The eyes of the world will be on the National Stadium when it hosts the opening and closing ceremonies of the Beijing Games. Home to the athletic track and field events, the Stadium sits in the Olympic Green and holds a massive 91,000 seats.

The structure's vast scale and dramatic form have created a new icon for China and the City of Beijing. The circular form of the National Stadium represents Heaven, while the adjacent square form of the National Aquatics Centre, also design-engineered by Arup, is a reflection of the Chinese symbol for Earth.

The form of the National Stadium is popularly described as a 'bird's nest' with interwoven twigs and the pattern was also inspired by traditional Chinese 'crazed' pottery, found in Beijing markets. Although seemingly random, the pattern abides by complex rules imposed on the structure in order to be able to define the geometry. Without this, the National Stadium would have been impossible to build.

To minimise the amount of materials used, the stadium was designed from the inside out. Firstly the seating was established and then the fa�ade was engineered to envelop the spectators. If unravelled, the steel tubes that form the structure would stretch 36 kilometres. Every one of the 7500 elements was designed individually.

The National Stadium is located in one of the world's most seismic zones and needs to withstand major earthquakes without collapse or structural damage. Advanced computer analysis was used to test the structure under different strengths and direction of earthquake. The National Stadium combines a sense of chaos with one of order so that the spectator will be left wondering which aspects of the structure are functional and which have been included for appearance alone.

The £280m Beijing National Stadium is set to be a stunning landmark building for the staging of the 2008 Olympic Games (opening on 8 August and closing on 24 August 2008).

The innovative structure was designed by Herzog & De Meuron Architekten, Arup Sport and the China Architecture Design & Research Group, and has been nicknamed the 'Bird's Nest' due to the web of twisting steel sections that form the roof.

As well as creating a modern stadium, the team was challenged with creating a venue that was part of the culture of China and that would put Beijing on the map.

The 91,000-seat stadium was designed to incorporate elements of Chinese art and culture; one of the design team is a Chinese artist. When the Olympics are finished the seating capacity will be reduced to 80,000. The stadium is 333m long from north to south, 294m wide from east to west, and 69.2m tall.

WORK PROGRESS

Construction work began on the stadium with earthworks and foundations in late 2003 and the main construction work started in March 2004. By August 2004 construction work had been halted due to the perceived high construction costs. The designers were asked to change the design to save money.

In the new design, the roof of the stadium was omitted completely. However, many experts believe this made the stadium safer from seismic activity. However the omission of the roof has significantly reduced construction costs. As a result of the design changes the total consumption of steel in the main structure has been reduced by 22.3% from the original design.

Also, because the hole in the top of the stadium is now enlarged, the total surface of its membrane structure has been reduced by 13%. The construction of the Olympic stadium resumed at the beginning of 2005; hence the adjustment from the original finishing date of 2006 to the start of 2008. The stadium was opened on 18 April 2008 (final work was completed in May 2008).

FINANCE

The China International Trust and Investment Corporation (CITIC) consortium, who raised 42% of the finance for the project in return for a 35-year tender after the Olympics are finished, comprises the CITIC Group, the Beijing Urban Construction Group, the Golden State Holding Group of the United States, and the CITIC Group affiliate Guoan Elstrong (a public, private partnership arrangement).

The remaining 58% is funded by the Beijing municipal government and this has been entrusted to the Beijing State-owned Assets Management Co Ltd as the city government's representative.

NATIONAL STADIUM DESIGN

As this is an Olympic venue, there are many standards that the team have to conform to. Everything from the width of the track to the size and location of the long and high jump pits needs to satisfy the requirements set out by the International Olympic Committee (IOC) and the International Amateur Athletics Federation (IAAF).

The stadium also had to be designed for the Paralympics, which takes place after the Games.

For this, the number of spaces for wheelchairs had to be increased considerably and put into various locations around the stadium, in both competitor and spectator areas.

The main requirements from the client, the National Stadium Company, which was established by the Beijing State-owned Assets Management Co Ltd, and the CITIC Consortium, were to create a bold, stand-out, world-class stadium, and to design in as much flexibility as possible for future use.

The stadium will host other sports such as football and events including concerts. One end of the stadium has amphitheatres that could be used to stage concerts once the grass is covered over.

As well as getting the inside of the stadium right, the concourses and space around the stadium also had to be carefully thought out for future use. The concourses are very wide to allow people plenty of space to access the refreshment and merchandising stalls. This is integrated with a large mixed-use retail development under the plinth of the stadium, with shops, restaurants, cinemas, a health club and parking.

The new stadium could be home to the Beijing GuoAn football club that plays in the Chinese Super League after the 2008 summer Olympics are over. This move though has yet to be confirmed by the football club.

CONTRACTORS AND CONSTRUCTION

Construction began on 23 December 2003 and was finished in early 2008. Beijing Mechanical Construction Company won the bid for earthwork and foundation treatment in November 2003 and work began almost immediately. CITIC Internationals Contracting Inc was the major construction contractor.

Structural engineering, mechanical and electrical engineering, fire safety engineering, acoustic design are the responsibility of Ove Arup & Partners. Beijing Urban Construction Group Co. Ltd (BUCG) is managing the project along with China Architecture Design & Research Group.

To minimise 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).

NATIONAL STADIUM ARCHITECTURE

The team wanted to get an optimum balance between making sure every spectator had a good view, creating a good atmosphere and designing an elegant building. It also needed to be aware of the different uses of the stadium; for example, when used as an athletics stadium, the most important view is at the finish line of the running track but when used for football, the best views are at the centre line.

Getting everyone close enough in such a big venue was a real challenge and getting the calculations right was an immense task. For example, changing the height of the first row of seating by just 100mm would make the stadium significantly larger and higher and increase the cost by several million pounds.

To achieve the optimum design, the team relied heavily on parametric design software. This helped to work out the sightlines, the bowl geometry, airflow to keep the grass in good condition, seismic studies and to design the external envelope.

While the surface of the structure is simple, the geometry is complex � the calculations were so numerous and complicated that they could not be solved manually. Software was needed to make sure that the web of twisting steel sections fitted together, as they have to twist and bend to follow the surface accurately.

The main elements support each other and converge into a grid formation. The stand of the stadium is a seven-storey shear wall system with a concrete framework. The upper part of the stand and the stadium steel structure are actually separated from one another, but both of these are based on a joint foundation.

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 spaces in the structure of the stadium are to be filled with inflated ETFE cushions. On the fa�ade, the inflated cushions are mounted on the inside of the structure where necessary, to provide wind protection.

Since all of the facilities – restaurants, suites, shops and restrooms – are all self-contained units, it is possible to do largely without a solid, enclosed facade. This allows natural ventilation of the stadium, which is the most important aspect of the stadium's sustainable design.

To keep costs down, all the structural elements of the stadium are contained within it, so there are no towers or cable nets. The bowl of the structure is split into eight zones, each with its own stability system, making each zone effectively its own building.

Entrance to the stadium will be controlled by tripod barriers supplied and fabricated by Kaba Gallensch�tz of Germany. The project has involved the installation of 138 of these units at the 12 ingresses of the stadium.

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