InfraStructures - March 2007 - Enerpac Helps Beijing's "Bird's Nest" to Stand On Its Own Feet

Enerpac Helps Beijing's "Bird's Nest" to Stand On Its Own Feet

Roberta Moring, Enerpac BV
Special Collaboration

After two years of construction, the 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.

When Swiss architects, Herzog & Meuron, presented their stadium design to the Chinese project team, they used the analogy of a bird's nest. A bird's nest is a Chinese culinary delight, believed to be extremely healthy and a delicacy eaten only on very special occasions. The team applauded the idea and construction began on the new Beijing National Stadium.

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 needed 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 could cut the welds from the 78 temporary piers. However, due to the phenomenal cost of hiring several 800 t cranes for several days, a smarter and less expensive solution needed to be found. Key to the cutting operation was safety, control, stability and cost. Enerpac, known from many complex hydraulic applications around the globe and in particular in China for their hydraulic solutions for moving roofs (NanTong stadium) and moving structures (Shanghai concert hall), was consulted.

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 50 mm thick leveling plates that were used during construction. Computer controlled hydraulic systems are ideal for these types of applications and Enerpac was awarded the contract because of their expertise with these systems.

The computer controlled hydraulic system consisted of a central computer networked with 10 satellite computers, 156 double-acting cylinders, and 55 custom Enerpac hydraulic pumps. System feedback and control was achieved by integrating multi-functional valves, load sensors, stroke sensors and shift detecting sensors.

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 and 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 t double-acting cylinders. At the central computer, all load and stroke data was preprogrammed 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.

After successfully disconnecting the 45 000 t steel structure from its temporary support piers, the bird's nest stood on its own "feet" for the first time.