Galliford Try is building a new test centre for the aerospace giant in an area of the UK renowned for its aviation heritage.
Project: Airbus Wing Integration Centre
Contract type: NEC Option A – Design and build
Contract value: £30m
Main contractor: Galliford Try
Steelwork subcontractor: Morgans of Usk
Structural engineer: Arup
Start date: January 2017
Completion date: June 2018
Bristol’s long aeronautical pedigree dates back to the very first years of powered flight.
Barely 12 months had passed between Britain’s first powered flight in 1908 and the 1910 production of the Boxkite Biplane by the Bristol and Colonial Aeroplane Company.
Bristol, and more specifically the Filton area on the outskirts of the city, soon became a UK centre for the aeronautical industry.
It was here that the Bristol F2 fighter plane, the go-to allied reconnaissance and fighter plane of the First World War, was designed and produced, as was the Bristol Beaufighter, the unsung night-fighting hero of the Battle of Britain and The Blitz during the Second World War.
In post-war Britain, the Brabazon provided Bristol’s first foray into transatlantic flight, having been adapted from a long-range bomber design. Unfortunately this was dropped in the early 1950s, but by the next decade it was the centre for the design and construction of the world’s fastest and most famous passenger aeroplane, Concorde.
Contemporary wing design
And the long connection continues to this day. To underline this connection, plane designer and manufacturer Airbus has called in main contractor Galliford Try to build its huge new wing-testing facility at its Filton site.
“This project will offer a purpose-built testing and research facility capable of carrying out full aircraft wing fatigue tests”
Jason Hunt, Galliford Try
The contractor has taken a £30m deal to build a 9,050 sq m research, testing and office facility as well as roadworks to create two new junctions onto the busy A38 dual carriageway alongside the site.
Galliford Try senior project manager Jason Hunt is in the pilot’s seat for the scheme, which will see the contractor deliver the completed centre by June 2018.
Galliford Try_wing testing facility_2
“This project will offer a purpose-built testing and research facility capable of carrying out full aircraft wing fatigue tests,” he says. “It will allow Airbus staff from four existing departments the opportunity to work in the same building to develop and test new ideas. It is a really important development for the Bristol site.”
The new Airbus Wing Integration Centre itself is broken down into three core areas: the strong wall and strong floor hangar; a second testing hangar; and the offices and laboratories that will accommodate the researchers and engineers.
Working with the strong floor part of the requirement for the test facility is a ‘strong wall’ for the fixing of equipment and test structures.
This must be capable of being moved in various positions and fixed using the tie-down bolts cast into the strong floor, offering engineers and researchers greater flexibility.
But this is no timid section of partitioning, manufactured using light steel framing systems. It’s a bespoke 13 m-wide, 10 m-high and 4 m-deep wall, fabricated in four sections by specialist firm Allerton Steel, using 65 mm-thick steel plate. Each section weighs 40-60 tonnes with the combined weight totalling 300 tonnes.
“It is being built to very high tolerances,” Mr Hunt explains, adding, “the front face of the wall will be milled down to make sure it is perfect across the sections.”
It is a bold vision for the manufacturer and also a challenging build for Galliford Try.
On the face of it, the new centre looks simple enough, but delve beneath its skin and there lies a building that is every bit as testing of structural and civil engineering knowledge as the completed facility will be of aeronautical engineering.
The team moved onto site in January 2017. A level brownfield footprint, it had been cleared and remediated in the past, albeit with a few asbestos hotspots left for the team to deal with.
“We effectively built top-down for the basement beneath the steel frame so that we didn’t impact on the delivery timetable
Jason Hunt, Galliford Try
“During the design stages our structural engineer Arup identified building on engineered ground as a potential risk,” Mr Hunt says. “We thought about lime stabilisation, but this would have been difficult due to the lack of space on site. It would also have proven time-consuming. It was easier and quicker to dig out and muck away, and it offered us more certainty.”
Some 11,000 cu m of material was removed from the site before construction work could begin in earnest.
The steel frame of the 64 x 24 x 23 m-high hangar building and the lower two-storey section that features the office and laboratories, is founded on a series of simple 1.5 x 1.5 m pad foundations. These double up to 3 x 3 m in certain locations.
Galliford Try wing testing facility 3
A complicated series of hydraulic ring mains serve the test floors. These offer flexibility for the facility by enabling hydraulic oil for test equipment to be diverted to any specific area on the floor. While this system will benefit the Airbus researchers, the Galliford Try team needed to change its approach to accommodate it and the huge tank that supplies the oil.
“We decided the tank should go in the deepest part of the site. We effectively built top-down for the basement beneath the steel frame so that we didn’t impact on the delivery timetable,” Mr Hunt explains.
All in the delivery
With more than 1,400 cu m of concrete poured during a 24-hour operation, the team had to be sure it had developed its delivery strategy correctly and had mitigated the risk from every angle of the operation as far as possible.
“We spent months working out exactly how we were going to carry out the pour. It was such a critical point in the project. We looked for every eventuality, every possible mishap and planned against it,” Mr Hunt says.
But even as the day of the pour loomed, the team could not rest easy.
It was bitterly cold in Bristol a few days prior to the pour and Mr Hunt developed plans for temporary heaters to blow warm air beneath the frost blankets. In the end the air temperature at the start of the pour was 2 deg C and rising. Temperatures peaked at 7 deg C, high enough not to cause any alarm.
“We had 247 deliveries lined up from three Cemex batching plants in the area that were dedicated to us that day,” Mr Hunt explains. “There were specified transport routes, a dedicated labour force and delivery vehicles. We were turning around a wagon every six minutes. It went very smoothly in the end, thanks to the work we had put in beforehand.”
About 650 tonnes of steel has been fabricated by subcontractor Morgans of Usk to provide the frame for the building, which is clad in a mixture of finishes including 100 mm composite insulated panels, aluminium window and curtain walling.
A raised access floor across the office space and an exposed concrete soffit throughout is part of the natural ventilated heating and cooling system.
It is the testing areas that have provided the biggest challenge to the construction team, though. Divided into two sections, the hangar comprises the ‘strong floor’ hall and a linked testing hall.
Galliford Try wing testing facility 1
The former (see box: The strong floor) comprises – as the name suggests – a super-strength floor featuring cast-in anchor bolts that will allow the Airbus researchers to fix the steel frame of a ‘strong wall’ (see box, below), aeroplane wings and testing equipment to the floor without any fear of movement under test conditions.
“The final facility will be able to carry out full-scale tests on wings,” Mr Hunt says. “They will simulate the stresses that a wing goes through during a 30-40-year lifespan so the strong floor and wall need to be able to withstand heavy loads, too.”
There are just a few short months before the completed Wing Integration Centre is handed over to Airbus, but with difficult engineering work of the strong floor installation carried out, the team is confident its efforts will help cement Bristol’s future in aeronautical design.
The strong floor
Key to the successful delivery of the test centre is the ‘strong floor’ in one section of the hangar space.
This is a 2 m deep heavily reinforced concrete slab, supported on 55 open bore piles of 1,050 mm diameter at depths up to 16 m. The slab was cast in a single 1,400 cu m pour over 24 hours (see box: All in the delivery).
It features 1,326, 1.8 m-long anchor bolts at 40 and 75 mm diameters, capable of supporting 350 kN. These are set at 1 m centres, cast to a tolerance of +/-3 mm and form the anchor points onto which the test equipment, strong wall and wings will be fixed.
The team cast the strong floor on a 150 mm-thick reinforced concrete support slab – a departure from the blinding concrete initially specified – to mitigate the risk of failure during construction of the strong floor.
The piles penetrate through this support slab with stubs placed on its surface to support 80 bespoke temporary work trusses. They have been specifically designed to hold the anchors securely and support the top mat of reinforcement in the final strong floor slab.
“The stubs were introduced to allow us to continue with the bottom reinforcement mat ahead of final positioning of the trusses, and yet continue with the initial control of their positioning,” Mr Hunt explains.
The bottom reinforcement mat features 40 mm-diameter bar throughout, with the top mat incorporating three layers of 40 mm-diameter bar and a further two layers at 16 mm diameter. The strong floor slab features 280 tonnes of bar in total.
Accurate final positioning of the anchors before casting the slab was paramount.
“Each anchor was checked for positioning through the X, Y and Z axis to an accuracy of +/-1 mm and signed off prior to loading out the top mat,” Mr Hunt says. “Once the top mat was sufficiently advanced the anchors were rechecked and wedged into final position. We then brought in a metrology specialist to carry out a final survey before we pour the concrete.”
Poured in one continued operation in 100 mm layers over 24 hours to avoid cold joints, the Cemex-supplied concrete met a design mix specified by Buro Happold. It features a reduced cement content to help try and keep the heat of hydration down and hit design strength after 56 days.
“We had data loggers set 200 mm from the top, bottom and in the core of the slab,” Mr Hunt says. “The mix couldn’t get any hotter than 60 deg C and there couldn’t be a differential of any more than 20 deg C between any of the data points. In the end the hottest it reached was around 30 deg C.”