Tuesday, February 23, 2010


Design&Construction of Beijing National Stadium a.k.a Bird's Nest



Located at the southern part of the Olympic Green in Beijing, the National Stadium is the main stadium of the 29th Olympiad in 2008. Occupying an area of 21 hectares, it has a floor space of 258,000 square meters. Its seating capacity amounts to 91,000, including 11,000 temporary seats. It is the world's largest steel structure which cost $423 million. The design, which originated from the study of Chinese ceramics, implemented steel beams in order to hide supports for the retractable roof; giving the stadium the appearance of a "Bird's nest".Ground was broken in December 2003 and the stadium officially opened in June 2008.

The stadium consists of two independent structures, standing 50 feet apart: a red concrete seating bowl and the outer steel frame around it.In an attempt to hide steel supports for the retractable roof, required in the bidding process, the team developed the "seemingly random additional steel" to blend the supports into the rest of the stadium. Twenty-four trussed columns encase the inner bowl, each one weighing 1,000tons. Despite random appearance, each half of the stadium is nearly identical. The upper section of the roof was altered to protect fans from weather. Due to the stadium's outward appearance, it was nicknamed "The Bird's Nest".

To minimize the formwork construction on the bowl, the design team have favoured the use of precast concrete. A terrace of L-shaped precast units spanning areas between the supporting reinforced concrete in situ beams will make up the section of the middle and upper tiers. The stadium will be supported by 24 main columns of 1,000t each, which is far more than the weight of those in a conventional stadium and spaced in what appears to be a random pattern (construction has required 42,000t of steel).
The roof is covered with a double-layer membrane structure, with a transparent ETFE (ethylene tetrafluoroethylene) membrane fixed on the upper part of the roofing structure and a translucent PTFE (polytetrafluoroethylene) membrane fixed on its lower part. A PTFE acoustic ceiling is also attached to the side walls of the inner ring. The membrane covering of the Bird's Nest is curved and double-layered, providing decorative, soundproof, wind-proof, rain-proof, and even UVA protection to its already impressive body. 
The spaces in the structure of the stadium are to be filled with inflated ETFE cushions. On the façade, the inflated cushions are mounted on the inside of the structure where necessary, to provide wind protection.

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