A world’s first for glasstec 2008

This animation clearly demonstrates the bridge structure, characterised by maximum transparency and seeming weightlessness.
Photos: seele, GSSG Holding GmbH & Co.KG

As part of the glass technology live glasstec 2008 special display, the Seele GmbH & Co. KG puts on show a cold-shaped glass bridge structure, spanning a distance of seven metres.

The Seele company developed a technology for shaping glass without heating it again for the Strassburg station refurbishment project. In 2007 the historical station building was complemented by a large glass-built reception wing. The bent glass panels for the highly-complex forms of the roof and façade structures, totalling 6,000 square metres, were made by the Seele company, using its new technology of shaping cold glass. The process starts when two plane glass panels, separated by an intervening layer of polyvinyl butyral (PVB) are put together into a compound safety glass sandwich. This will then be placed on a bending frame of steel with the required radius. Using tie-bars for the short sides, the Gersthofen specialists then shape the cold section as required. Only then will the entire set be laminated into an inseparable element in an autoclave at corresponding temperatures and pressures.

The eye-catching focus of the glass technology live special display: Bridge No 7, made of cold-shaped glass and spanning seven metres.

Fault-free surfaces

The glass-foil laminate produced by cold shaping represents a frictional entity of glass and intermediate layer in a configuration as imposed by the template. The result is a type of glass with defined internal stress as well as all the other favourable properties of cold-shaped glass.

Cold-shaped glass surfaces show none of visible waves as in hot-bent panels, and which result from the manufacturing process. This type of glass has a very homogenous surface and may be used especially for façades or roof sections with a wide span.

Developing the technology

The Seele company developed the manufacturing methodology for cold-shaped compound safety glass on the basis of available know-how as well the experience gained when implementing the Strassburg station project. The company now takes another step ahead for glasstec 2008. Referring to “Bruecke (bridge) 7”, the highlight of the glass technology live special display, the company offers the following description in a press release: “Not only does bent glass carry its own weight in this structure, as well as cope with potential wind pressures and snow loads, but it is itself the load-bearing element”.

The bridge is composed of separate, four-millimetre thick, bent glass panels, each measuring only 3.7 centimetres as part of the total structure. The elements are put together so that material-optimised panels can cope with extreme loads. Over a seven-metre span, 1.7 tons of glass carry a load of 7.2 metric tons.

Challenges to designing the supporting framework

Following information provided by the Seele company, the statical system of the experimental arched glass bridge also involved a number of challenges when designing the supporting framework. It consists of a double-hinged arch with a rising of the vault/span ratio of 1/17.The load of its own weight as well as useful loads are mainly transferred to the two bridge abutments via the structural arch effects of the glass surface. Its glass balustrade serves to stabilise the glass structure.

The arch-girder effect was employed to support the capping cross beam in the bent glass balustrades. The result is an optimised system in which the supporting structures of the glass pathway together with the glass rail offer a perfect optical solution. This transparent unsupported glass bridge spans a distance of seven metres, measuring two metres at its widest section. The use of materials such as steel was minimised to a number of linking elements for the glass railing with the glass walking path.

Constructive solutions for glass materials at glasstec 2008

Extraordinary projects and constructive solutions for glass materials have already been presented at previous glasstec exhibitions, either at the glass technology live special exhibitions or at numerous stands by different exhibitors. New products as well as innovative manufacturing technologies offer new chances of using glass as a transparent material for statical elements to this field of the glass sector as well. Latest developments will be on display at glasstec 2008.

Please see Glass technology live: Hall 11, Stand B26.