Temporary works & site · Formwork & falsework
Concrete formwork pressure (CIRIA R108) calculator
Lateral pressure of fresh concrete on wall or column formwork from the rate of rise, temperature, form height and mix (CIRIA R108), capped at full hydrostatic, with the tie load for a given tie grid and the form-face pressure envelope drawn to scale.
Standard: CIRIA Report 108 · AS 3610.1 formwork for concrete (design pressure) · tie loads
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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 |
|---|---|---|
| Element | Wall (C1 = 1.0) | |
| Form height | 4 | m |
| Vertical pour height | 4 | m |
| Rate of rise | 2 | m/h |
| Concrete temperature | 20 | °C |
| Mix coefficient C2 (0.3 OPC … 0.6 with retarder/blends) | 0.45 | |
| Concrete density | 25 | kN/m³ |
| Tie spacing (each way) | 0.9 | m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Temperature coefficient K | 1.000 | |
| CIRIA pressure | 53.4 | kPa |
| Hydrostatic limit Dc·h | 100.0 | kPa |
| Design pressure Pmax | 53.4 | kPa |
| Depth to Pmax | 2.14 | m |
| Tie load | 43.3 | kN |
- ✓ Design pressure ≤ hydrostatic
- ✓ Tie load ≤ 50 kN (typical 15 mm she-bolt SWL) — 43.3 kN
Method, formulas and assumptions
- CIRIA R108: Pmax = D[C1√R + C2·K·√(H − C1√R)], K = (36/(T + 16))², not exceeding D·h. AS 3610.1 permits recognised methods; confirm for self-compacting concrete (use full hydrostatic).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.