Etabs Mass Summary By Story Better Better Here
How to Get a Better ETABS Mass Summary by Story: Moving Beyond Default Reports
Tributary Distribution
: ETABS "lumps" mass at the center of each floor by taking half the weight of the story below and half from the story above.
- Mass Source for Modal Analysis: This should include
1.0 Dead Load + Specified Live Load (e.g., 0.25 for floors, 0.50 for roofs). Do not include self-weight manually if it is already part of the DL. - Mass Source for Seismic Weight (per ASCE 7): This is used for base shear calculations, not modal analysis.
| Symptom | Likely Cause | Fix | | :--- | :--- | :--- | | Mass at roof is too high | Penthouses, water tanks not modeled as separate stories | Assign point mass or model as a dummy story | | Mass is negative or zero | Invalid constraint or bi-axial hinge | Check Display > Show Undeformed > Joints for errors | | Cumulative mass changes after analysis | Mass source relies on load-dependent deflection (e.g., nonlinear) | Use linear static for mass source | | Mass differs between ETABS and Excel takeoff | Line loads, area loads not converted to mass | Convert all Uniform Loads to Mass via Assign > Area Loads > To Mass | etabs mass summary by story better
✅ Step 2: Diaphragm Rigidity
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). How to Get a Better ETABS Mass Summary
To ensure your story mass summary is reliable, follow these best practices: Avoid Double Counting Mass Source for Modal Analysis: This should include 1
exact IBC or Eurocode formulas
If you'd like to dive deeper into the technical side, I can help you with: The for mass source. How to export this data to Excel for faster reporting.
Here’s how to master the ETABS Mass Summary: