Volume 50, Issue 3 - March 2015
Vertical Limits: Buildings Get Taller, Glass Adjusts to Meet New Demands
In 2014 97 buildings towering 200 meters or taller—many sheathed in glass—were completed. That number, according to the Chicago-based Council on Tall Buildings and Urban Habitat (CTBUH), was a new record, soaring past the 81 completions in 2011. In January the CTBUH released its annual report, the 2014 Tall Building Data Research Report, part of the Tall Buildings in Numbers data analysis series. In it, the group also reported that a total of 11 “supertalls” (buildings of 300 meters or higher) were completed in 2014—the highest annual total on record. Since 2010, 46 supertalls have been completed, representing 54 percent of the supertalls that currently exist (85). Likewise CTBUH reported that the number of 200-meter-plus buildings in existence has hit 935, a 352 percent increase from 2000, when only 266 existed.
As the height of these buildings increase, so do the unique glazing considerations. For example, Alissa Schmidt, technical resources manager for Viracon, says the building design, including the glass, needs to be adjusted to resist the higher loads experienced with a taller building.
“The most common glass adjustment we see is an increased outboard thickness. Rather than a 1-inch insulating unit with a ¼-inch thick outboard, designers utilize a 5⁄16-inch or 3⁄8-inch outboard to minimize center of glass deflection and resist the increased loads,” says Schmidt.
Leigh Anne Mays, northeast region commercial sales manager for Guardian Industries Corp., agrees that the key change is the need for thicker glass to meet wind load requirements, and adds, “Also, the glass would certainly be heat-strengthened, fully tempered or laminated, depending upon wind load requirements or safety regulations,” she says. “The other significant change is how architects think about the visual impact the glass will have on the building. Architects typically want the building to be iconic. The glass is usually the biggest contributor to that distinctive image; so the glass tends to lean toward at least moderately reflective in order to make the building appear more monolithic, uniform, bolder and visible from a distance.”
There are also challenges.
“With tall buildings there tends to be a greater level of scrutiny throughout the glass selection process. This could be due to the high-profile presence these buildings have on a skyline, the cost to construct, or potentially even an owner’s desire to ensure their brand is adequately reflected in their building,” says Schmidt. “The time needed for this increased level of evaluation during the glass selection process can be challenging. It is important for us to adequately staff and train our design and technical teams to provide timely assistance including performance data, product samples, strength calculations, drawing reviews, on-site mock-up viewing and tours.”
“The biggest challenge is the length of time from design to the actual glazing of the glass on the building. While it may seem like the building team has all the time in the world to get the glass exactly as needed, the team often finds it does not have as much time as expected,” she says. “The metal design, technical concerns and testing take months and months to validate and confirm, especially with today’s taller structures. Usually all the issues have to be handled separately—but still coordinated—to assure the construction stays on-schedule. One minor change to the glass make-up or metal, and the whole process may have to be repeated. So it is best to select and confirm the glass and metal as early as possible.”
Carlos Amin with Tecnoglass, which is headquartered in Brazil, adds that complex jobs need more planning. “Glass is becoming a huge part of the design assist process for curtainwall, etc. Additionally, almost every job needs independent testing and also several visual mockups that simulate real job conditions.”
That ties directly into the importance of communication.
“An accurate understanding of when they [customers] need glass will help us schedule production and meet their needs,” says Schmidt. “Even though taller buildings require more glass overall, it isn’t necessarily feasible for our customer to install more glass at any given time than they would for a project that is not as tall. Rather, the glass for tall buildings is provided in multiple shipments stretching over several months, a year or more.”
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