Update on the treehouse bridge in the redwoods of the Santa Cruz mountains

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We reached a milestone this lovely sunny VD weekend in the mountains:
https://c4.staticflickr.com/8/7370/16360101847_a148c61f1f_c.jpg
After four 16-foot sections, we're only about 4 or 5 feet from the tree:
https://c1.staticflickr.com/9/8637/16359718379_a6cbb11e00_c.jpg
I can't get the whole bridge in the picture, but here's a side view:
https://c4.staticflickr.com/8/7284/16358527150_f314ed76cd_b.jpg
Here's an angled view showing the 10-foot wide sections:
https://c4.staticflickr.com/8/7370/16544303031_3c0511bfaf_b.jpg
And, here's a view showing the last set of 16-foot wide boards:
https://c4.staticflickr.com/8/7414/16358528340_99ca7a421f_c.jpg
We're not sure how we're going to attach the end to the tree though:
https://c4.staticflickr.com/8/7359/16358325088_d238b3ab6b_b.jpg
We wrestled two 16 foot beams to either side of the big tree for now:
https://c1.staticflickr.com/9/8566/16519997026_ee37d554c5_c.jpg
We're not sure how we're going to attach to the big redwood yet though, so, that is our next engineering task to figure out.
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On 02/15/2015 11:25 PM, Danny D. wrote:

Is that you Spiderman?
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On Mon, 16 Feb 2015 11:19:58 -0800, Oren wrote:

Drill a big hole through it, and put a stainless bar through the hole. Voila! Attachment pins!
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DecadentLinuxUserNumeroUno wrote, on Mon, 16 Feb 2015 19:24:43 +0000:

Right now, the two 16-foot boards to the side of the tree are unattached at the tree (they're screwed into the floating bridge only).
https://c1.staticflickr.com/9/8566/16519997026_ee37d554c5_c.jpg
At the moment, the bridge is wholly supported by the cables and, at the low end, by the posts we first cemented into the ground, when we started this project in the untrampled woods.
It is time for those attachment pins you speak of though...
What we are thinking is that they sell these $100 treehouse attachment bolts, designed specifically for trees (but they're expensive since we'd use probably use four or six of them overall). http://www.treehousesupplies.com/Treehouse_Bolts_s/41.htm
We can't find anything larger than one-inch wide bolts at our local Home Depot, so, we have to order our bolts online, at any measure.
We're debating right now the feasibility of 1 inch or 2 inch bolts, which are about twenty bucks each, versus the treehouse attachment bolts which are five times as expensive. http://treehouseparts.mybigcommerce.com/9-pirch-yellow-zinc-plate-certified-r-32-36-hardness/
So, that's our next question. What kind of bolts make the most sense, keeping cost in the equation (if cost were no object, the treehouse bolts would do quite well).
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On 02/16/2015 2:24 PM, Danny D. wrote: ...

...
That'd be cheap if it fails with somebody on it...

There's bound to be a local Fastenal outfit nearby or similar but it's not clear what you're comparing.
Those are a constant-diameter shank equivalent of a heavy-thread screw in a hardened material supplied with an integral bolster. I see no reason why one couldn't use any compatible compression sleeve; machining that is undoubtedly a large component of the cost of these.
There's a link to an engineer's report at the site that says ultimate capacity of these in shear is roughly 8500 lb in Doug fir; and Appendix is referenced that compares material properties of other species including redwood but it is, unfortunately not available. I'm quite certain redwood will derate that performance by a pretty sizable chunk but don't know a specific figure otomh.
Plus, again you need at _least_ a 2X (preferably imo 3X) safety factor.
I also noted the recommendation on one of these sites that before using these to get a qualified arborist and engineer involved...methinks we've been over that ploughed ground before that there's little heavy-lifting on the engineering side going on first...
--


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Danny D. wrote:

I don't know what kind of bolt you will use, but here is my experience with bolts in a living tree: I fastened some wooden squirrel feeders to trees using lag bolts and washers. In a year the tree grew AROUND the bolt, pulling it through the plank of the feeder. I learned to put a spring between the bolt head and the washer to allow for this.
A threaded SS bar through the tree might be a better option, making it longer than needed so you could back off the nut as the tree grows. Of course you would want a jam nut so that it would not back off by itself.
--
 GW Ross 

 I am a mental tourist. My mind 
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On Mon, 16 Feb 2015 20:24:59 +0000, Danny D. wrote:

Just order the stainless bar stock and have your local auto machine shop of chopper shop cut threads onto the ends.
Get square bar stock if you want to keep it from rotating.
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DecadentLinuxUserNumeroUno wrote, on Tue, 17 Feb 2015 00:30:01 +0000:

Good suggestion!
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On 2/16/2015 3:24 PM, Danny D. wrote:

Are these bolts going to support the weight of the bridge? That seems a bit awkward with the long length of the board. Does the support board run under the bridge to be supported at the other end?
I think rather than drilling into the tree, I would make use of the various branches and wrap a line around the tree trunk like a lasso somewhat higher up than the walkway. The branches will keep it from sliding down the tree without being tight. Drop the line to the walkway or even pass it under and back up on the other side to the same or another tree.
--

Rick

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rickman wrote, on Tue, 17 Feb 2015 20:17:21 -0500:

The bridge is already supported. It's supported by a 3/8-inch suspension cable on both sides. The bolts are simply for redundancy, and, because the treehouse, when built, will add additional weight, even if/when the cable is suspended for the treehouse itself.

We haven't decided what to do with the branches yet.
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On 2/17/2015 7:17 PM, rickman wrote:

Redwood branches tend to die off and fall out from time to time. Not all but here and there. Some are 4-6" in diameter. Consider that but end coming down on you, your car, your shop. One punched through my shop roof and kept out the rain with all of the green junk on top.
I had to cut it off on top and on the bottom - punch out the disk and replace the roof boarding. Glad it was in the shop.
Martin - relocated from my 100 or so tall tree home site.
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Martin Eastburn wrote, on Wed, 18 Feb 2015 23:26:19 -0600:

Some of those redwood branches are as thick as trees, so that's a valid concern. We may need to reinforce the roof, against them falling on it.
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Danny D. wrote:

A dozen years ago we owned a lot (around 4 acres) with many large trees. One huge oak had a horizontal limb about 2 feet in diameter and I dreamed of putting up a spiral stair and a platform on the limb, just for fun. We wound up selling the lot instead of building a house on it, and I went by to look at it a last time and the limb had fallen off and was lying on the ground.
--
 GW Ross 

 My wife has a slight impediment in 
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On Mon, 16 Feb 2015 11:55:31 -0800, Oren wrote:

You should get a less weak grip of the facts.
A one inch hole drilled through the center meat of a Redwood? Hardly. The stainless bar finishes the task. The tree would have no problem growing around the bar, and even if it did not, it would not weaken the tree ANY significant amount.
If the tree could take a 30 ton tornado force before, now it can only take a 29.8 ton force.
Pretty much negligible, is the point.
You'd break the gear you hang on the pins before you'd break the pins or the tree.
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On Mon, 16 Feb 2015 11:55:31 -0800, Oren wrote:

Pine and Redwood are two entirely different trees.
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On Sunday, February 15, 2015 at 11:26:33 PM UTC-7, Danny D. wrote:

When the wind blows the cradle will rock and down will come baby...cradle and all. ====
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Roy wrote, on Mon, 16 Feb 2015 11:45:21 -0800:

Ye who have no faith in the religion of alt.home.repair denizens <shakes head in dismay> I'll sic Chris on you, ye who does not believe! <said in a rising voice>.
The grace of God shines on these here Redwoods! We shall overcome the forces of Hell, and rise, beyond all those who wish us evil!
:)
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On Sunday, February 15, 2015 at 11:26:33 PM UTC-7, Danny D. wrote:

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. ===
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Roy wrote, on Mon, 16 Feb 2015 11:47:50 -0800:

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/8/7284/16358527150_f314ed76cd_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). 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.
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/8/7414/16358528340_99ca7a421f_c.jpg
We also may erect a few more nets so that we can walk out to the neighboring trees. In fact, if you look closely, you can see two different nets in the picture above. One is to the top left of the picture, and the other is in the center right, in the big redwood tree itself, where someone spent months sleeping in and writing a book, many years ago (his net is still there, 40 feet up in the tree; but we would replace it as it's not safe to use probably, being fifty years old).
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On 2/16/2015 3:42 PM, Danny D. wrote:

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/washington/15bridge.html .
We're also thinking of adding downward

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.

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
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