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CROSS Safety Report

Unauthorised alterations to Light Gauge Steel Framing on site

Report ID: 669 Published: 1 July 2018 Region: CROSS-UK

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Overview

Concerns were raised after Light Gauge Steel Framing (LGSF) acting as a structural system was trimmed locally on site to accommodate the installation of balcony brackets without approval from the design team.

Key Learning Outcomes

For principal designers:

  • The need for collaboration over boundaries should be recognised where multiple parties are involved

  • The transfer and coordination of relevant information is important to overcome interface issues as demonstrated in this report

For construction professionals:

  • Any alterations to structural elements should be approved by the designer prior to works being carried out on site

  • Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design

  • Independent supervision on site by the design team or a third-party inspector can reduce the risk of any unauthorised changes from occurring

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As an increasingly popular method of supporting building envelopes, Light Gauge Steel Framing (LGSF) was utilised on the residential project in question. The LGSF acted as a secondary structure to the main concrete frame to carry finishes, façade and glazing at structural openings. The frame was installed satisfactorily by a sub-contractor and handed over following completion.

Poor coordination leads to safety issues

After the installation, additional balcony elements were fitted to the primary frame located at the first and second storey. Balcony brackets were required at a number of opening jambs, but no prior arrangements were made within the concrete frame to connect the balcony. It also was not coordinated with the LGSF sub-contractor or designer. In order to connect balcony brackets to the primary frame, the LGSF jambs were trimmed short at both head and base connections (Figure 1).

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Figure 1: LGSF trimmed to allow for installation of balcony brackets

Remedial design required

The glazing to the structural openings had already been installed and due to the removal of the LGSF jamb connections, it was now the plasterboard which both suspended the LGSF locally and restrained the glazing against wind and other loading applied. Fortunately, the LGSF sub-contractor was made aware of the occurrence, raised the issue with the supplier, and a remedial design was produced to bridge the brackets and reconnect the LGSF jambs back to the primary frame.

Risk of concealing safety issues

If left unnoticed, this structural fault could easily have been covered and neglected, where under much lower loading than designed for, may have resulted in failure of the envelope and glazed openings. This could have led to the LGSF, glazing or other finishes failing and falling from their installed position.

If left unnoticed, this structural fault could easily have been covered and neglected, where under much lower loading than designed for, may have resulted in failure of the envelope and glazed openings

It is important to remember that LGSF is a structural steel system and it is of vital importance that notching, and material removal not confirmed within the design does not take place. Examples such as the above, where future elements of the site programme require space not previously provided, must be coordinated during the LGSF design and ahead of installation to mitigate scenarios like this.

Expert Panel Comments

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The LGSF sub-contractor is to be congratulated on their diligence in spotting the conflict which could have had serious consequences. It begs the question however as to what happened to the site supervision?

Dealing with interface issues

There are two main issues. The first is that there was a failure to recognise at the design stage that provision would be needed to accommodate the balconies. CDM Regulations 2015 (CDM 2015) promotes closer working between designers, facilitated through the principal designer, and the transfer of relevant information in order to overcome interface issues.

The second is the failure of the principal contractor to refer the issue back to the relevant designer once the problem became known and before allowing notches to be made. The report highlights the problems of multiple sub-contractor suppliers without one overall guiding hand. In any structure, the principal designer ought to ensure there is a viable load path which all parties understand and respect across all structural parts - whoever supplies them.

The structural importance of secondary elements

There is always a need to inform following trades (and indeed future occupiers through CDM 2015) of the structural importance of secondary elements. This case illustrates once again some of the flaws highlighted in the Independent Review of Building Regulations and Fire Safety: final report.

Balconies, particularly cantilever balconies, must always be treated with care. There are frequent failures and there have been many fatalities due to collapsing balconies. You can search for safety information on balconies on the CROSS website.

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