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I would like to build a monkey-bar/playground structure in my backyard. It's not your standard monkeybars, but I made a 3D visualization at staktrace.com/pub/structure.html if that helps. I'm planning to buy steel tubing (1.25" or 1.5" diameter) and getting a welder to assemble it. However I'm trying to figure out the best way to actually attach it to the ground.

My plan was to dig a 2.5' hole for each post, fill in 6" of gravel, put the post in on top, and pour concrete to fill the hole. After reading some of the info on this website I'm wondering if burying 2' of a 9' or 10' post is going to be enough. In terms of "load" on the structure it's going to need to hold maybe two people swinging around (let's say 500lbs). Also given that the posts are all going to be welded together using crossbars at the top I feel like it should be pretty stable already so I shouldn't have to go that deep.

Also I've never done stuff with concrete before so I have some general questions about that.

So my questions:

  1. Given the nature and intended use of this structure, how much of the post should be buried if I want the "ceiling" bars to be 7' off the ground?
  2. What diameter should the hole be?
  3. Would it be better to weld the structure first and then attach it into the ground? Or install the posts first and then weld the rest of it to the posts?

Any other advice or recommendations are also welcome.

[Edited to add: in terms of weather, this is southern ontario so it has to deal with +30 to -30 degrees C and everything in between]

  • Width of hole? That's kind of important – Tyler Durden May 1 '15 at 3:20
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    posts first and your holes will have to be pretty deep in ontario or you could have some very uneven bars in a couple years. – DMoore May 1 '15 at 4:21
  • @DMoore: why do you say the bars would be uneven in a couple of years? – staktrace May 1 '15 at 12:20
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    @stacktrace Because of frost heaving. – Tester101 May 1 '15 at 13:16
  • Lots of things to consider here. And not enough time for a complete answer, so here are some things to discuss. How long do you want this to last? Steel not specifically designed for use in concrete, especially hollow steel will have access to moisture and oxygen and corrode over time. Your structure has no cross-bracing/rack-strength so it's lateral deflection will be determined by the bending moment of the vertical members which is pretty small for 1.5-in tubing/pipe. What is the wall thickness of the steel? How much deflection will you allow? – Paul May 7 '15 at 14:42
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I put tie-downs in my driveway to guy down my boat canopy during the summer. I dug 2 foot holes, crisscrossed rebar diagonally into the ground, poured concrete, and sunk heavy duty eye-bolts with alternating nuts and washers into the concrete. I will be doing something similar this summer with posts, sinking them into concrete, with rebar through them.

  • This is the only answer here that even comes close. See the link here for how to pour real footings. – Mazura Aug 6 '15 at 8:09
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I built a similar thing out of 4x4 cedar posts and used "deck spikes" to hold the posts upright.

enter image description here

That might not be the brand I used, I just went to a hardware store and bought them. In 20 years of having a LOT of kids climb and swing on it, it hasn't budged in the slightest. (We're in probably-not-as-Southern-as-you Ontario and there's been no frost heaving.) I made sure the "collar" was buried so that nobody would get hurt if they fell against it - we have non compacting pea gravel all around the base of the structure and it covers the top of the deck spikes.

Much easier than digging, concrete etc. And connecting wood is much easier than welding metal - you can always use some premade metal sections to connect some wood sections if have small diameter bars to swing from is important.

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If the hole is 1 foot in diameter then each footing will be 235 pounds.

I would probably make the footings weigh triple the weight of the above ground apparatus plus any people on the apparatus.

Also I would have the top of the concrete at least several inches below the surface of the ground.

  • I'm not sure if this is an answer or a question -- are you asking him if his holes are 12" in diameter, or telling him to make them 12"? Is a 235 pound footing good or bad? Is there some ideal ratio between the weight of a footing and the weight of the structure? Is triple the weight a good ratio? – Johnny May 1 '15 at 4:10
  • Thanks for the reply. So if I estimate the above-ground weight to be 600 lbs the total footings should be 1800 lbs, which across the 6 holes would be 300 lbs each. So a little wider than 1 foot should do the job, I guess. I would also like to bury the concrente, but I'm not sure why you suggest that (most online info I've seen say to have it protrude as a dome to allow water runoff). Can you elaborate? – staktrace May 1 '15 at 12:24
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    @staktrace If the concrete is left exposed, someone could fall on it and hurt themselves. – Tyler Durden May 1 '15 at 14:30

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