Glazing Evolution Creates New Opportunities in Structural Glass

By Ellen Rogers

When the 5th Avenue Apple Cube in New York was originally built in 2006, with just 106 panels of glass and 250 primary fittings, it wowed the world as an impressive feat of architecture. At the time, that was the peak of structural glass capabilities. Fast forward five years to 2011, and the cube was re-built, this time with 15 glass panels and 40 fittings, providing an even more transparent, uninterrupted aesthetic. What’s next? That’s a question innovators, such as Apple, ponder constantly, especially since glass continues to get bigger, stronger and more transparent.

These seemingly impossible glass-on-glass structures are possible thanks to advances in glazing technology and materials, including sealants and interlayers. It’s the structural abilities of such materials, combined with advanced engineering, that have made it possible to minimize the use of metal—or even remove it completely—and use glass as the supporting element. While the glazing industry is stepping up to meet those needs, it’s not always simple. The process must be carefully orchestrated to ensure a safe, structurally sound installation.

First Impressions

If we’re giving credit where it’s due, let’s thank Apple—an organization that has dared to pushed the limits of architectural glass.

“The most progress we’ve seen [in structural glazing] is from Apple and its retail stores,” says Louis Moreau, head of technology and innovation with AGNORA, located in Collingwood, Ontario.

This work started with the now famous glass staircase in the Manhattan SoHo store built in 2002, and later expanded and refurbished in 2011. London-based Eckersley O’Callaghan (EOC) is the structural engineer behind many of Apple’s projects, including both the original SoHo staircase and the renovation, as well as the 5th Avenue Cube. One of the company’s most recent completions is the Marina Bay Sands retail store in Singapore. This 17-meter high, 30-meter wide dome creates an open and column free interior space that seemingly floats on the water. According to EOC, the sphere is a first-of-its-kind, all-glass dome that is fully self-supported and with only 114 panels of glass with 10 narrow vertical mullions for structural connection. Sedak fabricated the laminated glass with Kuraray’s SentryGlas interlayer; Josef Gartner was the façade contractor. The design allows the individual glass panels to brace and stiffen the structure. In addition, the
insulating glass panels were maximized, the largest measuring 10 meters wide by 3 meters high, to limit the number of joints, “hiding them only where there is structure, increasing the overall transparency of the building,” according to EOC.

It’s advances in bigger, stronger glazing that have made it possible to design and build innovative architecture such as this most recent Apple store.

“The current trend comes from a desire to create a structure-free enclosure where you can see directly outside and you don’t have any metal,” says Moreau. “Glass fins have been used for ages for windload conditions, but as spider fittings have become less popular, people aren’t integrating them in projects anymore.”

Maic Pannwitz, vice president of sedak, agrees, saying it wasn’t that long ago that architects were using structural glass fins as a vertical support structure for the facade glass.

“Now they are trying to avoid the glass fin as well. That requires more structural strength in the facade panels, which means thicker, multilayer laminated facade glass to accommodate structural loads and windloads.”

According to Dave Dunham, director of business development for Sentech Architectural Systems in Austin, Texas, the demand for oversized structural glazing applications stems from a desire for more transparency.

“As the glass gets larger you’re also reducing the frequency of the framing system components or eliminating them all together,” says Dunham. “The trend in architecture is definitely moving away from mechanical connections and fittings and shifting toward an aesthetic that’s more transparent.” Like Moreau, he says in many applications, structural silicone is replacing the use of spider fittings.

“On many applications we’re using silicone as the main structural connection component instead of a fitting,” he says.

Think it All Through

There are several challenges related to increasing sizes of structural glass that must also be considered. From a production perspective, it’s not just the glass that gets bigger.

“To process this glass we need bigger machines, autoclaves for lamination, tempering furnaces and coating lines,” says Pannwitz. “These are big investments for what’s still a niche market. Fabricators have to make these investment decisions; all of these machines are customized products.”

Speaking of the installation and application, Dunham points to three notable considerations: accommodating story drift movement; the logistics of getting the glass from the fabricator to the jobsite; and codes not applying well to certain glass applications.

Speaking of the amount of movement a glass wall sees, he says this is based on the height of the building.

“As panels get taller the magnitude of the drift that needs to be accommodated increases because the height increases,” he says. “Historically, the approach was to accommodate a bit of drift at every glass panel. With the glass panels getting significantly taller, accommodating large movements per panel has become challenging. Accommodating movement by isolating the walls is fairly simple in flat walls, but in corner conditions and curved glass where you have movement in and out of plane it gets complicated. Generally, for projects that have corner conditions or curved glass we have to design for the warping of glass. With corner conditions there will be some sealant stretch and some warp to accommodate movement between different panels.”

Another consideration is logistics. Dunham says most oversized panels come in from overseas in 40 foot containers.

“If they are longer than that it’s a real challenge and there is substantial cost and complicated logistics involved. For panel widths in excess of 8 feet wide you have to use open-top containers. That adds cost and potentially time, and there’s often limited space on the ships.”

This can also be a concern for the contract glaziers. Dunham says a lot of the glaziers’ concerns relate to the weight of the panel because at these sizes they can no longer set the glass by hand.

“The keys to success in setting the large panels is having the right equipment to lift the glass and a crane designed to lift the entire assembly. These panels are in crates that are much larger than what glaziers typically deal with—up to 10,000 pounds. So even the forklifts that take the box off the truck are required to be larger,” says Dunham.

Moreau agrees, and adds that it’s also important for the glass to be delivered in the right order, so that each piece can be picked up and installed in order.

“A lot of times you have limited space, so you need to have the right sizes positioned the right way and placed in the right order, because you can’t turn the equipment around,” he says. “The delivery also becomes important because you don’t want a 40-foot piece of glass sitting on the jobsite for a week and half. Logistics have to be tighter.”

There are also challenges when it comes to codes and standards.

“A lot of the ASTM standards don’t even reference glass of the sizes we’re building, and when you extrapolate to those sizes, the tolerances aren’t at an acceptable level for the applications,” says Dunham.

Moreau adds that 200 inches in most configurations is the maximum height covered by ASTM E 1300-16 Standard Practice for Determining Load Resistance of Glass in Buildings. However, work is underway within the organization to revise the standard to allow for sizes beyond the current charts. He adds that most of these applications currently are independently engineered.

Attention to Detail

As the size of glass increases, there are quality considerations that must also be addressed. Dunham explains that as glass gets bigger, it’s generally spanning further and that calls for it to be thicker, which can mean concerns with optical distortion. “We’re using multi-lites to span further and that means any distortion in each ply is magnified. So if there are bow or warping imperfections, for example, the opportunities for distortion are magnified. So, there are more opportunities for distortion, and that means we have to require tighter and tighter quality control standards.”

Moreau adds, “The float quality we have is pretty good, but when you start to do structural and you have more than an inch of glass, it’s going to be extra clear glass, so you also want to have the extra clear interlayers.”

And, as glass gets bigger, anisotropy—iridescence—in the glass can also become a concern.

“With structural applications you have to use laminated, heat-treated glass, so that can create a perfect storm because you have more opportunities for anisotropy when you’re combing the interlayers,” says Moreau, noting that the craftsmanship of the fabricators becomes increasingly important as the glass gets bigger.

Until recently, the industry had no standardized means of measuring anisotropy. Moreau chaired the ASTM International task group that recently published ASTM C 1901 Standard Test Method for Measuring Optical Retardation in Flat Architectural Glass. He says work on the standard began about three years ago, after anisotropy was noticed in an application, and no one knew what it was. He says fabricators have now learned to minimize the appearance of anisotropy so that “even with thick laminates we can offer the same clarity and look as others.”

In addition to aesthetics, thermal performance may also need to be addressed. Dunham says with large panels and large facades the thermal performance is critical because the glass application is such a large area of the building.

“That calls for improved thermal performance due to the percentage of building envelope. The goal is typically more transparency so you have a balance between allowing visible light through and blocking solar heat gain,” he says. “So, we see a lot of high-performance, low-E and 1-800-788-5942 | those coatings applied to larger and larger panels. At least half of these projects use jumbo insulating glass (IG); creating an IG isn’t the limiting factor. There are even triple IGs in these projects. The ideal starting point is a good thermal performance model of the building to see what can be achieved.”

Game Changers

Just as so many of Apple’s product innovations changed the world, the same could be said for architecture. From the structural glass staircases in retail stores to using glass as a self-supporting structure. It may seem impossible, but it can be done.

“Glass is not scary thanks to the engineering we have and the experience we have gathered,” says Moreau. “It’s not a century old science, but when you design correctly you have a perfectly sound product. Whether the glass is intact or it’s smashed, a good designer designs for all conditions.”

Ellen Rogers is the editor of USGlass magazine. Follow her on Twitter @USGlass and like USGlass on Facebook to receive updates.

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