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CROSS Safety Report

Column stability during erection

Report ID: 1038 Published: 13 December 2021 Region: CROSS-UK


Overview

A reporter highlights the importance of ensuring steel columns are temporarily supported until they are sufficiently tied and supported by the permanent structure.

Key Learning Outcomes

For civil and structural engineers:

  • Consider the stability of single columns during the erection stages
  • Consider adopting 4 holding-down bolts irrespective of whether the base is assumed to be pinned or fixed
  • If stability depends upon connections to a concrete structure then co-ordinate the detailed design with the steelwork contractor

For steelwork contractors:

  • Use the excellent BCSA Codes of Practice for the erection of buildings
  • Ensure that workers are properly trained for all stages of erection
  • If stability depends upon connections to a concrete structure then co-ordinate the detailed design with the designer for the overall structure

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A reporter, working in the steel erection industry, warns of the risk of the stability of steel columns during construction. They are concerned that foundations will not have been designed for a column to free stand and construction staff may not be trained to know they should not be stood freely in the temporary condition. A serious injury or fatality may occur if a column was to fall over.

They recall a fatality that occurred over 20 years ago. A column, being erected on a site that they were not working on, fell over and they would not want this happening to anyone else whether they work for them or a competitor.

Their business always looks to ensure that temporary works procedures prevent any columns to free stand unless designed to do so. They say that when they tender for projects to construct steel frames, they know that they must allow for the columns to be tied into a rigid structure before the crane is released from supporting the column.

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This is recurrent consideration for both designers and steelwork contractors. Designers should realise that one function of a foundation is simply to provide stability for a column via its holding down bolts until the column is in the framed-up structure. This is especially important when columns are supplied in two storey lengths.

For steelwork contractors there are two BCSA guides which contain excellent guidance:

They note: 'In order to erect steelwork it is necessary at some stage that single columns are stood upright. Ensuring that single columns do not topple before they can be tied in to form a stable box is sufficiently important that it is recommended that the Steelwork Contractor describes this in a Task Specific Method Statement'.

They also note that occasionally resin anchors are used as holding down bolts in which case their capacity has to be evaluated and a method of stabilising the column during erection must be provided. If conventional holding down bolts are replaced with resin anchor bolts on site, because of location problems or for other reasons, then the designer should be informed.

An erection sequence for a single column is given in Pages 34-35 of the low rise guide that sets down step-by-step what is required. This shows a 4-bolt arrangement which is the preferred method by some designers to ensure stability irrespective of whether the model is for a pinned or fixed base. The key is that the sequencing retains stability at all times. If a freestanding column stability is reliant on the holding down bolts (a steel to concrete interface) then it is also essential that the foundation is big enough to prevent overturning.

For safety the work should be carried out by competent persons who have been properly trained.

For safety the work should be carried out by competent persons who have been properly trained.

Steel fabricators often do not bear responsibility for steel to concrete interfaces this being a task for the engineer responsible for overall stability of frame and foundations. Very often the engineer thinks differently and tries to pass off the final detailed design responsibility to the fabricator of all steelwork connections and not just the steel to steel joints with 'catch all' notes on drawings and specifications. This practice is not recommended; the engineer should manage steel to concrete interfaces unless there is complete clarity that a 'non standard' approach to the steel column base to foundation details has been adopted in the steel frame design and supply contract. 

There are differences in responsibilities for steelwork to steelwork connections and connections there are cast or anchored into concrete. There needs to be coordination between the parties whether the connections are temporary or permanent.

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