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Aerial view of Davyhume wastewater treatment works in Manchester

DfMA - One of the keys to unlocking a more efficient industry Mark Enzer

If truly embraced across the infrastructure industry, design for manufacture and assembly (DfMA) could bring a step change in efficiency and waste reduction

DfMA uses BIM technology to design assets and components that are manufactured in factory conditions and transported to site for safe assembly. The industrial nature of DfMA brings production line efficiencies to construction, reducing waste not only in raw materials, but in human resources, time, cost and carbon too.

Broad take-up of DfMA could help the industry achieve the ambitious targets set out in Construction 2025, the UK Government’s blueprint for the construction industry, which includes a 33% reduction in initial and whole life cost of assets, 50% faster delivery and 50% lower greenhouse gas emissions.

Reducing material waste to landfill

With an estimated 25% of all construction materials ending up in landfill sites, the most obvious waste-related benefit of DfMA is its ability to cut material waste. The accuracy of manufacturing avoids the waste of over-ordered raw materials seen in traditional construction projects, and allows for cost-effective recycling of unavoidable process waste.

As well as avoiding material waste from unused resource on site, DfMA can also facilitate material savings in project design. For example, the expansion of the Davyhulme Wastewater Treatment Works in Manchester will see more than 5000 precast elements used for 17 new water treatment tanks and a new activated sludge plant (one of the largest of its kind) as well as walkway bridges, walls and pipework assemblies. The use of precast, pre-stressed concrete wall panels and post-tensioning strands around the tank perimeter (within cast-in ducts) allows the wall panels to be thinner than if the wall were constructed using traditional reinforced concrete cast onsite. The use of prefabricated elements will result in a saving in concrete and steel reinforcements of between 10 and 20%.

Reducing time spent on site

The use of precast panels on Davyhulme is expected to cut project delivery by three months, highlighting another of the key waste-cutting benefits of DfMA: the fact that replacing onsite construction with onsite assembly is far quicker. Indeed, we have found that when compared to traditional construction methods, working with prefabricated elements can bring time savings of 50-90%.

The reduction of time spent working onsite also has health and safety benefits, as more work is completed in a safer factory setting, and many of the hazards of a building site can be reduced or avoided.

Reduction of the time spent on site also minimises disruption. With so much work now being done on existing assets in busy or congested spaces, there is ever-greater economic, political and social pressure to get the work done as quickly as possible.

Reducing design costs

DfMA brings standardised designs to construction, removing the need to design the same component over and over again. For a profession used to creating bespoke solutions, the question is: are we ready for a shift in the industry towards components that are ‘designed once and used many times’?

Clients such as Anglian Water have worked with their supply chains to develop catalogues of pre-designed and easily manufactured DfMA products that can be used many times across their programmes of work.

Mott MacDonald Bentley (MMB) is developing a catalogue of more than 80 DfMA products, predominantly for the water sector, including all the elements needed to create a sewage pumping station as well as more general components.

DfMA is a key element of the Northern Line Extension project, where precast beams, columns, lattice slabs, twin walls and other concrete elements will be precast. Laing O’Rourke, which is leading the construction of the project, has invested heavily in DfMA with a purpose-built factory – Explore Industrial Park (EIP) – to develop precast components. As lead designers on the project, we are making use of EIP’s product catalogue in our designs.

The use of pre-developed components can lead to savings in time and human resources at the design stage. Many companies prefer not to share intellectual property, but in the water industry we are seeing initial moves towards sharing products more openly, to the benefit of client organisations and their customers – the bill-payers. But will the wider industry be brave enough to follow this example?

Reducing whole life cost and carbon

DfMA brings savings to the whole life cost of assets too. BIM data for DfMA-produced elements can provide asset owners with full procurement, assembly, operation and maintenance details, allowing assets to be managed through their lifecycle.

‘Plug-in, plug-out’ modular solutions also reduce time and cost spent on maintenance. Replacing a damaged component with an identical ‘off the shelf’ product is far more effective than traditional maintenance techniques which are costlier, more time-intensive and often cause more disruption.

DfMA can also be used innovatively to drive down the carbon footprint of components, which reduces whole life costs via improved resource and energy efficiency. The positive impact is seen throughout the DfMA process, with BIM used to design less material-intensive components, while the logistics associated with the manufacture of DfMA components at specialised factories are more efficient than those required to bring raw materials to site.

Industry-wide uptake of DfMA is an important part of reducing the waste endemic to the industry, not just in raw materials, but also in human resources, cost and carbon. Such a move requires a change in the mind-set of the profession, as we move away from bespoke, onsite construction to designing assets formed from modular, manufactured components for onsite assembly.

However, there is another potential step for DfMA that would reduce even more waste. At present, the industry is still wedded to the linear economy in which resources are extracted, used once and then end up in a landfill site. The real shift will see us embrace a circular economy, in which waste stops being waste, but rather becomes a resource. In this future, assets, assemblies, components and parts need to be disassembled and repurposed. DfMA is an important step, but its necessary evolution will be design for manufacture, assembly, remanufacture and reassembly (DfMARR), which will herald another step change in reducing construction waste.

This article first appeared in Construction and Civil Engineering on 3 September 2015.

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