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glass distinction

This eight-page supplement features buildings forming part of the Pilkington Pavilion at the Glass Processing and Technology exhibition being held at the National Exhibition Centre, Birmingham on 11-13 November. Details of the architectural seminar programme and registration can be found on page 58

Bullring: Birmingham Benoy

The Skyplane of Birmingham's Bullring has been designed to give a feeling of open streets, allowing maximum daylight and views. The concept of Skyplane developed as a flat single sheet of glass hovering over the internal streets.

A bolt-supported (planar-type) system was chosen and glazing was hung below the supporting structure, so that from inside it resembled floating glass.

The control of solar heat gain was critical to the design. The high-performance coatings available were able to offer 60 per cent reflectance, and using a neutral tint enabled the architects to reduce cooling loads without affecting exterior views.

Cleaning and maintenance were also important. The deflection of a single unit of glazing determined the pitch at which the system would allow effective rainwater run-off. Skyplane units were restricted to 2m x 1.5m, allowing the pitch of the glazing to be 4infinity, as close to flat as it is possible to achieve. The vertical glazed units were used in sizes up to 3m x 2m.

The supporting structural trusses are at 15m centres and include a cleaning and maintenance walkway. Cleaning requires a 7.5m demineralised water-fed carbonfibre pole. To allow the cleaning head access around the fixing points of the 'spiders', the spacing of the glass had to be increased by an additional 50mm.

The double-glazed units are made from a 6mm outer toughened sheet including a coating on the inner face, a 16mm cavity, and an inner laminated sheet of heat-strengthened glass comprising a 12mm inner layer, 2mm interlayer and a 6mm outer layer. The combination achieves a U-value of 1.4W/m 2.Once the units were installed onto the support system and lined and levelled, they were mastic-sealed at both ends with cruciform weep holes on the underside, offering effective leakage prevention.

Swiss Re: London Foster and Partners

The multi-layered facade of 30 St Mary Axe responds to the challenge of using glass in a socially and environmentally progressive manner. The building's fully glazed skin allows the occupants to enjoy the benefits of daylight and natural ventilation coupled with increased external awareness and excellent views. The glazing also allows the building's innovative structure to be legible from the exterior.

The glazing of the office areas comprises a double-glazed outer unit with a low-emissivity coating, and an internal screen of laminated glass to maximise daylight penetration and optimise views. The cavity between the two layers is ventilated by exhaust air drawn from the offices. It also contains perforated blinds to prevent solar gain and mitigate glare. The blinds intercept most solar radiation before it reaches the office spaces, reducing the large cooling load typical of conventional offices. The inner rectilinear glazed screen mediates between the external diagrid and the interior, allowing for the positioning of internal divisions.

The building will use natural ventilation to supplement the air conditioning for up to 40 per cent of the year, reducing energy consumption and carbon-dioxide emissions.

Voids between the radiating fingers of each floor combine in a series of light wells, which spiral up the building. They help to regulate the internal climate, effectively becoming the building's 'lungs'. The building's aerodynamic form generates pressure differentials that greatly assist the natural flow of air through the light wells.

The light wells are clad with opening and fixed double-glazed panels with tinted glass and high-performance coatings to reduce the penetration of solar radiation.

The darker appearance of the glass maintains the spiralling expression of the light wells on the elevation. The dome at the building's apex, housing corporate hospitality facilities on levels 38-40, is similarly clad, topped by a 2.5m-diameter lens, the only curved glass unit in the building.

The facades of the offices, light wells and top of the dome comprise a doubleglazed unit with the following make-up:

10mm toughened outer glass pane (body tinted in the light wells);

16mm air gap (the gap between the TOB glass is filled with argon);

4mm/0.76mm PVB interlayer/6mm laminated glass.

The office areas have an inner screen to form a ventilated cavity with the following make-up: 6mm/0.76mm PVB interlayer/ 6mm laminated glass.

Federal Building and Courthouse: Phoenix, Arizona Carpenter/Lowings Architecture & Design

A spherical suspended cable structure forms the ceiling of the Special Proceedings Courtroom of the new Federal Building and US Courthouse in Phoenix, a building designed by Richard Meier & Partners. The central 'lens' of the ceiling acts as a diffuser for artificial light, while the clear perimeter provides views of the sky. The rolled glass pattern transforms the lens area of the ceiling into a glowing surface.

The Special Proceedings Courtroom is a 32m-diameter open-topped cylinder clad in translucent glass, within the vast atrium formed by the southern and western blocks of the building. The atrium is open to the outside air, shaded with louvres above the glass roof, and cooled by units that introduce mist into the air at the top of the atrium, absorbing energy by evaporation.

The horizontal ring beams in the sixstorey frame of the courtroom provide compression rings, making the tension structure extremely efficient. The main cables are only 12mm in diameter, with circumferential rods that hold the spherical form of 8mm diameter. Small aluminium clamps attach to the main cables and the glass is hung from these via a series of stainless steel hangers at the perimeter and in the central area where the sphere, defined by the cables, lies below the intersecting plane.

A complete three-dimensional computer model of the structure was built to assist in the analysis. The structure uses the mass of the glass as a stabilising element, and the glass surface also acts as a diaphragm in an earthquake, transferring rotational forces to the base structure. Movements within the structure due to changes in temperature are accommodated at each panel, and after accidental breakage the glass is retained because the tough ionoplast interlayer of the laminated glass is mechanically attached to the small patch-plate at the corner of each panel. The sprinkler system is integrated into the cable structure, substituting for the cables where necessary, using flexible connections to accommodate potential movement.

The artificial light sources for the courtroom are all at the top of the cylinder and directed to shine through the dished lens. The glass in this area is a rolled, patterned glass with a known angle of diffraction, so that lighting levels can be predicted accurately when combined with sources with specific beam angles.

German Foreign Ministry: Berlin Carpenter/Lowings Architecture & Design

The Lichthof is the public space of the new German Foreign Office in Berlin.

Conceived by the architect Müller Reimann Architekten as a light-filled courtyard with a glazed roof and facade onto Werderstrafle, it is used as an orientation space for the public who enter the building, and as a space for semi-public and institutional gatherings.

The space is seen in relation to the future square on the other side of Werderstrafle, formed by Schinkel's existing Friedrichwerdersche Kirche and his Bauakademie, which was destroyed, but is to be reconstructed in the effort to revitalise the former cultural centre of the unified Berlin.

On an urban level, the facade of the Lichthof forms an important boundary through which the public views the Foreign Office, and the civil servants, in turn, view the city and the passers-by.

Images of both outside and inside are reflected in this glazed facade. The boundary condition and the northfacing orientation of the courtyard are the basic conceptual parameters of the facade design.

The reduction of the structure of the wall to the absolute minimum by the use of a tensioned cable-net, and the visual cues provided by the parallel planes of the roof beams and the clear horizontal banding of the building, were used to explore the possibilities of reflectivity, transparency and colour afforded by various glass coatings and specular metal.

In the roof, specular aluminium reflectors were mounted at such an angle that when the sun is at its lowest in midwinter, sunlight is still projected into the back of the space.

In designing the facade, three glass coatings were used in order to modulate the reflectivity of heat, sunlight and colour. Heat is reflected by an external coating on the single-glazed low-iron laminated vision glass panels to prevent condensation. Light and image are reflected by an additional colourless semi-reflective coating on the central area of the glass panels to create the impression of a semi-transparent mirror floating within the facade.

Special dichroic coatings were applied to horizontal bands of glass cantilevering from the facade. This coating divides sunlight into two halves: transmitting and reflecting opposite ends of the spectrum to produce a constantly changing field of colour on either side of the facade.

Douglas Power Station: Isle of Man Savage & Chadwick Architects 2double-skin planarglazed wall enabling a visual celebration of the complex engineering feat that lies within the building.

The impressive glazed facade spans up to 25m in height, and the sheer scale of this element posed a number of aesthetic, engineering and environmental challenges to the team.

Firstly, the design had to appear highly transparent and visually lightweight while still being able to withstand high wind loading. Secondly, the facade had to be designed to minimise the effects of solar reflectance and solar gain.

Thirdly, the design had to incorporate an acoustic performance which was sufficiently sophisticated to avoid any detrimental effects on the surrounding residential property.

The stepped plan is expressed externally by a series of curved aluminium standing-seam roofs which interlock and face in opposite directions. The largest of these roofs houses the main body of the turbine generation hall.

As part of the solution to overcome the solar gain and glare issues, the outer leaf of glazing is inclined at an angle of 8° outward and forms a clean junction with the roof by recessing the glazing panels into 3mm-thick aluminium channels aligned flush with the outer face of the sloping soffit panels. Solar gain is further minimised by ventilating the space between glazed skins and a 7m roof overhang.

The double-skin glazing allows the building to achieve an acoustic performance (Rw value) of at least 52dB, where the wall is at its narrowest point. The gradual increase in the wall void means that the average attenuation figure is much higher.

The wall itself is a point-fixed frameless planar facade supported by a tensioned-rod rigging system. The tensioned system allows for the visual and actual lightness demanded by the design concept. At the top and base the tension rods are fixed back to the main trusses and primary steel structure in order to provide the necessary rigidity against wind loading.

The London Marriott Hotel: Kensington Moren Greenhalgh

For the Marriott Hotel, Moren Greenhalgh developed the traditional concept of a hotel atrium to create a dramatic first impression and focal feature. The atrium and porte cochère provide a central glazed space, which links the entrance to the reception, restaurant, coffee shop, cocktail bar and leisure club.

A highly transparent skin was required to maximise light within the entrance atrium and overlooking bedrooms. At 880m 2and 21m high, the Pilkington planar glass facade is reportedly the tallest hanging glass facade in Europe. The frameless vertical and horizontal glazing creates uninterrupted surfaces.

Being of such size and with the complexity of bridging active underground rail lines, the technology of the atrium construction was innovative and exacting, requiring the close cooperation of architects, engineers, glass suppliers, fabricators and erectors. From a 500 x 200mm curved steel beam, 15 suspended structural glass fins of 19mm thickness in lengths of 3m are linked by purposemade stainless steel fixings. These support the 10mm curved glass facade by means of planar fixings. The glass is 100mm-thick toughened clear Pilkington Optifloat in approximately 1.5m x 3m size panes. Given 5mm dimensional tolerances, 15 tonnes weight of ballast was hung and removed progressively as each pane was installed. The glass in the atrium weighs a total of 60 tonnes, each of the nearly 200 pieces weighing 150kg.

More than 4,000 specially machined stainless steel bolts secure the glass to the atrium steelwork. The atrium roof and porte cochère use the same planar technology in the horizontal plane.

The Architects' Forum at GP&T

All sessions in The Architects' Forum will take place on the Pilkington Activ Stand, Hall 1, Stand B40.

Sessions are free but delegates should register.

TUESDAY 11 NOVEMBER 10.45-12.15 Architecture, glass and light Chair: Paul Finch, editorial director, The Architects' Journal Speaker: Luke Lowings, architect, Carpenter/Lowings Architecture & Design Projects: the Lichthof facade and roof, German Foreign Ministry, Berlin, and the Lens ceiling, Federal Court, Phoenix, Arizona 13.15 Pilkington on 14.00-15.30 Pilkington Technology - opening the window to the future Speaker: Dr Phillip M Ramsey, Pilkington An examination of the way that coatings, interlayer materials and glazing-system technologies have generated a stream of new products for buildings

WEDNESDAY 12 NOVEMBER 10.45-12.15 Pilkington Technology - opening the window to the future 13.15 Pilkington on 14.00-15.30 Glass on the skyline Chair: Susan Dawson, working details editor, The Architects' Journal Speakers: A presentation by Foster and Partners Project: Swiss Re headquarters, City of London

THURSDAY 13 NOVEMBER 2003 10.45-11.45 Glass in fire - CPD accredited session Speaker: Peter Gilbert, Pilkington 12.30 Pilkington on 13.45-14.45 Glass for energy management - CPD accredited session Speaker: Michael Metcalfe, Pilkington GP&T 2003 takes place in Hall 1 of the NEC, Birmingham from 11-13 November.For more information go to www. gptexhibition. com

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