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Below left is the default Mass source (MSSRC) after importing a SAP2000 model. This CSiPlant default Mass source ignores the gravity-direction assigned loads included in the SAP2000 model. In the screenshot below right we change the default Mass source to the one imported from SAP2000 (MSSSRC1). As you can see, this Mass source, like the default Mass source in CSiPlant, includes "Element self mass" which is the mass of piping and structural elements based on the sections and material as well as mass from fluid contents and insulation. However, the Mass source from SAP2000 also includes mass from gravity-direction assigned loads for Equipment weight, cable trays and small diameter piping. Heavy equipment such as air cooled heat exchangers can weigh over 150 kips each, and a battery of 4 or more air coolers on top of a pipe rack is not unusual. Mass for all that equipment plus mass from other objects need to be considered in static acceleration and dynamic analysis load cases. 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 frequency even one tiny bit, and that limitation could be a significant problem.
After importing the SAP2000 structural model, go to Define>Load cases to modify the GR weight case to specify the Mass source as the one we just specified which was imported from SAP2000, and also add gravity-direction load patterns imported from SAP2000 which can potentially effect piping vertical displacements. Equipment loads, for example, are assigned to the structure, not piping, but they can nonetheless cause vertical (and lateral) displacements on the support structure which affects piping displacements and therefore can affect code stress calculations and end reactions.
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