When presenting their stadium design for the 2008 Beijing Olympics to the Chinese jury, the Swiss architects Herzog & Meuron used the analogy of a bird’s nest.
Everyone loved the idea of a bird’s nest and they won. Perhaps because of the culinary association; in China, a bird’s nest is expensive and believed to be highly healthy, something people eat on special occasions.
During construction, the crisscrossed interwoven steel roof construction of the bird’s nest roof was supported by 78 temporary steel columns.
For additional stability, the huge twigs were welded onto the supports. After completion of the bird’s nest, these twigs had to be cut off the support piers, before dismantling of the piers could start.
In many western countries, cranes would have been hired to do the lifting job while welders would cut off the welds off the 78 supports laid during construction.
However, due to high cost of hiring a number of 800-ton cranes for several days in China, a smarter and less expensive solution needed to be found.
Key pre-requisites to the entire cutting operation were safety, control, stability and cost.
The job went to hydraulic specialists Enerpac, known for many complex hydraulic applications around the globe and in the Chinese market, especially for their hydraulic solutions for moving roofs (NanTong stadium) and moving structures (Shanghai concert hall).
According to Enerpac, basically the disconnecting and dismantling process of the temporary supports comes down to synchronically and fully controlled lifting the structure off its supports and cutting the welds.
This was followed by controlled and synchronised stage-lowering to allow the removal of the 50mm thick levelling plates that were used during construction.
Computer-controlled hydraulics is the perfect match for jobs like this. They have been proven worldwide on a huge variety of jobs, including hoisting of bridges in Australia and splitting of giant mining shovels for maintenance.
Because of the range of technologies and experience Enerpac has, Enerpac was granted the contract to perform the stage lifting and lowering of the roof.
The entire configuration (including the central computer, satellite computer-controllers, 156 double-acting high-pressure hydraulic cylinders and 55 electronically controlled hydraulic power units) was specified and custom designed by Enerpac .
For added safety, control and accuracy, multi-functional valves, load sensors, stroke sensors, shift detection and a digital feedback system were integrated.
The design of the bird’s nest is based on three construction circles; an outer circle, a central circle and an inner circle.
Each circle has a specific number of supporting piers, varying from 24 for the outer and central circles and 30 for the inner circle. For load, control and accuracy reasons the 78 support points including their hydraulic systems were divided into 10 regions, each of which had its own satellite controller.
For the actual stage lifting and lowering process, each support pier was equipped with two 150-ton double-acting cylinders.
At the central computer, all load and stroke data were pre-programmed for a fully controlled lifting and lowering process.
During the stage lowering process, the bird’s nest was alternatively supported by the hydraulic cylinders and the levelling plates on the temporary supports.
After successfully disconnecting the 45.000 ton steel structure from its temporary support piers, the bird’s nest stood on its own feet for the first time in preparation for the stadium’s completion this year.
Stadium key facts:
- Start of construction: Dec 2003
- Roof completion - Oct 2006
- Stadium completion - End of 2007
- Gross floor area - 258.000 square meters
- Seat capacity - 80.000 (11.000 temporary seats will be added after the 2008 Olympics.
- Structure - 36km of unwrapped steel length
- Height - 69,2m above pitch level