Node instability (type 1) issues

[Anonymous]

Hi,

I have generated a geometric model using Robot for a large frame.  Prior to introducing releases and adding loadcases I have run the model (under self weight only) and have found a huge number of node instabilities that I can't seem to fix.  There are also isolated nodes 23 to 28 that don't appear to exist in the model.

Trying to get to the bottom of things, I have deleted most of the model, leaving only the 'head house frame' and there are still al lot of node instabilities even though the simple frame looks OK.  Deflections remain too large, but I can't find where the problem is.

Only when I have deleted all members apart from a 2D 'head house truss' can I get reasonable deflections, albeit with type 1 node instabilities still remaining.

I attach the three models and some screen grabs to try and illustrate my point. If someone could direct me to the cause of these problems I would very much appreciate it.

Thank you and regards,

Mark

[Anonymous]

Head house frame and truss models attached

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

You cannot model your structure (full model.rtd) as a truss model (with no bending moment transfer). It has to be a frame one with applied releases or truss bars if/where required. Use Geometry > Structure type commands and select the 3D Frame model type.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.