Etabs Mass Summary By Story Better May 2026
You start at the bottom. This is your Story 1. You recruit the heaviest, strongest Sumo wrestlers you can find. They are massive.
Instead of relying on ETABS’ automatic story grouping, define Groups (e.g., Group-Roof-Beams, Group-Penthouse-Walls). Then modify the Mass Summary by Group table. This gives you control to exclude non-structural masses that artificially inflate the story summary.
Engineers typically search for a "better" version because they encounter these three specific failures:
| Story | Mass X (kg) | Mass Y (kg) | Total Mass (kg) | Cumulative % | |-------|-------------:|------------:|----------------:|-------------:| | Roof | 12,000 | 11,500 | 23,500 | 5.2% | | 10 | 24,000 | 23,000 | 47,000 | 15.6% | | ... | ... | ... | ... | ... | (Export actual values from ETABS for your project.)
A foolproof way to cross-check your "better" mass summary is to look at the base reactions from a static Load Case that includes the mass source loads with g = 386.4 in/s².
Run a DEAD load case and a MASS load case.
Compare this to the reported mass summary total. They must match within 1%. If not, your mass source is misapplied. etabs mass summary by story better
The default ETABS Mass Summary by Story is a starting point, not a finish line. A better mass summary is one that:
By taking 10 minutes to define a proper mass source, adjust story definitions, and validate with base reactions, you transform a confusing default output into a reliable engineering tool. Your plan checkers—and your building’s safety—will thank you.
Next Step: Open ETABS right now, go to Define > Mass Source, and verify your multipliers. You may be surprised at what you find.
Need a template? Download our free "Better ETABS Mass Summary Excel Checker" (link below)
Have a specific mass summary bug? Describe your model in the comments.
In ETABS, tracking and verifying building mass is a critical step for seismic and dynamic analysis You start at the bottom
. Users frequently encounter two different tables to evaluate this: Mass Summary by Story Diaphragm Mass Summary Mass Summary by Story
table is generally the superior and more reliable choice for extracting the total seismic weight of a structure. Direct Comparison: Story Mass vs. Diaphragm Mass Mass Summary by Story Diaphragm Mass Summary Scope of Mass mass assigned to the story (slabs, beams, columns, walls).
Only captures mass associated with nodes assigned to a specific diaphragm. Best Used For
Total seismic base shear verification & manual weight checks.
Evaluating torsional eccentricities (Center of Mass vs. Center of Rigidity). Handling of Off-Diaphragm Mass Includes it flawlessly. Ignores it, leading to underreported building mass. Sensitivity to Meshing High; requires proper node alignment to lump correctly.
High; unmeshed or improperly assigned shells will be ignored. Why "Mass Summary by Story" is Usually Better Mass Summary by Story Compare this to the reported mass summary total
table provides a much more holistic view of your structure's mass. The primary reasons it is considered the superior reference for total building weight include:
Mass Summary by Story is not the same as Mass Summary by Diaphragm ETABS 2016
Understanding ETABS Mass Summary by Story: A Comprehensive Guide
When working with ETABS, a powerful software for structural analysis and design, understanding the mass distribution of a building is crucial for ensuring its stability and performance under various loads, including seismic and wind loads. The Mass Summary by Story report in ETABS provides engineers with essential data to assess how mass is distributed across different stories of a building. In this post, we'll delve into the significance of the ETABS Mass Summary by Story, how to interpret it, and why it's vital for structural engineering projects.
For underground structures or tanks, the mass of water and soil is significant. Assign these via Additional Mass or as a special load case with a multiplier of 1.0 in the mass source. Do not rely on DEAD for these.