Shopping mall roof is made with lighter, stronger laminated glass

Shopping mall roof is made with lighter, stronger laminated glass

A thick glass structure would not have achieved what we wanted; we would have needed to introduce a heavier truss or membrane support system to the skylight and we couldnt have achieved the uncluttered sense of being outside that one feels inside the mall today. The solution was a Pilkington Planar point-fixed glazing system specially designed with DuPont SentryGlas structural interlayer. The laminated glass is about 35 percent thinner and lighter than any laminated glass system available in the past!

So says Chris Brown of MMC International Architects when describing how his firm has catapulted Torontos Yorkdale Shopping Centre, originally built in 1964, into one of the most attractive, fashionable and successful enclosed shopping malls in Canada today (completion: April 2005).

MMC reinvented Yorkdale Shopping Centres interior with the addition of a 60-foot high, barrel-vaulted atrium of laminated glass running 300 feet in length and soaring above a portion of the 180,000 square foot redeveloped area. The structural glass roof, made of insulated laminated glass based on the Pilkington Planar frameless glazing system with DuPont SentryGlas structural interlayer a new product called the Planar / SentryGlas system — uses open space and natural light to create the streetscape feeling that the architects wanted.

A contemporary, open-sky feeling

Brown told Laminated Glass News: Architects have been striving for years to create a sense of being outside inside buildings, even in the face of factors like harsh climates, external noise and other factors. In the case of the Yorkdale Shopping Centre, the creation of a contemporary, open sky feeling inside the mall was of primary importance to our client. The reopened shopping centre was to contain the flagship stores of well-known retail brand leaders, several stories high. We wanted to explore the verticality of the space in order to best display these storefronts against the sky, give them a unique character compared with sister stores in other Toronto shopping malls.

This was quite a challenge when you consider Torontos harsh climate: freezing winter temperatures often fall as low as minus 20 degrees C, and there is heavy and frequent snow. If we had wanted to create a large-span, barrel-vaulted glass skylight like this in Florida, it would have been a lot easier!

Laminated glass that is 35 percent lighter

The solution to our aesthetic and functional requirements was the new Planar/ SentryGlas system. The laminated glass is about 35 percent thinner and lighter than any laminated glass system available in the past including laminated glass with traditional PVB.

Our selection was the result of a dialogue with our structural engineers (Yolles) and Pilkington Planar distributor W&W Glass of New York. We wanted a glass structure that was as light as possible. A heavy glass structure would have meant a heavier steel over-casing, a second layer between the people inside and the sky that we wanted to avoid. We were looking for anything we could to lighten up the feel of the structure. Thick glass, normally required to support heavy snow load, would have required heavy trusses.

SentryGlas takes the load

Discussions with W&W Glass revealed that in a Planar/ SentryGlas system, SentryGlas actually takes part of the load itself. The structural interlayer also demonstrates excellent edge stability, which helps the glass construction to bear heavier loads at the sides, where the barrel-vaulted roof meets the walls and where the glass construction needs to be strongest.

The overall strength of SentryGlas structural interlayer means that we could design a glass roof with no visible clutter at the periphery. The result is that we could design a simple, elegant, clean architectural form, which met the tough technical specification and which also came within the budget. The client is ecstatic!

A step-change in design freedom

Jeff Haber, managing partner at Pilkington Planar North America distributor, W&W Glass of New York, explained: The architects wanted a frameless system for this large span skylight instead of a heavy, old-fashioned looking, aluminum-framed system. They also needed the overhead glazing to be strong and safe for the public in the mall below in the face of frequent heavy snow and ice loads.

We have been supplying Pilkington Planar point-supported glass systems to architects for skylights and glass canopies since 1993 — but the introduction of SentryGlas structural interlayer into the equation means a step change in design freedom for our customers.

Unbeatable edge stability

For example, SentryGlas offers unbeatable edge stability. This means that it will not discolor or delaminate over time from contact with the silicone used in point-supported glazing systems. Also, its innate structural strength and stiffness means that architects can design large, relatively thin glass panels with minimal support systems that can, incredibly, handle massive loads whether impact from hurricane or blast, or snow and ice loads.

We supplied 1,400 m2 of laminated Planar for the Yorkdale Shopping Centre; this great-looking barrel-vaulted glass roof in fact consists of a super unit; an insulated glass (IG) construction using a high performance coating for solar control, SentryGlas interlayer for structural strength and argon gas in the air gap for state-of-the-art insulation.

26 mm total glass thickness instead of 35 mm

The snow load specification was 65 pounds per square foot (3.1 kPa). In the past, to meet this specification, we would have needed to specify a unit utilizing a tempered and a laminated glass in it, with a total thickness of 35 mm. Now, with the Planar / SentryGlas system we have used one pane of 10 mm thick glass and one pane of 17.5 mm laminate: 26 mm total glass, instead of 35 mm previously. This underlines that SentryGlas is a highly engineered interlayer!

Shopping mall roof is made with lighter, stronger laminated glass

The precise construction is 10 mm clear, fully tempered heat soaked glass, a 16 mm air space, and a 17 mm interior laminate incorporating a 1.52 mm SentryGlas interlayer. The ceramic frit for solar control comes on no. 5 surface. Each panel of glass is 7 foot long by 4 foot 6 inches wide.

Using SentryGlas in the Planar system means that you can use the structural properties of the laminate to decrease the amount of glass used. The overall glass construction is thinner, more affordable and more transparent. You can achieve greater spans using thinner glasses because of the structural properties of the laminate. This means exciting design opportunities for architects, who can build larger spans using thinner glass and less metal supports and a reasonable price!

To my knowledge, this is the first large scale project in the world using the Planar/ SentryGlas system. Traditional glass laminates are not designed for long-term exposure to moisture or silicone so that traditional laminated glass can start to lose its adhesion properties over time in point fixed systems, which use silicone. SentryGlas solves this problem. Pilkington, W&W Glass and DuPont have all performed extensive tests on laminated glass samples containing this interlayer in Planar point-supported systems; the tests addressed sealant compatibility and adhesion. SentryGlas passed all of our testing with flying colors.

Design Manager at Pilkington Architectural, Tim Morgan, commented: In the past, increased design loads resulted in an inevitable increase in glass thickness and cost, but the advent of SentryGlas structural interlayer has opened up new dimensions for engineers and architects.

The increased stiffness of SentryGlas now allows the full potential of both glasses in Planar laminated glass to be realized. This makes DuPonts structural interlayer a powerful ally for both the architect intent on challenging convention and the engineer who finds himself or herself charged with delivering the solution!

At Pilkington Architectural we have had to upgrade our testing equipment so that the full potential of Planar systems containing SentryGlas can be explored. Whereas our test equipment was rated to 150 mph in the past, that value has had to be increased to around 300 mph.

Today, architects frequently ask us for thinner laminated glass spanning larger distances; for minimally-supported facades and skylights; for point-fixed systems where skylights have an incredible lightness about them. Architects want skylights and facades to be as invisible as possible.

This is the age of big glass panels so the Planar/ SentryGlas system is just what architects and engineers are looking for! We had reached the limits of what we could do using PVB and standard point-supported systems. We were only able to take advantage of the strength of one ply of glass. With SentryGlas, we can take full advantage of the total laminate thickness (both pieces of glass and the interlayer), resulting in a thinner, more structurally-efficient laminate and point-supported glazing system!

DuPont and SentryGlas are trademarks or registered trademarks of E.I. DuPont de Nemours and Company or its affiliates.

Pilkington and Planar are trademarks or registered trademarks of Pilkington plc.

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