A helical steel staircase and a glass steel-framed canopy
The staircase is an open helix, 2m in diameter, separated by two landings and leading to a third triangular landing which gives access to offices on the first floor. The main string is a continuous 219mm- diameter steel tube, 18mm thick; it maintains its helical form on plan; in section it is horizontal at landings and rises at the stairs. The tube was turned in Scotland and brought to London in 3m sections which were welded together on site.
The wedge-shaped treads are of stainless steel, their surfaces punched with rows of holes to give grip. Each tread rests on a pair of vertical tread supports welded to the string and cantilevering from it. The front support, a steel flat 290mm-deep, forms a riser; the rear support is reduced in depth to 180mm to accommodate the rise of the string. Both flats taper to a smaller 40mm-diameter chs, turned to follow the helical form, which ties them together.
The balustrade is made of 10mm toughened triangular glass panels. The bottom corners of the panels are supported by the outer 40mm diameter chs. The upper corners are bolted to lugs projecting from a continuous40 x 10mm steel rail welded to the balusters and following the line of the 25mm-diameter stainless steel handrail. The balustrade forms a faceted helix, with sharper angles at the facets on the inner balustrade compared to the outer balustrade.
The canopy comprises a spine of welded box sections which together act as a gutter, with support wings of 114mm-diameter tubes stiffened with tapered flats. 10mm diameter lugs, welded to the flats, prop the glass canopy panels above the steelwork and provide bolted connections.