Building: National Stadium in Beijing aka “Bird’s Nest”
Location: Beijing, China
Architects: Herzog & de Meuron, Hong Kong China Architectural Design & Research Group, Stefan Marbach
Project Architects: Linxi Dong, Mia Hagg, Tobias Winkelmann, Thomas Polster
Structural Engineer: Ove Arup & Partners
The Beijing National Stadium was created to hold 91,000 spectators during the Olympics and was then to be reduced to 80,000 post-Olympics. The way this stadium was created was to have the steel frame not touch the concrete seating bowl, but instead be raised by its own pile foundations.
The reason to have a seating bowl that is independent from the exterior frame was to ensure that the building was earthquake-resistant. The overall steel structure that forms the façade and roof have no movement joints between individual members, instead they are welded together to form a single entity. As a result, thermal changes cause concordant forces in the whole structure. Nonetheless, there are movement joints at connection points, where the steel columns meet the concrete decks or staircase landings, up to 30 cm wide in the upper levels. The estimated weight for the primary load-bearing frame is 45,000 tons. The concrete bowl which holds the seats is hidden behind the steel grid structure, and has parts of it painted the national color red. Thus, the concrete bowl is still visible from afar even with the steel structure seemingly penetrating the volume.
The roof doesn’t have a freeform area, but instead takes the shape of a torus and can therefore be described mathematically. It is symmetrical in area to the two imaginary vertical cutting planes in the central axes of the stadium. The roof is covered by lightweight cable-supported ETFE membrane panels (Asahi Fluon NJ 250 µm), which fill the 880 spaces between the roof steel members, also known as the “twigs” of the bird’s nest. Some areas of the roof were printed with silver-grey dotted patterns on the panels to reduce light penetration, forming about 38,000 square meters of transparent surface. The 4,690 stainless-steel cables supporting the panels have diameters of 10 mm and spacing between 0.8 and 1.4 m. Around the edges of each panel are aluminum clamps used to connect steel drainage gutters which feed into a rainwater collection system.
Also, below the ETFE membrane panels is an inner membrane of high-tech textile to cover up the view of the stadium roof from underneath and improves the acoustics inside the stadium. The overall enclosed volume covered by the stadium is approximately 3 million square meters, and has axial dimensions of around 330 m x 220 m x 69.2 m (above the playing field).
Special Detail: (Understanding the Structure’s Shape)
The load-Bearing frame looks like an entangled grid without any hierarchy of structure, but indeed has a very complicated organization behind it. The primary structure is basically composed of a system of primary girders aligned in a regular pattern. The primary structure is what creates the hole in the roof by having 24 portal girders that run tangential to a 12 meter high ring girder. Then, integrated into the primary structure are secondary girders whose positions were determined mostly according to aesthetic considerations; nonetheless, taking into account various technical aspects like wide enough emergency exits and head heights. “The overall geometry generated by this principle seems chaotic, but that impression is deceptive.” In the end, it was the combination of steel and ETFE membrane panels that gave rise to unusual architectural structures, and stole the show.
*All information and images were found in: DETAIL Magazine, Edition 5, 2008. “National Stadium in Beijing.” 483 – 491.