How strand jacking helped suspend a theatre three storeys above the ground

Hong Kong’s newly built Xiqu Centre theatre presented a unique challenge for the engineers at BuroHappold.

Because the site is close to underground railway lines, the theatre had to be suspended in the air from the roof, isolated as much as possible from the ground, to prevent vibration and noise disturbances. 

“The theatre is suspended in thin air, three storeys up.  Given that all the structure required to hold the theatre is at the top, you need to get the roof in before you can support the lower floors,” explains Tom Kember, associate structural engineer at BuroHappold. 

Instead of building scaffolding, the engineers used a technique called strand jacking to lift 1,800 tonnes of steel roof trusses into position. “We constructed six freestanding columns and put jacks on top of them that took cables all the way down to the trusses,” says Kember. “The trusses were then lifted by these jacks up to the top of the columns into the right place.” 

Strand jacks enable the precise movement of extremely heavy objects, and the Xiqu Centre construction used 12 in unison to move the roof into place. They have clamps at both the top and the bottom, and can inch objects upwards by releasing the clamp at one end, expanding the cylinder and clamping again, before contracting to start the process again.

“I was on site when they lifted all the trusses,” says Kember. “Having worked on it for years – and gone from hand sketches all the way through to it becoming reality – standing around on a rainy February morning watching the trusses slowly rise up the columns was probably the best thing I’ve done as an engineer.”