Mass Summary By Story | Etabs

. In a seismic event, the ground acceleration acts upon this mass to generate inertial forces

To ensure your model is accurate, follow this standard verification workflow using the table data: Step 1: Hand Calculation Comparison

: By default, ETABS lumps mass at story levels by taking half the weight from the story above and half from the story below. You can explicitly enable "Lump Lateral Mass at Story Levels" in the Mass Source definition to simplify the model into a multiple degree-of-freedom system. etabs mass summary by story

This is the rotational mass (polar moment of inertia) about each axis.

The coordinates of the Center of Mass for that specific story. This is the rotational mass (polar moment of

). If your Mass Summary shows significantly lower values than your manual "take-off" calculations, your seismic base shear ( ) will be underestimated, leading to an unsafe design. 2. Identifying Modeling Errors

The "Mass Summary by Story" table is more than just a data output; it is a vital diagnostic and design tool. By understanding how to define your mass source, where to find the table, and how to interpret its data, you can ensure your seismic loads are applied correctly, your building's dynamic properties are accurately captured, and your design is compliant with relevant codes. Checking this data should be a standard step in the quality assurance process of every ETABS project. If your Mass Summary shows significantly lower values

| Story | UX (mass) | UY (mass) | UZ (mass) | |-------|-----------|-----------|-----------| | Story4 | 86,425 kg | 86,425 kg | 86,425 kg | | Story3 | 138,283 kg | 138,283 kg | 138,283 kg | | Story2 | 138,283 kg | 138,283 kg | 138,283 kg | | Story1 | 138,283 kg | 138,283 kg | 138,283 kg | | Base | 15,858 kg | 15,858 kg | 15,858 kg |

You control this via: .

Occasionally, loads are applied to elements that are not properly connected to the diaphragm (e.g., a beam modeled without a support connection or a slab not meshed with walls).