R3 mass is extremely small or zero, yet the building has significant floor dimensions. Problem: The mass moment of inertia was not calculated. ETABS needs point masses or distributed masses over an area. Fix: Ensure floor loads are assigned as Uniform to Frame or Uniform to Shell , not as point loads at nodes only. Use area objects for slabs.
On a rainy Tuesday, Maya, a young structural engineer, opened ETABS to check the mass summary of a 12‑story apartment building she’d modeled. The model had been quiet for days, but tonight the mass summary promised answers. etabs mass summary by story
To get a "per story" breakdown in the Analysis tables, you usually need to have diaphragms assigned to your floor shells. If you want to verify the numbers , let me know: The building's total area Your typical dead load (PSF or kN/m²) R3 mass is extremely small or zero, yet