Prying Action

[ToadJones]

I'm working late and having a brain fart....
I have a simple connection with a beam whose top flange is bolted to the bottom flange of another beam (hanger-type).
Beams are 90 degrees to each other. The bolt gage on the lower beam is 3" and the distance between the bolts in the orthogonal direction is 2". So the bolt pattern is 3"x2".

Is the "p" distance in AISC's prying calc in this situation half of the 2"(or = 1") or could it be considered 2" since it is "the distance tributary to the bolt row". ????
I hope I am not completely embarrassed as I read the answers here
(P.S. dont blame me for the bolt pattern...its existing)

 

[ToadJones]

Connect-
You asked "I don't understand where the bolt grade applies to the prying capacity of the flange."

Isn't the prying check for the bolt itself?
Does not the prying mechanism induce more tensile load to the bolt?

 

[nutte]

Toad, the results are the same because bending on the flange controls, not tension on the bolt.

RB, tc is the plate thickness required to fully develop the bolt tensile strength with no additional prying forces induced. A stronger bolt requires a thicker plate to fully develop the bolt's strength.

 

[nutte]

Toad, the prying check is for both tension on the bolt and bending on the flange.

 

[connectegr]

I would select the bolt for the magnified tension on the bolt, or prying on the bolt. And then determine the minimum flange thickness for the same tensile force.

http://www.FerrellEngineering.com

 

[ToadJones]

Wow.
Pretty asinine on my part.
Apologies to all for wasting your time.

 

[dhengr]

I don’t know the exact machinations that AISC went through to arrive at their methods and formulas for this problem. But, it seems to me that there are two modes of failure here; either flg. plate bending and stresses, or flg. plate deformation which might cause prying, bolt bending plus tension and possibly failure of the bolts or a bolt. I believe AISC assumes the flg. plate moments are the same at the beam web and under the bolt line, one +M and one -M. And, if the flg. plate is stiff enough this bending will control and impart primarily tension to the bolts.

You keep throwing me curve balls and then laughing at me when I miss them. I thought you were talking about a larger difference. I’d call that round-off error too. And flg. plate bending is controlling your design, so bolt strength makes no diff. Your answer will be the same for either .75" dia. bolt.

 

[ToadJones]

I'll admit, in doing new design, I try to take prying out of the mix with geometry and plate thickness.
I dropped the ball here by simply getting tunnel vision on the bolt strength.
Quite pathetic really.
I'd like to blame it on the fact that it is an existing structure evaluation for which I have been asked to make an assumption on bolt strength that lead to my being a fool, but that would be more pathetic.
I usually check flange bending by other methods.

By the way, bolts will be replaced