John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700:

Better check the specs of the wire rope, the owner may be going by the
rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating
it 50%. Note the manufacturer recommends only a 20% load factor

I asked the owner about the weight of the deck, where this came back:
https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg

Hello Danny:

Thanks for your help last week. I couldn't have done it without you.h

You seemed skeptical about my estimate of the first bridge section.
Given a 2x10 weighs 3.37 lbs per foot.
Given a 2x6 weighs 2.00 lbs per foot.

3x16x3.37 = 162 lbs for the three long boards
2x10x3.37 = 68 lbs for the two end boards

2x6 2.00 lbs/ft
10x2x32 = 640 lbs for the decking

870 lbs per 16 foot section.

So if there are 5 sections (80 feet), or 6 sections (96 feet) we have
4,350 lbs or 5,220 lbs for the deck.

The cables can support 28,000 lbs.

That gives us 22,780 lbs for the house and occupants, assuming the only
support is the cable.

If we allow that some of the weight is supported by the posts and the
trees, we have even more leeway.

If the house is 24 feet long and ten feet wide, it will weigh about 8,000
pounds.

Add 4,000 pounds for furnishings and appliances.
That gives us 10,780 pounds of leeway for occupants.

But I plan to have most of the house weight supported by the redwoods,
not by the cable.

On 10/21/2014, 1:10 PM, Danny D. wrote:
John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700:

Better check the specs of the wire rope, the owner may be going by the
rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating
it 50%. Note the manufacturer recommends only a 20% load factor

I asked the owner about the weight of the deck, where this came back:
https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg

Hello Danny:

Thanks for your help last week. I couldn't have done it without you.h

You seemed skeptical about my estimate of the first bridge section.
Given a 2x10 weighs 3.37 lbs per foot.
Given a 2x6 weighs 2.00 lbs per foot.

3x16x3.37 = 162 lbs for the three long boards
2x10x3.37 = 68 lbs for the two end boards

2x6 2.00 lbs/ft
10x2x32 = 640 lbs for the decking

870 lbs per 16 foot section.

So if there are 5 sections (80 feet), or 6 sections (96 feet) we have
4,350 lbs or 5,220 lbs for the deck.

The cables can support 28,000 lbs.

That gives us 22,780 lbs for the house and occupants, assuming the only
support is the cable.

If we allow that some of the weight is supported by the posts and the
trees, we have even more leeway.

If the house is 24 feet long and ten feet wide, it will weigh about 8,000
pounds.

Add 4,000 pounds for furnishings and appliances.
That gives us 10,780 pounds of leeway for occupants.

But I plan to have most of the house weight supported by the redwoods,
not by the cable.


It again all hinges on the diameter of the cable (wire rope) they are
using and how it is secured. If it is 3/8" then I wouldn't go near it
assuming he is going by the maximum load.

Based on his reasoning (28,000 load spread over two cables) he needs at
least 7/8" (12,900 lb safe load each), but 1" (16,700 lb) would be better.

Attaching the house to the tree will save a lot of weight, however trees
grow larger in diameter so the support must allow for that somehow.

Also his securing of the wire rope must be flawless, and the fact that
he has already stressed the rope in a few places with the clamps has
weakened the original wire rope significantly.

However he doesn't appear to be willing to get an inspector, so I'll
assume I'll read about this upcoming disaster in the newspaper in the
near future (next couple of years).

Just because you are clever doesn't mean you are right. Some of us can
be quite smug...(ducking)

John :-#(#



--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

"John Robertson" wrote:

It again all hinges on the diameter of the cable (wire rope) they
are using and how it is secured. If it is 3/8" then I wouldn't go
near it assuming he is going by the maximum load.

Based on his reasoning (28,000 load spread over two cables) he needs
at least 7/8" (12,900 lb safe load each), but 1" (16,700 lb) would
be better.

Attaching the house to the tree will save a lot of weight, however
trees grow larger in diameter so the support must allow for that
somehow.

Also his securing of the wire rope must be flawless, and the fact
that he has already stressed the rope in a few places with the
clamps has weakened the original wire rope significantly.

However he doesn't appear to be willing to get an inspector, so I'll
assume I'll read about this upcoming disaster in the newspaper in
the near future (next couple of years).

Just because you are clever doesn't mean you are right. Some of us
can be quite smug...(ducking)
----------------------------------------------------------
You can buy them books, BUT if they eat the covers.

Lew

On Tue, 21 Oct 2014 14:25:46 -0700, John Robertson
wrote in

However he doesn't appear to be willing to get an inspector, so I'll
assume I'll read about this upcoming disaster in the newspaper in the
near future (next couple of years).

The lawyers are going to love it. Everyone from the wire rope
manufacturer to the water-boy will be sued.
--
I kill-file all messages posted through Google Groups.

On 10/21/2014 4:35 PM, Lew Hodgett wrote:
"John Robertson" wrote:

It again all hinges on the diameter of the cable (wire rope) they
are using and how it is secured. If it is 3/8" then I wouldn't go
near it assuming he is going by the maximum load.

Based on his reasoning (28,000 load spread over two cables) he needs
at least 7/8" (12,900 lb safe load each), but 1" (16,700 lb) would
be better.

Attaching the house to the tree will save a lot of weight, however
trees grow larger in diameter so the support must allow for that
somehow.

Also his securing of the wire rope must be flawless, and the fact
that he has already stressed the rope in a few places with the
clamps has weakened the original wire rope significantly.

However he doesn't appear to be willing to get an inspector, so I'll
assume I'll read about this upcoming disaster in the newspaper in
the near future (next couple of years).

Just because you are clever doesn't mean you are right. Some of us
can be quite smug...(ducking)
----------------------------------------------------------
You can buy them books, BUT if they eat the covers.

Lew


Now days Lew you buy them books and they eat the Teacher!

On 10/21/2014 3:10 PM, Danny D. wrote:
John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700:

Better check the specs of the wire rope, the owner may be going by the
rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating
it 50%. Note the manufacturer recommends only a 20% load factor

I asked the owner about the weight of the deck, where this came back:
https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg

....

870 lbs per 16 foot section.

So if there are 5 sections (80 feet), or 6 sections (96 feet) we have
4,350 lbs or 5,220 lbs for the deck.

The cables can support 28,000 lbs.

The problem as others have been saying generally and that Morgans points
out in another posting is this doesn't account for the geometry.

Consider for simplicity the condition if the cables were mounted on
telephone poles on level ground 100-ft apart. Say you tension the cable
so there's 10-ft sag in the middle. Using the tabulated weight for 3/8"
cable, I estimated that it takes only about 30 lbf to achieve that sag
so we'll ignore that for the time being.

With 10 ft drop at midpoint of 100 ft run, and considering that the
applied load will essentially straighten the cable, if the load were at
the center rather than distributed the angle between the horizontal and
the cable is invtan(10/50) -- angle ~11 degrees.

Now to support that load, the vertical component of the tension has to
balance the weight of approximately 5000 lb. That vertical component is
Tv=T sin(angle) or the cable tension T is Ty/sin(angle). Substituting
numbers and noting that for small angles sin(theta)~theta, the tension
to support that 5000 lb is

T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

So, you've taken up roughly half the total strength of the cable simply
by the decking. That's only a safety factor of ~2X and minimum
generally accepted is 3X while for overhead rigging and personal safety
of support 5X is considered prudent.

As said, this isn't going to approach that kind of margin and is
extremely risky going forward without more serious engineering than has
happened to date.

There are excellent design guides in the various handbooks that have
been linked to extensively before in the previous threads; no point in
reproducing them yet again if they're not going to be heeded.

But, your friend really needs some input from an engineer who
understands statics well enough to make some reasonable calculations for
the actual geometry and design.

--




That gives us 22,780 lbs for the house and occupants, assuming the only
support is the cable.

If we allow that some of the weight is supported by the posts and the
trees, we have even more leeway.

If the house is 24 feet long and ten feet wide, it will weigh about 8,000
pounds.

Add 4,000 pounds for furnishings and appliances.
That gives us 10,780 pounds of leeway for occupants.

But I plan to have most of the house weight supported by the redwoods,
not by the cable.

On Thu, 23 Oct 2014 07:36:12 -0500, dpb wrote in


T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

So, you've taken up roughly half the total strength of the cable simply
by the decking. That's only a safety factor of ~2X and minimum
generally accepted is 3X while for overhead rigging and personal safety
of support 5X is considered prudent.

As said, this isn't going to approach that kind of margin and is
extremely risky going forward without more serious engineering than has
happened to date.

There are excellent design guides in the various handbooks that have
been linked to extensively before in the previous threads; no point in
reproducing them yet again if they're not going to be heeded.

But, your friend really needs some input from an engineer who
understands statics well enough to make some reasonable calculations for
the actual geometry and design.

Good analysis. Unfortunately Danny D and Friends just don't seem to
understand what the effect of the catenary configuration has in
increasing the tension in the cable. I really hope someone convinces
them to have a engineer look at their exact config and do some simple
calcs as you have done above.
--
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
Email list-server groups and USENET are like having all of those
newspapers delivered to your door every morning.

On 10/23/2014 7:36 AM, dpb wrote:
....

Consider for simplicity the condition if the cables were mounted on
telephone poles on level ground 100-ft apart. Say you tension the cable
so there's 10-ft sag in the middle. Using the tabulated weight for 3/8"
cable, I estimated that it takes only about 30 lbf to achieve that sag
so we'll ignore that for the time being.

With 10 ft drop at midpoint of 100 ft run, and considering that the
applied load will essentially straighten the cable, if the load were at
the center rather than distributed the angle between the horizontal and
the cable is invtan(10/50) -- angle ~11 degrees.

Now to support that load, the vertical component of the tension has to
balance the weight of approximately 5000 lb. That vertical component is
Tv=T sin(angle) or the cable tension T is Ty/sin(angle). Substituting
numbers and noting that for small angles sin(theta)~theta, the tension
to support that 5000 lb is

T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

So, you've taken up roughly half the total strength of the cable simply
by the decking. That's only a safety factor of ~2X and minimum generally
accepted is 3X while for overhead rigging and personal safety of support
5X is considered prudent.
....

ERRATUM: I forgot to divide the cable limit by the two above -- the
actual limit per cable is (optimistically) as used by your friend 14000,
not 28000.

So, the decking alone is roughly 90% of the rated breaking strength and
adding a 200 lb person is 100/0.2--500 lb.

You'll gain a little by considering the decking as a distributed instead
of point load, but that'll be only a marginal improvement and you'll
likely lose some (and potentially a lot) for the non-uniform geometry on
the downhill side as that side may be almost perfectly horizontal so the
amplification factor of 1/sin(theta) goes way up as Morgans feared
(hence his 10X estimate).

THIS IS VERY BAD...

--

On 10/23/2014 8:05 AM, CRNG wrote:
On Thu, 23 Oct 2014 07:36:12 -0500, wrote in


T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

So, you've taken up roughly half the total strength of the cable simply
by the decking. That's only a safety factor of ~2X and minimum
generally accepted is 3X while for overhead rigging and personal safety
of support 5X is considered prudent.
....

Good analysis. Unfortunately Danny D and Friends just don't seem to
understand what the effect of the catenary configuration has in
increasing the tension in the cable. I really hope someone convinces
them to have a engineer look at their exact config and do some simple
calcs as you have done above.

Excepting I divided the load by 2 for each cable but then compared that
to the total rating of the two cables. So actually, the decking is
12,500 lb out of 14,000 breaking strength not 28,000 for the two.

See my followup to myself wherein I noted the fault...

--

On 10/23/2014 8:13 AM, dpb wrote:
On 10/23/2014 7:36 AM, dpb wrote:
...

....

T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

....


ERRATUM: I forgot to divide the cable limit by the two above -- the
actual limit per cable is (optimistically) as used by your friend 14000,
not 28000.

So, the decking alone is roughly 90% of the rated breaking strength and
adding a 200 lb person is 100/0.2--500 lb.

You'll gain a little by considering the decking as a distributed instead
of point load, but that'll be only a marginal improvement and you'll
likely lose some (and potentially a lot) for the non-uniform geometry on
the downhill side as that side may be almost perfectly horizontal so the
amplification factor of 1/sin(theta) goes way up as Morgans feared
(hence his 10X estimate).
....

On the last point -- the angle at which the total tension amplification
factor reaches 10X the applied load is invsin(10) -- 5.7 degrees as
opposed to the 11 degrees. That's not a lot of difference.

--

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


On 10/23/2014 7:36 AM, dpb wrote:
...

Consider for simplicity the condition if the cables were mounted on
telephone poles on level ground 100-ft apart. Say you tension the cable
so there's 10-ft sag in the middle. Using the tabulated weight for 3/8"
cable, I estimated that it takes only about 30 lbf to achieve that sag
so we'll ignore that for the time being.

With 10 ft drop at midpoint of 100 ft run, and considering that the
applied load will essentially straighten the cable, if the load were at
the center rather than distributed the angle between the horizontal and
the cable is invtan(10/50) -- angle ~11 degrees.

Now to support that load, the vertical component of the tension has to
balance the weight of approximately 5000 lb. That vertical component is
Tv=T sin(angle) or the cable tension T is Ty/sin(angle). Substituting
numbers and noting that for small angles sin(theta)~theta, the tension
to support that 5000 lb is

T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

So, you've taken up roughly half the total strength of the cable simply
by the decking. That's only a safety factor of ~2X and minimum generally
accepted is 3X while for overhead rigging and personal safety of support
5X is considered prudent.
...

ERRATUM: I forgot to divide the cable limit by the two above -- the
actual limit per cable is (optimistically) as used by your friend 14000,
not 28000.

So, the decking alone is roughly 90% of the rated breaking strength and
adding a 200 lb person is 100/0.2--500 lb.

You'll gain a little by considering the decking as a distributed instead
of point load, but that'll be only a marginal improvement and you'll
likely lose some (and potentially a lot) for the non-uniform geometry on
the downhill side as that side may be almost perfectly horizontal so the
amplification factor of 1/sin(theta) goes way up as Morgans feared
(hence his 10X estimate).

THIS IS VERY BAD...

I don't think they are taking heed. They have been successful with
their little neighborhood projects, and they are starting to get over
confident.
--
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
Email list-server groups and USENET are like having all of those
newspapers delivered to your door every morning.

On 10/23/2014 12:40 PM, CRNG wrote:
On Thu, 23 Oct 2014 08:13:06 -0500, wrote in

....

So, the decking alone is roughly 90% of the rated breaking strength and
adding a 200 lb person is 100/0.2--500 lb.

You'll gain a little by considering the decking as a distributed instead
of point load, but that'll be only a marginal improvement and you'll
likely lose some (and potentially a lot) for the non-uniform geometry on
the downhill side as that side may be almost perfectly horizontal so the
amplification factor of 1/sin(theta) goes way up as Morgans feared
(hence his 10X estimate).

THIS IS VERY BAD...

I don't think they are taking heed. They have been successful with
their little neighborhood projects, and they are starting to get over
confident.

I think Danny D is reading responses but the friend-in-charge is
apparently bullheaded-enough to not be willing to reconsider there's
anything to consider other than tensile strength in straight loading.

I do suggest that Danny not be committing himself to relying on this for
support from this point on as it's getting at least marginal already.
Of course, if the droop angles are significantly larger than the assumed
10 degree or so, then they gain a fair amount by there being a larger
vertical component but it's too spooky by far as described and shown.

--

On Thu, 23 Oct 2014 13:35:20 -0500, dpb wrote in


On 10/23/2014 12:40 PM, CRNG wrote:
On Thu, 23 Oct 2014 08:13:06 -0500, wrote in

...

So, the decking alone is roughly 90% of the rated breaking strength and
adding a 200 lb person is 100/0.2--500 lb.

You'll gain a little by considering the decking as a distributed instead
of point load, but that'll be only a marginal improvement and you'll
likely lose some (and potentially a lot) for the non-uniform geometry on
the downhill side as that side may be almost perfectly horizontal so the
amplification factor of 1/sin(theta) goes way up as Morgans feared
(hence his 10X estimate).

THIS IS VERY BAD...

I don't think they are taking heed. They have been successful with
their little neighborhood projects, and they are starting to get over
confident.

I think Danny D is reading responses but the friend-in-charge is
apparently bullheaded-enough to not be willing to reconsider there's
anything to consider other than tensile strength in straight loading.

I do suggest that Danny not be committing himself to relying on this for
support from this point on as it's getting at least marginal already.
Of course, if the droop angles are significantly larger than the assumed
10 degree or so, then they gain a fair amount by there being a larger
vertical component but it's too spooky by far as described and shown.

+1 on that
--
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
Email list-server groups and USENET are like having all of those
newspapers delivered to your door every morning.

On Tue, 21 Oct 2014 20:10:10 +0000 (UTC), "Danny D."
wrote:

John Robertson wrote, on Fri, 17 Oct 2014 23:46:50 -0700:

Better check the specs of the wire rope, the owner may be going by the
rated maximum capacity (12,200 lb for 3/8" wire rope) and only derating
it 50%. Note the manufacturer recommends only a 20% load factor

I asked the owner about the weight of the deck, where this came back:
https://c2.staticflickr.com/6/5608/1...8d70ba58_b.jpg

Hello Danny:

Thanks for your help last week. I couldn't have done it without you.h

You seemed skeptical about my estimate of the first bridge section.
Given a 2x10 weighs 3.37 lbs per foot.
Given a 2x6 weighs 2.00 lbs per foot.

3x16x3.37 = 162 lbs for the three long boards
2x10x3.37 = 68 lbs for the two end boards

2x6 2.00 lbs/ft
10x2x32 = 640 lbs for the decking

870 lbs per 16 foot section.

So if there are 5 sections (80 feet), or 6 sections (96 feet) we have
4,350 lbs or 5,220 lbs for the deck.

The cables can support 28,000 lbs.

That gives us 22,780 lbs for the house and occupants, assuming the only
support is the cable.

If we allow that some of the weight is supported by the posts and the
trees, we have even more leeway.

If the house is 24 feet long and ten feet wide, it will weigh about 8,000
pounds.

Add 4,000 pounds for furnishings and appliances.
That gives us 10,780 pounds of leeway for occupants.

But I plan to have most of the house weight supported by the redwoods,
not by the cable.

I see a complete failure to account for wind loads. Wind loads on this
tree house will be larger than the dead loads. Ask the owner to calculate
the wind loads as well.

?-)

On 10/23/2014 8:21 AM, dpb wrote:
On 10/23/2014 8:05 AM, CRNG wrote:
On Thu, 23 Oct 2014 07:36:12 -0500, wrote in


T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

So, you've taken up roughly half the total strength of the cable simply
by the decking. That's only a safety factor of ~2X and minimum
generally accepted is 3X while for overhead rigging and personal safety
of support 5X is considered prudent.
...

Good analysis. Unfortunately Danny D and Friends just don't seem to
understand what the effect of the catenary configuration has in
increasing the tension in the cable. I really hope someone convinces
them to have a engineer look at their exact config and do some simple
calcs as you have done above.

Excepting I divided the load by 2 for each cable but then compared that
to the total rating of the two cables. So actually, the decking is
12,500 lb out of 14,000 breaking strength not 28,000 for the two.

See my followup to myself wherein I noted the fault...

ERRATUM 2:

I outsmarted meself...I left the other 2X out on purpose originally and
then whiffed when came back. The free body diagram has T1 and T2
supporting the load, the tension force in each direction. Hence the
actual magnitude _is_ half the total, one half going each way.

So we're back to the ~2X SF for the decking which, while likely not
collapsing while they're building the basic deck, isn't a good starting
point for the overall structure.

Danny D. wrote, on Tue, 21 Oct 2014 20:10:10 +0000:

But I plan to have most of the house weight supported by the redwoods,
not by the cable.

We finished rigging up the second 16 foot section, which missed the
next set of redwood trees by about a foot or two.
https://c2.staticflickr.com/6/5611/1...49344c53_b.jpg

Unfortunately, those two redwoods straddling the end of the 32-foot
suspended section are just a tad under ten feet apart.

So, we're gonna have to engineer a slight bevel inward, to squeeze
in between those two trees, and then it's on to the next three or
four 16-foot long 10-feet wide sections, all of which is suspended
by ropes and temporary cables, at the moment, as we build it as we
walk out to the edge...
https://c4.staticflickr.com/4/3953/1...b58d5ecf_b.jpg

josephkk wrote, on Thu, 23 Oct 2014 18:23:37 -0700:

I see a complete failure to account for wind loads. Wind loads on this
tree house will be larger than the dead loads. Ask the owner to calculate
the wind loads as well.

This is a good point so I will mention it to him.

We worked on the second floating 16-foot section today, by the way.
https://c4.staticflickr.com/4/3955/1...2b960f68_b.jpg

So now we're suspended 32 feet straight out.

Only 60 or so feet to go!

dpb wrote, on Thu, 23 Oct 2014 07:36:12 -0500:

T=W/sin(angle) = (W/2)/sin(11) -- 2500/0.2 -- 12,500 lb

Wow. Those were wonderful calculations.
I forwarded it all to my friend, and will reply back with his response.

Meanwhile, we worked on the second section today, and we ended up stopping
about 2 feet away from redwoods which we need to squeeze through.
https://c4.staticflickr.com/4/3937/1...bffcce41_b.jpg

CRNG wrote, on Thu, 23 Oct 2014 12:40:15 -0500:

I don't think they are taking heed. They have been successful with
their little neighborhood projects, and they are starting to get over
confident.

I think the owner is taking heed, it's just that he's a third party
to this conversation (he doesn't know Usenet).

BTW, here's a view from below today, when I dropped my glasses
and had to climb down the steep hill to retrieve them.

https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg

dpb wrote, on Thu, 23 Oct 2014 13:35:20 -0500:

Of course, if the droop angles are significantly larger than the assumed
10 degree or so, then they gain a fair amount by there being a larger
vertical component but it's too spooky by far as described and shown

I'm sorry I haven't responded in a while. I hurt my back and was laid
up but hopefully I'm better now ...

The whole thing is supposed to hang from the cables, but we did anchor
one end because we needed a way for people to get "on" the decking.

Here's where we left it today...
https://c4.staticflickr.com/4/3945/1...22bf0914_b.jpg

CRNG wrote, on Thu, 23 Oct 2014 08:05:45 -0500:

Good analysis. Unfortunately Danny D and Friends just don't seem to
understand what the effect of the catenary configuration has in
increasing the tension in the cable. I really hope someone convinces
them to have a engineer look at their exact config and do some simple
calcs as you have done above.

I'm sorry I haven't been able to respond lately.

We had to readjust all the cables today, with a set of 5 winches, as
we had to re-balance everything once the second 16-foot section was
planked.

Unfortunately, I ruined my clothing, as I hadn't expected the oil
to still be soaking wet ... even though it was drying outside for
a day ...

https://c2.staticflickr.com/6/5616/1...c2665284_b.jpg

dpb wrote, on Fri, 24 Oct 2014 08:22:06 -0500:

So we're back to the ~2X SF for the decking which, while likely not
collapsing while they're building the basic deck, isn't a good starting
point for the overall structure.

I'm forwarding all this to the owner.

The only thing I can say is that it "seems" sturdy when we're both on
it, and that's almost 500 pounds of people alone ...

It's being supported, at the moment, by 6 separate winched vertical
cables (the winches are for level adjustments).

https://c2.staticflickr.com/6/5599/1...d812a890_b.jpg

VinnyB wrote, on Wed, 22 Oct 2014 05:58:58 -0500:

The lawyers are going to love it. Everyone from the wire rope
manufacturer to the water-boy will be sued.

You forgot the screw manufacturers!
https://c4.staticflickr.com/4/3935/1...e1cc2650_b.jpg

Notice we gave up on the lower screw (the one with the longer thread).

It was just too hard to drive into the wood.

Even with this nice pile driver thing from Harbor Freight!
https://c4.staticflickr.com/4/3934/1...3a566c90_b.jpg

The screw on top, with the shorter thread, goes in without pounding!

"Danny D." wrote in
:

josephkk wrote, on Thu, 23 Oct 2014 18:23:37 -0700:

I see a complete failure to account for wind loads. Wind loads on
this tree house will be larger than the dead loads. Ask the owner to
calculate the wind loads as well.

This is a good point so I will mention it to him.

We worked on the second floating 16-foot section today, by the way.
https://c4.staticflickr.com/4/3955/1...2b960f68_b.jpg

So now we're suspended 32 feet straight out.

Only 60 or so feet to go!

See http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
The chances of your bridge deck fluttering in a blow are fairly high.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL

Ian Malcolm wrote, on Tue, 28 Oct 2014 00:21:08 +0000:

See http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
The chances of your bridge deck fluttering in a blow are fairly high.

We actually joked, a few times, about the Tacoma Narrows bridge, and,
yes, I think just about everyone has seen that video of the car on
the bridge and the person getting out and making it just in time.

This bridge isn't nearly as long.

It's only about 100 feet long, by 10 feet wide, supported on one end
on the ground and on the far end about 40 or 50 feet up in a tree on
a (very) steep slope.

Here's what the first two 16-foot-long sections looked like today,
when we ran out of oiled wood:
https://c4.staticflickr.com/4/3945/1...22bf0914_b.jpg

I'm currently learning how to wash good clothes to get the oil
out!

"Danny D." wrote in message
...
CRNG wrote, on Thu, 23 Oct 2014 12:40:15 -0500:

I don't think they are taking heed. They have been successful with
their little neighborhood projects, and they are starting to get over
confident.

I think the owner is taking heed, it's just that he's a third party
to this conversation (he doesn't know Usenet).

BTW, here's a view from below today, when I dropped my glasses
and had to climb down the steep hill to retrieve them.

https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg



Pardon me for a silly suggestion but ...

.... in view of the - how shall we put it - challenging ? - nature of the
site, wouldn't it be a good idea to have your specs on one of those strings
around your neck ? And tools like hammers, roped to your belt ?

Arfa

On 10/27/2014 6:34 PM, Danny D. wrote:
CRNG wrote, on Thu, 23 Oct 2014 12:40:15 -0500:

I don't think they are taking heed. They have been successful with
their little neighborhood projects, and they are starting to get over
confident.

I think the owner is taking heed, it's just that he's a third party
to this conversation (he doesn't know Usenet).

BTW, here's a view from below today, when I dropped my glasses
and had to climb down the steep hill to retrieve them.

https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg

Where are the supporting cables in the picture--on top or just hidden by
the view?

What I'd like to know is can you measure the height differential between
the upper and lower mounting locations and the approximate distance from
the straight line between them to the low point and where that point
turns out to be between the two end points. In a _very_ crude sketch..


| |
A-|- |
| |
| -|-B
| |
= |
| X |
____ C =
xxxx _____
xxxxx

A and B represent the two tieoff points, the relative height between
them and then the distance from the lowpoint C in the middle somewhere
to either of those plus the horizontal distance from C to the two trees
represented by the vertical lines.

With that could at least crudely approximate the loadings and the
tension amplification from the angle of dangle, so to speak.

As you can see from the previous as the angle gets smaller, the
multiplier gets large quickly because there isn't much of a component of
the total tension in the vertical direction to support the load. You
also need to consider how much side load this is putting on those trees
and how large they are at that point to handle the lateral load plus how
well their root systems are capable of that additional continuous load,
particularly when the ground gets saturated when it finally does rain
again...

--

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

ERRATUM: I forgot to divide the cable limit by the two above
-- the actual limit per cable is (optimistically) as used by
your friend 14000, not 28000.

Here's the response from the neighbor building the deck...
https://c4.staticflickr.com/4/3953/1...1f28763d_b.jpg

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
16-foot-long section goes away completely, as does half the weight of the
next 16-foot-long section. And we still have the option of supporting the
other half by attaching it to the small redwood trees, along with half of
the third section.

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:

... in view of the - how shall we put it - challenging ? - nature of the
site, wouldn't it be a good idea to have your specs on one of those
strings around your neck ? And tools like hammers, roped to your belt ?

That's a good suggestion, as we have tools all over the place!
https://c4.staticflickr.com/4/3948/1...c6370a50_c.jpg

Usually, we tie in when we're out on the cable, with no firm footing:
https://c4.staticflickr.com/4/3947/1...fee9cb37_b.jpg

And, we tie in when we're working on the steep slope below the deck:
https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg

The harnesses we use are the same ones we use for climbing the hills:
https://c2.staticflickr.com/6/5602/1...2eb1ee32_b.jpg

Here's my setup, for example, as I was digging the fence post holes:
https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg

And, here's what I used when I had to double-line rappel downslope:
https://c4.staticflickr.com/4/3932/1...03b1b22c_c.jpg

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:

https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg
Where are the supporting cables in the picture--on top or
just hidden by the view?

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.
https://c4.staticflickr.com/4/3943/1...a8481615_b.jpg

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:
https://c2.staticflickr.com/6/5600/1...a7136264_c.jpg

Here is a picture taken earlier in the day, before we planked the second
16-foot-long section, showing how the 10-foot-wide deck is suspended from
the steel cables (this is the second of the two 16-foot-long sections):
https://c2.staticflickr.com/6/5601/1...53aa5e3e_c.jpg

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

You also need to consider how much side load this is putting on those
trees and how large they are at that point to handle the lateral load
plus how well their root systems are capable of that additional
continuous load, particularly when the ground gets saturated when it
finally does rain again...

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):
https://c4.staticflickr.com/4/3953/1...1f28763d_b.jpg

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:
https://c2.staticflickr.com/6/5600/1...a7136264_c.jpg

"Danny D." wrote in message
...
Arfa Daily wrote, on Tue, 28 Oct 2014 02:05:05 +0000:

... in view of the - how shall we put it - challenging ? - nature of the
site, wouldn't it be a good idea to have your specs on one of those
strings around your neck ? And tools like hammers, roped to your belt ?

That's a good suggestion, as we have tools all over the place!
https://c4.staticflickr.com/4/3948/1...c6370a50_c.jpg


Boy oh boy ... I thought I was making a bit of a silly suggestion there ...



Usually, we tie in when we're out on the cable, with no firm footing:
https://c4.staticflickr.com/4/3947/1...fee9cb37_b.jpg


Work clothes ?



And, we tie in when we're working on the steep slope below the deck:
https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg


That's concrete, yes ? Looks a little lean on the mix ... ?



The harnesses we use are the same ones we use for climbing the hills:
https://c2.staticflickr.com/6/5602/1...2eb1ee32_b.jpg

Here's my setup, for example, as I was digging the fence post holes:
https://c4.staticflickr.com/4/3950/1...b042e8a8_b.jpg

And, here's what I used when I had to double-line rappel downslope:
https://c4.staticflickr.com/4/3932/1...03b1b22c_c.jpg

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...


Hmmmm ...

Arfa

"Danny D." wrote in message
...
dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500:

You also need to consider how much side load this is putting on those
trees and how large they are at that point to handle the lateral load
plus how well their root systems are capable of that additional
continuous load, particularly when the ground gets saturated when it
finally does rain again...

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):

Animals have a sort of 'sixth sense' about this sort of thing. Perhaps this
should tell you something ... d:-}

Arfa

On 10/27/2014 10:56 PM, Danny D. wrote:
dpb wrote, on Thu, 23 Oct 2014 08:13:06 -0500:

ERRATUM: I forgot to divide the cable limit by the two above
-- the actual limit per cable is (optimistically) as used by
your friend 14000, not 28000.

Here's the response from the neighbor building the deck...
https://c4.staticflickr.com/4/3953/1...1f28763d_b.jpg

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
16-foot-long section goes away completely, as does half the weight of the
next 16-foot-long section. And we still have the option of supporting the
other half by attaching it to the small redwood trees, along with half of
the third section.

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.

Some validity to the above but...

While it is true that the end that is resting on the ground does have
that support, it's not necessarily so that the remaining load on the
cable is only half; it depends on the actual geometry of the
configuration. It _might_ be half; could be more, could even be less.

The previous "analysis" was simply intended as a demonstration of the
effect geometry has on the overall tension required in the cable
(actually, any supporting member--that it is cable in that sense is a
distraction) is that which will, for the given arrangement, provide a
vertical component that balances the gravity forces plus applied loads.
The key lesson intended to be shown is that the vertical component is
dependent upon the angle of the tension force.

Thinking that "it's harder to put that much tension on the cable" isn't
really so--while the trees may move some, the actual counteracting force
is whatever it needs to be given the loading. If the distance is
shortened enough, yes, the angle will increase but that's going to
exacerbate the other issues raised of whether the root structure can
sustain that continued side load (increased moment at the base)
indefinitely, particularly with the addition of wind load and ground
saturation and all the other things that go on.

I do agree that with the one end supported that certainly helps and the
idea of the second ground support at the outer end is also a good one
but I'd still think it only prudent to get the input of a competent
engineer to evaluate the overall structure, including the questions of
the ability of the soil to hold and what would be realistic wind loads
and so on. While one would presume nobody would be silly enough to be
out there during a storm, it seems a sizable investment in both time and
money to risk losing it all the first thunderstorm or the next coastal
front with a good blow. It's certainly not unheard of uncommon for them
to have 90 mph in WA where daughter is; don't know how far this is from
coast nor elevation and such but would think it not unreasonable
guesstimate.

It's just imprudent imo to not have more than just a "seat o' the pants"
look at something this ambitious and that has such a potential for
serious consequences if these guesstimates are wrong. Given the $$ that
have and are obviously going to be expended, a few more thrown at the
design/safety issues would seem a good investment. (Or, is the issue
that if does that it'll get stopped because it isn't within whatever
covenants are in place for the location?)

Anyways, I've had my say; simply hoping nothing does go wrong but it
seems a very risky venture as is...

(*) The unique thing about cable is that unless the loading is such as
was presumed before that the cable is essentially straightened by the
load, the tension is variable along the cable
--

On 10/28/2014, 2:57 AM, Arfa Daily wrote:


"Danny D." wrote in message
...
dpb wrote, on Mon, 27 Oct 2014 21:06:58 -0500:

You also need to consider how much side load this is putting on those
trees and how large they are at that point to handle the lateral load
plus how well their root systems are capable of that additional
continuous load, particularly when the ground gets saturated when it
finally does rain again...

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):

Animals have a sort of 'sixth sense' about this sort of thing. Perhaps
this should tell you something ... d:-}

Arfa

The dog is the only one paying attention to load factors.

John :-#(#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

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

https://c4.staticflickr.com/4/3947/1...fee9cb37_b.jpg
Work clothes ?

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!
https://c4.staticflickr.com/8/7474/1...aaff11cc_b.jpg

Maybe we should pick up a pair of these Ghillies as fitting
work clothes, since we're always hanging around in the trees:
https://c4.staticflickr.com/4/3943/1...d8aa3fd1_b.jpg

On Mon, 27 Oct 2014 23:46:30 +0000 (UTC), "Danny D."
wrote:

https://c4.staticflickr.com/4/3935/1...e1cc2650_b.jpg

Notice we gave up on the lower screw (the one with the longer thread).

Those screws are from GRK Fasteners...

http://www.grkfasteners.com/index.php/en/

Videos on Youtube:

http://www.youtube.com/user/grkfasteners/videos

On 10/28/2014 9:21 AM, dpb wrote:
....

(*) The unique thing about cable is that unless the loading is such as
was presumed before that the cable is essentially straightened by the
load, the tension is variable along the cable

Ignore the above; I thought I had deleted it before posting...I was
beginning an involved discussion regarding multiple loading points and
all and decided against it...

--

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

While it is true that the end that is resting on the ground does have
that support, it's not necessarily so that the remaining load on the
cable is only half; it depends on the actual geometry of the
configuration. It _might_ be half; could be more, could even be less.

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:
https://c2.staticflickr.com/6/5605/1...4969faac_z.jpg

Here is where we are right now:
https://c4.staticflickr.com/8/7575/1...ed414ac3_z.jpg

And here is the penultimate ending point static JPG:
https://c2.staticflickr.com/6/5600/1...66bb66b1_z.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:

Those screws are from GRK Fasteners...

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...
http://i62.tinypic.com/ieeakx.gif