Gin Pole Issue

[behoof]

Hi all,

Well, finally getting the conversion up in the air, at least that was the plan.

I had everything on the tower and was preparing for a test lift and was gonna let the rig sit hanging out of the cradle for a day or so as a test of cables and such... (probably not necessary, but that's just me) anyway, I was pulling ever so slowly forward with the tractor and the jenny and blade set didn't seem to be moving... uh oh, locked up the tractor after backing back to start point and got off to look...

Well, as luck would have it, my gin pole was the weakest link it seems... it took a big "wowww" and said bye bye... shoot...

But, after a moment of reflection... I need to be grateful that it happened as it did... could have been half way up and man, that would have been a disaster...

My lift is:

tower 65'  350lbs

jenny 100lbs

12' blades and mounts 70lbs

miscellaneous hardware (cable, clamps etc) 50lbs

4 sets of 4 guys

gin pole was 2.5" schedule 40  30' long with support lines at center to ground anchors points at sides, it wowwwed towards the tower not the lifting side? Prior to the lift I rechecked (again) all the tensions on the cables to be sure everything was equal. By the way, this tower was up for over three years with my other jenny on it, this is not a new set up just beefed up a bit for the new conversion.

the tower is three legs pivot at the bottom gin pole attached at tower base (fixed to tower as in picture when in use)






Tower Base with gin pole attached






Tower at rest on stands

Wondering if anyone would be able to offer some thoughts on this? I've studied DanB's 20 footer and how he worked that one out (very nice I might add) so I'm thinking that I need some idea of what would be an appropriate dimension and wall or type of pipe to use for this lift? Perhaps something thinner walled but larger diameter like 4 or 5" schedule 20 ??

This setup has a chevy small block in each ground anchor hole with cement (a piston missing for a ground anchor to pass through in each).

Would also like to know just what kind of weight or force is necessary to lift this bundle from a math perspective when considering how much it weighs and the length and all?? (What forces are really at work on this thing when lifting?)

Thanks to everyone for all the info and help you give, especially my friend Zubbly who helped me get this thing together (miss him).

Best,

behoof

[SparWeb]

You'd better sit down for this:  remember all that trigonometry you so proudly forgot after high-school?  Sort-of?  Well, the bad news is you'd better brush up, because it's come back into your life.

Don't worry this won't be too painful, but a bit more engineering terminology is necessary before we get to the end.

You've witnessed "column buckling" on your gin pole, a classic case.  The gin pole is under a large amount of compression during the lifting process and a 3" pipe isn't suitable, considering the +500 pounds lift and the 30 foot length.  It gets worse with the pin-joint attachment you've got there.

I use a 3" Sch40 pipe, rigidly attached to the pivot, to raise my 45' tower.  Since the gin pole is a "compression" member in the tilt-tower system, it must be stable under compression loads.  It is also important to attach it at the base in a way that does not induce extra bending and twisting.  I think that's what you've inadvertently done.

As you pull forward on the tractor, the cables go tight and stretch a little.  The gin pole has now rotated a few degrees from vertical, but the tower hasn't gone up yet.  The line of action through the gin pole doesn't point at the tower's hinge bolts.  The eccentric load starts the gin pole bending, just when the whole system is under the greatest load.

I would not attach the gin pole in the way you have done.  Please hinge it at the base plate, or rigidly attach it to the tower.

What size of bolts does the tower hinge around?

...chevy small block in each ground anchor hole with cement...

You know some day in the far far future, an archaeologist is going to start finding buried engines in square patterns around central concrete slabs, and wonder what strange primitive rituals the 21st century humans where doing there.

[Ungrounded Lightning Rod]

I take it by "wooow" you mean "bend", right?

A gin pole during raising may be loaded in compression more than the tower is, depending on how far away the tow point is when you're first starting up.  It needs to be strong against bending (unless you also guy the MIDDLE of the gin pole, which is getting silly).  So you want a large diameter pipe to be strong against bending.

The good part is that the forces on it are strongest just at the start, so if you're not hoisting irregularly it's more likely to fail right away rather than once your tower is halfway up.)

As for lifting force you can figure that out from the tower weight, top-load weight, the lengths of the tower and gin pole, the angle between the tower and gin pole, and a little trig.  If the tower is tapering you'll also need to find its center of gravity, rather than assuming that's halfway up.  The shorter the gin pole the higher the forces on the hoisting guy(s) at the start of the raising / end of the lowering.

[ghurd]

Hi Steven,

You mean the stretched part of the cable, between the tower and gin pole, somewhat bent the gin pole, and then it tends to keep bending in the same direction when under compression?

Hypothetical "what if" a second piece of 2.5" was connected to the first (say a 3x3" plate on both sides every 5') so it made a figure 8, oriented with the cable through the center of both pipes?

Make sort of a dual-circle concept of a spar web (hehe).

Humans thought so much of the 350 Chevy, they were ritually buried?

And with a steel rod through #5, in much the same manner as wooden stake in a vampire's heart?

G-

[SparWeb]

I think I'll add a bit more about the attachment problem; I don't think I got my concern across.

The gin pole moves before the tower does, thus opening up that angle.  The cable attaching the gin to the tower stretches an inch or so under load, opening the angle up firther.  Under the its own weight, the tower sags, and its bottom end turns away from the base plate.  Yet again, the angle between tower and gin pole becomes larger than 90 degrees.  It is entirely possible that the gin pole got itself to an "over-center" angle with your double hinge setup, and it was both holding the tower down, and on the verge of collapsing itself.  The compressive load was probably much larger than it should be in normal raising.

Again, please don't try to raise the tower without attaching the gin to something else, or in multiple places on the bottom of the tower.

[bzrqmy]

I have a excel spreadsheet that an engineering buddy of mine developed.  It's designed for tilt up tower with gin pole.  It has lots of variables that can be easily tweaked.  I am not sure how to post it on the site, so e-mail me and I can pass on a copy.

bzrqmy@yahoo.com

[behoof]

Steven,

Thanks for the thoughts on this.

I hope I understand your explanation on this but you mention the "double hinge"  and I'm not sure what you mean. The gin pole is attached to the movable leg of the tower by 1/2" grade 8 bolts but that point of connection is not meant to be a hinge. All it is would be a point to connect the pole to the tower. 30' out is a joiner for a shackle on one side to go to the gin pole and 4 turnbuckles on the other side up to the tower. So not sure about the double hinge point and its significance.

I do see your point of mounting a plate to the base plate of the tower for a gin pole mount. Thank can be done pretty easily and quickly.

But I still wonder what size tubing I should use for this lift? After having this failure I'm a bit more than cautious of what to use.

Also, trust me when I say that Trig is OUT of the question, so if there is a sympathetic soul out there that could help me figure out what the load on the cable might me I'd sure appreciate it... from the gin pole tip to the pulling ground anchor is three cable parts and of course, one to the tractor.

If you can think of anything else I need to watch out for I sure appreciate it.

If you get a chance drop me an email at skipb@greatlakes.net

Really appreciate the help,

Skip

[behoof]

Ungrounded,

Yeah, the woww was meant to bend, and the way it bent, when it happened I couldn't see it happen because it bent straight away towards the tower from me so I couldn't see what happened, only knew that the jenny and blades hadn't lifted off their cradle.

This gin pole was guyed both to the side at the top and the middle, and from the middle to the tower, nothing other than the lifting cables to the tow point.

And you think I can figure the lifting forces, sorry, math (Trig) and I really don't do well together.

Thanks for the reply,

Skip

[Ungrounded Lightning Rod]

This gin pole was guyed both to the side at the top and the middle, and from the middle to the tower, nothing other than the lifting cables to the tow point.

Yeah, it's hard to do a middle guy to the tow because the two cables would have to change lengths as you raised the tower.  Gotta keep it straight by making it stiff.

Take off the unopposed guy from the middle of the gin pole to the tower.  It contributed to the bending of the pole, big time.  The pole might not have been stiff enough to avoid bending anyhow.  But the extra pull from that guy greatly raises the stiffness needed to avoid the bending, by giving the pole the initial slight bend that starts the collapse.

You probably want to remove the side guys at the middle of the gin pole, too, and just guy it at the tip.  With it guyed against bending failure in only one plane any inequality in the side guys will start it bending, though they will also limit the amount.  But a slight asymmetry will let the bend also occur in the other plane (where it's not opposed) and the pole will continue to fold up.  The more it bends the weaker it gets against bending in a positive feedback collapse.

And you think I can figure the lifting forces, sorry, math (Trig) and I really don't do well together.

Post the measurements and we'll go over 'em.

[RP]

"and from the middle to the tower"  

I think that's where your problem came from.  I would suggest making all attachments to the tower from the top of the gin pole.  

With any amount of stretching of cables and flexing of the tower, that middle of the gin pole connection would've taken nearly the full brunt of the pulling force.

[behoof]

Ungrounded Lightning Rod,

Thanks for the comeback.

I must have raised and lowered this tower 20 times or more over the years of it being up with the other jenny... ahhh well, the weight was certainly less.

Anyway, what I have is:

tower 65'6" (the attaching point is at 60')----- 350lbs

jenny & 12' blades and mounts  --------------  170lbs

miscellaneous hardware

(cable, 4 AWG, elec box, clamps etc) --------   50lbs

tail and mount ------------------------------   40lbs

                 Total Weight of all parts      610lbs

4 sets of 4 guys at 15' 30' 45' 60'

Anchors set in a 30' circle around center point of tower hinge, not center of tower.

The weight of this set up is mostly at over 60'. The 60' cables are 5.5' down from the very top of the jenny and as you can see in the pictures, everything is pretty much above that except for 65' of 4AWG 4wire, attaching hardware and about 130lbs of the mast.

side view




view of top




view of top 2




view of top 3

Hope this is enough info and thanks again,

Skip

[SparWeb]

I can go overboard with the "thus" and "therefore" stuff.

If the situation I've drawn is what is happening, then you will never lift the tower.  Like I said before, the gin pole is in compression.  If it is pushing down on the tower like this, then it is holding the tower down.  

As you pull more, the offset gets bigger and the situation gets worse.  It may even magnify the compression load - causing more buckling than you would otherwise see.  You're very lucky that you were stopping to check things as you started to pull.

I can't really tell if this is actually what is happening - this is yet another case where figuring out this stuff has to be done by the guy standing right there.

Why isn't your gin pole attached to the free stub on the base plate?

[behoof]

Steven,

Appreciate your taking the time to follow up on this.

In your drawing you show the gin as if it were only attached to one leg of the tower, if you look at the pics you'll see that there is ample metal between all the legs but you are correct in that the gin would be able to pivot on its pin given the opportunity.

What I'm going to do is build a plate to attach directly to the back 3 - 1 1/2" base plate studs that go down into the footing and mount the gin directly to the base plate behind the pin currently looking open. It's the pin for the third leg of the tower when it comes over and anchors.

As I mentioned this tower has been in use for a number of years and been up and down probably more than 20 times without incident. Perhaps it was a disaster in the making and I was just very fortunate that it all happened as it did?? I feel pretty happy that it happened in the cradle rather than on the way up, damn, I am lucky.

I was still hoping that some kind engineering/math knowledgeable person would help me out with some numbers on what kind of forces are REALLY at work here, I'd sure like to know?

Also, if you care to use it, my email is skipb@greatlakes.net perhaps that way I won't clutter the board with all my gibberish?

Thanks again,

Skip

[SparWeb]

...help me out with some numbers...

Well that's what I'm here for.  We're still trying to define the problem, so the numbers come later.

Seriously, it is really hard to work this stuff out through a web forum or e-mail, because details missed in a photo could have major consequences.  Sometimes just changing your perspective, plucking a tight wire, sighting along the length of the pole makes all the difference.

Just in case you didn't see the posting, I've seen my own tower crashing to the ground.  Not fun at all, and I have to live with wondering if I had just checked this or that more carefully, maybe I would have caught the mistake before the accident.

[SparWeb]

...build a plate to attach directly to the back 3 - 1 1/2" base plate studs that go down into the footing and mount the gin directly to the base plate behind the pin currently looking open...

Okay, that will help.  I picture the gin pole coming down on top of the third stud, but of course you've probably thought of that and it won't be in the way.  That will get rid of the knee joint so that will help a lot.  Attaching all wires to the tip of the gin pole is also important.  If you do both of those things and still see your gin pole buckling please let us know because then something else is happening.

Thank you for sharing the other photos.  That's a very tidy setup.  I don't usually spend much time painting things.

[wpowokal]

I have read this post a few time and still fail to fully follow all comments, so I add my own.

You are lifting a lot for what you have, I use two 1 1/2" pipes side by side joined with flat bar. I guy them back to the side anchors at mid length and end. All cables on the lifting side connect to the gin pole end which is then tied to that anchor point, I use a separate hinge point. On your arrangement you place much stress on the tower base.

I fail to understand why your gin pole bent toward the tower unless cable's were badly adjusted. You do understand that you must have a second person holding via a cable, the mid point of the tower in the opposite direction, during raising and lowering. Please refer to Bergy's site.

allan down under  

[Qmark]

Hi,  if you attach the cable to the top of the gin pole, around a pulley on the tractor hitch and back to the centre of the gin pole where the cable is attached to the tower it should help balance the force and prevent the said bend.       mark

[behoof]

Well,

I spent an hour + with a very knowledgeable gentleman structural engineer. He has a frikkin' wall full of "I love me" stuff. Heck, he's at least my age LOL.

Anyway, he took the time to explain all the particulars and helped to me try to better understand the failure that took place with the collapsed gin pole.

As was mentioned in the replies to my post this is truly a classic case of "oily collapse" . His words not mine, I understand it to have to do with all metals having the inherent ability to collapse under compression load. This was obviously that.

Anyway the long and short of it is that he broke out his engineering books and programs and we went over the numbers of my set up and arrived at some loading factors and projections.

So, after all that, what I've arrived at is that instead of using "round" tubing, it will be far superior to use 4" x 3/16" wall square tubing by a factor of 4 over using 4" Schedule 40 round pipe.

He also advised something I would have done anyway and that's to pull my new jenny off the tower and just add dead (dummy) weight and do a lift or two and let it stand for a day or so. Which was what I was doing when this failed.

In one of my posts to this thread I put in all my particular weights and such but after talking to him what we came up with is:

cable tension should be approx. 1100 lbs

horizontal force should be       750 lbs

vertical or compression force   1700 lbs

all approximate

Well, now to fab up a new mounting device to mount to the base plate mount for the gin and gather up some 4" square tubing.

Don't we all just love "FREE" electricity?  

[behoof]

Hi allan,

I spent a lot of time adjusting the cables to be equal in lifting force.

Yes Allan I have a second block n tackle set on the back side and a safety cinch to keep it from crashing over towards the pulling side.

Like I had mentioned in another part of this thread, this tower has been up and running for a long time, not a new install, but the jenny going on it now is new and heavier.

Thanks

[ruddycrazy]

G'day Behoof,

              I use the same type of tower on my genny next to the shed and although its only 9 metres high i use a detachable ginpole so to lower and raise my tower its a one man job in less than 5 minutes. Ok how my gin pole is set up, I use 40x5mm square tube and it's basically a 'L' config. The gin pole itself is just on 4 metres and the other part of the 'L' is welded at a right angle to the end of the pole. I welded a plate which mounts in 2 slotted holes at the base of the tower then i slide a length of 50x10mm flat bar through the tower and secure it with some bolts- I drilled and tapped some holes for the bolts. I reckon with my 3 metre blades, the 2hp conversion and tail i'm lifting near 100kgs. I have had the tower buckle as silly me didnt loosen the side guys and while trying to take the blades off i rocked the tower and she buckled. i did manage to repair the buckle but i did lose 1/2 a metre of height. Oh with my gin pole i have one wire with a turnbuckle thats normally lose but when the gin pole starts to work it tightens up and everything is secure. For my tower base I made a round bar attachment and my tower base is 2 lengths of 40x5mm square @ 1 metre deep and concreted in.

Cheers Bryan

[behoof]

Thanks Bryan,

Any chance you'd have a drawing of your setup?  Sounds rather interesting and I'd really like to see your picture of it to be sure I have it clear.

Thanks

Skip

[SparWeb]

I must applaud you for taking your project so seriously that you asked for expert help when it was needed.  I suspected our earlier exchanges were not helping as much as you wanted.  Hard to explore a topic in that much depth on a forum.

Those loads look a lot like the figures for my 45' tower, which are pretty fresh in my mind as I am installing a winch to raise it.  Did he mention anything about loads and/or safety factors on the cables?  

[behoof]

Hi Steven,

Yes he did stress safety factors both built into materials when spec'ing your project. i.e. a piece of schedule 40 3" tubing has a built in safety factor in its MSDS, and so on.

On the cables he suggested to be careful and be sure not to exceed the recommended safety limits. Example: If all you know is the breaking strength of a given cable do not exceed 20% of that number. so as in my case, I have a compression factor +/- 1500 lbs and I'm using 5/16" cable for guys and 3/8" for lifting cable. The 5/16" 7x19 I'm using has a breaking strength of 9800lbs so I won't exceed 20% of that number or 1960lbs for my guys, and remember I'm using 4 sets of 4 guys so there is a multiple of strength there. And on the lifting cable the 3/8" is rated at a breaking strength of 14400lbs, so, my safety factor for lifting weight (considering compression factor too) is 2880lbs which leaves me well within a very good safety range.

I'm also wondering why, after all I've learned from this Engineering Firm, folks don't consider using square tubing for towers? Just a thought of course, perhaps there's some really good reason for it but the strength factor of square is way higher for a given diameter when compared to an equal diameter of round. Just a thought??

Anyway, I really appreciate your keeping up with this thread, I don't mean to be a bug about it, usually not my style but when you see a reasonably substantial piece of material bend like spaghetti it definitely gets my attention.

If you're interested, I sent you my email address, feel free to use it, would love to chat regarding all this.

Thanks again,

Skip aka behoof

[SparWeb]

That is good guidance you have been given.  You can boil it down to a set of instructions that keep you safe, or you can delve into details that may make you more knowledgeable, but not necessarily much safer.  I go for the latter but that's just me and my nerdy ways.

A square tower has more drag in the wind - a negligible effect compared to the wind turbine loading.  But when you consider that for free-standing truss towers, three legs are the norm because 3 legs have less drag than 4, then you can see that most tower builders get away from using square anything.  The philosophy can carry you along to places where it doesn't matter, like pipe towers, where a few 10's of pounds do not matter.  Besides, round is cheaper and easier to buy, and the yawing joints are simpler, etc...

I will send you an e-mail because I want to "check up" on some things the engineer told you... :^)