Zipline Design Forces 3

[North2South]

Can anyone point me in the direction for determining design forces as a result of humans using zip lines?

 

[IRstuff]

Humans are probably a small fraction compared to the tension on the lines themselves, I would think.

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[Denial]

On my website (rmniall.com) you will find a spreadsheet that performs a STATIC analysis of an inclined cable with a SINGLE point load applied in any specified direction at any specified point along the cable.

However if you want to include the DYNAMIC effects of the motion of the applied load I suspect you'll be facing a lot of iterating as you try to track the load's position, speed (calculatable from its position by equating kinetic and potential energies), and path curvature (for the additional centripetal force).[ ] If I had this problem, I suspect I would just apply an extra "factor of safety" to the static load, then at the end of the exercise perform some sort of rough check to show that the dynamic effects were adequately covered by the extra factor of safety.

 

[Tomfh]

Humans are probably a small fraction compared to the tension on the lines themselves, I would think.

The weight of the riders causes a fairly significant load in the cable. I built a zip line for my kids. The cable weighed around 100kg, which is similar to the load of me plus one of my kids riding the zip line. All up I calculated several tonnes of tension in the cable.

There is also the stopping at the end, which can apply a bit of a shock to the cable as you decelerate.

 

[North2South]

Tomfh’s situation is similar to mine. I have a client wanting to tie his old zipline that ran tree to tree to his new pavilion - tree to wood post. I appreciate the feedback.

 

[Tomfh]

It’s a catenary and vector forces problem. You have cable self weight plus the hanging load on cable.

A critical factor is the cable sag (drape). The more sag the less severe the tension load. I used an initial drape of ~5% (about 10m sag over 180m span). If you string them up really tight (as some people do) the tension loads are worse because the vector triangles are flatter.

I ran my cables through the trunk of the support trees, and then ran them down at 30 degrees and anchored through the base of other trees.

I also built a smaller zip line (50m long) using swaged cables looped around the forks in large trees (trunk 800mm), ie cantilevered support. You can do that if you’re happy for your tree or post to carry several tonnes of lateral load.

 

[DBronson]

North2South:

The Association for Challenge Course Technology (ACCT) has an ANSI Standard 03-2019 that covers the design and construction of zip lines.

Link

Regards,

DB