Volume 50, Issue 4 - April 2015

Lean On Me

The New Frontier for Structural Glass

By Megan Headley

A structural glass drum, part of the Apple store in Shanghai, helped redefine the parameters for large-scale, curved, tempered, laminated glass.

Glass as a structural material offers perhaps the ultimate “wow” factor for a designer: visitors might find themselves “walking on air” or marveling at a building seemingly made of nothing more than light. But can this desire to create a sensation push the envelope too far?

As glass gets bigger, and supports minimal, manufacturers are responding with tougher products—but in some cases, they’re also being stretched past the limits of today’s technology.

Fins and point-supported fittings, the typical tools for “invisible” walls, still create amazing structures, and are much more common today than in years past. W&W Glass describes the glass fin as “the original back-up structure first introduced by Pilkington more than 40 years ago. Today, it is still the most widely specified support member in structural glass design.”

But in a presentation at the 2014 GlassCon Global (see page 46 of the August 2014 USGlass), Marcin March, a senior engineer in the New York offices of Eckersley O’Callaghan & Partners, described “the next step in this progression” as “the use of structural glass as a fully integrated structural element: not only self-supporting and stabilizing but also acting as a support for the non-glass structures, bringing glass alongside steel, concrete, timber and masonry as a viable building material.”

Is glass as a supporting material really the future for designers?
Apple stores around the world, such as this one in Santa Monica, Calif., are recognized for their innovative use of structural glass designs.

A Structural Case In Point

March’s example was his firm’s recent work on the flagship Apple Store in Stanford, Calif., which used glass columns to support a steel roof in a significant seismic zone. However, he’s quick to point out that in this landmark cube, glass does not technically stabilize anything, “it merely supports the roof dead weight while articulating freely in a seismic event.”

The same goes for the firm’s other glass structures, such as the Fifth Avenue Cube and Apple Upper West Side in New York, which are self-stabilizing laterally. But the jaw-dropping final appearance is a steel roof held up by virtually nothing at all.

From an engineering standpoint, March says, “It really didn’t strike us as a shocking concept—we had designed glass compression members before, but these were more limited to supporting hanging façade systems.”

The challenge, he says, was meeting the needs of both the façade and the building itself, meaning, “The façade wanted the building as stiff as possible to minimize the movements it would need to accommodate.”

Looking back, he critiques the work in the way that every innovator does—by comparing it to the following project. “Soon after Stanford was complete, we worked on a project in Istanbul that used carbon fiber to create the roof. The amount of seismic movement is directly related to the weight of the roof, so had we done this again, I guess we would have used a much lighter weight material than steel. Good thing we didn’t have to accommodate a green roof,” March adds.

It’s the challenge, and the thrill, of being first. But the problem with being first is that in no time there are imitators.
The 5th Avenue Apple store was first built with 106 glass panels and 250 primary fittings. This was later reduced to 15 panels and 40 fittings.

Experience in the Unknown

Each time the bar is raised in terms of how glass can be used, it inspires other designers to explore fresh new
approaches to the initial challenge.

“These design concepts can be very complex, requiring extensive engineering analysis and process knowledge. They can be challenging as well. However you look at it, there is not a book or a school that you can go to to understand intimately how to design and engineer with glass. While those can be building blocks as a foundation for understanding, you cannot overlook hands-on knowledge and experience,” says Manuel Marinos, president of Innovative Structural Glass Inc., a fabricator based in Three Rivers, Calif.

Marinos pinpoints one significant challenge: while fabricators and glazing contractors tackling these structural applications do benefit from experience, each application pushes the envelope further into new territory. Even so, experienced glass professionals are able to recognize areas of concern in this trend.

“I see design mistakes quite commonly in this area made by design professionals, even the well regarded, who really do not have comprehensive understanding of what they are doing. I find this disturbing due to life safety concerns,” Marinos says. “We have been called in on many occasions to either remediate mistakes made by others or complete forensics on system failures. Unfortunately, there is little to no regulation as to who is qualified to create these glass structures.”

According to Marinos, the evolution of technology is making it possible for anyone to attempt this work, for better or worse. “There are several companies that distribute hardware for creating these types of structures that has made it readily available to the glazing community. This makes it all too easy and tempting for one to attempt to cobble a system together in a competitive bid environment,” he says. “Due to the litigious nature of our society, I personally do not believe that is a wise business model. But at this point, the horse is out of the barn. It likely will take something unfortunate to happen to drive a change.”

Structural glass staircases have seen increasing interest over the past decade.

The Allure of Self-Supporting Glass

Given the challenges, and potential dangers, why self-supporting glass at all?

There’s really only one answer.

“The end-user layperson is intrigued subliminally by glass as a structural material,” says Kevin Nash, sales and marketing for Architectural Glass North America (AGNORA) in Collingwood, Ontario. “At least subconsciously, you may ask yourself ‘how can this floor and these stairs be strong enough to safely support me if they’re transparent? I can see right through them!”’

Nash adds, “To the average person, unlike steel and concrete, glass as a building material is sexy, taken for granted for its transparency but not generally understood for the nature of its strength.”

The “wow factor” was certainly the draw for Bohlin Cywinski Jackson (BCJ) when called upon to design its latest Apple store.

As Karl Backus, the San Francisco-based design principal for BCJ’s work with Apple, explains, “For the initial high-profile Apple Stores, which were the company’s first multi-level retail spaces, we wanted to add a few special features, such as skylights, stairs and bridges to enhance the customer experience. Seeking a greater amount of visual transparency, as well as an expression of advancing technology and aesthetics, led us to research and develop designs using self-supporting structural glass.”

But, for now, achieving that impressive look requires some sacrifice.

“While the primary benefit of glass is visual transparency, it also introduces thermal control challenges,” Backus says.

“For this project [Stanford], the team selected a combination of interlayers, ceramic frits, low-E coatings and tints to provide a static design solution to address the majority of the climatic conditions.” Backus adds, “We hope to explore more ideas of adaptive solar control assemblies to integrate with the continued ambition of transparent building enclosures.”

In many cases, however, the use of structural glass is overlapping today’s trend toward larger glass expanses and revealing the limits in today’s fabrication equipment.

“And the requests are getting bigger and bigger,” Nash says, citing a recently completed project with 23-foot-tall fins. He adds, “Glass fins are getting taller, to promote and support transparent sightlines. Multi-ply laminates with structural interlayers are being laminated extra-long for use as, in effect, ‘glass girders.’”

According to Marinos, one of the greatest challenges with domestic glass production is the limited capability to supply large-span, high-performing, low-E coated glass. “This is especially true as it relates to heavy glass construction,” he says. “Many of the projects that we are working on in this area are requiring that we use offshore product, as the production capability domestically is simply not there.”

“Right now you’re limited basically to having clear glass in these jumbo sizes,” explains Jeff Haber, a managing partner of glazing contractor W&W Glass LLC in Nanuet, N.Y. “Having all the value-added architectural processes in the [larger] sizes available today from the fabricators is the next step.”

The truth is that adding those processes will further increase the already astronomical costs of these impressively sized panels. This only helps the glass industry if there are clients willing to pay.

Backus admits structural glass is likely to remain a niche demand until “the industry expands and becomes more accessible to typical budgets.”

Haber adds, “Eventually the price will come down, the more that it’s done, because eventually the fear of the unknown will go away. Manufacturers will get more used to fabricating it. But,” he predicts, “it’s still going to be reserved for those not of the faint of heart.” Especially when there are already time-tested technologies that can reach impressive new heights in transparency.

“High transparency can be admirably achieved without the gymnastics of structural glass; cable nets and cable mullion facades are a fine example,” says Mic Patterson, director of strategic development for the Advanced Technology Studio – Enclos in Los Angeles. “There are many reasons not to pursue structural glass solutions, primary among them being cost. Few designers can command the budgets required to implement this structure type. Applications are highly custom. Glass doesn’t really want to be used as a structural material, so it has to be highly engineered to accomplish this—all of which adds to the cost. All the way through the building process, from design to installation, the challenges are amplified when utilizing structural glass technology. The exception can be glass fin walls.”
Glass Curtainwall Finds a Fresh Support in Wood

In addition to its evolving role as supporting player, glass is also being paired more frequently with new players. Timber curtainwall, for example, is finding a role in more specifications.

Tiltco, a division of Windoworld Industries Inc. based in Newmarket, Ontario, has been offering a timber curtainwall product for eight years. Sanjay Madha, general manager of Tiltco, notes, “We find that our M50 [wood aluminum] system is mainly used in high-end residential projects.”

Greg Header, president of Solar Innovations Inc. in Pine Grove, Pa., finds that the look is most popular in the Pacific Northwest, the mountain regions and other areas where natural wood finishes are a standard part of the architectural design. The company has offered wood window walls and wood sloped glazing systems for more than 16 years.

As architects become familiar with the product, many are diving in due to the thermal properties the timber framing provides, according to these experts.
Though still a relatively new product, wood curtainwall is starting to grow in interest.
“We find that with more awareness and flexibility to design that architects and owners are really jumping on board with the product. It also provides a very high-thermal performance,” Madha says.

Header adds, “These units offer higher thermal efficiency than many of their aluminum or steel counterparts.”

Madha agrees. “The wood curtainwall out-preforms all other curtainwall on the market. It’s warm to the touch and has the performance of a window but in a large-scale, structural curtainwall.

However, there are still a few factors holding this product back.

Header notes that the systems generally are used in a thermally controlled/moisture-controlled environment. Plus, fire ratings are more difficult to achieve. “Solar Innovations is in the process of testing our next generation of supplied glulam layups for their structural and fire ratings with several different fire-retardant products,” Header says.

A final caution: wood curtainwall does demand installation by an experienced professional, Header says. “Glaziers tend to struggle due to the limited number of wood projects in the field, limiting repetition. Touch-up and service work may also be a challenge to installers who are less skilled in the art. Finally, some glaziers shy away due to the lack of information and familiarity, so they mark up the product to cover costs, which may then result in inflated pricing.”

Wood curtainwall products can be used in the same manner as traditional, aluminum curtainwall products would be used.

A Viable Alternative

For the foreseeable future, structural glass applications are likely to make a splash here and there, but engineers and installers are unlikely to be demanding it at break-neck speed.

“What I see more of in applications are high-transparency glass facades that emphasize the expression of the structural system, often highly refined and elegant tensile or cable structures that support simple point-fixed glass,” Patterson says. “The technology to implement such structures is far more advanced than structural glass, with a robust infrastructure of designers, engineers, fabricators and erectors experienced in its application, thereby bringing down the costs and mitigating the risks associated with highly custom structural glass applications. That said,” he adds, “if the will and the budget are there, structural glass can provide a uniquely phenomenal solution.”

Backus agrees that this use is still uncommon. “We are seeing more examples of self-stabilizing glass assemblies constructed around the world, though it does generally remain a rarity. Only a few engineers and fabricators are thoroughly versed in the tectonics of glass as a structural element, so it may take some time before self-stabilizing glass becomes commonly used,” he says.

“It is something that we will see more of in the future, but the practice will never be nearly as widespread as the interest,” Patterson predicts. “There are only a few reasons to pursue structural glass works, and ultimately perhaps only one: the unique and phenomenal aesthetic impact characteristic of these structures.”

the author

Megan Headley is special projects editor for USGlass magazine.
She can be reached at mheadley@glass.com.

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No reproduction of any type without expressed written permission.