CIRIA Report 108 remains the definitive guide for calculating lateral pressures of fresh concrete on vertical and inclined formwork in the UK construction industry. While it predates the current European standards (EN 12812), it is widely regarded as the most practical and reliable document for this specific aspect of temporary works design. It bridges the gap between complex rheological theory and the pragmatic needs of a site engineer.
Unlike the triangular distribution of a true liquid, CIRIA 108 describes a trapezoidal or parabolic pressure envelope:
The report provides graphs and empirical relationships to determine this transition depth, typically 1–2 meters for ordinary concrete. Below the setting height, pressure is essentially constant.
This distribution has major implications for formwork design: tie rods and walers can be spaced more widely in the lower half of a tall wall, reducing congestion and cost. ciria report 108 concrete pressure on formwork
The report’s most influential contribution is the formula for maximum lateral pressure (P_max) at the base of a vertical form:
P_max = C1 × (R / T) + C2
Where:
For typical structural concrete (slump 50–100 mm, without retarders), C1 ≈ 7.2 and C2 ≈ 18, giving:
P_max = 7.2 × (R / T) + 18
Importantly, the report states that pressure never exceeds the full hydrostatic head (ρgh ≈ 24 × height in kN/m²), and it sets a minimum pressure for low rates or high temperatures. CIRIA Report 108 remains the definitive guide for
Example calculation:
If the form height is 3 m, full hydrostatic would be 72 kN/m². The CIRIA method allows a far lighter formwork system, saving material and labor.
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CIRIA Report 108 remains the definitive guide for calculating lateral pressures of fresh concrete on vertical and inclined formwork in the UK construction industry. While it predates the current European standards (EN 12812), it is widely regarded as the most practical and reliable document for this specific aspect of temporary works design. It bridges the gap between complex rheological theory and the pragmatic needs of a site engineer.
Unlike the triangular distribution of a true liquid, CIRIA 108 describes a trapezoidal or parabolic pressure envelope:
The report provides graphs and empirical relationships to determine this transition depth, typically 1–2 meters for ordinary concrete. Below the setting height, pressure is essentially constant.
This distribution has major implications for formwork design: tie rods and walers can be spaced more widely in the lower half of a tall wall, reducing congestion and cost.
The report’s most influential contribution is the formula for maximum lateral pressure (P_max) at the base of a vertical form:
P_max = C1 × (R / T) + C2
Where:
For typical structural concrete (slump 50–100 mm, without retarders), C1 ≈ 7.2 and C2 ≈ 18, giving:
P_max = 7.2 × (R / T) + 18
Importantly, the report states that pressure never exceeds the full hydrostatic head (ρgh ≈ 24 × height in kN/m²), and it sets a minimum pressure for low rates or high temperatures.
Example calculation:
If the form height is 3 m, full hydrostatic would be 72 kN/m². The CIRIA method allows a far lighter formwork system, saving material and labor.
