Etabs Mass Summary By Story: Fixed

The distribution of mass across stories directly dictates mode shapes and periods. A top-heavy model will produce longer periods and higher overturning moments. By reviewing the summary, you can quickly spot if a penthouse or water tank mass was accidentally omitted.

Expected $5 \times 600 = 3000 \text kN$. Error = 0.07% → Acceptable. etabs mass summary by story

Building codes (ASCE 7, IBC, Eurocode 8, IS 1893) require the seismic weight (W) to calculate the base shear ( V = Cs * W ). If your Mass Summary shows an inconsistent total weight—say, you forgot to include partition loads or a heavy mechanical unit on the roof—your seismic forces will be dangerously wrong. The distribution of mass across stories directly dictates

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. Expected $5 \times 600 = 3000 \text kN$

If you are just getting started with these summaries, you can find introductory structural analysis tutorials on YouTube to walk through the basic table generation. Mass Source