Etabs Mass Summary By Story [better] Jun 2026

If you’ve ever asked yourself:

A common pitfall in ETABS modeling is ensuring that all mass is correctly accounted for, especially for "null" areas (areas not part of a structural slab). If you apply loads to a null area, you explicitly assign a diaphragm to that null area for its mass to be included in the building's seismic mass for modal analysis. Otherwise, the load contributes to reactions but not to the building's mass matrix [7†L31-L34], making the structure seem lighter than it is.

Understanding the ETABS Mass Summary by Story In structural engineering, specifically when performing seismic or dynamic analysis, the distribution of mass is just as critical as the stiffness of the members. ETABS provides a dedicated output called the to help engineers verify that their model’s inertia is correctly accounted for.

Which (e.g., ASCE 7, Eurocode 8) are you design for? Are you dealing with a torsional irregularity warning? Do you need help setting up the Mass Source definition?

Unusually high mass at a single floor could indicate a modelling error (e.g., duplicated elements or incorrect material density). etabs mass summary by story

Before running the analysis, you must tell ETABS how to calculate the building's mass. Computers and Structures, Inc. Define > Mass Source Specified Load Patterns

The natural periods of vibration of your building are highly dependent on the mass and stiffness distribution. Mass that is improperly lumped into the wrong stories will result in erroneous dynamic characteristics. How to Define and Extract the Mass

The portion of the story mass that is assigned directly to rigid or semi-rigid diaphragms.

A null area (no diaphragm) can have loads applied and show correct reactions, but the mass may be added to the building seismic mass at all. The required solution is to assign a diaphragm to the null area, which then transfers the mass to the building for seismic calculations. If you’ve ever asked yourself: A common pitfall

The output will be presented as a spreadsheet-style table that can be exported, copied, or included in design reports.

Double-click on to open the data grid.

If a load was applied improperly, or if certain heavy elements (like mechanical equipment) were omitted, the mass summary table will immediately show anomalies. A sudden spike or drop in mass between adjacent stories is a major red flag that usually requires troubleshooting.

Calculate the dead weight of a typical floor by hand (tributary area Understanding the ETABS Mass Summary by Story In

Once you have successfully run your analysis in ETABS, follow these steps to view the data: Navigate to the on the left-hand side. Go to Tables > Analysis > Results > Structure Results . Double-click on Mass Summary by Story .

for specialized structural elements.

Lateral mass lumped at story levels for accurate seismic response. 3. Mass Summary Table