at most 5.0 kN/m², except garages and places of public assembly. Ev = kv·D with kv = 0.5·ah = Z·S/3 (Sec 2.5.13.2); 0 leaves it out. 3 strength (Sec 2.7.3) + 3 service (Sec 2.7.2) combinations, listed under Load states. The service ones check the soil.

Column & footing

Column along Lc1inColumn along Bc2inColumn offset along LeLinColumn offset along BeBinLengthLftWidthBftThicknessTinFounding depthDfftClear coverinLoads applied above footing tophin

Offsets are from the footing's centre to the column's; a column flush with an edge loses that side of its punching perimeter.

Soil & stability

Allowable bearing (gross)qaksfPedestal / other weightkipSoil unit weightpcfConcrete unit weightpcfBase frictionμ

FS overturnFS sliding

Materials & reinforcement

Footing concretef'cksiSteelfyksiColumn concretef'c,colksiAnchorageBars along LSpacing along L (0 = design)inBars along BSpacing along B (0 = design)in

Lower (outer) layer

Everything you have entered is in the address bar, so the link reproduces this exact calculation.

Adequate — all 13 checks pass

Governing: Minimum steel, bars along L · DCR 0.98 · ACI 318-08

Footing: 10.00 × 10.00 × 24.0"; d = 20.25 in avg
q max / qa: 3.77 / 4.00 ksf; D+L
Bars along L: 12 #6 @ 10"; As = 5.28 in²
Bars along B: 12 #6 @ 10"; As = 5.28 in²

Plan

Section along L

Check summary

Check	Demand	Capacity	DCR
Bearing
Allowable gross pressure · full contact · D+L	3.77 ksf	4.00 ksf	0.94	OK
Stability
FS ≥ 1.5 · FS = 72.45 · D+L	37.50 kip·ft	1811.3 kip·ft	0.02	OK
One-way / beam shear
ACI 318-08 §11.2.1, §15.5.2 · section at d from face +x · 1.2D+1.6L	107.1 kip	203.3 kip	0.53	OK
ACI 318-08 §11.2.1, §15.5.2 · section at d from face +y · 1.2D+1.6L	105.8 kip	195.9 kip	0.54	OK
Punching shear
ACI 318-08 §11.11.1.2, §11.11.2.1, §11.11.7.2 · 4-sided perimeter, b0 = 153.0 in, αs = 40 · 1.2D+1.6L	122.1 psi	164.3 psi	0.74	OK
Flexure
ACI 318-08 §15.4.2, §10.3 · 12 #6 @ 10 in · 1.2D+1.6L	381.7 kip·ft	477.8 kip·ft	0.80	OK
ACI 318-08 §15.4.2, §10.3 · 12 #6 @ 10 in · 1.2D+1.6L	368.5 kip·ft	459.9 kip·ft	0.80	OK
Detailing
ACI 318-08 §10.5.4, §7.12.2.1 · ρ = 0.0018 of b·T	5.18 in²	5.28 in²	0.98	OK
Column to footing
ACI 318-08 §10.14.1, §9.3.2.4, §15.8 · column governs; dowels ≥ 1.62 in² · 1.2D+1.6L	408.0 kip	716.0 kip	0.57	OK

Click a check with ▸ to see its worked calculation.

Reinforcement

Layer	Bars	As req / min	As prov	Ends
Bottom, along Louter layer	12 #6 @ 10"	4.20 / 5.18	5.28	straight, ld 32.9"
Bottom, along Binner layer	12 #6 @ 10"	4.21 / 5.18	5.28	straight, ld 32.9"

Dowels across the column interface ≥ 1.62 in² (0.005·A1). Cover 3" bottom and sides.

Load states

State	P	Mx	N on soil	ex / ey (ft)	q max	Contact
str1.4DSec 2.7.3 (1)	252.0	21.0	339.2	0.06 / 0.00	3.52	full
str1.2D+1.6LSec 2.7.3 (2)	408.0	34.0	482.7	0.07 / 0.00	5.03	full
str1.2D+LSec 2.7.3 (3)	336.0	28.0	410.7	0.07 / 0.00	4.28	full
svcDSec 2.7.2 (1)	180.0	15.0	242.3	0.06 / 0.00	2.51	full
svcD+LSec 2.7.2 (2)	300.0	25.0	362.3	0.07 / 0.00	3.77	full
svcD+0.75LSec 2.7.2 (4)	270.0	22.5	332.3	0.07 / 0.00	3.46	full

Mx, My are the base moments about the footing centre (column moment + load × offset + shear × height), kip·ft. Strength q is the gross factored pressure.

Design checks

Check	Demand	Capacity	DCR	Status
One-way shear, along L	107.132 kip	203.342 kip	0.527	✓ OK
One-way shear, along B	105.825 kip	195.948 kip	0.540	✓ OK
Punching shear	122.129 psi	164.317 psi	0.743	✓ OK
Flexure, bars along L	381.679 kip·ft	477.751 kip·ft	0.799	✓ OK
Minimum steel, bars along L	5.184 in²	5.280 in²	0.982	✓ OK
Flexure, bars along B	368.475 kip·ft	459.931 kip·ft	0.801	✓ OK
Minimum steel, bars along B	5.184 in²	5.280 in²	0.982	✓ OK
Development, bars along L	32.863 in	48.000 in	0.685	✓ OK
Development, bars along B	32.863 in	48.000 in	0.685	✓ OK
Depth above the bottom bars	6.000 in	19.875 in	0.302	✓ OK
Column bearing on the footing	408.000 kip	716.040 kip	0.570	✓ OK

Calculation

1Effective depths (two bar layers)
$d_{outer} = T - c - \tfrac{d_{b,o}}{2},\quad d_{inner} = T - c - d_{b,o} - \tfrac{d_{b,i}}{2}$
$d_{outer} = 24.0 - 3.00 - 0.750/2 = 20.63,\ d_{inner} = 19.88,\ d_{avg} = 20.25$
$d$ 20.25 in
2Footing and soil weight
$W = \gamma_c L B T + \gamma_s (LB - c_1 c_2)(D_f - T)$
$W = 30.0 + 32.3 = 62.3$
$W$ 62.3 kip
3Soil pressure, governing service state (D+L)
$q_{max} = \frac{N}{BL} + \frac{6|M_x|}{BL^2} + \frac{6|M_y|}{LB^2}$
$N = 362.3,\ M_x = 25.0,\ M_y = 0.0 \Rightarrow q_{max} = 3.77$
$q_{max}$ 3.77 ksf
4Punching, governing strength state (1.2D+1.6L)ACI318 11.11.7
$v_u = \frac{V_u}{b_0 d} + \frac{\gamma_{vx} M_{x} c_x}{J_{cx}} + \frac{\gamma_{vy} M_{y} c_y}{J_{cy}} \le \phi v_c$
$V_u = 366.5,\ b_0 = 153.0 \Rightarrow v_u = 122.1\ \le\ 164.3$
$v_u$ 122.1 psi
5Bottom bars along LACI318 15.4.2
$A_s = \max(A_{s,req}, \rho_{min} b T)$
$M_u = 381.7,\ b = 120,\ d = 20.63 \Rightarrow A_s = 5.18$
$A_{s,prov}$ 5.28 in²
12 #6 @ 10 in
6Bottom bars along BACI318 15.4.2
$A_s = \max(A_{s,req}, \rho_{min} b T)$
$M_u = 368.5,\ b = 120,\ d = 19.88 \Rightarrow A_s = 5.18$
$A_{s,prov}$ 5.28 in²
12 #6 @ 10 in

Notes

Soil bearing (service) (D+L): 3.77 vs 4.00 ksf — full contact. OK.
Overturning along L (D+L): 37.50 vs 1811.29 kip·ft — FS = 72.45. OK.
All 13 design checks pass. Governing DCR = 0.98.

What this calculator does not check

Rigid footing: the soil pressure is taken as planar (no tension), not from a subgrade-modulus or finite-element analysis.
The column's bars are not developed into the footing here (dowel embedment and hooks are to be checked by hand); only the minimum dowel area is given.
Sliding takes base friction only — passive resistance and any key are ignored. No global stability or settlement check.
A combination given directly takes the footing and soil weight at a factor of 1.0.
Combinations of the cases by BNBC 2020: strength Sec 2.7.3 for the concrete, allowable stress Sec 2.7.2 for the soil (bearing, overturning, sliding). L takes 1 in 1.2D + L and the strength combinations with W or E; Ex and Ey act one at a time; no vertical seismic effect (Ev = 0). W is taken as service level (Sec 2.4), factored 1.6 for strength; it acts along x or y, both senses. Roof live, rain, snow, fluid, soil-pressure and self-straining loads are not cases here.

Results are for preliminary sizing and educational use. They are not a design and must be reviewed, verified and sealed by a licensed or registered engineer before being used in construction.

isolated-footing-design v2.1.0 · ACI 318-08 · input bef08671599683af