If your "Mass Source" (Define > Mass Source) is set to include "Element Self Mass" AND "Loads," but you’ve also manually assigned mass, you might be double-counting.
Whether you are checking for modeling errors or prepping data for base shear calculations, here is everything you need to know about the Mass Summary by Story table. 1. How to Access the Mass Summary Table
By comparing the from this table to the Center of Rigidity (CR) (found in a separate table), you can determine the structural eccentricity. High eccentricity leads to significant torsional (twisting) effects during an earthquake. 4. Tips for Accurate Mass Results
