FEM MESH HAS NO VOLUME ELEMENTS

Hi cti2019,
I had a look at your model. Running a 3D-FEM analysis is
an overkill of work and not necessary. It is much easier to use
a frame program for such a problem
http://members.ziggo.nl/wolsink/
https://www.ftool.com.br/Ftool/

Your load case uses only vertical loading near by the knots of the structure.
The (static relevant) bending-moment in the beams is nearly zero, the load directly
runs into the columns. The complete structure will tilt, you must use anchors
at the floor (or more selfweight).

You can divide the 3D-structure into several 2D-subproblems (the yellow frame
for instance). Critical loading is horizontal / diagonal.
regards Thomas
tilt.JPG
2D_frame.JPG

or the good old fashioned way “by hand”…
https://structx.com/frames.html

The problem is that the structure always yields in the 3 points indicated in green.
And I do not know if increasing the thickness of the tubular I can solve the problem.
tilt.JPG

ah, ok.
But that means, that only a part of the whole structure is of interest.
Is there horizontal loading at the plate (especially perpendicular to plate)?
Before meshing: eliminate the bolts and some holes…
Use mesh refinement at the cracking zones.
remaining_problem.JPG
refinement.JPG

how can I do?

I unrefined your model, maybe this helps…
prova1_part.FCStd (38 KB)
mesh-refinement:
mesh body
click on mesh in tree, select mesh refinement,
then select the lines you want to refine.
FEM_part.JPG