A steel and oak staircase
The Floral Hall is separated from the main circulation space by a glass wall stiffened with laminated glass columns. A mezzanine, used for interval drinks and pre-theatre dining, runs along the side of the wall, reached by a staircase. To fit between the original cast-iron columns of the Floral Hall, the staircase takes the form of a dog-leg - three steps up to a landing followed by a straight flight to the mezzanine.
The stair strings are a pair of 260 x 90mm parallel-flange channels (pfcs) with steel stepped tread supports welded to their top flanges. Treads and risers of 60mm thick solid English oak are tongued and grooved together and bolted to the supports; the bolt heads are concealed with oak pellets. Two rows of 19 x 8mm stainless steel strips are routed into the top of the tread to give grip.
The staircase is pin-jointed to the mezzanine and landing structures. At each end a 76mm diameter chs tube is welded to the paired strings to connect them. The tube is fitted with a pair of 170mm diameter steel collars which fit over a projecting hook-shaped support bracket, bolted to the mezzanine and landing structures, to form the pin connection.
The stair has a 19mm toughened glass balustrade with a 50mm diameter stainless steel handrail silicone-bonded to it. The glass panels are bolted with M20 stainless steel pig-nosed bolts to projecting threaded stubs welded to the webs of the pfc strings. The stubs are concealed with stainless steel spacers.
The oak landing is supported by a steel framework clad with oak-veneered mdf.