Rebar Lifting
Prefabricated Reinforcement Lifting: Key Considerations
Prefabricating reinforcement cages has become standard practice in modern construction, significantly enhancing efficiency. However, this approach introduces challenges related to lifting, handling, and positioning the cage in its permanent location. This guide outlines the key aspects to consider during these operations to ensure safety and structural integrity.
Risks and Temporary Works
The increasing use of advanced analysis tools has led to lighter, more economical rebar cages. However, these designs often result in reduced rigidity, creating risks during lifting and handling. Structural designers typically do not account for temporary works in their calculations, as construction sequences are determined by contractors, site engineers, or project managers. These stakeholders must assess risks and decide when lifting designs are required.
Lifting rebar cages falls under the Temporary Works category as per BS 5975:2019 – Code of Practice for Temporary Works Procedures. While compliance with this standard is not mandatory, implementing its recommendations helps create a safer site environment and mitigate risks.
Design Challenges in Rebar Lifting
The design for lifting operations is influenced by several factors, including the cage type, lifting equipment, and site conditions. Key considerations include:
- Elastic Modulus Limitations: As rebar cages lack rigidity, their structural behaviour aligns with the geometry and angle of lifting chains. Designs must prioritise elastic rather than plastic section modulus calculations.
- Chain Angling and Compression Forces: The angle of lifting chains can induce compressive forces in the cage, increasing the risk of buckling.
Dynamic Factors: Lifting and transporting the cage introduces dynamic forces as per Table 1:
Recommendations for Safe Rebar Lifting
- Lifting Equipment Selection: Ensure all equipment is suitable for the weight and dimensions of the cage.
- Pre-Lifting Analysis: Evaluate cage stability under the anticipated dynamic forces and chain configurations.
- Additional Bracing: Install temporary stiffening elements or bars where required.
- Comprehensive Planning: Engage all stakeholders, including designers, contractors, and site engineers, to anticipate risks and plan accordingly.
References
- TWf2020:03 – Temporary Condition of Reinforcement Cages Prior to Concreting – Part 1: Management Guidance.
- TWf2021:01 – Temporary Condition of Reinforcement Cages Prior to Concreting – Part 2: Technical Guidance.
- BS 5975:2019 – Code of Practice for Temporary Works Procedures.
- Figures 1 & 2 taken from TWf2021:01 – Temporary Condition of Reinforcement Cages Prior to Concreting – Part 2: Technical Guidance.
- Figure 3 taken from an IDH project.
All information provided is based on industry standards and best practices at the time of publication. Users must ensure compliance with local regulations and seek professional advice where necessary. Independent Design House disclaims liability for any direct or indirect consequences resulting from the use of this guide.