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Re: Timber shear values

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Title: Timber shear values
I had thought that there was probably some explanation, but I just couldn't find it myself.
Joseph R. Grill, PE
----- Original Message -----
From: AWC Info
Sent: Thursday, March 27, 2003 5:45 AM
Subject: Timber shear values

Here's a link to a white paper we published that gives a little more detail on the changes to shear design values for lumber:

The pertinent information is:

"Review of ASTM procedures used to establish allowable shear stresses revealed that shear values were being reduced by two separate factors for effects of splits, checks, and/or shakes. One of these adjustments was made to the base value; the other was an adjustment to design values for grade effects. In 2000, ASTM standard D245 was revised to remove one of these adjustments, which resulted in an increase of nearly two for allowable shear design values; however, grade effect adjustments were eliminated. In the 2001 NDS Supplement, shear design values for sawn lumber are generally 1.95 times higher than values printed in the 1997 edition in response to the change in D245. With this change, shear-related provisions in the NDS were re-evaluated and modified where necessary to provide appropriate designs. Changes include: removal of the shear strength increase factor, C_H, which previously permitted shear design values to be increased..."

Additional changes to notching provisions, etc. are also covered in the paper.

Wrt changes in shear design values for glulam, AITC and APA have information about those changes. Here's a link to a pdf file on the APA website:


Buddy Showalter, P.E.

p.s. roger, I've been meaning to pick up one of those "round tuits" as well. I think they sell those in stores now.

From: Roger Turk <73527.1356(--nospam--at)>
Subject: Timber shear values
To: seaint(--nospam--at)

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

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

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