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No convergence with uplift

7 REPLIES 7
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Message 1 of 8
bjornhgr
1741 Views, 7 Replies

No convergence with uplift

Hi.

 

I'm doing a non-linear analysis on a simple model with static loads from a seismic analysis (separate file) to determine necessary moment in my foundation slab. However, whenever I get negative reactions, that should result in uplift, i get "no convergence of nonlinear problem". Why does this happen?

 

See attached image of a corner of my basement, showing support conditions. There are core walls as well, supported in the same way as the column showed.basement-support.png

7 REPLIES 7
Message 2 of 8
tony.ridley
in reply to: bjornhgr

add the self weight case as a starting case for the non linear load case

 

Untitled.jpg

Message 3 of 8
Artur.Kosakowski
in reply to: bjornhgr

Please check if you defined the uplift in the correct direction (UZ+ or UZ-) as well as make sure that the overturning moment is smaller than the stabilizing one. If both are true then make sure that you marked both matrix updates in the parameters of nonlinear analysis.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski
Message 4 of 8
Rafacascudo
in reply to: bjornhgr

one thing that sometimes helps is on non linear parameters ,mark " matrix update after ech iteration". It will take a longer time to solve but it has more chance to converge


Rafael Medeiros
Robot Structural Analysis

Message 5 of 8
bjornhgr
in reply to: bjornhgr

Thanks a lot, guys! The update matrix options did the trick!:)

Message 6 of 8
jo2ny
in reply to: bjornhgr

Hello,

Similar problem with convergence. (i think)

I have a simple rectangular steel structure, with a lots of load cases.

For most of the cases, the results seem to be accurate, but for one (5 - Equipments) the results are totaly wrong.

 

Can anyone give me some advice, pls ? Why is this happening?

Please find model with results here http://www.filemail.com/d/chfrecyznfzhzdu

 

Thanks

Message 7 of 8
Artur.Kosakowski
in reply to: jo2ny

To get the convergence for case 5 it is enough to change the relative tolerances from 1e-4 to 1e-3. On the other hand as the load increases there is the warning about the critical load which might have been actually exceeded. I think you should investigate this as well as the reason for instabilities (I have ignored them as my focus was on the convergence issue you indicated). Mind that if you want to combine this load with others you may actually be not interested in results obtained for case 5 alone as such situation does not happen in reality.

On more remark: I'm not sure what was your intention but you set that the first load case should be used as the starting case for case 1 - perhaps you should check that too.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski
Message 8 of 8
jo2ny
in reply to: Artur.Kosakowski

Thanks for your response Artur.

 

I will investigate further.

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