Seismic codes (like ASCE 7 or Eurocode 8) calculate the base shear based on the total "Seismic Weight" (

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

If a story shows a mass significantly higher or lower than expected, it’s a red flag. Common culprits include:

Ensure your Dead Load pattern has a self-weight multiplier of 1, so the program automatically includes the weight of beams, columns, and slabs. 5. Exporting for Documentation

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.

. Double-check that your Mass Source definition reflects your local code.

In ETABS, the is one of the most critical outputs for structural engineers. It provides a concise breakdown of how weight is distributed across the height of a building—a factor that directly dictates seismic forces and dynamic behavior.

The center of mass for the entire structure from that story upward. 3. Why This Data Matters A. Seismic Base Shear Verification

Accidental double-modeling of slabs or beams.