deck vs. balcony live loads

huangyhg

deck vs. balcony live loads
after all the confusion about definition of "deck" versus "balcony" that endured for years under the ubc codes, the ibc supposedly cleared this up. this relates to residential and multi-family construction.
looking at 2003 ibc table 1607.1 (2000 ibc is similar),an exterior balcony gets a live load of 100 psf, with the exception of one or two-family residences only, not exceeding 100 sq. ft., you may use a live load of 60 psf.
i would think the opposite would make sense: a smaller balcony would have more of a chance to be crowded with people. therefore, why isn't the live load 100 psf for 100 sq. ft or less, and 60 psf for greater than 100 sq.ft.?
now, to make matters more confusing, read the definition of "deck" versus "balcony" - it states that "deck" is supported  on at least 2 opposing sides, i.e., it is not a cantilever affair. now the since the code seems to consider this more "fail-safe", it allows live load same as occupancy served (40 psf for residential/multifamily). now isn't 40 psf unconservative? i would think it should be at least 60 psf, especially for a small deck. you could easily have a party with many people on that deck. just because it isn't cantilevered, why allow the individual joists or edge beam more of a chance to fail?
to put things in perspective, we did a load study (measured area on floor of people standing close as possible). assuming everyone told the truth about their weight, it came to about 73 psf.
we found another distiction between a deck and a balcony. that being, a balcony has a roof covering it. a deck doesn't. so why should the roof induce a larger load on the balcony?
perhaps it's got something to do with snow. or with people rushing to the nearest convenient place of shelter in a downpour.
also, if you consider the decks serve only a basic single family dwelling, and a balcony serving multiple tenants, in that case, the balcony would require the higher live load since it's serves as a collector exit route. at least this seemed to make sense to me.
alohabob,
the concept of balcony serving multiple tenants in an apartment structure, as a collector exit route, falls under the classification of "stairs, corridors, and exit balconies", with a live load of 100 psf. that makes sense. my op describes what doesn't make sense (at least to me).  
sacrebleu....you make some good points. this is a great example of "engineering judgement". this is why someone cant just read the code or plug numbers into a program and be an "engineer". i have no problem using loads larger than the code if i feel they are applicable to the situation.
factor in the idiot load coef. for balcony. check out the collapse of the balcony in chicago a couple years ago. i don't have a link, sorry.