Watercube – National Swimming Centre, Beijing, China

In July 2003, Australian-based architects PTW and engineering firm Ove Arup won the contract to design and build the 2008 Olympic National Swimming Centre in Beijing.

Construction of the $140m landmark project, nicknamed the 'Watercube', began in December 2003, with the projected completion date of December 2006 revised to January 2008. The 70,000m² site is situated opposite the main stadium in the Olympic Green Precinct, which lies at the northernmost end of Beijing's north-south axis.

The design of the project associates water, as a structural and thematic leitmotiv, with the square, important in Chinese tradition and mythology.

Conceptually the square box and the interior spaces are carved out of an undefined cluster of foam bubbles, symbolising a condition of nature that is transformed into a condition of culture. The overall appearance of the aquatic centre is a cube of water molecules.

WATERCUBE DESIGN HISTORY

Architects, PTW and engineering group, Ove Arup, both based in Sydney, designed the Watercube in partnership with the China State Construction Engineering Corporation (CSCEC) and the CSCEC Shenzhen Design Institute (CSCEC+DESIGN).

As well as providing a multi-functional aquatic centre, the brief required extensive use of digital technology, energy-reduction and water-saving methods, as well as the incorporation of new construction materials.

With proposals from ten countries, including China, the USA, Japan, the UK and Germany, three designs were short listed for the design competition. These were submitted by Chinese architects, Shanghai Xian Dai Architectural Design, Rafael Vinoly Architects from the USA and the subsequent collaborative Chinese-Australian winning design.

The winning Watercube, the focal point of the swimming centre grounds, measures 176m on each side, rising to a height of 31m. It will hold 6,000 permanent seats with capacity for an additional 11,000 temporary seats to accommodate Olympic Games spectators.

DESIGN DETAILS

The Ove Arup / PTW design plays on the geometry of water bubbles within a square form. The structure's shape is specifically designed to work in harmony with the circular main Olympic stadium by the Swiss architectural team of Herzog & de Meuron Architekten with China Architecture Design and Research Group and Arup Sport London, known as the 'Bird's Nest', giving the area a visual 'yin and yang' balance.

The square form was also used in acknowledgement of its significance in Chinese culture, architecture and town planning.

There are two parts to the Watercube's structural framework – internal and external. The external structure forms the actual roof, ceiling and walls and comprises a flat web of rectangular boxed sections. These sections are then clad with the inflatable material transparent 'teflon' material known as ETFE.

The internal steel frame is based on the unique geometry of biological cells or soap bubbles. Ove Arup and PTW based this 'soap bubbles' structural concept on a solution from two Irish professors of physics at Trinity College, Dublin, known as the Weaire-Phelan structure, whereby a recurring pattern of polyhedrons is packed together to occupy a three dimensional space in the most efficient way possible.

Over 22,000 stainless steel members form the sides of these 'bubbles', which are welded at the joints to more than 12,000 spherical steel nodes. The benefit of this frame design, as well as resembling water bubbles, is that it is ideally suited to the seismic conditions found in Beijing.

WATERCUBE CHALLENGES

One of the challenges encountered by the designers, according to PTW managing director John Bilmon, was convincing Chinese authorities of the value of ETFE.

"There were a lot of myths about the use of ETFE," he says, regarding the material growing mould and being ineffective in muting external noise, "which had to be dispelled." Bilmon's team put the claims to bed by conducting extensive tests and making some adjustments to the material that would reduce the acoustic impact of outside noise.

The material was also shown to be superior in terms of lighting and thermal efficiency, and will protect the internal steel members from exposure to the harsh chlorinated aquatic environment – preventing their corrosion.

The eventual acceptance of the futuristic-looking ETFE, Bilmon says, is indicative of China's forward-thinking mentality.

The building's envelope required 100,000m² of ETFE, making it the largest ETFE structure in the world. The ETFE used was produced by Vector-Foiltec of Germany and Yuanda Group of Shengyang, China.

ENVIRONMENTAL CONSIDERATIONS

Where swimming pool systems usually pump water into the local wastewater networks as they backwash their filtration systems, the Beijing scheme will run the backwash water through a two-stage filtration system before returning it back to the swimming pools. This system will be highly water efficient in the face of Beijing's sporadic rainfall patterns and potential low water levels.

The equipment used for the water system was not the specific equipment originally suggested by the designers. Locally manufactured hydraulic equipment that met design requirements was used in its place.

CONSTRUCTION

At the time of design PTW and Ove Arup had envisaged the highly detailed structural members to be manufactured offsite and bolted together onsite, however a more traditional construction approach was taken by partners CSCEC.

The roof and walls were constructed in east-west strips on site, which were then moved into position. This enabled work to proceed on the building and roof construction simultaneously while preventing the need for any cranes or scaffolding within the pool halls, which may have damaged the pool structures and finishes, but the approach, says Bilmon, may have contributed to the delayed completion date.

"Hoisting balls of steel 1m in diameter into space, maybe up to 30m off the ground, positioning them with the [structural members] then pack-wadding them into position would have raised a number of very interesting constructional issues," says Bilmon. He is, however, ultimately impressed that such a sophisticated structure was built using traditional methodologies.

The landmark building will be used both before and after the Games as a multi-purpose leisure and swimming centre that, as well as swimming pools, will include a gym, ice-skating facilities and a cinema.