NDS Section 3.4.3
NDS Section 3.4.3
(OP)
How many use the provisions of this section to reduce the design shear stress, similar to the ACI provision for concrete? Just wondering. I have never used it just to be conservative, especially with the allowable shear stresses having been doubled in recent years. Seems like the envelope is being pushed here.
Mike McCann, PE, SE (WA)






RE: NDS Section 3.4.3
Then they doubled the shear value and basically said Cv = 2.0 everywhere. I assume this was due to testing and the fact that shear failures aren't common.
If you have a big point load near the support of a beam, crushing will likely control before shear.
When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.
-R. Buckminster Fuller
RE: NDS Section 3.4.3
I talked to an AFPA(? The little green lumber grading book) guy about the split length multipliers for various split lengths back after the 1994 quake. He said, which I can still hardly believe, was that the horizontal shear of the day for solid sawn, 90psi for DF type if I recall right, assumed split the full length of the board, I dare say a slight bit conservative.
Well of course, same species DF glulam allowed 165 psi shear, almost double, at the same time. Same species.
Now I understand it's where it should be. But observed splits in the field for modern framing in heavy shear may not be OK.
RE: NDS Section 3.4.3
I've also used the provisions for notched-end members but feel less comfortable with that since the effects of poor workmanship could be more problematic in that circumstance, in my opinion.
Also, I would look at everything more carefully now that they've almost tripled the allowable shear stresses.
RE: NDS Section 3.4.3
"Review of ASTM procedures used to establish allowable shear stresses revealed that shear values were being reduced by two separate factors for the 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 245 was revised to remove one of these adjustments which resulted in an increase of nearly 2 for allowable shear design values; however, grade effect adjustments were eliminated.
In the 2001 NDS Supplement, shear design values for sawn lumber are approximately 1.95 times higher than values printed in the 1997 edition due to a change in the basis of the values established in ASTM standards. With this change in basis, shear related provisions in the NDS were re-evaluated and modified where necessary to provide appropriate designs. These changes showed up prominently in Chapter 3."
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: NDS Section 3.4.3
RE: NDS Section 3.4.3
Yea, I remember that factor.
Mike McCann, PE, SE (WA)
RE: NDS Section 3.4.3
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)