Showing posts with label storefront. Show all posts
Showing posts with label storefront. Show all posts

Tuesday, November 19, 2013

Codes Changes Creating a Cladding Mess

If you’re a glazing contractor or a building envelop contractor; an estimator or project manager, you’ve probably tried to size your storefront and curtain wall members off of a wind design pressure.  

The wind design criteria are usually given on the contract structural drawings.   Sometimes design wind pressures for components and cladding are given as well.  However, the changes with the 2012 IBC have created much confusion regarding the actual design pressures to be used.

Many times the components and cladding pressures listed on the structural drawings are given in terms of “Ultimate strength design”, which is not used in any of the wind load charts given by manufactures.   Using these pressures will ultimately lead to overly conservative design.

Designers need to be able to calculate the allowable strength design loads from the information given off of the structural drawings.

If you have a question about what is on a structural drawing, give us a call.   

Stewart Jeske

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.

Sunday, November 21, 2010

How experience for design calculations saves time and money

Some glazing contractors don’t budget enough for appropriate engineering calculations (structural calcs) on projects. Those who do, understand the value of industry expertise. Some glaziers brag, “I’ve got a guy that does it on the side.” The truth is, a structural engineer with industry experience will save you time and money.

Structural engineers with glazing system experience are familiar with industry manufactures and have worked with their components and framing, so you’ll end up with system components and anchors that will work. An experienced engineer will always look at the boundary joints to make sure that excessive movement will not compromise the joint water barrier. In addition, years of experience usually results in a quick turn around using better software, specifically for aluminum curtain wall and storefront design.

Experts in aluminum code won’t over design your project. Aluminum design is specialized and requires adherence to the complex 2010 Aluminum Design Manual. This 469 page book larger is larger than the steel code! Few engineers ever pick up aluminum design, due to it’s specialization. University curriculums for structural engineers focus on steel, concrete and CMU. Aluminum is never used in the design of building or bridge structures so most structural engineers just don’t come across it in their everyday work. This type of experience is essential if you want your glazed system to work without problems for years to come.

So next time you need design calculations, hire experience. You’ll save money in the end.