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Wood Gurus - "Shakes"

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This issue has been resolved in the 2001 National Design Specification®
(NDS®) for Wood Construction with an increase in shear design values (nearly
double) and elimination of the C_H factor. Here's a link to a paper
outlining the justification and related changes:


Buddy Showalter, P.E.


Subject: Wood Gurus - "Shakes"
From: "Dave Adams" <davea(--nospam--at)>
To: <seaint(--nospam--at)>

Hello all,

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.

Dave K. Adams, S.E.
Lane Engineers, Inc.
979 N. Blackstone St.
Tulare, CA 93274
PH: (559) 688-5263
FAX: (559) 688-8893
E-mail: davea(--nospam--at)

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