Formwork Lateral Pressure Calculator
Smaller of the two GB 50666 formulas, plus effective head height.
With the default inputs: Concrete temperature 25 ℃ · Pour rate 2 m/h · Pour height 3 etc.Maximum lateral pressure 42.9 kN/m²
Edit the inputs below to recalculate.Inputs
Result
| Setting time t0 | 5.00h |
| Admixture factor β1 | 1.00 |
| Slump factor β2 | 1.15 |
| Formula 1 | 42.9kN/m² |
| Formula 2 | 72.0kN/m² |
| Governing formula | Formula 1 governs (pour rate) |
| Effective head height | 1.79m |
Per GB 50666-2011 clause 4.3.1, take the smaller of the two formulas. Pressure is triangular up to the effective head and constant above it - which is the key point: lateral pressure does not keep growing with pour height. Pumping impact, drop height and vibration surcharges are additional. Actual formwork and shore design must follow the approved temporary works scheme.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
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 |
How to work it out
- Compute the setting correction first: t0 = 200 / (T + 15), where T is the concrete temperature as placed — not the air temperature and not the temperature at the plant.
- Apply equation one from GB 50666: F1 = 0.28 × γc × t0 × β × V^(1/2), where β is 1.2 with a retarder and 1.0 without, and V is the pour rate in m/h.
- Apply equation two: F2 = γc × H, where H is the height of the lift actually being poured, not the full formwork height.
- Design for the smaller of F1 and F2. The code explicitly requires the lesser value, not the greater.
- Effective head h = F / γc, which defines the pressure distribution diagram over the height.
Where it goes wrong
- Using only one equation — the code requires the lesser of the two. F2 governs squat massive pours, F1 governs tall fast pours, and using one alone errs either way.
- Using air temperature — T in the equation is the concrete temperature as placed, which can run 3-5 °C above air in summer and below it in winter.
- Taking H as the full formwork height — with layered placing the pressure depends only on the lift height and rate; the full height grossly overestimates.
- Using average pour rate — when pumping, the rate at the base often exceeds the average, and since pressure rises with the square root, doubling the rate adds 41%; that is where blowouts start.
Material and cost
Lateral pressure has no cost of its own, but errors cost either way: too high and the formwork is over-tied (30-50% extra through-bolts), too low and it blows out (5000-20000 CNY per incident).
On site
- This pressure sizes the through-bolts and the studs. Below 30 kN/m² standard details work; above 60 kN/m² it needs specific design.
- Retarders extend setting time and set β to 1.2, raising pressure by 20% — a summer concern.
- Control the pour rate in columns and walls, and keep moving the pump outlet rather than holding it in one place.
Basis
- GB 50666-2011 Code for construction of concrete structures, Section 4.3
- JGJ 162-2008 Technical code for safety of building formwork, Chapter 4 (loads)
- GB 50204-2015 Code for acceptance of concrete structure construction, Chapter 4
FAQ
Why does doubling the pour rate only raise pressure by 1.4?
What is the effective head height for?
How do I pick parameters for layered mass pours?
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Formwork Lateral Pressure Calculator. 2026-10-25. https://jianzhujisuan.com/en/formwork-pressure