Foundations · Pad, strip & combined footings
Strip footing with eccentric load calculator
Strip footing under a wall with moment: eccentricity, effective width B′, trapezoidal pressure and ultimate bearing on B′.
Standard: Meyerhof effective width · Vesic factors
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Footing width | 1.2 | m |
| Founding depth | 0.6 | m |
| Vertical load per metre (service) | 150 | kN/m |
| Moment per metre | 20 | kNm/m |
| Cohesion c′ | 5 | kPa |
| Friction angle φ′ | 30 | ° |
| Unit weight γ | 18 | kN/m³ |
| Required FS | 3 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| e = M/N | 0.133 | m |
| B′ = B − 2e | 0.933 | m |
| qmax = N/B(1 + 6e/B) | 208.3 | kPa |
| qmin | 41.67 | kPa |
| Nq | 18.40 | |
| Nc | 30.14 | |
| Nγ | 22.40 | |
| qult = cNc + γDf Nq + 0.5γB′Nγ | 537.6 | kPa |
| q on B′ = N/B′ | 160.7 | kPa |
| FS = qult/(N/B′) | 3.35 |
- ✓ e ≤ B/6 (no uplift)
- ✓ FS ≥ required
Method, formulas and assumptions
- e = M/N = 20/150 = 0.13333 m
- B′ = B − 2e = 1.2-2*0.13333 = 0.93333 m
- qmax = N/B(1 + 6e/B) = 150/1.2*(1+6*0.13333/1.2) = 208.33 kPa
- qmin = 150/1.2*(1-6*0.13333/1.2) = 41.667 kPa
- Nq = EXP(PI()*TAN(RADIANS(30)))*TAN(RADIANS(45+30/2))^2 = 18.401
- Nc = (18.401-1)/TAN(RADIANS(30)) = 30.14
- Nγ = 2*(18.401+1)*TAN(RADIANS(30)) = 22.402
- qult = cNc + γDf Nq + 0.5γB′Nγ = 5*30.14+18*0.6*18.401+0.5*18*0.93333*22.402 = 537.61 kPa
- q on B′ = N/B′ = 150/0.93333 = 160.71 kPa
- FS = qult/(N/B′) = 537.61/160.71 = 3.3451
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.