Located in the south of Beijing Olympic Park, the National Stadium is the main stadium of the 29th Olympic Games in 2008. It covers an area of 2 1 hectare with a building area of 258,000 square meters. Its seating capacity is 9 1 000, including 1 1 000 temporary seats.
This venue will host the opening and closing ceremonies of the Beijing Olympic and Paralympic Games, track and field competitions and football finals. After the Olympic Games, this stadium will become a large-scale sports and entertainment facility for Beijing residents, an architectural landmark and an Olympic legacy.
Main design life of National Stadium 100 year. Its fire resistance is first-class, and it can resist an earthquake of magnitude 8. The waterproof ability of its underground engineering is also first-class.
The main body of the National Stadium is a huge saddle-shaped oval steel structure weighing 42,000 tons. It is 333 meters long from north to south, 294 meters wide from east to west and 69 meters high.
The elements of the main body support each other and converge into a grid-like formation, just like a bird's nest with interlocking branches. The grandstand of the stadium is a concrete frame and a seven-story shear wall system. The upper part of the stands and the steel structure of the stadium are separated, but both are based on joint foundation. The roof of the National Stadium is covered by a double-layer membrane structure, with transparent ETFE membrane fixed on the upper part of the roof structure and translucent PTFE membrane fixed on the lower part. PTFE foam ceiling is fixed on the side wall of the inner ring.
The construction of the National Stadium follows the PPP model (private+public+cooperation), which is jointly owned by Beijing State-owned Assets Management Co., Ltd. (BSAM) and China International Trust and Investment Group (CITIC). The former owns 58% of the total assets and the latter owns the rest.
The National Stadium Company composed of BSAM and CITIC Company is responsible for the financing, construction, operation and management of the project. CITIC has a 30-year post-game franchise.
The National Stadium is a complex structure, which brings great difficulties to designers and constructors.
1. Large and heavy steel parts
The fracture surface of the largest truss column (the main load-bearing component of the roof structure) is 25m x 20m, and its height is 67m. The maximum weight of a single column is 500 tons. The height of main truss is 12m. The maximum span between and through two columns is145.577+12.788m, and the maximum span between two trusses is102.39m.. Each truss column has a large volume and weight, so does the main truss.
2. Complex node joints
Because the structural elements in the project are box-shaped, many elements intersect between steel parts in space. In addition, the complexity of the secondary structure leads to the diversity of the main structural nodes, which requires accurate and complicated manufacturing and installation.
3. A tight schedule
Apart from the huge workload, the allocated construction period is very short. The project started on February 24th, 2003/KLOC-0, and is expected to be completed by the end of 2007 and in March 2008. Therefore, many operations have to be carried out on limited terrain, resulting in a very tense situation.
The hoisting work lasted all winter and spring, so the workers had to continue working in the cold and rainy conditions in winter.
The workers overcame great engineering and technical challenges during the construction:
1. Difficult work arrangements
They need to study the operation very carefully and follow careful arrangements to complete all kinds of work in a limited working space.
2. Steel parts are difficult to hoist.
In order to facilitate the assembly of steel parts, workers have to use prone position to assemble truss columns, which needs to be overturned before they are hoisted. In the face of huge and bulky steel parts, it is very difficult to choose lifting points and hooks, and the change of tensile stress in three directions must be considered. Workers need to carefully correct the angle and position of box-section components to ensure accurate docking during hoisting.
3. Difficult stabilization process
They must also resist strong wind load and maintain the stability of steel parts by following strict working sequence and using lateral stability measures (including anchoring methods and wind-resistant ropes).
4. Difficult to weld
Welders not only face a huge workload, but also have to work on thin steel plates and thick steel plates, high-strength and cast steel components, and take a downward, vertical or overhead position when welding. They face temperature changes, steel deformation and intensive labor. They need to work on the ground, in the case of rain and wind in winter.
5. Installation is difficult
Workers face difficulties in ensuring accurate installation because steel parts and related fixtures and fixtures are easily deformed under self-weight and temperature changes. Workers must take pre-installation measures to correct and mitigate possible errors during installation.