Epoxying anchor rod in concrete (at wrong angle)

[Bobbyb]

Hi,

I this is my idea.





I have four 150kg concrete block's (already cast when i got them) that will be in a hole but will not by under any soil.

Now i want to attach my turnbuckles to them





The red part is something i made to increase tensioning since the turnbuckles alone were not enough during a test raise.

I read this a long time ago and remembered the epoxying rebar in to rock.

http://www.otherpower.com/otherpower_wind_towers.html

Now that I red it again I see that the rebar is at a 90 degree angle of what I want to do.

Will my idea work?

My tower is 20'high and will carry a 6 square feet lenz turbine. In the future I plan to put a 7' diameter "normal" blade on the same tower.

[Flux]

I haven't read your link but I think I can see where you are coming from. Your first drawing is normal for a rod cast into the concrete with some form of projections on it.

I think you are asking if holding a threaded rod into a hole drilled in concrete with epoxy will work. in reality I suspect it will but I would never trust it or have the nerve to try it. With a decent depth of hole the thing looks every bit as strong as some of the chemical anchor fittings and some of these use polyester ( far less effective).

If you turn the thing at right angles then The M16 rod is possibly not strong enough and may bend between the concrete block and your attachment ( may be ok if you keep the attachment right down to the concrete).

I have more faith in taking the pull at 90 deg as long as your anchor rod is strong. You have to satisfy yourself that the concrete block can't rotate under this condition. A direct pull on the anchor block probably needs a smaller block than one subject to rotation.

I have welded a complete strap round a concrete block to get a direct pull rather than chance a rod held in with glue but Some of the modern adhesives are pretty good. I have also seen some glue failures in applications that others seem to consider normal. Just what you feel comfortable with I suppose.

Flux

[MattM]

It's a bad idea to use epoxy to do anything but tack to the concrete.  The weather will penetrate the concrete and the two materials will eventually separate.  Anything under tension like that becomes a danger when it breaks.  I've seen the investigation pictures of a rail yard worker that got nicked in the shoulder by a breaking cable; it mostly took his head off.  High tension cables are nothing to screw around with.

[Airstream]

There are epoxies designed specifically for bedding anchors in concrete - look at subway systems where the track running rail fasteners are bonded into concrete.

Look for glass ampules that just fit inside the drilled bore and shatter when the bolt-anchor is driven home. Then a surface 'potting' in a shallow depression relief perhaps 3-inches across around the neck of the bore gets filled seperately to provide a gasket effect. eBay may be a good source, the stuff sealed in glass has a long shelf life.

[zap]

It's been used in the construction industry for decades.

I assume your picture depicts a 16mm threaded rod?

Have a look at this link.  The third row shows figures for a 5/8 inch (15.9mm)rod.

http://www.simpsonanchors.com/Catalog/adhesives/set/loads_rod_conctension.html

[bob golding]

hi matt,

while it is true that cables under a lot of tension are dangerous, for a wind turbine they dont want to be that tight. the tension should only really be when there is a very strong wind. if they are dangerously tight in no wind they are too tight.

cheers

bob golding

[toothy]

I believe your drawing shows the rod at the correct angle. Having the rod at 90 degrees is inviting fatigue.

I would as previously suggested look over the Simpson web site and use their products. If the hole is in good concrete and prepared properly that stuff is tough.

I have tried to remove some 5/8 threaded rod set with their epoxy and found it impossible. I harassed that rod with my backhoe (18000lbs) and a sledge at the same time and finally wound up cutting it off with a sawsall. My holes were not even prepared to Simpson specs, I just blew the dust out but didn't scrub them.

Wade

[electronbaby]

your tower loading requirement does not seem that great at only 20' tall with 7ft^2 swept area. Whats the expected gust and duration?  what is your guy radius?

It almost would make more sense to drill completely through the block and put a galvanized threaded rod all the way through. This will give you more strength. Use only hot dip galvanized parts as they will be buried below grade. Stainless would be even better.

I would not rely on the epoxy to hold your anchor in the concrete at the same angle you intent to pull on it. It would almost make more sense to beef up your hole, use a much heavier expansion type anchor, and turn the anchor 90 degrees from the pull direction. You must calculate the pull force on your guys in order to figure out the size of the anchor required and still maintain a safety factor. Be careful how much force you put on the expansion anchor because there is no rebar in your casting,...is there? I personally would not put any anchor in concrete without some type of rebar in it.

Again, Im not sure where you are located, but if you dont bury below the frost line, your anchors will walk out of the soil.

Be careful not to disturb any soil in front of the blocks when you place them. This will insure that you keep a solid holding position in the earth. Not sure what type of soil you have, but on LI, we have quite a bit of sandy loam. I make sure to water tamp when back filling, and letting the anchor sit for a few weeks before putting any force on it, to allow the water to settle out, and make everything lock up tight.

Just some thoughts...

[SparWeb]

You wrote you did a 'test raise".  Can you tell me more about that, because it sounds like the turnbuckles gave you trouble there.

Using the materials that are easily at hand can be made to work, but when you have the option to do it better and safer, you know which one has got to win.

The concrete block weighs 150kg (350 pounds) and isn't buried.

When you tighten the guy wires, you want about 500 pounds of tension in each of them.

Those blocks will come out of the ground as you try to tighten them.  Load from the windmill is added to that pre-tension, so even if you can tighten it, you've used up all the margin of safety before the wind started to blow.

Straight anchors in a blind hole also aren't trustworthy, as has already been mentioned.  Too bad the block is already cast.  This is the kind of bolt usually put in concrete:

Obviously the bend resists both rotation and pull-out.

One thing you can do with it is to bury the block under a couple feet of soil, after mounting a long bar in it that goes all the way through, out the bottom side, and has a big nut & washer underneath.  That would probably work well and stay put.

Good luck, and be careful.

And make sure to post pictures when it up.  We love seeing new windmills up in the air!

[Bobbyb]

Wow lots of replys, thx

Let me sum it up:

Putting the rod at an angle is a bad idea.

Drilling completely through the block will work for sure.

Using commercial product will also work according to Wade (the only one with hand on experience?).

During the test raise (my first time raising anything) the turn buckles were completely turned in (short).  This was because of not so perfect measurements and I used a rod pounded in to the ground as an anchor, which gave an inch or two. So just to be sure I made the red extensions. The guy radius was around twenty feet during test raise. Don't know the final radius because I have not been appointed a final location, but it wont go under 10 feet.

The concrete block's do have re bar in them (I changed the picture). They are the top's of concrete pole's they build houses on.

Soil is really wet clay/sand most of the time, only in summer it dries up.

Drilling completely through the block will mean buying a new drill, but since this will solve the tensioning and fastening problem and bury the blocks three feet under ground I guess its the way to go?

And for all a picture of the test raise