want to know about a steel post/pipe thickness

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BigDutchy
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want to know about a steel post/pipe thickness

Unread post by BigDutchy » February 1st, 2016, 8:06 pm

G'day people

I have to explain what I am doing to make my question kinda clear.....So bear with me....

I work at Flexible Learning Center in Brisbane.
We have built a 10 person hammock. It hangs between 2 big trees, the kids love it. We made it out of an old 3 tonne cargo net. For support (to get the triangle shape at the end and begin of the hammock) we used 2 massive lengths of bamboo.
This lasted 2 days so we replaced this bamboo with 2 lengths of steel poles/posts.
I guess the diameter of the poles/pipes/posts is about 100mm and about 1.5mm thickness. But it bent big time today.
So, now I am thinking of replacing the steel pipes/posts/poles with something thicker and welding an L bracket on it to give it strength.
I am not an engineer and need some ideas to make this hammock bullet proof.

What do you think I should look at?

Thanks

Cheers and thanks a lot

Shann Low
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Re: want to know about a steel post/pipe thickness

Unread post by Shann Low » February 2nd, 2016, 2:30 am

Umm a bigger public liability insurance cover to start with probably! :lol:

I salute you sir, for your efforts for the kids, to be lauded indeed.

I have some trouble "accepting" that one hammock should accommodate a heap of kids tho...for purely safety reasons.

Trees for starters - what amount of side load can they safely accommodate before one or both tip over - say on a windy day when the crown and leaves of the tree are already sustaining wind loading?

Cyclones & big winter storms will push healthy trees over, just from wind loading.

2 big trees MIGHT share the 1.5 tonnes a side shared potential loading from a gaggle of kids in a 3 tonne cargo net on a still day when the grounds dry and hard, BUT what happens after a weeks solid rain when the grounds soft and its blowing its tits off and the whole school of kids pile in at the same time for some fun?

The trees didn't know they would be put to that end use when nature grew their root systems. They simply aren't engineered to perform this test / work loading in possibly adverse conditions.

I have constructed a 'gin pole' out of heavy walled (6mm) 100 mm dia pipe.

Image
You can see that it's braced with stainless wire rope backstays.

Image :cry:
It was able to lift this almost 2 tonne Perkins 4cyl diesel and 45KVA genset, with a endless chain out of the vessel and down onto the winching trolley!

But it was set into concrete 2 feet down into the plate coral seafloor base as its pivot/stay point.

The trees supporting your big hammock have no such engineered back stays to support the side strain load. Typically their root system probably only extends to the leaf drip zone of the canopy.

Believe me, I don't want to kill off the idea of a play hammock for the kids, quite the opposite... I would just like to help prevent a potential disaster if it pulls one of the trees down on top of the kids is all.

Could this be done "better" if it was actually engineered and constructed to be safe rather than just relying on a couple of trees? Termites get into trees as does dry rot and fungal rot etc - much of which is never seen by the you until the tree fails.

As a former forester and saw miller (20+ years) and have seen every fault imaginable inside of trees once you open them up - but until they are felled and opened up in the mill you'll never see the potential faults. Most of the trees were perfectly healthy and stout as all get out, so would probably make perfect hammock supports (for one person) but a 3 tonne cargo net hammock at a school capable of talking a dozen or so kids at a time?... that's just asking for trouble.

Some species of trees even (Eucalypts) have a habit of limb shedding in Autumn just with afternoon change in temp and a sea breeze.

Could you maybe engineer some kind of galv steel supports in concrete to take the hammock - & something engineered (like the gin pole with back stays) to actually take the sideways strain...

Just me thinking out loud...

These days in our litigious society... I'd hate to see any kids hurt or people sued for just trying to give the kids some fun.

jfoldbar
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Re: want to know about a steel post/pipe thickness

Unread post by jfoldbar » February 2nd, 2016, 6:10 am

big dutchy.
need more info. like how are the steel poles joined to the ground? are they concreted in or chemset to a concrete slab?
at what point were they bending?
can u draw a little pic?

Rogers Cruiser
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Re: want to know about a steel post/pipe thickness

Unread post by Rogers Cruiser » February 2nd, 2016, 1:47 pm

Id be happy to help but a drawing would be very usefull.
'98-'06 - FJ-45 Ute fell over one day and didnt survive
'06-now - HJ-47 Troopy, restored and now daily driver.
'13-now - HJ-47 Ute, Farm fresh rust bucket, needs a restoration. viewtopic.php?f=22&t=152811

now - Off Road Box/Camper Trailer. viewtopic.php?f=134&t=153968&p=1792444#p1792444

Dont listen to me, Ive got an opinion on everything!

BigDutchy
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Re: want to know about a steel post/pipe thickness

Unread post by BigDutchy » February 2nd, 2016, 6:00 pm

Thank you for taking the time to even look at this.

About the trees....I am not worried about them. They are about 100 year old Moreton Fig type of trees and I think a
Camphor Laurel. The Hammock hangs about 50cm above the ground.
The Hammock it self is about 7M x 2.5M. It is an old 3t army cargo net.
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BigDutchy
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Re: want to know about a steel post/pipe thickness

Unread post by BigDutchy » February 2nd, 2016, 6:03 pm

The brown pipe/pole as seen in the picture above has bent. By the way we have connected the hammock a different way than shown here on this illustration. We have 2 connecting points and a sling around the tree..

I am not worried about the safety aspect of it all. I just want a fix for the bending pipe.

Thanks a lot again!! This is really appreciated.

Rogers Cruiser
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Re: want to know about a steel post/pipe thickness

Unread post by Rogers Cruiser » February 2nd, 2016, 10:42 pm

I would just replace it with something thicker. If you're in any way worried, get some extra-heavy pipe.

I have the bluescope steel book and you can get 100mm diameter pipe at 3.2, 3.6, 4.5 and 5.4mm thick - seeing as weight isn't an issue, I would just go with the heaviest you can get.
'98-'06 - FJ-45 Ute fell over one day and didnt survive
'06-now - HJ-47 Troopy, restored and now daily driver.
'13-now - HJ-47 Ute, Farm fresh rust bucket, needs a restoration. viewtopic.php?f=22&t=152811

now - Off Road Box/Camper Trailer. viewtopic.php?f=134&t=153968&p=1792444#p1792444

Dont listen to me, Ive got an opinion on everything!

BigDutchy
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Joined: November 6th, 2009, 6:58 pm

Re: want to know about a steel post/pipeWould square thickn

Unread post by BigDutchy » February 3rd, 2016, 7:29 pm

Would square be better than round?

Thanks

Aaron Schubert
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Re: want to know about a steel post/pipe thickness

Unread post by Aaron Schubert » February 3rd, 2016, 7:59 pm

Box is slightly stronger by the looks of it, but pipe would be more practical for your application. 1.5mm thickness is pretty thin - no wonder it bent. I very much doubt you would bend pipe at 5 - 6mm wall thickness, and 100mm OD.

Aaron
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Rogers Cruiser
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Re: want to know about a steel post/pipe thickness

Unread post by Rogers Cruiser » February 3rd, 2016, 9:27 pm

no round will be stronger. 5mm thick 100mm steel pipe would take tons of force to deform.
'98-'06 - FJ-45 Ute fell over one day and didnt survive
'06-now - HJ-47 Troopy, restored and now daily driver.
'13-now - HJ-47 Ute, Farm fresh rust bucket, needs a restoration. viewtopic.php?f=22&t=152811

now - Off Road Box/Camper Trailer. viewtopic.php?f=134&t=153968&p=1792444#p1792444

Dont listen to me, Ive got an opinion on everything!

Shann Low
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Re: want to know about a steel post/pipe thickness

Unread post by Shann Low » February 5th, 2016, 1:46 am

You can actually calculate how much force it takes to bend that pipe!.

It's called Euler's wall buckling theorem!.

Pdes < P cr = π^2 EI/L^2eff

Details available here:- http://www.esm.psu.edu/courses/emch13/d ... cdes1u.pdf

Good luck with it. ;) :lol:

BigDutchy
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Re: want to know about a steel post/pipe thickness

Unread post by BigDutchy » February 5th, 2016, 4:32 pm

Mate.....what are you doing...I might work at a school but I ain't no professor....

But I have bought bought 2 lenghts of 89x89x6mm....that should do the trick!

Shann Low
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Re: want to know about a steel post/pipe thickness

Unread post by Shann Low » February 5th, 2016, 6:10 pm

That should do the trick I reckon, but if the pipe doesn't bend, maybe the trees will likely get pulled over!. :lol:

Them Morton Bay Figs have huge root systems that spread a long way just like the canopy - all being well, you should be OK!

Unless of course some white ants, fungal rot etc have got in there... :confused:

No way to tell unless you cut the tree down to look!

When I was a lad we had a wire rope Zip line stretched between 2 trees across the back yard & a hemp rope "coight" soaked with oil, looped over it, as "the pulley" to ride it!.

It was freakin' awesome and kept us out of trouble most of the school holidays. No one got hurt and we all got fit climbing up the tree to take a turn next, these days you'd have the council inspector out declaring it a safety hazard. :rolleyes:

Go for it I reckon. Should be more of it!

We had a big rope swing out into the local water hole off a branch of a big river gum... mooring rope off a ship and a loop of chain and shackle holding it around the branch so it was strong as all get out BUT one day the steel chain link wore thru from years of swinging and just movement of the rope in the wind... wore the steel away & the link broke and a youth fell on to his back on the bank and broke a vertebrae in his back and was paralyzed.. from the waste down!.

He sued the Conservation Dept for millions and won.. it was our "recreation site" at the water hole and we had a duty of care to the public who used it - yto have forseen the possibility and maintained the swing rope / chain in good condition etc.

As a result the new policy was we had to remove all rope swings into water holes throughout the state on CALM land!.

Then the cliff at Margaret River collapsed during a rain storm - when the school surf carnival was on and a heap of students were sheltering inside the cave at its base from the rain to watch the surfing! Several died before they could be dug out, so then we went around with our shot firer - blowing up caves under cliffs to collapse them all so no one could shelter in them.... coz we got sued for that (and lost) too.

Then a few peeps got swept in and drowned off the rocks by freak waves fishing for salmon, and we got sued for that too (and lost) - so we had to put stainless steel rope anchors into the rocks for the fishers to attach themselves too and install life buoys at the rocks as well so they could be thrown into the water when someone got swept in.

The trouble is when **** goes wrong the lawyers look for someone (with money) to sue!.

It's all fun and games until someone pokes an eye out! :rolleyes:

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