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COMMENT Rolling out offsite benefits
Marian Kubisz of Adept Consulting (UK) looks at the increased specification of cold rolled steel frames in the current push for offsite construction solutions, and why system design considerations need to be brought into projects at the earliest stage
H
ot rolled steel frames are generally being considered as the original offsite framing solution, but the advent of cold rolled and formed steel products has seen them play a much bigger part in delivering panelised and volumetric modular construction solutions.
Steel Framing Systems (SFS) are now commonly used supporting cladding facade materials, as infills or oversailing the hot rolled steel or concrete frame. They are replacing blockwork solutions, being much quicker and cleaner and eliminating wet trades. The systems are generally designed at the last stage of the project – either by the manufacturer or in most cases by the subcontractor. This process can be lengthy and painful however, as too many people are involved, notwithstanding the client team’s expectations that it will be short and straightforward. By involving a specialist structural engineer/detailer in the early stages as part of the client side design team this problem would be eliminated. Another advantage is that by fully developing the design as early as RIBA Stage 2 or 3, an early dialogue with the supply chain can be established that will ensure lead times are adhered to. Delays on site can occur when the preferred supplier has reduced time to order materials or allocate labour, and these can be extremely costly.
By discussing and co-ordinating the process based on the end goal (the handover date), all parties – architect, structural engineer, detailer and principal contractor – can ensure the SFS system is 3D modelled and detailed before the manufacturer and or subcontractor is involved. The more complicated details and structures that require hot rolled steel in hybrid form (parapets, large openings, wind posts etc) can be identified and detailed prior to the tender process. The tender, based on a generic design, can then be priced very accurately – so the cost difference is in the subcontractor ‘prelims,’ rather than a design variation. This eliminates misunderstandings and boosts post-supply chain selection, hence giving client and contractor cost certainty.
We have in recent years seen cold rolled replacing hot rolled steel in areas, such as small to medium portal-framed and beam and column structures within the retail, commercial, agricultural and leisure industries. The increase in panelised framing means
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Involving a specialist structural engineer/detailer in the early stages as part of the client side design team would eliminate the problem
better quality factory assembled units that can include sheathing boards and insulation, speeding up the programme onsite.
Light approach
Light Gauge Steel Framed (LGSF) structures are made up of cold rolled or pre-formed ‘C’ and ‘U’ sections bolted together in factory jigs to ensure accuracy. Onsite assembly often utilises rolled formed metal decks within the structure – load bearing solutions that can be used up to 15 storeys. These are increasingly common in private and social housing as well as student accommodation. We are also seeing an acceleration in the use of
ADF OCTOBER 2021
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