gymnasium & running track deflections
gymnasium & running track deflections
(OP)
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 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






RE: gymnasium & running track deflections
RE: gymnasium & running track deflections
RE: gymnasium & running track deflections
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
RE: gymnasium & running track deflections
RE: gymnasium & running track deflections
RE: gymnasium & running track deflections
RE: gymnasium & running track deflections
Modern Steel Construction, March 2001
http://www
MSC, September 2001
http://www
MSC, April 2003
http://
MSC, April 2004
http://ww
Institute for Research in Construction
http://irc.nrc-cnrc.gc.ca/pubs/ctus/ctu22e.pdf
and AISC Design Guide 11
www.SlideRuleEra.net
RE: gymnasium & running track deflections
DaveAtkins
RE: gymnasium & running track deflections
RE: gymnasium & running track deflections
About the vibration issues: I've dealt with alot of vibration issues, and enjoy keeping up to date on the procedures. Whatever you do, make sure you are using a walking/runing resonance analysis method. SlideRuleEra's suggestion of AISC's Guide 11 is bang on. It is THE reference for your situation, and has easy to follow design examples in both Imperial and proper metric units (sorry guys, couldn't resist!).
You will be designing against an acceleration limit, and I suspect that DaveAtkins is right, but only being too mild. I would hazard a guess that you absolutely will have to stiffen your system to a much greater extent than that required for deflection criteria. A good primer for vibration issues is Dr. David Allen's article: Allen, D.E., Pernica, G., “Control of Floor Vibration”, Institute for Research in Construction – National Research Council of Canada. It's available as a free download. If you can't find it, let me know... I'll either post it for you, or find the link.
ALSO: Do keep in mind that specifying your OWSJ and steelwork should include the resultant requirements with respect to vibration. I worked for a very good structural engineering firm back in Canada that has adopted Guide 11 as a standard on their structural notes for OWSJ load plans. Basically I would say that you should speficially dictate that OWSJs be provided which have been checked against Guide 11, and stipulate your requirements to be met. The Guide will fill in the gaps for you.
Please let me know if you want any help. I love vibration problems, but really appreciate those opportunities to prevent them, rather than spend time trying to get them to go away once they've come up.
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: gymnasium & running track deflections
One other question...considering 2000 IBC loads (table 1607.1), I'm applying 100 psf live load to the running track. The 100psf LL equates to 1400+/- really big persons (250lb) on the track. I realize that with running, impact forces are greater than static loads, being cautious about vibration is important, etc.
For purposes of calculating deflection only (I will design strength for full 100psf), and also realizing that IBC 1607.9 doesn't allow live load reduction for public assembly occupancies, am I going outside the bounds of engineering judgement if I consider a lower live load for purposes of deflection?
Put another way - I don't consider it realistic that the track can be fully loaded, more like 140 people instead of 1400 people, BUT, I can't shake the feeling that I am cheating if I consider such a drastic reduction in live load to deal with my deflection concerns. Any comments would be welcome.
Thanks again,
Erik
RE: gymnasium & running track deflections