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Hanging Truss across 27' span question

Discussion in 'Scenery, Props, and Rigging' started by variable, Oct 3, 2013.

  1. variable

    variable Member

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    I am trying to put up an electric between two towers 27' apart. I need to hang it 6' above the towers and am looking for advice on the best way to go about it.

    The towers have metal flanges around them, much like I-beam, so I was thinking of attaching 6' long 2" pipes with beam clamps to the towers and clamping 30' of 12" box truss to the pipes. I need to hang 8-10 instruments, probably 2 tree packs, and about 100' of cable from the truss. There is absolutely nowhere in between to support the truss from. I am concerned about the beam clamps holding the pipes securely and wether pipe is the best way to raise the truss the 6' I need it to go. I would appreciate any advice and all suggestions.
  2. kicknargel

    kicknargel Active Member Premium Member

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    Sorry, the internet is not the place to get this kind of advice. You're going to need to hire a pro rigger.
  3. MPowers

    MPowers Well-Known Member

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    Indoors? How are the towers constructed? Are they truss? Got Pix? Budget? Time frame? If indoors what is the building structure? Is this for a one night-er or........?

    For the 27' span, truss is the correct answer. What do your "tree packs" weigh?

    Is there an Event Production company near you that rents truss and equipment? If so, I reccommend you contact them for a consultation or installation.
  4. variable

    variable Member

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    If you says so. I've been putting in installations like this since 1996, I've just never tried to span that big of a gap before, not without a point in the middle. I see no reason why a professional couldn't look for advice on the subject wherever he can find it.
  5. variable

    variable Member

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    Indoors, towers are welded steel, no pix, trying to keep it under $1k, one week install & strike. "Tree packs" are (usually) 4 or 6 channel dimmer packs that hang in the grid. They weigh a few pounds. I really want advice about the beam clamps and if holding that much truss on pipe is viable. I have contacted a local production company, the guys I used to work for, and they think it's fine but I am dubious. Ergo, I posted here to see if anyone had any thoughts.
  6. photoatdv

    photoatdv Active Member

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    Um, 27' is nothing for truss to span. If you've never done a 27' span of truss you are not qualified to rig this project. My current show does well over 40' spans (much larger than 12" truss obviously). Get a pro in there. The pipe bit does sound a bit questionable. Could you not put a truss tower next to the column or on the far side?
  7. Footer

    Footer Senior Team Senior Team Premium Member

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    How would the beam clamp attache to the pipe? What is going to keep the beam clamp from slipping on the beam? What is the schedule of the pipe used? How long is the pipe?

    The pipe thing does really freak me out. 6' is a pretty big span for pipe... and you are going to be putting some really weird loads on it.
  8. MPowers

    MPowers Well-Known Member

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    Very good advice. As photoatdv says, 40' span for 12" truss is nothing, especially with the rather light load you describe. For example: Total Structures 12" box, Light Duty Generic Truss is rated for 23# plf or 933# total edl load on a 40' clear span http://www.totalstructures.com/techdata/pdf_datasheets/generic_light_duty_truss.pdf. I can not recommend any beam clamp for the use you have described. There are many types of beam clamps, clam shell bolt, "C" clamp type for threaded rod, hinged with an acme screw clamp, sliding rod and hook, et. al. but they all are designed for supporting a load hanging vertically from the beam, not horizontally. In addition, there is no good way to attach and support 12" box truss horizontally from a single vertical pipe. my advice is the same as photoatdv. i.e. mount a box truss column next to each beam and support the horizontal truss from the floor with two truss towers. Truss is designed with corners and "T"s and other connecting sections to do exactly what you're describing without any questionable hardware or connections. The existing beam could well be used as bracing for the truss tower and reduce or eliminate any need for a large base or any angle or guy bracing.
    Last edited: Oct 3, 2013
    variable likes this.
  9. variable

    variable Member

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    I have been on crew that's done it before, spanned two 2' pipes with truss using rigid rt angle cheeseboroughs. It's really not the tricky part. Like I said, I'm just trying to figure out the beam clamps.

    That's good advice, but the trip to the floor is not an option for me. The towers are over a 30" opening for the public, I cannot impede it at all. Whatever supports the truss has to be attached to the tower, though whatever holds up the span is going to be attached vertically, not horizontally. I am a little dodgy about the rig too, though, if the beam clamp was bolted to a truss clamp, which held on to the vertical truss span (or pipe) the only concern would be using enough beam clamps to support the load.

    Still, since your apprehension of the beam clamp validates my concerns, I may have to find a third option.
  10. variable

    variable Member

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    Beam clamps have a bolt you can attach a truss clamp to (some of them do), I've never had a beam clamp slip but I have only used them on a few jobs, usually to hang lights or projectors from, though I've seen some seriously heavy loads hung from a bean clamp.

    I'm pretty much talked out of using pipe. Too many questions about it.
  11. egilson1

    egilson1 Member

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    Are the "flanges" horizontal or vertical? I'm having trouble visualizing the towers.
  12. MPowers

    MPowers Well-Known Member

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    I'm definitely having trouble with the picture. Any chance you can do a quick sketch of what your plan is along with a cell phone pix of the beam/tower?
  13. BillConnerASTC

    BillConnerASTC Well-Known Member Premium Member

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    Feels like the tower extension should bear load on top of the tower rather than trying to grip a vertical flange, that the extension should "overlap" tower to have a rigid extension rather than any possibility for a hinge point, and the extension should not be eccentrically loaded with all weight to one side. Albeit, I'm imagining tower as a vertical wide flange beam.
    variable likes this.
  14. variable

    variable Member

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    I did get a picture. Here is the tower it's going to be attached to. The upright will sit right in front of the pin spot, behind the ERS. That's about 18". Height from bottom lip to the top flange is about 32". The flanges are incredibly sturdy, all welded to 4" steel posts, but they're not real I-beam.
    [​IMG]

    And here's a quick Photoshop of the plan with truss supports bolted to the towers.

    [​IMG]

    Uploaded with ImageShack.us
  15. egilson1

    egilson1 Member

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    Pictures are worth a million words.

    Can you access behind the grating that is on the back side of the angle iron? My concern is that beam clamps that are just tighten onto a single flange vs. ones that encompass a pair of flanges (like an I beam) rely solely on friction to remain on the flange. Not a great choice in this application as their is no way to eliminate the possibility of the beam clamps being pulled of the flange. Being able to run an appropriately sized safety (span-set, rig steel) would help reduce the risk of that happening. The other thing that is going to help prevent that is the fact that the truss span itself will prevent the beam clamps from being able to move assuming the span can be matched perfectly to the width between the two towers. Doing this will keep your beam clamps in compression against the angle irons.

    In terms of how to attach the truss to the tower, I would hang (2) vertical pipes on (4) beam clamp to half borough. Each pipe then would attach to the (4) horizontal angle irons. Then Swivel borough your vertical leg of truss to those two pipes. Again, compression is your friend here.

    Hope I explained that well enough.

    DISCLAIMER
    This is only a conceptual idea based off of your picture and the information presented in this thread.
    variable likes this.
  16. variable

    variable Member

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    Hello egilson! Aside from using 2 pipes instead of 1 that pretty much corresponds with my original idea. I'd like to use truss for the verticle run, but nailing exactly 27" and some inches in box truss is going to be tricky. It hadn't actually occurred to me, but there's nothing at all stopping me from wrapping the whole tower in spanset or even loading strap to reinforce the pipes. Unfortunately I can't punch holes in the mesh, otherwise I would just use U-bolts to strap the pipes in place. The nice part about using pipe is that the span can be over 27' since it's going to have to overlap the pipes by at least a few inches in order to clamp a cheeseborough on it.

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