Frame buckling

[JPNR87]

Hi,

I've question about frame buckling.

As you see "bridge" connecting braced columns has bracing on one surface "stronger surface" and chords are splitted to members in every node. All members are defined as simple beam.

In steel design modul is buckling length members length. Thats is true if we analyze stronger surface but on weaker surface buckling is not limited (no bracing on upper and lower bridge surface) in nodes. I hope you understand.

How to define those chord members to have adequate result?

Thanks for answers! 

[Artur.Kosakowski]

Hi @JPNR87

If the chord is defined as number of short elements from node to node then define a superbar out of it and assign (different) internal bracings for each of the buckling defections.

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[JPNR87]

I don't understand superbar and this internal bracing part. Please some explanation.

[Artur.Kosakowski]

Hi @JPNR87

Something like this:

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[JPNR87]

Thanks for reply!

I understood, that in case where you need to split the beam in every node and want to make buckling analysis to whole compressed chord (member+member+...) which has not y/z buckling directions fixed in every node (Robot is calculating node to node member as simple beam) then you need to make in addition superbeam where is considered real situation. Right?

But I have a problem. Tried to make superbar from marked members from node 1131to1130 but with no suceess. Robot is not considering members/buckling length reducers on y-direction. Option is to set hem manually. Any help?

[Artur.Kosakowski · Accepted solution]

Hi @JPNR87

I understood, that in case where you need to split the beam in every node and want to make buckling analysis to whole compressed chord (member+member+...) which has not y/z buckling directions fixed in every node (Robot is calculating node to node member as simple beam) then you need to make in addition superbeam where is considered real situation. Right?

No, if you define a chord as a sigle bar there is no need tto divide them into smaller parts and create a superber which in fact is what you originally defined. Just define the local bracings for the (single bar) chord as it is defined.

But I have a problem. Tried to make superbar from marked members from node 1131to1130 but with no suceess. Robot is not considering members/buckling length reducers on y-direction. Option is to set hem manually. Any help?

As you used an angle defined in its principal axes there are no adjoining bars defined in these directions (planes). In such situation  you should manually add the positions of the bracing bearing in mind the direction of the buckling of the angles being in the planes of its local axes rather than vertical and horizontal.

 

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