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Elevated running track 1

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WWTEng

WWTEng

Structural
Nov 2, 2011
391
Please see the attached sketch for a description. It’s for a field house, 130’ wide with long span truss/joists. There is going to be an elevated running track all around the field house. The track is 10’ wide and will consist of concrete on metal deck or composite construction, whichever works out better. The track is to be supported by precast wall on one side and is to be hung from the joists on the other end.

The architect has experience designing a similar facility that was built several years ago (I received the existing drawings from the arch). I asked if there have been any problems with the track and he is not aware of any.

I am not sure about this detail. The track is to be connected to a rigid wall on one side and is to be hung from a joist that will deflect on the other end. The fact that the joist will be built with camber and then will deflect differently under live loads makes me somewhat nervous about this arrangement.

The other question I have as in regards to the live load for the track. Is 100 psf (gymnasiums) adequate or should it be higher or include some impact factor?
 
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Good afternoon WWTEng,
Strength should be easy enough to deal with, vibration could be the real challenge. The forcing function from runners and the natural frequency of the long trusses are probably pretty close to being in sync. You'll want to be looking at different configurations for hanger and truss spacings. Even adding some knee braces to the wall (in addition to the hangers) might be a good idea to help cancel the vibration.

regards,
Michel
 
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In the winter I sometimes run on a 6' wide track at the local Y that is built in a very similar fashion to what you describe. This one is supported on the block perimeter walls for the gymnasium and the inner c-channel is hung from the long span joists. The deck is supported by transverse steel beams between the block wall and the c-channel. Very solid feel to it, no discernable vibration, however, I have never seen more than a dozen people on it at a time.

In most scenarios, the trusses/joists will only deflect downwards (snow loads, etc ..). Deflections due to wind uplift will be very short term. Most tracks are cambered in the corners and any additional deflection of the trusses/joists will only marginally increase the camber at these locations, likely not noticeable.

The track overlooks the gymnasium and could easily be used for spectators to an event in the gym, as well as running. I would design for 100psf and then also consult with the truss/joist designer to discuss your questions.
 
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Pretty straight forward design - 100 psf should be more than adequate - BUT I might worry about vibration.
 
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Looks like you can use Design Guide 7 for industrial buildings!!!
 
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Yes, vibration is the main concern here. The key is to have enough mass in the running track slab to minimize this.

I would agree with 100 psf live load for the overall strength.


 
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Thank you all. Well I guess I was overly worried about the connection to the roof joists. However, I think I need to do a couple of things:
1) Put a note on the drawings indicating that they build the track after the gym roof has already been in place so that the dead load deflection doesn't play a factor. Could become a sequencing issue but if I specify it, the contractor should plan accordingly.
2) connection of track beam to haunch: The existing example that I was given shows embed plate at the haunch and the beam is directly welded to it. I am wondering if it would be a good idea to show a bolted connection instead with a 1" compressible filler in between to account for any live load movement at the other end (connected to roof joist).
 
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And of course check for vibration.
 
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1) The truss connection will probably involve some added web elements but providing your truss joist/girder manufacture with a good loading diagrams should get those covered. Also providing the manufacture with your preferred hanger connection would be a good idea. Maybe a gusset plate between the bottom chord angles?

2) An embed plate is probably sufficient and pretty simple to deal with in the field. There's not much restraint. But I don't see any reason to not provide a bridge pad/bearing if you find if preferable.


regards,
Michel
 
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What is happening at the ends of the building where the track is parallel to the trusses?

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
 
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I have done this in a gym with tilt-up concrete wall panels.
We had long span joists, but our span was not as great as yours.
We placed the hangers at every other joist space, mid-way between the joists with a small beam between the joists. This placed the load on each joist which helped reduce the impact of the load on the joists as each joist only supported half the hanger load. We provided loading diagrams to the joist supplier and indicated a maximum live load deflection at the hanger location.
As Woodman 88 indicated, the hard part is the section of track parallel to the joists. We used two W36 beams spaced about 3' apart with small beams between them to support the hangers. With you long span you may need a plate girder, or at least a large smart beam. We chose using a beam at this location in order to have more control over theses members that supported a number of hangers along their full length.
I have run on the track and have never noticed any vibration issues.
 
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Woodman, great question. The track will run parallel to the trusses, so I'll have to hang it from 2 trusses or may be even set of double trusses.
 
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