With its clear span of 120m and tricky geometry, the roof of Zaha Hadid Architects’ Aquatics Centre is one of the most complex structures in the London 2010 Olympic Park.
Architect: Zaha Hadid Architects
Structural engineer: Arup
Location: Olympic Park, East London
Completion date: June 2011
It’s hard to believe that the 2.5sq km Olympic Park site, currently crawling with construction workers, cranes and partly completed sports buildings, was once a heavily contaminated, largely industrial site dotted with electricity pylons, breakers’ yards, chemical factories and timber merchants.
“I used to go past the site when I was young when there were still steam trains, and it was very depressing,” says Stuart Fraser, project director at Balfour Beatty. “By leading the construction process, I’ve seen a complete transformation of the site over the last four years and it’s fantastic to see a whole regeneration of the area not only for the games but also from a legacy point of view.”
The main gateway to the games will be Zaha Hadid’s Aquatics Centre, the practice’s third building in the UK and its most high profile. As the centre is the first building visitors to the Olympics will see, it’s important it has aesthetic drama – and the Aquatics Centre’s roof has it in spades. Walk over the vast new 45m wide land bridge and see the soaring 160m-long x 90m-wide column-free wave-like steel roof, which rests on only three concrete supports, cantilevering out in a powerful gesture. It’s an impressive testament to design, engineering and construction.
Located on a very constrained site, with a railway line on one side and a river on the other, in the southern part of the Olympic Park, the £303 million building houses two 50m swimming pools, a diving pool and a dry diving area. One of the drivers of the roof’s form was the need to accommodate temporary seating stands on either side of the centre to seat 17,500 visitors during the games, reducing to 2,500 once the Olympics are over and the stands dismantled. The roof had to be column-free on the east and west sides to allow for unobstructed views of the pools.
The design team cites the Aquatics Centre as the most complex of all the Olympic buildings to build, not only because of its roof structure with its clear span of 120m and tricky geometry, and its tight challenging site, but because of the sequential nature of the construction process, which has also involved relocating the power transmission lines underground and constructing the pool tanks once the roof was in place.
Source: ODA/London 2012
Steel truss structural system
The structural system used to create the form of the roof comprises a series of long-span steel trusses laid in a fan arrangement.
At the north end of the roof, the transfer truss is supported by two reinforced concrete cores spaced 54m apart, each measuring approximately 4m x 10m, and supported via fixed spherical bearings.
At the south end of the roof, the fan trusses are supported by a transverse truss which is, in turn, supported on a reinforced concrete wall 10m tall and 25m wide, via sliding spherical bearings – two free bearings sliding north-south and east-west and one guided bearing sliding north-south but resisting wind loads in the east-west direction.
Spherical bearings have been used to connect the roof structure to the substructure. These allow for a degree of rotation required at the supports as the roof deflects, as well as for resisting very large loads. The bearings will need to accommodate significant horizontal movements throughout the building’s life.
All the trusses are formed from fabricated H-sections, and the plates used to form these are of varying thicknesses, up to 115mm.
The roof’s overall stability is provided by a system of horizontal and diagonal cross braces in the roof surface between the top chords of the fan trusses. Structural members and connections will be fully concealed since the roof structure is fully clad and features a timber soffit to its underside.
The curved roof soffit is being lined with approximately 37,000 timber strips, each 2.5m long. The timber used is red louro, a sustainably sourced Brazilian hardwood, chosen for its durability and its ability to withstand a humid environment.
The timber is screwed to a substrate of counter battens fixed back to a Kerto sub-frame which is suspended from the structural steel to form the overall geometry of the timber cladding surface. The strips had to be laid exactly parallel to the main pool to help swimmers doing backstroke to swim straight.
Jim Heverin, associate director at Zaha Hadid’s, says the practice specified timber because it wanted “a natural material that was more tactile”.
He adds: “It was quite challenging geometrically to set out every piece of timber and we had to look at the fluidity of the lines.” They had to ensure that the timber surface remained smooth and free-flowing without the need for breaks or seams.
In the roof’s soffit, 37 large apertures or “light bubbles” – the largest 4m in diameter and the smallest 2.3m in diameter – have been made to allow for lighting, cameras and speakers. Externally, the roof is being covered with an insulated standing seam aluminium (stucco embossed) clip system.
Architect Zaha Hadid Architects, Client ODA, Structural & services engineer Arup, Contractor Balfour Beatty, Sports architect S & P Architects, Reinforced concrete subcontractor A J Morrisroe, Roofing subcontractor Lakesmere, Steel roof subcontractor Rowecord Engineering, Timber ceiling Finnforest Merk