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Working details

The staircase serves three floors, one a lower ground floor, and has semicircular half-landings. Because it acts as a means of escape, it is enclosed in one-hour fire-resistant materials.

The staircase comprises a pair of 210 x 12mm steel strings which rise to the half-landings and curve in a semi-circle to support them. The stair treads are 1200mm x 310mm x 25mm clear float glass sandblasted to give grip; they rest on 40 x 25mm steel angles welded to wedge-shaped steel stringers which in turn are bolted to the insides of the strings. The glass is fixed to the angles with V2100 Norton tape and pointed in structural silicone.

For economy the stair is enclosed in plasterboard on studwork - intumescent glass was not affordable. To counter the feeling of enclosure, the inside is faced with galvanised steel panels. The delicate and translucent staircase is lit from below with metal-halide lamps. A 'starcloth' - a screen inlaid with fibre-optic filaments - hangs between the flights of stairs.

At floor levels the strings are bolted to the undersides of the concrete floor slabs. At the half-landings they are supported by brackets which pass through the plasterboard wall and are clamped to 12mm-diameter steel cables which run within the wall structure and are tensioned between roof and floor to stabilise the stair structure.

The staircase was designed without preliminary sketches as a 3D model in 'Spirit'; it was rendered in '3D Studio' to provide images for presentations. Twodimensional output from the model provided working drawings.

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