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These columns represent the summation of forces acting on the individual diaphragms.
: The translational mass along the X, Y, and Z axes. In most lateral analyses, the vertical mass (UZ) may be ignored unless vertical seismic effects are being considered.
Verify that the total seismic mass matches the design calculation.
Engineers use this table to cross-check ETABS calculations against manual dead load take-offs. A discrepancy of more than 5% usually indicates an error in material density, slab thicknesses, or skipped superimposed dead loads. Base Shear Calculations
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
If your Mass Summary table displays zeros, check your diaphragms. ETABS requires a defined rigid or semi-rigid diaphragm at a story level to accurately calculate and display the discrete Center of Mass coordinates for that floor. Best Practices for Structural Audits
: The running total of mass from the top story down to the current story.
ETABS automatically converts defined dead, live, and superimposed loads into mass based on user-defined mass source definitions (per ASCE 7 or similar).
Elements like structural framing, concrete slabs, and cladding should generally be included at a multiplier. These columns represent the summation of forces acting
Compare the total weight (multiply mass by ( g )) against your hand calculation. If the ETABS total is 5,000 kN but your Excel sheet says 7,500 kN, you likely forgot to include cladding, finishes, or the live load percentage in the Mass Source.
A very specific topic!
(Vertical Mass): The mass active in the vertical direction (often ignored for standard seismic lateral loads but necessary for vertical dynamic evaluations).
The standard table has a simple, columnar layout listing each story and its corresponding mass. A typical example from a project in Ecuador shows the mass at each story in kilograms (kg) for the horizontal UX and UV (UY) directions: Verify that the total seismic mass matches the
Click OK to display the table. To export the data to Microsoft Excel for further calculations, right-click the table and choose Export to Excel . Key Terms and Columns Explained
Detect weight/mass irregularities where adjacent stories vary significantly in mass, triggering strict code-mandated analysis adjustments. How to Access the Mass Summary Table
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