We started the 100-foot long 10-foot wide deck high up in the California redwoods

dpb wrote, on Thu, 23 Oct 2014 08:13:06 -0500:

Here's the response from the neighbor building the deck...

The 3/8" steel suspension cable is a good deal higher than 10 feet above the deck at the ends. Currently that 3/8" steel cable is anchored at a tree about 25 feet above the deck at the beginning end of the deck.

Also, the 100 foot final length of the deck was a guess that is probably a bit high, where perhaps 80 feet might be closer to the final length. So the 11 degrees may no longer still be the result of the calculations.

Looking at the photos, the angle of the cable looks like around 30 degrees to me. If the height of the suspension cable above the deck is 25 feet, and the length of the deck is 80 feet, we now have 32 degrees.

Using his tension formula, we get a tension of 4,718 pounds. So, I believe, that means the 3/8" suspension cable can support almost six times what we are assuming.

While the deck was originally supposed to be free floating, since we decided to anchor the close end of the deck on the dirt path (so that people could just step onto the deck from the path), that end of the deck is now supported by the two fence posts, so half of its weight goes away.

If, additionally, we add another fence post, in a "T" shape support, at the end of the first 16-foot-long section, then the weight of that first

If we really did get to 28,000 pounds of tension, the trees would pull closer together, reducing the distance, and making the angle steeper. It thus gets asymptotically harder to actually put that much tension on the cable.

The treehouse itself, when it's built, will be supported mostly by the redwood trees.

Arfa Daily wrote, on Tue, 28 Oct 2014 02:05:05 +0000:

That's a good suggestion, as we have tools all over the place!

Usually, we tie in when we're out on the cable, with no firm footing:

And, we tie in when we're working on the steep slope below the deck:

The harnesses we use are the same ones we use for climbing the hills:

Here's my setup, for example, as I was digging the fence post holes:

And, here's what I used when I had to double-line rappel downslope:

Even so, we've had a few of the typical gotchas, from dropping the spool of wire (where it rolled a hundred or so feet downhill before getting wedge under a fallen tree) to the inevitable search for missing glasses and hammers.

Such is the nature of working in the trees...

dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500:

All the supporting cables are above the deck.

It's a bit hard to see in that picture from below today, but the 3/8" steel cable is glinting in the sunlight a few feet *above* the deck.

The deck is not attached to *anything* other than the cable on the free- floating end, as we build it out. In fact, while it's hard to tell from the angle of this picture, but the end of the second 16-foot-long section is still shy of the leftmost redwood by about a foot, and maybe it's two feet shy of the right-most redwood tree:

Here is a picture taken earlier in the day, before we planked the second

dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500:

This is a good point, in that sometimes it pours out here, and this is a steep slope, so the runoff could be great.

We just had a half inch of rain over the weekend, and this is a shot of the cables and the people on the decking (the dog won't go on the deck):

We're still about a foot from the left-most redwood here, and about two feet from the right-most redwood, so we "can" attach to them (if decided) with the third 16-foot deck section:

Arfa Daily wrote, on Tue, 28 Oct 2014 09:53:11 +0000:

We're all retired, and, getting a bit complacent, so, we tend not to own (real) work clothes.... :)

But, we're getting real good at buying army surplus static line!

Maybe we should pick up a pair of these Ghillies as fitting work clothes, since we're always hanging around in the trees:

dpb wrote, on Tue, 28 Oct 2014 09:21:42 -0500:

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 circumference. 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 square foot. 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 local.)

Oren wrote, on Tue, 28 Oct 2014 10:37:43 -0700:

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:
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2. All brown lines are 16-foot long lengths of lumber:
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3. This approximates the "ladder network" you've seen in the photos:
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4. This was the first (thin) cable that went from tree to tree:
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5. From that thin cable, we hung two large safety cargo nets:
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6. Then we hung the thick cable, which was initially 250 feet long:
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7. We sunk two fenceposts, so that the platform rested on the ground:
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8. Then we built & suspended the first 16-foot by 10-foot section:
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9. Yesterday, we hung the second 16-foot-long section which is a foot or two shy of the smaller redwood pair of trees:
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10. The plan is to add successive 16-foot sections, one by one:
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11. We keep that up until we finally reach the big redwood tree:
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12. And, finally, we'll add 8'x4' sheets of plywood as a railing:
    formatting link
    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!

Oren wrote, on Tue, 28 Oct 2014 15:22:29 -0700:

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

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).

Looking at the animated sequence, the uphill end of the carrying wire is tied to a tree, not anchored in the ground otherwise? That tree is going to bend over.

Likewise, no matter how huge the downhill tree may be, watch the roots on the downhill side for signs of popping.

Good luck with the parade ground in the sky!

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 stainless?

Do you have an inspection plan in effect to detect future failure conditions?

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.

Regards

least.

It never was a question about the strength of the trees. It has always been about the cables and the load.

?-)

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 circumference).

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.

dpb wrote, on Thu, 30 Oct 2014 08:13:07 -0500:

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 exec).