Trends in Structural Glazing and Kinetic Façades
By Jordan Scott
Imagine a truly transparent façade without visible structural elements. Now imagine a façade that can adapt immediately to surrounding environmental conditions. Modern day façades are able to do both. Architects can incorporate structural systems with large expanses of glass yet minimal hardware into their designs. Kinetic façades that are connected with technology to respond to the environment in real time are just another example of building envelope evolution. Trends in laminated structural glass and kinetic façades now allow architects to do more with glass to create unique designs that provide ultimate transparency or thermal comfort.
Structural Glass Advances
As a result of advances in fabrication, laminated glass is being used increasingly as a structural element for high-end entrances or small-scale structures. Not only can glass be used structurally, but it can be used with minimized horizontal joints, minimal fitting connections, narrower fins and larger glass lites.
Richard Kaire, engineering manager for Sentech Architectural Systems of Austin, Texas, says more fabricators are able to process large glass lites, which has driven down the cost thanks to increased supply. Additionally, more glaziers have adapted and are able to accommodate the installation of jumbo glass.
“Structural glass walls of the past were point supported, had fin segments with splices and a lot of visible hardware. Today that would be an undesirable way to construct a structural glass wall,” says Kaire.
He says that current design trends in corporate taller and narrower glass fins that span the entire height of a wall opening, which has been made possible by fabricators expanding the limits of the glass.
“A lot of manufacturers were using a 15-1 ratio for height and width maybe five to ten years ago. Today, several manufacturers have pushed that to a 25-1 ratio,” says Kaire. “A 40-foot tall fin can be manufactured with a 20-inch width. That was unheard of five to ten years ago; it would have been a feat. Single height fins up to 50 feet can now be made by a handful of manufacturers in the world.”
Florian Doebbel, business development manager of façades for Sika, located in Lakewood, N.J., says that glass fins can act as mullions carrying the load of a façade.
“It’s a good example of glass and its bonding connections taking over the structural loads and stability of a façade structure,” he says.
Some structural glazing projects forego fins entirely. Kaire credits fabricators for this as well. He says panel bow tolerances have become tighter, allowing glass lites to span larger distances without compromising vertical joint alignments.
Structural glass systems can be designed to reduce panel deformations without vertical or horizontal elements at the joints. For example, Sentech has used a fully clamped bracket at both the top and bottom of a wall to keep panels from rotating so the project could be designed with a thinner glass façade panel and not require the owner to spend a large amount of money on glass.
“The support system can be hefty but concealed in the finish of the building. We have intricate brackets that clamp the glass but we also need to allow for the building to move around the wall. The panels are so large that we can’t allow them to move with the building. We have to isolate the glass from any movement of the building imposing on it,” says Kaire, adding that a traditional shear wall or diaphragm can provide stiffness so that if the building moves the structure isn’t overloaded and can support itself back down to the ground.
Another advantage of having larger glass lites is that there are fewer joints, which makes replacement easier. If one layer of a laminated glass fin breaks the other layers will stabilize and take over the loads. These redundancies protect the structural façade and, since there are fewer joints, the fin can be replaced without having to remove outside façade panels.
“This gives us flexibility. If the fin were supporting a second row of glass, we would have to remove the panels around it,” says Kaire.
While advances in glass technology and fabrication are allowing for more fully transparent structural façades, they are also facilitating more complex shapes. Doebbel says that some companies are using cold bending to laminate glass, which allows fabricators to form the glass and its interlayers into unique shapes.
The Future of Structural Glass
The combination of large glass panels, minimized or hidden supports and taller and narrower fins have led to structural systems that appear to be made entirely of glass.
“There’s been a progression from point-supported to patch supports to more concealed joint brackets and now up to more fully transparent systems,” says Kaire.
While he expects to see an increase in designs specifying structural glazing for entrances, storefront car dealerships and smaller structures, Kaire does not anticipate that structural glazing will replace traditional curtainwall, which is relatively inexpensive.
The next step in structural glazing is impact-resistance. Sentech is working on a procedure (based on physical energy methods) to predict the breakage of thick laminated assemblies. Kaire says that with the cost of jumbo lites and fins there needs to be more reliable testing with a higher degree of certainty so that engineers aren’t over- or under-designing a system. The test would determine how the glass would deform after impact. Kaire says his company will perform this test soon for Florida building code approval.
Doebbel emphasizes that it’s important for the laminated glass to be tested in combination with the structural sealants and the framing system. Together they act as one structural unit.
“When the glass breaks, the glass will stick together due to the interlayer but the destroyed lite of laminated glass is retained in its frame by the bonding joint,” he says.
Adaptive Façade Trends
Adaptive, or kinetic, façades are able to respond to the environment. Lucas Treder is building physics leader for Permasteelisa North America (NA) Corp., which is headquartered in Windsor, Conn. He describes these façades as being there when needed and unobtrusive when not needed.
Treder says adaptive façades are used to control more than just sunlight. Permasteelisa currently is working on the Uber headquarters project in San Francisco, designed by SHoP Architects. The project includes a steel-framed glazing system featuring motorized bi-fold operable window units to ventilate the building’s semi-conditioned atrium space inside the glazed envelope. The large operable units are computer controlled in conjunction with operable skylights to allow in fresh air and maintain comfortable temperatures.
In addition to the Uber project, Treder says he’s noticing an increase in the specification of adaptive façades.
“There’s certainly a wide variety of ways to put kinetic façades into practice. It gives us a fun challenge,” he says.
Alex Cox, North America marketing communications manager for Permasteelisa NA, adds that new adaptive façades are not just moving parts, but parts controlled in a smart and responsive way to improve comfort and lower energy costs. For example, blinds can be tied to a weather station or the building’s operation system so they change as the sunlight changes throughout the day.
“These parts can be integrated with technology. They’re not just a component on the façade,” says Treder.
Cox adds that more companies are using improved control systems that learn from user habits and allow the building operator to make appropriate adjustments to prevent people from becoming uncomfortable. His teams discuss technology solutions early on with the architects and building owners when an adaptive façade is being considered.
The maintenance aspect of kinetic façades also has improved in recent years. One solution is closed cavity façade systems. Treder says adaptive façades paired with these types of systems don’t need to be cleaned or maintained as often compared to the traditional adaptive façades of the past.
He believes that most projects could benefit from the inclusion of an adaptive façade.
“It’s just a matter of whether there’s time to implement it properly. You can’t rush into it. We have to make sure the systems work together properly and we need time to test it properly as well,” says Treder. “From a purely performance-driven standpoint, there’s no reason why an owner or architect shouldn’t consider an adaptive element … I think there’s a considerable benefit. It allows the architect more expression and possibilities. They don’t have to worry about the strict window-to-wall ratio to control solar heat gain.”
However, Cox emphasizes that it’s important to start these discussions early to best implement a kinetic façade into a building’s design.
Project Spotlight: The International Spy Museum
As people approach the new International Spy Museum building in Washington, D.C., they see a zigzagging glass façade that hangs in front of an exposed structural steel façade like a glass veil. It plays on the idea of the covert actions of the espionage activities and memorabilia displayed inside the museum.
Dirk Schulte, pre-construction executive for Roschmann Steel & Glass Constructions Inc., located in New Haven, Conn., explains that the museum is off of the National Mall in an area featuring brutalist architecture typical of Washington, D.C. The architect, Rogers Stirk Harbour + Partners, wanted to create a stark contrast from the surrounding architecture, instead opting for a post-modern aesthetic that highlights the character of the building’s function. Schulte’s company, along with structural engineer Eckersley O’Callaghan, helped design the façade. Glas Troesch supplied the coated glass that was laminated by BGT.
The pleated glass veil is not only a design feature, but a functional element that is a true part of the building envelope. The structural glass façade incorporates 17-foot high laminated glass suspended from the top of the building. The zigzag shape helps minimize the visual appearance of structural elements such as the filigree steel construction, which provides for the requisite static load carrying capacity. The steel structural element allowed for thinner lites and lower costs. The pleats also stabilize the façade by supporting themselves laterally between each other without vertical mullions. Each connection in the zigzagging façade are structurally bonded, similar to unitized curtainwall with
four-sided structural glazing.
“In this case the glass is bonded to the steel element at the top and bottom and only includes steel members which are connecting glass panels between each other along the vertical. This creates a load transition from one panel to the other when the glass is being impacted by lateral loads such as windloads,” says Schulte.
The zigzagging glass also allows the façade to point both north and south. The south-facing panels include ceramic frit vertical stripes to shade the interior while providing a diffused, almost secret translucency, says Schulte. The north-facing panels are clear and have a low-E coating.
“They provide a completely different view of the museum from the outside,” says Schulte.
Engineering studies and laboratory tests were conducted, verifying that if a laminated glass lite or an entire panel broke the structural system would still be intact and maintain the integrity of the entire envelope.
Jordan Scott is an assistant editor for USGlass magazine. She can be reached at email@example.com.
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