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Wood Gurus - "Shakes"

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Splits, checks and shakes are nebulous things that are a function of the 
moisture content of the wood when it is graded and the equilibrium moisture 
content of the wood installed.  As such, I always take the Csubh as 1.0.

Here in the desert southwest, equilibrium moisture content for wood is ~ 6 
percent.  Regardless of the grade, it could have as much as 19 percent 
moisture content when it is graded and still be classified as being graded, 
"dry," yet it will have a lot of shrinkage occur before it gets to its 
equilibrium moisture content.

Not too long ago, I was examining some 4Xs (No.1 and SS DF-L) that had 
checks/shakes and was able to slip a business card into the space 1-3/4" 
before it stopped.  The check/shake probably extended further, but not 
completely thru, and the business card was probably stopped by wood fibers 
crossing from one side of the check/shake to the other side.  (This was a 
place where a bracket was going to be bolted and I wanted to demonstrate to 
the worker that there wasn't very much wood left to bolt to.)

Maybe the next revelation by the wood industry will be testing of wood graded 
at 19 percent moisture content and its strength, particularly horizontal 
shear strength, when it dries to 6 percent moisture content.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Dave Adams wrote:

. > NDS shear stress factor Ch is limited by splits, checks and shakes.  I
. > understand what each of these is, but I'm still a bit fuzzy on the shake
. > & how to determine it's effect on lumber.  It is defined in the "Wood
. > Handbook" (Forest Products Society) as a separation of fiber bond,
. > between or through the annual rings, which is presumed to extend
. > lengthwise without limit.

. > The allowable shake size is very small if one wants to take a Ch greater
. > than 1.0.  It seems to me that "Select Structural" should qualify for at
. > least a Ch of 1.33, but the descriptions for grading by WWPA appear to
. > allow for larger shakes, which knocks us back to a Ch of 1.0 (max) ...
. > the obvious answer is that one cannot just automatically use a higher Ch
. > than 1.0, or else it would have already been factored into the values
. > listed in Table 4A.

. > Anyway (ramble, ramble, ramble), if anyone has information regarding
. > grading and shakes (especially as it relates to good quality lumber such
. > as "SS"), I'd greatly appreciate it.

. > TIA,
. > Dave K. Adams, S.E.

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