From concept stage in 2005 through to completion of construction in 2011, Felicetti were the structural engineers for the project. Peter Felicetti worked in close collaboration with Nonda Katsalidis during the concept stage, to design a structural system that integrated the various geometrical epochs and mediated the museum spaces through a regular column and grillage beam grid. The grillage integrates and provides support at discrete locations to the folds of the waffle roof slab. Where it seperates from the waffle slab, it creates a Cartesian scalar reference plane when viewed against the waffle slab above. A helical self supporting steel stair referencing Escher’s continuous loop provides connection between the various floors. Walkways and bridges along the sandstone wall link back to the main entrance circular shaft. The complex nature of the  xpressed structure required our office to design the waffle slabs as a post tensioned system. The project is cut into the siltstone creating an exposed rock wall of 14m height. To create this cut under the existing building Felicetti designed a series of underpinning beams that were installed prior to tunnelling and cutting. After the underpinning was installed, the wall was progressively cut with a large excavator mounted circular saw. With each cut layer rock anchors were installed. The circular shaft similarly was excavated from the top down