Contact Surface in Shell

Hi,

I'm trying to simulate a Square hollow box beam that is connected to an endplate and undergoing torsion. The problem I am having right now is the contact surface between the endplate and the column that it is supposed to be attached to. Since I am only looking at the endplate I made the column into a single rigid shell. I am using shell element because my beam is too thin to be using solid.  I am using a static linear pertubation step for my simulation and as such I'm no sure how to simulate the contact surface. I want to model the contact surface because I want the endplate to be able to warp to the outside and not into the rigid body.

In the image that I have attached I am simulating the beam being pushed into the rigid body, this is just so you may get an idea of what I am trying to do. Note that I have fixed the endplate at the edges to simulate a weld.

My question is how do I model the contact surface so that my endplate will be able to warp outside of the rigid surface and not into the rigid surface.

Another unrelated question is how do I simulate the beam being pushed into the endplate into a certain depth or twisted to a certain angle. As I want to push the beam 100mm into the endplate and twist it to a angle of 90degrees.

Thanks in advance