Wind Load on Windows

[dcarr82775]

I have to provide the architect with C&C wind loads. Vult=145mph. I know IBC has provisions that allow a 'reduction' in wind loads for checking deflections. I doubt it does, but am looking to see if and similar reductions on window design pressures exist.

 

[JAE]

Reductions in deflections, not pressures.

For window wind pressures - use the window area to get an area to use for C&C.

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[Ron]

dcarr82775....unless you are dealing with a storefront or curtain wall system, manufactured windows are products that generally must undergo some level of approval testing. For wind loads, they are generally required to meet the requirements of the American Architectural Manufacturers Association (AAMA) and carry an AAMA rating for wind loading, air infiltration and water leakage. The rating that is given for the window is its working rating....so for example if your C&C pressure is 32 psf, you would need a window rating of 35 or greater. Since the products are tested to 1.5 times the structural rated load, there is no component deflection measured and to my knowledge, no acceptance criteria available for deflection. There is a glazing deflection criterion listed in ASTM E1300 for windows and other glazing. In this standard, the design load is used and deflection of the glass support system is limited to L/175.

 

[Signious]

(Sidebar) Ron, you brought up an interesting point, if windows are rated to 1.5x the capacity they are specified to, do you factor your wind loads as well (ie. 1.4W) when providing to the architect? I'm sure the most prudent engineer would say yes - but playing devils advocate you could say that the window is designed under ASD methodology and factored loads are not required.

 

[dcarr82775]

JAE: Yep that is what I was doing, just hoping windows might have a break somewhere.

Ron: Thanks. I have a couple that are 43psf at the corners. The arch tells me once over 40 is the tipping point for drastic increase in window costs. I was hoping to find an out to get to 40, but 43 it shall be.

 

[XR250]

@Signious:

I imagine service loads are used for window design.

 

[boo1]

FL requires window pressures to be identified on the drawing

 

[boo1]

The window design pressures we use are based on the Low-rise Buildings (mean roof heights less than or equal to 60 ft) provisions of Section 30.4 in ASCE 7-10.

 

[StrEng007]

When applying wind loads to windows, it's important to use the components and cladding pressures derived from ASCE 7. If you're applying wind loads from the low rise provisions, you're most likely using a MWFRS load. These are typically lower in magnitude than the CC loads, so double check that you're using the correct loading.

Windows and other fenestration products are typically tested per ASTM for static, impact and cyclic loading in addition to water and air infiltration tests if required. Typically, a test load is done at 1.5 times the design rating for the product. Skylights are required to be tested to a 2.0 in some jurisdictions. The design rating that is issued on a window will be done in an official document such as Florida Statewide Approval, Miami Dade notice of acceptance, ICC evaluation service report or a Texas Department of Insurance product approval. Most of these documents list the allowable load rating for the system (always check the notes to verify this).

Your loads need to be calculated as ASD loads. If you're using ASCE 7-10, which most of you should be, make sure to use a 0.6W as the calculation of wind load is in terms of LRFD since an "Ultimate wind speed" is used (it's already factored).

Check your local building codes for allowable deflections on glazing support members. Most of you will find a L/175 and some will see L/180 for Miami Dade HVHZ. You're permitted to take your components and cladding wind pressure as .42W for deflections (think 0.6W times 0.7).