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.

The venue will host the opening and closing ceremonies of the Beijing Olympic Games and Paralympic Games, the track and field competitions, and the football finals. After the Olympics, the stadium will become a large-scale sports and entertainment facility for the residents of Beijing -- an architectural landmark and Olympic legacy.

The main body of the National Stadium has a design life of 100 years. Its fire resistance capability is first-rate, and it can withstand an eight-magnitude earthquake. The water-resistance capability of its underground project is also first-rate.

The main body of the National Stadium is a colossal saddle-shaped elliptic 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 tall.

The main body's elements support each other and converge into a grid formation, just like a bird's nest with interlocking branches and twigs. Being a seven-story shear wall system, the stadium's stand has a concrete framework. The upper part of the stand and the stadium's steel structure are separated from each other, but both are based on a joint footing. The roof of the National Stadium is covered by a double-layer membrane structure, with a transparent ETFE membrane fixed on the upper part of the roofing structure and a translucent PTFE membrane fixed on its lower part. A PTFE acoustic ceiling is attached to the side walls of the inner ring.

The construction of the National Stadium followed the PPP mode (Private + Public + Partnership ), and it is co-owned by the Beijing State-Owned Assets Management Co. Ltd (BSAM), who shares 58 percent of the total assets, and the China International Trust and Investment (CITIC) Consortium, who holds the rest of the assets.

Composed of BSAM and CITIC, the National Stadium Co. is responsible for financing, construction, operation and management of the project. CITIC has a post-Games licensed operation right for 30 years.

The National Stadium is a complex structure, posing great difficulties for its designers and constructors.

1. Large and heavy steel parts

The fracture surface of the largest truss column -- the major load-bearing component of the roof structure -- measures 25m x 20m, with a height of 67m. The maximum weight of a single column is 500 tons. The main truss is 12m tall. The maximum span between and through the two columns amounts to 145.577+112.788m, and the maximum span between the two trusses stands at 102.39m. Each truss column is of great bulk and weight, and so are the main trusses.

2. Complex nodal joints

Because the structural elements in the project are box-typed, many elements intersect spatially among the steel parts. Besides, the complex nature of secondary structures has resulted in the diversity of nodal joints of the main structures, requiring accurate and sophisticated manufacturing and installation.

3. Tight schedule

In addition to the huge workload, the allotted construction period is short. Having started on December 24, 2003, the project is expected to be completed by the end of 2007, with the inauguration time scheduled for March 2008. Therefore many operations have to be conducted on a limited terrain, causing a very tense situation.

4. The hoisting work extended across the winter and spring, so the workers have had to defy both rainy and cold conditions in the winter to continue their work.

The workers have overcome tremendous engineering and technical challenges in the process of construction:

1. Difficult work arrangement

They need to do very detailed research of operations and follow meticulous arrangements to complete various kinds of work within a limited workspace.

2. Difficult hoisting of steel parts

To facilitate the assembly of the steel parts, the workers have to use a prone position to assemble the truss columns, which requires a turnover process before they are hoisted. The choice of the hoist points and lug hooks pose great difficulties in the face of bulky and cumbersome steel parts, and the change of pulling stress from three directions must be taken into consideration. The workers need to meticulously rectify angles and positions of the box-typed sectional parts to ensure accurate abutment during the hoisting process.

3. Difficult stabilizing process

They also have to fight the heavy wind load and keep the stability of the steel parts by following a strict working order and use lateral stability measures including the use of anchoring method and wind-holding ropes.

4. Difficult welding

The welders not only face a huge work volume, but also have to work on both the thin steel sheets and thick steel slabs, on high-strength and cast steel elements, and take downward, vertical or overhead positions while welding. They face temperature changes, steel deformation and intensive labor. They need to work above ground, in winter rain and under windy conditions.

5. Difficult installation

The workers face difficulties in ensuring accurate installation as the steel parts and the related gigs and fixtures can be deformed easily under their own dead weight and the change of temperatures. The workers must take pre-installation measures to rectify and relieve the errors that might occur in the process of installation.