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RE: NOA Based Tributary Area

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I am not acquainted with NOA.  Did you mean NOAA?
You need to be careful here.  The hurricane people use a sustained wind as opposed to the 3 second gust contained in the ASCE 7.  You will need to convert velocities.  Hurricane wind velocities must be converted to 3 second gust prior to calculating pressures.  There is no good way to convert sustained wind to pressure. 
Be very careful of testing data.  The velocities have to be comparable to the in-situ condition.  The testing protocols should be studied to see if the tests performed are germane to your condition.  And to what was the assembly tested is important.  Ideally one tests assemblies to incipient failure. 
Look at the appendix of the ASCE 7. 

Regards, Harold Sprague


From: RichardC(--nospam--at)
To: seaint(--nospam--at)
Date: Mon, 29 Mar 2010 17:23:18 -0400
Subject: NOA Based Tributary Area

If you have an NOA specified maximum wind pressure determined based on testing performed to an overall system (i.e. roof panels over several spans of purlins) consistently loaded over the overall system, is one to use the tributary of any one component or the tributary area of the entire system, as tested?


Is there any official documents that describe which method is correct?


Richard Calvert, EIT 

Project Engineer


Lindemann Bentzon Bojack

Architects & Engineers

290 Citrus Tower Blvd, Suite 200, Clermont, Fl. 34711

tel: 352.242.0100 ext.141 fax: 352.242.0302

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