: The total mass from the top of the building down to the current story. Story Weight : The vertical weight (
The total seismic weight of the structure is: $$W = g \times \sum_i=1^n m_i$$ where $m_i$ = U1 (or U2) mass of story i , and $g$ = gravitational acceleration.
The story mass summary table is essential for checking vertical mass irregularity as defined by codes like ASCE 7, IS 1893, or BNBC. A vertical mass irregularity is often defined as a story's mass being significantly different (e.g., greater than 150% or less than 70%) of the mass of an adjacent story. A sudden jump or drop in the "Mass" column of the table serves as a clear and immediate warning sign of such an irregularity. Furthermore, the coordinates of the CM are used to calculate the accidental torsion demands in your seismic load cases.
The coordinates of the center of mass for all levels above and including the current level. Step-by-Step Verification and Troubleshooting 1. The Hand-Calculation Check (Rule of Thumb) etabs mass summary by story
Understanding Mass Summary by Story in ETABS Structural engineers must verify building mass to ensure accurate seismic and dynamic analysis. In ETABS, the table provides a clear breakdown of how mass is distributed vertically throughout a structure. This data is critical for confirming that your mass source definitions match your design assumptions. How to Access the Mass Summary Table
Verify that the total seismic mass matches the design calculation.
) match your expected engineering units to avoid decimal placement errors. : The total mass from the top of
Select and then click on Other Output , or find the Story Data and Mass Summary options.
In practice, the correct choice is for building structures where the seismic weight is defined by building codes as a function of loads (DL + LL). According to a 2022 comparative study, the From load with DL+0.5 LL option yields results closest to manually calculated seismic mass and complies with ASCE 7–10 recommendations.
The should generally exhibit a lower mass compared to standard floors due to lighter live loads and absence of upper-level vertical columns/walls. A vertical mass irregularity is often defined as
ETABS automatically calculates the mass of structural elements (beams, columns, slabs) based on their geometry and material density. It also includes any manually assigned point, line, or area masses.
Design codes use the effective seismic weight of the structure to determine lateral seismic forces. The sum of the horizontal masses ( UXcap U cap X UYcap U cap Y
Before running the analysis, you must tell ETABS how to calculate the building's mass. Computers and Structures, Inc. Define > Mass Source Specified Load Patterns
