very concerned - i may have underestimated load

huangyhg

very concerned - i may have underestimated load
i was designing a second story floor of a two story wood frame building for the intended use as a conference room (2 offices on first floor).  building is quite small, 12' wide by 21' long. i used no. 2 so. pine 2x10 joists at 16" oc, span = 12' and my ll was 80 psf.  i'm quite concerned that maybe this should have been 100 psf.  sbc is not very clear for office buildings and i'm beginning to wonder if i was wrong.  i used the loading for corridors above first floor under office buildings in the sbc.  should this have been equivalent to a public room in a hotel, 100 psf?  anticipated number of people in the room is 12-15.  the floor has already been built.  
  if it is going to be used as a conference room, my first thought would have been to use the assembly area with movable seats of 100psf.
  now that it is already constructed.
for 100psf you have to have people packed together, standing right beside each other. 80psf is still over 100 people standing in this size room. document you were notified the expected occupancy of 12-15 people for this room.
the places that worry me are balconies. i'll go above the 100psf for these. this is from personal experience of college, not just because one collapsed the other day. i certainly wouldn't use 60psf as in sbc.
thanks.  i too thought about the assembly area with moveable seats, but thought that it did not apply.  in the future, i will definitely opt for 100 psf, just to make sure.  
i am confused, if the space to be used as an office, asce 7 requires a live load of 50 psf for offices and 80 psf for corridors. use of asce is permissible in the sbc. refer to the start of chapter 16 of sbc. i have not used the code in a while but i would be surprised if this has changes.
i disagree with you regarding the sbc not being clear as far as the office floor loading. use the classification for the entire building, which is, in this case is office building. i would use heavier loading for storage rooms, or computer rooms to name a few.
what is the problem? do you think you should have used a loading of 100 psf for assembly space? it seems to me that you over designed the floor ll load by 30 psf unless you have undersized the floor joists. am i missing something?
now to make you feel better follow my calculations:
floor area = 12鈥橷21鈥?252 ft^2
assume a person will occupy an area of 2鈥?by 2鈥?=> 4 ft^2 per person
total number of people that can stand shoulder to shoulder = 252/4 = 63 people
assume average person weighs 200 pounds
total weight = 63x200=12600 pounds
convert this to a uniform load = 12600/252=50 psf
you can go to sleep now.
good luck.
  if there was a room in an office building that i was labeled as conference or assembly i would not just go directly by the standard office loading. i worked for a large company once and when we had meetings in the conference room it would get really packed.  as much as a corridor during our fire drills. "everybody try to get in here so you can hear".
   i don't think the 80psf is overkill (maybe in this particular case it is), but hey, that's just me. maybe if you go directly by the standard office you will be covered if something gives.
ctw,
the asce 7 shows 4 subcategories for office buildings:
   file and computer rooms    load based on equipment weight
   lobbies and first floor corridors     100 psf
   offices                                50 psf
   corridors above first floor            80 psf
i would consider conferences rooms as offices and design it for 50 psf.   normally a conference room has a big table and to the most 2 rows of chairs around the table.  a office space has at least a table, several file cabinets (very heavy stuff), a couple of chairs, and not much open space.  the maximum number of people in an office space is not posted.   the load in the conference room will be lighter than any office area unless it is used as storage area.
as lufti said if the conference room is packed with people the average load is still 50 psf.
i thought you had to use at least an additional 20 for partition (whether they are shown or not) for any part of an office building? what if the conference room is eliminated in the future?  
guys,
i did not mean to spark up a debate. all i was trying to say that i would consider a conference room located within an office building as an office space unless someone would tell me about some unique and unusual requirements.
at face value, i do not see this design requiring additional load. of course we are no informed about the full circumstances and uses. as dlew said, less space would be occupied if table space is needed and less people would be in if chairs were to be used. i have checked the mil-hbk for office floor loadings and i found it to be in concert with the asce 7.
if the engineer of record wants to classify, for his comfort, the second floor as an assembly space/building that would be fine. in florida these types of structural classifications imply that they may hold 300 people or more which makes them threshold buildings. threshold building status will trigger many special requirements for life safety, inspection, fire protection etc.
i would read the code鈥檚 definition of assembly occupancy and go from there. my initial read of assembly is theaters, churches, public gathering arenas.
having this said and done, i still would design that room for 50 psf. structural engineers these days are faced with the vibration problem because most offices are gone paperless. hence they see less live loads than what they are designed for.
as one of my college instructors used to say, 鈥淯se your engineering judgement鈥?br>
  judgement or not, if you're going to meet code i still think you have to design it for 70 psf. i don't see anything that allows you to forgo the additional 20 because it's called a conference room. it could be a project storage room in 10 years. i don't know how sbc reads on this but 1607.5 of ibc seems to be pretty clear.
i'm not a 100% sure but if i'm wrong on this i would like to know it for my own future reference. what other rooms can i omit the 20 psf partition load?
haynewp,
i agree with you that the provision of 20 psf for partitions should be included in addition to the 50 psf live load (per asce 7).     
partition load must be included. all codes and common sense requires it. i would include it as part of the dead load (although it does not make any difference except for concrete design or steel lrfd design). sbc requires that actual load be used for partitions if the quantity and location are known. if not, it requires 20 psf. the point i was discussing is the 50-psf live load. i think the 80 psf live load is adequate if it included the 20 psf.
now i want to argue the engineering judgment for this particular room. the foot print is 12'x21'. i want all reasonable engineers in hereto tell me how many partitions is it going to take to accommodate the 20 psf. see this is where i think the code does not make sense and i still maintain that the engineer should be entitled to exercise his engineering judgment.
i think this question provoked a healthy debate and exchange of ideas.
good night