The 2008 Beijing Olympic Swimming Center, the National Aquatics Center also known as the Water Cube, was the collaborative effort between Arup, PTW Architects, and the China State Construction & Engineering Co. The competition-winning consortium was awarded the design commission in July 2003. The “bubble” structure intended to combine the lightweight, insulating and light-diffusing qualities of a greenhouse. Thus, for the skin of the building, Ethylene Tetrafluoro-ethylene (ETFE) cladding was specified to promote de-materialization - an efficient and lightweight membrane pillow-panel construction that does not require a secondary structure, yet provides improved insulation over conventional glazing.
The Water Cube, which housed the swimming center facilities, was sited next to the iconic Bird’s Nest - the Olympic Stadium designed by Herzog & de Meuron. Its geometry is based on the interface between soap bubbles, researched by Belgian scientist Joseph Plateau as well as Professor Denis Weaire & Dr Robert Phelan of Trinity College in Dublin. Mimicking the soup bubble structure, the swimming center’s pattern is composed of sets of four lines coming to a point at 104.9 degrees, which is the tetrahedral angle.
Tristram Carfrae, structural engineer of Arup, explored the structure by using the Fablon software for non-linear analysis. An accurate physical model would consist of 22,000 structural elements and 4,000 ETFE cladding pillow-panels. The sizes of all the structural elements were made of simple circular tubes. Those were automatically selected by the engineering software, and then welded to the spherical nodes at each end to form the bubble structure frame. The structure was designed to be energy absorbent for seismically active Beijing. The proposed ETFE pillows provides for a continuous and insulting skin for the walls and roof.
Some of the bubble cladding are as large as 9 meters across. The roof is made of 7 different bubble-types, the walls of 15, which are repeated throughout. Despite this repetition, a random pattern is created. Each pillow is permanently inflated by a pump, and this internal air pressure transforms a 0.2-mm-thick plastic into a cladding panel capable of spanning relatively long distances. In pillow form, ETFE is also a better insulator than glass and, when equipped with frit patterns for shading, achieves the desired light-diffusing effect. While the material is translucent blue during the day, at night it is lit by an LED system.
ETFE is a tough, durable plastic closely related to PTFE, commonly known as Teflon. It transmits more UV light than glass and, like Teflon, is non-stick, non-staining and therefore requires no cleaning. An estimated 20,000 people are expected to use the Water Cube at any one time. And although ETFE is combustible, it is fired-rated and complies with China's prescriptive building code with its performance in fire safety. It is non-flammable, self-venting (it melts itself) and lets the smoke out of the building.
The ETFE cushions allow a high level of natural daylight into the building, which passively heats up the building and pool water and thus maximizing energy efficiency. The variation in shading of the facades is achieved by screening the membrane with translucent fritting. The material allows for ventilation of heat out of the cavity in summer and containment of heat in winter to help further reduce energy consumption. Furthermore, in order to protect the membrane façade from corrosion due to condensation and evaporative chlorine, air nozzles have been placed around the perimeter of the building spraying air up the walls to regulate temperature and provide constant air movement.
-- Clara Wong
References and Images:
-LeCuyer, Annette. ETFE: Technology and Design. Basel; Boston; Berlin: Birkhauser, 2008.
-Carfrae, Tristram. “Engineering the Water Cube” Architecture Australia. V. 95, n. 4, July-Aug 2006: 102-5.
-Merrick, Jay. “The new star in the brilliant Arup firmament is structural engineer Tristram Carfrae, whose exploration of structures deserves great acclaim” Blueprint (London, England). N. 252, Mar 2007: 31.
-Pohl, Ethel Baraona. Watercube: the book. Beijing National Aquatics Centre, People’s Republic of China. Barcelona, Spain: Actar, 2008.