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RE: 3X Plates and Washers on Intermediate Anchors

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I know that the allowable values in the code are based on testing. I would think that the clamping force from the nuts with plate washers greatly contribute to the capacity. If there weren’t any nuts, the walls would slide and bang ever so slightly back and force because the holes in mudsill will not be snug and with shrinkage, the holes size will increase over time.

 

-gm

 

-----Original Message-----
From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
Sent: Thursday, March 02, 2006 9:02 AM
To: seaint(--nospam--at)seaint.org
Subject: 3X Plates and Washers on Intermediate Anchors

 

So, as I understand it, the requirements for 3X sill plates for shear walls with Fv > 350 PLF (CBC Table 23-II-I-1, footnote 3) and square plate washers (CBC Section 1806.6.1) on intermediate anchors are a result of observations that, when wood shear walls lift (due to lack of restraint at the hold downs), the sill plate will tend to split. The square washer distributes the load better and the thicker 3X sill plate will provide a better section to resist flexure. O.K., I understand that.

 

Maybe these are two separate issues.

 

What about another solution? What if the nuts (and washers) were left off entirely? It certainly seems to me that would eliminate the requirement for the square plate washers (if none were required in the first place). I’m not sure if this would be a remedy for the 3X sill plates. I understand the requirement for 3X members at abutting panel edges to reduce splitting, but I’m guessing the 3X sill plate requirement is to reduce flexural failure. I’m sure I will be corrected if I’m mistaken.

 

All code references are to the 2001 CBC (sorry).

 

Just a thought. Comments are welcome.

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
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