Suspended glass assemblies

Suspended glass assemblies using glass as the load-carrying material were first developed with Foster Associates in 1973 for the Willis, Faber and Dumas Insurance building in Ipswich (Fig. 7.1 8). The system consists of two glass components: a wall skin formed from sheets for 12 mm toughened glass (armour plate) and vertical fins fixed perpendicularly to the skin to provide lateral resistance to wind loads.These are formed from I 9 mm armour plate.

The system is constructed from the top down. The topmost glass panels are independently suspended from the main structure using one central bolt, the load being spread across the width of the glass by means of a top clamping strip. Figure 7.19 shows the original sketch of the fixing back to the concrete structure at the head of the assembly.

Subsequent panels are hung from those above using I 65 mm square brass patch connectors with stainless steel fixing screws.The height of the assembly is limited by the shear strength of the bolt holes that are drilled through the glass, the maximum height being 23 m.

At Ipswich, the glass fin to resist wind loads is fixed back to the floor structure. Because the wall skin is suspended, the glass expands downwards. In order to allow vertical movement between the wall and the fin, the inside patch connector comes in two parts, one for attachment to the fin and the other to the facade (Fig. 7.20). The two parts dovetail together; allowing the fins and facade to slide vertically independently of one another

The early design of the dovetail, as shown In the Pllklngton design guide (Pilkington, 1975), included a square dovetail, which allowed the two parts of the fins to separate under horizontal movement. Later versions used a rounded sleeve dovetail (Fig. 7.20). At the base of the assembly, a channel section is fitted, which supports the glass laterally and has sufficient depth to accommodate the cumulative downward expansion of the facade.

Joints between the glass are totally exposed to the weather, and rely for their efficiency solely on the

7.18 Willis Faber Dumas at Ipswich.

7.18 Willis Faber Dumas at Ipswich.

7.19 Original sketch of clamping strip at head of assembly at Willis Faber Dumas.

properties of the silicone-based sealant and the correctness of its application.

The whole system was designed to be capable of accommodating errors in the concrete frame of 50 mm in any direction.

Within ten years Pilkington had reduced the means of securing toughened glass to a flush countersunk machine screw fitting. This fitting, known as Planar; was first used on Briarcliff House, Farnborough, by Arup Associates and at the Renault Centre by Foster Associates (Fig. 7.21), where 4 m x 1.8 m glazing was restrained using 'spider' connections back to the horizontal steel framing at 1.33 m centres (Fig. 7.22). Later; the span between fittings was increased at Lime Street Station, Liverpool, where 1.95 m x 1.05 m glazing was fixed back to a vertical steel framing at 1.95 m centres (Fig. 7.23 a and b). Generally, a rule of thumb is that Planar fittings should be connected on a grid of pick-up points approximately 2 m square in order to reduce the deflections between the fittings. Fittings for double glazing typically comprising I 0 mm outer toughened glass, I 6 mm air space and 6 mm

7.20 Attachment between glass fin and facade at Willis Faber Dumas.

7.21 Renault Centre glazing.
7.22 Detail of glazing fitting at Renault.

inner toughened glass were first used on the Porsche UK Headquarters, Reading, by Dewhurst Haslam Partnership in the form of 4° rooflights.

Later (I 989) developments in reducing the number of supports for suspended glazing included East Croydon Station by Brookes Stacey Randall Fursdon

(Fig. 7.24), where cast stainless steel outriggers are used to reduce the effective span of the glass between fittings.Thus the span of the 12 mm toughened glass is reduced from 3000 mm to 2400 mm.

The vertical mast is held at its head and base by stainless steel castings with an articulated head detail, to accommodate the vertical and differential movement between the structure and the vertical

7.23b (contd) Spans of glazing at Renault (left), and Liverpool Street (right).
7.24 East Croydon Station (architects: Brookes Stacey Randall Fursdon).
7.27 Plan detail of glazing at East Croydon Station.

cladding (Fig. 7.25).The 10 mm clear toughened glass roof glazing is suspended below stainless steel twin armed castings using 902 mark 2 Planar fittings (Figs 7.26, 7.27).

Other elegant solutions for the problem of picking up the four bolts for the fittings include Nicholas Grimshaw's stainless steel 'dinner plates' at the Financial Times Print Works (Fig. 7.28) and Mark Goldstein's aluminium bronze cast brackets for III Lots Road in London.

A refined support system for suspended glazing is the stainless steel wire wind bracing developed for the Pare de la Villette in Paris by Rice, Francis and Ritchie, for Adrien Fainsiber in 1986, where a special detail allowed a span between the main structure of 8 m square, and enabled flexing of the wire-braced intermediate structure and also alignment of the glass (Figs 7.29, 7.30).

An increasing diversity of supply of countersunk and plate patch fittings were then developed. As well as the Pilkington Planar fitting these would include countersunk fittings by Greenburg UK, Marcus Summers UK, MAG Design & Build UK, Seele in Germany, Eckelt in Austria and GME in Belgium (Fig. 7.3 I).

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7.29 Detail of Pare de la Villette glazing.

7.30 Parc de la Villette structure support of glazing.

7.31 Variants from Planar and RFR fittings with different degrees of movement: (a) Marcus Summers, UK; (b) GME, Belgium; (c) Seele, Germany; (d) Eckelt, Austria; (e) Eckelt; (f) MAG Design & Build, UK.

At the Montmartre funicular transport station project in Paris, Groupe ALTO developed a new countersunk fitting in conjunction with the manufacturers, SIV. This has a 48 mm face diameter, compared with the 28 mm diameter of the Planar fitting. The 12 mm plus 8 mm laminated glass (not toughened) provides canopies in which the glass is moulded to the desired radius and the fittings are able to accept 22° of rotation (Fig. 7.32).

In most cases the span of the supporting framework is one or two storeys, but at the Reina Sofia Museum of Modern Art in Madrid (architect: Ian Ritchie) the entire glass envelope to each 36 m high tower is suspended by stainless steel rods from roof level. Here, each panel of glass is individually supported. The size of each panel is determined by wind load, economic glass thickness, structural module and heights between floors. Each I 2 mm thick pane of toughened glass is 2966 mm wide by I 833 mm high and is suspended from one central panel fitting on its top edge (Fig. 7.33). Flush Planar fittings at each corner provide fixing points for the wind bracing system.

It is noticeable on some projects using suspended glazing that many four-way joints, each nominally 10 mm, are misaligned. Manufacturers are helping to improve this by reducing acceptable variations of the glass size and increasing the accuracy of drilling the countersunk holes.This is being achieved by investment in new automated machinery, which has the added facility of polishing edges.

The maximum available size of glass for use with the Planar system is limited by the need for the glass to be toughened. The toughening process of pre-stressing the skins by heating them to 620°C followed by controlled cooling increases the load capacity of the glass.The maximum size available therefore depends on the size of the toughening ovens at St Helens.The present maximum size for clear toughened glass is 4.2

m x 2.1 m. Some European glassmakers have larger or different aspect ratio ovens and so there is the opportunity for Pilkington to collaborate with them or invest in larger ovens also. Pilkington can combine Planar with body tinted glasses, reflective glasses, double glazing, low-emissivity coatings and even the screen printing of dots orfrettings.AII these additional processes influence the maximum size.

Of all the types of cladding discussed in this book, suspended glazing and structural glazing are undergoing the fastest development in the application of new systems and environmental control.

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