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Re: Plywood Shearwall Testing

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Todd,
As you are probably aware, there is another school of thought that that takes strong
exception to your test methodology/conclusions. Rawn Nelson has written an excellent
piece on the subject which is, as yet, unpublished.
The essence of my objections is that it is impossible to duplicate multi-story load
levels with an 8' tall shearwall and your posts were carefully selected to be defect
free.  I don't believe your testing proved much of anything, whereas your post to
the listserver makes it sound like the issue is settled.
With Simpson's recent acquisition of Anchor Tie Down, it's pretty easy to avoid
eccentricity in highly loaded posts.  Given the unsettled technical issues and the
installation problems inherent in big, bolted tie downs, they seem to me to be a
highly imprudent choice.
Chuck Utzman, P.E.

"Todd W. Erickson" wrote:

> Regarding the plywood shear wall testing article in the March 2001 "Structure"
> magazine by Jonh Shipp, Mike Rhodebeck, and myself, it has come to our attention
> that some readers of "Structure" magazine are concerned that there are some
> similarities with this article in the March 2001 edition and another published
> article in the July 2000 edition of
>
>   ------------------------------------------------------------------------
>
> "Structural Engineer".  While this article
> discussed some issues mentioned in the other article, the manuscript submitted
> to "Structure" offered significant additional findings with regards to UBC
> deflections, recommendations for design of hold-downs, and an end-post
> connection detail.  The article as submitted offered sufficiently more
> information than the previously published article.  However, we apologize for
> any concern that anyone may have had over any similarities to past publications.
> In any case, we would like to thank both magizines for publishing our work, and
> getting it out to the profession.
> While the article accurately presents our position on non-linear behavior of
> plywood shear walls, there were a few errors and omissions with our article as
> published.  Please note the following errata:
>
> §    The article erroneously stated that 2x4 and 2x6 end-posts were used.  The
> actual size of the end-posts used in the samples was either 4x4 or 4x6.
> §    The article also stated that a design methodology, which includes
> consideration for eccentricity between the end-post and the hold-down, results
> in end-posts longer than historically specified.  This is a typographical error,
> and should state that consideration for eccentricity between the end-post and
> the hold-down results in end-posts larger than historically specified.
> §    In addition, Table 1 was inadvertently omitted, but can be accessed at the
> USP Lumber Connectors web site at www.uspconnectors.com.  Click the "Technical
> Reports" button.
> §    An important recommendation was omitted in the article.  Based on the
> findings of these tests, hold-down eccentricity may be neglected for the design
> of 4x4 and 4x6 end-posts in tension when the hold-down in installed at the
> inside face of the end-post, and the post is edge-nailed to the plywood
> sheathing.  It is extremely important that the end-post be sized for bearing
> perpendicular to grain of the sill to control seismic displacements and damage.
> §    For more information regarding this testing program, including the raw test
> data, please access the USP Lumber Connectors web site.
>
> In addition, one figure and the supporting verbiage, was not published, which
> was unfortunate.  This figure reflected the wide range of cyclical load testing
> scatter among ALL of the walls tested, which when compared with the
> comparatively tight scatter of Figure 4 for the high strength walls,
> demonstrated the striking tightness of the force-deflection data for walls of a
> given strength and aspect ratio (in a very visual way).  Unfortunately this
> publishing deletion took a lot of the meat out of our conclusions, and was one
> significant finding not published in any prior article.  For those interested,
> the raw test data accessible at the USP Lumber Connectors web site reflects this
> scatter.
>
> Finally, some contractors and engineers have been missing the point of our
> artrticle, at least that is my understanding based on some crazy discusions
> brought to our attention.  These people seem to think that the article is
> suggesting that hold-downs aren't necessary.  This is definately NOT TRUE, and
> how they got that conclusion is beyond me.  To clarify: hold-downs for shear
> walls are essential, a fact demonstrated by simple statics.  The article even
> offers what we believe to be a better design methodology for the design the
> hold-downs, one which compares the very real overstrength (Omega nough) level
> forces observed during testing (2 to 2.5 times larger than the plywood shear
> capacity), to the ultimate capacity of the hold-down.
>
> The most important thing we are suggesting in the article, is that based on the
> test data, consideration of end-post bending due to hold-down eccentricity is
> not necessary for traditional plywood sheathed shearwalls having 4x4 and 4x6
> end-posts and eccentric hold-down devices mounted in the plane of the wall.
> End-posts should be sized for bearing on the sill.  We also feel that the
> non-linear behavior and of plywood shear walls is more sensitive to the wall
> aspect-ratio than to hold-down stiffness - behavior that we believe the testing
> data strongly supports.  Obviously, a stiffer hold-down will control drift
> better, and result in less non-structural damage to finishes than a more
> flexible hold down.
>
> If you design wood shear walls you should read the article and check the USP web
> site for the testing report.
>
> Sincerely,
>
> Todd W. Erickson, S.E.



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