Combinded Stress Steel Pipe - AISC 13th Ed 1

[RFreund]

A hollow pipe section subject to axial, shear, torsion, and bending in 2 perpendicular directions.
How should the unity check be made in accordance with AISC 13?


I would think it would be Pr/Pc + Mr/Mc + (Tr/Tc + Vr/Vc)^2 where Mr=sqrt(Mx^2+My^2)

However this doesn't seem clear in AISC 13th it actually appears that it should be:
Pr/Pc + Mx/Mc + My/Mc + (Tr/Tc + Vr/Vc)^2
This seems conservative but what do i know?

subscript r = required strength
subscript c = capacity of section

Thanks!

EIT

http://www.HowToEngineer.com

 

[JAE]

I don't think you add axial/moment unities with shear/torsion.

 

[msquared48]

Try SQRT [(P + sum M)^2 + (T + V)^2] <= 1.0 ?????

Sounds like a triaxial stress state to me...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[paddingtongreen]

I'm not familiar with your equation but the moments do not add for a pipe, where one stress is maximum the other is zero. put another way, there is no metal whetre the maximums would occur together.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JStephen]

The moments on perpendicular axes would be resolved into the combined moment. I was thinking one of the codes showed this for pipe.

 

[paddingtongreen]

@JStephen, it was drummed into us at school, logically, you can resolve forces but not moments, you must resolve forces and calculate a new moment, or you can add/subtract the stresses resulting from the moments. This is a must if the moments are caused by horizontal forces at different elevations in different directions. As I said earlier, the maximum stresses due to moments in different directions are not additive because the roundness of the pipe means there is no metal there.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ToadJones]

I would say use equation H1-1 or H3-6 depending on the magnitude of the torsion.

I can kind of see what Pad is getting at but I think ultimately, if you resolve the forces that are causing moments in different directions, you will simply have one moment on the pipe.

 

[RFreund]

I'm really trying to stay within the bounds of AISC 13 unity check (but I wouldn't mind knowing how to 'actually' combine the stress either) and I'm trying to apply H3-6 but I guess the question is what is Mr/Mc or how to apply it? Mr is force resultant or do you need to consider the directions independently?

If you combine the force components into a resultant then solve for the moment isn't that the same as Mr=sqrt(Mx^2+My^2)? Or are am I missing something?



EIT

http://www.HowToEngineer.com

 

[paddingtongreen]

@RFreund, sorry, I didn't mean to screw things up. Your Mr=sqrt(Mx^2+My^2) gives the right answer.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ToadJones]

Pad-
You had me really questioning myself!

 

[paddingtongreen]

Sorry Toad, It is one of those funny cases where an illogical operation is a shortcut to the right answer. I was concerned because I have found several people over the years adding max to max and "failing" a perfectly good pipe. The illogicality of combining moments was drummed into us.

Michael.
Timing has a lot to do with the outcome of a rain dance.