Autodesk Robot Structural Analysis

[#1]

I have an unusal problem which is driving me crazy!  I have a model which when I run my analysis, which happens to be p-delta, it runs once and everything seems to be workiing and the analysis seems to be correct and converging.  I do have an instablity, but when I say yes to proceed with the analysis eveything works fine.  At the end of the analysis it automaticaly restarts for no apparent reason, the instablity is now different from what I had initially and it does not want to converge at all.  I have tried this with combinations and regular non-linear analysis and I get the same result.  I have cables so I can't run a simple static analysis. 

Does anyone have any idea what is happening?  Oh, one last thing, if I edit a memeber after the analysis is done the crazy non-coverged results go away and what appears to be the correct results are displayed, that is, the results from the first set if analysis. 

Thanks in adavnce for your help! 

Anton

[#2]

Could you send the model?

[#3]

Artur

Please see attached.

Anton

[#4]

Two points:

1. The second run of the analysis is caused by geometrical imperfections you defined on some bars. In fact only one run would be enough but due to current internal architecture of Robot it is necessary to first run model without imperfections and then with imperfections. The improvement in this area is on the wish list. Please mind that the displayed results are of course for deformed model.

2. Lack of convergence for the 2nd analysis run. As then the model is deformed the 2nd/3rd order effect are larger which prevents the analysis to converge.

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