gymnasium running track deflections

huangyhg

gymnasium & running track deflections
hello,
i've got a 120'x108' gymnasium. the roof joists span 108'. there is also a 10' wide running track on the inside perimeter of the gym hung from the joists every 21'-8" to 24'. the joists are spaced at 12'o.c., with each end where the track is parallel with the joists, the joists are spaced to match up with track below.
when the joist is parallel with the track, the track is hung from an individual (or double) joist(s) at 4 equally spaced points along the joist. when the track is perpendicular to the joist, the support is about 10' in from the building's perimeter.
not having run dealt with this situation before, i think my primary concern is deflection of the track, especially where the joist and track are parallel as the track will be influenced by the full deflection of the joist.
so, my thought is that i should determine what amount of movement i will allow in the track due to live loads, then translate that in to an allowable deflection for my joist. i was originally thinking of about 1/2 inch in the track, equating to about l/2160 in the joist which seems a bit extreme for a 108' joist. is this general approach valid? is 1/2 live load deflection too conservative?
i'll be happy supply additional details, though right now i'm thinking about this problem in more general terms. my thinking goes that if i determine a realistic deflection for the track, the question of joist layout will solve itself.
thanks,
erik
i've designed a number of buildings as you've described.  i double up the joists where the track runs parallel with the joists and hang the track from each joist where the track is perpendicular.  i support the track at approximately 10' on center in both directions (12' shouldn't be that much difference).  the 10' on center allows me a place to connect a continuous handrail around the track at each hanger location.  i've never had a problem with excessive track deflection or roof deflection.  it sounds to me like you are on the right track.
i just look at it seperately.  start with the running track with live load/total load deflection you need.  then you will have a point load at the roof joist consisting dead and floor live load.   then design the joist/beam with that point load+roof dead and live load.
few points to ponder:
1. i like to caution you to check the vibrations from human impact due to running. sji does not require you to check vibrations on roof joists while they require it for floor joists!
2. the deflection at the track will be calmative. you will need to add he track deflection to the joist deflection!
3. i read that the joists will be spaced 12 foot on center! or is that only spacing for rood joists that will support the track? if the roof joists will be spaced at 12 foot on center, you need to select proper deck.
regards,
lutfi
lutfi - you read correctly, joists are at 12'oc. i'll be using 3", 18 gage deck. per your other comment, the cumulative deflection is what concerns me - a small deflection for the joist is not small for the running track.
ahh.. now i kinda understand it now.  you only have to add the live load deflection of the roof to the track right?  
coengineer - yeah, actually 42psf snow, but that's correct. live load on the track will cause some deflection, and snow load on the roof will cause some deflection.
two years ago i was involved in the evaluation of an existing structure similar to yours. here are general background documents that i found useful:
modern steel construction, march 2001
i just finished the design of a building similar to yours.  i did a vibration analysis of the channel at the edge of the track, as well as the steel beams i put in the roof to hang the track from.  if you do a vibration analysis, you may find that you need stiffer   
have you considered designing the running track with a camber? from a visual standpoint, a camber is more desirable than an excessive deflection.
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