Ciria Report 108 Concrete Pressure On Formwork Direct

To appreciate Report 108's place in the industry, it helps to compare it with the American standard, ACI 347.

CIRIA Report 108: Concrete Pressure on Formwork - An In-Depth Review

Introduction

Formwork is a crucial component in the construction industry, particularly in the building of concrete structures. The temporary structure is used to hold and shape concrete until it sets and gains sufficient strength. One of the primary concerns with formwork is the pressure exerted by the concrete on the formwork, which can lead to deformation, instability, or even collapse. CIRIA (Construction Industry Research and Information Association) Report 108, titled "Concrete Pressure on Formwork," provides a comprehensive guide on the subject. This report aims to summarize and expand on the key findings and recommendations of CIRIA Report 108.

Background

The pressure exerted by concrete on formwork is influenced by several factors, including:

Key Findings

CIRIA Report 108 provides a detailed analysis of the factors influencing concrete pressure on formwork. Some of the key findings include:

Design Methods for Concrete Pressure on Formwork ciria report 108 concrete pressure on formwork

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:

P = (ρ × g × h) × (1 + (α × V))

where:

Case Study

A case study was conducted on a recent high-rise building project in London. The project involved pouring a large concrete slab using a climbing formwork system. The CIRIA Report 108 method was used to estimate the concrete pressure on the formwork. The results showed that the maximum pressure occurred at the bottom of the pour, with a value of 65 kN/m². The formwork was designed to withstand this pressure, and the pour was completed successfully without any incidents.

Recommendations and Best Practices

Based on the findings of CIRIA Report 108, the following recommendations and best practices are proposed:

Conclusion

CIRIA Report 108 provides a comprehensive guide on concrete pressure on formwork, highlighting the key factors influencing pressure and recommending best practices for design and construction. By understanding and applying the principles outlined in this report, engineers and contractors can ensure the safe and efficient construction of concrete structures.

References

Appendices

The appendices provide additional information and examples to support the report's findings and recommendations.

This report aims to provide an interesting and informative review of CIRIA Report 108. It is essential to consult the original report for detailed information and guidance on concrete pressure on formwork.

The report doesn't give one number; it gives a maximum pressure (( P_max )) based on the slower of two rates:

The key takeaway: Temperature is a variable, not a constant.

Project: 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 To appreciate Report 108's place in the industry,

Hydrostatic pressure (traditional): 24 kN/m³ × 2.8 m = 67.2 kN/m² CIRIA 108 pressure: P_max = 7.2 × (3/18) + 18 = 7.2 × 0.167 + 18 = 1.2 + 18 = 19.2 kN/m²

Outcome: 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.

The core of the report is the design pressure formula. For internal vibration (the standard method of compaction), the design pressure $P_max$ is given by:

$$P_max = C_1 \sqrtR + C_2 \sqrtH + C_3$$

However, in practice, designers usually utilize the simplified charts derived from the report's regression analysis. The standard CIRIA equation is often presented as:

$$P = D \left[ C_1 \sqrtR + C_2 K \sqrtH \right]$$

Where: