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Re: Hold downs with "Perforated Shear Wall Method" and "Force Transfer Method"

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There is not a minimum for MWFRS on the horizontal plane that I am
aware of.  The Guide to the ASCE 7-02 Wind Provisions also shows the
application of the 10 psf minimum acting only on the vertical
projections.

On Fri, May 23, 2008 at 10:55 AM, Joseph R. Grill <jrgrill(--nospam--at)cableone.net> wrote:
> I'm going to confuse the issue some more.  O.K. in using the net uplift in
> overturning calculations that means the roof uplift forces are loading the
> MWFRS.  ASCE 7-05 (6.1.4.1) uses a 10psf minimum on the vertical plane.
> What about the horizontal plane for uplift?  I don't see a minimum required
> for that. For the uplift can you just use the vertical component of the
> outward forces on the roof from 7-05.  Or is there a minimum that I am not
> seeing?
>
> I guess the reasons for these questions is I have a small box addition. I am
> getting a lot of hold downs using the traditional segmented design. I am
> going to get some real comments from the number of hold downs for this small
> structure.  Therefore, I started looking at the other two methods to cut
> down on the number of hold downs.  But as things go sometimes, there are
> more questions that come up.
>
> Joe
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)umich.edu]
> Sent: Friday, May 23, 2008 7:01 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Hold downs with "Perforated Shear Wall Method" and "Force
> Transfer Method"
>
> I think I understand the intent of what you are saying, but wording does
> bother me.
>
> With wind or seismic in one direction so that the shearwall is not loaded,
> but there is overall uplift on that wall, there would be no possible
> "double-dipping" as the wall would not be subjected to overturning (assuming
> a simple diaphragm, thus no torsional effects).
>
> With the wind or seismic in the other direction, the wall (if a shearwall)
> should be exposed to both overturning and potentially net uplift (due to
> wind uplift or the vertical component of a seismic force...overall, more
> logical to think about it in terms of net wind uplift) AT THE SAME TIME.
> Thus, the same dead load should be resisting both the uplift AND the
> overturning.  In other words, your FBD of the shearwall will have the wind
> overturning force, the net uplift, and the 60% of the dead load that would
> work to resist both...all as loads applied to the shearwall.  I don't
> consider that "double-dipping".  I agree that if, for some reason, you check
> the wall seperately for uplift and for overturning, then the same dead load
> should not be used in both check...but I would think you should be checking
> both uplift and overturning in the same check.
>
> Am I missing something?
>
> Regards,
>
> Scott
> Adrian, MI
>
> -----Original Message-----
> From: Showalter, Buddy [mailto:Buddy_Showalter(--nospam--at)afandpa.org] On Behalf Of AWC
> Info
> Sent: Friday, May 23, 2008 9:47 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Hold downs with "Perforated Shear Wall Method" and "Force
> Transfer Method"
>
>
> One caveat however, the WFCM does not use dead load to offset uplift and use
> the same dead load again to offset overturning (double-dipping). So in the
> WFCM tables, we only show dead load offsetting uplift loads.
>
>
>
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-- 
William

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