Surface Contact

[Anonymous]

Hello

I have some doubts about the surface contact, mainly in the difference between sliding/no separation and separation/no sliding.

Because when I define sliding/no separation  between the bolts and top plate and column in linear analysis. It failed because it is a singularity in the stiffness matrix. But calculatin by non linear analysis, it solves. 

When I define separation/no sliding, it solves with problems, but the tension results are not correct. The pcitures are below:

For me, the correct contact is sliding/no separation, but it isn't solve the problem.

Can you help me?

Thank you!