Etabs Mass Summary By Story ((hot)) -
Seismic lateral forces are directly proportional to a structure's mass (
The engineer must distinguish between Dead Load (DL) and Superimposed Dead Load (SDL). The mass summary captures the "real" mass—the construction materials—plus a portion of the live load (typically 25% to 50% depending on the seismic code) representing the probable mass during a seismic event. An anomaly in the total mass usually points to a misinterpretation of the "Mass Source" dialog—specifically the inclusion or exclusion of "Additional Mass" assignments versus pattern-loaded live loads. If the summary does not reflect the intended Mass Source combination, all subsequent spectral analyses are rendered null.
The name of the floor level defined in your story data.
The total mass assigned to that story acting in the global X and Y horizontal directions. In most standard buildings, UX and UY will be identical.
The is a structured table in ETABS that lists the accumulated mass of the building at each story level. This table displays the translational mass ( ) and the total weight (Peso por Piso) for each story. Mass ( ): Often in units like etabs mass summary by story
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Go to Display > Show Tables > Analysis Results > Structure Output > Story Information > Mass Summary by Story . 2. Key Components of the Mass Table
The global X and Y coordinates where the mass of that specific story is concentrated. Seismic lateral forces are directly proportional to a
The Mass Summary by Story is not merely a data table but the foundation of a building's seismic "identity." By meticulously reviewing these values, an engineer ensures that the mathematical model accurately reflects the physical reality of the structure, leading to a safe and optimized design.
Before you finalize your ETABS model for seismic design:
ETABS attributes half the mass of vertical elements (walls and columns) to the story above and half to the story below. If your ground floor columns are exceptionally tall, the mass distribution between the first floor and the base might look skewed. Keep this geometric division in mind during your manual verification. Neglecting Non-Structural Elements
Unlike simple gravity takeaway, this summary specifically focuses on (force/acceleration), which is the primary driver of inertial forces during an earthquake. If the summary does not reflect the intended
Alternatively: Check for the raw input mass before analysis. What to Look For
To view the Mass Summary by Story in ETABS, follow these step-by-step instructions after running your structural analysis:
. This is the gravity load calculated from the defined mass source (usually
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.
If your mass seems too low, check your Mass Source definition. Ensure you included a percentage of the live load (typically 25% for storage warehouses) if required by your local building code. Double Counting Mass
When reviewing the table, the most immediate metric is the vertical consistency of mass per story. A building follows the laws of physics; typically, lower stories have larger masses due to bigger column sections, thicker shear walls, and heavier floor plates, tapering off as the building rises.