Convergence error

[pgaire]

Hello everyone,

I am trying to run a time history analysis of the RCC building with shear walls. My modal and gravity analysis run fine, however, I get the following convergence issue when I run time history analysis. Can anyone suggest a way to trackback this error?

(Here, a warning shows an error for element 356, how can I track this element in my model?)

Thank you.

[Clarabella]

You will have to check your model. Are you able to get some results and then you have the problem of convergence?
Try to increase the number of steps and play with the convergence tolerance. You could also try to see if your model works with a pushover analysis and then run the TH.

[pgaire]

Hello Clarabella,

Thank you for your reply.

Yes, I have results for the first 6.27 sec then my model has a convergence issue. I also followed suggestions from the forum and some lecture videos by the STKO team but couldn't solve the problem. (I have attached my displacement output for the first 6.27 sec as reference.)

One doubt about the modeling is the way I'm creating the geometries which are;
i) created beam-column elements
- created a wire
ii) created shellMITC4 element for shear wall;
a) merged common faces for shear wall
b) Selected the faces of the shear wall and assigned the respective frame (beam-column) element
(doing this there exist 2 nodes at the corner of each shell element)
iii) Merged the ii) with i)

I'm not sure about this modeling approach. (I followed the example files and videos to model, I might have misunderstood the concept).

Thank you for your support.

[STKO Team]

The modeling approach seems correct.
If you applied element and physical properties before doing the "merge", make sure the assignment is maintained also after the merge.

Post your model so that we can have a look

[pgaire]

Hello STKO team,

Thank you for your reply.

Yes, the element is assigned to respective properties after merging too.
I have attached the model file.

Thank you for your support.

[STKO Team]

I think you have issues because the compressive fracture energy of concrete is too small.. try to increase a bit the epsCU

[pgaire]

Hello STKO team,

Thank you for the reply.

I tried with higher epsCU, however, that did not change the convergence issue.

Thank you.

[Clarabella]

Dear pgaire,
apologies unfortunately your trial license does not cover model checking. We advise to check the parameters and convergence tolerance. There is also a webinar we provided for convergence issues.
Regards

[pgaire]

Hello Clarabella,

Thank you for the reply.
I have using OpenSees couple of years and wanted to shift to the graphical interface, and I think the STKO team has developed a great tool.

By model checking, do you mean there is some technique within SKTO to check the model, or is that the service provided by the STKO team separately?

Thank you.

[STKO Team]

By model checking, do you mean there is some technique within SKTO to check the model, or is that the service provided by the STKO team separately?

We mean that if you find an issue in the STKO pre-processor / post-processor itself, we can easily answer and solve it, teaching users how to use STKO.

Instead, when you have convergence issues, it is not a problem related to OpenSees or STKO, it's just the nature of non-linear analysis...
We do offer assistance for that because we have good expertise on these topics, but it's out of the standard maintenance.

Anyway, here are some tips:
Your problem is the Force-Beam column that is not able to find compatible deformation.
This typically happens when your section response is too brittle. So check carefully if the fracture energy is computed accurately.
Another hint:
Try to play with other solvers, like the Krylov-Newton or Modified Newton with initial tangent.