Etabs Mass - Summary By Story Better !new!
Display > Show Tables > Analysis Results > Structure Results > Mass Summary by Story Cumulative Mass X (Sum to N) Total Mass
When you open the table, you will see several critical columns. Understanding what these values represent is key to a better engineering review: : The specific floor level being evaluated.
For critical projects, perform a quick manual calculation of the story weight (
Interpreting between the Center of Mass and Center of Rigidity. etabs mass summary by story better
Dynamic lateral analysis requires an accurate Center of Mass (CM) and Center of Rigidity (CR) to calculate torsional effects. Inspecting individual nodes to find the balance point is impractical.
Verifying the story mass summary helps you catch critical modeling errors early:
View the combined mass of frames, shells, and links instantly. Display > Show Tables > Analysis Results >
The Center of Mass coordinates; compare these to the Center of Rigidity. How to Improve Your Mass Source Setup
The translational mass in global directions.
This method calculates mass based on the loads defined in your model, which is the . It correlates directly with the building's actual weight. A key tip: the load combination 1.0DL + 0.5LL (Dead Load + 50% Live Load) is used in many codes, such as ASCE 7, to represent the effective seismic weight. Crucially, the 'From Loads' definition with DL+0.5LL was found to produce results closest to manually calculated values, accurately aligning with code recommendations (ASCE 7–10). Dynamic lateral analysis requires an accurate Center of
Ensure that the sum of the effective modal masses in the X and Y directions equals at least 90% of the total mass listed in your Story Mass Summary. If they don’t match, your structure is either too flexible (need more modes) or your constraints (rigid diaphragms) are preventing proper mass participation.
For a deep dive, download the official CSI Analysis Reference Manual (Chapter 3: Mass and Weight). Or, check your local building code (ASCE 7, IBC, Eurocode 8, IS 1893) for specific mass combination factors—they vary, but the principles above remain universal.
If you are encountering any specific during your mass source checks?
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.
Run the analysis ( F5 ) to ensure all mass matrices are formulated.