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RE: Relative Stiffness of Wood Shearwalls

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While I am certainly no expert on ICC ES AC 130 (which is the acceptance
criteria that I believe Hardy and other propiertary shearwall manufacturer
must use to gain their ICC ES evaluation report), I do believe that it
does require the manufacturer to test most (if not all) different
configurations of their prefabbed/propiertary shearwall.  This can include
different support conditions (i.e. on concrete foundation, on wood framed
first floor, on wood framed upper floor, etc) as well panel sizes/aspect
ratios.  And I believe that it means that the values that they have in
their report come from testing (although there might be an analysis
option...but from my experience with ICC ES on AC 04 [for SIPs] they are
not too terrible fond of the analysis options at times).


Adrian, MI

On Wed, 26 May 2004, Keith De Lapp wrote:

> I too spoke to Hardy just yesterday before sending my previous email.  The
> point I was trying to make with you was that you said, something to the
> effect...I don't care what the numbers say, I don't combine different
> systems in the same line...  Or something like that, I believe the intent of
> your thought is clear.  You mentioned that intuition and experience tell you
> not to.  Which is fine.  I believe clarification may be in order though.  We
> each have "our way" (ie some rational) to add either redundancy or ductility
> which we believe improves LFRS performance.
> I thought the comment you made was liken to forget what P over A plus M over
> S tell me, I'm gonna do something different.  Now not exactly, but sort of.
> Considering the world stage this forum is being viewed on, I thought the
> topic warranted further consideration.  To me relative stiffness is
> foundational and I'm sure you agree.  And, I don't take "the numbers" as
> gospel.
> But your remarks sounded a bit, "prescriptive" to put it in building code
> terms.  Which surprised be coming from you.  I referenced the Hardy Frame
> because if testing is only used to verify the allowable shear and drift
> based upon calculations, then I don't see a difference with enveloping the
> performance of a plywood wall and a Hardy Frame based on a relative
> stiffness calculation.  There probably isn't a one of us who hasn't used
> steel to reinforce a tilt-up panel opening retrofit for out-of-plane loads
> using relative stiffness.  The elements don't know how the load gets there,
> they just do what their geometric/material properties demand they do.
> Would you recommend a Hardy Frame "Panel" and "Frame" be used in the same
> line?  Or how about a Hardy Frame installed on concrete and another
> installed on a wood sill plate and another installed on wood framing?  Each
> of the above two cases will vary in relative stiffness (all other things
> being equal), now swap in a plywood shearwall and you have the exact same
> problem.  You have to pay attention to their relative stiffnesses to see how
> the load will be shared throughout the LFRS system.
> The preaching is not meant to be belittling in any way, it's just a style
> thing.
> Keith De Lapp, P.E.
>   -----Original Message-----
>   From: Dennis Wish [mailto:dennis.wish(--nospam--at)]
>   Sent: Wednesday, May 26, 2004 9:09 AM
>   To: seaint(--nospam--at)
>   Subject: RE: Relative Stiffness of Wood Shearwalls
>   Keith,
>   I spoke with Hardy the other day and this is not correct. Their values are
> based on testing and their current ICC reports indicate that the drift
> calculations can be interpolated in a straight line interpolation which is
> considered conservative to their test data. Hardy (Mitek) has been listening
> to this thread and I would recommend that they respond to your comments.
> They asked if it was appropriate for them to participate and I felt it was
> as long as they were not attempting to sell product. I think they are in a
> better position to respond to you than I am, but I do know that they
> recommended an interpolation of in plane drift based on height changes in
> each frame or panel. Also, as I mentioned, when different panels/frames are
> used in the same line of shear, the drift/stiffness should be calculated
> based on relative rigidity.
>   Shearmax also uses an interpolation for non-standard frame heights. I have
> not spoken to Simpson or TJ, so others may respond to this.

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