best roof system on a loadbearing cmu building when stuff ge

huangyhg

best roof system on a loadbearing cmu building when stuff ge
hi everyone,
i am trying to see what is practical engineering. i have a one story cmu  building (loadbearing walls) which i been told that there is going to be pipes and hvac units and electrical trays hung from ceiling and the location of them at this point is not determined. my question is is it better i use wide flange beams to cover the roof or bar joists are better? then for design of beams or joists how do i apply the pipe loads when i don't know where they are getting hung?
please if anyone knows a book or paper has an example or have talked about it please let me know. any simple calculations that deals with this issue would be greatly appreciated. i also appreciate if you draw a sketch so i can see what you are explaining.
but please don't forget the main question that is for the cases that you are told that the ceiling is getting used to hang stuff which system ( w shapes v.s. joists) would be better? or if these two system gets used equally?
thanks.
bfstr  
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it depends.....
if the owner/architect wants wide, open, long span bays, i would use open web lh joists with a uniform allowance for piping, cable tray, etc. allowance, plus special joists to support the hvac units. if there are monorails, cranes, misc. equipment, etc. hung from the roof, then i probably would use wf beams on shorter spans.
someone will have to furnish you a rough idea of how much piping and cable tray there will be before committing to using joists.
i would stay away from joists.  every time you hang something (unless it's at a panel point), you've got to add an angle.  if you make a mistake with your loading (for instance if they want to hang more pipes than expected off one joist), it's very difficult to get information on the joist design, much less reinforce it.
and if someone wants to change the function of the building, it's much easier with wide flange sections than joists.  take a look on how many posts above are asking questions about capacity or types of joists.  with a wide flange, you can take field measurements and determine the beam size and recalculate the capacity.
i agree - wide flanges.
mike mccann
mmc engineering
thank you all for your responses. but the other question was howmuch and where do i apply the pipe loads when i don't know where they will get hung? also i don't know if they are parallel or perpendicular? any suggestion? any where code has addressed this? anyone has been asked same thing?
thanks
bfstr
that depends on the pipe size and what they're filled with.  if they're 3" pipes filled with water, for example, figure that all the pipes will be filled with water, find the weight per linear foot (or look it up).  design your beams with two worst case scenarios- the a pipe being hung parallel to your beams, supported by only one beam, and a pipe running perpendicular to all your beams at their midspans.