New Tower Build

[SparWeb]

This topic was split from "Turbine lowered, Tower dismantled" -
Turbine lowered, Tower dismantled

Photos as promised.

I bought this used tower.  It's a sectional tower, 64 feet (20 meters) tall.  I laid it out on the grass to make sure that all the sections fit together, weren't damaged, etc.  If you're interested, it's a Wade DMX-68N.


These are robust free-standing towers, but of course if being used for a wind turbine, will need guy wires.  Attachments for these will be easily added because they are already part of the top stub tube.  I can re-use the one I already have meaning I don't have to re-build the head, either.

Right now I'm making the parts to mount the stub at the top.  The mounting plates for antennas are too flimsy and don't offer a collar that can hold the size of stub tube I need.  So they have been removed, and will be replaced with some skookum plates and couplings that are proving to be fun to make on the lathe.







It was only after I got that chucked in that I realized there was only a few mm of clearance to the bed!
This project was also an excuse to rig up a little drill guide mounted on the tool post.  It was a handy way to put in some pilot holes for the collar mounts while the plate was secure and easily "indexed".
Next to the collars themselves, which I'll be making this weekend (from a solid bar of cold-rolled steel).

[SparWeb]

Forgot the picture of the drill guide!

[Mary B]

Those area VERY light duty tower not designed for guying(it adds down force on the legs). Weakest link on them is the rivet on the x bracing. They are notorious for pulling thru then that section of tower becomes weak.

From the website

https://wadeantenna.com/wp-content/uploads/2016/09/Load-Tests-Wade-Antenna-DMX-68N.pdf
Failure was observed at a load of at least 330 lb
maximum allowable effective wind area
of 4.4 ft2
Guys can be used BUT loading is limited to what is mentioned above and that is 3 sq feet of wind load(paraphrase from the brochure)

For guying they use a reinforcing ring around the tower with ears that slope down and out https://wadeantenna.com/wp-content/uploads/2020/01/390358_F01_GUY-STATIONS_N0901.pdf


VERY light duty! Long boom ham antennas destroy those towers via twisting force... the rivets pop then a leg buckles. I won't use them for even my smallest antenna installation... I have seen to many crumple with just a TV antenna as a load!

This tower is rated at 35 sq feet of wind load, the H frame to hold the antennas is 11x11 feet and the 4 antennas are 20' long. Total wind load is ~14 square feet with the H frame, cables, rotor, antennas...  I would not go any higher without keeping it cranked down most of the time due to torsional load on the tower. And I wouldn't put a wind turbine on it, not heavy duty enough!

Here the tower is cranked down to 12', it cranks up to 33 feet.

[SparWeb]

You are not wrong Mary about how light they are.  The method of loading and the support matters, too.  Without guy wires it's hopeless for a wind turbine.  And with guy wires installed the way Wade puts them on, also very limited.  Looking at the Wade guy wire fixtures (drawings) I can understand why they did what they did but it induces some other problems that I'm seeking to avoid.  Another method is needed.

Thank you for pointing out the load test.  It's got me thinking.  It's not directly comparable to a guyed tower but the fact that they tested to failure is very informative.  I'm doing a strength check on the leg that buckled in their test, using measurements from the tower I have here.  My first pass says that their tower's leg collapsed at only 50% of the expected buckling allowable strength.

I'm not panicking yet, but I share your concern.

[SparWeb]

The result of that test proves to be very useful!

It appears the leg collapsed at about 32,000 psi compressive stress. (224 MPa).  That's less than I'd expect for a steel member.  I can come up with an aluminum shape that resists that much.  I was looking at a design text for this that led me to expect the buckling failure of the DMX leg at 68,000 psi.  More than twice as strong as the tower leg actually is.  So they must be using a low-grade hot-rolled steel sheet like ASTM A570.

This isn't daunting me.  The test they did is 100% bending stress.  The stresses in free-standing towers are about 90% bending and 10% weight.  When a tower is guyed, the stress is 90% weight and 10% bending, approximately.  But the total stress is lower.  The physical weight added to the down-ward pull from the guy wires is nowhere near as stressful as bending.

The guy tension I used in my 40-foot tower was about 500 pounds.  This will probably go up to 750 with the taller tower.  With 4 guys, pulling at a 30 degree angle makes the downward load 1500 pounds.  That puts stress in the tower legs, but not much.

[SparWeb]

Time for a quick update.

First, though - sorry about that last reply Mary, I went all "blind you with science" which went overboard.  The DMX is too light as an un-guyed tower (by far) but with guying done the way I'm doing, it should be fine.

You can now see the way the guy wiring is going to work, now that I'm at this stage of assembly.

[SparWeb]

After  posting I noticed the guy lugs are almost all cropped off the pic.  Here is another view.
There are 4 lugs for guy wires on the stub tube, not the tower frame.  Which is what allows more load to be put on this tower.  Putting the guy wires on the frame (the way Wade does it) leads to high stress points, which would be a problem indeed.  They use little lugs with tabs that bolt to the tower legs.  I get why Wade does it their way, but that won't work here.

[Mary B]

Wade uses the guy collar due to twist stress antennas can put on a tower. Lot of start/stop torque especially with an HF antenna that can weight 125 pounds or more.

Swapping the X brace rivets from aluminum to steel bolts can add a LOT of strength because that is where failure will start, I have seen it multiple times. Go out on a buckled tower and find the rivets popped all over the tower, usually so bad that we have to bolt as we climbed to make it safe enough to secure the stub to a crane before cutting it loose(this is always a fun ride, tower will whip back a couple feet!). Got to the point I would drill all the rivets before putting up a rohn/dmx/wade(they are all clones of each other) tower and replace them with grade 8 bolts. Those towers would survive bad wind events that took out other towers.

No clue how much twisting force a wind turbine will put on a tower, shouldn't be a lot but I am sure it is there. Plus off center weight loading if it isn't balanced between the head and tail assembly. Most antennas I can balance so they are not adding stress to one side of the tower.

[SparWeb]

As you can see, I do have some rivets drilled out already.  Those are the plates for the tube collars.

Rivets are not created equally.  The rivets in this tower are very cheap low grade Al alloy.  Drilling them out was like butter.  I have bags of high strength aircraft alloy rivets that I will replace them with.  I still believe rivets are a suitable fastener- but only if they are stong types.  I expect to be able to drive these into this steel structure with less fuss than into aluminum sheet, which distorts if you pound too hard.

[SparWeb]

  tower will whip back a couple feet!

Ugggghhhh. 
I'm going back down now.

No clue how much twisting force a wind turbine will put on a tower, shouldn't be a lot but I am sure it is there

Agree.  There is a gyroscopic moment that "nods" the head up and down as it actually yaws left and right.  I avoid trying to visualize the way this works, just have to respect it.
Twisting, though, can't be much, except in moments when the tail hits the furling stops.

[kitestrings]

We did a similar type of treatment, with the steel tube within the guyed tower section at the top.  I think it worked well.  Our tower top section already had a horizontal flange plate that we mated to.  Guys were located at the bottom of the tube section.  We also put a lighter weight plate at the mid- span of the section to help reduce the deflection there.  I'm not sure how much that helped, but it was easy to do and seemed logical.  I looked at the forces much like a cantilevered beam; probably an over-simplification.

[Mary B]

Tower forces, VERY math intensive explanation... http://www.va3cco.com/towersheight.pdf

[SparWeb]

Have you posted that to Fieldlines before?  I already had a copy and had wondered where it came from.  Noticing now that the author signs with W9JCC, yeah it looks like another ham.

That is almost exactly what I'm doing, Mary.  Travanty has made use of a maximum base moment value that he was provided by the tower manufacturer.  In my case, Wade has provided similar data, and the test you dug up before was useful in corroborating that.

I take issue with his assumption of steel strength 108,000 psi.  Yes, many such grades exist, but they are not likely to be used in the legs of the tower he is using.  It is extremely unlikely that the tower sections were heat-treated or even properly stress-relieved after welding, and there could even be locations where the welds limit the fracture strength.  If his tower really does have chrome-moly tube legs, then 80 ksi yield is about all he should design to.  That seems to match the stress he reverse-engineered from the manufacturer's load and wind speed limitations.  He shouldn't assume it's any stronger than that.

I do like the method he used to work through the loads section by section.  He accounted for weight and wind load, and I've done the same but also included ice and (obviously) moments from the turbine itself.

[SparWeb]

Hello Kitestrings,

I've seen photos of that joint in your tower before, but not that particular picture.  It was of interest to review how you and others had done your towers, because I want to avoid any vibration noises being communicated through the tower or made worse by it.  I've tried to eliminate as many fasteners as possible as potential "degrees of freedom" that might allow things to move.

Yeah, yours is cantilevered above the top bolt circle, as you say.  Not an oversimplification.  The reinforcement you use is different but the structural principle is the same.

There's really no way to be sure that all my plans will be successful until the machine is raised and running.  I'm trying to put together 15 years worth of reading Fieldlines and thinking about good and bad ideas, and put as many of them into practice here.

[Mary B]

Have you posted that to Fieldlines before?  I already had a copy and had wondered where it came from.  Noticing now that the author signs with W9JCC, yeah it looks like another ham.

That is almost exactly what I'm doing, Mary.  Travanty has made use of a maximum base moment value that he was provided by the tower manufacturer.  In my case, Wade has provided similar data, and the test you dug up before was useful in corroborating that.

I take issue with his assumption of steel strength 108,000 psi.  Yes, many such grades exist, but they are not likely to be used in the legs of the tower he is using.  It is extremely unlikely that the tower sections were heat-treated or even properly stress-relieved after welding, and there could even be locations where the welds limit the fracture strength.  If his tower really does have chrome-moly tube legs, then 80 ksi yield is about all he should design to.  That seems to match the stress he reverse-engineered from the manufacturer's load and wind speed limitations.  He shouldn't assume it's any stronger than that.

I do like the method he used to work through the loads section by section.  He accounted for weight and wind load, and I've done the same but also included ice and (obviously) moments from the turbine itself.

I may have posted it in the past... yes his yield strength is nuts.

Section by section analysis is required to be certified for zoning. While I have no zoning laws pertaining to towers some counties and cities have insane requirements and towers have to meet national standards to be put up. Those studies let me pick and chose antenna towers based on where antennas may be mounted on the tower, I do have one side mounted antenna still that is fixed east. Smaller and it lets me copy locals if I have the big array spun around. The big antenna array takes 45 second to rotate 360... not very fast.

[SparWeb]

Update!

This week the piles for the tower were installed.

[SparWeb]

I really love these screw piles.  So much less work than concrete, and for a given bearing load they even cost less.
Ready to use the moment after they're in the ground.

While the installers were here, they helped me remove all the old screw anchors at the old tower.
Once they were out, I was amazed to see that most of them were still in very good condition.
So the decision was easy - they went straight back into the ground as the anchors for the new tower!

[bigrockcandymountain]

What is the load rating of the piles?  You old screw anchors look really good.  How long are they and what would you call the load rating on those?

 I think mine are 4" discs, but i never did find a decent load chart for different soils.  Mine are 4' long i think.

[SparWeb]

I can post datasheets... just let me find them...

Your 4" disc, 4' long screws are probably "grain bin anchors".
Maybe good for 1000 pounds, maybe 2000 in a tight rocky soil.  Not so much in my sandy stuff.  I can put those in by hand without breaking a sweat.
I was looking for much, much more.

[SparWeb]

Screw Anchors:
I think Hubbell set the standard, but it may be more like they and 2 other manufacturers have copied eachothers' forging tools, so you can find the same thing from Maclean and ECP.  All in the USA and at this moment, it seems not a single screw anchor available in Canada.  If I hadn't been able to use the ones I removed from the ground, I would have had to wait weeks for a delivery from the USA.  I called every wholesaler I could think of and some I'd never spoken to before.  It got really annoying when searches online turned up lots in US websites for 50 bucks each. Delivery plus Hoser tax, was going to run me about 150$ each.
https://www.hubbell.com/hubbellpowersystems/en/Products/Power-Utilities/Anchoring-Foundations/No-Wrench-Screw-Anchor/Anchor-No-Wrench-6in-x-66in-Tripleye/p/1915216#

Earth Screw Piles:
Almita is based in Edmonton, so it's also "buying local".
I started by contacting Almita to check with their engineers for a recommendation.  He specified (Richard Schmidt) that I use a Type 4 pile (4.5" diameter) 15 feet deep, with a minimum torque of 4,000 foot-pounds.  The actual installation torque was 15,000 foot-pounds (wow!) so much stronger than I expected. That pushes the load rating up to about 40,000 pounds so I'm looking at a safety factor of about 10!  If I do this in the future I could specify a smaller pile, but each pile is only about 220$ and the next size down was 170$.  Under-sizing the pile is probably a false economy for a one-off project like this.  I'll take my oversized foundation, and dream of the "next" tower, freestanding with no guy wires at all... 

The bobcat you see in the photo is a more local contractor (if Red Deer is local) who did the install.  We worked very well together and he was well-equipped to do the piles and the anchors at the same time.  He also welded on the capping plates - allowing me to fuss and bother to make them all neatly aligned first.

You will also see a pile "upwind" of the trio on the base.  That one is for the lifting winch.  I'll post a photo later of what that looks like.

On the Almita website, you can read as much as you want about their screw piles.  They have fully-engineered these piles with technical tests, research reports and certification.  Look for the CCMC report for very specific load details that you can line up with specific pile types.  I'm still happy I consulted with their engineering for confirmation.  Being very conservative on this doesn't cost much extra.
https://almita.com/project-education

[Mary B]

Other than the specialized equipment needed to install them the specs look good... My free standing crank up tower rated for 35 square feet of wind load produces 30,000(approximate, not awake enough to do the math...) pounds of compression/tension under 90mph winds

[bigrockcandymountain]

I think that you have a great foundation there.  It should last a couple lifetimes at least. 

The hubbel anchors you used are definitely better quality with forged eyes etc than the ones I used.  Mine are from an ag supply store for anchoring grain bins.  They are welded eyes, and not great quality control.  They are cheap though, at about $35 apiece.

I found a site that claims a 6" x 48" has a pullout rating of 4000+ lbs in hard clay.  I would have guessed a bit higher than that in my rocky hilltop, but 4000lbs is probably lots. 

What do you figure your guy wire anchors at where you are spar?

[SparWeb]

Yes, compared to the agri store anchors these are much better.  They are almost 6 feet long and the plate is more than 6".  The spec sheet from Hubbell tells me about 5000 pounds in my soil, which is sandy loam.  Explore the site I linked, there is a lot of info there, if you look.

If you still wanted the grain bin anchors, two or three in a cluster would add up to a strong anchor for a guy wire. 

In you rocky soil, you get more per anchor than I can.

[joestue]

what's the cost of taking a disk of 1/8" steel and plasma cutting a disk out of it.. and making your own screw anchor using 1" schedule 40 steel pipe?

[bigrockcandymountain]

Aha i went back to that site and found the good stuff.  It looks like i can expect 4000lbs from mine. 

I expect the materials would cost about $10 to make your own.  Then add your time and consumables and the fact that it isn't hot dip galvanised.  That would be the kicker for me.  We have saline soils that would eat 1" sch40 in about 10 years.  It certainly could be done though. 

I think the disc is over 1/8". More like 3/16" maybe even 1/4"

[Mary B]

what's the cost of taking a disk of 1/8" steel and plasma cutting a disk out of it.. and making your own screw anchor using 1" schedule 40 steel pipe?

Getting the angles right so it pulls itself in with minimal soil disturbance is critical to holding power... more the soil is disturbed the weaker the holding power it will have.

Friend lost a tower because of defective anchors, the blade was welded on wrong and combined with his sandy soil it pulled an anchor on one side, cost the anchor company a bundle in the lawsuit. His next anchors were flat plate with a screw eye bolted through at an angle then welded, that was then sent out to be hot dip galvanized and then buried 6' deep. Since the hole to bury it went straight down it could pull against the side towards the tower which was undisturbed soil. Dead man anchor... he tested the design by trying to pull it with the big 4wd tractor. The eye bolt bent but the plate didn't move. Pulling force was well over 10k pounds...

[SparWeb]

More progress on the tower this weekend:

[SparWeb]

[SparWeb]

Next steps are to layout the guy wires, install the gin pole, then the winch, then lay cable.

[ruddycrazy]

Just remember to back off the side guy wires when raising and especially lowering as oneday with my tower which is similar to yours just buckled and bent until the genny hit the water tank. Ok the tower will rock from side to side but as soon as it is vertical the going gets easy and a helper can tighten up the side guy wires.

[bigrockcandymountain]

The base and hinge look very professional.  Things are getting exciting.  Here's to hoping for no excess excitement when you raise it. 

[DamonHD]

Just the right amount of excitement, and just the right range of windspeeds!

Rgds

Damon

[Mary B]

Winds here would be challenging it, 24mph sustained, 35mph gust so far for peak... just saw my recycling can(one of the big 60 gallon heavy plastic cans the garbage company supplies) head for the garden... harbinger of winter storm winds hitting 70mph gusts and sustained at 60mph....