Are Using Monopole Towers Taboo?

[fabricator]

         I've pretty much abandoned the monopole possibility for a wind generator. Why? Mainly because it's not cost effective on any level. Some very smart engineers can figure it out (when they're not disagreeing), but you'll have to pay for it big time, because it's all become "proprietary info", with huge price tags. It all dead-ended when Mike Bergey told me on the phone, "You should hire an engineer". Gee, thanks.
         Whether i'll construct a self-supporting lattice tower made of angle vs round steel tubing is all up for grabs, kids. What's the verdict? (Think we could come to an agreement without killing one another?)
       

If you want to spend at least twice the time and and at least twice the money build it out of round or square tube, in the case of round you will need to cope the ends of the cross members where they meet the legs or flatten the ends of the cross members and weld flanges to the legs for the cross members to weld to.
As Tom stated earlier there are literally thousands of angle iron towers just in the lower 48 alone, likely millions all over the globe because they are cheap, and quick to build, there is no trade off in terms of structural strength in any way shape or form.
If you live in the mid west or plain states you can see angle iron towers with broken down water pumpers on top that are close to one hundred years old, the towers stood till the pump seized up and the blades rotted or blew off but it's still there, then you have the power companies big angle iron soldiers stretching off as far as the eye can see holding up tons of transmission lines.
I'm done in this thread, as I've stated before I'm a fabricator by trade and a certified welder, I'm a builder not a talker, I'll leave you with these two simple things to remember, ANY tower is only as good as its foundation, AND, EVERY single weld on it. Good luck.

[zvizdic]

I met a many engineers who are dumb. One of them retired not knowing difference between left and right tread.
In my experience round pipe or angle iron it be the same .
Use common sense when constructing and if you think it is OK ad a safety factor to it.
Helped me through the years.

[doubledipsoon]

JoeStu does have a point. I can get 2.37" O.D. pipe with 0.154 wall thickness around these parts for $2 a foot, used, but not rusty. Used angle doesn't exist (don't know why) so new comparable angle- 2 1/2" X 2 1/2" X 3/16" is $3.80 a foot. If round resists twisting and bending better than angle for a tower, then it's sounds like a no-brainer, unless another catch 22 comes up that I'm not aware of (like spending time and $ welding feet to the pipe to connect them together)...Sounds like "pay now or pay later to me, Joe

[joestue]

The question is do you know how much force your tower snaps at, and where it snap/kink, fold up etc.
if not, you shouldn't be building one.

Unless you're an expert welder, the welds fail before the pipe does, and the tower does one of four things. the pipe kinks and folds over as the tower falls. It crumples up at the flange, and quite possibly might stay vertical. Or the pipe tears out of the flange. Or the bolts snap because you over-torqued them. Massive bracing and short (less than 10-16:1 length:diameter ratio) means it crumples up but stays straight, or the pipe tears, or the bolts snap. this ratio is not the same as the cut off between a short vs slender column.
longer than 10-16:1 and it folds up. i don't believe the ratio varies with the sidewall thickness much. I can't find any papers on optimum sidewall thickness.
With angle iron the welds would not fail, the angle iron folds over  in compression, (generally along an axis bisecting the triangle) before the other side fails in tension.

People say the subject is too complicated for charts....here they are.
http://www.steeltubeinstitute.org/pdf/brochures/lrfd.pdf
If you print out and compare equal area, square wins if the diameter to thickness ratio is less than a number i haven't figured out yet.
once the thickness drops to reasonable values like 1/24 then the equal weight tubes of similar dimensions round tube wins, in some cases by a lot, but i'm not about to put all their numbers in a spreadsheet and look at the variations bettween themselves. most of this data is probably from fea simulations anyway.

for 2.375" ouside diameter .154 thickness you're looking at 17 thousand pounds at 6 feet, 6000 pounds at 10 feet. 4 thousand pounds at 13 feet.
just because you have bracing welded every 2 feet doesn't mean you have a "fixed" end every 2 feet, and thats where the "rules of thumb" come from.

[doubledipsoon]

          Hey, I'll never know at exactly what force ANY tower would snap at. And, yeah, maybe I shouldn't be considering building one. I aint no engineer, nor do I ever want to be one.......I grow plants and like to watch wind generators spin and solar trackers track.......Hey, what about those 3-sided angle iron Wincharger Towers that were 3-legged. Do you think one of those would handle an XL-1? They seem slim enough to not protrude more than 6 inches out, 4 foot down from the tower top. I'm real stubborn, and won't quit until I figure out an old fashion way to solve what I thought was a pretty simple problem.  The XL-1 isn't a huge machine, but it's beginning to sounds like a black hole. You've all spooked me with failure-syndrome. If anyone knows anything about that 3-sided angle iron that was used on old Jakes and Winchargers, let me know. Maybe that's the answer....

[neilho]

Count me as one of the people who think it's reasonable to put your Bergey on a monopole. I've been a part of hanging 13' diameter turbines on Rohn monopoles (both 40 and 60' tall) with a tower diameter of 4" at the top. No failures in 30 years, so it is possible. The key, as pointed out before, is that there be some sort of taper to the pole. IIRC, Rohn did it by welding different diameters of tubing together. A larger unit (20' diameter) also was put up on a two piece hollow tapered 60" Combustion Engineering pole made out of Cor-Ten. We also used a foam foundation (!! pretty wild stuff) and the tower and machine still stand, 28 years later. Now, I don't suggest that you do that without engineering advice, but your Bergey is a fairly small machine, and with a bit of caution could be hung on a very tall light pole, which are available, used. Combustion Engineering was making 120' light poles (standards, they called 'em) and I think with some nosing around on manufacturer's sites and substituting your own thrust values, you could do a pretty good approximation of an engineering analysis, both for the tower and the foundation. I did an unrelated-to-wind project using a Lexington Standard pole and used their (EIA approved for wind loading) engineering procedure to arrive at an installation that met Uniform Building Code requirements, including foundation design complete with rebar schedule. So it's possible to get to a reasonable foundation without involving an engineer.
 
A Wincharger tower should be adequate for your Bergey.  Rotor diameters are similar, and the 3 legged Wincharger towers (at least the ones I've seen) are overbuilt. Another possibility, if you're worried about blade clearance, is to put a short pipe/tubing extension, at the top of whatever self supporting tower you find. I don't remember what diameter tubing your Bergey requires as a mount, but using that as an extension would probably work.

So...I say, go for it, if that's what you want, and keep us posted! Sounds like an interesting project!

Neil

[DanB]

People say the subject is too complicated for charts....here they are.
http://www.steeltubeinstitute.org/pdf/brochures/lrfd.pdf
If you print out and compare equal area, square wins if the diameter to thickness ratio is less than a number i haven't figured out yet.
once the thickness drops to reasonable values like 1/24 then the equal weight tubes of similar dimensions round tube wins, in some cases by a lot, but i'm not about to put all their numbers in a spreadsheet and look at the variations bettween themselves. most of this data is probably from fea simulations anyway.

Joestue -
Not being an engineer and such, I'm not sure I understand the chart, but I think I do, and my understanding is that it only addresses concentric loads, which I understand to mean 'straight down on a column' - and it's not addressing side forces - like those against a wind turbine, or the odd forces placed on a tower when a heavy gyroscope turns quickly.  It is all pretty complicated in my mind....

Tilt up towers are perhaps even more complicated when one tries to estimate the forces involved in raising them with a given machine on top.  All I know about those, is lots of people get it wrong all the time.  Tricky / scary stuff....  and probably really hard to put in a chart but I could be wrong.

[joestue]

People say the subject is too complicated for charts....here they are.
http://www.steeltubeinstitute.org/pdf/brochures/lrfd.pdf
If you print out and compare equal area, square wins if the diameter to thickness ratio is less than a number i haven't figured out yet.
once the thickness drops to reasonable values like 1/24 then the equal weight tubes of similar dimensions round tube wins, in some cases by a lot, but i'm not about to put all their numbers in a spreadsheet and look at the variations bettween themselves. most of this data is probably from fea simulations anyway.

Joestue -
Not being an engineer and such, I'm not sure I understand the chart, but I think I do, and my understanding is that it only addresses concentric loads, which I understand to mean 'straight down on a column' - and it's not addressing side forces - like those against a wind turbine, or the odd forces placed on a tower when a heavy gyroscope turns quickly.  It is all pretty complicated in my mind....

Tilt up towers are perhaps even more complicated when one tries to estimate the forces involved in raising them with a given machine on top.  All I know about those, is lots of people get it wrong all the time.  Tricky / scary stuff....  and probably really hard to put in a chart but I could be wrong.

Once you put three pipes a few feet apart tapered if you like, then weld them together with sufficiently stiff bracing then the forces on the tubing is a concentric load.
But this requires very heavy cross members. so manufacturers save time and money by making the outer load bearing members heavier and make the bracing lighter, as in the case of cross members manufactured from relatively thin cross section steel rod, bent into a Z shape and welded to the sides of the pipe, and then they just derate it. looking at the photos of failed towers this is my conclusion. you don't see any broken members, its just a pile of bent metal.
the problem with this is its no longer easy to say what happens when you apply a horizontal force to the tower, which is why i don't like that one bit.

If OP wants to build a tapered 50 foot tower from 2.3 inch diameter pipe, provided the bracing is of sufficient strength, it would be as strong as the foundation. the cross members will require a lot more steel than the outer three or four load bearing members. determining how heavy the cross pieces need to be is a job for a bridge designer, or you can just make them out of 1.5 inch thin wall pipe and call it good. which is tempting but you may want to weld a band around the steel pipe to prevent the inside of the pipe from being crushed under the pressure of that 1.5 inch pipe being pushed into it. probably not a concern for .154 thick tubing but if it were .054 6 inch diameter tubing it would be a different story.

once you actually have a figure for what worst case wind loading then you can figure out how far apart the base of the tower needs to be.
say its 4000 pounds at 60 feet. with the base of the tower spaced 12 feet apart that's 20,000 pounds. requiring very heavy bracing every 6 feet to get that within ratings. not impossible, but 4000 at 60 feet is also a lot higher than actual worst case senario. (considering he only wanted a 40 foot tower)

anyway, with 2.3 inch pipe this thing is going to look more like an oil derrick than a tower.

[DanB]

yes I see...
I was thinking about monopole towers and guyed tilt up towers and that chart, while useful...  doesn't address some of the major concerns.  In this case though I see your point.

[doubledipsoon]

The wild and wonderful wierd forces on any tower would spook anyone into throwing in the "cost effective" towel, and blowing 10 grand on a Rohn tower, better known as paying for their engineering know-how. But, for the rest of us in a build it-mode, all you can conclude is that it's builder beware. I would suggest eye-balling the Rohn SSV tower, and duplicating it as accurately as possible (specific parts are listed on some web-site), and for us angle iron-lovers, beefing up the sizes. The big mystery now is why there were so few cross bows on the old angle iron towers, as compared to the Rohn SSV's. With all the old wincharger towers still standing it makes you wonder what's really necessary for a Bergey XL-1, not exactly a large machine. That little voice keeps telling me that the jury will be out on this one indefinitely.....Any three-legged angle iron tower builders out there with an XL-1? 

[kcxd]

I am a freight forwarder & exporter, working with an engineer on  a monopole design project.

instead of shipping tons of steel pipes, we'd like to send over a smart kits.

before we go into actual calculation and designing, better know how easy access for an end user to purchase steel pipes in US.

price is another concern, for steel pipe retail price in US, to my knowledge, 2 grand per ton average.  what we can get from FOB China, 1 grand per ton. we can ship 30-40 pipes @3000usd in a 20ft container to any of US ports. yet, from port to end user, another 400-2000usd for overland just for one tower.

would be appreciate if somebody here familiar with steel pipes, pls get in touch, kentcxd@yahoo.com.cn

[defed]

Even the best tower is only as good as it's foundation, my tower will take somewhere in the neighborhood of five to six yards of concrete, which is ten or twelve tons.

Fab, what are the dimensions for your base in regards to using 6 yds of concrete?  did your tower engineer do the load calcs that will be applied at the top of the tower?  i have a 60' rohn SSV, and i was thinking more along the lines of 12-15yds for a base...so just curious about the #'s you came up with.

thanks.

[fabricator]

You can get all the foundation drawings for Rohn self supporting towers right on their web site, for just about any possible combination with several foundation options.

[defed]

i have a bunch of manuals from rohn for foundations, but none state (that i see) a load rating that can be applied to the top of the tower.  seems i had looked online but was unable to find anything more...i'll have to look again.

i was told by a guy who called them, that they aren't too free w/ the info for 'non-sanctioned' uses, due to liability.

did you calculate the force that could be applied to the top of your tower?  you have a 10', correct?

[ChrisOlson]

Rohn only builds their towers for wind turbine manufacturers that submit an engineering and loading analysis of the structure.  Rohn designs a tower to the specifications required by the engineering and loading analysis.  The tower specified for that turbine is designed ONLY for that turbine, and a complete new engineering analysis has to be done if you intend to put a different turbine on it.

They no longer sell to the general public, nor provide any engineering or loading analysis for any wind turbine.  That is up to the manufacturer of the turbine to determine that.

In the case of homebrew you are on your own with a Rohn tower, and you either have to hire an engineer, or do the engineering work yourself to determine the suitability of the tower for the application.
--
Chris

[fabricator]

Do you know what section numbers you have?

[kcxd]

The foundation for the tower can vary greatly depending on choice of tower and the foundation required based on the soil composition or topography.

will you consider an upsidedown T shape concret that rooted into ground reinforced with steel bars?

[defed]

Do you know what section numbers you have?

my base is 6N, which has a 5' spread.  i would have preferred a larger one, but at 50' to 60' (with 5N and 4N), and the right base, i'd think it would be heavy enough for a 10 footer.

the guy i bought it from claimed he had it spec'd by rohn to be adequate.  he worked for a company that installed many rohn towers, and at the time (several years ago), they were more willing to give out the info.  naturally, he couldn't find the paperwork, so he could have been full of it, but for $500 for a never installed, 3 section rohn SSV, i decided to buy it anyway.

i've seen many types of foundations.  some use a deeper but smaller diameter footer, one for each leg.  some use one massive monolithic block.  the one thing i haven't quite been able to find is how to calculate the load applied at the top of the tower.  ie, how much force is there on a 10' turbine in a XX mph wind.  i know that there are also gyroscopic forces to consider.

[tecker]

You Might have a problem with a single mast then It may end up on your todo list with an expensive rework .
I guess your talkin a hefty pole of some sorts .
 

[fabricator]

Rohn's thin slab (2'thick and about 10 feet square) that's based on the size of your base section, the thin slab is the worst case scenario foundation, for places with a high water table, it takes soil capable of a minium load bearing capacity of 3000 lbs/sq ft.
You can get a local soil testing out fit to check that for around 400 bux, they pound a rod of a certain diameter with weight that they just pull up to a stop and let it fall, then they calculate the number of blows per measured mark on the rod how compact your soil is and what it will bear in lbs/ sq ft.
Those sections with the slab foundation would easily support a 10' turbine, Jacobs puts 23 foot turbines on Rohn towers, a seventy foot tower for a Jacobs uses a 7N base.

[tecker]

I think I got it now but what is the optimum support at the base of the tower . Maybe some 60 or 70 degree supports?
 
 Tom doesn't Pick .
The Pick operating system (often called just "the Pick system" or simply "Pick") is a demand-paged, multiuser, virtual memory, time-sharing computer operating system based around a unique "multivalued" database. Pick is used primarily for business data processing. Though its popularity is diminishing, its capabilities were far ahead of their time and there is still a strong enthusiastic user community .

[fabricator]

I'm not sure what you are talking about, if you are talking about an SSV you don't need any additional supports.

[tecker]

Just alot of stress at the base .

[fabricator]

Nothing that Rohn hasn't taken into account, there are hundreds of thousands of Rohn SSV towers standing all over the planet, I know where there's a one hundred footer that has stood for thirty years with a 23 foot Jacobs on it.
They don't need extra braces and if you did add something not on the original stamped tower drawing a building inspector wouldn't pass it, and any warranty would be void.

[Mary B]

Monopole towers can handle some heavy loads http://www.wix.com/ustower/usttest#!__product-pages/ham-towers/vstc11=ma-series. I had an MA-40 that was loaded pretty heavy and it survived multiple 90mph wind events. 4 1/2 OD bottom, top slid into that and was 3 1/2 round (older version). Specifications were for 10 square feet of antenna load so extrapolate. Would still need to do loading analysis though.

[fabricator]

The monopole I got a quote on was 70' tall, it would base would be an 18 sided polygon, two sections, the be 34" dia, the top would be 14" dia, the foundation called for a round pier 4' dia and 14' deep with about a ton of rebar. this was for a 12' turbine.
The cost for the tower and anchor bolts was around $8K, shipping from Texas was $4K.
Add about $1K for concrete, $200 bux for rebar, $2K for excavating, $500 bux for permits and inspections and you are bumping $15K for a turbine that cost me about 300 bux to build.
I'm going a different direction.
The National Municipal Association, the organization that all local areas of government get ideas for zoning ordinances from has decided they don't want residential wind power in America, and they especially DON'T want home brewed turbines or towers of any kind unless they have and engineers stamp on everything.

[ChrisOlson]

There's nothing wrong with monopole towers.  They have less wind loading than lattice type.  This monopole tower is 9 miles from us.  It has a 69 foot diameter 50 kW Endurance E3120 on it.  The tower is 190 feet




--
Chris

[ghurd]

They have less wind loading than lattice type.

Are you sure about that?

My kneejerk reaction is the lattice will have less wind loading.
G-

[fabricator]

There's nothing wrong with monopole towers.  They have less wind loading than lattice type.  This monopole tower is 9 miles from us.  It has a 69 foot diameter 50 kW Endurance E3120 on it.  The tower is 190 feet

(Attachment Link)
(Attachment Link)
(Attachment Link)
--
Chris

Is that thing utility owned or privately owned?

[Watt]

They have less wind loading than lattice type.

Are you sure about that?

My kneejerk reaction is the lattice will have less wind loading.
G-

Glen, have you ever pulled an expanded metal enclosed trailer across country?  Man, I was surprised to find out how much wind load and turbulence those things create empty.  Fill the same trailer with a bunch of junk and it pulls much easier than empty.  Just a thought as I have no real idea regarding the subject of your reply. 

[ChrisOlson]

Is that thing utility owned or privately owned?

First to answer Fabricator's question - the turbine is privately owned by Infiniti Retail Services.  It is located inside the city limits in the village of Turtle Lake, WI and was installed in December.

Are you sure about that?

My kneejerk reaction is the lattice will have less wind loading.

The geometric complexity of lattice towers over monopoles means that, unlike a monopole, the loading on a lattice tower is NOT independent of wind orientation.  The wind loading of a lattice tower is calculated on the solidity of the front face, and it sometimes requires engineers to consider up to eight different orientations to find worst case loading, depending on the geometry of the tower.

The drag coefficient is then applied, and depends on the shape of the tower members, worst case wind orientation, and for circular members whether or not the wind flow is super or sub-critical (and whether the flow on the members is laminar or turbulent).

AS3995 also specifies a different Cd depending on whether the tower is three or four legged.  Lattice towers are much more complex than monopole structures, and always require extensive FEA work to design.

In short, yes, I am sure about the loading differences between the two tower types.  I just got done going thru better than three months of engineering work with Rohn to spec a tower for my turbines.
--
Chris

[ghurd]

have you ever pulled an expanded metal enclosed trailer across country?.

That is comparing a solid disk to an efficeient (Betz) set of blades set to a screwdriver.  Apples and oranges.
But yes, not across the whole country.  Only takes a few miles to know what you meant.

[SparWeb]

The geometric complexity of lattice towers over monopoles means that, unlike a monopole, the loading on a lattice tower is NOT independent of wind orientation.  The wind loading of a lattice tower is calculated on the solidity of the front face, and it sometimes requires engineers to consider up ....
Chris
[/quote]

Do you think they include the ladder in their calculations?  Two ways to look at the effect of the ladder, actually: 
1- Wind and Ice loads on the ladder that would "peel" it off the main tower, and
2- The additional loading that the tower must resist.

and always require extensive FEA work to design.

FEA sure has come a long way since the 1940's, hasn't it?

Ghurd:  My kneejerk reaction is the lattice will have less wind loading....

The only way to compare "apples to apples" would be to produce one monopole tower with exactly the same wind strength characteristics as a truss...  easier said than done, because you could find one of each with the same projected area loading, but each would have different weight (mounted on top) limitations.  Also, the two "similar" towers would have different stiffness.  The top of a monopole can wave around more than a truss would (if the truss is designed right).

Lastly the turbulence shed behind a monopole is typically one big vertical vortex, pushing the whole monopole side-to-side, while the truss tower has many little broken-up eddies spinning this way and that, so they can't act together to move the tower as a whole.  That can happen, even if the sum of the drag load on the truss tower is more than the drag load on the monopole.  Combine that "vortex shedding" with the flexibility of a monopole tower, you can get into trouble quickly. 

Pound for pound, a truss tower will resist more load than a monopole, usually.  Despite having more drag.