Shattering Myths About Glass

As architects and builders put more faith in the structural properties of glass, its use has expanded to all areas of design.
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From Architectural Record
Josephine Minutillo

The 2-inch-thick laminated glass, fabricated by the German manufacturer Seele, incorporates another recent innovation. An ionoplast seal binds the layers of glass together for full composite action, making the material itself part of the structure and allowing for a very stiff and relatively thin panel. Panels using earlier bonding materials like polyvinyl butyral (PVB) were not as strong, because the laminated sheets would behave independently rather than as a single unit. "If we didn't use ionoplast, the glass would probably be 3 to 4 inches thick," Macfarlane explains. "It's a big savings in terms of weight." Another project by Dewhurst Macfarlane, for a balustrade at the Victoria & Albert Museum in London, uses ionoplast to bond glass to metal.

Since the canopies' unveiling earlier this year, Macfarlane and his team have noticed that some visitors - who don't seem to have as much faith in the glass as the engineers do - prefer to walk around the glass structures rather than beneath them. For an underground entrance at Dilworth Plaza in Philadelphia, "There's no ‘walking around it' option," Macfarlane jokes.

Designed by KieranTimberlake in collaboration with Olin, two 17-foot-wide, all-glass pavilions connected by a single arcing gesture are planned as gateways to a below-grade transit concourse. "A continuous circle is set against a Classical facade," says Macfarlane. "It's a simple gesture that deserved a simple solution."

In a design by KieranTimberlake in collaboration with Olin, two all-glass pavilions act as gateways to the transit concourse below Philadelphia�s Dilworth Plaza. Connected by a single arcing gesture, each rises 20 feet.

Image: KieranTimberlake

 

That solution eliminated any steel structural members or metal connections whatsoever. Instead, the 2-inch-thick laminated-glass panels of the curving roof are joined by structural silicone and supported entirely by vertical glass panels - without fins - of equal thickness. "It's basically a giant glued structure," says Dewhurst Macfarlane associate Nicholas Roach. The walls support all vertical and lateral loads, including wind and snow. Wind loads present the greatest challenge, especially at the top of the staircases, where the wall reaches nearly 20 feet in height. "We needed to transfer those loads down the cantilever where it is stiffer," Macfarlane explains. "The closer you get to the bottom, the more capable the structure is of supporting the load."

Dewhurst Macfarlane can predict to some extent how the structure will perform, since its parts - including finless vertical glass walls - and scale are similar to the TKTS Booth in New York City's Times Square they worked on [Record, January 2009, page 47]. But they used NEi Nastran, a finite element analysis program typically used for designing complex machine parts, to understand all the stresses in the structural silicone, or glue. As currently designed, the silicone will only be used for the 1⁄2-inch-wide gaps between the roof panels. Those same gaps between the vertical panels will be left open, keeping the pavilions ventilated and capturing light during the evenings for a dazzling enhancement to a grand urban space.

Structural glass can be used on a much smaller scale to create equally dazzling interior spaces. AMG Design, a high-end steel-and-glass specialty contractor, is using its new facility in Plainview, New York, to showcase its fabrication capabilities. The showstopper is a dramatic glass-and-cable staircase designed by Grimshaw Architects together with Thornton Tomasetti engineers.

In a design by Grimshaw Architects, a tensegrity structure was used for an innovative glass staircase.

Image: Grimshaw Architects

 

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Originally published in Architectural Record
Originally published in May 2010

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