Concrete · Columns & walls
Basement wall propped top and bottom calculator
Basement wall spanning vertically between the floor slab at the top and the basement slab at the bottom, loaded by at-rest earth pressure (moist above, submerged below the water table), hydrostatic water pressure and a surface surcharge. The bending moment is found exactly along the height for the piecewise-linear pressure; reinforcement on the soil face satisfies both the ULS moment and a service steel stress limit for crack control in water-retaining construction.
Standard: At-rest earth pressure K0 with groundwater and surcharge · simply supported between the ground slab and the floor · AS 3600 flexure · AS 3735 crack control by steel stress for watertightness
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 |
|---|---|---|
| Span between props | 3.6 | m |
| Wall thickness | 300 | mm |
| Soil γ (moist) | 19 | kN/m³ |
| Soil γ′ (submerged) | 10 | kN/m³ |
| At-rest coefficient K0 | 0.5 | |
| Groundwater depth below the top prop | 1 | m |
| Surcharge at ground level | 10 | kPa |
| ULS load factor (earth + water) | 1.5 | |
| f′c | 40 | MPa |
| fsy | 500 | MPa |
| Cover (soil face) | 50 | mm |
| Bar diameter | 16 | mm |
| Service steel stress limit (crack control) | 150 | MPa |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Pressure at the base | 53.0 | kPa |
| Reactions top / bottom (service) | 33.8 / 63.7 | kN/m |
| Maximum service moment (at 2.07 m) | 44.2 | kNm/m |
| ULS moment | 66.3 | kNm/m |
| Steel for ULS | 659 | mm²/m |
| Steel for the service stress limit | 1,400 | mm²/m |
| Steel provided (governing) | 1,400 mm²/m → N16 @ 125 | |
| ULS shear at the base / φVuc | 95.5 / 144.6 | kN/m |
- ✓ Flexure (section adequate)
- ✓ Shear ≤ φVuc (no shear steel)
- ✓ Thickness ≥ 250 mm for watertight walls
Method, formulas and assumptions
- Pressure: K0·q + K0·σ′v + γw·(z − dw), σ′v using γ above and γ′ below the water table.
- With F(x) = ∫₀ˣ p(ξ)(x − ξ)dξ (closed form for the piecewise-linear pressure), the top reaction is F(H)/H and M(x) = R_top·x − F(x).
- Steel: the larger of the ULS requirement and Ms/(fs·0.87d) with fs limited (≈ 150 MPa) for crack control in water-excluding walls (AS 3735). Add the propping force from the floor diaphragm to its design.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.