Metal box framing

The term 'curtain walling' is most commonly associated with a rectangular grid of vertical and horizontal frame members, introduced from America during the 1950s mainly for use in high-rise office buildings. Two buildings in particular helped the popular aesthetic approval of the framed curtain wall: the United Nations Secretariat (architects: Harrison and others, 1947-50) and Lever House (architects: Skidmore, Owings and Merrill, 1952), both in New York. Important forerunners of these were buildings such as the Gropius factory at Alfeld (191 I), the Bauhaus, Dessau (1925-26) and Le Corbusier's Maison Suisse at the Cité Université, Paris (1930-32).

7.2 Sections of nineteenth-century glazing bars.

There are two basic approaches to assembling a box-framed curtain wall (Fig. 7.4). Either:

- the component parts of the system are assembled on site, with panels being offered up to a frame (sometimes known as the 'stick' system); or

- the panel system is bolted together; the panels themselves becoming the frame.

Both systems have the advantages associated with a high degree of préfabrication; the first method has more easily handled components, but site construction time may be longer.

— Extruded aluminium bar

Outsic

Inside

— Extruded aluminium bar

Outsic

Inside

Outsi

Insidi

Outsi

Insidi

Extruded aluminium bar

7.3 Two forms of patent glazing: (a) traditional; (b) inverted.

7.4 Basic forms of curtain walling construction: (a) stick system; (b) unitised system.

Means of support

The means of support and the layering of the arrangement can totally change the appearance of the facade. There Is clearly an Interest In providing diversity in the means of support for a particular project to reduce the visual bulk of the supporting framework or to achieve a particular span requirement. At the YKK M&E Centre in Japan by Roy Fleetwood, the two-storey curtain walling of the ground floor is supported by a transom and mullion of a similar section. However, the mullions are stiffened by the use of a pin-jointed lattice truss. This truss mullion, a combination of cast and extruded aluminium, was developed by YKK Architectural Products (Fig. 7.5).

A similar structural approach was taken by Benthem Crouwel in their extension to Schiphol Airport in The Netherlands, where once again a consistent mullion and transom box is supported by a vertical truss. However; with the truss, the architects have opted for a curved vierendeel beam, very similar to that designed for Stansted Airport (Fig. 7.6).

The curtain walling designed for the British Airways Combined Operations Centre (developer Lynton for Heathrow Airport) by Nicholas Grimshaw & Partners demonstrates the potential of extruded sections, which are more visually interesting than a simple box section and capable of accepting many functions that interact with the building envelope. This is achieved by a family of extruded components (Fig. 7.7).

Renzo Piano, when designing a curtain walling system for Alucasa of Milan, Italy, used cast aluminium sections, which, when bolted together acted as wind bracing between floors, replacing the traditional box extrusion (Fig. 7.8).

7.5 YKK M&E Centre in Japan by Roy Fleetwood.

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