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For the OP , 'flange' meaning there is a thing you make and bury in the concrete with the top poking out. The gate post then bolts to it.
As an example here's a road side structure being installed while already attached to its' flange (this is a bit different in that the bolts are designed to snap off when hit by a car)
Strong as feck.
Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21
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You don't need to overthink it.. That 600 square 500mm deep foundation should do it.
Three years ago we concreted in a bunch of 6m IP camera poles out in the bush.
Dug some holes roughly 1m deep and 500x600mm, mixed the concrete at 6:1 in a standard contractors size mixer, 6 or so wheelbarrows per hole.
We used M20 threaded stainless rod and nuts to hold the 400x500mm 12mm base plates down, tacked onto 10mm rebar bent into a rough rectangle to keep them located.
Very roughly surfaced the concrete, leveled up the poles using stainless washers as spacers then grouted the surface before bolting the plates down.
The 150x150 steel poles have remained upright in very strong (170km/h) winds, salt spray, the shock loading of a large tree falling against one, and a 100kg mate shimmying up them occasionally to clean the lenses.
Rough as, but would have been simple to make them look nicer, and easily strong enough to swing a 3m galv steel gate off.
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elpenguino:
For the OP , 'flange' meaning there is a thing you make and bury in the concrete with the top poking out. The gate post then bolts to it.
As an example here's a road side structure being installed while already attached to its' flange (this is a bit different in that the bolts are designed to snap off when hit by a car)
Strong as feck.
again thanks for all the advice.
where would I get a flange post to put in the concrete like the pic above? would I just get a local welder to make me one up?
"if in doubt add more concrete". Does this mean that if I only made up enough concrete to fill half the hole, would it be okay to add more concrete later? I mean is this noticably less stronger than pouring the concrete all in one go? Just want the hole to be big enough for enough concrete to hold this gate.
I am thinking at this stage, although the above flange might be better, to set stainless steel rods in the concrete. Bending them at the bottom so they don't turn. I hope to achive this using a wooden template to hold the rods in position when pouring the concrete. As further strengthening, I then want to put a wooden post beside this so I can then bold the top of the post to this wooden post. this wooden post would be at least 1/3rd of the wooden post height in the ground.
here is a rough image of what I am thinking, I am even thinking of a second wooden post, but I may be over over engineering it.
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Fred99:
I'm a fan of concrete screws these days - they're easy to remove and replace if you need to, but presumably if they're going to have to be 12mm and long enough to do that job (perhaps 150mm), you'll need an impact wrench to drive them in. The top of the concrete you'll need to pour will have to be dead flat and level, or you wont get the post plumb unless you pack it under the base flange - which is another reason I'd use concrete screws - then set it up and tighten, check it's plumb, remove the post and grind concrete to adjust as needed - rather than try to pack it. If it's wonky and you've used chemset anchors, epoxy and threaded rod, or dynabolts that won't come out easily, then it sound like there's plenty of potential to stuff it up and make it very hard to correct, as the bolt threads will be in the way.
It's going to have to be a very solid concrete base based on description of the size and weight of the gate - it's hard to believe that the supplier hasn't specified what's needed.
Yes the concrete base will need to be substantial to handle that sort of leverage, but I wonder if it also needs to be reinforced? The concrete screws above are stronger than the normal sleeve-anchor "dynabolts", but there is another type of concrete anchor (maybe a wedge anchor?) with a kind of expansion tip thats even stronger. I suspect you will need really big bolts and several of them, and special ones called "rag bolts" might be the things you are looking for to set into the concrete. I'm guessing you will need some kind of rig to hold the flange exactly level while the concrete sets.
BTW, that picture has a flanged pole bolted to a flange base but your scenario is just a flanged post, and if there were big enough rag bolts available then you just have to work out how many and how deep to set them into the concrete.
Time to find a new industry!
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