Ciria Report 108 Concrete Pressure On Formwork Today
Properly rigid formwork prevents bowing, deflection, and grout loss, ensuring the finished concrete meets tight architectural tolerances. CIRIA 108 vs. CIRIA Report R108 vs. CS 164
: Dependent on the concrete group and temperature, representing the rate of stiffening. C2cap C sub 2
Highly adaptable via customized concrete groups (GGBS, PFA, Admixtures). Uses chemistry modification factors ( Cccap C sub c ), which can sometimes be less granular.
CIRIA Report 108 moved away from overly simplified hydrostatic assumptions by identifying specific variables that dictate how fresh concrete exerts force: Rate of Concrete Rise (
A maximum ceiling limit based on the full fluid behavior over a specific operational height, adjusted for structural dimensions. ciria report 108 concrete pressure on formwork
CIRIA 108 defines the as a value between two extremes:
The "H" method, as presented in CIRIA Report 108, is a widely used approach for estimating concrete pressure on formwork. The method assumes a linear pressure distribution with depth, with the maximum pressure occurring at the bottom of the pour. The pressure (P) at any point is calculated using the following equation:
If formwork is designed for a pour rate of
The formula is elegant, powerful, and—when used correctly—profoundly safe. It recognizes that concrete is not an enemy to be contained, but a material to be understood. CS 164 : Dependent on the concrete group
): Temperature directly dictates the hydration rate of cement. Higher temperatures accelerate the chemical reaction, causing the concrete to stiffen and set faster, which reduces the duration and magnitude of the fluid pressure. Conversely, cold weather prolongs the liquid state, increasing the load on formwork. Concrete Density (
In modern practice, users often look for updates to this classic text. While CIRIA Report 108 laid the groundwork, it was heavily incorporated into later standards like the Concrete Society's and CS 164 . Additionally, modern European standards (such as BS EN 12812 for falsework) refer back to these core pressure calculation principles. Despite newer publications, the empirical constants and physics-based logic of CIRIA 108 remain highly respected and widely integrated into modern structural engineering software.
Don't rely on lab data. Take a trowel to the concrete in the jump form. If it isn't green (setting), you are still at maximum pressure.
Where is the concrete temperature at the time of placing (measured in degrees Celsius). CIRIA Report 108 moved away from overly simplified
Order a penetration resistance test (ASTM C403 / BS EN 480-2) on your specific mix at the expected site temperature.
Most contractors take E from a concrete test certificate done at 20°C. If your pour is at 10°C, E might be 3x longer. Always adjust E for ambient and concrete temperature. A 5°C drop can double E.
What are the of your concrete element?
As concrete technology evolved, structural design standards advanced. While CIRIA Report 108 is a classic baseline, engineers frequently compare it to newer European codes. Feature / Standard CIRIA Report 108 DIN 18218 (German Standard) BS EN 12812 / Eurocode Empirical formulas based on field data. Consistency class and setting time data. Comprehensive framework referencing updated data. Admixture Handling Uses basic correction factors.
