Water Cube, Chinese symbolism, the Kelvin problem, Weaire-Phelan and ETFE Technology

Beijihttp://www.flickr.com/photos/52381548@N00/463714674/ CN-Peking-Swimming Centre 2008-02-05.03.07ng National Aquatics Centre and Beijing National Stadium (background)

More than a platform for extraordinary athletic feats, the Olympic Games have become a Cultural Olympiad whose purpose is to display the hosting nation’s cultural economy on a global scale. It’s a platform for designers to realise challenging architecture, make grand statements and introduce bold innovations, an opportunity to show-case and recreate a nation’s image through ambitious projects that in some cases, reinvent a nation, and make a contribution to its urban development.

With the building of the two main stadia for the Beijing Olympics in 2008, China’s architectural and engineering reputation soared. Both The National Stadium (known as the Bird’s Nest) by Swiss architects Jacques Herzog and Pierre de Meuron, and the National Aquatic Centre (known as the Water Cube) by the Australian Firm PTW Architects, surpassed all architectural expectations.

Increasingly, stadia have become the new cathedrals of our times. The dual cathedrals, The Bird’s Nest and the Water Cube, situated along the axis that was once the preserve of the Forbidden City and its associated buildings, inspired and awed visitors to the 2008 games. Today these buildings have become tourist attractions outliving their life expectancy as venues for the Olympic Games.

In the 15th century Beijing was symmetrically laid out on a north-south axis along which it’s most symbolic structures aligned with the Forbidden City at its centre. The Drum Tower and the Bell Tower (used for centuries to tell the time)  and Jingshan Park (originally the Imperial Gardens) all lie to the north. More recently the communist regime introduced Tiananmen Square and its Monument to the People’s Heroes and Mao Zedong’s Mausoleum to the south in 1958. Tiananmen Square, monument to self-sufficiency, now sits opposite the country’s symbol to its latest aspirations and global ambitions, the Olympic Green Precinct.

The two most notable contemporary additions at the northernmost end of the north-south axis are now the Bird’s Nest and the Water Cube. Their outstanding architectural structures push the boundaries of imagination, innovation and engineering while they continue to observe Chinese symbolism and yin yang balance. The Water Cube’s rectangular form represents the earth and compliments the circular shape of the adjacent Bird’s Nest, symbol of heaven. The bowl-shape of a giant bird’s nest, symbolising abundance, glows red at night representing the red phoenix for protection.

Since the 2008 Beijing Olympics the Powerhouse Museum has acquired the original model for the National Aquatic Centre developed by ARUP International. The sectioned construction model is an excellent representation of the outstanding structural and material engineering features that have made the Water Cube so unique. It shows the sectioned interior of the main foyer while accurately mimicking the building. In addition, one can clearly see the geometry adopted by the structural engineers and the specialised roof and wall cladding materials and design. Made for professional and promotional use, the model assisted ARUP engineers to model the Water Cube design in physical space and to visualise the unique cladding on the structural framework.

Water Cube Model, Powerhouse Museum

Water Cube Model, Powerhouse Museum

In the design and construction of the Water Cube, PTW worked with a consortium that included engineers from ARUP International engineering group, China State Construction Engineering Corporation (CSCEC ) and China Construction Design International (CCDI ) of Shanghai to achieve their vision. The Water Cube introduced a range of engineering and architectural innovations to make the building look like a cross-section of foam in the shape of a cube. It required new technologies and engineering solutions but it also needed to be functional and efficient in its use of water, energy and resistance to earthquakes. The end result is inspirational.

Conceptually, water in the form of foam, offered the best architectural solution which led to a structure made to look like a cluster of bubbles. To solve engineering issues designers and engineers at ARUP pursued the work of physicist Lord Kelvin who in the 1880s attempted to determine the least surface area of a volume and the space and surface area they occupy when packed closely together. At first Lord Kelvin’s work seemed to offer the right solution to achieve this however through digital reproduction at ARUP, engineers found they were unable to reproduce a convincing naturalistic pattern that mimicked foam effectively. It was found that Kelvin’s structure was too regular.

Engineers then turned to the research carried out by Denis Weaire and Robert Phelan in 1993 and found their structural solution used 0.3 percent less surface area than that of Kelvin. The structure was made up of two different shapes that when clustered, digitally reproduced cross-sectioned patterns that were more organic. One shape was a slightly irregular dodecahedron and the other was 14-sided shape with two opposite hexagonal faces and 12 pentagonal faces. The cross sections were reproducible, more naturalistic and produced a repetitive and buildable pattern. In fact the pattern repeated in such a way that was very difficult to detect.

Each bubble is outlined by steel beams and provides the weight bearing structure of the building. This structure is so strong that the entire building could be turned on its side without loosing structural strength. Buildings usually rely on triangles to provide stiffness. Without triangles the Water Cube is more flexible and more able to withstand earthquakes.

The bubbles are made of ETFE pillows. ETFE (or copolymer of ethylene and tetrafluoroethylene), has specific qualities such as translucency, high absorption of radiation and low UV absorption. Its flexibility makes it easily used for pneumatic cushion structures. It is also fire and heat resistant, deteriorates far less than other materials, possesses ductility and crushing resistance and is self cleaning as the friction coefficient of the material prevents dust collection.

The pillows are made of three layers; an outer, middle, and inner layer. The air inside is pressurised to 200pa and the pillows are placed in the polygonal openings created by the steel beams creating the roof and ceiling as well as the exterior and interior walls. The middle layer offers thermal and acoustic insulation and also protects from bird strikes and flying debris during typhoons. Superior in terms of lighting and thermal efficiency, ETFE also protects the steel structure from corrosion and it is estimated that it will help the building last 100 years.

By combining ETFE technology, comparing the Kelvin problem to Weaire-Phelan structures and the use of Chinese symbolism, Architects at PTW were able to provide a multifunctional aquatics centre that reduces energy consumption, incorporates new construction materials and methods that can withstand seismic activity. The Water Cube is now the largest ETFE structure in the world consisting of more than 4,000 bubbles, some as large as 9 metres in diameter. Today the Water Cube has been converted into an underwater themed water park with colourful air bubbles, sea weed, coral and jelly fish to extend the aqueous atmosphere of the building. Whether or not it is sophisticated enough to complement the geometry of the architecture will be the test of time.