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CROSS Safety Report

Erecting reinforcement cages

Report ID: 327 Published: 1 April 2013 Region: CROSS-UK

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Overview

A reporter asks about best practice guidance for the installation of pre-assembled reinforcement cages, as he can find very little guidance on the web.

Key Learning Outcomes

For the construction team:

  • Having a competent temporary works designer/adviser in place to supply an engineered solution can ensure all temporary works, such as the stability of rebar cages, are carefully considered and planned

For civil and structural design engineers:

  • If there is a risk of temporary instability to rebar cages, noting this on the drawings and risk register can ensure these are addressed on site

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A reporter asks about best practice guidance for the installation of pre-assembled reinforcement cages, as they can find very little guidance on the web. In the attached photograph (Figure 1), the contractor appears to have left the solution to the steel fixers on site. Whilst the reporter is not suggesting they are not suitably experienced, they do not consider that this is the right approach. They would have expected a qualified Temporary Works Engineer to have designed a system for the work which should have included:

  • Consideration of the bending moment and shear force induced as the cage is moved from the horizontal to the vertical, the dynamic loading effects and where applicable, the loads induced by the cage trapping onto a casing or guide-wall

  • Individual cage weights

  • Specification of lifting points including details of type (bands, bar or helical), steel grade, size and connections details (tying wire or welding)

  • Position of lifting points for horizontal lifts, vertical lifts, lifting from horizontal to the vertical and for moving c (note: these may be the same)

  • Method of identifying lifting point. For example, coloured spray or tags

  • Details of how cage is to be lifted (i.e. single cage or multi-cage lifts)

  • Details of pre-slinging requirements, including details of sling type (i.e. single or multi-use), length and safe working load

  • The amount and position of ties required and thickness of tying wire to take into account the strains placed on the ties by the cage in buffeting winds. It may be necessary to weld some vertical steels together

  • Any temporary support necessary

  • Establish that the recently poured concrete slab containing the starter bars had reached sufficient strength to withstand the uplift forces that would be imposed upon it by movement of the installed cage, which may be buffeted by the strong winds

Image
Figure 1: reinforcement cage

Expert Panel Comments

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The reporter has made very valid observations and it does seem that little advice is publically available. The comments made on report 357 which discussed the collapse of wall reinforcement cages are general and may be of some help but more work is needed and the views of readers will be welcome.

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