) to find the total weight of the structure. Compare this value to the total dead load reaction in your base reaction tables ( Support Reactions ). They must match exactly. 6. Troubleshooting Common Issues
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 etabs mass summary by story
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. ) to find the total weight of the structure
Often, the culprit is a massive story mass that ETABS cannot move due to stiff supports. Go back to the Mass Summary, verify the U3 values, and ensure your vertical elements (columns/walls) are not artificially restraining movement. By default, ETABS only considers element self-mass
After you verify the mass summary, run a modal analysis. The report depends entirely on the Mass Summary.