A precast concrete staircase
A vault of faceted glass panels structurally bolted to curved steel ribs forms the enclosure to the two-storey office building. A staircase set at its centre is the key link between open-plan workspaces on first and second floors. In contrast to the delicate, transparent facade the staircase is a solid, organic construction of fair-faced precast concrete with bulbous treads which socket over an arched skeletal spine like the vertebrae of a dinosaur.
The spine, cast as a single piece in a plywood mould, rests on the cast in-situ concrete floor slab. It is stepped to support individual precast treads, and has a curved underside which tapers to a 'dolphin-nose' end. Parts of the underside are cut out to reduce weight and indicate the path of structural forces.
The first and second treads form a landing to comply with regulations limiting the number of treads in a flight. The treads above are identical; they were cast with flat bases which rest on the steps of the spine and are bolted to it through cast-in holes.
To reduce weight, each tread is cast with a concavity, which is covered with a curved panel of acid-etched 12mm, toughened glass; this forms the walking surface of the tread. The glass, bedded on a neoprene gasket, rests on a 25mm recessed lip cast at the tread perimeter. A light fitting below the glass illuminates the tread. The curved corners of the concavity are fitted with base plates to which the cranked steel balusters are fixed.
A 40mm diameter stainless steel handrail, supported on the balusters, runs at each side of the stair; it is set inside the curved edges of the treads for safety; 13mm diameter stainless steel rods, welded to the balusters, form the balustrade.