Ciria Report 108 Concrete Pressure On Formwork File

CIRIA Report 108 (1985) provides a standard method for calculating lateral concrete pressure on vertical formwork using a bilinear model that accounts for modern construction variables like mix design, temperature, and placement rate. The formula, which calculates maximum pressure ( Pmaxcap P sub m a x end-sub

The formwork supplier designed ties at 1.2 m horizontal × 1.5 m vertical spacing, versus 0.6 × 0.8 m for hydrostatic. Material savings: 60% less tie hardware, lighter walers, and faster assembly. The pour completed without any deflection or leakage. This project alone saved over £15,000 in formwork materials. ciria report 108 concrete pressure on formwork

P_max = 1.2 × 24 × 2 × 2 = 115.2 kN/m² CIRIA Report 108 (1985) provides a standard method

The formula above does not apply infinitely. CIRIA 108 imposes two absolute limits: The pour completed without any deflection or leakage

In the late 1970s and early 1980s, CIRIA undertook a massive research project, observing real-world pours in walls, columns, and slipforms. The result, published in , provided empirical evidence that concrete stiffens (develops "shear strength") as it hydrates, thereby reducing peak pressure significantly below the hydrostatic maximum.

Before CIRIA 108, engineers primarily relied on hydraulic pressure formulas, assuming that fresh concrete behaved like a liquid (Pressure = Density x Depth). While this approach (often called the "hydrostatic" model) is safe, it is wildly uneconomical. It assumes that until concrete hardens, every inch of height exerts full fluid pressure.

Unlike the triangular distribution of a true liquid, CIRIA 108 describes a :