Design Load Tests for Windows

Log Out | Topics | Search Moderators | Register | Edit Profile

Author Message Robin E. Snyder Senior Member Username: robin Post Number: 239 Registered: 08-2004 Posted on Wednesday, February 18, 2009 - 05:12 pm:    Here's something I have never really understood. How do I make the determination of what classification a window should be? For example, HC60, HC80, HC100 or HC120. I had this explained to me years ago, but it obviously didn't get ingrained in my brain very well. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 163 Registered: 01-2008 Posted on Wednesday, February 18, 2009 - 05:46 pm:    Robin, Go to the AAMA web site, but here is the Readers Digest version. WINDOW TYPE CODE There are 21 distinct product types indentified. H, HS, DW, VS, AP, C, VP, HP, SHW, TH, F, DA, BW, HE, GH, J, JA, TA, HGD, DA-HGD, and SGD PERFORMANCE CLASS R = Residential LC = Light Commercial C = Commercial HC = Heavy Commercial AW = Architectural PERFORMANCE GRADE R = 15 psf LC = 25 psf C = 30 psf HC = 40 psf AW = 40 psf WIND SPEED ASSOCIATED WITH EACH CLASSIFICATION R = 78 mph LC = 100 mph C = 110 mph HC = 127 mph AW = 127 mph Size matters What performance do I need: ANSI/AAMA/NWDMA 101/I.S 2 NAFS-02 (a.k.a "101/I.S. 2/NAFS-02") defines four mandatory performance requirements within each Performance Class for a completely fabricated window: - Structural adequacy to withstand wind loads - Resistance to water penetration - Reistance to air leakage - Forced entry resistance Christopher E. Grimm, CSI, CCS, LEEDŽ-AP, MAI, RLA Senior Member Username: tsugaguy Post Number: 179 Registered: 06-2005 Posted on Wednesday, February 18, 2009 - 05:57 pm:    Somewhere I read that AAMA is phasing out one of these classes (is it Architectural, or Heavy Commercial?) Wayne Yancey Senior Member Username: wayne_yancey Post Number: 164 Registered: 01-2008 Posted on Wednesday, February 18, 2009 - 06:31 pm:    Christopher, This may be true but it is still in the new North American harmonized standard AAMA/WDMA/CSA 101/I.S.2/A44-05. Last update I am aware of is March 2007. In this standard, performance class and optional performance grades are idential for HC and AW. Design Pressure starts at 45 PSF topping out at 100 PSF for HC and No Limit for AW. There is more but it gets into to much minutia. Water resistance test pressure (psf) is higher for AW (8 PSF) versus HC (6 PSF). Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 731 Registered: 03-2003 Posted on Wednesday, February 18, 2009 - 07:16 pm:    In AAMA/WDMA/CSA 101/I.S.2/A440-08, the C and HC classes were dropped and CW added. The Performance grade (the number following the class designation) is based on the minimum design pressure (DP) in psf. The minimum DPs (gateway requirements) for each of the clases are unchanged, except that CW has a minimum DP of 30. The new way to designate a window is R-PG15; which means an R-class window with a 15 psf performance grade. Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP RLGA Technical Services www.specsandcodes.com John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1012 Registered: 03-2002 Posted on Thursday, February 19, 2009 - 08:20 am:    I do suggest checking out the AAMA web site. While the full standard needs to be purchased (and every specifier should own this) there is a good amount of free info there. Relating the wind speed to the class is very misleading. AAMA has backed away from relating the class designation from the type of building. You must select the class and grade based upon the wind loads. Class includes a minimum test size and a minimum test pressure, but there's no other correlation between class and wind speed. Wind speeds create different pressures on different parts of the building, and this must be considered. The AAMA Window Selection guide has a methodology to calculate the wind loads, or you can use the "Components and Cladding" portion of ASCE 7. There are also some simple tools on the web that can do this. I found one with a Google search that is an excel spreadsheet. It may be daunting at first, but is not really that hard. Though I'm familiar with the method, I rarely spend more than an hour, usually less, to figure out the loads. You find the wind zone and exposure from the charts and with building height you can calculate the wind loads. The wind load will dictate the minimum performance grade you need. The class selected will depend on the size of the windows, since you want to use a class with a minimum test size at least as big as your windows. Once you have the wind loads for components and cladding, these are usable for all of the exterior wall components. Taking it another step, you can calculate the roof loads, too. Typically, I have found that the performance grade required is less than that of the product we want to use. In that case, I will find my preferred equal products, and use a performance class and grade that allows each of them, but will keep out lesser performing products. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 123 Registered: 10-2007 Posted on Thursday, February 19, 2009 - 09:45 am:    If you need to use ASCE 7 I would suggest that you at least coordinate your interpretations with the structural enginee on the project. Otherwise there is the potential that the framming supporting the windows could be designed for different loads than the window is rated for. Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 732 Registered: 03-2003 Posted on Thursday, February 19, 2009 - 10:15 am:    Mark: The window performance grade should not drive the structural design. A building may only require a performance grade of 35, but the manufacturer only has a performance grade 40 window--there's no need to upgrade the structural design just because the window is rated higher. Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP RLGA Technical Services www.specsandcodes.com Christopher E. Grimm, CSI, CCS, LEEDŽ-AP, MAI, RLA Senior Member Username: tsugaguy Post Number: 180 Registered: 06-2005 Posted on Thursday, February 19, 2009 - 12:26 pm:    Our firm's consulting structural engineers calculate the zone 1 - 5 components and cladding for us and show on structural notes sheet. We use this information when selecting products and setting criteria, and we cross reference to it in our specifications. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 124 Registered: 10-2007 Posted on Thursday, February 19, 2009 - 01:07 pm:    Ronald: I am not concerned if the window is able to resist a higher pressure but I am sure you would not want the window design pressures to be less than the minimums calculated by the structural engineer. The process of determing the wind pressures is not simple. It could be embarassing if the engineer puts basic wind load information on his drawings that conflicts with what the architect puts in his specifications. The emphasis is on coordination. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1013 Registered: 03-2002 Posted on Thursday, February 19, 2009 - 02:48 pm:    Often the structural engineer will indicate wind pressures for components and cladding, but not always. I have noticed that this seems to be a regional practice to some degree. Sometimes I only see the wind speed and exposure indicated--sometimes not even that. To the extent sufficient information is on the structural drawings, no need to duplicate it in the specs, I agree.