A facade with an exposed structural steel frame
Office, Devonshire Square, London Bennetts Associates
In sympathy with nearby Victorian warehouses, the office building expresses its structure with a rugged, load-bearing steel and glass facade. The exposed steel frame, which is constructed to half National Structural Steelwork Specification tolerances, supports six stories of composite concrete slabs on cellular steel beams.
The steel frame consists of a series of 356 x 406mm universal columns and 686 x 254mm universal beams. Fire protection is achieved by a combination of strategies; the members are oversized in relation to their loading, and they are backed with a series of 60-minute integrity and insulation fire-resistant composite panels, which extend beyond them at the sides, shielding them from heat. The gap between structure and panel is drained and ventilated to avoid condensation.
Thermal bridging is minimised by a thermal break between internal and external structural elements. Shear bolts with ferrule spacers separate column and beam connection plates, and the gap formed by the spacers is filled with rigid insulation.
The cladding is a grid and panel system supported by thermally isolated brackets.
The polyester powder coated aluminium frames are structural silicone-glazed.
The double-glazed units have a toughened outer pane and a laminated inner pane with a Low-E coating to the outer face. The lower glazed panels open to vent the office floor for smoke evacuation. On the south facade, the glazing is screened with solar shades which are pivot-hung to allow the glazing to be cleaned.
The steel frame is painted to a high specification using a zinc-rich primer and M10 barrier coat with a decorative finish to match the cladding.