Liebherr tower cranes were used to construct a landmark tower development in Auckland which includes a self-erector replacing a typical Building Maintenance Unit.
PWC Tower is a new NZ $850 million, landmark 39 storey tower development within the Commercial Bay precinct transforming Auckland’s CBD and waterfront – bringing together world class commercial space, international quality retails public spaces and hospitality environments.
The design of Commercial Bay’s tower includes a unique feature at the top of the tower where the foil façade’s supporting structures sail past the roof. The tower’s builder, Fletcher Construction had to come up with a way of replacing glass anywhere on the tower should glass break during construction or into the future.
A concept had to be designed that would service everything from the roof and below including the facade and other areas of the building all the way down to street level. The design also had to include the seismic requirements for New Zealand, this was also another first for the project as the application was complex and had not been done before.
Four concepts were considered for the Building Maintenance Unit (BMU) but none of them could deal with the replacement of glass panel at the top of the foil. A number of the BMU options were a larger and heavier than the self-erecting crane which meant the structure of the building at the roof level would have to be beefed up to accommodate the BMU. And it wasn’t going to be able to manage all of the requirements for the tower. So, the planning had to involve getting a hook up higher than the tower basically to manage future building maintenance and replacements.
The Liebherr 53 K self-erector is now permanently on level 40 which is the roof level and is designed to have a high-level maintenance regime to ensure it is operable throughout the years to come. The connection point detail between the building and the crane base is the critical point and had to be designed to withstand an earth quake and high wind loads taken from NZS1170 series.
Liebherr basically took a 53 K and had their engineers in the German factory, redesign and rebuild it. Self-erectors are bottom slewing cranes, usually on the ground and so the hoist rope lengths and hoist rope drum and counterweights are for dealing with a hoist rope suitable for the height of the self-erector. For this project, the crane is on top of a 170m tower which meant a lot of re-engineering, including redesign of the hoist gearbox, hoist drum, reeving system, and a special split type, steel counterweight, which allows the crane to erect and dismantle without the time-consuming need to remove and reinstall the counterweight each time. The Liebherr engineers were excited to produce a custom engineered one off for the project.
The radius of the self-erector can reach two streets on the block. The hook can get all the way down to street level to pick up loads of up to 1,000 Kgs from delivery trucks etc. and it was actually used during the construction phase to help remove some of the tower crane components and scaffolding, and it has also been involved in reglazing of the façade when panels were broken during the construction phase. So, it has already proven its abilities on site.
Mark Clayton is Tower Crane and Hoist Manager for Fletcher Construction and he was responsible for the deployment of the new Liebherr 357 HC-L luffing tower crane. When the crane was first erected it stood at 97m to the tip of the jib and as the tower was constructed the crane followed it in seven different increments of climbing. At each of these increments of climbing, it was secured back to the building which kept the structure as rigid as possible. The crane was fitted with a 45m boom which meant the crane required 38t of counterweight.
The Liebherr 357 HC-L was fitted with a special hook which meant it could be used as a single line or double line on the hook which provides either 18t or 32t capacity and this project it was used in its 32t capacity configuration. This meant it needed a hoist rope of 550m and the hoist rope alone weighed 2.5t. the hook required specialised chains and rigging. The crane was one of four cranes used on the Commercial Bay project and this with another crane was climbing with the tower. The Liebherr 357 HC-L luffing crane went on to be the tallest crane in New Zealand at 225m in height to the tip of the jib.
The Commercial Bay Precinct opened in early June 2020 and Fletcher Construction Chief Executive, Peter Reidy congratulated Precinct Properties on its investment in the city of Auckland.
“This is so much more than a retail and hospitality precent. Commercial Bay is an ambitious development designed to transform Auckland’s CBD and waterfront returning the area to a centre of trade and activity in the city.
“As many as 2000 people, including contractors, were working on the Commercial Bay project as its peak. It has been a once-in-a-lifetime opportunity for our people to be involved in such a challenging and transformational which will leave a huge legacy in this city.
“I’m immensely proud of our team and what they have achieved. They showed true Fletcher spirit in completing this iconic project, which will have pride of place in the city for generations to come,” said Reidy.