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Re: October Structural Engineer " Resisting Lateral Forces Cumulative overturning design"

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Simpson doesn't sell foundations so they probably don't care how you
design them....maybe they give some guidance is their footnotes  ;)

Or the "catch all"...foundation by others.

Seriously though, foundations under factory built shear walls have to
be pretty substantial to resist the over turning and the rather high
hold down loads.

Many designs do not adequately address these issues.   A generic slab
on grade foundation won't cut it.

cheers
Bob

On Nov 6, 2007 1:27 PM, Jeff Smith <jeffsmith7(--nospam--at)comcast.net> wrote:
> And BTW, I could not find any Simpson commentary for a foundation required
> to resist 36,000# and 72K-ft overturning within a 2 foot wide strong wall.
>
>
> -----Original Message-----
> From: Jeff Smith [mailto:jeffsmith7(--nospam--at)comcast.net]
> Sent: Tuesday, November 06, 2007 1:20 PM
> To: seaint(--nospam--at)seaint.org
>
> Subject: RE: October Structural Engineer " Resisting Lateral Forces
> Cumulative overturning design"
>
> Funny...I was just watching this simpson strong tie video:
> http://www.strongtie.com/overturn/index.asp   which is how I have always
> done it.
>
> My October Structural Engineer is in the same place, thanks for bringing
> that to my attention.
>
> Jeff
>
>
>
> -----Original Message-----
> From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)poa02.usace.army.mil]
> Sent: Tuesday, November 06, 2007 12:42 PM
> To: seaint(--nospam--at)seaint.org
> Subject: October Structural Engineer " Resisting Lateral Forces Cumulative
> overturning design"
>
> Last night I finally pulled the October 2007 Structural Engineer magazine
> off the flush tank and read the  " Resisting Lateral Forces Cumulative
> overturning design..."
>
> The author says that wood shear wall overturning forces  should be based on
> the moment arm from the center of the compression chord to the center of the
> anchor rod, fine...  The article says that the only way to get accurate
> overturning forces for a multistory wood shear wall is to calculate the
> overturning moments and draw a free body diagram of the multi-story wall.
>
> The article says that using the unit shear times height method understates
> the uplift for multistory walls and is only for preliminary approximations,
> uh. uh. if you do it right.
>
> The unit shear times height method is derived with a free body diagram and
> summing moments. It assumes forces are distributed to walls proportional to
> their lengths. If you add the tension from the wall above to the tension to
> the wall chord below and use the full floor to floor heights and subtract
> out the tributary resisting loads you get the exact same result. If the
> problem is the moment arm is too long, you would be conservative by either
> designing with the wall lengths as the moment arm length to calculate your
> unit shear or dividing your tension by the ratio of the moment arm length to
> wall panel length. I say to anyone who disagrees with this to draw a free
> body diagram and sum the moments.
>
> I think that this article is going to cause a bunch of needless permitting
> hassles for design engineers.
>
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