Building a treehouse in the redwood grove of a neighbor (pics included)

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

Only that each cable supports 14,000 pounds! :)

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

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. :)

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).

Oren wrote, on Sun, 28 Sep 2014 10:31:43 -0700:

I had forwarded this thread to the owner of the treehouse in the redwoods, who replied with the following ...

-----------

People worry too much.

I simply design for 10 times the expected load, and pay the premium. Trying to finely engineer the solution where torque and special fasteners are important is a way to save money, and I'd rather spend the money and not waste my time. I've never seen a malleable cable clamp. Drop forged ones are cheap, and I use more than normal anyway, not because I think they are needed, but because they help keep the cable from slipping out of place on the wood block spacers.

The reason for keeping the U-bolt on the dead end of the cable is because the saddle has a lot more surface area, and thus does not reduce the strength of the cable as much as the U-bolt does. But they make dual-saddle cable clamps, for those who don't use the over-engineering approach I do.

Each cable can support 7 tons, so the total weight of treehouse and occupants can be 14 tons. (Although there will be other supports besides the cable -- one end will rest on the ground, and another end will be anchored to the tree, and there may be other support cables used just to make installation and leveling easier.)

If half of the weight is treehouse and the other half is people, we have 7 tons of treehouse possible (although the actual treehouse will probably weigh less than 1.4 tons fully furnished), and 7 tons of people (70 people, if they are all 200 pounds). I doubt we will ever have 70 people in the treehouse -- they'd be shoulder-to-shoulder.

Oren wrote, on Mon, 29 Sep 2014 16:02:48 -0700:

I guess it's like calling an Asian an Oriental? Who is insulted when I equate Mexico with Spain anyway? The Mexicans? Or the Spaniards?

(I don't know these things.)

Oren wrote, on Mon, 29 Sep 2014 15:20:20 -0700:

The good news is that, if the whole thing collapses, *he* gets sued, not me! :)

No, that's pretty much correct (if rather dated). "Oriental" literally means somebody from "the East". Asia is usually defined as "East of the Urals". Both are somewhat vague terms with meanings that have changed over the centuries, but Wikipedia says the're pretty much the equivalent:

The Orient means the East. It is a traditional designation for anything that belongs to the Eastern world or the Middle East (aka Near East) or the Far East, in relation to Europe. In English, it is largely a metonym for, and coterminous with, the Continent of Asia.

Calling a Mexican a Spaniard is like calling somebody from the US "English" or "British". Rather than being insulted, I think people are just going to be puzzled over where you've been for the last 250 years.

Either, both, maybe neither (it probably depends on the crowd). Regardless of whether it's insulting, it's incorrect.

I hear that about over engineering stuff. When I was getting ready to pour the floor for my shop I calculated the concrete thickness for the various machines and then though about what happens if I move a machine and then what happens if I buy a heavier machine or one with a smaller footprint and so on. Then I realized how pointless this was in my situation, So I had the concrete poured to 7 inch minimum thickness, had fiber put in the concrete, and I put rebar and wire mesh in place before the pour. It's a good thing too because I later bought a lathe that covers 10 square feet with the base and sits on 4

You keep talking about WiFi. More important is a refrig for the beer. Why would anyone want WiFi in a treehouse. I would think this would be a place to escape all that stuff.

G. Ross wrote, on Mon, 29 Sep 2014 20:38:51 -0400:

Good point, but, this *is* the Silicon Valley environ ...

---------------------------------------------- In days of yore I worked as a design engineer for heavy duty steel mill and foundry equipment, but that was then and this is now.

For designs involving steel cable and human safety, the basic safety factor applied was 5.

IOW, 14,000/5 = 2,800 pounds as the basic design limit.

Dynamic loading would apply another 50% derate.

IOW, 2,800*50% = 1,400 pounds for dynamic loads.

Based on the posts I have seen, your group needs some serious help before people get hurt or worse.

Lew Hodgett, PE Retired

I think everyone's offended, now days. And you hurt my feelings by writing that.

. Christopher A. Young Learn about Jesus

Does PRC have more attorneys, or Mexicans?

. Christopher A. Young Learn about Jesus

Sounds like my elementary school lunch room monitor woman. We used to call her Bubbles.

. Christopher A. Young Learn about Jesus

Hmm, well with two separate cables your power requirements are fine, just run them on 24VAC @ 50A (120VAC @ 10A equivalent) and then use step up transformer or AC to DC regulators to power everything in the tree house. No unsightly wires!

John :-#)#

Lew Hodgett wrote, on Mon, 29 Sep 2014 18:29:57 -0700:

Times two cables, which is 5,600 pounds, at least. :)

My last comments - this is not looking so good..

Bending a cable around a support weakens the cable - there is a formula for that:

So that derates the cable strength from 10% to 60% depending on the curve. Note too that they are using wooden standoff/chocks to hold the wire, I hope they chamfered a notch - but in any case the load is not consistent on the tree, rather it is concentrated on only a few of those wooden chocks. This is a derating aspect too.

Looking at picture:

It looks like the cable does a bit of a sharp bend where it leaves the standoff...this is potentially a real problem - kinks are possible. The pinching of the cable at the clamps also derates the cable strength...

Wire Rope is certainly varied in structure. However I do keep seeing the

It does appear that the folks selling wire rope are only too happy to advise in its use - your friends would be advised to show them the proposal for comment before they put too much weight on these wire ropes.

John

You better check it. Wind loads can exceed the dead loads by many times. Wind loads may be the real issue.

?-)

That's generally considered offensive, racist, and ignorant.

Perhaps they have better manners.

----------------------------------------------

"Lew Hodgett" wrote:

----------------------------------------------------- What I forgot to include was that the above design loads are for tensile loads.

Bending loads require a further derate.

The reader is left to determine the value from any decent structural engineering text.

And now you know one of the reasons why I'm retired.

Lew Hodgett, PE Retired

Sounds like not much fort, at derate we're going.