Floating 110 Tonnes of Steel over Sydney Skyline

For construction manager Leon Taylor and his team at Watpac Ltd, a leading building contractor in Australia, the morning of Friday February 1 represented the culmination of a project that had been two and a half years in the making.

At 5 a.m. that morning, the team began the three-hour process of hoisting a 110-tonne reflector frame 100 metres in the air and onto a cantilevered steel structure extending from the 29^th storey of the East Tower at the mixed-use multi-residential development at One Central Park in Sydney.

The frame will support a heliostat – a reflective set of mirrors which captures light reflected from the roof and reflects it further down into an atrium which encompasses otherwise shaded retail areas of the building – as well as a garden terrace and a spectacular arrangement of light artwork which at night will form a dazzling display.

The heliostat will be the first of its kind ever used on an Australian residential building.

A video posted by Watpac shows the structure wafting gently through the Sydney sky. Yet behind this apparent ease, Taylor says the project involved three key challenges and required two and a half years of meticulous planning.

Taylor outlined three key areas of challenge.

1)      Deciding how to build it.

Originally, the heliostat was engineered to be part assembled on level 29 and launched out from the floor in a similar manner to the way one might construct a bridge. The building team, however, was not comfortable trying to do this at such a great height. Another option, using multiple cranes to share the lift, was  disregarded due to safety considerations.

“So we took the approach of ‘let’s put this thing together on the ground, get the biggest tower crane we can and lift it up in a manner that we are more familiar with,’ which is lifting the steel up with the bolts in it,” Taylor said, adding that the lift was done in three stages with two major truss boxes going up beforehand and the final hoist of the frame going up on February 1.

2)      Finding a crane with enough guts.

When trying to lift 110 tonnes of steel, Taylor said, none of the standard 16-tonne capacity tower cranes used on commercial buildings in Australia would be of much use, so Watpac bought in the 330-tonne M2480 from Favco. The crane, named Tinkerbell, is typically used for resource projects and had never before been used in residential construction.

Locking this in early, Taylor says, enabled the team to finish the design within the capacity and parameters of the crane and perform the major assembly on the ground rather than 100 metres up in the air.

3)      Arranging perfect weather.

Normally, the weather is out of a construction management team’s control. With the frame measuring 30 metres by 30 metres and with just 25 millimetres of clearance on either side between two buildings, however, there was no room for error. Even a light wind would have caused serious difficulty. Perfect weather was needed.

With that in mind, the team chose the date carefully and started early to allow sufficient time before a light southerly stirred up. That turned out to be a good move; the job finished at 8:00 a.m. and the wind got going at around 8:05.

With the reflector frame now in place, the next task revolves around fixing 320 large mirrored panels to it, each panel being fitted with nine LED lights which combined will form the night display.

Taylor said there was a sense of relief once the frame went in. Not that they doubted it would work – meticulous planning for every contingency all but guaranteed that – but because completion of the most complex part of the task had capped off 30 months of preparation.

“We just needed the weather to play its part on the day, and it did,” he said. “It’s been a very windy month [before the lift] so we’ve had lots of delays because of weather. So that was the main relief – that we got there in the morning and the wind wasn’t blowing and we could get on with it.”

By Andrew Heaton