Adjusted Shear Value - NDS

[jonathanwilkins]

I have to calculate a beam that has been notched on the tension face more than the building code allows. I'm reading the NDS and I think I'm on the right track but would like a little help.

Section 3.4.3 talks about shear design and goes into evaluating notches. They use a term..."adjusted design shear." Is this the maximum allowable shear applied to the beam? All other analysis uses shear stresses, etc. but this formula has no term for any applied load, shear, etc.

I do believe this is (Vr') the max allowable shear in the beam. Thanks.

 

[Cadair]

Yes, Vr' is the maximum allowable design shear. However, even with 3.4.3, you are still limited by the notching requirements of 4.4.3 (or whatever product it being used).

 

[JAE]

Notches can cause stress risers in "bad" spots where the grain in the wood can split open down the length, and upwards, rendering your beam worthless - i.e. collapse.

It all depends on the grain and since grain in wood is highly variable, the NDS limits notches. If your notch is exceeded - I would proceed very carefully.

 

[jonathanwilkins]

Here's what I'm faced with...a contractor is redoing a deck. The deck girders were notched around the piers 2-1/2". Not sure why. Local inspector (correctly) noted that this is too much of a notch and that's where I come in. Running the NDS equation, applied shear is not close to exceeding design shear (1.2k vs 1.9k). I'm inclined to say it's ok based on calcs + the fact that it's been in place for 10-15 years.

I previously misinterpreted the NDS thinking that notches greater than 1/6d should be evaluated using equation. Thanks.