A GLASS AND STEEL STAIRCASE
The new art gallery is housed in a restored Victorian school; the three floors are reached by a new staircase and lift set in an existing 6.5 x 4m recessed bay which has been enclosed with a Planar frameless glass wall. To maintain the feeling of lightness and transparency, the lift and staircase are made of glass and steel.
The staircase and lift structure had to be independent of the school building to prevent overloading the walls. The resultant support structure consists of eight 193.7mm-diameter chs columns, 15m high. The lift and its landing are supported by six columns; the staircase is suspended from two columns. The stair and lift columns are independent but brace each other at floor and roof levels.
The staircase is an unusual form of dogleg, with a long landing on one side which gives access to the lift, and semi-circular half-landings at the ends, one of which gives access to the first and second floors. A headframe of 76mm-diameter chss, with semi-circular ends to match the staircase, is welded to the columns just below the roof. A series of 25mm- diameter suspension rods branch around it like umbrella spokes and drop down to support the staircase edges. The staircase does not touch the building except at doorways to the first and second floors.
The treads (19mm clear float glass) and landings (32mm toughened laminated glass) are set between continuous stepped strings made of paired 12.5mm steel sheets with 25mm spacers welded between for rigidity. The balustrade - 12mm toughened glass panels - is slotted into the gap between the sheets. Perforated Z-shaped steel risers, bolted to the strings, support the glass treads. Tests at Spiral Staircase Systems showed that large impact loads might crack the treads but would not shatter them.