Siliconebonded glazing

Throughout Europe, there has been a considerable growth and development in the use of structural glazing, predominantly to form the non-loadbearing glass envelope of major building projects.

The end walls of the Sainsbury Centre, UEA (Fig. 7.34), installed by Clark Eaton in 1976, remain one of the most elegantly and minimally detailed assemblies of clear annealed glass, 15 mm thick, stiffened by 25 mm, 600 mm wide, full-height glass fins.When Solaglass replaced two units, owing to their size, 2.5 m x 7.5 m, they could only be supplied as 15 mm annealed glass by Saint-Roch of Belgium, edge finished by Solaglas in Coventry. The maximum size of toughened glass is primarily governed by the toughening oven. Pilkington's current maximum size for toughened glass is 4.2 m x 2.1 m. Where larger sizes are required, Plyglass can offer laminated glass up to 6 m x 3.2 m.

It is interesting to note how under BS 6262:1982 it would not have been possible to have replicated the end wall of the Sainsbury Centre, as the standard would have required the first 800 mm from ground level to be toughened or laminated glass. Requirements have changed since its issue, and on I June I 992

7.32 Curved laminated glass used at Montmartre funicular the revised Building Regulations' Section N: Glazing Materials and Protection was introduced.This specifically recognizes the strength characteristics of annealed glass; it is in effect a relaxation of the requirements of BS 6262. Diagram 2 states the size of annealed glass that can now be used. At 15 mm thick the panel size is not limited by Section N, and the end walls of the Sainsbury Centre are once again a legitimate solution for a building in England and Wales. However; one must remember that annealed glass is not tolerant to local stress build-up of a loadbearing bolted fitting.

The facade glazing of the Sainsbury Centre is restrained against wind suction by a continuous vertical silicone seal only (Adshead Ratcliffe ARI08I translucent). It is designed to withstand wind loads up to 1400 N/m2. Overall, the glass is retained by a glazing channel set flush with finished floor level and fin boxes at the head of the glazing, which are fixed back to the main structure via slotted holes to accommodate tolerance and movement.

In contrast, many current assemblies opt to back up the silicone seal by using a mechanical patch plate or a countersunk fitting. The success of fittings such as Pilkington's Planar has encouraged their use in glass fin assemblies, where it is questionable if in fact they are necessary.

More recent applications of silicone-bonded glazing that have caught architects' imagination include the Sculpture Pavilion at Sonsbeck,The Netherlands, by Benthem & Crouwel Architekten. This pavilion is a direct development of the earlier relocatable house for Jan Benthem in Almere (Brookes and Grech, 1990, p.5). By taking the idea of structural glazing even further; this pavilion is a totally glazed 24 m long, 6.2 m wide,

3.65 m high transparent box (Fig. 7.35). Unfortunately, the museum was designed as a temporary building, and has now been dismantled. A similar proposal was developed by the Faculty ofArchitecture (course leader Ulrich Knaak) for a pavilion at Aachen University (Fig. 7.36). Such proposals, offering maximum transparency through the use of large sheets of glass and minimizing the apparent means of support, have been adopted

7.33 Suspended glazing at Reina Sofia Museum, Madrid.

almost as a style of architecture identified with the I 990s. Brookes Stacey Randall Fursdon's use of curved toughened glass and cast stainless steel fittings at the Thames Water Tower, London (Anon, 1996), led the judges of the RIBA Awards 1995 to comment: 'Such is the inspirational nature of the tower that the panel felt its qualities transcended the question -is this sculpture or architecture?' (Fig. 7.37).

7.34 Sainsbury Centre glazing.
7.35 Sculpture Pavilion, Sonsbeck (architects: Benthem and Crouwel).
7.36 Pavilion at Aachen Faculty of Architecture.
Architectural Details Tower London
7.37 Detail of Thames Water Tower, London (architects: Brookes Stacey Randall Fursdon).

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