Type 3 Instability with Inventor 2012 Frame Analysis

[ajlarson]

Hi Guys,

So I've been looking around the forum for a solution to this problem; but I just can't seem to find one just like mine. I am currently using the Inventor 2012 frame analysis software to analyze a steel frame, but after running the simulation I recieve a type 3 instablility at node number ten. Looking through the Robot analysis forums, I learned that this can be ignored if you run this through the skyline solver and recieve a similar result, but I can't seem to find where the skyline solver is in the attached frame analysis in inventor, or if it even exsists. If it doesn't exist is there another way to verify that the instability is not effecting my calculations? Attached is a picture of the frame with the instablillity.

Thanks in advance for any help on this!

Thank you,

Andrew Larson 

[innovatenate]

Hi Andrew,

There's a list of common error messages for Frame Analysis in the help, below.

http://help.autodesk.com/view/INVNTOR/2015/ENU/?guid=GUID-A85A3B54-75F7-4BF1-9705-773459515E8C

There doesn't appear to be anything integral connected to Node 10. It may just be a really short member since a type 3 instability may be:

"There is a suspiciously high ratio between maximum and minimum values on the diagonal of inverted stiffness matrix

Occurs when there are large differences in section profiles of some elements or an abnormally short element exists."

This seems likely to be a benevolent warning message. Let me know if this helps.

Thanks,