Mass Summary By Story | Etabs

: The gravitational force associated with that story's mass. Critical Setup Requirements

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:

) to find the total weight of the structure. Compare this value to the total dead load reaction in your base reaction tables ( Support Reactions ). They must match exactly. 6. Troubleshooting Common Issues

In standard buildings, Mass X and Mass Y are identical because mass is a scalar quantity derived from the material density and volume. They are split into directional columns because ETABS allows for directional mass scaling or localized modifications under advanced seismic settings. Troubleshooting Common Discrepancies

Before looking at the summary table, you must understand where ETABS gets its mass data. This is controlled via . You can define mass based on: etabs mass summary by story

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.

Understanding ETABS Mass Summary by Story: A Complete Guide for Structural Engineers

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.

The accuracy of dynamic analysis in structural engineering is highly dependent on the correct definition and distribution of mass. ETABS (Extended Three-dimensional Analysis of Building Systems) provides a critical output called the "Mass Summary by Story." This paper explains the theoretical basis of mass summation in ETABS, differentiates between mass and weight, interprets the tabular output, and demonstrates how this summary is used for seismic load calculations (base shear), center of mass determination, and dynamic property verification (modal analysis). : The gravitational force associated with that story's mass

Once your mass source is defined and you have successfully run the analysis, you can access the summary data: Navigate to the top menu and select . Expand the Analysis Results folder.

Note: If you use specified load patterns, ensure you uncheck "Element Self-Mass" if your Dead Load pattern already includes the self-weight of the structure. Otherwise, you will double-count the mass. How to Access the Mass Summary Table in ETABS

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Include a rough allowance for columns and walls dividing upper and lower halves of the story. Convert this total weight to mass ( Compare this value to the total dead load

In the realm of computational structural engineering, the "Mass Summary by Story" table is not merely a ledger of weights; it is the quantitative biography of the building. While ETABS provides a plethora of complex output displays—from moment diagrams to shell stress contours—the Mass Summary remains the fundamental diagnostic tool for verifying the physical integrity of the analytical model. It serves as the bridge between the architectural intent and the structural reality, translating volumetric geometry into the inertial forces that govern seismic response.

When reviewing the , ask yourself these three questions:

After analysis, open the .log file or the .f2k text file. Search for STORY MASS . This raw data is useful for scripting or batch verification.