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RE: Tale 6-1 of ASCE 7-05

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Scott,

Beat me to it. Section C6.5.5 of the commentary talks about the importance factor and notes the difference in return periods between the non-hurricane zones (50-year MRI) and hurricane zones (500-year MRI factored down to 50, and incorporating the old coastal multipliers). So the lower importance factors in the hurricane region bridge that "jiggering" and give about the same reliability for both the hurricane and non-hurricane regions.

Gary

Gary J. Ehrlich, PE 
Program Manager, Structural Codes & Standards 
National Association of Home Builders (NAHB) 
1201 15th Street, NW, Washington, DC 20005 
ph: 202-266-8545  or 800-368-5242 x8545 
fax: 202-266-8369 
gehrlich(--nospam--at)nahb.com 

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)umich.edu] 
Sent: Friday, May 30, 2008 5:46 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Tale 6-1 of ASCE 7-05

That and the wind speed maps are kind of "wonky" and "jiggered" to work with
the importance factor and the combination of hurricane zones and
non-hurricane zones.  I am offering this based upon the fact that there are
discussions about going to three different wind speed maps for different
importance factors/levels/occupancy types.

Regards,

Scott
Adrian, MI

-----Original Message-----
From: chris.slater(--nospam--at)gmail.com [mailto:chris.slater(--nospam--at)gmail.com] On Behalf Of
Chris Slater
Sent: Friday, May 30, 2008 2:42 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Tale 6-1 of ASCE 7-05


This is a guess, but hopefully a logical one.

Since wind loads are a function of V squared, and since Category I buildings
are just storage and Ag buildings, it seems likely that they're giving a
break in the Importance factor for those buildings in the higher wind areas
to reduce the overall outcome of the calculation.

The calculated loads will still be higher in the V > 100 mph areas, since
they will be a function of V squared.

Hope that makes sense...

Chris

On Fri, May 30, 2008 at 11:22 AM, Casey K. Hemmatyar <khemmatyar(--nospam--at)gmail.com>
wrote:
>
> Is anyone familiar with the logic behind the coefficients 0.87 and 
> 0.77 in Tale 6-1 (page 77) of ASCE 7-05? The Importance Factor "I" for 
> Hurricane Prone Regions with V>100 mph is 0.77.
> While for Non-Hurricane Prone Regions & Hurricane Prone Regions with V<100
> mph, it is 0.87.
>
> Regards
>
> Casey (Khashayar) Hemmatyar, SE
>

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