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Feedback on Rope Bridge

  1. Jun 1, 2017 #1
    I'm designing a rope bridge that will span around 40 ft over a pond. First off, I know its not recommended to build a bridge like this without having it designed by a professional. However, I plan on overbuilding it and it will not be very high. I'm also thinking about using 3 or 4 ropes to support the deck instead of the normal 2.

    Using the formula H = w L2 / (8 d) I've calculated the midspan force to be around 583 lbs (estimating 350 lbs for wood, 40 foot span, and a sag of 3 feet). This is without accounting for people.

    Here are my questions:
    - Will the tension be distributed across the number of ropes used to support the bridge? Ex. two ropes would be 291 lbs on each rope.
    - Is this the right formula to be using? Would I need to use a different formula to account for people since that weight is not even distributed?

    Thank you for the help!
  2. jcsd
  3. Jun 1, 2017 #2


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    Gold Member

    You need to allow for the maximum number of people in the worst position, presumably the centre, standing at one edge. I think it would be difficult to ensure that the load is shared equally by the ropes and I would be inclined to make each one able to carry the full load. I presume you will also apply a factor of safety somehow, especially as things deteriorate and you may (or may not?) have people's safety involved.
  4. Jun 1, 2017 #3


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    Staff: Mentor

    Thread closed for Moderation...
  5. Jun 1, 2017 #4


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    Staff: Mentor

    Welcome to the PF. :smile:
    That pretty much sums up our advice on your project. For liability reasons, we cannot allow this thread on the PF. Thread will stay closed.
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