Modeling interaction between steel and concrete

[namitan]

I have a steel I-girder which is subjected to heat and it is resting on concrete floor. I wanted to model in such a way that they are not tied and steel I-girder is simply resting on concrete. I employed hard contact interaction between the surface, however, I ended up with an error that there are unconnected regions found. Tie interaction although resolved the error, i cant use that in my model. Can someone suggest me the appropriate modelling technique?

 

[FEA way]

I guess you are using Abaqus. Contact would be the way to go in such a case but you have to make sure there are no rigid body motions if it's a static analysis. So apply proper BCs and use some artificial stabilization if needed.