Etabs Mass Summary By Story Better ❲Verified Source❳
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The story-based mass summary provides a high-level overview perfect for peer reviews and senior principal approvals.
Engineers often apply live load reduction factors (for gravity design) to the mass source. For seismic mass, use unreduced live loads multiplied by the code factor (e.g., 0.25). Never apply area reduction to mass.
If your definition includes both Element Self-Mass and a dead load pattern that already contains the self-weight multiplier (set to 1), ETABS will double-count the structural weight. A quick glance at the Story Mass Summary will reveal floor weights that are roughly twice what your hand calculations estimate. Unassigned Diaphragm Omissions etabs mass summary by story better
Navigate to Display > Show Tables (or use the shortcut Ctrl + T ).
To ensure your story mass summary is reliable, follow these best practices: Avoid Double Counting
The building's safety depends on the accuracy of every input and every calculation. By taking control of the "Mass Summary by Story," you're not just improving your workflow; you're ensuring that your designs are ready to withstand the forces of nature with unwavering reliability. If you want to optimize your design workflow
Display > Show Tables > Other Definitions > Mass Data > Mass Summary by Story Calculation Logic
The table in ETABS is often considered "better" or more reliable than other mass tables because it provides a comprehensive accounting of all structural mass assigned to a level, regardless of whether a diaphragm is present. Why "Mass Summary by Story" is Often Preferred
If a floor slab is not assigned to a diaphragm, ETABS distributes the mass to individual joints rather than lumping it at the story level. This can make the story summary look deceptively low or fragmented. Never apply area reduction to mass
), which can cause catastrophic failures if not properly addressed.
The "Mass Summary by Story" is not an isolated number. It is the starting point for two crucial outputs in your seismic design: Modal Participating Mass Ratios (MPMRs) and Story Shears.
Do not trust the number until you complete this checklist.
When you run Analyze > Run Analysis > Display > Show Tables > Analysis Results > Structure Results > Mass Summary by Story , ETABS reports:
It helps you verify which parts of the structure (e.g., superstructure vs. substructure) are contributing to specific Modal Mass Participation Ratios . Where to Find It You can access this table by following this path in ETABS: Go to the Display menu. Select Show Tables .