Box section under Torsion and bending. 2

[EngDuck]

I am having an issue finding a good guide or explanation of how to to apply design calculations to my loading conditions. Most guides/ standards etc describe methods for open section beams.(I beams etc) but i want to use square box section as it is renowned for standing up to torque and twist. I need to justify my selection.

I'm fine with simple bending calcs and torsion calcs( well i don't remember torsion being an issue at university anyway) but i've never designed for both.
Here is a basic sketch of my application:

Can anyone help with how to approach this?

The closest thing i can see in literature is to assume an eccentric load to the bottom section of the beam to twist. Obviously as an equivelent load to cause the same moment caused by the load on the verticle beam.

 

[rb1957]

it's easy enough ... torsion on a closed section (google that if you've time) prodcues shear stresses = T/(2*[A]*t) where [A] is the area enclosed by the mid-plane, something like (b-t)*(d-t). and add shear stress to normal stress (from bending) to determine principal stress.

Quando Omni Flunkus Moritati

 

[fegenbush]

I recommend reading H3.2 of AISC 360-10. It is a free download from AISC if you do not have a copy of the Steel Construction Manual.

Equation (H3-6) specifically deals with the combined effects of axial, flexural, shear, and torsion effects.

 

[EngDuck]

Thanks for the Tips guys. No doubt i'll be back on after trying this all out.