Section Modulus Reduction Due to Bolt Holes
Section Modulus Reduction Due to Bolt Holes
(OP)
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
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






RE: Section Modulus Reduction Due to Bolt Holes
I would check the section for torsion.
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
could work, depending on the load. it'd be nicer to weld the angle to an angle piece, welding on the long leg, aligned to the load, weld in shear, IMHO
RE: Section Modulus Reduction Due to Bolt Holes
Seeing that your load lines up with your resistance, torsion may not be such an issue. But that connection sounds like a problem.
Could you show a sketch of that connection?
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
Torsion would not be a problem only for the connections, right? The load is applied relatively far from the shear center of the angle (which would be off to the left of the vertical leg in the graphic), which would imply quite a bit of torsion for the actual angle design, no?
RE: Section Modulus Reduction Due to Bolt Holes
You're right, there would be torsion in the angle. But with this support, it seems as though the torsion in the angle would be highest near the support, where the bending would be lowest.
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
If the two hanger attachments align with the line of applied loads, there is no net moment to be carried by the hanger.
The angle itself carries bending moment and torsional moment with maximum value at one or both supports.
BA
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
but take a section thru the angle between the loads. the long (inloaded) leg of the angle is the stiffer loadpath for shear, so this'll be reacting the applied loads, and therefore the torque on the section. the torque in the angle will be highest near the supports.
there's no moment to the rest-of-the-world, but there is twist in the angle ...
RE: Section Modulus Reduction Due to Bolt Holes
miecz,
What is not adding up? If the reaction is R, the torsion at the support is R*e where e is the eccentricity to the shear center of the angle. If the hanger is not connected to the vertical leg, the horizontal leg must be capable of carrying the reaction in localized bending.
BA
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes
The torsion at the end of the angle is NOT zero. It is maximum. If the reaction is offset by 'e' and the loads are offset by 'e', the hanger sees no moment but the angle sees a torsional moment because its shear center is offset by 'e'.
It is no different than a loose lintel in a brick wall. The angle has torsion at each end but if the brick is centered on the support, the supporting brick sees no moment.
BA
RE: Section Modulus Reduction Due to Bolt Holes
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.
RE: Section Modulus Reduction Due to Bolt Holes
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
RE: Section Modulus Reduction Due to Bolt Holes
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.
RE: Section Modulus Reduction Due to Bolt Holes
RE: Section Modulus Reduction Due to Bolt Holes