Section Modulus Reduction Due to Bolt Holes

[BadgerPE]

Good evening all,
I am checking a contractors sketch of a pipe trapeze made out of a single angle section with unequal legs. The long leg is oriented in the vertical direction and the short leg is oriented in the horizontal direction. 6 unequal pipe loads are hung from the short leg by unequal sized rods. My question is, how would I go about determining the reduction in the section modulus to effectively determine the bending capacity of the angle? I apologize in advance if there is a simple solution to this question, but I have been staring at it for a couple hours and could use a little push in the right direction. Thanks much!

PS Sorry for the crude sketch

 

[miecz]

BAretired

I hadn't read your 15:44 posting before I posted at 15:49. I don't see how the angle can have a torsion near the connection if the connection plate has no moment about the axis of the angle. Seems like the force in the weld would have to be uniform. I'm gonna have to think about this.

 

[BAretired]

miecz,

Thinking about it is good. If the beam had been an HSS instead of an angle, there would be no moment in the hanger and no torsional moment in the beam. The only reason we have a torsional moment in the beam is because it is not a symmetric section.

BA

 

[miecz]

BAretired

We've cross posted again. I agree that it's no different than a loose lintel in a brick wall. I still don't see where the torsion comes from if there's none at the support. I'll just have to sleep on this.

 

[BadgerPE]

Ended up going with a HSS tube to eliminate torsion. Thanks for all the input guys. You helped me realize that I really need to brush up on my mechanics of materials!

 

[BadgerPE]

One other question though. The rods that support the individual pipes for this hanger will go through both flanges of the section and then be fastened down with a washer and nut. Are the two failure modes (base metal only) yielding and rupture using the area of the washer that will be in contact with the HSS section? Or does block shear need to be checked as well? If so, what dimensions are used for Agv and Anv? Thanks much!