Composite box section weld requirements? 1

[Lion06]

I have a situation where I am cantilevering a 4' WF outrigger from the web of a WF to pick up some lighting. It is a relatively small load, but the WF will not work with the torsion. I have detailed this beam to have a single plate welded to the top and bottom flanges on the side opposite the outrigger for the entire length of the beam so that I can analyze it as an HSS with a wall thickness equal to the thinnest piece (plate, web, or flange).
This section now works, but I am wondering how to calculate the required stitch welding for this detail. I think that continuous welding at the top and bottom flange will add too much heat and cause problems, but I am not sure how to calc the required weld. The shear flow from strong axis bending is straightforward, but what about the torsional stresses?

 

[kslee1000]

There should be stress in all three directions on the welds - due to shear, bending and torsion produced by the outrigger. I would simplify the analysis by assuming the flanges resist the torsion, the added web plate takes the shear, and the box takes care of the bending, then check the welds required for the combined stresses.

 

[haynewp]

This exact calculation is done in Blodgett's book for a built up box beam, if you are willing to ignore the contribution of the web of your WF shape. I can give you the formulas if you don't have the book.

 

[Lion06]

haynewp-
Are you referencing problem 5 on page 2.10-9? If so, thanks for the letting me know of it. If not, please tell me the formula.
Thanks.

 

[haynewp]

There is that one and also problem 10 on page 2.10-21.

 

[Lion06]

That is an EXCELLENT example and discussion.
Thanks for pointing them out!!!