Wire Tension Grid Load Calculations

Discussion in 'Scenery, Props, and Rigging' started by Yaro, Apr 21, 2016.

  1. Yaro

    Yaro Member

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    Hi,

    I am reading the Specs for a theater that is currently being built, and one sentence caught my attention:

    "Design the wire rope grid so that when wire rope assemblies are torqued to factory recommendations,

    the wire rope shall not deflect more than 2 inches under a maximum concentrated

    load of 300 pounds."


    So my question is, how do one approach the load calculations for a wire tension grid? Do you treat it as a walking surface (say, a deck) and calculate load per square inch (ft), or do you isolate every single cable and calculate point loads for it? In the latter case, how do you approach the fact that wires are interwoven on 2" centers? The same with the deflection: do you calculate it for a single cable, or for a certain area?


    By the way, I am of course not designing a wire tension grid, I am just curious about how it works.
    Thanks a lot!
     
  2. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    Yaro likes this.
  3. Yaro

    Yaro Member

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    Thank you very much Bill! The concept of a wire tension grid is a complete mistery to me. Aren't all these interwoven wires just tensioned catenaries? If so, isn't it true that as the vertical angle increases, the tension in the wire grows exponencially? The tension in the cable would be 28 times the load at 89° and 280 times the load at 89.9°?
     
  4. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    Yup. It's a tensile fabric calculation (stretched grid method) rather than a beam deflection calculation. Interweaving of the grid wires makes for some complex modelling. In practice, most systems are constructed of rigid panels of tension grids to simplify design and installation, so grids of grids.
     
  5. robartsd

    robartsd Active Member

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    If you have an panel engineered to meet the deflection specification, any smaller panel constructed with the same wire, spacing, and tension would also meet the deflection specification. The smaller the panels, the easier it is to keep the absolute deflection low.

    @Yaro you're right that the greater the deflection, the less tension required to hold the load; however, the math isn't quite as simple due to the fabric providing support in all directions.
     
  6. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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