Instability type 3 - arch truss structure

[mathias_peron]

Hi everyone,

It has been few time that I restart my model paying more and more attention when I apply the releases to the structure but I still get a type 3 instability.

I verified the displacement and all seem ok. And if really everything is ok, why the software keep warning me? What should I rectify?

Have a nice day,

Mathias.

[Artur.Kosakowski · Accepted solution]

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[mathias_peron]

Thank you it resolved my problem but I don't understand what happened. Could you explain me what it changed?

Thank you.

[Artur.Kosakowski]

Blocking RX at both ends prevents rotation of bars about their own axes due to releases applied to other bars defined at their end nodes. You may check values of Mx and apply them in only in the locations where you find torsion excessive.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[mathias_peron]

I made the modification for all my releases, is it not correct then?

[Artur.Kosakowski]

You need to judge this by obtained results,. Usually connections are created in such a way that they doesn't allow for rotation along own axes of bars so you should be fine but as I wrote you may just have a look at Mx values. You may also decide on partial releses for Rx at both ends of bars - see:

http://forums.autodesk.com/t5/robot-structural-analysis/instability-pinned-bar-truss-bar/m-p/5810980

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.