Autodesk Robot Structural Analysis

[#1]

I have a model which was created by a colleague of mine and i've now taken over. It was giving instability errors, and i could not get rid of them so i went through and deleted all the releases but i was still getting instabilities.

Is there any common reason that this might happen? If not would someone be able to have a look at the model and see if they can find any errors in it that might be causing this? I will upload it somewhere if so.

thanks!

[#2]

Send us model to check

Check also

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Instabiliyty-of-type-3/m-p/3179932/highlight...

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

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Instability-type-3/m-p/3505360/highlight/tru...

[#3]

http://www.yousendit.com/download/TEhVblFONmNlaFIzZU1UQw

thanks!

[#4]

IN short - too many or wrong releases in some (many) nodes.

It will take me some  time to correct.

[#5]

Yes - i thought this might be the case. But when I removed all the releases I was still getting instability errors - is there some further underlying problem?

file with no releases:

https://www.yousendit.com/download/TEhYZm1kbThCMTd2WnRVag

Thanks for looking into it.

[#6]

Should I correct file with releases or not?

[#7]

 I was still getting instability errors - is there some further underlying problem?

merge nodes 796 1402

[#8]

Model corrected http://wtrns.fr/oZNEZn3anfttNz - check diagrams etc.

I have removed some releases, new releases added : PP  and Fixed Pinned no rx ; nodes merged.

[#9]

Hello, thanks for your help so far. However when I open your fixed model and run it – I get a warning that says ‘Matrix is not positive definite’. This suggests that the model is unstable? (see image below)

<error1.PNG>

If I run the analysis with the DSC Algorithm turned on then I am still getting unstable nodes where they should be stable. (see image below)

<error2.PNG>

Is there any reason why this would be happening for me, but the model runs cleanly for you?

Thanks!

[#10]

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PaulGrimes2282 wrote:

Hello, thanks for your help so far. However when I open your fixed model and run it – I get a warning that says ‘Matrix is not positive definite’. This suggests that the model is unstable? (see image below)

Read the warning to the end ... check buckling.

Critical coeffs below 1 for nonlinear selfweight - check "upper branches of trees"