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NDS Table 11.3.1A

Yield Limit Equations

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#1 McEngr

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Posted 04 January 2012 - 05:07 PM

If anyone has reviewed the NCEES practice problems, one would find that the yield limit equations are important in the wood design aspects of the exam.

It appears that Yield mode Is, IIIs, and IV double the single shear value, but Im does not. Can someone explain to me why equation 11.3-1 and 11.3-7 are exactly the same but both mentioned? Thanks.

#2 Tam

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Posted 04 January 2012 - 10:16 PM

Eq 11.3-1 is for single shear and Eq 11.3-7 is for double shear. Im is the bearing failure mode in main member......it doesn't matter whether it is single or double shear, you only have one main member. Is is the bearing failure mode in side member (2 side members for double shear connections)....same for III and IV but the failure is due to the formation of plastic hinge in the fastener in main/side members and main&side members, resp.

#3 McEngr

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Posted 04 January 2012 - 10:45 PM

Tam: thanks. That makes sense. I guess I'm not sure why the equation isn't just omitted in double shear. Thanks!


Another question: do you have a judgement "feel" for what failure modes will fail before others will? Also, why couldn't equation J-3 be used in lieu of all of these and pick it from the values tabulated from chapter 11?

It seems that J-3 is much quicker than the method done on the NCEES practice exam problem on the Vertical PM portion. Thoughts?

#4 McEngr

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Posted 05 January 2012 - 12:19 AM

http://www.awc.org/p...mentary2005.pdf

The NDS commentary has helped me understand what to do. I believe the yield limit equations on the exam should be avoided if one can use the J-3 values applied from the NDS tables. If anyone is interested, you can click on the above link and do a search for "J-3". It should take you straight to the commentary discussion.

#5 Tam

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Posted 05 January 2012 - 01:45 AM

I can't tell...... but what I have seen is mode IIIs or IV controls for most of the cases.

In the exam, I would say try to use the tables, it'll save your time. Please make note of the foot notes i.e.the tabulated values are for 10D penetration (I don't have the NDS with me now, please check). If it is less than 10D but greater than the minimum required (6D), you have to take a reduction.




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