Combined & Strip Footing Design

Rigid-method bearing, one-way and punching shear, top/bottom flexural design with reinforcement curtailment, and per-column transverse design, for a rectangular footing carrying 2 to 8 columns in a row, by ACI 318-08.

ACI 318-08ASCE 7

Columns

Number of columns

Column 1

Width (c1, along L)inDepth (c2, along B)in

PDkipPLkipPEkip

Span to column 2ft

Transverse barSpacing (0 = auto)in

Column 2

Width (c1, along L)inDepth (c2, along B)in

PDkipPLkipPEkip

Transverse barSpacing (0 = auto)in

Footing geometry

Left projectionplftRight projectionprft

Founding depthDfftFooting widthBft

ThicknessTinCoverin

Footing length (derived): 20.33 ft

Soil & bearing

Allowable bearingqaksf

Soil unit weightpcfConcrete unit weightpcf

Materials & longitudinal reinforcement

f'cksifyksi

Bar (effective-depth basis)

Top bar (hogging)Spacing (0 = auto)in

Bottom bar (sagging)Spacing (0 = auto)in

Include a longitudinal grade beam (discrete bars, no curtailment)

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

d = 22.25 in · 9 checks · all pass

Plan view

Footing length

20.33 ft

Gross bearing demand

1.83 ksf

Governing DCR

0.52

Design checks

Check	Ref	Demand	Capacity	DCR	Governs	Status
Bearing (gross, service)	ASCE 7 §2.4	1.83 ksf	4.00 ksf	0.46	Governing combo: D+L	PASS
One-way shear, station 1 L	ACI §11.2.1 / Eq. 11-3	3.23 kip	308.02 kip	0.01	x = 0.15 ft	PASS
One-way shear, station 1 R	ACI §11.2.1 / Eq. 11-3	90.66 kip	308.02 kip	0.29	x = 5.19 ft	PASS
One-way shear, station 2 L	ACI §11.2.1 / Eq. 11-3	98.38 kip	308.02 kip	0.32	x = 14.15 ft	PASS
One-way shear, station 2 R	ACI §11.2.1 / Eq. 11-3	22.96 kip	308.02 kip	0.07	x = 19.19 ft	PASS
Punching shear, Column 1	ACI §11.11.2.1	204.00 kip	604.19 kip	0.34	Eq. 11-33, position: int	PASS
Punching shear, Column 2	ACI §11.11.2.1	224.00 kip	604.19 kip	0.37	Eq. 11-33, position: int	PASS
Transverse steel, column 1	ACI §15.4.2	28.59 kip.ft	55.04 kip.ft	0.52	#6 @ 9.4 in o.c. (auto)	PASS
Transverse steel, column 2	ACI §15.4.2	26.65 kip.ft	55.04 kip.ft	0.48	#6 @ 9.4 in o.c. (auto)	PASS

Governing longitudinal moment

M top (hogging) = 127.3 kip.ft

M bottom (sagging) = -410.8 kip.ft

Base mat

Top: #6 @ 9.4 in o.c.

Bottom: #6 @ 9.4 in o.c.

Design checks

Check	Demand	Capacity	DCR	Status
Bearing (gross, service)	1.828 ksf	4.000 ksf	0.457	✓ OK
One-way shear, station 1 L	3.225 kip	308.021 kip	0.010	✓ OK
One-way shear, station 1 R	90.658 kip	308.021 kip	0.294	✓ OK
One-way shear, station 2 L	98.381 kip	308.021 kip	0.319	✓ OK
One-way shear, station 2 R	22.958 kip	308.021 kip	0.075	✓ OK
Punching shear, Column 1	204.000 kip	604.194 kip	0.338	✓ OK
Punching shear, Column 2	224.000 kip	604.194 kip	0.371	✓ OK
Transverse steel, column 1	28.585 kip·ft	55.038 kip·ft	0.519	✓ OK
Transverse steel, column 2	26.650 kip·ft	55.038 kip·ft	0.484	✓ OK

Calculation

1Footing length, from the left projection, column widths and spans
$L = p_L + \sum \text{spans} + p_R$
$L = 2.00 + \ldots + 3.00 = 20.33$
$L$ 20.33 ft
2Rigid-method resultant and eccentricity, governing service combo
$\bar x = \frac{\sum P_i x_i}{\sum P_i}, \quad e = \bar x - L/2$
$\bar x = 10.00, \quad e = -0.17$
$q_{avg}$ 1.19 ksf
Governing service combo: D+L

Notes

All 9 design checks pass. Governing DCR = 0.52.

What this calculator does not check

This engine ports the rigid-method statics/beam analysis, punching/one-way shear, curtailed flexure and transverse design shared by the source's own Combined and Strip tabs — but not that source's Nilson resultant-centering / auto-size-B buttons, nor its trapezoidal/stepped alternative footing shapes, since the source itself documents that neither one feeds the actual design checks. Size L, B and the spans directly instead.
Eccentric punching-shear moment transfer (ACI §11.11.7) and bar anchorage/development length are not checked — the source defines helpers for both but never calls them from either the Combined or Strip tab.
No common service (bearing) combination is enforced across stations when eccentricity from a station-specific moment is present — bearing uses the governing station-sum service combo's own average pressure, without a separate per-combo eccentricity re-check beyond the rigid-method e already folded into qavg.
Reinforcement is curtailed: a minimum base mat everywhere, plus extra bars only in the zones where demand exceeds the base mat's capacity, extended max(d, 12 bar diameters) past the theoretical cutoff (ACI §12.10.3).
No published worked example has been reproduced against this port; verification is internal cross-checks with the original tool's own engine, disclosed as such.

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.

combined-strip-footing-design v1.0.0 · ACI 318-08 · input 7bd7334832b20860