Raising the roof

The potential of hydraulicEnerpac at two famous sports stadia on jacks in lifting operations has been demonstrated by Topposite sides of the world. When the 2008 Beijing Olympic Games are broadcast to the world next year, one of the lasting images to remain in the minds of viewers and spectators will surely be the striking Olympic stadium, otherwise known as “The Bird's Nest”.

Swiss architects Herzog & Meuron won the design commission by tapping into the significance that pensive and healthy treat to be eaten on special occasions. There are 36 km of steel sections interwoven to give the structure its resemblance to a and it reaches a height of 69.2 m above the level of the playing surface.

During construction, the criss-crossed interwoven steel roof construction of the bird's nest was supported by 78 temporary steel support columns. For additional stability, the huge were welded onto the supports. After completion of the cut from the support piers, before dismantling of the piers could start.

Elsewhere in the world, large cranes might have been used to do the lifting work while the welds were cut from the support columns. However, due to the prohibitively high cost of hiring several such cranes in China, a less expensive solution was needed.

Hydraulics specialist Enerpac was consulted. Enerpac was already known in Chinese engineering Hydraulics specialist Enerpac was consulted. Enerpac was already known in Chinese engineering.

Disconnecting and dismantling the temporary supports required synchronised and controlled lifting of the whole structure off its supports; then cutting the welds, and then lowering it again. Levelling plates, 50 mm thick, that were used for construction also had to be removed. Enerp proposal to use computer-controlled hydraulics secured it the contract to carry out the operation in November 2006.

The entire configuration, including the central and satellite computerised controllers, 156 double-acting high pressure hydraulic cylinders and 55 electronically controlled hydraulic power units was specified and custom designed by Enerpac. Multifunctional valves, load sensors, stroke sensors, shift detection and a digital feedback system were also integrated for extra control and accuracy.

The design of the circles of structural steelwork: an outer circle, a central circle and an inner circle. Each circle has a specific number of supporting piers – 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 with its own satellite controller.

For the actual lifting and lowering each support pier was fitted with two 150 tonne double acting cylinders. At the central computer all load and stroke data were pre-programmed for a controlled lifting and lowering sequence. During the lowering the 45,000 tonne steel bir s nest structure was alternately supported by the hydraulic cylinders and the levelling plates on the temporary supports.

The 80,000-seat Beijing Olympic Stadium is on course for completion by the end of this year, four years after work began.