Session 7: Greenland Centre Sydney: Extending a 25-Story Office Building into a 70-Story Residential Tower

Andrew Johnson
Principal
Arup, Sydney

Creating an iconic residential tower linked to a hotel within the adjacent heritage building, the Greenland Centre will be the tallest residential building in Sydney at completion in early 2020. It is the first building in the world that we are aware of where 45 stories have been grafted onto the top of an existing 25-story building, resulting in a slender tower of 10:1 aspect ratio integrating the existing structural frame and foundations into the redeveloped building.

Constrained by the planning requirements of retaining the existing building structure—once the second tallest building in Sydney and completed in 1965—the structural design has integrated the original primary vertical steel structure into new composite columns, existing steel girders into the new low-rise floor structures, and augmented the deep pad footings founded on sandstone to support the higher gravity and wind loads of the new building. The existing retained tower structural grid and geometry, combined with contemporary set-back requirements from adjacent boundaries, have dictated the form and location of outrigger and transfer structures at the interface between the existing and additional floors, also used to articulating the massing of the old and new.

The challenges and evolution of the structural system, from concept structural studies of viable solutions, through the design excellence competition, use of the existing structure in both the temporary and permanent conditions. construction solutions were developed with the main contractor(s) to realize the project within the constraints of site, function, planning, and economical requirements.