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EEJ: Inside an Engineering Enterprise

Manufacturing for all sectors

There has been much discussion about the benefits of Design for Manufacture and Assembly (DfMA) in the construction sector over recent years. By developing designs around a range of standard factory-made components, DfMA delivers better quality, faster and safer installation and better value.

In the UK, DfMA is usually associated with larger building developments, such as housing and hospital projects. The combination of standardised digital designs, repetitive room layouts and sophisticated delivery teams on such projects has rightly led to increasing adoption of DfMA to reduce onsite risk and increase productivity.

However, DfMA is applicable to a much broader and more diverse project base, ranging from small building projects to major one-off infrastructure schemes in the transport, water and energy sectors. Indeed, the offsite manufacture of major components for remotely located energy projects − both onshore and offshore − is rapidly becoming very much the accepted norm.

DfMA is also not limited to standardised projects within a repetitive structure or layout. Every one-off project and its bespoke, monolithic elements can usually be broken down into a series of readily manufactured and assembled component packages that are able to utilise standardised approaches.

In terms of component size, the primary limitation is generally the transport capability and network between factory and site. For road transport this normally restricts the maximum width to around 3m and the weight to around 30t. But if the factory and site both have direct access to port facilities, the only real restriction is lifting capacity −typically 1,000−3,000t for large land-based crawler cranes.

If it is not practical to manufacture all components off site, another option is to set up temporary manufacturing facilities on site. For example, temporary concrete batching plants and precast concrete yards are frequently established on major transport projects, providing near-factory standard conditions on site. Slip-forming and pipe-welding machines are other examples of using semi-automated manufacturing processes in situ.

The key to successful implementation of DfMA in any construction sector project is the early engagement of the delivery and supply chain partners. This ensures all options for offsite (and onsite) manufacture can be fully analysed prior to any key design decisions being taken, such that the design is optimised and developed accordingly. A common digital engineering model is also vital to ensure the accuracy, integrity and connectivity of all manufactured components.

This article reviews some of the latest DfMA and construction product innovations from around the world, ranging from structural floors to rectangular and circular tanks, road bases and temporary solar power. They all have one aim: to de-risk projects and to deliver greater certainty for clients.

Structural slab solutions

Solid precast concrete floor systems for buildings are a classic DfMA solution, offering many advantages over cast-in-situ concrete or composite floors. There is less propping, no formwork and no large-scale wet concreting, plus significantly reduced mess, waste and noise.

The concrete quality of the individual floor planks is factory controlled, and reinforcing steel and fixings for façades, internal walls, safety rails and services can be precisely positioned. Fewer people are needed on site, improving overall safety levels. Above all, the floor-to-floor construction cycle is much quicker, with a saving of at least 50 per cent on programme possible.

There are a number of precast flooring solutions available, including those designed and manufactured by Laing O’Rourke businesses Explore Manufacturing and Bison. For example, the company designed, manufactured and installed over 5,000 lightweight precast planks at the 50-storey Leadenhall Building in the City of London as an alternative to the specified in situ composite floor design. The 150mm thick, typically 4.5m long units were designed to work compositely with the steel framework via a patented shear plate and dowel bar detail.

The client and site team quickly became big supporters of the plank system because of its speed and simplicity. However, opportunities for further refinement were identified. Key lessons learnt from the project were that further design optimisation and standardisation was needed to enable fully automated and flexible production. The fixing brackets could be simpler and more cost effective, while larger elements and fewer joints would lead to greater efficiency.

The result was the E6 megaplank design, launched by Laing O’Rourke’s Engineering Excellence Group (EnEx.G) in 2015. Due to simplified detailing and larger sizes, this is easier to manufacture, quicker to install and better integrated with the steelwork design. E6 megaplanks are now being supplied in up to 9m x 2.8m sizes at the Clarges residential and office development in central London.

The key to the design is the use of standard shear studs on the steel beams and at the ends of the planks to create the joints. After the 8t planks are lifted onto the steel frame, two reinforcing bars are placed into the joints and these are then grouted. The compression and tension stresses in the joints have been extensively modelled and tested to ensure they provide a robust connection and deliver the required structural diaphragm action of the floor plate.

In addition, the slabs are designed to span in both directions, which gives them further robustness during handling and allows for future modifications. For example, it would be possible to cut a 600mm service hole in the floor slab at a later date without compromising the floor strength.

Looking further ahead, the planks can also be removed and recycled by using hydro-demolition techniques. High-pressure water cutters can remove the grout in the connections but not damage the studs, enabling each plank to be lifted out and reused.

Research is currently underway to optimise manufacturing processes and drive product efficiency further. The patented E6 joint can also be adopted in conjunction with Laing O’Rourke’s existing hollow core and lattice plank flooring systems. For example, the roof structure of the Guy’s and St Thomas’ project was built using a combination of E6 planks and lattice slab.

In addition to structural flooring solutions, the E6 system has many potential applications in the infrastructure sector, including for rectangular tunnels, tanks and bridges. The EnEx.G is currently undertaking full-scale testing of E6-jointed tunnels for the nuclear sector, for example.

Sludge treatment tanks

DfMA is being increasingly applied on infrastructure projects in the water sector.

In the UK, water companies work to five-year Asset Management Plans (AMP) agreed with industry regulator Ofwat. The current AMP6 plans for 2015-2020 have changed the requirement to deliver defined outputs to one of delivering defined outcomes, which is likely to result in many smaller projects being undertaken than in previous periods.

To ensure smaller projects are delivered cost-effectively, water companies are now looking at how to produce a range of standard designs for smaller-scale water infrastructure products which can be readily adapted for each situation. The EnEx.G has developed a set of standardised small, medium and large designs for activated sludge treatment tanks. These were based around similar ‘parametric modelling’ solutions for standardised road and rail bridges, supported by grant funding from Innovate UK.

By capturing knowledge of how sludge tanks perform in practice, a parametric model has been developed which automates a design solution based on a standard range of the company’s twinwall precast concrete panels. Effectively the design output is a series of flexibly sized interconnected square tanks, which can be delivered to site as a series of prefabricated assemblies and parts. These can be designed, installed and commissioned in less time, with greater efficiency and reliability when compared to the more traditional approach whereby products are designed from scratch and use in-situ formwork and concrete construction methodologies.

The solution was developed through a process of top-down, bottom-up modelling. At the top there were the process requirements, customer needs and constraints, while at the bottom are models capturing the manufacturing requirements of the DfMA components. The models have been iterated both upwards and downwards, and they now form a viable and highly cost-effective design solution that can be adapted for all types of rectangular treatment tanks in the water and process industries. 

Further refinements will include an online ‘configurator’ for clients, similar to those used by car manufacturers. Once the site and process parameters are entered, the model will initiate an end-to-end delivery mechanism, starting with component manufacture.

The model will also be able to plan the logistics, based on the maximum size of assembly that can be transported to site, as well as the necessary foundation and temporary works designs, a detailed method statement for construction and commissioning, and a comprehensive maintenance schedule.

Cryogenic Storage Tanks

At the other end of the DfMA scale, extensive offsite fabrication is being used to deliver four large cryogenic tanks for the AUD$34 billion (£17 billion) Ichthys natural gas project near Darwin, Australia. The project is a joint venture between Inpex of Japan and Total of France and will deliver 8.4Mt of liquefied natural gas (LNG) and 1.6Mt of liquefied petroleum gas (LPG) annually from the Timor Sea Ichthys field.

Laing O’Rourke and its partner Kawasaki Heavy Industries (KHI) of Japan have an Engineer-Procure-Construct (EPC) contract for two LNG tanks, each with 165,000m3 net pumpable capacity, plus two LPG tanks of 85,000m3 and 60,000m3 capacity (for propane and butane respectively). 

The highly insulated tanks – effectively large sophisticated cool boxes − at the Bladin Point onshore processing plant are designed to keep LNG at –162°C, just below its boiling point at atmospheric pressure. The 90m diameter, 55m tall, full-containment structures have an inner tank made from 17−34mm thick, 9 per cent nickel steel alloy, which remains ductile at extremely low temperatures. The inner tanks and their 1.1m thick insulation are surrounded by slip-formed post-stressed concrete outer walls, a reinforced-concrete-covered structural steel roof, reinforced concrete foundations and associated piping, instrumentation and electrical infrastructure. The outer tank structures are designed to provide a vapour-proof containment as well as a secondary protection containment.

The site working hours needed to be reduced to an absolute minimum for a number of reasons. The Darwin area is second only to Texas, USA for lightning strikes, leading to significant downtime in addition to the heavy rainfall during the wet season. Heat, coupled with high humidity, makes for a physically demanding work environment for much of the year. With a local population of approximately 100,000, most skilled workers also need to be flown in from other parts of the country. Furthermore, Australia has one of the highest labour costs in the world. 

As much of the tank structures as possible have therefore been designed to be fabricated offsite. KHI manufactured the alloy tank plates at its Harima works in Japan to the largest size possible. Elements were welded in pairs at the factory to form the biggest units logistics could handle on the 35km journey between Darwin’s East Arm port and the site without a police escort. This effectively cut site welding by 50 per cent. The critical site welding and checking process was also largely automated, using a number of unique shell welding and digital NDT machines specifically developed for the project.

Likewise the domed steel roof structures were delivered to site from a factory in Batam, Indonesia as ‘petals’ up to 22t, 40m long and 5m wide. They were then assembled on the tank floors and the completed 1,100t roof structures were ‘air raised’ some 33m into position to the top of the tank. The aluminium suspended deck carrying the upper insulation under the roof structure was prefabricated in similarly shaped units in Japan.

The tank roof infrastructure will be able to be installed in far bigger units in early 2016 following recent completion of a module-offloading facility at the site. This has enabled KHI and Laing O’Rourke to design, assemble and commission offsite modules weighing up to 530t and measuring up to 40m by 20m. Delivery of these will be via a heavy-lift ship. 

Self-propelled modular transporters will then convey them around 1km to the tank site, where a 1,350t crawler crane will lift them into position. The modules will be complete with structural steelwork, fully spooled stainless steel pipework, fire mains, instrumentation and electrical infrastructure. They will have been tested and commissioned in the factory, ready for immediate use once in place.

Road stabiliser additive 

Offsite manufacturing is not limited to making and delivering major components; the design philosophy also extends to molecular engineering solutions at the nano-scale. A recent example is Stabilor, a patented liquid additive that enhances traditional cement stabilisation.

Cement stabilisation, involving mixing cement with water and soil, is a well-established technique to improve pavement performance. However, the treated layer needs days to cure before it can be used, the technique is not compatible with some soils and the treated soil tends to crack, making it vulnerable to water damage. Stabilor addresses these issues with rapid curing (enabling the treated layer to be driven on immediately), applicability to a wider range of soil types and improved waterproofing.

With major sites in Australia looking at downtime costs in the order of AUD$100,000 per day or more, the loss of haul roads or working areas during heavy rains is a major concern. In 2012, the additive was trialled on the Bladin Point site roads near Darwin, which were degrading during the annual monsoon period.

The rehabilitation trials were so successful that the product now forms part of the default temporary pavement solution at the multi-billion dollar works site. The largely unsealed site roads and hardstands – typically consisting of a 200−250mm layer of soil mixed with cement and Stabilor − have performed extremely well over the 2014/15 wet season. Recycling the existing pavement material overnight rather than importing new aggregate has prevented road deterioration from impacting site productivity and realised construction savings of more than 30 per cent for the client.

After its initial success at Bladin Point, the EnEx.G invested nearly a year in laboratory tests and field trials to validate the product’s performance. Laing O’Rourke subsequently purchased and relaunched the business under the Stabilor brand in April 2014. The formulation has since been improved, now containing synthetic copolymers, set-time modifiers, soil modification agents and biocide preservatives. It is non-toxic and non-hazardous, and can be applied wherever cement stabilisation is used.

In addition to use in short-term site infrastructure, Stabilor is working closely with highway agencies to validate the product for use in permanent pavement base, sub-base, and subgrade layers. A base course rehabilitation trial was completed on the Timboon to Colac Road, Victoria, in December 2014. This field trial, completed in conjunction with VicRoads, compared the Stabilor cement trial section with a cement-only section and found superior performance characteristics, confirmed by independent testing. Monitoring is continuing. Stabilor was also used by the Northern Territory Department of Infrastructure to rehabilitate sections of the Arnhem Highway suffering from flood damage. The repaired sealed road has performed well and monitoring is again ongoing.

Mobile solar power

Much of the world’s construction takes place in remote locations, requiring temporary accommodation villages for the workforce. These need water supply, sanitation, heating/cooling, catering and, above all, energy −which is traditionally provided by large mobile diesel generators.

In Australia, where such temporary villages are fairly common, a 500-person facility typically consumes 3Ml of diesel over its average two-year lifespan. This costs £1.5 million, generates 8,000+ tonnes of carbon dioxide and requires 80 road tanker deliveries.

Laing O’Rourke, which is frequently involved in building and managing temporary worker villages, started looking at more sustainable options to the energy issue in 2014. With the support of an AUD$900,000 government grant via the Australian Renewable Energy Agency (ARENA), it has successfully developed and manufactured a mobile solar farm solution. With suitable battery technology, this could ultimately remove the need for diesel generators altogether.

The first patented ‘SunSHIFT’ system was installed at a temporary village in Queensland serving a remote gas-processing project. In the previous four months the village had been running solely on diesel generators. In the next three months it derived up to 60 per cent of its daytime power from a 120kW solar power plant and saved over 75,000 litres of diesel.

According to ARENA Chief Executive Ivor Frischknecht: ‘The speed at which this game-changing solution has progressed from the drawing board to the field is testament to the clever design and its potential to bring more renewable energy to off-grid Australia’.

The system consists of a series of sturdy, reuseable, fully engineered 20kW solar panel arrays that can be quickly installed and connected on site. They are manufactured by Laing O’Rourke’s Redispan factory at Tomago in the Hunter Valley, which also produces modular, pre-engineered conveyor systems for materials-handling applications.

The ‘plug and play’ solar modules are designed for fast and reliable connection on site and are also ruggedised for repeated handling and to withstand severe tropical cyclones. They are delivered in containers together with steel tilting mechanisms, inverters and controllers, and then installed via flatbed trucks.

The system can be readily expanded and contracted to suit energy requirement through adding or removal of 20kW arrays. It readily integrates with new or existing diesel generator mini-grids and can either be purchased outright or paid for on a kWh basis.

By providing energy storage in the form of batteries, a much larger solar installation is viable as excess solar power generated during daytime can be stored for use at night. Power penetration can safely reach 100 per cent and, if solar arrays and batteries are large enough, SunSHIFT could potentially do away with the need for diesel generators.

In the immediate future hybrid diesel-solar or diesel-solar-battery systems are the most likely solutions to be adopted. In addition to construction-worker accommodation villages, SunSHIFT also has potential applications for short mine-life mines, remote communities and emergency power generation.

In 2015, SunSHIFT was named best ‘environmental innovation’ at the NSW Government’s Green Globe Awards.

David ScottStructural Engineering Director for the Engineering Excellence Group
John RobertsCivil Engineering Director for the Engineering Excellence Group
Ian BakerProject Director of the Ichthys EPC Cryogenic Tanks project
Dr Will Rayward-SmithClean Technology Leader, Engineering Excellence Group
Dr Kieran MacKenzieInnovation Engineer in the Engineering Excellence Group

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