You can locate this data through the ETABS menu interface after running your structural analysis.
: The rotational mass around the center of mass.
These should generally be equal unless you have strange property modifiers. This represents the total translational mass per floor. etabs mass summary by story
Does your project feature any structural complexities like or skip floors ? Share public link
Elements like structural framing, concrete slabs, and cladding should generally be included at a multiplier. You can locate this data through the ETABS
: Ensure rigid or semi-rigid diaphragms are correctly assigned. ETABS calculates story mass based on the objects associated with that specific story level and its diaphragm boundaries. Share public link
If a story shows a mass significantly higher or lower than expected, it’s a red flag. Common culprits include: This represents the total translational mass per floor
These represent the total mass considered for horizontal motion in the X and Y directions. In most cases, these values are identical unless you have assigned specific directional mass properties.
| Observed Problem | Likely Cause | Solution | |----------------|--------------|----------| | Zero mass on a story | No assigned area/shell objects or missing mass source | Check Assign > Area Loads or revise mass source definition | | Asymmetric U1 vs U2 mass in symmetric building | Incorrect diaphragm assignment or accidental eccentricity | Verify rigid diaphragm assignments | | Unrealistically high mass | Duplicate loads or self-weight included twice | Review load patterns and mass source (exclude self-weight if already in dead load) | | Mass moment of inertia = 0 | No diaphragm or mass assigned | Assign a rigid diaphragm or specify rotational mass |
option if you want the mass concentrated at the floor levels for simplified lateral analysis. Include Lateral Mass
If your Mass X and Mass Y values look lower than manual hand calculations, verify your Mass Source. Ensure you manually added the load patterns (SDL, LL) with their respective multipliers. By default, ETABS only considers element self-mass. 2. Unassigned Diaphragms