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Re: office live load

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Jeff, I ran into a similar concern 2 years ago, in a new building's office
occupancy over an irregular arrangement of ground story bearing lines. While
the upstairs occupancy used fixed non-bearing and bearing walls, prospective
TI work meant that exit routes and corridors might relocate. My occupancy
load was 30; the two exit stairs were at opposite corners of a square-shaped
plan.

The rationale tendered to (and accepted by) the plan reviewers, a small but
highly regarded (and committee-active) independent SE firm here, was that an
exit corridor could occur most anywhere, but not everywhere simultaneously.
All 30 people could accumulate enroute to either exit, but not toward the
two corners that had no exit, or into other dead ends.

Further, the plan extent of fully loaded exit corridor was inherently
limited by the occupant load itself: 30 persons at 200 lbs each is 6000 lbs;
that much load at 100 psf is 60 sq ft, an extent of corridor 4ft wide by 15
ft long. 

Joists anywhere near either exit were made good for any forseeable
configuration of exit corridor, but beams, girders, and columns were not
necessarily subject to 100 psf LL on their whole tributaries. When everyone
was crowding into an exit corridor, they were not all elsewhere at the same
time. Joists in remote corners that were enroute to no exit could not
conveniently be made good for 100 psf LL, and weren't. I placed in the calcs
a plan showing what portions were fit for exit load should TI remodeling occur.

The conference room issue didn't arise, but I would argue that such rooms
are inherent in office occupancies; such usage could occur in most any
office room from time to time, and thus is included in the standard code
office LL figure. Further, a room containing a conference isn't at the same
time barricaded with 20 psf-type partitions running through it. 

Hope some of these ideas may help.

Charles O. Greenlaw, SE    Sacramento CA
---------------------------------------------
At 09:10 AM 12/2/99 -0800, you wrote:
>I just got plan check comments back for a tenant improvement and seismic
>upgrade. The upper (second) floor is about 5000 sf of single tenant open
>plan, no corridors. There are exit stairs at each end. Like most new high
>tech offices it is crammed with desk work stations with very little actual
>open floor space. The occupant load is around 60. The plan checker told me
>that I need to design the entire floor level for 100 psf because it has no
>designated "Exit Facilities" and the occupant load is greater than 10. The
>office conference rooms require 100psf as well. They accept using 80psf live
>plus 20psf partition =100psf.
>
>Fortunately, this is not double, I used 50LL plus 20psf partition. I can
>understand the plan checkers point, but it seems physically impossible to
>get 100 psf live load in our project, so it seems a bit severe. The plan
>checker said that signage or bolted down furniture was an unacceptable
>alternative to a blanket 100 psf, since it is not enforceable. Am I the only
>one that has ever made this mistake?
>
>Is an exit facility a place of public assembly, i.e. can you use a live load
>reduction factor (I would think that might be skirting the intent of the
>100psf exit load)
>
>Any comments?
>
>Jeff Smith