Torsional properties of built-up section

[IngeIvan]

Hello,

I just wanted to see if any of you have a good reference for calculating the effective radius of gyration and the torsion properties of a built-up section (Cw, J, rts). The built-up section is composed of two wide flange beams on top of each other, connected with a continuous plate. I have a pretty big unbraced length, so I'm having to calculate LTB in the elastic range. I seem to find that rts has a big effect in decreasing the moment capacity.

Anything will help.

Thanks.

 

[KootK]

Two wide flanges stacked and oriented strong axis, right? For that, just treat it as one big wide flange and ignore the flange material at mid-depth (assuming it's there). It won't contribute enough to be worth calculating. Built up J is easy enough. Just that business where you sum the bt^3/3 of all the individual plates. Could probably call the three plate thing in the middle one plate for these purposes if you're welding everything together.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.