Torsion on a beam

[Wintio 1]

Hi,

I've got an existing 200 UC goal post (span about 4m) with a T-post sitting on top of it in the middle (in plane). We're looking at hanging another support off the T-post out of plane by about 1m. This is going to put a couple kNm worth of torsion on the 200 UC beam, which can really only take a bit over 1kNm in torsion if I remember correctly.

As I understand it, gussets don't do anything to help torsion, but a plate welded from flange to flange (to make a box section) will greatly increase the strength by making it act as a hollow section. My question is how far does this need to go. I'm told that it only needs to be done for the width of the T-post above it, but this doesn't make a lot of sense, as that torsion is just going to get passed straight to the regular beam at either side. I would have thought you would need to box all the way back to the vertical supports.

Does anyone have any experience with this sort of situation?

Cheers,
Daniel

 

[hokie66]

You are correct. Plating the beam only at the post makes no sense. The torsion has to be resisted at the ends, so the torsional reinforcement has to go to the ends.

 

[Wintio 1]

Excellent. Thanks for your help hokie.

 

[BAretired]

If you are placing a torsional load of 2 kNm at midspan, then the beam would need to resist a torsion of 1 kNm between the applied load and each support.

BA