Michael, thank you much for the detailed explanation!

I think case 4 is exactly what I'm trying to model. I fully agree option #3 gives most accurate representation. You say: "The friction between the pipe and support is large enough to cause the structure to bend before the pipe slides". I'm trying to understand what the stiffness represents in K1 vs K2 if the piping isn't sliding. Wouldn't I just want to use regular X/Z with stiffness values (based on the physical properties of my T-pole provided by the structural engineer) in each direction?

The result would look like:

Option 3: +Y without friction, X/Z with stiffness values of the T-pole in both directions provided by my structural engineer.