# Zip Line attached to Fort

1. Sep 7, 2009

### Airman

I'm building a fort in the backyard, which will be 8 by 16 feet. I plan on attaching a zip line to the middle of the fort, and need to know how to stabalize the fort. If I assume a maximum allowed weight on the zip line of 250 pounds, and a minumum angle of decent of 10 degrees, the maximum force pulling on the fort would be 750 pounds, most of which would be directed horizontally. I am using 6 4 by 4's as the supports for the fort, and zip line would be attached 14 feet above the ground inbetween the middle two 4 by 4's. My question is how should I anchor the fort into the ground? My plan is to sink the 4 by 4's into the ground and possibly use cement as well. I willl also use small stakes, but how deep does everything need to be? I am also building a small attachment for the zip line at the other end - this will not be a fort, but I can not attach it to a tree. However, it also needs to be able to withstand the 750 pounds of force without toppling.

2. Sep 8, 2009

### stewartcs

Can you attach a sketch (long weekend for me...lol)?

CS

3. Sep 20, 2009

### nvn

Airman: It sounds like your zip line is attached to the centerpoint of the fort floor, and is parallel to the 16 ft dimension. Please correct me if wrong. I don't need a diagram if you describe this orientation.

Using your minimum deflection angle, you correctly computed the cable tension due to your applied load. It might also be good if you tell us the initial sag of your cable prior to applying the point load, and the distance between your cable end connections, and the cable cross section and properties. We would also need the coordinates of any guy wires.