Cable-Stayed Bridge

2003 October

Cable Stayed Bridge

Shortly after I built the tree platform I began thinking about the best way to access it. Some sort of ladder was the obvious choice but building a bridge seemed like more fun, so that is what I did. The distance from deck to deck was over 20 feet so I either had to use deep members or get creative. I chose the latter for aesthetics and cost, as a low profile bridge would be less obtrusive and the materials would be much cheaper and easier to handle.

Construction was rather straightforward and started with fixing the three 2x4's to each deck. At the tree platform the 2x4's are hanging in 2x10 joist hangers while at the house deck I make a shelf for them to rest on. Next my father and I jacked up the center of the 2x4's and ran the aircraft cable. The wire is one single strand that wraps around the 10-inch diameter horizontal log at the house. Based on my calculations I could have used a smaller diameter wire but this was all that they had at the lumber yard. When we released the jack the bridge had a nice camber to it. Nailing the decking was the last step. To maintain the low profile I chose 5/8" x 6" redwood which is usually used for fences in this area. All of the work was done in one day and all in all I am very pleased with this project.

Here we see the substructure of the bridge, three pressure treated 2x4's along with the cable. To get the camber my Dad and I jacked up the joists before we ran the wire.

Pa tests out the completed bridge. I am very happy with its unobtrusive low profile and the way that the cable disappears into the background.

A view from the tree platform showing the width. Scoobie would not cross the bridge of his own accord so I had to drag him across. That proved to be a good load test, 120 pound dog plus 170 pound human (my rough calculations were based on a 300 pound load).