live load reduction in RAMSS 4

[Saedhalteh]

Hello all

Is there is a condition where we do not want to reduce the roof live loads or the roof live load is unreducible ?

Also if someone ccan help me understand the Determining number of stories for Live Load reduction option I would really appreciate it, like if could give an example of when we should include or exclude the roof level and the unreduced levels when determining the number of stories for LL reduction

Note: I am using RAM Structural System program

 

[JoshPlumSE]

Take a look at your building code. ASCE 7-2016, for example has a section (4.7.3) which says:

Heavy Live Loads: Live loads that exceed 100 psf shall not be reduced.
EXCEPTION: Live loads for members supporting two or more floors are permitted to be reduced by a maximum of 20%....​

I believe that option in RAM is merely helping you to dictate what constitutes (two or more floors). Does it mean only levels with floor live load? What about floors with unreducible live load, or floors with roof live load? These code provisions require some engineering judgment to interpret. And, your engineering judgment may be different than other users, so they want you to be able to interpret this term however you wish.

 

[rscassar]

Are you using IBC or AS1170. Your last building was AS1170 I thought.

Depends on roof occupancy type. Roof supporting mechanical equipment unreducible. Roof that can be used as a floor like activity likely 40psf reducible minimum. Any concrete roof is likely to have a access hatch as a minimum and should have at least 40psf.

 

[wannabeSE]

Sometimes, engineering judgement dictates that live reduction is not appropriate. Also, if you are using the 2018 IBC, occupiable roofs with assembly areas are not reducible per table 1607.1 footnote m.