Thanks for all the insight.
Below is the owner's response to your concerns.
BTW, I created an animated GIF of the entire process, as I see it,
but I can't get Flickr to show the animations since Flickr turns
an animated GIF into a static JPG.
I'll post the animation separately, if I can figure out how to
preserve the animation, but here is the starting point static JPG:
Here is where we are right now:
And here is the penultimate ending point static JPG:
Here's the owners response to your valid concerns ...
I wonder if they realize how huge the final redwood tree is?
The tree probably weighs in excess of 2,000 tons, and has a 30 foot
The smaller set of redwood trees I would estimate weighs 15 tons.
In a wind of 50 mph, the small tree experiences 200,000 pounds of force
due to the wind.
The idea that 28,000 pounds of tension on a cable is more than it
encounters in a light wind does not seem tenable.
The root structures of both trees routinely handle much larger forces
during a typical day.
A wind blowing at 100 miles per hour generates 25 pounds of force per
If that wind were blowing straight down on 800 square feet of deck, we'd
have 20,000 pounds of force.
I consider that unlikely. :-)
Edge-on, we have 67 square feet, or 1,666 pounds of force. But that is
also somewhat unlikely.
Sideways forces will add a little to the cable tension, but will mostly
be taken up pushing against the trees and the support posts.
The deck will weigh in the neighborhood of 5,000 pounds, and has 800
square feet of maximum surface area. Lifting that, requires 6.25 pounds
per square foot, or a wind speed straight up of 50 miles per hour. But
the deck is held down at the ends and in the middle by either trees or
posts, which also limit the amount it can tilt or twist. The surrounding
trees limit the wind considerably.
The assumption that the engineering is "seat of the pants", or that the
mathematics have not been done is incorrect, but the ideas are all good
because I don't want to miss something, by not thinking about it at least.
Let them know that I appreciate their advice!
(Please invite them to lunch on Wednesdays in Redwood City if they're
The ones with the longer threads were really stinky because
you needed four hands, while suspended on the cable, to
screw them in.
The ones with the shorter threads only take 3 hands.
Here's an animated GIF, I just made, of the suspension bridge...
Danny D. wrote, on Tue, 28 Oct 2014 20:48:36 +0000:
Flickr turned the animated GIF into a JPG but tinypic seems to keep
it as an animated GIF ...
Here's my rendition, as I understand the plans so far ...
I am omitting the actual building structure, but what you see here
are the following:
1. The starting point, on a steep slope, with a path near the top:
2. All brown lines are 16-foot long lengths of lumber:
3. This approximates the "ladder network" you've seen in the photos:
4. This was the first (thin) cable that went from tree to tree:
5. From that thin cable, we hung two large safety cargo nets:
6. Then we hung the thick cable, which was initially 250 feet long:
7. We sunk two fenceposts, so that the platform rested on the ground:
8. Then we built & suspended the first 16-foot by 10-foot section:
9. Yesterday, we hung the second 16-foot-long section which is a
foot or two shy of the smaller redwood pair of trees:
10. The plan is to add successive 16-foot sections, one by one:
11. We keep that up until we finally reach the big redwood tree:
12. And, finally, we'll add 8'x4' sheets of plywood as a railing:
After that, we begin to build the actual treehouse, complete with
WiFi, refrigerator, bar, running water, and heating (no kidding).
It will take time, of course, so, I'm not sure if I should continue
to update this thread, but, since we've never done this before, any
and all advice is welcome.
PS: Jeff Liebermann and SMS are both welcome to attend the Internet
WiFI setup party since they both live in the area!
On Tuesday, October 28, 2014 3:34:02 PM UTC-6, Danny D. wrote:
Danny,I am predicting complete and utter destruction of the whole shebang come one god-almighty storm. All of your considerable work will be for naught. Mother nature is going to tag you real good. Please be careful.
There's almost no way you would have known how absolutely huge the
big redwood tree is downslope.
There were a few pictures of it, early on, in a different thread,
when we had laid the first few ladders and the cargo netting.
As you can tell from this diagram, there are three sets of trees
that matter, for our purposes (although many other trees exist):
Here's a quick look downhill, from the path near the uphill path:
This is the uphill anchor point, on a small Monterey Pine tree:
Here's a picture of the two small redwoods at the 1/3 point:
Here's another picture of those small redwood trees where you
can see we strung a cargo net across so we could get to the big
This cargo net is how we get over to the big redwood which is
about 30 or 40 feet downslope of the beginning of the netting:
But, I don't seem to have a picture of the big redwood for you,
so, I'll need to take one and upload it so you can see how massive
it is. It's about 100 feet downslope, and it's hard to get back
up that slope, so, I don't generally go down there unless I need
to. But, I'll do that for you, especially since you've been so
helpful with the engineering advice.
I don't need a picture of the big redwood; I'm perfectly willing to
allow as how they can and do get big; I've been through redwood country
a number of times. I was simply noting from the pictures posted near
that point in the thread there didn't seem to be much of any real size
and was more concerned of potential on the root system with the load
than whether the tree itself was sufficient presuming it was.
When the response to the question regarding angles for trying to
estimate tension needed to provide a given vertical force component
includes the justification that the angle will increase owing to the
tree flexure doesn't lend itself to thinking they're terribly big,
either. And, again, just "devil's advocate" position raising the
From a diagram such as that with a few measurements one could get at
least a reasonable approximation using simple-enough analyses as
outlined in the following (beginning at 7-30ff)--
And again for specificity, it's not the force itself that I'm raising
caution over but the moment arm that force creates at the base given
that it's being applied (presumably) fairly far up in height.
I drew it, by hand, with Kolourpaint, on Linux, which,
according to Wikipedia, is a Microsoft-Paint like drawing app:
After drawing each line, I just saved the file to a new name,
e.g., drawing01.jpg, drawing02.jpg, drawing03.jpg, etc.
Then, I slapped it all together with this Linux command:
$ convert -delay 50 -loop 0 *.jpg animatedplans.gif
That created this:
The "loop 0" just means loop forever; and the delay is something
like 50 milliseconds between images, I think.
I use this method only because it's trivially simple to do,
so, I'm sure there are *better* ways to make animated drawings.
For example, on Windows, I'd just draw using "Paint.NET" or even
Microsoft Paint. Then, I'd slap it together using one of the
programs described here:
How to make animated GIFs, by PC Magazine
We *do* get winds upwards of 90 mph very commonly out here, since we're
exposed to the Pacific Ocean. When it rains, it often rains horizontally,
coming in from the Pacific Ocean, and hits the windows sideways.
Danny D. wrote, on Wed, 29 Oct 2014 05:04:53 +0000:
I found only one picture of the big redwood, but it doesn't show
how massive the trunk is (measured at 30 feet in circumference).
There's actually a person, close to the tree trunk up there, in
the cargo net, setting up the blocks of wood for the cable to go
around (this picture was taken a few weeks ago).
Here are a few things that come to mind:
Has the owner checked with his insurance provider to see if he is protected
from liability? Things like this are known as an attractive nuisance and
everyone involved might be at risk should anyone get hurt.
Have you considered corrosion of the cable? Is it steel, galvanized, or
Do you have an inspection plan in effect to detect future failure
You might apply some paint to the cable clamps to serve as a witness mark to
see if anything slips.
It is pretty neat and will have all the kids in the area interested.
josephkk wrote, on Wed, 29 Oct 2014 21:11:45 -0700:
I would tend to agree, as the big redwood is massive (30 feet in
For scale, there's actually a person, wearing blue, in the cargo net
right next to the tree, fixing the blocks for the cable that we later
wrapped around that tree.
BTW, even the little redwoods are not all that little:
Tom Miller wrote, on Wed, 29 Oct 2014 15:56:20 -0400:
The owner is an ex Google executive, so, he has the disposition to have
lots (and lots) of "attractive nuisances" on his property! For example,
you can travel in another part of his property, high up, from tree to
tree to tree to tree (etc) by cargo net, for HUNDREDS of feet!
I always find a way to take my grandkids to his place for fun stuff.
Steel. When I asked, he said there's plenty of zinc fittings, so, he
wasn't worried about rust.
Good question. I'll ask.
This is a GREAT idea!
I will suggest that to the owner!
Kids love his place. I can't count the number of "attractive nuisances"
he has on his rather large (scores of acres) property.
I apologize that most of my pictures were from the uphill side (where
the suspension bridge is currently forming), where those trees are puny
in comparison to "General Sherman" (which is what we call the big one).
The only time I climbed down the 100 feet to General Sherman was when we
were setting up the cables around it, and I was the gaffer who passed up
tools and supplies.
So my only pictures of General Sherman are the ones I showed, which don't
quite show the massive girth of the thing, especially at the bottom,
because what you see above is already split in two.
I agree with you, that when I first saw the angle stuff, I too wondered
about bending a tree that much to make *any* difference. I'll forward
your comments above on to the owner to see what he makes of that.
I will forward that "Chapter 7: Forces in Beams and Cables" PDF to the
owner, who, while he isn't an engineer, he has multiple graduate degrees
and can handle almost anything we throw at him (he was an early Google
BTW, just to be clear here -- the angle of concern is _NOT_ the angle
between the cable and the tree itself; whether the tree is vertical or
already leaning is immaterial.
The angle of concern is the angle of the cable relative to true
horizontal/vertical as it is the force component in the vertical
direction counteracting gravitational force that is what controls how
much tension is required to generate that load-balancing force. The
side load on the tree/support is the horizontal component; the two
combine to be the total tension per the free body diagram force/moment
balance as illustrated in the previous example statics calculations
If the response was based on thinking about the cable shifting with
respect to the tree itself, that's the wrong frame of reference.
[followup trimmed to just ahr]
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