The Glebe.

The majority of external walls are maintained on a temporary basis using flying shores and horizontal trusses. Once a central core is in place it provides restraint to a system of horizontal bracing, which is used until support can be provided by the concrete frame. Above the third floor the form becomes more intricate and any concrete columns would be offset from the floors below; here we specified steel frame with concrete floors.

Top-down construction, utilising perimeter embedded retaining walls and plunge columns from ground floor level, was chosen for the two-storey basement, allowing the substructure and superstructure to be built simultaneously. This creates a challenge since the retained façade has to remain unaffected by any works below, so sequencing was important to avoid complications.

Steel is more lightweight, and thus we can minimise the load transferring into the basement and foundations below, and reduce the thickness of the third-floor slab. In tower locations, mezzanine levels are introduced both above and below the first floor slabs; all three levels are supported using RC wall-beams. The renovated main roof comprises a moment frame with secondary trusses attached. Where towers extend further vertically, mansard roofs have been designed, supported by portal frames located at four sides of the tower.