Etabs Mass Summary By Story _verified_ -

Understanding Mass Summary by Story in ETABS In structural engineering, the Mass Summary by Story is a critical output in

Rotational Mass (or Moment of Inertia)

: This includes the rotational inertia about the X, Y, and Z axes for each story. It represents the resistance of the mass to changes in its rotation. etabs mass summary by story

Mass Summary by Story

When reviewing the , ask yourself these three questions: Understanding Mass Summary by Story in ETABS In

Analysis Results

To access the report, navigate to: > Structure Results > Mass Summary > Mass Summary by Story 📊 Understanding the Data Columns Story: The specific floor level. Mass X / Mass Y: Total mass in horizontal directions. Mass X / Mass Y: Total mass in horizontal directions

For rectangular floor plates, this value follows a predictable physical formula ($\fracm(a^2 + b^2)12$). However, for complex geometries—L-shapes, H-shapes, or floors with large atriums—the summary table is the only reliable source for the true rotational inertia. If this value is reported as zero, the engineer has likely neglected to define the rotational mass, leading to an underestimation of torsional response and an incorrect calculation of higher mode shapes.

Seismic Weight = Dead Load + Applicable Live Load (Percentage) + Partition Loads + Equipment Loads

Total Mass

: A summary of the total mass for each story.

Incorrect Mass Source:

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.