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Re: Timber shear values

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97 NDS allows up to a twofold increase in shear, given there are no shakes or splits.  That increase is based on shear values that account for splitting mid-depth, which is the worst case.  2001 NDS now seems to presume that designers can account for this behavior on their own.  I personally feel that halving the shear value is unnecessarily conservative, but it would be nice to see some statistics on the size and location of shakes and splits to find an appropriate adjustment factor.  I will also try to find dialogue on the increase that is lost on my desk somewhere.

>>> 73527.1356(--nospam--at)compuserve.com 03/26/03 01:05PM >>>
Joe Grill wrote:

. > My boss just came to me with his new copy of the 2001 NDS.  He pointed to
. > DF shear values (190 psi?).  It seems I have heard that the values have
. > increased, but this is the first I have seen it.  Do any of you have some
. > history or a reference for commentary on the subject that we could read.

Buddy Showalter posted a message a while back on this saying that this
reflected changes is ASTM D245 or D2555.  I went to the library to see what
the changes were that permitted doubling of the shear values in lumber.  The
only thing that I could see was a statement similar to, "All horizontal shear
values are established as if a piece were split full length ... " [WWPA 91
Grading Rules] has been removed from the ASTM spec.

Since timbers in this dry climate typically split/check full length, I will
continue to use the 85 psi or 90 psi values for shear included in the 1997
NDS.

I had intended to privately discuss this with Buddy, but have not gotten a
round tuit.

One of these days, when I do get a round tuit, I'm going to become a
procrastinator.

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

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