It is interesting to follow events relevant to this issue. Some time ago
there was commentary presented that a certain holdown manufacturer's posted
allowable values of eccentric holdowns are misleading, if not incorrect,
because they do not take into account the holdown post net section and
combined stresses due to eccentricity. This commentary claimed that
allowables should only be determined from a statics analysis. Coincidently,
a competitor comes out with a patented, tested *concentric* holdown. Since
the original manufacturer of eccentric holdowns can not develop a similar
concentric holdown because of patent infringement, they now establish new
tests of eccentric holdown shearwall *systems* that confirm that the
eccentricity does not develop the stresses predicted from statics. Of course
we know that this phenomenon would never apply to a rigidity evaluation of
wood diaphragms, this should only be determined from established analysis
and empirical formulas. If we are lucky someone will patent wood diaphragm
and shearwall *systems* with various desired flexibilities.
> -----Original Message-----
> From: SEConsultant [mailto:seconsultant(--nospam--at)earthlink.net]
> Sent: Tuesday, February 15, 2000 8:28 PM
> To: seaint(--nospam--at)seaint.org
> Cc: William Nelson; Mike Cochran
> Subject: Holddown Eccentricity
> I received a call from my Simpson Representative this morning. He
> wanted to
> stop by this Thursday to drop off the latest results from the testing that
> Simpson did on the concern of holddown eccentricity and post failure.
> The report draws attention to the issues that the shearwall was not
> considered a "system" when the concerns were voiced. As a "system" the
> plywood sheathed panels performed much better than the post and holddown
> alone. The failure, as was related to me, occurred in the edge nailing of
> the sheathing far earlier than a failure in the wood column.
> This seems to alleviate some of the concerns that the engineering
> had regarding holddown failure (or should I say post failure) due to the
> eccentricity of the anchor to the center of the post.
> Do any of you have any other information? I have not seen the test results
> yet and will make a determination when I have a chance to review the data.
> However, I am interested in hearing from others on this issue.
> Dennis S. Wish, PE
> Structural Engineering Consultant
> (208) 361-5447 E-Fax