storage live load

huangyhg

storage live load
how is a "storage" room on an office building architectural plan usually loaded for design purposes?  table 4-1 in asce 7-02 requires 20 psf for "storage above ceilings" and "uninhabitable attics with storage" in residential dwellings.  it also requires 125 psf for "light storage warehouses", and table c4-1 suggests 80 psf for "nonresidential attic storage".  my kneejerk reaction in the past has been to use 125.  does anyone else do the same, or use higher or lower?
is this a steel-framed structure? if there was any chance at all that the floor space were to be occupied by doctors or lawyers, i would be using 125 psf to be safe for the possibility of large amounts of file storge.
we have several times had to go into steel-framed offices buildings (designed by us, as well as by others) to reinforce floors above the original 100 psf office + partitions + some-extra-just-in-case design load.  these have been for things like fireproof filing cabinets and tall rolling file storage systems.  
if it designated "storage", i would go for at least 125 in that area, and maybe more.  frequently it doesn't start out as storage, but by the time the third or fourth tenant moves into the same space, things get moved around, and what was once open office is now the new storage area.  hence the "some-extra-just-in-case" design load, which sometiimes is enough to take care of the problem, and lets us tell the building owner "oh, no problem, we figured on something like this from the start," which lets us be the heroes, if only for a minute!
paper stacked tight weighs about the same as water.  i use this analogy to help clients visualize the weight of (just some file drawers".
this can be a confusing issue for structural engineers.  the 125 is what should normally be used in "office" type environments where a storage closet, or room, is designated on the initial architectural design documents.
the problem is, of course, that the designated room may move someday and a file cabinet area may appear in what would normally have been a cubicle city area.
we usually try to pin down the storage areas initially, making sure that the owner isn't intending on using dense file storage cabinets (200 to 300 psf).  
also, the floor system (say a deck and concrete floor) can and is usually designed to accept higher loads - look in some of the sdi tables and you will generally see numbers in the 100 to 400 psf range.  if your deck can take locally high pressures, say from a group of heavy file cabinets, the overall joist or beam system can usually accept these smaller, high-load areas without overcoming the beam/joist capacities.
the problems come when a few years later the occupant puts in a library of high-stack books, an mri unit, a dense file cabinet, or simply loads up a room with boxes of paper.  that's when the strengthening is required.
250 psf storage, i believe, is intended for those higher stacked warehouse floors, not for 12' floor-to-floor situations in office buildings.
we use:
- 3.0kpa for general office use (~ 63psf)
- 2.4kpa per meter of useable height for general storage (~ 15.3psf per foot of useable height)
- 4.0kpa per meter of useable height for stationary and packed-book storage (~ 26psf per foot of useable height)
- 4.0kpa per meter of useable height, but not less than 10.0kpa, for compactus-style file storage (~ 26psf per foot of useable height, but not less than 209psf)