Welcome to WaterCube, the experiment that thinks it's a swimming pool

The showpiece of Beijing 2008 is just an Olympian test of theoretical physics, Peter Rogers reports


The story starts in 1887 - nine years before the first modern Olympics in Athens - with the great Victorian physicist Lord Kelvin. What, Kelvin asked himself, was the most economical way to divide space into cells of equal size with the least surface area between them? Kelvin proposed a solution in which the cells - which could, for example, be the soap bubbles in a foam - were 14-sided shapes called tetrakaidecahedra.

For more than a century Kelvin's structure remained the most efficient way to divide space. Then, in 1993, Denis Weaire and Robert Phelan used a computer program called Surface Evolver to find a new solution to the problem that was 0.3% better than Kelvin's. Three quarters of the cells in the Weaire-Phelan structure have 14 sides, while the rest are dodecahedra with 12 sides. Both cells have the same volume.

A decade later, Weaire and Phelan's record still stands and the £60m National Swimming Centre based on their structure is taking shape in the Chinese capital. When it is finished in 2006, the arena - which is also known as the Water Cube - will cover a floor space of 70,000sq metres and have room for 17,000 spectators. The building will have a steel frame based on a modified version of the Weaire-Phelan structure and will be coated with a transparent form of Teflon, called ETFE.

The Water Cube was chosen from 10 proposals in an international competition and was designed by two Australian companies, PTW Architects and the Arup Australasia engineering group, together with the China State Construction Engineering Corporation (CSCEC) and the CSCEC Shenzhen Design Institute. PTW and Arup had previously worked together on the Aquatic Centre for the 2000 Olympics in Sydney.


"For this project we were researching the meaning and relevance of water, and we were intrigued by images of foam, soap bubbles, molecules and corals, and the organic structures behind them," he explains. "Then we became interested in what a uniform structure that occupied three-dimensional space might look like, and we came across the original Kelvin foam on the web."

Although the Kelvin structure did not have the organic quality the team was looking for, it led them to the work of Weaire and Phelan. Wagner says they rotated a bit of Weaire-Phelan foam and a subsequent slice through the structure was more to their liking. Although the Weaire-Phelan structure contains just two different shapes, by the time the architects had finished with it they needed one hundred or so different shapes.

The team did not simply integrate the Weaire-Phelan foam into a traditional building design but took a radically new approach. In a conventional stadium, the walls, roof and so on are supported by a system of columns, cables and other structural elements. In the Water Cube, on the other hand, they are all one and the same.

"What we did was cut the overall shape of the building out of the foam structure, and then carve the internal spaces from the inside of the same piece of foam," Wagner says. "The resulting structure is seamless from wall to roof and back down again."

At first glance, a foam design might appear less robust than a more conventional structure, but appearances can be deceptive. Indeed, Wagner points out that seismic activity is a major worry for architects in Beijing, and says that the Water Cube design is ideally suited to absorbing the energy from earthquakes.

Swimming pools require a lot of heating and the Water Cube has been designed to be highly energy efficient. Some 90% of the solar energy falling on the building will be trapped within the structure and used to heat the pools and other areas. Not surprisingly, swimming pools get through a lot of water, but very little rain falls in Beijing. The designers have overcome this problem by recycling most of the "backwash" that would normally be drained away, and by storing whatever rain does fall on the building to top up the pools.

And how does Denis Weaire - who will not make any money from the design - feel about his work being immortalised in an Olympic venue? "Any immortality goes with the structure itself, and that is still debatable," he says.

Indeed, no one has proved that the Weaire-Phelan structure is the most economical way to divide space. However, Weaire is confident. "Will it ever be surpassed or disproved? I think not."