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Plywood Shearwall Testing

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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.