Curved laminated glass made with DuPont™ SentryGlas® Plus used for interior stair railing

With 14 screens at a new multiplex cinema in the Fiumara area of Genoa, Italy (completion: February 2004), architects Design International of London calculated that as many as 3,000 people could be exiting the cinema after a movie showing at peak time, typically on a Saturday night. The architects quickly realized that they would have to provide an additional exit route in addition to the planned two escalators in order to avoid unsafe overcrowding. As space was limited, they decided on a spiral stairway.

The aesthetic challenge then was how to attract moviegoers to use the stairs. Meanwhile, the functional challenge was how to design an attractive stairway going down through two floors of the cinema, with very limited space. Both problems were solved by the use of an attractive laminated glass stairway balustrade with a very tight radius incorporating DuPont™ SentryGlas® Plus™ structural interlayer.

Managing director of Design International, Davide Padoa, said: "The glass balustrade looks and feels inviting, attractive and safe all at once. The transparency of the balustrade lets through the light and also eliminates ‘the fear of the unknown’ that such a tall and broad balustrade (needed for safety on a tight, open spiral stairway) could foster if it was opaque."

"A major concern on our part was that a glass balustrade could look or feel wobbly but thanks to the new method of structural engineering made possible by façade engineer Teleya using SentryGlas® Plus interlayer the balustrade is functionally extremely strong and looks it too.

"Most important, the balustrade needed to be rounded in very tight radii at the two landings. We thought this would kill our dream for a glass balustrade because testing showed that other laminated glass interlayers including PVB could not withstand such tight radii without cracking. However, to our delight, laminated glass with SentryGlas® Plus passed all engineering and safety tests with flying colours, even at these tight radii. Use of DuPont’s structural interlayer therefore allowed us to marry our aesthetic dreams with functional strength and enabled the stairway project to be successfully realized."

Teleya’s Marketing and R&D manager Fabio Frambati said: "The laminated glass panels of the stairway balustrade had a maximum dimension of 1,195 mm (height) x 1,240 mm (length) with a tight curve radius varying from a minimum of 135.5 mm to an intermediate of 669.5 mm, to a maximum of 2,185.5 mm.

"Vital for the success of this project was the fact that we could clamp the point supported fixings directly into the 1.52 mm SentryGlas® Plus interlayer, not into the glass itself. This relieved the tension on the glass and was key to the achievement of such tight radii in curved laminated glass. Furthermore, the post breakage integrity of SentryGlas® Plus was a key advantage in this application. The total thickness of the glass was 13.52 mm, made up of two toughened panes of glass with a 1.52 mm structural interlayer."