Technical
22 NSC
Apr 20
Offsite solutions
David Brown of the SCI reports on a recently completed research project, with
some suggestions to increase still further the offsite content of steel-framed
multi-storey buildings.
Offsite modular steelwork
Many designers would immediately comment that fabricated
steelwork is already an offsite solution, produced in factory
conditions – so what further is needed? This was the question for
a research project funded by Innovate UK, led by BCSA, involving
SCI, WSP, Severfield and Trimble, started in 2019. Before BREXIT
and COVID-19, the UK Government had identified increased
construction efficiency as a priority. Many will have heard of
the so-called ‘platform’ approach to design for manufacture
and assembly (P-DfMA) and possibly seen early examples of ‘kit
of parts’ solutions intended to be used across a wide range of
structures. The UK treasury are on record as suggesting that this
approach can boost productivity whist reducing waste by up to
90%. The time was right to consider solutions that might meet
this ambition.
The project was short – and was completed in February 2020.
BCSA and SCI members will have received the two project
deliverables – a short guide for building clients and a longer
guide aimed at building designers. Both may be freely
downloaded from steelbiz or steelconstruction.info
This article presents some of the project outcomes, hopefully
as ideas to consider and develop in detail as required.
Project objectives
One of the initial objectives was to investigate the opportunities
to integrate services into the steel frame, taking lessons from the
light gauge modular industry, where this is normal practice.
Repeatable units such as student accommodation or hospital
wards (Figure 1) may be prepared as ‘plug and play’ units with
most services pre-installed – so what can be done with multistorey
buildings? Opportunities exist, as the Latham report of
1994 identified: The contributions of … M&E contractors and
consultant to the construction industry is immense. The more
complex the building, the higher is the likely value of the M&E
input…
Initial enthusiasm for increased integration was dampened by
a series of (current) militating factors:
• Often, the M&E design is executed by the contractor and
therefore commences relatively late in the programme. By this
stage the structural design is mature and opportunities for
integration are limited;
• Detailed M&E design is undertaken by the contractor, so the
scheme design must accommodate alternative solutions;
• Currently, M&E contractors may offer a lower price for a
solution that does not require an offsite assembly facility.
If the benefits of prefabrication and preassembly of services
are to be realised, the key principles are:
• An early decision that the services will be prefabricated;
• A design which is specific to offsite manufacture;
• An overall programme which delivers timely information.
Structural solutions
The project also considered structural solutions involving
increased offsite fabrication and assembly, which offer benefits to
the end client. It should be recognised immediately that the
‘benefit’ may not be in reduced initial cost – in a competitive
environment, one would image that initial cost has been driven
down already. Instead, the benefits arise from:
• reduced site construction periods;
• reduced waste;
• fewer site deliveries and less disruption;
• increased precision;
• earlier access for following trades;
• in some cases, more lettable floor area;
• a more readily demountable structure;
• in some cases, reduced foundations, saving cost and time.
The project team recognise that the solutions described below
(and in more detail in the guides) have the status of ‘proof of
concept’ rather than a ready-made solution. It is anticipated that
solutions need finessing and modification to suit individual
requirements and company manufacturing processes. Similarly,
some of the solutions demand changes in responsibility
compared to today’s construction processes, and probably
revised commercial arrangements. As an example, casting large
composite floor panels offsite would demand a change in
responsibility, as a minimum.
Steel composite cores
Many multi-storey buildings are stabilised by a concrete core, slip
formed or jump formed. Conventional wisdom is that this is the
most cost-effective and appropriate solution. A steel composite
Figure 1 - Typical modular hospital ward (from mtxcontracts.co.uk) 24
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