On 2/16/2015 3:42 PM, Danny D. wrote:
Roy wrote, on Mon, 16 Feb 2015 11:47:50 -0800:

I saved a copy of all of those pictures in case I need
a "before and after" scenario...but seriously I hope you
succeed in your project.

Thanks for your well wishing.
It is one of a kind, so, we're learning as we go.
In the end, it will be pretty neat though, don't you think?

It a 10-foot wide suspension bridge, which starts at ground level
on a path in the redwoods about a thousand feet (or so) from the
nearest anything, and then goes for about 70 feet to a large
second-growth redwood, where the deck expands to 16 feet wide.

Sitting on the wide decking, about 40 feet above the ground, will
be a two story treehouse, with a bathroom, kitchen, electricity,
gas heating, and WiFi Internet (which is something we're experts
at by now, given that we all maintain our own radio antennas).

We're thinking of suspending the treehouse with 1/2 inch cable
wrapped from the big tree to the two smaller trees cradling
the bridge at about the half-way point that you see to the
right in this picture.
https://c4.staticflickr.com/8/7284/1...14ed76cd_b.jpg

So, that way, the treehouse and the suspension bridge would
be, in effect, supported separately (or we might make the support
mutual and redundant).

Redundant would be good. Bridges without redundant support fall down,
e.g. the one in Minnesota--see e.g.
http://www.nytimes.com/2008/01/15/wa.../15bridge.html .

We're also thinking of adding downward
hanging support cables, again from the smaller redwoods to the
decking, to add redundancy once the treehouse weight goes up.

You can't wrap the cables round the trunks, or you'll kill the trees in
a few years. Nice big eye bolts are the ticket, I expect, provided you
don't put any torque on them (i.e. you have to drill the pilot hole in
the direction of the pull). The tree can easily grow around them,
unlike wraparound cables. The problem with wood fasteners is that they
aren't load rated, unlike machine bolts.


One problem we have been having is we have had to constantly
adjust the tilt and leveling of the bridge, as weight was added
to the end. We ended up buying a dozen cable winches, which are
what is holding the bridge up now, one of which can be seen in
the left in this photo below.
https://c4.staticflickr.com/8/7414/1...ca7a421f_c.jpg

Sure beats turnbuckles.

I think George Dyson probably published construction details of his
famous tree house.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net