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ACI 318-19 Isolated Spread Footing — Concentric Column Load

Bearing area from service loads, then strength design with factored loads: two-way (punching) shear, flexure with the 0.0018A_g minimum and flexure-driven punching (8.6.1.2), and the ACI 318-19 one-way shear equation that depends on the flexural steel ratio ρ_w.

Footing and column

B (short side) ft

L (long side) ft

Thickness h in.

h − d in.

Column c₁ (along L) in.

Column c₂ in.

f′c psi

f_y psi

Size effect λ_s

Loads and soil

Factored P_u kip

Service P_a kip

Allowable q_a ksf

Extra service weight (footing + soil, if q_a is gross) kip

Results

Bearing: service pressure vs q_a—

Two-way: v_uv / φv_c—

Flexure (along L): M_u · A_s required · min · FDPS—

A_s design · φM_n—

One-way: V_u vs φV_c (ρ_w)—

ACI 318-1913.3.1.1 (bearing area), 13.2.7.1 (critical sections), Table 22.5.5.1(c) and 22.5.5.1.1 (one-way shear), Table 22.6.5.2 (two-way), 13.2.6.2 (λ_s in footings), 8.6.1.1 (A_s,min = 0.0018A_g), 8.6.1.2 and 8.4.2.2.3 (flexure-driven punching), 21.2.2 (φ), 13.3.3.3 (band steel). Clause numbers only.

VerifiedWire Reinforcement Institute ACI 318-19 spread-footing example reproduced within 1% at every step (differences are the example's intermediate rounding). One-way shear equation cross-checked against a published ACI 318-14 vs 318-19 comparison.

Preliminary calculation tool. Final design requires the full text of ACI 318 and review by a licensed PE. This tool follows ACI 318-19, the edition referenced by the 2021 and 2024 IBC; ACI CODE-318-25 was published in January 2025 and is expected in the 2027 IBC (changes include development length equations and seismic provisions).