If your mass summary looks incorrect (e.g., lower than expected):
Navigate to > Structural Results > Other Definitions > Mass Data > Mass Summary by Story . Key Data in the Table The table typically includes the following columns: Story: The specific floor level.
When it comes to verifying the core dynamics of a building, looking at the macro picture is always more effective than getting lost in micro-data. The table is better because it bridges the gap between complex finite element modeling and practical engineering intuition. It saves time, minimizes errors, provides instant Center of Mass tracking, and streamlines the structural review process.
When applying upward loads (like wind uplift or certain equipment loads), you might encounter "negative mass". ETABS does not allow negative mass in the final assembly; it sets the mass at any joint with a net upward load to zero. This can lead to discrepancies between the "Mass Summary by Story" and "Mass Summary by Group" tables, as the Mass Summary by Story may not account for these negative values. For accurate verification of total mass, the "Mass Summary by Group" is often more reliable in such cases. etabs mass summary by story better
Quickly spot anomalies, such as an unexpectedly heavy mid-rise mechanical floor.
The Center of Mass coordinates; compare these to the Center of Rigidity. How to Improve Your Mass Source Setup
Senior engineers and municipal plan checkers rarely look at individual beam or shell masses. They look at the macro behavior of the building. Presenting a Mass Summary by Story table in your calculation report demonstrates an organized, high-level understanding of the building's weight distribution. It provides a clean audit trail that proves your dynamic model mirrors the actual physical structure. 4. Seamless Troubleshooting of Dynamic Analysis Anomalies If your mass summary looks incorrect (e
: Ideally, for a regular structure, the center of mass should coincide with the center of geometry. Significant deviations may indicate a potential torsion problem.
: It helps identify if Superimposed Dead Loads (SDL) on null areas are failing to transfer to the seismic mass because a diaphragm wasn't assigned. How to Access the Report To get this better view of your structure’s data: Navigate to the Display menu. Select Show Tables . Go to Output > Other Output Items > Mass Summary by Story . Pro-Tip: The "Mass Source" Secret
Save this post for your next model check. ✅ The table is better because it bridges the
: The absolute coordinates of the Center of Mass for that specific story.
If your Mass Summary shows a sudden drop in mass at a residential floor, check if the "Live Load Reduction" was applied in the Mass Source definition. 3. How to Interpret and Utilize the Mass Summary Table
Run the structural model to generate the results.
