Etabs Mass Summary By Story Better __exclusive__ -
When modeling slabs, the choice of element affects mass calculation. Using "Shell-Thick" elements for slabs ensures their self-weight and inertia are fully captured, contributing to a more accurate UX and UY value in your mass summary. D. Verify the "Diaphragm" Assignment
: If your model uses diaphragms, also include the Center of Mass and Rigidity table to show eccentricity. 3. Verification & Quality Checks
It combines structural self-weight, superimposed dead loads, and specified live load reductions into a single, clean value per floor.
The table typically presents data for each story, showing the total effective mass (often in or kN·s²/m ) participating in lateral (UX, UY) and vertical (UZ) directions, as well as rotational inertia (RX, RY, RZ) when applicable. The most critical columns for seismic analysis are UX and UY , which represent the mass that will generate seismic forces in those lateral directions. etabs mass summary by story better
Merges self-weight and applied loads into one comprehensive narrative per story. 3. Direct Verification of Center of Mass (CM)
Mastering ETABS Mass Summary by Story: Better Analysis & Seismic Design
If the ground floor has more mass than the floor above, despite identical geometry, you likely assigned different load patterns. If a floor suddenly has zero mass, your diaphragm assignment is likely missing. When modeling slabs, the choice of element affects
A "better" mass summary means one that matches manual calculations and aligns with seismic design intent. A. Avoid Double Counting
By default, ETABS calculates mass from element self-weight. If you modify the Mass Source to include specified load patterns (like 100% Dead + 25% Live) but forget to uncheck "Element Self-Weight," ETABS may double-count the structural self-weight. 2. Overlapping Slab Areas
Ensure that the sum of the effective modal masses in the X and Y directions equals at least 90% of the total mass listed in your Story Mass Summary. If they don’t match, your structure is either too flexible (need more modes) or your constraints (rigid diaphragms) are preventing proper mass participation. Verify the "Diaphragm" Assignment : If your model
Go to Define > Story Data :
The mass of your building is the primary driver of inertial forces during an earthquake. The Mass Summary by Story report serves several high-stakes engineering purposes:
Spot extreme accidental eccentricities by comparing CM and CR coordinates.
Cumulative mass from the top down; used to check total building weight.
Beyond basic interpretation, using the mass table strategically can drastically improve your analysis results.