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Offsite construction - or should it be, offsite design?

Cityscape with DfMA in background

Offsite Construction remains a major topic within the industry, thanks to the UK government’s presumption in favour of offsite. Yet, despite the title, perhaps the emphasis should instead be on Offsite Design, if we are indeed to reap the benefits of these modern methods. 

Here, Stuart Campbell, Business Development Manager, Civils & Engineering at Trimble (UK), talks more about how shifting to an Offsite and, in particular, a Design for Manufacture and Assembly approach is key, if this dream is to become a reality. 

The subject of Offsite Construction is everywhere, frequently proclaimed as holding the key to the industry’s future and featuring heavily in the UK Government’s plans to build better, faster and greener. 2020’s The Construction Playbook is just one example of this, calling for the adoption of a manufacturing-led approach and the use of innovation and Modern Methods of Construction. 

Infographic showing RIBA Plan of Work 2020

Yet, why is the focus predominantly placed on the construction phase, especially when this is one of the final stages in a Plan of Works? If you take a step back, the success and delivery of any project will often be determined as early on as the initial concept and design phase, with each completed stage in turn influencing and shaping the next. Clearly, if we as an industry are to deliver on Offsite, then a change of mindset is required, with the offsite way of thinking and offsite processes required right from the initial stages of a project. Only if a project is designed, modelled and detailed with offsite manufacturing and assembly in mind, can the value of these modern methods be truly realised. 

While the term ‘offsite’ is often thrown around, perhaps the real term that needs to be learned, understood and incorporated is DfMA (Design for Manufacture and Assembly). DfMA works to take offsite further, from construction to assembly; with an approach that focuses upon driving the design process towards creating a manufactured solution using standardised components, for ease of manufacture and efficiency of assembly. Structures designed in this way can help to push the well-publicised benefits of offsite even further; from a reduced construction programme time and cost savings through to better construction quality and improved efficiency and productivity levels on site. 

So, how can we all best incorporate DfMA on our next project? Start with the end in mind. In many ways, digital technology, including BIM software, is at the heart of delivering the DfMA approach, with the benefits of BIM perfectly aligning with the demands and requirements of offsite. 

Bridge component library within Tekla Structures

When it comes to Offsite and DfMA, accuracy is essential. With the aim for all structural components, whether it be standardised precast concrete bridge beams or retaining wall components, to be fabricated and manufactured off-site, digital design ensures the high levels of precision needed between components is first tested within the digital environment. The use of standardised components, first modelled in 3D and then tested virtually to prove the delivery, assembly and erection process, together with the use of self-propelled modular transporters (SPMTs), has allowed the offsite process to be scaled up massively. Now, even huge elements such as entire bridge decks can be delivered to site, moved into place and assembled through carefully planned, choreographed and well-rehearsed processes. 

Transportation and assembly of Peace Bridge

Failure to satisfy these tight tolerances runs the risk of Offsite’s time-saving benefits being lost, with the need for extensive rework or even re-fabrication. Here, the level of detail contained within a 3D model and the ability to solve design issues in the digital environment - rather than on site - can be invaluable, resulting in correct first-time components and a reduction in waste.

Moving on to fabrication, another integral stage in the Offsite sequence, and again digital technology can be key in helping to maintain and boost the benefits of these modern methods. As well as the 3D model making it easier to visualise and consider alternative design, connection or weld options, contributing to a more efficient fabrication process, the link between BIM software and CNC machinery can help to ensure that the aforementioned accuracy isn’t lost. For example, the automatic cutting and bending of reinforcement and the advanced fabrication of large structural steel elements, rather than bolting together parts on site.

Team in fabrication shop placing rebar using augmented reality

Ultimately, you need a structure that is designed to be built – a statement that may sound obvious but is perhaps even more critical when it comes to delivering on Offsite Construction. As well as using BIM technology to detail the individual components and ensure an easy and smooth fabrication process, you also need an efficient assembly process once on site. Using the 3D model, project and site teams can benefit from a digital rehearsal of the assembly works, from the overall phasing of the project through to the individual crane positions and any temporary works needed during the assembly process.

Finding best position onsite for crane using the Crane tool within Tekla Structures

While Offsite may appear to be everywhere, much still needs to be done if we as an industry are to truly deliver on this modern promise, starting with a change of approach. The Offsite way of thinking needs to be present throughout the project sequence, from the initial concept, design and detailing through to the on-site assembly, with DfMA a key part of ensuring that the vision is not diluted or lost as a project moves forwards. Offsite Design is the future.

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