Etabs Mass Summary By Story (2026)

Mass Summary by Story in ETABS provides a high-level overview of a structure's distribution of mass, which is critical for seismic and dynamic analysis. To extract this, navigate to

Display > Show Tables > Analysis Results > Structure Results > Mass Summary by Story

Below is a drafted report structure for presenting this data. Structural Mass Summary Report 1. Project Overview ETABS 2026 Model Status: Analysis Completed Mass Source: Defined as [e.g., Self Mass + 25% Live Load] 2. Mass Source Definition

The mass used for dynamic analysis was derived from the following criteria: Element Self Mass: Additional Mass: [e.g., Cladding or Floor Finishes] Lumped Mass:

Lateral mass lumped at story levels for accurate seismic response. 3. Mass Summary Table

The following table summarizes the mass distributed at each floor level. Mass X (kg) Mass Y (kg) Cum. Mass X (kg) Cum. Mass Y (kg) 4. Observations & Verification Mass Summary for ETABS Stories | PDF - Scribd

ETABS Mass Summary by Story: A Comprehensive Guide

ETABS, a popular structural analysis software, provides a powerful tool for engineers to analyze and design buildings. One of the essential features of ETABS is the ability to generate a mass summary by story, which is a crucial step in understanding the dynamic behavior of a building under various loads. In this article, we will delve into the concept of ETABS mass summary by story, its importance, and how to interpret the results.

What is ETABS Mass Summary by Story?

ETABS mass summary by story is a report that provides a detailed breakdown of the mass properties of a building, organized by each story or floor. The report includes various mass properties, such as: etabs mass summary by story

These properties are calculated based on the structural elements, such as beams, columns, walls, and slabs, that make up the building.

Importance of ETABS Mass Summary by Story

The mass summary by story is a vital tool for structural engineers, as it helps them understand the distribution of mass within the building. This information is essential for several reasons:

  1. Dynamic Analysis: During dynamic analysis, such as earthquake or wind load analysis, the mass of the building plays a critical role in determining the structure's response. The mass summary by story helps engineers to identify the mass distribution, which is crucial for accurate dynamic analysis.
  2. Structural Stability: The center of mass and center of rigidity are essential for evaluating the structural stability of the building. A significant difference between the center of mass and center of rigidity can indicate potential stability issues.
  3. Load Distribution: The mass summary by story helps engineers to understand how loads are distributed throughout the building. This information is critical for designing structural elements, such as foundations, beams, and columns.

How to Generate ETABS Mass Summary by Story

Generating the mass summary by story in ETABS is a straightforward process:

  1. Open the ETABS Model: Open the ETABS model of the building for which you want to generate the mass summary.
  2. Go to the "Analyze" Menu: Click on the "Analyze" menu and select "Mass Summary" from the drop-down menu.
  3. Select the Story: In the "Mass Summary" dialog box, select the story or floor for which you want to generate the report.
  4. Choose the Mass Properties: Select the mass properties you want to include in the report, such as mass, moment of inertia, center of mass, and center of rigidity.
  5. Run the Analysis: Click "OK" to generate the mass summary report.

Interpreting ETABS Mass Summary by Story

The mass summary by story report provides a wealth of information about the mass properties of the building. Here's how to interpret the results:

  1. Mass: The mass value represents the total mass of the building at each story. A higher mass value indicates a greater amount of material or load at that story.
  2. Moment of Inertia: The moment of inertia (Ix, Iy, Iz) values represent the resistance of the building to bending and torsion. Higher moment of inertia values indicate greater stiffness.
  3. Center of Mass: The center of mass (X, Y, Z) values represent the location of the building's center of mass at each story. The center of mass should ideally coincide with the center of rigidity.
  4. Center of Rigidity: The center of rigidity (X, Y, Z) values represent the location of the building's center of rigidity at each story. The center of rigidity should ideally coincide with the center of mass.

Common Issues and Troubleshooting

When generating and interpreting the ETABS mass summary by story, engineers may encounter some common issues: Mass Summary by Story in ETABS provides a

  1. Inconsistent Mass Values: Inconsistent mass values may indicate errors in the structural model or loading.
  2. Center of Mass and Center of Rigidity Mismatch: A significant difference between the center of mass and center of rigidity may indicate potential stability issues.
  3. Missing or Incorrect Data: Missing or incorrect data in the mass summary report may indicate errors in the structural model or loading.

Best Practices

To ensure accurate and reliable results from the ETABS mass summary by story, follow these best practices:

  1. Verify the Structural Model: Verify the structural model for accuracy and completeness.
  2. Check Loading: Check loading for accuracy and completeness.
  3. Use Consistent Units: Use consistent units throughout the analysis.
  4. Review Results Carefully: Review results carefully to identify potential issues.

Conclusion

The ETABS mass summary by story is a powerful tool for structural engineers to analyze and design buildings. By understanding the mass properties of a building, engineers can identify potential issues and optimize the structural design. By following the guidelines outlined in this article, engineers can generate and interpret the ETABS mass summary by story with confidence, ensuring accurate and reliable results.

To get a clear picture of how your building’s weight is distributed, follow these steps in ETABS. This summary is essential for verifying your seismic mass and ensuring your model’s gravity loads make sense. How to Find the Mass Summary

Run the Analysis: You must have a completed analysis run (the lock icon should be closed). Navigate the Menu: Go to Display > Show Tables. Find the Specific Table: Expand Analysis Results. Expand Structure Results.

Select Center of Mass and Rigidity. (This is the most common way to see story-by-story mass).

Alternatively: Check Model Definition > Structural Data > Mass Summary by Story for the raw input mass before analysis. What to Look For

Mass X / Mass Y: These should generally be equal unless you have strange property modifiers. This represents the total translational mass per floor. Mass Moment of Inertia (Ix, Iy, Iz) Center

Cumulative Mass: Check the bottom story to see the total mass of the entire building. Compare this to your hand calculations (Area × Dead Load) to ensure you haven't missed any loads.

Center of Mass (XCCM, YCCM): These coordinates tell you where the "weight" of the floor is centered. If these are far from the geometric center, you’ll have high accidental torsion.

Check your Mass Source: Go to Define > Mass Source. Ensure you’ve included 100% of Dead Loads and the required percentage of Live Loads (usually 25% for storage or as per your local code).

Diaphragms: To get a "per story" breakdown in the Analysis tables, you usually need to have diaphragms assigned to your floor shells. If you want to verify the numbers, let me know: The building's total area Your typical dead load (PSF or kN/m²)

Which building code (ASCE 7, Eurocode, etc.) you're following

Method 2: From the Analyze Menu (After Analysis)

  1. Run the analysis (Ctrl + F5).
  2. Click File > Save Tables.
  3. Select Mass Summary and export to Excel or text.

D. Center of Mass (CM)

Introduction

In the world of structural engineering, few calculations are as critical—or as frequently misunderstood—as the building’s seismic mass. When you run a response spectrum analysis or a time history analysis in CSI ETABS, the software doesn't just look at the weight of the structure. It calculates the mass (force/acceleration) and distributes it across each floor level. The primary report that controls this behavior is the "Mass Summary by Story."

For many engineers, this is just a table they check before sending off a report. For expert modelers, it is a diagnostic goldmine. An incorrect mass summary leads to incorrect base shears, unrealistic drifts, and a fundamentally unsafe design.

This article will dissect the ETABS Mass Summary by Story. We will cover what it is, how ETABS calculates it, how to interpret every column of the output, common sources of error, and how to troubleshoot discrepancies.

A. Story and Output Case

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

In structural analysis, verifying the mass of your building is just as critical as verifying its stiffness. An incorrect mass distribution leads to incorrect period calculations, base shears, and seismic forces.

ETABS provides a powerful output table known as the "Mass Summary by Story," which allows engineers to audit the gravity load distribution throughout the model. This article explains where to find this table, how to interpret the columns, and how to troubleshoot common discrepancies.