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CROSS Safety Report

Proper design and use of cold rolled steel frames

Report ID: 93 Published: 1 January 2008 Region: CROSS-UK

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Overview

A reporter has been designing structures in cold rolled steel for approximately twenty years, mainly portal frame buildings, and some concerns.

Key Learning Outcomes

For clients:

  • Be aware that building regulations compliance is required for all buildings that members of the public have access to

For civil and structural design engineers:

  • A quality assurance system within your organisation, that includes the internal checking of calculations, can help prevent safety issues with computer programs from occurring

  • Competent supervision of design by experienced personnel can allow less experienced engineers to develop a feel for the right solution

Full Report

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A reporter has been designing structures in cold rolled steel for approximately twenty years, mainly portal frame buildings. They have informed CROSS that recently they have had a fairly close look at a commercially supplied portal spanning 9.0m, with a height to the eaves of 6.0m, and frames at 6.0m centres. Their calculations indicate that the rafters and stanchions are significantly overstressed even if all flanges were continuously restrained. There appear to be no inner flange restraints.  The reporter’s analysis is that, under dead + live loading alone, the rafter and stanchion frames need to be at half the spacings given.

The method of fixing the rails and purlins is also, they say, worthy of note. Normally cleats are used but this system seems to dispense with these and fix the flanges of the zeds directly to the flanges of the rafters and stanchions using self-tapping screws. The reporter considers that the information they have gleaned is sufficient to indicate that the frames could be dangerous in certain circumstances. They believe that members of the public have access to the building in this case and wonders how such the frames are getting local authority approval.

Expert Panel Comments

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It may be that these frames are intended for agricultural use and do not fall within the scope of the building regulations, in which case the public should not have access. There are two considerations here.

Firstly, are there very lightweight portals that are being given building regulation approval despite that fact that they do not comply with the relevant codes? Designing lightweight portal frames is complicated and designing cold rolled section prone to local buckling is even more complicated so it is important that a suitably high level of engineering is adopted.

Secondly have planning permissions and building regulations been violated so that buildings apparently intended for agricultural purposes, into which the public do not normally go, are being used for other purposes? CROSS will be extremely interested to hear of similar experiences.

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