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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).
Do you need steps to resolve a specific in your model?
Seismic design is a battle against torsion. The Mass Summary report typically includes the coordinates for the Center of Mass etabs mass summary by story better
Always verify the active units (e.g., kg, kN, or kips) before exporting the table to Excel to avoid catastrophic scaling errors.
ETABS provides three primary ways to define the seismic mass:
A rigid diaphragm is necessary to obtain the center of mass (CM) and center of rigidity (CR) from ETABS. For final analysis and design with semi-rigid diaphragms, you can temporarily assign rigid diaphragms to extract these values, then convert back. Save this post for your next model check
The table provides the exact format required for calculation reports. It directly outputs the total story weight, which allows reviewers to quickly cross-check the base shear calculations ( ) and ensure that the fundamental building weight ( ) matches the design assumptions.
Mass moments of inertia; critical for capturing torsional effects.
When reviewing the Mass Summary by Story , you will see the following key data points: Floor level identification. UX/UY: Total mass in the X and Y directions. RZ: Rotational mass moment of inertia around the Z-axis. A key tip: the load combination 1
Create a second Mass Source for Gravity Design ( MASS_GRAVITY ) that uses 100% of Dead + Live for P-Delta and vertical acceleration checks.
Go to Define > Mass Source . According to best practices, use "Specified Load Patterns" to ensure control over the mass contribution. Dead Load (SDL + Self Weight): Multiplier = Live Load: Multiplier = (based on code, e.g., IS 1893). Include Lateral Mass: Crucial for dynamic analysis.
> Results > Structure Results > Mass Summary by Story Why This Table is "Better"