# Formwork Lateral Pressure Calculator

Smaller of the two GB 50666 formulas, plus effective head height.

- Page: https://jianzhujisuan.com/en/formwork-pressure
- Category: Temporary Works (https://jianzhujisuan.com/en/c/temporary-works)
- Chinese version: https://jianzhujisuan.com/zh/formwork-pressure.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Concrete temperature 25 ℃, Pour rate 2 m/h, Pour height 3 m, Unit weight 24 kN/m³, Admixture No retarder (β1 = 1.0), Slump 110-150 mm (β2 = 1.15)): **Maximum lateral pressure 42.9 kN/m²**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Concrete temperature | number | 25 | ℃ |  |
| Pour rate | number | 2 | m/h |  |
| Pour height | number | 3 | m |  |
| Unit weight | number | 24 | kN/m³ |  |
| Admixture | select | No retarder (β1 = 1.0) | — |  |
| Slump | select | 110-150 mm (β2 = 1.15) | — |  |

## Formula

- **F1 = 0.22·γc·t0·β1·β2·V^(1/2)**: t0 = 200/(T+15)
- **F2 = γc·H**: hydrostatic from pour height
- **F = min(F1, F2)**: smaller value
- **h = F/γc**: triangular below h, constant above

## Worked example

25 ℃, 2 m/h pour rate, 3 m form height, 110-150 mm slump, no retarder: t0 = 5 h, β1 = 1.0, β2 = 1.15. F1 = 42.9 kN/m², F2 = 72 kN/m², so 42.9 governs with an effective head of 1.79 m - pressure increases only over the bottom 1.79 m.

## Questions

### Why does doubling the pour rate only raise pressure by 1.4?

Because formula 1 uses the square root of the rate. Doubling V takes √V from 1 to 1.414. Faster pouring stacks fresh concrete on layers that have not set, but those layers are also stiffening and absorbing pressure, so the effects partly cancel. Low temperature (longer t0) and high slump raise pressure far more.

### What is the effective head height for?

It defines the pressure profile: triangular growth over the top h metres, then constant maximum below that. Tie bolts and walers are designed for that one maximum, so no need to densify the lower rows. Designing for full hydrostatic over the whole height (72 kN/m² at 3 m) wastes a lot of steel.

### How do I pick parameters for layered mass pours?

Use the worst case. If the lower layer has set, treat each layer separately by its own height and rate. If it is still plastic, add the residual pressure from below. In practice the allowable pour rate is back-calculated from layer thickness and the shortest setting time - that decision belongs to the site technical lead.

## Related tools

- [Scaffolding Calculator](https://jianzhujisuan.com/en/scaffolding): Enter the wall perimeter and scaffold height to get the area plus tube, coupler and board quantities.
- [Formwork Turnover Calculator](https://jianzhujisuan.com/en/formwork-turnover): Initial formwork area and replacement allowance from total area and cycles.
- [Full Scaffold Material Calculator](https://jianzhujisuan.com/en/full-scaffold): Standards, tube length and weight, couplers and board area.
- [Roof Drainage Calculator](https://jianzhujisuan.com/en/roof-drainage): Catchment area to flow to downpipe count.
- [Roof Slope Layer Calculator](https://jianzhujisuan.com/en/roof-slope-layer): Average thickness and volume from span and slope.
- [Insulation Thickness Calculator](https://jianzhujisuan.com/en/insulation-thickness): Insulation thickness from a target U-value.

---

Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.