I am attempting to model structural steel elements attached to a piping model in an attempt to get more accurate results (as opposed to rigid restraints or displacements directly on pipe nodes).

The structure in question is attached to a boiler shell in real life. In order to model the thermal growth of the boiler I want to add displacements to the structural model instead of rigid FIXs. I want to do this because another part of the piping is truly fixed and I want to know what resulting restraint forces are.

Is it possible to assign rigid displacements to structural steel nodes instead of FIX?