Footing design calculator

Footing type

Concentric or eccentric service loads on a rectangular spread footing, or a continuous wall footing designed per 1-ft strip. Bottom reinforcement only.

Isolated column footing Rectangular pad under one column; two-way action. Wall footing Continuous strip under a wall; loads per foot of wall.

Geometry and soil

B (footing width, in)

Isolated: 24 to 240 in. Wall: 12 to 120 in.

L (footing length, in)

Isolated footings only. 24 to 240 in; must exceed the column dimension.

h (footing thickness, in)

Overall thickness. Range 12 to 60 in. Effective depth is computed from this, the cover and the bar size.

cover (clear cover, in)

Cast against earth: 3 in minimum (Table 20.5.1.3.1). Range 3 to 6 in.

qa (allowable soil bearing, ksf)

Gross allowable bearing pressure from the geotechnical report. Range 1 to 20 ksf.

γ_soil (soil unit weight, pcf)

Backfill above the footing. Range 90 to 150 pcf.

D_f (depth of footing below grade, ft)

Soil overburden and self-weight are deducted from qa to get the net allowable pressure. Range 0 to 10 ft.

Column

Column shape

Column position

Sets the punching shear location factor and the critical perimeter.

col_L (column dimension parallel to L, in)

Range 8 to 48 in.

col_B (column dimension parallel to B, in)

Range 8 to 48 in.

D_col (column diameter, in)

Converted to an equivalent square column per §13.2.7.3. Range 8 to 48 in.

Edge parallel to

Which footing edge the column is near. Required for edge and corner columns.

Wall

t_wall (wall thickness, in)

Must be less than the footing width B. Range 6 to 24 in.

Materials and reinforcement

f'c (compressive strength, psi)

Specified concrete strength. Range 3,000 to 10,000 psi.

fy (yield strength, ksi)

Range 40 to 100 ksi.

λ (lightweight concrete factor)

1.0 for normal weight concrete; 0.75 to 0.85 for lightweight (Table 19.2.4.2). Range 0.75 to 1.0.

Bottom bar size

Same bar size in both directions, #4 through #11.

Bar coating

Epoxy coating increases the development length (ψe).

Factored loads

Enter factored loads from your ACI 318-19 load combinations. These drive the flexure, shear, punching, development and interface checks. Footing self-weight is not included in factored loads.

Generate factored loads from service loads on the load combination page.

Pu (factored axial load, kip)

Must be greater than 0. Maximum 2,000 kip.

Mu_L (factored moment about the L-axis, kip-in)

Optional; blank is treated as 0. Any moment above 0 means punching shear is reported as not checked.

Mu_B (factored moment about the B-axis, kip-in)

Optional; blank is treated as 0.

Pu (factored axial load, kip/ft)

Per foot of wall. Must be greater than 0. Maximum 100 kip/ft.

Mu (factored moment, kip-in/ft)

Optional; per foot of wall. Blank is treated as 0.

Service loads

Unfactored loads for the soil bearing, kern, overturning and sliding checks (§13.2.1). Do not include footing self-weight or soil above the footing; they are added from the geometry above.

P (service axial load, kip)

Must be greater than 0. Maximum 1,500 kip.

M_L (service moment about the L-axis, kip-in)

Optional; blank is treated as 0.

M_B (service moment about the B-axis, kip-in)

Optional; blank is treated as 0.

V (lateral force at top of footing, kip)

Optional; used for overturning and sliding.

P (service axial load, kip/ft)

Per foot of wall. Must be greater than 0. Maximum 75 kip/ft.

M (service moment, kip-in/ft)

Optional; per foot of wall. Blank is treated as 0.

V (lateral force, kip/ft)

Optional; per foot of wall. Used for overturning and sliding.

μ (soil-concrete friction coefficient)

Sliding resistance is friction only (passive pressure neglected). Range 0.2 to 0.6.