Standard design key to offsite manufacture

The UK construction industry is facing two key issues: a skills shortage and an increasing demand for improved infrastructure.

The government-commissioned Farmer Review identified that the number of skilled workers in the industry is likely to decline by at least 20% over the next decade (Farmer, 2016).

Offsite construction using standardised factory-made components has the potential to reduce the current risks to future infrastructure delivery.

As seen in the housing sector, it offers shorter programmes and reduced costs coupled with higher outputs and more consistent quality.

The reduction of headcount onsite also improves health and safety.

But though offsite is well suited to large housing schemes the often linear nature of infrastructure projects and programmes and their greater geographical spread are perceived as barriers to offsite delivery.

Need for standard designs

Traditionally bridges, retaining walls and other transport infrastructure assets are designed on a bespoke, site-specific basis. As a result, there is a lack of repetition.

Motorway gantries are a good example of where standardisation has been possible allowing the benefits of offsite fabrication to be realised.

Standard design families have been created that are adjustable for specific locations but allow automated design and manufacturing processes, which in turn improves buildability and reduces cost.

Similar processes could be used for road and rail bridge construction – but there is added complexity due to greater variation in loading, geometry and aesthetic influences.

Geotechnical interactions can also be diverse, particularly where integral construction leads to complex soil-structure interaction.

To realise the benefits of offsite for infrastructure, a compromise is needed from what might traditionally have been considered an ‘optimised design’.

Small concessions made in designing bridges to standard skews, or to modules of fixed span length, will most likely be offset by productivity benefits.

It would allow the use of standardised components (including multiple-use of expensive precast moulds) that lend themselves to automated digital engineering, manufacturing and traceability.

Attractive working environments

Offsite also enables many construction activities to be moved into climate-controlled, dry factories that are safe and pleasant places to work in compared to remote, weather-exposed site locations.

In time this could lead to a growing number of construction workers, with the industry once again becoming attractive.

There is also great potential to minimise exposure of the workforce to road and rail traffic and associated safety hazards.

Issues such as lifting heavy manufactured units and temporarily stabilising them during assembly need to be carefully addressed, but familiarisation and practice will bring its own safety benefits.

As well as greater education on how the industry can further utilise offsite construction, close collaboration in the design process between clients, designers, contractors and manufacturers is also important.

With a move towards increased early contractor involvement as a form of procurement, and the opportunities currently presented by the major infrastructure projects in the UK, the civil engineering industry is now at a point where it can and must seize the opportunity to change and modernise.

This means adopting standardised offsite construction.

This blog is based on an article published in the February 2018 (171 CE1) issue of the ICE Civil Engineering journal.