Saturday, July 16, 2011

Be Careful With Manufacture Storefront Design Charts

Design wind load charts put out by manufactures are usually only good for estimating overall span deflection of a mullion, and do not typically consider proper methods for stress design.

The 2010 Aluminum Code has new criteria for considering the unbraced length of open sections. The unbraced length for a vertical mullion is usually considered to be the distance between horizontal mullions. However, design wind load charts put out by many manufactures 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?

I believe that the manufacturers are considering lateral bracing from the glass and the mechanical gaskets. However, after review of many industry specs it is clear that mechanical gaskets should not be considered as a means of lateral bracing for open shaped storefront mullions. Therefore, the charts error on the side of being too liberal. When it comes to the calculations, they can’t match up and the mullions usually don’t perform as well as the charts indicate.

Unfortunately, it’s in the interest of the manufactures to keep the charts the same because they are competing against one another for framing systems with the highest performance standards.

Glaziers should keep this in mind when selecting open shaped vertical mullions and stay well under the curve projections that are indicated. If glaziers use the charts, as is, reinforcing structural glazing or heavier mullions will likely be needed.

Automatic Sliding Doors Have Operational Limitations

It’s important for glazing contractors to get information from the automatic sliding door manufacturers, in advance, on operational limitations for their systems. 

Some automatic door manufacturers have stringent criteria on how much the supporting header and jambs can deflect from wind load and how much can be supported vertically on top of the header.

Floor Movement & Glass Railing

For interior glass railing one of the things you need to watch out for is glass railing on stairs that traverse floor levels. If the floors are designed to deflect with live load, care is needed to make sure load doesn’t transfer to the glass railing system.

We saw a project with glass railing that goes between floors and the top portion of the metal handrail continued to the second floor wall framing. There is the possibility that the second floor framing can deflect and if you have a continuous rail that goes between the second floor wall and is attached to the stair, load can be transferred into the glass causing breakage.

It’s more appropriate to break the railing at the floor transition or provide a joint that slides.

Title: Staircase Glass Railing Designs, Glass Railing, Glass Balustrade

Description: JEI offers staircase glass railing designs, glass railing, glass balustrade and glass railing calculations for glazing contractors.