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[SEAOC] Re: [SEAOC] Re: [SEAOC] RE: [SEAOC] simpson strength values

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Sandy, 

In response to your question about holdowns being mounted several inches
above the sill plate on the post, eventhough Simpson designs the holdown to
be flush mounted on the sill plate.  The primary reason for this is to help
remove some of the slip potential which could occur if the bolt holes are
oversized in the post.  When the nut is tightened down on the anchor bolt
cast in the the concrete foundation, this pulls the holdown downward which
helps to set the holdown bolts in the post it they happen to be in oversized
holes.  If the holdown is mounted directly to the sill plate in oversized
holes, then the post will slip before the holdown engages.  Also, there is no
way to tell if the post holes are oversized once the holdown is installed and
washer plates are used on the backside of the post unless you observe the
hole size before the holdown is installed. 

I do not see why the holdown deflection would be any greater because the
holdown is raised off of the sill plate instead of being installed bearing
directly on the sill plate .  The bottom plate of the holdown still wants to
bend about the anchor bolt head as you pull up on the holdown assembly.  Does
the holdown bearing on the sill plate help prevent rotation of this bottom
plate underneath the anchor bolt head?

Michael Cochran
Brian L. Cochran Associates
Los Angeles, CA

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