Stability of a beam with variable cross-section

[CEst]

Hello!

I should design an industrial hall with moment resisting portals having pinned bases.
For economic reasons the girder is made of prefabricated welded sections of class 3.
Both the column and girder are tapered.
The girder is not only tapered at the zone of the haunch, but after a zone of constant cross-section, it is variable at the apex too, to best suit the internal efforts.
I got in trouble with making the stability checks (I should design it in accordance with Eurocode 3) - I mean resistance to in-plane and out-of plane buckling. The shear buckling checks I've done. That seems easier being a local buckling mode.
Could you help me out with any tips - examples? Have you ever designed such a girder?

Thanks in advance!

 

[JoshPlumSE]

It's based on a different code. But, AISC Design Guide 25 (design of web tapered members) may be a good place for you to start. It is the most comprehensive and modern treatment of these types of members that I have seen.