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Rigging truss

Discussion in 'Scenery, Props, and Rigging' started by StageTech620, Jul 13, 2017.

  1. StageTech620

    StageTech620 Member

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    I'm planning on mounting or hanging a truss between two beams in an older theater. (They currently have gas pipes across the beams for basic par can hanging, but of course they wouldn't be suitable for intelligent fixtures). The only thing in my way is this unistrut. Here are the options I can think of.

    I plan on hanging 5 Rouge R2 Spots across the 20 foot span. Each fixture will weigh around 50lbs.

    Do I need a 12"x12" truss? Or is there an easier solution? (Double rail?)

    1: Cut the unistrut, slide the trust between the beam and ceiling like I was originally planning on.
    2: Use a sling to hang the truss off of the unistrut, but my concern here is can the unistrut take that weight.

    Anyone have other ideas? There aren't any higher beams to use a clamp, chain hoist, and spanset on.

    Thanks!
     

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    Last edited: Jul 13, 2017
  2. porkchop

    porkchop Well-Known Member

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    This is a lot of detail to ask for over the internet when we don't have the ability to know every detail of your situation. That being said I have a few suggestions:
    • Talk to whoever you will or have gotten the truss from. They should be able to tell you what kind of uniformly distributed load the truss is rated to handle. If you don't know what your truss is rated for you shouldn't be using it truss anyway.
    • Despite several theatres wishing otherwise, I have yet to come across Unistrut that is rated for overhead rigging. If somehow the Unistrut you have has been rated then don't exceed that rating. Otherwise I would avoid rigging from it.
    • If you have slings and a beam I would try to design the rigging to go around the beam (avoiding the Unistrut). This may or may not be possible depending on the trim you need and what the back side of that beam looks like.
    • There are beam clamps that exist that are rated to be used on a vertical beam with the steel coming off them at a 90 degree angle to the clamp body. The rating is significantly lower than when used with the steel in line with the body, but you're not talking about a ton of weight. Also you have to ensure that the clamp cannot slide when used like this.
    Be smart, be safe, don't put anything in the air you wouldn't want your wife and children to sleep under.
     
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  3. Footer

    Footer Senior Team Senior Team Premium Member

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    ....You can hang moving fixtures off of standard 1-1/2" Sch 40 black pipe.... nothing stopping ya. The only reason you see truss used more is due to how many points it takes to rig vs pipe. As long as you are not over loading your pipe you can hang whatever you want from it.
     
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  4. StageTech620

    StageTech620 Member

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    But if the pipe is 20 feet long, won't it start to flex?
     
  5. Footer

    Footer Senior Team Senior Team Premium Member

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    If its 20' long and only picked up at the ends you have a lot more issues then just truss vs unistrut. I wouldn't hang a thing in there until you get the place looked at if that is the case. You don't know what things hide in corners. You can't trust anything... including the building steel itself.
     
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  6. josh88

    josh88 Remarkably Tired. Fight Leukemia

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    Not just theatres though. TV studios too. I'm near an entire complex of studios that have unistrut all over being used in that capacity. And they've got a rigger that they make sure looks at everything and signs off on that usage. I'm mostly pointing it out and agree with your statement about unrated and usage.
     
  7. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    About unistrut, I have many projects where the rigging contractor has used unistrut for overhead rigging applications and the shop drawings are sealed by an engineer. One of the most common is clipped perpendicular across the bottom of truss joists and battens clipped to the unistrut.

    I think it was clear that 1 1/2" pipe won't hardly support itself safely on a 20' span but there are options other than 1 1/2" pipe, truss, and unistrut. Is this to be permanent? Is there for sure no option for mid span support? Being over cautions, I probably would not do this without an engineers review except maybe truss installed by a qualified rigger.
     
  8. BillESC

    BillESC Well-Known Member Premium Member

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  9. Protech

    Protech Member Premium Member

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    While I cant comment on the OP's situation specifically, Unistrut is commonly used for overhead rigging, and safely, so long as it is done properly. Engineers and designers often prefer to use it because it is a pre-engineered product with a clearly labeled load rating (among a wealth of other performance data that can be found in catalogs). Thus, the system can be designed to a specific factor of safety without "re-inventing the wheel", so to speak. A custom mounting solution including beam clips, split plates, throat/clamp plates, etc all need to be individually engineered, whereas there is pre-written data to rely on with strut. This is not to say that "all unistrut is safe to hang things from", but a properly engineered system that uses strut can be safely constructed.

    I think you'll be hard pressed to find many products that are "rated for overhead use". Often times, the opposite is the case. To my knowledge, Unistrut does not claim that it is "not rated for overhead use", merely that here are the safe working load limits and performance data... the rest is up to the system designer, engineer, and contractor to design a safe system. Some of the largest Structural Engineering/third party review firms we've worked with including ESG and Clark Reder have reviewed and stamped such designs, including for things like seismically braced pipe grid systems in Southern California (which must be additionally blessed by the Department of the State Architect (DSA)).
     
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  10. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    I'm sensing a disconnect on the unistrut issue. I agree with Protech. That's for a designed and engineered and more or less permanently installed system. I have to wonder if Brett's using "rated for rigging" as in a beam in an arena that is designed for throwing a spanset around and hanging a truss from it. I would agree that I would not assume a piece of unistrut installed previously by who knows who for what should be used for rigging being added. It is probably already at its design capacity.
     
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  11. Protech

    Protech Member Premium Member

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    100% Agree! My response wasnt directed at any one person in particular, sorry if I gave that impression
     
  12. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    I knew that - just slightly contradicting statements from respected posters and thought it needed clarifying.

    I'm always fascinated by the unique perspectives we share.
     
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  13. porkchop

    porkchop Well-Known Member

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    By "rated for overhead rigging" I mean that the product comes off the shelf with a guarantee that it can be used with no additional questions asked. I too have had engineers stamp drawings specifying the use of unistrut components, but it is only after a professional engineer approved that specific application that I would use it.
    My point was that you can't just look at the unistrut that exists and say that point can be used as a rigging piont. If an engineer has looked at the whole system including fasteners, attachment, and load bearing elements they may be able to determine a maximum allowable load (and the acceptable directions of the forces from that load), but just the fact that some designs use a similar product doesn't mean you can assume that any stick of unistrut in the building can be used to rigging.
     
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  14. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    I think that's what I suggested.
     
  15. ruinexplorer

    ruinexplorer Minion CB Mods Premium Member Fight Leukemia

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    No harm in clarifying redundant statements in my book.
     
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  16. egilson1

    egilson1 Well-Known Member Premium Member

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    The issue isn't "for overhead rigging". It's does the materials design account for dynamic loads? Taking a engineered strut and de-rating it might be all that an engineer will require in order to be able to use it for "rigging" as we say.

    Rigging isn't black and white. It's all grey.

    Ethan
     
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  17. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    Manufacturers do for some products state that the product is not for overhead rigging. Two I think of right away are some winches and grade 30 chain. Pretty sure I've seen that stated for other products. That seems black and white.
     
  18. egilson1

    egilson1 Well-Known Member Premium Member

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    Except for the one chain manufacturer who approved gr30 proof coil chain to be used as trim chains.
     
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  19. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    I would like to see the paperwork on that. I contacted all of the chain manufacturers and have seen the "letters" that rigging companies used for this and am skeptical. It's been based on claiming trim chains are not overhead rigging, to which I day bs. So please share who approved this application. I have to assume they are not a member of the National Association of Chain Manufacturers, who agree grade 30 is not to be used for overhead rigging.
     
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