Words by Tony Whitehead
WSP has worked with Laing O’Rourke on off-site fabrication techniques since 2004, and has helped the UK contractor to develop its industry-leading Design for Manufacture and Assembly (DfMA) programme. DfMA can involve re-engineering an original design so that on-site techniques such as in-situ concrete pours can be replaced with increasingly sophisticated off-site construction.
“At the start we assisted in defining designs for elements that could be effectively mass produced,” says WSP director Malcolm Davidson. “But since 2004 we have been progressively pushing the envelope in terms of the modern construction agenda. For example we have now reached the point where we can often specify a component by a reference rather than having to draw it and schedule it out. The reference tells the plant computer exactly what is required, and the computer will build it, incorporating any variables such as cast-in items.”
More often than not this will happen at one of LOR’s own plants, like the Explore Industrial Park in Nottinghamshire. Here, a variety of components make their way rapidly through a state-of-the-art production line. The whole process, including reinforcement, pouring and finishing, is highly automated. For example, robots add strengthening lattices before panels are oven-cured, flipped, and new panels added to create a hollow twin-wall element.
Alder Hey Children’s Hospital in Liverpool, designed by BDP, is a recent example of the DfMA method in action. While most buildings of this type would feature a steel or in-situ frame with non-structural cladding, Alder Hey was engineered by WSP to take advantage of LOR’s off-site manufacturing capability from the outset. The cladding comprises pre-glazed precast elements, which also act as loadbearing external walls. This has been achieved by a factory-engineered triple-layer system featuring a structural concrete interior, insulation, and an exterior layer of pigmented architectural concrete.
Floors and walls were added using lattice slab and twin-wall elements and, of course, bathroom and toilet pods were all manufactured off site. In all, the building used some 12,000 precast units along with 3,000 other pre-assembled components such as glazed screens, wiring assemblies and air handling plant. As a result, LOR calculates the building was completed 20% quicker than could have been achieved with traditional techniques.
Both LOR and Davidson believe there is more to come from modular. “We are getting better at it all the time. For example we are now creating precast components which incorporate wiring ready to be connected,” says Davidson.
He concedes, however, that while companies like LOR can further the cause of off-site manufacturing, progress depends on the whole industry, including clients and subcontractors, making adjustments to the procurement schedule. He points out that car manufacturers, for example, would find it strange that various specialists traditionally concentrate their effort at different times in the design and construction process. “Lighting designers might need to think about light locations before the frame components are made rather than afterwards,” he says. “So we have to bring a lot of design forward to make the best use of DfMA.”
But here too technology is coming to the rescue. At Alder Hey 3D visualizations of wards were used early on, to ensure services were correctly placed. Davidson says: “It enabled us to take a nurse, doctor or patient representative into a virtual room at design stage — and then if equipment could be better placed we could make that adjustment as a result of their timely input.”