Structure

A New Beginning in Design Thinking

The National Aquatics Centre in Beijing marks a new beginning in design thinking. It responds to an idea about what a structure should or could be. This new thinking has been spurned on by one question: “How does structure fill space?”

Traditionally, structure is all to do with forms and services such as beams, slabs and columns. In big roofs, structural engineers have explored the idea of manipulating the shape to enhance the structure such as arches and domes. Sometimes it was experimented with separating the structure from the shape of the thing it supports. For example, the cable net supporting the roof of the stadium is not the same shape as the roof itself.

Previously, structure has been viewed as a surface. But in nature, structures that fill space are a regular occurrence such as crystals that combine to form rocks. And so is the structure that is the Aquatics Centre.

The Structure

The Water Cube is essentially a structure made from an organic network of steel tubular members and clad with translucent ETFE pillows. The huge complex is 177x177x31m.

The cube is comprised of a series of steel tubes welded to round steel nodes, which vary according to the loads placed upon them. There is therefore a huge variety in sizes, with around 22000 steel members and 12000 nodes in total. If all the steel members were lined up in a row the line would travel for more than 90km!

The two internal compartments and the roof structure are designed around a steel space frame never previously used for an architectural or engineering construction.

There are 4,000 bubbles making up the Water Cube, with some as large as 7.5m wide. The roof comprises seven bubbles and the walls 16 bubbles, which are repeated throughout. The key to the randomness of the façade is that the repeating cells are made up of two different size cells, which give this effect when cut by the building surface planes.

The square shape of the complex reflects the Chinese philosophies of the square representing Earth, and circles representing the heaven. The resulting structure is a very simple regular building form, but with very complex geometry in the façade which creates a transfixing and beautiful effect.

ETFE

ETFE is ethyl tetra fluoro ethylene – a strain of fluoro polymer. The skin of the Aquatics Centre, which covers both the inside and outside of the structure, has 100,000m2 of ETFE bubble cladding. A tough recyclable material with a durability of more than 20 years, ETFE weighs just one percent of an equivalent-sized glass panel.

This plastic material is strong, lets in more UV light than glass and thoroughly cleans itself with every rain shower. It is also a better insulator than glass, and it is much more resistant to the weathering effects of sunlight.