Etabs Mass Summary By Story Better -

Roof mass is 39% higher than typical floor due to penthouse and water tank weight being mis-assigned. Better ETABS Output (after our steps): | Story | Mass DL | Mass 0.25LL | Total Mass | Seismic Weight (W) | Cumulative W | |-------|---------|-------------|------------|--------------------|---------------| | Roof | 850 | 50 | 900 | 8820 kN | 8820 kN | | PH | 300 | 10 | 310 | 3038 kN | 11858 kN | | 5 | 890 | 60 | 950 | 9310 kN | 21168 kN |

Why is the mass in my penthouse higher than the roof? Why is the mass contribution from diaphragms different from my dead load takeoff? Why does the seismic weight not match my hand calculations? etabs mass summary by story better

Have a specific mass summary bug? Describe your model in the comments. Roof mass is 39% higher than typical floor

The default ETABS Mass Summary by Story is often misunderstood. To make it —meaning more accurate, transparent, and useful for seismic design (ASCE 7, UBC 97, or IS 1893)—you need to move beyond the default settings. Why does the seismic weight not match my hand calculations

Open ETABS right now, go to Define > Mass Source , and verify your multipliers. You may be surprised at what you find. Need a template? Download our free "Better ETABS Mass Summary Excel Checker" (link below)

If you have ever run a seismic analysis in ETABS, you have likely stared at the Mass Summary by Story table. It appears innocent enough: a simple spreadsheet showing mass, weight, and lateral stiffness. But for experienced structural engineers, the default output often raises more questions than it answers.