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• To: "SE Web List (E-mail)" <seaint(--nospam--at)seaint.org>
• From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
• Date: Wed, 16 Apr 2003 23:00:27 -0400 (EDT)

```Andrew,

To my knowledge the 0.6D+W has nothing to do with the 1.5FS for uplift in
the High Wind portion of hte code.  The 0.6 on the dead loads is to
example, you might typically use 7 psf for mechanical (or something else)
but in reality you may only have 2 psf in a significant area.  Bascially,

Thus, as I see it for the high wind area, your overturning moment would
typically due to W with your resisting moment being due to the 0.6W.
Then, your overturning moment divided by the resisting moment would have
to be greater than 1.5.

Thus, for non-high wind areas, you would still have a "FS" of higher than

HTH,

Scott
Ypsilanti, MI

On Wed, 16 Apr 2003, Andrew D. Kester wrote:

> Pretty basic question here:
>
> I am specifically designing a foundation for a pre-fab metal building, but
> it could be uplift design for any foundation.
>
> I have always applied a 1.5 FS to the size of the foundations to resist
> uplift from my net wind loads. So if I get a reaction of 10kip, I supply
> 15kip worth of foundation. I have based this on a section in the Florida
> BC - 1620. But now that I am looking closer that is in a section under High
> Velocity Hurricane Zones, which only applies to Broward and Dade counties.
> However, nowhere else does it mention in the rest of FL if you are to abide
> by this 1.5 FS.
>
> If I then go to  the ASD Factor Section 1609.4, #4:   0.6D+W, which would
> mean for a 10kip uplift, you would need 10k/0.6= 16.67k of foundation.
>
> Now, this is worse then the FS=1.5, since 0.6D equates to 1/0.6W=1.67. Now,
> I do not think the code is implying that they want you to supply both
> factors, just one or the other. So which one is it? I know most of you out
> there are not using the FBC daily, but this is just a common sense factor
> question I think. But why would the High Velocity factor be less then the
> regular ASD factors. Or are they implying they want 0.6D + 1.5W in High
> Velocity Zones, and just 06D + W in the rest of FL?
>
> IBC 1609.1.3- Tells you to use the long used standard of 2/3 of the DL to
> resist the Wind Load, which is the same as FS=1.5.
>
> IBC 1605.3 ASD
> 0.6D+W - same as FBC (codes are essentially the same thing but no seismic or
> snow in FL and slightly different wind)
>
> So is everyone out there taking only 60% of their dead loads to resist the
> wind uplift, or are most people still using 2/3?
>
> I am assuming ASD factors are to be used for stability analysis as well as
> actual member design. Maybe that is where I am getting screwed up.
>
> Anyone care to shed some light on this subject or give their interpretation
> or "what I do"s would be appreciated.
>
> TIA
>
> Andrew
>
>
>
>
> Andrew D. Kester, EI
> Structural Engineer
> Bentley Architects & Engineers
> 665 W. Warren Ave.
> Longwood, FL 32750
> 1-407-331-6116
> andrew(--nospam--at)baeonline.com
> www.baeonline.com
>
>
>
>
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