Etabs Mass - Summary By Story

Double-click on to open the data grid.

: Some versions provide the total mass from the top down to the current story, useful for checking base shear calculations manually. Importance in Seismic Analysis

Incorrect mass source is a leading cause of erroneous dynamic results.

: The rotational mass calculated about the center of mass, used for dynamic and seismic analysis. etabs mass summary by story

: Some reports might include statistical measures or code compliance checks based on the mass distribution.

). Discrepancies here will lead to incorrect base shear values and unsafe lateral design. 3. Torsional Sensitivity Analysis RZcap R cap Z

Scan down the U3 column. Mass should change gradually. A massive jump at one story (e.g., a 200% increase from Story 2 to Story 3) usually indicates a modeling error—such as a duplicate floor slab, an overly thick concrete mat, or an accidental 10 kPa load. Double-click on to open the data grid

Discrepancies in the story mass often reveal modeling errors, such as duplicated elements, forgotten area loads, or incorrect unit assignments. Conclusion

Ensure the calculated center of mass aligns with the architectural layout to accurately capture torsional effects. 2. How ETABS Calculates Mass

Base shear depends directly on the structure's total seismic weight ( : The rotational mass calculated about the center

Pick a typical intermediate floor in your building and estimate its weight manually:

For rigid diaphragm assignments, the Mass Summary by Story is also the source for center of mass (CM) and center of rigidity (CR) calculations. These are not directly shown in the summary table, but the underlying story mass data is required. For semi-rigid diaphragms, the FAQ recommends modeling with rigid diaphragms first to obtain CM/CR, then converting to semi-rigid for final analysis.