Finally, a practical hallmark of a better engineer: unit discipline. The Mass Summary typically reports in kg-s^2/m (metric) or kip-s^2/in (imperial). This is mass, not weight. To get weight (force) for base shear: $$Weight = Mass \times g$$

Before issuing a report, convert these summary values into kips or kN for the client or reviewer. Presenting mass in force units prevents confusion and demonstrates technical maturity.

For underground structures or tanks, the mass of water and soil is significant. Assign these via Additional Mass or as a special load case with a multiplier of 1.0 in the mass source. Do not rely on DEAD for these.

A concise guide on generating and interpreting mass summaries by story in ETABS, useful for structural engineers performing seismic and dynamic analysis.

The Mass Summary by Story report in ETABS is a detailed analysis that presents the mass distribution of a building across its various stories. This report includes several key components:

The default ETABS Mass Summary by Story is a starting point, not a finish line. A better mass summary is one that:

By taking 10 minutes to define a proper mass source, adjust story definitions, and validate with base reactions, you transform a confusing default output into a reliable engineering tool. Your plan checkers—and your building’s safety—will thank you.

Next Step: Open ETABS right now, go to Define > Mass Source, and verify your multipliers. You may be surprised at what you find.

Need a template? Download our free "Better ETABS Mass Summary Excel Checker" (link below)

Have a specific mass summary bug? Describe your model in the comments.

Here’s a professional, engaging post you can use on LinkedIn, a blog, or an engineering forum like Eng-Tips.

Title: Stop Guessing: How to Actually Use the ETABS Mass Summary by Story

Post:

We’ve all been there. You run an ETABS model, check the modal participating mass ratio… and something’s off. The period doesn’t match your hand calcs. The base shear feels wrong.

The culprit? The Mass Summary by Story.

Many engineers just glance at the total mass and move on. But if you want a better, more reliable dynamic analysis, you need to read this table like a detective.

Here’s how to master the ETABS Mass Summary:

1️⃣ Understand what “Mass” ETABS is actually using

2️⃣ Check the distribution, not just the total

3️⃣ Compare UX, UY, and RZ mass values

4️⃣ Use the story mass to validate your center of mass (CM)

Pro tip:
Run Display > Show Mass Summary and toggle “Show as Table”. Then click “Export to Excel.” Plot story mass vs. height. Any anomalies will jump out visually.

Better ETABS mass summary = Better seismic design. Period.

Save this post for your next model check. ✅

#ETABS #StructuralEngineering #SeismicDesign #Dynamics #StructuralAnalysis #CSIsoftware

Understanding ETABS Mass Summary by Story: A Comprehensive Guide

When working with ETABS, a powerful software for structural analysis and design, understanding the mass distribution of a building is crucial for ensuring its stability and performance under various loads, including seismic and wind loads. The Mass Summary by Story report in ETABS provides engineers with essential data to assess how mass is distributed across different stories of a building. In this post, we'll delve into the significance of the ETABS Mass Summary by Story, how to interpret it, and why it's vital for structural engineering projects.

Before you submit your next seismic design, verify these items: