A 41-level Premium grade office tower at the Paris end of Melbourne’s Collins Street is one of Australia’s most complex construction projects, says Multiplex regional managing director Graham Cottam.
The $800 million mixed-use precinct at 80 Collins Street in Melbourne’s CBD will soon boast 43,000 sqm of office space in the new South Tower. Major refurbishments of the North Tower, an existing 47 level A-grade office building, and construction of a 255-room boutique hotel are also ahead.
The precinct is owned by Dexus and Dexus Wholesale Property Fund following QIC’s divestment of the asset in May. The development project is being delivered by QIC Global Real Estate until completion.
Constructed by Multiplex and designed by local architects Woods Bagot in collaboration with Dutch firm UN Studio, the 216-metre-tall South Tower boasts panoramic views across Melbourne.
“80 Collins is also one of the most complex builds we are currently delivering in Melbourne,” Cottam explains.
“The new South Tower has been constructed to cantilever 12 metres over existing buildings on Collins Street – the first time the engineering feat has been achieved to this scale.”
The faceted glass cantilever has been designed to withstand the tensile force of 30,000 kilo Newtons – around three million kilograms – through the concrete core.
According to Cottam, Multiplex developed an innovative construction method using steel ducts, traditionally used in plumbing and fire service applications, to form a new tension bar system.
“The system effectively withstands and transfers the tensile loads of the cantilevered structure to the building core, without the requirement for additional structural support columns.
“Multiplex worked with the structural engineers and key subcontractors on a series of experiments to develop the tension bar system, including initial prototype development and 3D modelling. The innovative final design is now being patented for use on future projects.”
Other innovations include the first use of a double-decker lift system in Australia. Stacking two lift cars on top of each other doubles the lift capacity without requiring extra space within the lift core. This will allow 18 lift cars to be operational within nine lift shafts, minimising the size of the lift shaft and maximising net lettable area.
The new South Tower has a 6 Star Green Star rating for design and is targeting a 5 star NABERS Energy rating. The building is also “WELL ready”, which allows tenants to pursue further fitout certification.
Around 550 workers are on site every day and approximately 6,000 tonnes of structural steel and 50,000 cubic metres of concrete have been used to date, Cottam adds.
80 Collins is on track for completion in 2020.