ETABS: Automatic Live Load Reduction 1

[StructuralAddict]

Hi All,

I am modeling a sample project to understand how ETABS reduces the live load automatically.

I modeled the 10-storey building shown in the attached file by defining the live load pattern one time as (Live) and the other time as (Reducible Live) from "Define --> Load Patterns..."

I also chose the Canadian Building Code (NBCC2010) from "Design --> Live Load Reduction Factors... --> Tributary Area (Based on Design Code)".

I assumed that the live load on the slabs is 2.873 kPa and the span between each two adjacent columns is 6.0 m. Dead load is not considered in the analysis (Self-weight multiplier = 0).

Surprisingly, the results for both cases (live and reducible live) are the same! This means that ETABS did not reduce the live load as it should do.

Can anyone please help me with this issue? What should I do to let ETABS consider the live load reduction?

Thanks in advance!

Monir

 

[MrHershey]

ETABS does not reduce live load until you run a design. If you're just looking at plain analysis results, your live load reduction won't be in there yet.

If you're looking at tables, the table that would have live load reduction incorporated is Tables>Design>Design Forces. It will also only give you results for load combinations that are designated for design, not individual load cases.

 

[StructuralAddict]

Thank you MrHershey, you are right! I checked the design forces and they were reduced as expected. I made a quick comparison between ETABS results and manual calculations for the reduction factor:

Reduction Factors (ETABS):
Story 10: 0.832
Story 9: 0.683
Story 8: 0.613
Story 7: 0.571
Story 6: 0.542
Story 5: 0.520
Story 4: 0.503
Story 3: 0.488
Story 2: 0.476
Story 1: 0.466

Reduction Factors (Manual Calculations):
Story 10: 0.822
Story 9: 0.669
Story 8: 0.601
Story 7: 0.561
Story 6: 0.533
Story 5: 0.513
Story 4: 0.497
Story 3: 0.484
Story 2: 0.474
Story 1: 0.465