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If the combined model requires analysis of static accelerations (static seismic or transportation loads) or any dynamic analysis load case, users will usually need to modify the default Mass Source in the combined model in order to obtain realistic reactions and stresses. The default mass source for CSiPlant includes piping and frame member selfweight, fluid contents, insulation, inner liner, and cladding if modeled. However, structural analysis models also account for heavy equipment, cable trays, and other objects with significant weight as assigned gravity-direction (-Z) distributed loads and/or gravity-direction concentrated point loads. Those assigned loads need to also be considered in the mass model if the user is going to analyze static accelerations or any dynamic analysis load cases.

The Mass source feature enables users to convert selected gravity-direction assigned loads into mass in all 3 translational directions (X, Y, and Z). With most other pipe stress programs, if you were to assign a 50,000 lb. gravity-direction load to the piping or structure, it would not change the calculated natural frequencies or static seismic loads even one tiny bit, and that limitation can be a significant problem if you want to realistically consider combined pipe/structure interaction.