Dismantling the support structure for a Chinese “bird’s nest” was a complex, but doable, project ... and we're not talking trees in your backyard.
After two years of construction, the 45,000-ton steel stadium for the 2008 Beijing Olympic Games came to a final and very important phase in its construction – dismantling the temporary support piers from its uniquely designed roof.
In designing the Beijing National Stadium, Swiss architects Herzog & Meuron used the analogy of a certain Chinese culinary delight, a “bird’s nest,” believed to be extremely healthy and a delicacy eaten only on very special occasions.
During construction, the criss-crossed, interwoven steel “twigs” of the bird’s nest roof were supported by 78 temporary steel piers. For additional stability, these huge twigs were welded onto the piers. When the construction was completed, the twigs had to be disconnected from the temporary piers and the piers dismantled.
In most western countries, cranes would have been used to support and lift the roof while welders cut the welds from the 78 temporary piers. However, due to the excessive cost of hiring several 800-ton cranes for several days, a better, less expensive solution was sought.
Enerpac, known for its complex hydraulic applications, was able to provide a cost-effective solution that also offered safety, control and stability. And they had a history of providing hydraulic solutions in China from their previous work in moving the roof of the NanTong stadium and moving the entire Shanghai concert hall to another location.
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78 Temporary supports were needed to support the birds nest roof during construction. |
The disconnecting and dismantling process of the temporary piers was accomplished by synchronously stage-lifting the structure from its supports, cutting the welds and synchronously stage-lowering the structure. This process allowed the removal of the 50mm thick leveling plates that were used during construction.
Enerpac’s computer controlled hydraulic system consisted of a central computer networked with 10 satellite computers, 156 150-ton double-acting cylinders, and 55 10,000 psi custom Enerpac hydraulic pumps. System feedback and control was achieved by integrating multi-functional valves, load sensors, stroke sensors and shift detecting sensors.
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Enerpac hydraulic systems on each of the 30 piers of the inner ring. |
The design of the bird’s nest was 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 to 30 for the inner circle.
For load control and accuracy reasons, the 78 support points including their hydraulic systems, were divided into 10 groups, each with its own satellite computer. 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 was 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 leveling plates on the temporary supports.
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The Beijing National Stadium for the 2008 Olympic games. |
After successfully disconnecting the structure from its temporary support piers, the bird’s nest stood on its own “feet” for the first time.
