CFST Local Buckling

[Valewish]

Hi everyone,
I am new in the forum and I hope you can help with this problem.

I am trying to model a Concrete filled steel tube (CFST) column subjected to axial compressive load.
The model should validate the an experimental test: the "force-shortening" curve is very similar to the experimental but I am not able to have a local buckling failure as happened in the actual test. I used a reference point to simulate the displacement control on top.

I have used CDP model for the concrete and Von-Mises yielding criterion for the steel tube. I chose C3D8R element mesh for the concrete core and S8R shell element for steel. The ends of the columns are both fixed.
I used general contact command for the interaction between concrete and steel in which I choose the steel as master surface. While the normal behaviour governed by "pressure-overclosure" - Hard contact option; I have used a friction coefficient of 0.45 for the tangential behaviour.

I have performed static general, riks, implicit and explicit dynamic analysis (all with geometric imperfections) but I cannot get the local buckling yet.

I am not such an expert in using ABAQUS - Any suggestions?

I really appreciate any help.

 

[Valewish]

I forgot to say that I am using General contact interaction: perhaps I should use "Pair" or "Surface-to-surface" contact.
However, I am not that confident with contact command then I prefered use the easiest one.

I really appreciate any suggestion.

Thanks, Valentino