Etabs Mass Summary By Story ^new^ -

Compare adjacent floors. If any story mass exceeds 150% of an adjacent story's mass, your building has a Mass Irregularity , which may require dynamic Response Spectrum Analysis instead of simpler Equivalent Lateral Force procedures.

| Issue | Possible Cause | Solution | | :--- | :--- | :--- | | | Mass Source defined incorrectly. | Go to Define > Mass Source . Ensure "Include Lateral Mass only" is not checked if you need gravity mass, or check that loads are included in the definition. | | Mass is Double | Self-weight counted twice. | In Mass Source, check if "Element Self Mass" is checked AND you have also applied a Dead Load case that includes self-weight. Usually, let ETABS calculate self-weight automatically. | | Inconsistent Story Mass | Unmeshed slabs/walls. | Ensure slabs and walls are meshed ( Assign > Shell > Auto Mesh ). Unmeshed areas may not transfer loads correctly to the frame/diaphragm. | | Units Confusion | Mass vs. Weight. | Check your display units. Remember that Mass is force/gravity ($kips \cdot s^2/in$ or $ton$), while Weight is force ($kips$ or $kN$). |

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.

: Define this under Define > Mass Source . You must specify whether to use element self-mass, additional mass, or specific load patterns (like 100% Dead Load + 25% Live Load). etabs mass summary by story

When you run the analysis and navigate to , you will see a table with the following key columns:

The calculated gravity load associated with each level, derived directly from your defined mass source. Why is the Mass Summary Table Important?

The running total of the mass from the top of the building down to that specific story. How ETABS Calculates Story Mass Compare adjacent floors

By understanding where your mass comes from and how ETABS organizes it by story, you move from being a software operator to a true structural analyst.

If you are facing a (like mismatched mass or twisting modes) in your current ETABS model? What version of ETABS you are using? Share public link

Before designing lateral systems, you must calculate the Seismic Response Coefficient ($C_s$). This requires the total seismic weight ($W$). | Go to Define > Mass Source

Before looking at the numbers, confirm what ETABS is counting as mass. Go to . Ensure your mass source includes:

). This table consolidates all mass defined in your and attributes it to specific floor levels. How to Access the Table To view the data after running an analysis: Go to the Display menu. Select Show Tables .

By comparing the mass distribution at different stories, you can detect if the mass is concentrated heavily on one side of the building, which would lead to high torsion ( RZcap R cap Z C. Consistency with Architectural Plans

Alternatively: Check for the raw input mass before analysis. What to Look For