2nd Floor Lobby Live Load

[jdgengineer]

We are working on a small tenant improvement on an existing two-story office building which consists of infilling a small two-story element to allow for additional floor area at the 2nd floor.

The architect has this space labeled as "2nd Floor Lobby". In this area we are widening the space at the top of the stairs from 8' to 16' wide (it is 45' long). The usage of the building is office space.
What would the appropriate live load be for this space? 80 PSF for "Corridors above first floor", or 100 PSF for "Lobbies and First-Floor Corridors". The existing framing can work for the 80 PSF but not for the 100 PSF. The original 2nd floor framing was designed for 80 PSF.

 

[dik]

I'd probably use 100 psf LL, but some jurisdictions may allow 60 psf... I think as a lobby, it could be used for assembly, hence the 100 psf.

Dik

 

[hokie66]

Have the architect change the label to "waiting room".

 

[dik]

Good point hokie if you want to maybe reduce loading.

Dik

 

[KootK]

Yeah, if it's the costly choice between doing nothing at 80 and something at 100, I'd seek out every reasonable way to justify 80.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[tempeng]

Limey Question: Do your codes allow for a reasonable live load reduction? It's a gamble saying that the probability that both floors will be fully loaded at any one time is low but if it appears in the relevant codes, it's at least justifiable.

 

[Archie264]

jdgengineer,

If there's no other way and you wind up having to make your case to the building official here's some back up data, in case it's of use. It was generously provided by AELLC on the following thread: link

It's an article by Russle S. Fling, who was a practicing engineer, President of ACI and author of a concrete textbook. The following is a quote from it:

Live loads specified by building codes are usually higher than expected in actual service, but not always. Consider the school classroom where everyone rushes to the window to see the passing parade. Actual loading could easily be double the specified live load. On the other hand, I have yes to see a places of assembly loaded to the 100 psf normally specified. It is usually in the range of 3 psf to 8 psf, but occasionally may reach as high as 20 to 25 psf.