Foundations · Pad, strip & combined footings
Combined footing (two columns) calculator
Length placing the resultant at the centroid (uniform pressure), width for allowable bearing, and maximum longitudinal moments.
Standard: Rigid footing statics (uniform pressure)
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 |
|---|---|---|
| Column 1 load (service) | 600 | kN |
| Column 2 load (service) | 900 | kN |
| Column spacing | 4.5 | m |
| Footing edge to column 1 (property line limit) | 0.3 | m |
| Allowable bearing | 200 | kPa |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Resultant | 1,500 | kN |
| Resultant from column 1 | 2.70 | m |
| Footing length 2(a1 + xr) | 6.00 | m |
| Width R/(qa L) | 1.25 | m |
| Line pressure R/L | 250.0 | kN/m |
| Zero shear from col 1 | 2.10 | m |
| Max moment between columns | -540.0 | kNm |
- ✓ Footing extends past column 2
Method, formulas and assumptions
- Resultant = 600+900 = 1500 kN
- Resultant from column 1 = 900*4.5/1500 = 2.7 m
- Footing length 2(a1 + xr) = 2*(0.3+2.7) = 6 m
- Width R/(qa L) = 1500/(200*6) = 1.25 m
- Line pressure R/L = 1500/6 = 250 kN/m
- Zero shear from col 1 = 600/250-0.3 = 2.1 m
- Max moment between columns = 250*(0.3+2.1)^2/2-600*2.1 = -540 kNm
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.