Etabs Mass Summary: By Story Better
aggregates all structural and non-structural loads—including dead loads and specified live load reductions—into a single value per level. This allows an engineer to immediately identify mass irregularities
) matches perfectly. This happens because the Center of Mass and Rigidity tables only account for mass successfully lumped to nodes associated with an assigned diaphragm. Utilizing the story mass summary allows you to catch these unlumped lateral masses before they distort your seismic force allocations. 3. Provides Exact Inputs for Code-Based Lateral Forces
I can provide targeted troubleshooting steps for your exact situation. Share public link
ETABS calculates story mass based on the objects assigned to that specific level and its associated diaphragms. The story summary perfectly aligns with how lateral seismic forces (like the Equivalent Lateral Force procedure) are applied in practice—floor by floor. Key Data Fields Explained
| Story | UTotal (ton-s²/m) | RTotal (ton-s²-m) | Verification Check | |-------|------------------|-------------------|--------------------| | Roof | 125.4 | 8,420 | ✅ Cladding + roof live 20% | | 5 | 210.2 | 12,150 | ✅ Partition added | | 4 | 210.5 | 12,140 | ✅ Uniform | | 3 | 210.3 | 12,160 | ✅ Uniform | | 2 | 211.0 | 12,170 | ✅ Slight increase from stair infill | | Base | 0.0 | 0.0 | ✅ No mass at fixity | etabs mass summary by story better
Mass should generally decrease as you move up the building. The roof level is typically lighter than typical floors because it carries lower live loads and lacks rising vertical elements like columns or shear walls.
Compare total calculated mass against initial estimates in seconds. 2. Seamless Integration of Mass Sources
In ETABS, the table is a critical output for verifying your building's seismic weight and ensuring your Mass Source is defined correctly. It provides a lumped mass per level, which is more intuitive for global checks than viewing individual joint or element masses. How to Access the Table
You reach the roof. Here stands a tiny, lightweight acrobat. Utilizing the story mass summary allows you to
Seismic lateral forces are directly proportional to a structure's mass (
With a correctly defined Mass Source, the Mass Summary by Story table shows the total mass assigned to each floor. Here's how to interpret some key components and common challenges:
To locate the data after running an analysis, follow this simple path in the software menu: Go to on the top menu bar. Select Show Tables . Expand the Analysis Results folder. Expand Structure Results .
Ensure floor finish/partition loads are applied to the correct shells. Conclusion Share public link ETABS calculates story mass based
Only captures mass associated with nodes assigned to a specific diaphragm. Best Used For
When reviewing the Mass Summary by Story , you will see the following key data points: Floor level identification. UX/UY: Total mass in the X and Y directions. RZ: Rotational mass moment of inertia around the Z-axis.
: For seismic mass, it is common practice to include of Dead Load and a percentage (e.g.,