Volume 47, Issue 4 - April 2012


New Criteria in Aluminum Code Means Higher Cost for Glazing Contractors

New criteria used for considering the unbraced length of open sections in the Aluminum Association’s Aluminum Design Manual (2010) calls for glazing contractors to be more careful with manufacturer storefront design windload charts, according to industry experts.

“The unbraced length for a vertical mullion is usually considered to be the distance between horizontal mullions,” says Stewart Jeske, president of JEI Structural Engineering in Kansas City. “However, design windload charts put out by many manufacturers of storefront systems are often based on the assumption that the mullion has full lateral buckling support and an unbraced length of zero. How can this be?”

Consequently, contract specifications for storefronts written by architects are now including the requirement for engineering field calculations, Jeske says.

As a result, glazing contractors are facing difficulty getting a manufacturer storefront design to work with engineering calculations. “Before the code and specification changes, a glazing contractor would read the architect’s requirements, go to the manufacturers’ catalogues that show wind load versus span/height, select a manufacturer system from that catalogue, print out the catalogue chart and submit that to the architect, along with testing data and other info,” Jeske says. “This is the component that’s broken right now. Because the updated specs require field calculation from an engineer, now the glazing contractor has to take the system, get the shop drawing and then ask an engineer to substantiate what they show. And often the engineering calculation will show that the mullion spans selected from manufacturer’s catalogues are insufficient due to unbraced length requirements. This leaves the contractor in a bad bind because they’ve already purchased the material.”

The cost in trying to bid a project that has a storefront that needs to be engineered could be 25 to 50 percent higher because of the extra work you have to do to meet the new requirement, says Lee Lemmon, project manager at Jim Plunket Inc., a glazing contractor in Kansas City. “The engineering analysis cost is upfront at the bid time,” he says. “We don’t know what the engineer will say to make the bid work. Then you get the job and the engineer comes back and says that this won’t work. It’s not pre-engineered is the issue. The design team needs to get this looked at before they put the job up for bid. If they want an engineering analysis, they need to get that looked at before, and not just go with manufacturers’ windload charts.”

Charley Judge, project manager/estimator for Brothers Glass and Glazing in O’Fallon, Mo., says the requirement shows up in some jobs, but not others.

“It’s a per-job requirement,” he says. “Right now I’m looking at three small windows, 3 by 5 feet, in a school, and they’re calling for engineering calculations.” He adds, “It’s a little overkill. To me it’s a waste of money on such a little job. I’d understand if it was a curtainwall, 15 feet tall, and that’d make sense. But in this case, it doesn’t make sense.”

Architects are making sure they protect themselves, Judge says. The small school job calls for engineering calculations, but he says he did another curtainwall job around the same time that didn’t call for the calculations. “It’s all over the place. There’s no rhyme or reason for when it shows up. It’s per the architect,” he says. “It’s making a difference to the glass company estimator, because it’s another step I have to add in there, and I have to make sure what I’m bidding will meet calculations. If it doesn’t make calculations I have to add mullions and spend that extra money. I have to make sure that it meets calculations of the next heaviest material to cover what we calculated.”

JEI Structural is working with manufacturers to revise their design charts to account for lateral buckling, as required by code, says Carrie Jeske, director of new project development. “Glazing contractors will appreciate this because they’ll be able to better select the right system for the project that will be able to have calculations verified,” she says. “Forward-looking manufacturers are leading the way in this initiative even though their storefronts may require more horizontals mullions for lateral bracing to effectively span the opening. This way, the architect, the manufacturer and the glazing contractor are on the same page, resulting in a safer installation and a longer lasting product.”

Groups Release Joint Bulletin about Windloads
The American Architectural Manufacturers Association, Window and Door Manufacturers Association, Fenestration Manufacturers Association and Door and Access Systems Manufacturers Association have jointly endorsed a new technical bulletin relating ASCE/SEI 7-10 design wind loads to fenestration product ratings. The bulletin, available free for download, is intended to inform interested users that the 2010 version of ASCE/SEI 7 cannot be intermixed with earlier versions, and that it is not necessary to test exterior fenestration products (i.e. windows, doors and skylights) differently as a result of the updated 2010 version of this technical bulletin. Additionally, the bulletin explains how design loads from the 2010 edition of ASCE/SEI 7, Minimum Design Loads for Buildings and Other Structures, relates to exterior fenestration product ratings and performance grades.

The bulletin does not highlight all of the changes between the 2005 and 2010 versions of ASCE/SEI 7, such as those related to where opening protection in windborne debris regions is required.


—Sahely Mukerji

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