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RE: 3X Plates and Washers on Intermediate Anchors

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Bill:

This brings up another question on the intent of the 3x foundation sill plate and plate washer code requirements.  It is my understanding that these provisions were developed for shear walls connected directly to the foundation. It seems like joists sitting on top of a foundation sill plate every 12", 19.2", 16", 24" would prevent the behavior of the foundation sill plates splitting.  I think there should be an exception in the code for plate washers and 3x sill plates not being required when the sill plate in question has platform framed joists bearing on it.
 
In Alaska it is common on residential construction to platform frame on top of a foundation sill plate.  You would typically see if plate washers were missing in the crawlspace and  I think omitting the plate washers might not pass the inspection when they try to sell the building.
 
Respectfully,
 
Scott.
 


From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
Sent: Thursday, March 02, 2006 8:02 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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