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

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I think the idea here is to prevent the 2x sub purlins from turning into 
swiss cheese.  With a double row of nailing from the top at a sheathing 
joint, and holes going through the side for the ties, you may not have too 
much wood left.

Technically, I think you only need the 3x where you have wall anchorage & 
continuity ties through the diaphragm... Hopefully the contractor gets the 
3x's lined up with the anchor locations : )

Howard Silverman, PE
Covert Operations, Inc.
Long Beach, CA
Anchoring and Injection Systems
www.covertoperations.com

In a message dated 6/20/0 1:21:09 PM, kevink(--nospam--at)vlmk.com writes:

<< 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
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