How do I properly define boundary conditions for multi-cell object in Matlab using the structuralBC function?

Hello!

I am currently trying to perform a finite element analysis on a wing’s spar rods for my senior design project I am working. I think I have a decent understanding of how to do FEA using the PDE toolbox and have had success at performing FEA on simple single cell structures (like a simple cantilever beam). However, for the project I am working on the wing’s spar rod system is quite complex. To attempt to do FEA on it in Matlab I have greatly reduced its structural make up into 7 different parts which makes for 7 different cells and I believe the issue im having lies with in my knowledge of properly defining the boundary conditions for the separate cells. The part that I am modeling is shown below:

This simplified model has 2 main spar rods, 4 'extendable' spar rods (appear thicker and darker), and plate in the middle so it can be cantilevered and fix the rods in place. However when I attempt to recreate this model in Matlab and run the FE analysis on it, it seems to want to pretty much explode as shown in the von Mises stress picture below, despite everything appearing correctly in the face and cell photos.

In the von Mises stress picture It looks like the two main spar rods have moved into the plate (not physically possible) and one has enlarged in size/exploded(?), and the 4 extendable spar rods are doing whatever they want. The way I currently (think I) have this defined in my code should have all the plate faces fixed and everything else free to move, and additionally I have applied the loads to all 8 of the outer most faces of the spar rods (if you wish to view my code it is attached and well commented. The needed STL file can be retrived here: https://drive.google.com/file/d/1e9j4NdOlct2rA95OijgWT0DOuIto_D4U/view?usp=sharing ). I guess Matlab does not automatically recognize that the parts are rigid and in contact, and I believe this is where my issue is.

So, ultimately my question is: How do I properly define the boundary conditions I need to apply to the structure or does Matlab not support this kind of multi-part structure?

Additionally, I have been using the structuralBC function to define these boundary conditions and on mathworks it shows 4 different types of constraints, namely 'free', 'fixed', 'roller', and 'symmetric'. I'm assuming 'free' and 'fixed' are as straightforward as they sound, however if you have knowledge about what the 'roller' and 'symmetric' constraints mean, please do explain them!

Thank you for your time!