Etabs Mass Summary By Story Better Here
ETABS: Mass Summary by Story — Draft Article
Introduction
A concise guide on generating and interpreting mass summaries by story in ETABS, useful for structural engineers performing seismic and dynamic analysis.
A "better" report includes validation to ensure the model is accurate: etabs mass summary by story better
7. Case Study: How a "Better" Mass Summary Saved a 30-Story Tower
The Scenario: A firm in a high-seismic zone (Seismic Design Category D) ran ETABS and got a base shear of 1,500 kips. The design was proceeding. ETABS: Mass Summary by Story — Draft Article
You look at the bottom of your Mass Summary table. There is a number: Total Building Mass. Mass : The total mass assigned to a
R3 (Mass Moment of Inertia about Vertical Axis): This is the most overlooked and most critical value for torsional irregularities. A better engineer checks whether R3 is physically plausible. For a rectangular floor, $R3 \approx \fracMass12(a^2 + b^2)$. If your ETABS R3 is off by an order of magnitude, your torsional response (and consequently, accidental torsion) will be wildly inaccurate.
The report provides a tabular breakdown of mass at each story level, derived from the Mass Source definition. Otte International : Found under
- Mass: The total mass assigned to a story, which could be from the self-weight of structural elements, architectural elements, and any other loads that contribute to the mass.
- Mass X, Y, Z: These represent the mass moments of inertia about the X, Y, and Z axes, respectively. They are crucial for understanding the rotational inertia of the mass at each story level.
- Center of Mass: This indicates the location of the center of mass for each story, which is vital for determining the torsional response of the building under lateral loads.
- Self-mass of frame, shell, and solid elements (from material density).
- Added mass from specified loads (Dead, Live, Snow, etc.) modified by mass source definitions.
- Diaphragm constraints (lumped mass at the center of rigidity).