A Sustainable Landmark in Sydney's CBD
The new upcycled tower is a 216 m tall building with a hybrid structure consisting of the existing and new structural elements and an extended service life until 2070. It added 45,000 sqm of new office space to the existing building at the heart of Sydney without the demolition of the existing tower.
Innovative Construction Process
The construction involved the simultaneous top-down demolition of 30% of each floor in conjunction with a bottom up construction of the composite steel jump structure. The partial demolition of each floor saw 30% of the floor plates and their supporting structural elements being demolished to enable the extension of concrete core walls (main lateral stability system) and composite floor plates on the north side of the existing core walls.
Every floor was extended by about 30m to the north, which provided an additional 1,000 sqm of office space in each floor. In addition, five stories were added atop the building, increasing the height of the building by approximately 30m.
Assessing Material Properties
To assess the in-situ material properties of the existing building, several destructive and non-destructive test methods were adopted. Around 1,600 cylindrical samples were taken from the concrete walls, columns, foundations and slabs to determine the characteristic compressive strength of the concrete. The durability of the existing concrete was also investigated via carbonation and chloride diffusion tests to ensure that the design life of the structure can be extended for the next 50 years.
The structural solutions employed in the design of QQT met the radical sustainability strategy of the developer (AMP Capital) by upcycling an existing high-rise commercial building.
In this structure, 65% of the existing tower’s concrete beams, columns and slabs, and over 95% of its existing concrete core walls were retained which resulted in an embodied carbon saving of over 12,000 tons.
QQT demonstrated how the structural engineering process could reduce the demolition and reconstruction of components, thereby reducing the carbon footprint and achieving the Intergovernmental Panel on Climate Change (IPCC) net-zero carbon budget in 2050.
In addition, these solutions qualified a more cost and time efficient construction compared to the conventional demolition and rebuilding, saving 13 months and $A140m AUD from the construction time and cost, respectively. These savings had a significant impact on the people and community in the centre of business district of Sydney.
