A quick glance at the cumulative mass helps verify if you are working in kips, tons, or kilograms. C. Calculating Eccentricity
The total mass of the building is the fundamental variable in the formula (Base Shear = Seismic Coefficient
The is an indispensable diagnostic tool for structural engineers. It bridges the gap between raw finite element modeling and the macro-level physics governing seismic design. By routinely checking this table, verifying the Center of Mass coordinates, and validating the total building weight against hand calculations, you ensure that your structural model is safe, code-compliant, and ready for advanced lateral design. To help tailor further engineering workflows, If you are interested, I can:
It acts as a diagnostic dashboard. A quick glance can reveal if you accidentally omitted a floor's dead load, double-counted a slab, or misconfigured your Mass Source settings. How to Access the Mass Summary Table in ETABS etabs mass summary by story
Equivalent Lateral Force (ELF) and Response Spectrum analyses rely directly on the mass ( ) assigned to each story (
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I can provide targeted troubleshooting steps based on your setup. Share public link A quick glance at the cumulative mass helps
In ETABS, the is one of the most critical outputs for structural engineers. It provides a concise breakdown of how weight is distributed across the height of a building—a factor that directly dictates seismic forces and dynamic behavior.
: The vertical mass active in the global Z direction (only populated if vertical mass is included in your mass source).
Confirm the mass used by the software to calculate the fundamental period and seismic base shear. It bridges the gap between raw finite element
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.
A practical note: when comparing, remember to convert mass to weight ( W = m × g ) if necessary. One engineer reported a 20% discrepancy until discovering they had not included superimposed dead loads (SDL) in the mass source definition. The official CSI answer is: Building mass always refers to the definitions specified in the Define > Mass Sources menu. To account for SDL, add an SDL case to the Load List .
: The rotational mass about the global Z-axis. This value is critical for determining the torsional response of the building. 3. The Role of the Mass Source
Comprehensive building analysis requires a deep understanding of how structural mass is distributed throughout a building. In Extended Three-Dimensional Analysis of Building Systems (ETABS), evaluating this mass—and where it is applied—is essential for accurate seismic design, dynamic analysis, and calculating story drift. The is one of the most critical built-in tables engineers rely on to verify the total mass and weight distribution of their structural models before running a final analysis. What is the "Mass Summary by Story" in ETABS?
