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Foundation Bearing Pressure

Spread Footing · Uniform & Eccentric · Kern Check

When to use: Compute soil bearing pressure beneath a rectangular spread footing carrying an axial load P and a moment M. When the eccentricity e = M/P stays inside the kern (e ≤ L/6) the footing remains in full contact; outside it the heel lifts off and a triangular partial-bearing distribution governs. Results check the peak pressure against the allowable bearing q_allow.

Footing & Loading

Axial load P

kip

Moment M

kip·ft

Length Lmoment dir.

Width B

Allowable bearing q_allow

ksf

Key Formulas

e = M/P

kern: e ≤ L/6

q = P/A ± Mc/I = P/A ± M/S

S = B·L²/6

partial: q_max = 2P/(3B(L/2−e))

Max Bearing Pressure

3.59

ksf

Results

Area A64.00 ft²

Eccentricity e0.200 ft

Kern limit L/61.333 ft

Bearing conditionFull contact (e ≤ L/6)

q_max3.59 ksf

q_min2.66 ksf

q_allow4.00 ksf

✓ PASS

bearing q_allow 4.00 ksf

✓ KERN

e ≤ L/6, no uplift

References

P/A ± Mc/I — combined stress

Kern of section — middle-third rule

IBC §1808 — soil bearing

Bowles Foundation Analysis & Design