[patched] | Etabs Mass Summary By Story

Understanding the ETABS Mass Summary by Story In structural engineering, the Mass Summary by Story

Conclusion

Story Identification: This includes the name or number of each story (e.g., Story 1, Story 2, etc.). etabs mass summary by story

  1. Uniform distribution: U1 and U2 are nearly equal (good for symmetrical building).
  2. Reduced roof mass: Roof has no imposed live load and lighter finishes. This is correct.
  3. Higher first story: Story1 has slightly more mass due to shorter columns and heavier spandrel beams. Realistic.
  4. Non-zero base: The base should be ZERO. If the base has mass, you forgot to assign supports as fixed or you modeled soil springs incorrectly. This would cause unrealistic base sliding.

Summary Table: The direct export from the Display > Show Tables > Structure Output > Other Output Items > Mass Summary by Story. Understanding the ETABS Mass Summary by Story In

Common Pitfalls & How to Fix Them

Pitfall 1: Overlooking the Mass Source Definition

Many users assume ETABS uses the same load combinations for mass. It does not. By default, ETABS uses Dead Load (1.0) and Live Load (0.0). For seismic design, you must define a proper mass source via: Define > Mass Source > Add New Mass Source. Uniform distribution: U1 and U2 are nearly equal

  1. Mass of columns is split between the story above and below (half to each).
  2. Mass of walls is distributed based on height centroid.
  3. Floor area loads (DL/LL) are automatically lumped.

2.2 Mass Source Definition

Engineers must define a Mass Source via Define > Mass Source: