Requiring a quarter fewer workers and delivered 20 weeks faster than possible using traditional construction techniques, a new healthcare facility at Edinburgh’s Western General Hospital is one of the first UK buildings to have been designed for manufacture and assembly. By value, 55% of the Royal Victoria Building was made offsite under factory conditions and delivered just in time to be craned into place. We provided detailed civil and structural engineering design for contractor Laing O’Rourke.
The £35M facility was built for NHS Lothian, part of the National Health Service. It provides 147 bedrooms, specialist geriatric, rheumatology and dermatology wards, plus assessment and treatment centres.
As well as saving time, design for manufacture resolved the challenges presented by the site. Located on the main hospital campus, working space was restricted and construction-related noise, minimised. The campus itself is bounded on one side by a main traffic artery and on the other three by a one-way ‘blue light’ route used by ambulances. The consequences of disrupting traffic were severe so we set out to reduce the number of delivery trucks, concrete wagons and staff cars coming to the site.
Design for manufacture and assembly involves bringing together large, ready made components instead of combining raw materials in situ, involving multiple deliveries and many different specialist trades. The Royal Victoria Building was designed as a precast reinforced concrete structure. Wall panels were ready fitted with windows, making the building weather-tight without the need for glaziers. Stairs came with handrails pre-fixed and were safe for use straight away. En-suite bathroom pods for each of the 147 patient rooms were delivered to site plumbed and finished, ready for connection to building services.
Collaborative 3D design
Precast components came from Laing O’Rourke’s factory in Nottinghamshire, which uses robotic production methods comparable to those in the automotive industry. The design for manufacture process was carried out with the aid of building information modelling (BIM). It started with a detailed 3D model developed in close collaboration with the architect and the client’s staff, the building services designer and Laing O’Rourke’s fabrication supply chain.
3D design allowed health service staff to visualise the facility and comment on the layout during the early design stages. It enabled alignment between the architectural vision and detailing requirements imposed by the method of construction. We coordinated and rationalised the structural elements to eliminate clashes. And with Laing O’Rourke’s supply chain we optimised the structure for fabrication.
At the factory, dimensions and structural information from the 3D model then became the reference point for production. Reinforcement was cut, bent and laid out robotically. Concrete was mixed to the right strength in precisely the right quantities, eliminating waste.
Components were selected from a predefined ‘kit of parts’. Unique elements such as walls were made on giant casting tables. As part of the automated process, form work edges were positioned on casting tables to create precast concrete panels with millimetre-accurate dimensions. Casting tables were shaken to achieve good concrete placement and compaction. Stairs and shafts were created the same way.
After casting, all elements were cured in temperature-controlled chambers. The chemical reaction when concrete hardens generates significant heat. Concrete cast in situ is prone to cracking as it cools. By carefully managing the cooling process, Laing O’Rourke was able to control concrete strength and minimise cracking.
We adopted a simple but highly effective method for joining the components together. Conventionally precast elements are made with reinforcement bars protruding from the edges. Bars from adjoining elements are overlapped and ‘stitched’ with concrete poured in situ. The components for Royal Victoria Hospital had almost no exposed reinforcement, but were fabricated with matching sockets. 40mm diameter steel dowels were inserted into these and a permanent structural connection achieved by pouring cement grout around them. The grout cured within hours, allowing a swift erection process.
20% time saving, zero accidents
The schedule was reduced from an estimated 110 weeks using traditional techniques to 90, allowing the hospital to take shape with amazing speed. Laing O’Rourke the handed the finished building over to NHS Lothian in April 2012, two weeks early. The manufacture and assembly process also delivered outstanding safety performance. Approximately 60% of construction injuries occur while workers are fixing steel for in situ cast reinforced concrete. Lifting and fitting lightweight formwork for pouring concrete on site can also be hazardous, particularly in windy conditions.
Considerate Contractors, a body promoting higher standards in the construction industry, gave the project its highest award – Gold.