[{"_1":2,"_30":-5,"_31":-5},"loaderData",{"_3":4,"_6":7},"root",{"_5":-5},"user","routes/t.$slug",{"_8":9,"_29":21},"tool",{"_10":11,"_12":13,"_14":15,"_16":17,"_18":19,"_20":21,"_22":23,"_24":25,"_26":27,"_28":27},"id","04f827b2-9f64-489c-a0cd-7792dce8aa90","slug","footing-design-suite","title","Footing Design Suite — Isolated, Shear-Wall, Combined & Strip Footings","description","Comprehensive footing design calculator per ACI 318-08 and ASCE 7. Perform live bearing, flexure, one-way shear, and two-way punching shear checks for isolated, shear-wall, two-column combined, and multi-column strip footings, with direct ETABS joint reaction import support.","html","\n\n\n

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Footing Design Suite — Isolated, Shear-Wall, Combined & Strip Footings

\n ACI 318-08 Ch. 15 & 11\n CRSI Design Guide\n PCA Notes on ACI 318 / SP-17\n Bowles — Foundation Analysis & Design\n ASCE 7 load combinations\n US customary (kip · ft · in · ksi)\n

One worksheet, four footing families: an isolated column footing,\n a continuous strip footing under a shear/bearing wall, a two-column combined\n footing, and a multi-column strip footing (slab-only or with a longitudinal\n strip beam). Bearing, one-way shear, two-way punching shear, flexure/reinforcement and a shear &\n moment envelope are computed live in your browser as you type — nothing is uploaded anywhere. A fifth tab\n imports an ETABS Joint Reactions and/or Design Forces — Piers/Columns\n export (real .xlsx, CSV, or pasted cells) for many points at once, separates service (ASD) from strength\n combos, auto-groups points into standardized footing marks, and can feed real point loads straight into the\n Combined/Strip tabs.

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\n Footing Design Calculator\n ACI 318-08 strength design · φ_flexure=0.90 · φ_shear=0.75 ·\n service loads per ASCE 7 §2.4 for bearing, factored loads per ACI 318-08 §9.2 for concrete design\n

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Position & geometry\n

PositionInterior columns get a 4-sided punching perimeter; edge and corner columns get reduced 3- and 2-sided perimeters (lower shear capacity) per ACI 318-08 §11.11.2.1.\n

Founding depth Df ft

c1 (long) in

c2 (short) in

Plan L ft

Plan B ft

Thickness T in

Clear cover in

d ≈ T − cover − bar dia ≈ —

Service loads (unfactored)\n

PD kip

PL kip

PE kip

MD kip-ft

ML kip-ft

ME kip-ft

Soil & bearing\n

qa gross allow. ksf

γsoil pcf

γconc pcf

Pedestal/col. wt. kip

Materials & reinforcement\n

f′c ksi

fy ksi

Bar size (each way)\n

Anchorage\n

\n \n \n \n \n

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Wall & geometry\n

Wall thickness tw in

Founding depth Df ft

Footing width B ft

Thickness T in

Clear cover in

Total length of this wall ft (actual wall/pier length — checks whether the continuous-strip idealization below applies; does not scale the per-ft design itself)

d ≈ T − cover − bar dia/2 ≈ —

Service loads per ft of wall\n

wD kip/ft

wL kip/ft

wE kip/ft

Soil & bearing\n

qa gross allow. ksf

γsoil pcf

γconc pcf

Materials & reinforcement\n

f′c ksi

fy ksi

Main bar (transverse)\n

Distribution bar (long.)\n

\n \n \n \n \n \n

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Columns & spacing\n

c1A in

c2A in

c1B in

c2B in

Spacing A→B (c/c) ft

Left projection (edge→A face) ft

Right projection (B face→edge) ft

Founding depth Df ft

Adopted plan & thickness\n

Footing L (auto, editable) ft

Footing B ft

Thickness T in

Clear cover in

Minimum L (proj.+spacing+proj.) = — · d ≈ —

Service loads — Column A / Column B\n

PD,A kip

PL,A kip

PE,A kip

PD,B kip

PL,B kip

PE,B kip

Soil & materials\n

qa gross ksf

γsoil/γconc pcf

f′c ksi

fy ksi

Bar size (top & bottom)\n

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Stations & spans\n

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Left projection ft

Right projection ft

Founding depth Df ft

Footing B ft

Section\n

Include longitudinal strip beam (grade beam)

Slab thickness T in

Clear cover in

Beam width bw in

Beam total depth h in

Soil & materials\n

qa gross ksf

γsoil/γconc pcf

f′c ksi

fy ksi

Bar size (top & bottom)\n

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1 — Import design forces\n

Upload an ETABS export directly as\n .xlsx (parsed in your browser, nothing uploaded anywhere) or .csv — or paste cells copied\n from the ETABS table view or from Excel. Two export tables are recognized, and an .xlsx workbook is\n scanned sheet-by-sheet so both can be combined from one file:

Joint Reactions / Joint Design Reactions — Story, Point/Label (or Unique Name), Output Case,\n Case Type, FX/FY/FZ, MX/MY/MZ — for isolated columns.
Design Forces – Piers (shear walls) — Story, Pier, Combo, Location (Top/Bottom), P, V2, V3,\n T, M2, M3.
Design Forces – Columns — Story, Column, Combo, Station, P, V2, V3, T, M2, M3.

Units are auto-detected from the file's\n own units row when present; the dropdowns below are the fallback for plain-text paste. Pier/column axial\n force sign is normalized so positive P always means compression, matching Joint Reactions.

Upload .xlsx or .csv

Force unit (paste fallback)

Moment unit (paste fallback)

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Uploads and pastes add to the\n current batch — e.g. upload the Joint Reactions export, then the Column/Pier export, to combine both\n into one batch. Use Clear imported data to start over.

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2 — Classify load combinations (ASD/service vs. strength)\n

Service (ASD, unfactored — e.g.\n Dead+Live) governs the bearing check; strength (factored — e.g. 1.2D+1.6L) governs concrete design.\n Combos are auto-guessed and pre-sorted below (numeric prefixes/suffixes like \"111 …\" or \"…-1\" are\n ignored for matching, since ETABS repeats them per design instance) — move any into the right bucket,\n then leave the rest in the pool to ignore them (drift-only, modal, response-spectrum-only cases, etc.).

Filter pool

\n Pool (0)\n \n

\n \n \n \n

\n Service (0)\n \n Strength (0)\n \n

\n Ignore moment (Mx/My) from combos — use axial P only\n ?Some exports report small/noisy Mx,My even for\n simple gravity columns. Checking this zeroes M everywhere a load is pulled from ETABS (sizing, \"Send to\n Isolated\", \"Design this mark\", and Combined/Strip groups) — P alone then governs bearing eccentricity\n and the strength envelope. Re-send/rebuild after toggling for it to take effect.\n

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3 — Preliminary sizing & footing marks\n

Each point gets a preliminary\n square isolated-footing size = √(governing service P / qa),\n rounded up to the size increment (excludes self-weight — refine in the Isolated tab). Points with\n equal rounded size are auto-grouped into a footing mark; edit any point's mark to override.

qa gross allowable ksf

Size increment in

Footing mark summary

\"Design this mark\" pushes the\n governing (worst-case) load among all members of that mark into the Isolated tab — the\n standardized footing must work for every member, not just one.

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4 — Build a combined/strip group from imported points\n

Enter member point IDs in physical\n order along the strip. Geometry (spacing, spans, projections) is still entered manually in the\n Combined/Strip tab — only the loads come from the import, aligned by matching combo name\n across every member. If no strength combo was run for all members, the group is blocked rather than\n silently using a mismatched load.

Point IDs (comma-separated, in order)

Group name

Type

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Everything runs in your browser — nothing is uploaded.\n Loads and moments update the plan/section drawings, the shear & moment diagram, and the reinforcement\n results together — there is no separate \"recalculate\" step.

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Footing schedule

Click Save to schedule on any tab to add the current design as a row below. The schedule is\n kept in your browser's local storage only — it is private to this device and is not sent anywhere.

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Mark	Type	L × B (ft)	T (in)	Reinforcement	Governing DCR	Status

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Design basis and assumptions

All four modes share the same underlying checks — bearing, one-way (beam) shear, two-way (punching)\n shear where a discrete column exists, and flexure/reinforcement — evaluated per ACI 318-08\n Chapters 11 and 15, using the sizing approach and worked-example format of the PCA Notes on ACI 318,\n the CRSI Design Guide, and SP-17 foundation examples, with the general shallow-foundation\n and bearing-pressure framework (service-load combinations, eccentricity/resultant location, allowable\n bearing checks) following ASCE 7 and standard shallow-foundation design references such as\n Bowles' Foundation Analysis and Design.

Gross vs. net bearing. Bearing pressure is checked as gross pressure —\n service column load plus footing concrete self-weight, soil overburden above the footing, and any\n pedestal/column weight above the footing top — against a user-entered gross allowable bearing\n pressure qa. One-way shear, punching shear and flexure instead use the\n net factored pressure from the column loads alone (self-weight is self-balancing and does not\n produce net shear/moment in the footing itself), consistent with PCA/SP-17 practice.

ASCE 7 §2.4\n Service (bearing) combinations: D + L and D + L ± 0.7E (envelope) · \n ACI 318-08 §9.2 Strength (concrete design) combinations, run as an envelope:\n 1.4D, 1.2D + 1.6L, 1.2D + L ± E, 0.9D ± E\n

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Isolated column footing

Punching (two-way) shear uses a position-aware critical perimeter d/2 from the column face:

ACI 318-08 §11.11.1.2\n Interior: b0 = 2(c1+d) + 2(c2+d) · \n Edge: b0 = 2(c1+d/2) + (c2+d) · \n Corner: b0 = (c1+d/2) + (c2+d/2)\n

Eq. 11-31/32/33\n vc = min[ 4λ√f′c , (2+4/βc)λ√f′c , \n (αsd/b0+2)λ√f′c ] · \n αs = 40 (interior), 30 (edge), 20 (corner)\n

One-way shear is checked at d from the column face in each direction (φVc =\n 0.75·2λ√f′c·b·d), and flexure is checked as a cantilever from the column face in each direction, using\n the minimum footing reinforcement ratio of 0.0018 (Grade 60) per §10.5.4/§7.12 rather than the\n beam minimum. Eccentric (unbalanced-moment) punching-shear stress transfer (the Jc/J\n method of §11.11.7) is not automated here — where Mx/My\n are more than a small fraction of P·d, check unbalanced moment transfer separately.

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Shear-wall / strip-wall footing

A continuous footing under a bearing or shear wall is designed as a repeating 1-ft strip: bearing and\n one-way shear/flexure are computed per foot of wall, with the slab cantilevering each side from the face\n of the wall. There is no two-way punching check (no discrete column), and a longitudinal\n distribution/temperature steel (0.0018 b h) is required parallel to the wall.

Cantilever from wall face\n Mu = qu·a²/2 per ft · \n Vu = qu·(a−d) per ft, \n a = (B − tw)/2\n

When this per-foot idealization does not apply. Treating the footing as an\n infinitely repeating 1-ft strip is only valid when the wall actually runs for a length several times the\n footing width — e.g. a long basement or shear wall. A short shear-wall pier (say 5 ft long) often\n needs a footing pad much larger in plan than the wall itself (e.g. 12 ft × 12 ft) to spread the axial load\n and overturning moment; that is a discrete, two-way footing, not a continuous strip, and one-way shear per\n §11.3 alone is unconservative for it — punching shear per §11.11, biaxial bearing with eccentricity, and\n longitudinal (end-to-end) flexure all have to be checked, exactly like an isolated column footing. The\n Shear-Wall tab now flags this automatically (comparing the entered wall length to the footing width) and can\n hand the loads to the ① Isolated Column Footing tab, treating the wall as a rectangular pier\n (c1 = wall length, c2 = wall thickness) — that tab already performs the two-way and biaxial checks a discrete\n wall pad needs. Note that tab has no overturning-moment input of its own, so any lateral/seismic overturning\n moment on the wall must be added on the Isolated tab after the transfer.

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Combined and strip footings — the rigid (statical) method

Both multi-column modes use the same classical rigid-footing method described in Bowles and the\n PCA/CRSI combined-footing guides: soil pressure is found directly from statics (resultant location and\n eccentricity of the column loads on the footing plan), then the footing is cut like a free body and the\n shear/moment diagram is integrated in closed form along its length — no indeterminate frame analysis is\n needed because the soil reaction is itself derived from equilibrium.

Resultant & pressure\n x̄ = Σ(Pixi)/ΣP · e = x̄ − L/2 · \n q(x) = (ΣP/BL)·(1 ± 6e/L), linear between the two footing ends (valid for e ≤ L/6)\n

Shear & moment by statics\n V(x) = B∫0x q(t)dt − ΣPi, x_i<x\n · M(x) = B∫0x∫0s q(t)dt·ds − ΣPi(x−xi)\n

Sign convention used here. The strip is treated as a free body loaded upward\n by soil pressure and downward by the column loads, starting from a free end (V=M=0). With that convention\n a positive M means the top fiber is in tension (hogging — typical over/near the columns and in\n cantilever projections beyond them) and a negative M means the bottom fiber is in tension\n (sagging — typical near mid-span between columns). The tool labels every row \"top steel\" or \"bottom\n steel\" directly so you never need to track the sign yourself. As a QA check, V and M both return to\n ≈0 at the free right-hand end when the resultant location is computed correctly — the tool reports this\n residual.

If |e| > L/6 part of the footing would need to resist tension from the soil (uplift), which soil\n cannot do. The tool flags this rather than modeling partial contact — resize the footing (usually by\n shifting the resultant toward the plan centroid) until |e| ≤ L/6.

For the combined footing (exactly two columns) the punching perimeter at each column uses the\n exact combined-footing geometry: if the actual edge distance from the column face to the nearby footing\n end is less than d/2, a 3-sided exterior perimeter is used (no critical section exists beyond the\n concrete edge); otherwise a full 4-sided interior perimeter is used. The same logic applies to the first\n and last stations of a strip footing; interior stations always get the full interior perimeter.

The strip-with-beam option carries the longitudinal one-way shear and flexure on a beam stem\n (width bw, total depth h) while the full-width slab (thickness T) spans\n transversely from the beam face to the footing edge as a cantilever and also carries punching shear at\n each column; the without-beam option carries longitudinal one-way shear/flexure on the full width\n B at the slab thickness T, i.e. a single uniform-thickness strip.

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ETABS batch import, sizing and grouping

The ETABS tab reads two ETABS export tables directly — as a real .xlsx workbook (parsed in the\n browser with a minimal ZIP/SpreadsheetML reader; nothing is uploaded anywhere), a .csv, or pasted\n cells — and a workbook is scanned sheet by sheet so both can be combined from one file, or imported one\n upload at a time (uploads and pastes add to the current batch):

Joint Reactions / Joint Design Reactions (Story, Point/Label, Output Case, FZ, MX, MY) — the direct\n support reaction, used for isolated columns.
Design Forces – Piers and Design Forces – Columns (Story, Pier/Column, Combo, Location or\n Station, P, M2, M3) — the shear-wall and column internal forces at the story just above the foundation.\n ETABS reports these member forces with compression negative; the sign is flipped on import so\n positive P always means compression, consistent with a joint reaction, and a row that is still negative\n after the flip is flagged as an uplift case rather than treated as a (wrong-sign) bearing load.

Every load combination in the file is classified once, into service (ASD, unfactored — e.g.\n Dead+Live — governs bearing) or strength (factored — e.g. 1.2D+1.6L — governs concrete design), using\n the same three-bucket \"choose combinations\" pattern ETABS's own UI uses: an unclassified pool plus a Service\n and a Strength list, moved between with buttons. Classification is automatically normalized — ETABS\n repeats a combo under a numeric index and a per-instance suffix (e.g. \"111 1.4D\" at one point and \"1.4D-1\" at\n another), which the importer treats as the same combination — and auto-guessed by name so a real file with\n a hundred load cases needs only a few manual corrections (drift-only, modal, and response-spectrum-only cases\n are left unclassified/ignored by default, since they auto-guess to neither bucket). Units are auto-detected\n from the file's own units row where present.

A preliminary square isolated size is then found from √(governing service P / qa),\n rounded up to the size increment, and points that round to the same size are grouped into a common footing\n mark automatically — you can always override any point's mark by hand. Designing a mark picks a single\n design representative: the member with the highest strength demand, since concrete design (shear,\n flexure, punching) is governed by factored loads — matching CRSI/PCA practice — rather than mixing the\n worst service value from one member with the worst strength value from another. The max-service member is\n only noted for reference when it differs.

For a combined or strip group built from imported points, only the loads come from ETABS —\n spacing, spans and projections are still entered by hand, since a reaction/design-force export carries no\n footing-geometry intent. The member points' strength rows are aligned by matching (normalized) combo\n name; if the same combination was not run for every member (or one point has none classified as\n strength), the group is blocked with an explanation rather than silently combining mismatched load cases.

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Worked example — strip footing 1–3–2

Three columns in sequence 1 – 3 – 2, spans measured column-centerline to centerline:\n 14 ft from 1 to 3, then 9 ft from 3 to 2 (23 ft between the two outer centerlines). Loads: column 1:\n PD=90, PL=60 kip; column 3:\n PD=140, PL=95 kip; column 2: PD=100,\n PL=65 kip. Left/right projections 1.5 ft / 2 ft, B = 7 ft, T = 24 in.

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Quantity	Value	Note
Footing length L	27.83 ft	projections + spans + half column widths
ΣP (service)	550 kip	D+L, all three columns
x̄ (resultant from left edge)	15.05 ft	column 3 is the heaviest, so the resultant sits right of L/2 = 13.92 ft
e	1.13 ft < L/6 = 4.64 ft	inside the middle third — no uplift, pressure is trapezoidal not uniform
qavg (net, columns only)	2.82 ksf	ΣP/(B·L)
q gross demand (incl. self-weight)	3.45 ksf	check against qa = 3.5 ksf — 99% utilized

Click “Load worked example” on the Strip tab to load these exact numbers — including four\n independently editable column stations for the three spans — and see the shear/moment envelope and\n reinforcement the tool derives from them.

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Frequently asked questions

Why does bearing use \"gross\" pressure but shear/flexure use \"net\" pressure?

The footing's own weight and the soil sitting on top of it are already balanced by an equal volume of\n soil that would otherwise occupy that space (Archimedes-style reasoning used throughout PCA/SP-17\n practice) — that self-weight pushes down on the footing and down on the soil below it equally, so it\n does not create net internal shear or bending in the footing slab itself. But the *soil* still has to\n carry all of it, which is exactly why the bearing check against qa (gross\n allowable) must include self-weight and overburden.

When is a strip footing designed \"with a beam\" instead of a uniform slab?

When the span between columns is long relative to the practical slab thickness, a uniform slab\n thick enough to carry the longitudinal moment becomes uneconomical (excess concrete and excavation).\n Adding a longitudinal grade-beam stem lets the beam carry the longitudinal bending at a much smaller\n footprint while a thinner slab spans transversely between the beam and the footing edges.

Why do combined and strip footings often need top steel near the columns?

Between columns the soil pressure (acting upward, roughly uniform) tends to sag the strip — tension\n at the bottom. But beyond the columns, in the cantilever projections, soil pressure acts upward on an\n unsupported overhang, which hogs that segment — tension at the top — and that hogging typically\n extends a short distance past the column face into the main span as well. This is exactly the pattern\n every combined/strip footing detail you've seen (top bars over the columns, bottom bars at mid-span)\n is built to resist.

What is NOT covered by this tool?

Eccentric (unbalanced-moment) punching-shear stress transfer (Jc/J),\n headed-bar anchorage, trapezoidal-in-plan or sloped-section geometry, partial-contact (uplift) pressure\n distributions, settlement, and DXF/Word export are out of scope for this worksheet. The ETABS import reads\n joint coordinates from neither table, so combined/strip geometry (spacing, spans, projections) is always\n entered by hand — only the loads come from the file. All of the above need project-specific engineering\n judgment or a dedicated tool.

How does the ETABS import decide which footings to group together?

Every imported point gets a preliminary square size = √(governing service P / qa),\n rounded up to the size increment (6 in by default). Points that round to the same size are grouped\n into one footing mark automatically (F1, F2, …) — that mark is then designed once, for the member with the\n highest strength demand (the design representative), not for whichever point happens to be listed\n first. You can always move a point into a different mark by hand; the tool keeps your override on the next\n recompute.

Why does the ETABS import flip the sign of pier/column axial force?

ETABS reports a support's joint reaction as positive when it pushes up (resisting a downward\n load) but reports a pier or column's own internal axial force the opposite way — compression is\n negative, per the usual member-force sign convention. Importing both tables into the same batch would\n otherwise mix two opposite sign conventions, so pier/column P is flipped on import: positive always means\n compression, exactly like a joint reaction. A row that is still negative after the flip is a genuine\n uplift/tension case and is flagged rather than silently treated as compression.

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\n Need the beam-side calculators too?\n

See the companion ACI 318-08 tools on this blog for beam\n flexure, shear + torsion, and deflection design.

\n Browse all structural calculators →\n

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\n Disclaimer. This calculator is intended for preliminary engineering calculation and\n documentation support. Final footing dimensions, reinforcement, anchorage, soil parameters, load\n combinations, constructability, and code compliance must be independently reviewed and approved by the\n responsible licensed structural/geotechnical engineer for the specific project. The equations follow\n ACI 318-08, the CRSI Design Guide, the PCA Notes on ACI 318 / SP-17\n foundation examples, general shallow-foundation practice consistent with ASCE 7 and Bowles'\n Foundation Analysis and Design. Always verify against the governing building code edition and\n project geotechnical report. ACI 318 is a registered publication of the American Concrete Institute;\n this post is not affiliated with or endorsed by ACI, ASCE, CRSI, or PCA.\n

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