Addition of 1D elements reduces Buckling Factor

[Emi.Cor]

Hello !

I have one question. I'm studying buckling in a composite skin which has a large hole for a system.
I have modeled the skin and a metal piece attached to the skin via fasteners (represented by RBE2).
The metal piece has a grille on it, which I also modeled with 1D elements hoping that it will increase the Buckling Factor, nonetheless its addition reduces the buckling factor (from 1.0418 to 98913) and I can't understand why does this happen.
I leave attached screenshots of the model in CATIA (only the metal piece) and the DFEM (shaded & wireframe).
CATIA :

https://files.engineering.com/getfi...64-42d0-45eb-ab43-6405a9f8618b&file=CATIA.jpg

DFEM :

https://files.engineering.com/getfile.aspx?folder=5781f99b-d5ac-4866-9e0e-d2fb77b3b437&file=DFEM.png

Any ideas/thoughts ?

Thanks in advance !

Sincerely,
EC