Is My Rope Bridge Design Safe? Seeking Feedback on My Plans

[Sundog]

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!

 

[tech99]

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.

 

[berkeman]

Thread closed for Moderation...

 

[berkeman]

Welcome to the PF.

First off, I know its not recommended to build a bridge like this without having it designed by a professional.

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.