A steel staircase with semi-circular landings
The circulation hub of the five-storey office building is a top-lit atrium. On two sides it is flanked by a series of curved steel balconies, one to each floor, which act as 'streets in the sky'and give access to a projecting steel staircase and a pair of glass lifts, housed in a concrete tower.
The balconies are supported by cantilevered tapered I-beams and edged with a curved 430 x 100mm steel channel, with outward facing flanges. Two 355.6mm diameter CHS columns, one of which also supports the staircase, give intermediate support to the balconies.
The staircase, a delicate, lightweight construction, has open treads and paired strings, formed from the same 430 x 100mm channels as the balcony edges. The semi-circular half landings project into the atrium, supported by a vertical 'scissor' truss of 200 x 200mm SHS members, which runs diagonally between the inner strings of the staircase. This is welded at each balcony floor to the CHS column. At the edge of each half-landing, a 200 x 200mm SHS beam extends to support the outer strings.
Steel tread trays are connected to the strings, with welded brackets concealed within their depth. They are filled with lightweight screed and topped with treads of honed Broughton Moor slate and recessed stainless steel anti-slip inserts.
The 60mm diameter handrails are designed to give a sense of security and solidity to users. The balustrade is formed of 100 x 18mm steel flats, welded into frames and bolted at the base to 335 x 80 x 25mm spigots, welded to the strings. At the top, the frames are bolted to spigots which support the handrail.