John Robertson wrote, on Mon, 29 Sep 2014 09:54:57 -0700:

Have you allowed for a windstorm where the trees may be moving in
opposite directions to each other?
Have you allowed for maximum and minimum temperatures?

Only that each cable supports 14,000 pounds!

You want some sort of shock absorption built in too.

Hmmmmmm.... The cables don't "give" a little when you walk on the bridge
that would be hanging below it?

May I suggest you find an engineer to look over your design?

The neighbors are all owners of companies and people with graduate
degrees, so, they *are* engineers (of all types). The one having the most
fun with the design is the retired carrier fighter pilot.

Suspension bridges are close to what you are building

Yes. I'm told the catenary will turn into a parabola once we hang the
bridge off of it. Since the bridge starts uphill about 15 feet above the
trail, it will be fun to just step onto the bridge, at the level of the
trail, and then walk "downhill" level but going higher and higher above
the steeply sloping ground, to get to the two smaller redwoods in the
middle of the span.

At that point, we will be in the "treehouse" which will have a deck and
WiFi and a great open view of the mountains.

Then, if we want, we can walk further to the *big* redwood, which will
have sleeping quarters (hammocks and cargo nets) for the nights we'll
spend there.

It should be fun, once done, and I'll try to keep you guys informed; but
I personally am not designing or building it; I'm just the free help (we
all have Spanish nicknames when we do free labor. I'm "Rodruigo", and my
wife's nom-de-labor is "Marisol", for example).

I keep threatening that I'm gonna call OSHA on them if I fall or if they
don't provide cold soda (the free soda has been warm, to date).