Ciria Report 108 Concrete Pressure On Formwork [exclusive]

12-story reinforced concrete core wall, London Formwork: Crane-lifted gang forms, 2.8 m tall panels Concrete: C35/45, slump 80 mm, rate of placement 3 m/h, temperature 18°C

| Feature | CIRIA 108 (UK/Global) | ACI 347 (US) | | :--- | :--- | :--- | | | Setting time (E) and Rate (R) | Column size and pour rate | | Pressure Equation | P = 1.2 x D x R x E | P = D x (C1√R + C2) | | Minimum Value | 25 kN/m² | 30 kPa (624 psf) | | Best For | Walls, deep sections, controlled rates | Columns, moderate pours | ciria report 108 concrete pressure on formwork

CIRIA Report 108 provided a semi-empirical method for calculating pressure. It moved away from the "worst-case scenario" of hydrostatic pressure and introduced a formula based on observed site behaviors. Since 115

The report identifies several variables that influence pressure, but the two most critical are: Rough form liners (e

Hydrostatic check: D × H = 24 × 8 = 192 kN/m². Since 115.2 < 192, the CIRIA value controls. You can design formwork for 115 kN/m², not 192. That is a in required tie strength.

Rough form liners (e.g., plywood) and stiff formwork can reduce measured pressure compared to smooth steel forms. CIRIA 108 provides reduction factors but recommends caution—friction effects are unreliable.