A strong film provides for transparency and safety

The glass balustrades create a very open atmosphere in the London Westfield Shopping Center. They consist of around 2,000 free-standing laminated safety glass panes with high-strength SentryGlas® interlayer by DuPont. Photos: Kite Glass

In one the biggest European inner-city shopping centres, laminated safety glass balustrades using SentryGlas® interlayers made by DuPont offer the highest standard of transparency while being compliant with the strictest requirements to safety.

In October 2008, the London Westfield Shopping Center opened its doors. Comprising more than 280 retail shops distributed on a sales area of approximately 150,000 square metres, almost fifty restaurants, recreation areas, a library and a cinema, the two-storey shopping mall intends to attract more than 20 million visitors every year. Maximum transparency combined with a very open ambience within the building unit are achieved by using glass balustrades designed by the company CMF Ltd., Feltham, Middlesex (Great Britain), and manufactured by the British construction glass manufacturer Kite Glass.

A total of 2,000 round and free-standing laminated safety glass elements will edge the shopping arcade in the first storey, as well as staircases and parts of the external entrance. The design of 1,500 laminated safety glass elements is planar, the remaining elements are bended. An unobtrusive support arm construction is used to fix glass panes with the dimension of 1.1 x 1.3 metres to the ground. Handrails fixed by means of point fittings connect the glass elements, but have no additional support function.

SentryGlas® interlayers for improved load capacity

The balustrades made from laminated safety glass using a SentryGlas® interlayer meet the highest requirements to its load capacity as set out in the British Standards and Building Regulations.

Free-standing glass elements, which are used as a barrier in shopping centres and possibly must bear up under the massive load of crowds, must fulfil the highest requirements of the British Standards and Building Regulations with regard to its load capacity. The relevant standards BS 6180 and BS 6399-1 require a maximum deflection of 20 millimetres with a linear load of 3 kN/m.

Despite of the high safety requirements, the glass constructions in the Westfield Shopping Center should not appear as an excessively massive structure. “Therefore, CMF asked for a solution providing for improved stability and thus lower thickness at efficient costs as opposed to structures using PVB interlayers“, explained Leroy Reed, Director of Kite Glass. The solution was a laminated safety glass construction using SentryGlas® film made by DuPont. The laminated safety glass, intended for the balustrades of the Westfield Shopping Center, is composed of two panes made from toughened safety glass (ESG) with a thickness of twelve millimetres, and a SentryGlas® interlayer with a thickness of 1.52 millimetres.

Thus, according to DuPont, the entire laminate unit is around 20 percent thinner as an appropriate construction designed with PVB film, where glass panes with a thickness of 15 millimetres would be necessary to meet the construction regulations.

Impressive residual strength

SentryGlas® interlayers significantly improve the load capacity of laminated safety glass for all three thickness options available at the moment. Diagram: DuPont

Another advantage of laminated safety glass using SentryGlas® interlayers is the high post-breakage residual strength of the glass. Even if the glass will break due to extremely high load, debris remains adhering to the interlayer.

This significantly reduces the risk of injury for pedestrians. At the same time, the balustrades made from this glass fulfil a barrier function. According to DuPont, its proprietary SentryGlas® manufactured on the basis of ionomers (thermoplastic polymers) offers a five times higher durability, a ten percent lower thickness and an increased resistance against humidity, and lower vulnerability for edge defects. Therefore, the product allows for the use of laminated safety glass in heavy duty building applications, and it enables architects and structural engineers new opportunities.

Björn Sanden, Development Programs Manager at DuPont Glass Laminating Solutions comments: „SentryGlas® enables economically efficient solutions. Thanks to the excellent mechanical properties of this interlayer, laminated safety glass panes and their support structures can be designed with less weight. SentryGlas® interlayers keep their high strength and transparency even being exposed to environmental influences over years.

For outdoor applications, as in the case of a part of the balustrades for Westfield London, high humidity and weather-resistance of the laminated safety using SentryGlas® interlayers provide for a long lasting edge stability and transparency.“