Park,

The answer to your question may be found in my previous post. I'm afraid you are not aware of the actual structural model you need to consider.
Pipe-rack piping should typically be assimilated with CONTINUOUSLY SUPPORTED BEAM model. Simply supported beam or double anchored beam models are not relevant for such situation. Such simple models are used for fast and conservative assessment of supporting span length.

Go to a Strength of Materials or Mechanics of Materials book and review what means such CONTINUOUSLY SUPPORTED BEAM model. Then, consider a continuously supported beam with 4...6 supporting spans. One terminal support may be considered fixed point. Then consider the uniformly distributed weight load and calculate the deflections of the center-points of the middle span lengths.
You might need Mathcad for such calculations, since the formulas are complex enough.

You'll find the sagging deflections are closed enough to those given by Caesar II, if your computer model is identical (e.g. same dimensions, same span lengths, no valves etc.) with your analytical model.