Ensure your Dead Load pattern has a self-weight multiplier of 1, so the program automatically includes the weight of beams, columns, and slabs. 5. Exporting for Documentation
ETABS does not automatically know what to include as mass. You must define the .
: Total translational mass active in the X and Y directions.
to compare against your ETABS model.
Understanding ETABS Mass Summary by Story: A Comprehensive Guide etabs mass summary by story
Which (e.g., ASCE 7-22, Eurocode 8) you are designing under?
A typical Mass Summary by Story table will include the following crucial columns:
Finding the table is very straightforward. There are two main ways:
Go to Display > Show Tables > Analysis Results > Structure Output > Story Information > Mass Summary by Story . 2. Key Components of the Mass Table Ensure your Dead Load pattern has a self-weight
For structural engineers, accurately determining the mass of a building is one of the most critical steps in seismic design. In , the Mass Summary by Story table is a crucial output tool used to verify that mass is correctly calculated, distributed, and assigned to the structure's stories.
A common pitfall in ETABS modeling is ensuring that all mass is correctly accounted for, especially for "null" areas (areas not part of a structural slab). If you apply loads to a null area, you explicitly assign a diaphragm to that null area for its mass to be included in the building's seismic mass for modal analysis. Otherwise, the load contributes to reactions but not to the building's mass matrix [7†L31-L34], making the structure seem lighter than it is.
: In standard orthogonal buildings, Ux and Uy should be identical because mass is a scalar property independent of direction. If they differ, it usually means structural properties or constraints vary directionally.
The is an output table in ETABS that aggregates the total calculated mass of your structure on a floor-by-floor basis. You must define the
By mastering the Mass Summary table, you move from simply "running the model" to truly understanding the behavior of your structure.
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.
If the Mass Summary shows Story 1 with only 600 kN, you may have forgotten finishes or a transfer slab. If Story 5 shows 1200 kN (equal to lower floors), your model likely has an incorrect load pattern on the roof—unrealistic for most structures.