The total mass accumulated from the top story down to the current story. The value at the base story represents the total seismic mass of the structure. Translational Mass vs. Rotational Mass
Estimated Floor Weight=(Floor Area)×(Average Dead Load per Unit Area)Estimated Floor Weight equals open paren Floor Area close paren cross open paren Average Dead Load per Unit Area close paren
If you'd like to dive deeper into your specific project, tell me: building code you are following (e.g., ASCE 7-22, Eurocode 8). If you need help resolving irregularities (like torsional imbalance). How to export this data for manual base shear calculations.
At its core, the Mass Summary by Story is a tabulated report that calculates and displays the total mass and weight (W) for each floor level of your model. ETABS automatically computes these values based on the assigned dead loads, live loads, superimposed dead loads, and mass source definitions.
Mastering the ETABS Mass Summary by Story: A Step-by-Step Guide for Structural Engineers etabs mass summary by story
You defined mass source from load patterns but forgot to assign any load pattern to the roof diaphragm. Or, you used a rigid diaphragm but the beams are not connected to the diaphragm constraint.
The "Mass Summary by Story" table is used in several critical design steps:
You can access this summary in three ways:
The total translational mass assigned to that story in the X and Y directions. This is calculated as (acceleration due to gravity). The total mass accumulated from the top story
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 (force/acceleration) and distributes it across each floor level. The primary report that controls this behavior is the "Mass Summary by Story."
: The translational mass active in the global X and Y horizontal directions.
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
Elements like structural framing, concrete slabs, and cladding should generally be included at a multiplier. At its core, the Mass Summary by Story
Always do a "back-of-the-envelope" check on a typical floor.
Pick a typical intermediate floor in your building and estimate its weight manually:
The software automatically calculates mass based on structural geometry and material density.