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Re: 3x Member w/Anchorage Forces in Sub-Diaphragm

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You want to use 3x's in the wall anchorage system.  Wherever you anchor,
that is where you want a 3x.  That may mean every other subpurlin in the
first bay, or first two bays, whichever members you chose to include in
the anchorage system.

The use of a 2x6 does not achieve what the code is after.  You want your
connection to remain ductile.  In order to achieve this, you want
"slender" bolts that maintain a minimum (length/diameter) ratio.  In a
typical situation where you have a 3x subpurlin and a 5/8" stud bolt,
your (l/d) is 4.  Use this (l/d) ratio as a minimum throughout your

Jeff Coronado, S.E.
West Covina, CA

Kevin Kaplan wrote:
> If anyone can shed some light to the following code exerpt, it would be
> appreciated.  Our office has been "discussing" this item for quite some time
> now.
> UBC Section 1633.2.8.1 Out-of-plane wall anchorage to flexible diaphragms.
> Item 5 reads as follows:
> 5.  The strength design forces for wood elements of the wall anchorage
> system shall be 0.85 times the force otherwise required by this section and
> these wood elements shall have a minimum actual net thickness of 2-1/2".
> Our office has been discussing whether this 3x requirement for the wall
> anchorage system, requires all of the sub-purlins in the sub-diaphragm to be
> 3x's, or just the first bay where the anchorage actually occurs.
> Furthermore, in cases where a Simpson Tension Tie is anchored below the roof
> to the side of the sub-purlin, could the thickness of the member be
> considered to be the actual depth of the sub-purlin (5-1/2" for a 2x6
> sub-purlin)?  This seems to make sense if the code is trying to limit the
> potential of splitting of the sub-purlin.
> Any thoughts?
> Kevin M. Kaplan, P.E.
> Associate / Project Manager
> VLMK Consulting Engineers
> 3933 SW Kelly Avenue
> Portland, Oregon 97201-4393
> Phone (503) 222 - 4453
> Fax (503) 248 - 9263
> Mobile (503) 799 - 0814