Tube beam in compression flange width-thickness ratio 1

[aquacata]

I have a tube beam HSS12x6x3/16 under compression. AISC ASD Table B5.1 has the flange width-thickness ratio limitation of b/t < 238/SQRT(Fy). Since it is a beam, I think flange is 6" wide, so 6/(3/16)=32 < 238/SQRT(50) = 33.6. It meets the requirement. However, from the software RAM SS, they think 12" is also the flange, so they did 12/(3/16)=64 > 33.6. I am confused here. I think my tube is a beam, not a column, so 12" is a web, not a flange. Please let me know your opinion on this. Should the 12" be treated as a flange? Thanks a lot!

 

[JAE]

It might depend on the relative magnitude of the compression compared to the shape. Go look at the combined compression + bending formulae in the AISC Spec and you will see somethink like Pu / [&phi;]Pn compared to 0.2 or something like it that determines which of the two equations you use for strength. That would be my limit on whether this is more like a beam or more like a column.

Then call/email RAM or check their help screens for some background. They are pretty good about answering email questions - usually less than 24 hours.