Volume 44, Issue 7 - July 2009
“Acing” the Test
by Megan Headley
Having been a hard-hit target for hurricanes in the past, one might think architects in South Florida would stay away from the brittle appearance of glass in their high-rises. A glance at Miami’s glittering skyline shows that’s hardly the case.
“The construction industry has learned from the recent experiences with these major hurricanes,” says Mic Patterson, director of strategic development of Enclos Corp., in Eagan, Minn. “Katrina and Wilma, in particular, were a real lesson to the building community about what we’ve got to do to construct buildings that are safe in these extreme loading conditions.”
Architectural firm Nichols Brosch Wurst Wolfe & Associates Inc. in Coral Gables, Fla., embraced glass as the cladding of the expansive curtainwall of 1450 Brickell Ave., a Class-A office building in downtown Miami, but kept security in mind. The 35-story building features approximately 586,000 square feet of glass across its façade. Viracon fabricated the 9⁄16-inch-thick laminated glass, which is comprised of a ¼-inch lite of Pittsburgh-based PPG Industries’ Caribia® spectrally selective tinted glass and a lite of ¼-inch clear glass with Viracon’s VE-42 low-E coating sandwiched around St. Louis-based Saflex’s Vanceva Storm™ interlayer.
Test One, Test Two
“The wind resistance testing [for this project] was severe but it is the new norm,” says Richard Sembello, vice president of Construction Research Laboratory Inc. (CRL) in Miami. “The severe testing … is required for all new similar scope projects in Miami.”
The requirements are tough enough, but some designers choose to go above and beyond for added protection.
“This developer made the decision to do hurricane-resistant glass all the way up the entire building when that’s not required by code,” Patterson says.
“The entire skin of the building uses a large-missile [laminated] glass,” adds Jeff Rigot, sales representative for Owatonna, Minn.-based Viracon.
To ensure that protection is properly in place, rigorous testing is required. Suppliers, fabricators and installers took part in watching the abuse put upon a full-scale mock-up at CRL’s facilities.
The reason for such testing is simple. “Custom wall systems include hundreds of components put together for the first time,” Sembello says. “Only testing an entire system can identify problems.”
“You have standard testing on any job,” Rigot says.
CRL followed test procedures set by AAMA E-330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference to test the building.
“It’s a very rigorous test to simulate a hurricane coming
and going through this environment,” Rigot says.
Patterson explains, “Design load, as determined by wind tunnel testing, is +139/-183 pounds per square foot (psf), making the testing load -274.5 psf, which is 1.5 times the design load.” In other words, he says, “The building [was tested to] wind speeds up to 327 miles per hour (mph).”
As a basis for comparison, peak sustained wind speed for Hurricane Wilma reached 175 mph, Hurricane Andrew reached 165 mph and Hurricane Katrina reached 125 mph.
The Windy City
Rigot adds, “It presented a lot of challenges not only in the design of the curtainwall, the engineering of the curtainwall, the selection of the glass, but also through the testing process getting a lab to hit those kinds of pressures was quite difficult.”
Sembello breaks the wind test down: “Testing of a curtainwall consists of installing a sample of the wall system, in the same manner as intended for the project, in front of a test chamber. The perimeter of the sample is then sealed to the test chamber and air is exhausted from or blown into the test chamber to produce the desired inward or outward acting windload on the sample. Deflections and deformations of the specimen are measured and observed during the windloads.”
“We certainly had some curtainwall failures along the way,” Rigot says.
But, as Patterson says, “Things never go as expected in a mock-up test.” After all, that’s the point—to find those things one wouldn’t expect before completing a project and subjecting it to the tests of Mother Nature.
“There’s a lot of complexity in a custom curtainwall system,” Patterson says. “There’s the strength of the system itself, there’s the interaction of the system with the building and the anchorage systems that tie the two things together—the building and the curtainwall system.” He adds, “We did modify certain aspects of the design and system as a result of what we saw going on with the test.”
“There haven’t been a lot of curtainwall systems used on projects in this particular area of South Florida. Most of them have been window wall systems,” Patterson says. “So the project was probably subject to a little bit more scrutiny than what’s usual, by both us and by the people who review these things.”
And yet, Patterson adds, “I do believe this project is important, as it clearly points to the future of curtainwall clad buildings in the Miami area.”
“Most buildings in the last decade or decade and a half for impact have been primarily been window wall,” Rigot says. “Indeed the curtainwall design of this project created a lot of challenges to overcome because this job was a true complete curtainwall skin.”
Still, Patterson says the system itself really isn’t that different from more typical curtainwall projects. “What makes it different is the higher windloads,” he says. “In terms of an engineering problem we just needed to strengthen the system with larger members, in some cases reinforced members.”
To The Code And Beyond
“There’s always code minimum,” Rigot says. “What made this unique is this is a building that’s for the open spec of the lease market … Typically they would build the bare minimum—[owners usually are] more concerned about cheap costs and construction per se, and meeting code would be their overall objective.”
Simbello adds, “The Florida Building Code structural and impact requirements are very severe. I doubt many developers would go beyond code unless there is very little cost.”
Still, some do.
The Brickell Ave. building wears its strong glass cladding as a value-added feature.
“[The owner’s] selling this building as being something in which you could potentially ride out a Hurricane Andrew and continue working. That’s the thought anyway: ‘if you want to remain in business in the financial district in Miami, if you’re connected globally you can’t afford to be down for a week while we reclad the building and turn your power back on,’” Rigot says.
The desire to go beyond minimum building codes is more evident in today’s green trend.
“I think we’re seeing a lot of this kind of thing not just in the area of security but also in the area of energy performance,” Patterson points out. “A lot of the buildings that we’re doing are pursuing some level of LEED certification, for example. That’s not anything that is required by code; it’s something that building developers are choosing to do that makes the building more marketable and more comfortable.”
Not surprising for a building going beyond requirement, 1450 Brickell is also aiming for LEED certification.
With the emphasis designers put on exceeding code in the area of energy, one can only hope they double that effort when it comes to safety.
Onsite at 1450 Brickell
Keymark Corp., which has a facility in Lakeland, Fla., supplied 900,000 pounds of extruded, Duranar-coated aluminum for the curtainwall.
According to Brent Slaton, national sales coordinator of Keymark, “It’s one of the largest buildings in Miami.” Slaton adds, “It was a monumental project for us. It’s been going now for a year and a half, and we just completed it (in June).”
The designers had specified larger than typical floor-to-floor spans in the first 15 stories, to augment those breathtaking views of the city and its waterways. Each unit spans 18 feet, rather than the more typical 13-foot 6-inch spans found on the higher floors. To strengthen those 18-foot spans, Enclos used steel reinforcing in the aluminum mullions of those unitized units.
“Beyond that, the strength is manifest in … shorter spacing between fasteners, and those kinds of fundamental things,” says Mic Patterson, director of strategic development for Enclos Corp., headquartered in Eagan, Minn.
Enclos worked closely with Halfen Anchoring Systems in Converse, Texas, and the curtainwall design team in fashioning the proper anchors for securing the glass. All Halfen embeds were provided by Meadow-Burke/Halfen, and steel embeds were provided by C&R Metals in Miami.
Victor Yakin, national sales manager of Halfen Anchoring, says three different high-capacity corner anchors were used to secure the glass. “These designs, based on two 1-foot long channels, were welded together to form unusual corner angles—125, 109 and 90 degrees—with rebar tails welded to the backside of the channels. Embeds such as these offer the highest possible load capacity when installed in thin floor slabs.”
According to Yakin, Halfen reviewed the suitability of such anchors and T-bolts.
“In addition to the high tension and shear capacity that these anchors offer, the adjustability feature of cast-in channels typically allows the glazing contractor to install the curtainwall in a quick and efficient manner,” Yakin explains. He adds, “Not having to weld or drill at the face of the slab in these corner conditions gives the contractor a safe environment in which to work.”
In addition, “About 50 percent of the system here is structurally glazed, so you’re relying on the silicone to keep the glass attached to the system,” Patterson adds. He points out that the structural sealant was provided by Dow Corning, adding, “In a more conventional system (with more conventional loading conditions) you might have a ¾-inch bite of the silicone material joining the glass to the framing system … In this case the bite was 2 ½ inches.”
The use of unitized lites, fabricated and assembled by PGT Industries in Venice, Fla., also helped ease logistics on the project.
“You’ve got a dense urban site, which is always challenging,” Patterson says.
Using unitized panels helped the glaziers to better navigate the constrained site.
“Almost everything we do now is unitized for that very reason,” Patterson says. “It tremendously simplifies the site logistics. If it’s required we can deliver units to the site on a just-in-time basis so there’s basically no material storage onsite; they get lifted right off the truck and placed right on the building. It can really minimize the impact on the building site in instances where that’s required.”
Patterson notes that working closely with the building team and the general contractor to coordinate site logistics also eases the process for the installers.
Enclos started setting curtainwall units in October of 2008. The company now is ready to sign off on this job, with the building braced for anything nature can throw at it following its full completion this fall.
Megan Headley is the editor of USGlass.