: The Mass Summary by Story table explicitly prints the X-Mass and Y-Mass coordinates for every level. This allows you to immediately see if a heavy localized equipment load or a structural setback has severely shifted your COM, increasing the risk of structural torsion. 3. Simplified Quality Assurance for Peer Reviews
When applying upward loads (like wind uplift or certain equipment loads), you might encounter "negative mass". ETABS does not allow negative mass in the final assembly; it sets the mass at any joint with a net upward load to zero. This can lead to discrepancies between the "Mass Summary by Story" and "Mass Summary by Group" tables, as the Mass Summary by Story may not account for these negative values. For accurate verification of total mass, the "Mass Summary by Group" is often more reliable in such cases.
For a given story, manually compute:
Accidentally adding live load to the mass source while also converting it via load cases. etabs mass summary by story better
Understanding the mass distribution of a building is the foundation of accurate seismic analysis. In ETABS, the "Mass Summary by Story" table is your primary diagnostic tool for verifying that your mathematical model reflects physical reality.
Checking the mass of every beam, column, and slab individually is virtually impossible in large models. Conversely, looking only at the total base reaction can hide localized errors. If a single story has an unusually high or low mass, the Mass Summary by Story table highlights it instantly. 2. Direct Alignment with Seismic Lateral Force Procedures
ETABS calculates story mass based on your defined . : The Mass Summary by Story table explicitly
Accurate mass distribution is critical for seismic and lateral load analysis. In ETABS, engineers often struggle to verify total building weight and center of mass locations.
Why the ETABS Mass Summary by Story Table Offers a Better Engineering Workflow
Here’s a professional, engaging post you can use on LinkedIn, a blog, or an engineering forum like Eng-Tips. Simplified Quality Assurance for Peer Reviews When applying
Solution: Use "Specified Load Patterns" and turn off "Element Self Mass" to prevent adding the building weight twice. B. Handle Non-Structural Loads Properly
This number is the most critical number of all.
Before any mass summary can be understood, the engineer must define exactly what constitutes the building's mass. This is done in the menu. Getting this definition right is the single most critical step. A major international study analyzing a 17-story building found that the choice of mass source definition directly impacts key results: the 'From self and specified mass' option produced the lowest values for time period, base shear, and story drift; the 'From loads' definition was the most accurate ; other options produced results that were overly conservative.
: Code-compliant drift checks must be based on the Center of Mass coordinates provided in this summary.
If a floor slab is not assigned to a diaphragm, ETABS distributes the mass to individual joints rather than lumping it at the story level. This can make the story summary look deceptively low or fragmented.