Columns and rigid links

[Grohl]

Hi.

I have a steel structure almost like a frame on top of concrete columns. To connect the bottom of two steel columns to my top concrete column I've used rigid links and released (pinned) the bottom of the steel columns. Rigid links are also applied to the walls for interaction between concrete column and wall.

With these boundry conditions I get an instability in node 56 UX direction. This is with DSC on. With it off I do not get the instability issue, but my deflections are displayed kind of weird so I think something is wrong.

Loads are applied in both steel and concrete structures.

The file can be downloaded through the dropbox link:

https://www.dropbox.com/s/yqx12bom93ezk4l/Shaft%20transformer%20substation.rtd

Here's a simplified model where it works like I want and I'm not getting error or weird deflections.

https://www.dropbox.com/s/mxkraex6vy4m17n/Test.rtd

[Rafal.Gaweda]

Check defnition of releases at the bottom of frame legs.

[Grohl]

Frame legs pinned in bottom. I want rotation allowed.

[Rafal.Gaweda]

So everything is correct unless you show me this "weird diagram".

You can not compare results between models with and without releases at legs. They are different because of releases.

[Grohl]

Thanks for reply!

Please look at attachments. Same releases in legs. Much smoother without the whole strucure.

[Rafal.Gaweda]

You are comparing FE maps deformation diagram with Bars deformation diagram.

(Deformation for FEs just displays deformation basing only on displaced nodes)

[Grohl]

Thanks!

But, the issue with node (56) instability type 3 still bothers me. Any thoughts on that? 

And, is the way I've connected the wall with the concrete column with the frame an appropiate way to do it?

Thank you again.

[Rafal.Gaweda · Accepted solution]

Check these

http://docs.autodesk.com/RSA/2012/ENU/filesROBOT/GUID-52C292E1-5C73-4FB1-B4E0-E5E8107777D-615.htm

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/instability-type-3-RX-direction/m-p/3364875/...

In your case message 4 is the explanation.

So you can neglect this instability

To find short elements (if they are in model) you may use this addin http://forums.autodesk.com/t5/Autodesk-Robot-Structural/API-addin-for-short-calculation-elements-det...