As you build upward, the people get lighter.
Accurate mass calculation is the foundation of reliable seismic and dynamic analysis. In ETABS, structural engineers often grapple with different ways to verify the mass of a building. While checking individual element masses or global totals works, leveraging the table is a vastly superior workflow.
Extracting the mass summary data in ETABS is a straightforward process. Follow these steps after running your structural analysis:
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. etabs mass summary by story better
Explore the CSI Knowledge Base for detailed FAQs on mass application. Mass Source
The table acts as a foolproof internal audit. It presents the net integrated mass that ETABS actually utilizes during the modal analysis execution. What you see in the story summary is exactly what the solver runs, eliminating any mismatch between spreadsheet math and software math. Summary of Comparison Feature / Metric Mass Summary by Story Element Mass Joint by Joint Data Volume Low (One row per floor) Extreme (Tens of thousands of rows) Processing Speed Instantaneous Slow (Prone to Excel freezing) Center of Mass Data Built-in and calculated Must be manually calculated Audit Readiness High (Ready for calculation reports) Low (Requires heavy filtering) Risk of Human Error High (Due to manual sorting) Conclusion: Work Smarter, Not Harder
Diving straight into complex modal shapes or element stresses without verifying global model properties is a recipe for structural design errors. Utilizing the table provides a faster, clearer, and more holistic method to audit your structural model. By making this table your first stop after running an analysis, you ensure your lateral designs are built on accurate, code-compliant foundations. As you build upward, the people get lighter
A common pain point in structural modeling is when your report displays less mass than your manual calculations, even when your total vertical load ( Fzcap F sub z
For Modal Analysis, the distribution of mass per story dictates the mode shapes and natural periods of the structure. Using story-based summaries allows engineers to easily calculate the for each level. This is critical for identifying whether the structure is prone to torsional irregularities. By viewing mass through the lens of individual stories, engineers can better understand how specific levels contribute to the overall dynamic response, leading to more targeted optimizations in stiffening or softening the frame. Conclusion
If your definition includes both Element Self-Mass and a dead load pattern that already contains the self-weight multiplier (set to 1), ETABS will double-count the structural weight. A quick glance at the Story Mass Summary will reveal floor weights that are roughly twice what your hand calculations estimate. Unassigned Diaphragm Omissions While checking individual element masses or global totals
Only captures mass associated with nodes assigned to a specific diaphragm. Best Used For
The primary benefit of the Story Mass Summary is its role in "Mass calculated manual" verification. By breaking down the weight floor-by-floor, you can easily compare ETABS’ output against manual calculations for: