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Re: 85mph overhang pressures

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Andrew,
 
        I think wind pressures are calculated by the equation
F = 0.0027*V^2
 
For 85 mph; .0027*85*85 = 19.5 psf.
 
For 90 mph; 0.0027*90*90 = 21.9 psf.
 
21.9/19.5 =1.123 or 12.3%
 
so you/re right.  And the only way I can come to 26% is to push the {squared} key twice.. I apologize for misleading anyone.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
To: seaint
Sent: Thursday, May 01, 2008 11:44 AM
Subject: 85mph overhang pressures

Doug,
 
As someone else said, pressure is a function of V^2.
 
So if my math is correct, the difference between 85mph and 90mph:
 
(90)^2-(85)^2   x 100% = 12%
   (85)^2
 
Now a 12% increase in overhang uplift in my opinion affects nothing. So you end up MAYBE with a slightly larger uplift strap. Great, that is the weakest point of the structure and money well spent. Since straps are less than a buck anyway for the most part. I have seen lots of roof and structural failures that started with the uplift strap.
 
I would use 90mph and rock on.
 
 
Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Ave., Suite 301
Orlando, FL 32803