Ciria Report 108 Concrete Pressure On Formwork Instant

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.

By trusting the CIRIA 108 calculation, they saved over £2 million in formwork costs and completed the walls safely and on schedule. Nearly 40 years after its publication, CIRIA Report 108 "Concrete Pressure on Formwork" remains the gold standard for rational formwork design. It shifted the industry from fearful over-design to intelligent, risk-aware engineering. ciria report 108 concrete pressure on formwork

Introduction In the world of concrete construction, few elements are as critical—and as often misunderstood—as lateral pressure on vertical formwork. Over-pour a wall or misjudge the setting rate of a column, and the result is a blowout: thousands of dollars in wasted material, potential worker injury, and crippled project timelines. In the late 1970s and early 1980s, CIRIA

| 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 | Nearly 40 years after its publication, CIRIA Report

Have a ready-mix engineer track the concrete temperature. If the truck arrives cooler than expected, recalculate P_max immediately. Case Study: The Heathrow Terminal 5 Pours When constructing the massive diaphragm walls for Heathrow Terminal 5 (London), engineers faced pours up to 15 meters deep. Ordinary hydrostatic assumptions would have required 200 kN/m² formwork—impractical and expensive.

Rearrange the formula: R_max = P_allowed / (1.2 × D × E) If your formwork is rated for 80 kN/m², you solve for R to determine the maximum trucks per hour.