The 40-storey building is a prolate spheroid in shape. It has a central steel core from which floor beams radiate to a perimeter superstructure, creating column-free interiors.
The superstructure is a diagrid, formed from a series of two-storey A-shaped frames bolted together. Each frame consists of a pair of columns bolted to a fabricated steel node. The columns have circular end plates which are bolted to matching circular connection plates, welded to the nodes at the precise angle needed to create the diagrid.
Both sets of plates are machined smooth and flat in the factory and drilled to achieve an accuracy of within 1mm when bolted face-to face.By prefabricating components to precise dimensions before assembly, the complex angular relationships between components are resolved before erection.
The sequence of construction is as follows: as soon as two floors of core structure are erected, a perimeter row of A-shaped frames is craned into position.
Tie plates at both sides of each node are bolted to hoop-ties by means of tapered flanges, connecting the nodes horizontally. A series of floor beams, radiating from the core, are bolted to the backs of the nodes. They support a composite concrete structural slab, the metal deck of which is laid in trapezoidal sections.
The diagrid steelwork is fire-protected with foilbacked mineral wool blanket and clad with V-shaped panels of white polyester powder-coated aluminium.
Cladding brackets bolted to the node and to the hoopties support a curtain wall of diamond-shaped panels which are faceted at their edges in both plan and section.