Wall footing

A continuous reinforced footing under a wall, designed per foot of wall to ACI 318-19 (Chapters 7, 13, 22, 24 and 25) with ASCE 7-22 load combinations. The soil checks use the service (ASD) combinations of ASCE 7-22 2.4.1 against the allowable pressure you enter; the concrete is designed for the factored combinations of 2.3.1. ACI 318 has no allowable-stress method for concrete, so the type has no LRFD / ASD switch.

Inputs of the wall footing #

• Wall: concrete, masonry or steel studs on a sill plate. The choice sets the critical section for moment (Table 13.2.7.1): the face of a concrete wall; halfway between the center and the face of a masonry wall. The table has no row for studs, so the program uses the row of a column on a steel base plate, halfway between the stud face and the sill edge, and says so in a note. Choose another wall type if you judge otherwise. Also the wall thickness and its offset e from the footing center, positive toward +x.
• Footing: width B, thickness h, the depth of soil over the footing, the soil and concrete unit weights, a surcharge on the soil with its load type (D or L), and whether the soil weight counts over the wall width too. Off: the soil and surcharge act beside the wall only, because the wall weight is part of your D. On: over the full width, as many hand calculations do.
• Loads per foot of wall at the top of the footing, per load type, unfactored: P (compression positive, at the wall centerline), M (moves the resultant toward +x) and V (at the top of the footing, toward +x; it adds V × h at the base). Wind and seismic loads act in both directions.
• Soil: allowable bearing pressure qa and its basis (gross pressure, or net pressure above the original overburden γs Df), base friction μ, allowable passive pressure on the footing face (equivalent fluid, 0 to ignore it), and the factors of safety for sliding, overturning and uplift (1.5 prefilled; with the 0.6D combinations some engineers use 1.0, which is your choice).
• Concrete and reinforcement: f'c, fy, λ, the exposure and clear cover (3 in cast against the ground, Table 20.5.1.3.1), transverse bars and their spacing, longitudinal bars and their number across B, which layer is at the bottom, straight or hooked ends of the transverse bars, epoxy coating.
• Code options: the size effect factor λs, which 13.2.6.2 lets you neglect for one-way shallow foundations (prefilled); the crack control spacing of Table 24.3.2, which 13.3.2.1 and 7.7.2.2 reach for a strip footing and is checked as written unless you decide otherwise (with 3 in of cover and Grade 60 bars it limits the spacing to 7.5 in); and the reduction of ℓd for excess reinforcement (25.4.10, straight bars only), where As,required is the larger of the steel for the moment and As,min.

Auto-design (editor toolbar) varies the width B (1/2-ft steps), thickness h (1-in. steps), the transverse bars (size and spacing) and the longitudinal bars (size and count). Objectives: lowest cost index (concrete, formwork, reinforcement); least concrete, then cost; narrowest footing, then cost. Every other input is kept; see Auto-design.

Checks performed #

Moments and shears in the check tables are for a 12 in strip of wall. The key result Mu is per unit length of wall.

Limitations #

• No top reinforcement: where top tension fails its plain-concrete check, the program tells you and you design the top bars by hand or change the footing. Plain concrete footings, stepped or sloped footings and thickened sections are not covered.
• The wall load acts at its centerline and the footing is free to rotate, so the moment of an offset wall goes to the soil. If a floor or a slab restrains the wall, enter what you judge it takes as a load moment.
• Wall dowels, wall reinforcement, splices of the longitudinal bars and the wall's own bearing are not designed.
• Seismic foundation provisions (18.13) are not included. The 0.5L permitted in ASCE 7-22 2.3.1 exception 1 is not applied: 1.0L is used.
• Concentrated loads along the wall and longitudinal bending of the footing (differential settlement, discontinuous walls) are not analyzed; the design is per foot of a uniformly loaded wall.

Verification examples #

Verification status: 78 values compared in 13 examples (7 published, 6 hand calculations from the cited equations): 63 within tolerance, 15 recorded deviations. Code basis: partial. Only some provisions were read in the target edition; the rest rests on older editions, examples or summaries.

Published worked examples (backend/tests/test_verify_wall_footing.py). Most are to an earlier ACI edition or use a simplified formula; where ACI 318-19 or the method differs the value is a deviation, explained on the Verification page.

Hand calculations of the same file cover the default design, the masonry critical section, the closed-form partial contact pressure, the size effect, the stud case and the stability of a wind moment. Under ACI 318-19 the StructurePoint and UET footings fail one-way shear with the thickness those older methods accepted: the 318-19 strength of a member without stirrups depends on the flexural steel and is much lower for a lightly reinforced footing.