Spiral stairs

Steel spiral stairs are also the subject of industrial production and supplied as a package of parts. A typical assembly comprises a centre column and base plate, over which the cantilever treads or landings are sleeved, with cotter pins to secure each component in place (Figure 7.4a). The handrail and rod balustrade stiffen the outside edge of the spiral. Welding the balustrade to guard rails can provide a structural lattice which acts as a supporting member; another method is to design a trussed balustrade (Figure 7.4b). The tread details follow the principles of 'steel trays' already discussed, with var-

Well end Flights at landing

Figure 7.2e Balustrade details

Figure 7.2f Minimal escape stairs with glass enclosure, 'Novo'factory, Copenhagen, 1961, Architect: Arne Jacobsen (Danish regulations permit spiral escapes)

ious materials acting as a facing or infilling. Designer spirals have reached beyond the limit of common sense in France with polished aluminum castings resembling giant teaspoons that are jettied off a spinal vertebra (Figure 7.4c). Patterns of nineteenth-century engineering are still manufactured, the developments in replica casting means that historic features can be matched. The spiral stairs and balconies at the Palm House, Kew, are a case in point (Figure 7.1a), where the naturalistic forms still perfectly echo the natural plant material.

Figure 7.2g Security enclosure to stairs (courtesy of Weland Grating (UK) Ltd)

Figure 7.2h External escape stairs, Apple Computer's Facility Stockley Park, 1989, Architects: Troughton McAslan

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