Foundations · Pad, strip & combined footings
Footing uplift resistance calculator
Uplift capacity from footing self-weight plus the soil frustum spreading at angle α, against wind uplift.
Standard: Soil frustum (cone) method
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 plan size (square) | 1.5 | m |
| Depth to footing base | 1.8 | m |
| Footing thickness | 0.5 | m |
| Frustum spread angle α | 20 | ° |
| Soil unit weight | 17 | kN/m³ |
| Design uplift | 80 | kN |
| FS on soil weight | 1.5 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Soil depth above footing | 1.30 | m |
| Frustum top width B + 2h tanα | 2.45 | m |
| Frustum volume h/3(B² + Bt² + B Bt) | 5.16 | m³ |
| Footing weight (24 kN/m³) | 27.00 | kN |
| Uplift resistance Wc + γs Vs/FS | 85.46 | kN |
- ✓ Uplift ≤ resistance
Method, formulas and assumptions
- Soil depth above footing = 1.8-0.5 = 1.3 m
- Frustum top width B + 2h tanα = 1.5+2*1.3*TAN(RADIANS(20)) = 2.4463 m
- Frustum volume h/3(B² + Bt² + B Bt) = 1.3/3*(1.5^2+2.4463^2+1.5*2.4463) = 5.1584 m³
- Footing weight (24 kN/m³) = 24*1.5^2*0.5 = 27 kN
- Uplift resistance Wc + γs Vs/FS = 27+17*5.1584/1.5 = 85.462 kN
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.