If ( UX ) or ( UY ) mass moment of inertia is zero, ETABS cannot calculate torsion correctly. This happens when you model all mass as point masses at the center of mass instead of using a diaphragm. Ensure you have assigned a Semi-Rigid or Rigid Diaphragm to every floor.
In structural engineering, verifying a building's mass distribution is a critical quality control step. In ETABS, the table is the primary tool for validating structural weight, calculating seismic forces, and checking center of mass locations.
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 .
Show you how to verify to check for torsional irregularity.
In structural engineering, especially when designing for lateral loads (earthquake and wind), understanding how mass is distributed throughout a building is critical. provides a specialized table called the "Mass Summary by Story" to streamline this process. etabs mass summary by story
These represent the mass contributing to inertia in the global X (U1), Y (U2), and Z (U3) directions.
When the report loaded, the first line showed the total seismic weight per story. Maya read it like a heartbeat: lower floors carried more—concrete podiums, parking slabs, and heavy mechanical rooms—while the upper residential stories were lighter, filled with drywall and furniture assumptions. The variation was clear in the table: Story 1 held 1,200 kN, Story 2 had 1,000 kN, and by Story 12 it tapered to 650 kN. The building’s center of mass whispered its position: slightly offset toward the west because of the heavier stair core.
By mastering the Mass Summary by Story table, you ensure your dynamic structural analysis stands on a structurally sound, perfectly weighted foundation.
) match your expected engineering units to avoid decimal placement errors. If ( UX ) or ( UY )
[Your Name] Course: Structural Engineering / Computer-Aided Design Date: [Current Date]
The Mass Summary by Story table provides a aggregated view of the mass calculated at each floor level. ETABS calculates this data based on your Mass Source definition. It lists the total mass, the center of mass, and mass moments of inertia for every story in your structure. 2. Key Output Parameters Explained
To verify that the structural mass assigned in the model accurately reflects the designed building mass, ensuring accurate base shear calculations (
Indicates if a rigid or semi-rigid diaphragm is assigned. If no diaphragm is assigned, the mass is treated as lumped at the joints. Go to Tables > Analysis > Results > Structure Results
When reviewing the table, engineers look for consistency. Sudden spikes or drops in mass between identical floors usually indicate a modeling error, such as a missed slab or an accidental "null" property. Ensuring a clean Mass Summary is the first step toward a reliable Seismic Response Spectrum Time History Analysis Should we look into how to troubleshoot discrepancies
If your "Mass Source" (Define > Mass Source) is set to include "Element Self Mass" AND "Loads," but you’ve also manually assigned mass, you might be double-counting.
The in ETABS is a standard output table that aggregates the distributed and point masses assigned to a building model at each floor level. It serves as a primary verification tool for structural engineers to ensure that the total seismic weight used for base shear calculations is accurate and adheres to building codes. 1. Accessing the Table
: By default, ETABS lumps mass at story levels by taking half the weight from the story above and half from the story below. You can explicitly enable "Lump Lateral Mass at Story Levels" in the Mass Source definition to simplify the model into a multiple degree-of-freedom system.