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Hello @mjmiddle

Thank you very much for the detailed information. I have some follow up questions. Below is further information about my case and I finally listed my questions in the end. Thanks in advance for your patience.

I created the geometry in Spaceclaim and imported it for the analysis. You are correct. The surface selection shows "face" instead of "Cylinder". How do I fix this? And is it logical to expect that the results will not differ by large extent after changing this. The screw geometry was just created using "pull" command in space claim. I do not understand why it takes as surface instead of cylinder.

I am doing a static structural analysis. I am trying to model stresses in screws, concrete block and deformation in rectangular pipe as shown in below image.

Geometry:
A concrete block with dimensions 400mm*400mm*150mm is the base. On top of this concrete block, a steel flange of thickness 20mm is placed. A rectangular pipe is placed on top of the steel flange. The steel flange is attached to concrete block using M12 Anchor screws. 20kN force is applied on patch surface of the rectangular pipe. The displacement of a point on the rectangular pipe at distance of 110mm from the steel flange is to be validated against the experiments.

Contacts:
1. Frictional contact between concrete and steel flange
2. Frcitional contact between steel flange and bottom face of screw head
3. No contact between screw shank and steel flange since the hole diameter is atleast 1mm bigger than the shank diameter
4. Below is the image of anchor screw. The length of shank inside the concrete is 80mm. In real time, only the black part is in contact. So the surface of screw shank and the hole in concrete were split and the bottom 10mm was assigned as bonded contact (i.e., a simplified model)

5. Remaining screw shank inside the concrete block (70mm) can be assumed as frictionless contact or frictional contact with small friction coefficient of 0.1.
6. Bonded contact between steel flange and rectangular pipe.

Boundary conditions:
1. Bottom surface and sides of concrete block are fixed support
2. A ramped load of 20kN force is applied in 11 steps on a surface as shown in the picture.

3. Bolt pretension of 5kN on each bolt during first step and stays locked for all further steps

Like you mentioned, I am already using the contact tool. The gap in contact tool show gap between concrete and the steel flange. But I see that this originates from the mesh in the contact region but not directly from the geometry itself. Here is the picture.

I just ignored it proceeded further. The convergence was not reached and the newton raphson residuals showed some problems in the contact regions. So instead of modelling the contact between screw shank and concrete (point number 5 in the contacts list) I suppressed the contact and run the simulation. If I understand correctly, I am just not modelling the contact (assumption in point number 5). All other contact settings that you suggested were left default.

In the Non-linear controls, the minimum reference value was changed to 5E-2 . The solution converged after 2 hours with this message "The time for solution exceeded 1 hour. A High Performance Computing (HPC) license will reduce your solution time. Consider using an HPC license or purchasing an HPC license from your Ansys Representative." The result is achieved and it is within expected range. 1mm in experiment and 0.968mm in simulation. But when I double the load, 40kN instead of 20kN, the displacment at point of interest is also doubled which does not match with the experiments. 12mm in experiment and 2mm in simulation. In experiments, the deformation is in plastic region but in simulation it is still in elastic region.

So my questions are:
1. How do I fix cylindrical face problem in the geometry? And is it logical to expect that the results will not differ by large extent?
2. Is my assumption of completely suppressing the contact between screw shank and concrete is correct?
3. Is there a particular way to model the plastic deformation or what am I missing in modelling this?

If you need, I would be happy to share the archive file of the simulation case. This case was setup in ANSYS student version 23.

Regards,
Saketh