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RE: Shear Walls and 3x Framing (UBC)

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Title: RE: DC PE needed (drawings review)
FWIW, I've been told that the thought process for this provision is to differentiate between standard walls (conventional construction) which are typically nailed at 6" oc and walls that are specifically designed to resist shear, which typically have nail spacing of 4" oc and closer.  Although I don't agree with the way the "trigger" is set, it appears that it is meeting it's supposed goal.
 
For example:
 
15/32" Str. I sheathing 8d nails @ 6" oc = 280 plf
3/8" Str. I sheathing 8d nails @ 4" oc = 360 plf (bumped to 430 if studs @ 16" oc)
 
15/32" Str. I sheathing 10d nails @ 6" oc = 340 plf
15/32" Str. I sheathing 10d nails @ 4" oc = 430 plf
 
Now the question I have is why not just write the code provision to state the intended purpose instead of coming up with what most rational people would think is an arbitrary trigger.  Why not just state that if nails are closer than 6" oc....?  
 
Just my take, and APA had nothing to do with this code language.
Tom
-----------------------------------------------------------------------
Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
7011 S. 19th Street
Tacoma, WA 98466
ph: 253/565-6600
fx: 253/620-7235
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From: Gerard Madden, SE [mailto:gmadden(--nospam--at)maddengine.com]
Sent: Thursday, December 11, 2003 09:54
To: seaint(--nospam--at)seaint.org
Subject: RE: Shear Walls and 3x Framing (UBC)

I shear DEMAND is 350 plf AND LESS = 2x framing

Greater = 3x.

 

This falls under the “Very stupid code” category, like we really know the if the actual shear is going 349 plf or 351 plf…

 

Anyway,HTH

-gm

 

-----Original Message-----
From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
Sent: Thursday, December 11, 2003 8:07 AM
To: seaint(--nospam--at)seaint.org
Subject: Shear Walls and 3x Framing (UBC)

 

According to footnote 3 under UBC Table 23-II-I-1, any shear wall with a capacity greater than 350 PLF in seismic zones 3 & 4 need 3x members at abutting panel edges and foundation sill plates (unless the anchor bolts are designed for half…).

 

According to the table, a shear wall 15/32” CDX w/8d @ 4” has a tabulated capacity of 380 PLF.

 

Question:

 

If I design a structure such that wherever I have a shear wall meeting the above specification the design load is no more than 349 PLF, do I still need 3x members at abutting panel edges and foundation sill plates when my anchor bolts are not designed for half capacity? The concern I have is that, even though I limit the design force in this shear wall to no more than 349 PLF, it still has a capacity of 380 PLF.

 

TIA,

 

T. William (Bill) Allen, S.E. (CA #2607)

V/F (949) 248-8588

San Juan Capistrano, CA

http://members.cox.net/ballense/