Known for its audacious buildings, the UAE’s Abu Dhabi has added a spectacular undulating airport roof to the region’s tally
As might be expected of the world’s biggest construction site, the scale of Abu Dhabi International Airport’s new Midfield Complex is immense. Now almost half way through construction, the 700,000 m2 complex boasts a roof width of up to 319m - nearly twice that of Heathrow Terminal 5 – topped by a sinuous undulating form inspired by the contours of sand dunes and designed to seemingly float over the terminal like a large sky.
‘It’s one of the most spectacular pieces of structural engineering ever put on this planet,’ says a member of the construction team. ‘It’s monumental. People can’t believe the scale of the project when they visit. It leaves them speechless.’
It’s hard not to talk in superlatives when confronted with the magnitude of this endeavour.
When it completes in 2017 after an estimated 130 million man working hours, the complex will have an initial capability of handling 30 million passengers a year – the vast majority of which will be transferring to other flights. With ceilings rising to 52m and interior arches spanning from 65m up to 180m, it is intended as a spectacular gateway to the UAE capital of Abu Dhabi, and is part of the Emirate’s 2030 Vision to reduce the economy’s dependence on the oil sector through diversification.
The complex is designed by KPF with structural engineering by lead consultant Arup. Its unusual ‘X’ shaped plan is formed by four piers stretching roughly 500m from a ‘processor’ passenger hub. This arrangement is designed to ensure that it takes no longer than 10 minutes to reach any of the 49 gates from the processor.
The central processor space is akin, says KPF design principal Mustafa Chehabeddine, to an urban square while each pier refers to a different aspect of Abu Dhabi – sea, desert, oasis and city – through its graphics, material and colour palette. This approach is part of the aspiration to create a sense of place rooted in the UAE, says a spokesman, rather than an airport that could be anywhere in the world.
With its distinctive undulating contours, the vast 177,000m2 central processor roof is set to be one of the most memorable features of the new complex. This comprises three areas: a roof over the main body of the terminal that begins at full width over the entrance before narrowing and flaring out again towards the rear; two areas of saw tooth infill where the main roof narrows; and a perimeter wrapper roof.
KPF’s key design intent was that this organically shaped roof, though in reality supported on inclined steel arches, should appear to float above the airport building, draping over the glazed facade of the 5.5m pier perimeter in a wave form to provide solar shading. At the front of the processor building, this cantilever extends to 17m.
‘The design alludes to a vast roof floating above the arches. This was achieved by the delicate detailing of interfaces between the arches and the roof, always leaving a visual gap between the ceiling surface and the top of the arches,’ says Chehabeddine.
Realising such a complex and vast project with so little geometric repetition is just the sort of challenge that Arup likes, according to Dervilla Mitchell, project director of the Arup team responsible for engineering the complex.
‘We’ve had to put the best minds at Arup on it,’ she said, adding that the engineer worked with its Advanced Technology Group on the project, using applied car design technology. A BIM environment that allowed full 3D analysis was essential. Arup also carried out extensive structural analysis by creating a computer simulation to model and understand the 16,000 modes of vibration that would occur on the roof structure during an earthquake.
The crux of the engineering solution to enable such a spectacular form was the use of nine pairs of soaring, inclined steel arches. These mega-arches spring out in four directions like trees from concrete encased steel bases to form the huge curving spans that provide the largely column-free environment that the client desired.
GRC cladding will be used to create a seamless interface between the arches and bases.
Above the arches is the undulating roof grillage. Rather than touching these arches directly, the grillage is supported on ‘pedestal’ columns that sit on top of the arches.
‘In comparison to the very large scale of the spans these columns appear very, very slender, and make it look as if the roof is floating,’ says Mitchell. ‘You get the same sense of space as in cathedrals or great railway stations.’
By soaring high over key areas such as the departure lounge and retail hall, the roof and its series of nine rooflights is intended to aid passenger navigation by offering a sense of direction and progression.
‘The rhythm of arches and the associated use of skylights reinforces the building’s intuitive wayfinding,’ says Chehabeddine.
‘Very few public buildings have this fluidity of movement,’ adds a member of the construction team. ‘There’s a dynamic expression in everything from the arches to the roof structure.’
Across the full building, including the piers, the undulating roof is topped with 275,000m2 of standing seam aluminium, which is well suited to accommodating the changes in direction. Drainage was a major issue since when it does rain in Abu Dhabi, the downpour is intense, with the added risk of wind-blown sand clogging the drainage channels. There was also a need to avoid obtrusive guttering and pipework. The solution was to create a sufficient incline from front and back to channel the water off the central roof via main and valley gutters into very large guttering on each of the flanking saw-tooth roofs. Here it discharges through a syphonic drainage system capable of handling any sand carried by the rainwater.
The underside of the roof is finished in a suspended ceiling of approximately 50,000 perforated metal tiles below acoustic board and insulation. These tiles are illuminated by 18 chandeliers that project light upwards.
The design of the ceiling and roof was tested using full scale mock-ups of various elements of the complex. This particularly assisted in the dimensions of the ceiling tiles, which despite their large size look more like mosaic tiles from the ground 50m below.
Construction of such a dynamic roof has been complicated further by the extreme fluctuations in temperature, which can rise to a high of 50˚C – affecting both the temporary and permanent works.
The project is now 47% complete, with China State installing a total of 40,000 tonnes of structural steel. When it is finished, the roof will top a transparent structure which is expected to be visible some 1500m away from the highway when illuminated at night.
Processor roof grillage
- More than 2400 steel members form the roof grillage.
- Ten primary girders up to 300m long and 3.2m high run across the width of the central processor, interspersed with elliptical skylights ranging from 17m to 67m in length and 8m to 25m in width.
- Primary girders are linked by secondary trusses and tapered fabricated girders running front to back to form the main grillage.
- Edge beams span 45m between primary support girders to support the infill sawtooth roof that flanks the narrowing main roof on hangers.
Client Abu Dhabi Airports
Master architect KPF
Lead structural and MEP consultant Arup
Joint venture contractor TAV, CCC and Arabtec
Steel structure contractor China State Construction
Roof surface contractor Chadwick Group