Indetity pairs should be fixed?

hello

I am running a static structural mechanics problem on comsol multiphysics 3.5 . I have a building and i want to see the effect of a seismic load on my structure ..

My problem is that the building is an assembly of masonry walls and wooden floors , so i have to set identity pairs between them .... I want to ask , when we create identity pairs , we should set that these pairs are fixed?