Etabs Mass Summary By Story Better |verified| Jun 2026

Are you troubleshooting a specific in your mass source?

| Component | Description | Key Details & Potential Pitfalls | | :--- | :--- | :--- | | | The total mass in translational and rotational directions per story. | Mass is "lumped" to the defined story levels following specific rules (e.g., identical point coordinates for meshed elements). | | Mass Summary vs. Mass Summary by Diaphragm | Different methods can yield different values. | Discrepancies often arise if mass is assigned outside a defined diaphragm. Ensure all mass-contributing elements are connected to a diaphragm. | | Mass vs. Weight | Weight = Mass × g . | ETABS uses mass for dynamic analysis ( m = W/g ) but may use weight directly for static base shear calculations per some codes. | | Story Mass vs. Group Total Mass | The sum of story masses often differs from the total of all structural elements' mass. | Hypothesis: In many cases, Story mass is less than Group All mass. Root Cause: This signals a modeling error. A common reason is surfaces with more than 4 sides that are not auto-meshed; the program may effectively ignore them. Resolution: Edit the geometry to use only 3- or 4-sided polygons. | | Reactions vs. Mass Summary | Reactions from a DEAD load case may not match the weight in the mass summary. | Hypothesis: The reactions and mass summary are not matching. Root Cause: This mismatch is possible when elements are meshed across story levels. Check diaphragm assignments and ensure points at floor levels are not shared with other stories. |

For response spectrum or time history analysis, the Mass Summary is your truth serum. Compute the from the modal analysis. The Mass Summary gives you the total mass of the building. The modal output gives you the effective modal mass.

Based on seismic codes like IS 1893:2016, you should typically define your mass source using a load combination of 1.0 * (Dead Load) + (Applicable % of Live Load). For the "From Loads" option, a common combination is 1.0 DL + 0.5 LL (for residential buildings) or 1.0 DL + 0.25 LL (for others). . etabs mass summary by story better

Non-structural elements like parapet walls, water tanks, or heavy facade elements must be added to the mass source.

Use the summary to verify the total building weight (

Go to Display > Show Tables > Analysis Results > Structure Output > Story Information > Mass Summary by Story . 3. Key Components of the Mass Table Are you troubleshooting a specific in your mass source

In structural engineering, particularly when designing for seismic loads, accurately defining and reviewing the building mass is paramount. ETABS, a premier software for building analysis, provides the output, a critical tool for verifying effective seismic weight.

If you are running an or a Dynamic Response Spectrum analysis.

ETABS calculates story mass based on:

Display > Show Tables > Analysis Results > Structure Results > Centers of Mass and Rigidity CSI Knowledge Base

Display > Show Tables > Analysis Results > Structure Results > Mass Summary by Story Cumulative Mass X (Sum to N) Total Mass