Beam instability

[phi.sch]

Hi!

Hopefully someone can help me with this problem that I don't understand.

I have a structure with an roof that looks like the following below where there are HEA 160 pillars and HEA 160 connecting between the pillars with an IPE 220 laying on top of the pillars. The roofing consisting of thin sheetmetal is laying on the IPE beams. The type of sections in the picture below continues for ~20m. The IPE beam is attached to the HEA beams with 4 screws on each pillar as in the picture below.

The IPE beams can be seen in the picture below.

Where the structure standing on the beams are new as can be seen in blue below.

Between the web of the IPE beam where the structure is standing I have added 2 UPE beams.

But when I  try to run the buckling analysis I only get bad results on the stability.

With the following parameters.

a.

But if I change the buckling in Z and add an extra point in 0.4l I get the following results.

Should there be this large difference if I add an extra stabilizing in the Z-buckling on 0.4l? It is very far from where the load is attacking the structure.

Or am I going about this problem wrong since the beam is only attached on the flange?

[Artur.Kosakowski]

Hi @phi.sch

IMHO you should have set (internal) buckling Z restrains at the same locations as the ones for the lateral buckling.

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[phi.sch]

Thank you for the answer but can you please clarify why I should set the internal buckling at the same positions as the lateral buckling? 

Maybe the lateral buckling restraints are wrong too, I'm not sure how to set up the buckling analysis when the beam is only attached at one flange. The upper flange is almost free (only sheetmetal holding it in place) and the web is also free.

[Artur.Kosakowski · Accepted solution]

Hi @phi.sch

I'd say that the columns and perpendicular beams which create a frame system can be treated as restrains against the buckling in the horizontal direction for these two beams. These beans will provide restrains against LTB for the flange they are bolted too as well. 

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