zero pivot warning Abaqus

[Tinni1]

Hello,

I am conducting the post-buckling analysis of a cold-formed steel C section column that is connected to a small length U section at the top and bottom.

The displacement-controlled loading has been applied at the top through a rigid plate(discrete rigid).

I have applied the fixed boundary condition at the mid-reference point of the rigid plate at the top and bottom.

While running the analysis I am getting zero pivot warning and the analysis is being aborted after a few time steps.

Could you please advise, how I can improve the boundary conditions and what are the other alternatives that I can explore to avoid this zero-pivot warning?

The image of the model is attached as a ready reference.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1659888562/tips/Zero_pivot_warning_ziard0.docx[/url]
Many thanks!

 

[FEA way]

What are the connections between the column, U section and rigid plate ? Do you use tie constraints for these interfaces ? If yes, make sure that they work properly, maybe adjustment is needed.

 

[Tinni1]

Thanks for your response.
The connections I have used are:
1. Tie constraint between the rigid plate and u section.
2. Contact condition between the C section and the tracks: Node to the surface and Normal condition: Hard, tangential condition is frictionless.

What kind of adjustment do you suggest?

The attached picture shows the contact condition that I have applied.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1659890183/tips/Zero_pivot_warning_qhvnmm.docx[/url]

 

[FEA way]

Contact may cause problems like that. Try replacing it with tie constraints, for now, to see if it starts working. Modal analysis should show you disconnected regions if there are any.

 

[Tinni1]

Great thanks!

 

[IceBreakerSours]

If you read up on Gaussian Elimination from a book on finite elements, you will get where "zero pivot" comes from. However, it is not required so don't bother too much about it. The key engineering insight is that something might be "free".

I agree with the previous suggestion - an eigenvalue analysis will reveal if something is free by showing near zero frequency for that entity.

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[Tinni1]

Thanks for your response. I will check this out.