Inside Beijing's National Swimming Center

(page 2 of 3)

The building's honeycomb exterior was designed to invoke the spirit of water. Getty Images

Cool air is pumped through an underseat system to keep spectators cool and dry. Solar energy heats the pools and the building and lights its interior. Getty Images

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The result is a seemingly irregular, but in actuality a rigorous and buildable structure-and-building-envelope combination appropriate for earthquake-prone Beijing. The on-site welded space frame, with column-free spans of up to 396 feet, is highly efficient, nonlinear, nondirectional, and remarkably stable. The ETFE cladding, which weighs just 1 percent of an equivalent glass panel, contributes to the building's seismic performance, since it helps reduce the gravity and lateral loads that the structure would be subject to during a temblor, explains Carfrae.

The ETFE cavity wall and roof also provide thermal efficiency. The double skin is designed to capture solar energy to heat the swimming pools and the building and light the interior spaces. The building collects 20 percent of the solar energy that lands on it, equivalent to covering the 340,000-square-foot roof with photovoltaics, according to Arup. The firm estimates that the Water Cube saves 30 percent of the energy typically devoted to lighting and half of the energy that would be required to heat a well-detailed and well-insulated metal-clad box.

The Water Cube relies on the thermal mass provided by the pool water and surrounding concrete to retain heat during the day and release it at night. The double skin allows the venting of excess heat in the summer but permits its containment during the winter, when solar gain is most beneficial. The concept was realized almost unchanged from the design team's original competition entry scheme.

One of the few features of the envelope implemented differently in the built Water Cube is the solar control strategy. The team originally imagined the inner ETFE cladding as an operable and variable surface, providing the facility's managers with the ability to turn shading on or off, depending on the desire to admit sunlight and control glare within the Water Cube's various spaces. But in the end, the designers opted for a fixed aluminized frit pattern that blocks between 10 to 95 percent of visible light. The frit is most dense on areas of building skin that enclose areas where direct sun is least desirable and glare would be most distracting. For example, the roof over the competition pool admits only 5 percent of visible daylight due to strict broadcast-industry lighting-control requirements.

Though much of the building's heating needs are satisfied through passive means, some spaces within the Water Cube do require mechanical cooling, setting up a challenge for designers. In the competition pool area, "it was tricky to keep the swimmers warm and wet and the spectators cool and dry," says Carfrae. In order to cope with the differing requirements of the building's various types of occupants, the engineers relied on the displacement ventilation principle, supplying cool air through an underseat supply system, conditioning only the zones occupied by spectators.

Digitally driven

The Water Cube's structure is the outcome of applying sophisticated analysis and optimization software that Arup's engineers created in-house specifically for this project. The program helped the designers examine the space frame under various loading scenarios to determine the size, shape, weight, and other properties for each of the 22,000 steel tubes. These characteristics were automatically recorded in a database and a 3D model, which in turn were used to produce the construction documents.

Team members say that the process of digital form finding, analysis, and documentation employed to produce the Water Cube was cutting edge for a building designed largely in late 2003 and completed earlier this year. "There is a lot of talk about autogenerated architecture, but this was one of the first projects where such a process was realized," says Chris Bosse, a former project architect at PTW and now head of the Laboratory of Visionary Architecture (LAVA), in Sydney.

Because of the high degree of automation that the parametric process afforded, the team could generate a complete set of new construction documents in less than a week following a major change in the Water Cube's configuration, according to Carfrae.