# Will two 2x6s provide the support I need for swingset



## Goose22j (Mar 2, 2015)

Hi - I'm hoping you can help.
My dad and I made a swingset for my three children. A picture is below, or at this link: https://www.dropbox.com/s/3esasw76g22c5en/Photo%20Feb%2028%2C%204%2055%2010%20PM.jpg?dl=0










(ignore the 2×4 on each side that is propped at an angle, that was just holding it in place while the concrete dries).

Here is that we have (all the wood is Redwood - "Construction Common"):
1. Two 4×4s on each side, 3.5 inches apart. There are a couple support pieces in between the 4×4s in the middle (16 inches long) and near the top (10 inches long) for added support. The 4×4s were about 12 feet long and nearly 4 feet of them are in concrete. I feel confident these aren't going anywhere. 

2. TWO 2×6s at the top span with width of the structure.
The 2×6s are on the long edge (right term?) and are glued and screwed together, forming a piece that is 3.5 inches in depth and 5×5 inches tall. 
The 2×6s are bolted in between the 4×4s at each end and are also supported by one of the above-mentioned support pieces.
-Here's the concern

We will have 3 swings hanging from the 2×6s. We previously got advice that the 2×6s would be sufficiently strong to avoid any bowing in the wood, but a family member that works in construction has now told us he believes that we are "overspanned" at 20 feet. My two questions are

1) are we overspanned and will the wood bow in the center
2) if so, what is the best, most full-proof, and most aesthetically pleasing way to resolve it.

Thank you very much!


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## LiveEdge (Dec 18, 2013)

Google something called the "sagulator". With the numbers I put it it said it would sag about an inch across the span for a load of 300 pounds. 20 feet is a fairly substantial span…


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## SirIrb (Jan 12, 2015)

Holy smoke that is some green grass. Do you paint it?

Bolt through and dont lag-eye-screw is my suggestion. I would think that 2 2×6 is good but like LiveEdge said, check the google machine.


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## patcollins (Jul 22, 2010)

Hi Goose

It may sag, even from it's own weight. Everything deforms, it is just a matter of how much.

If you wish to make the top stronger there are two things you can do. You can either split the beam up by providing a support in the middle effectively shortening your span or you can increase the height of the beam up top.

The moment of inertia is what determines beam strength and for a rectangular section the moment of inertia increases by the cube of the height (power of three). You can greatly increase the bending strength of that beam by increasing its height by an inch. You could simply lay another board on top of it and screw it together every foot or so and you will have a much stronger structure.


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## Goose22j (Mar 2, 2015)

Thanks guys - what do you think of these solutions…
First -here is some more detail about the current setup, followed by an image with possible solutions


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## MakerofSawdust (Mar 28, 2011)

I hate to say it, but ignoring the 2×6 issue, I think you'll have a problem with the posts in the ground/concrete moving. I did the same thing and mine moved a lot. I even had one end attached to a building. There's a reason virtually all swing sets have A-frame ends. I switched to an A-frame years later without any issues and no anchoring in the ground.


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## Goose22j (Mar 2, 2015)

MakerofSawdust - how big where your post holes? Ours are about 40 inches deep and i widened them out at the bottom.
the soil is pretty dense down there too - we rented a two man auger and the soil stopped it about 2.5 - 3 feet down (and we had dampened the ground for two days before).
Does that dampen your concern at all or…?


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## MrUnix (May 18, 2012)

I had the same problem, with 3 foot deep holes in basically solid coral rock (South Florida). Wound up going A-frame to solve the problem and still had to sink them pretty deep.

Cheers,
Brad


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## WillliamMSP (Jan 3, 2014)

I don't have the knowledge set to calculate what would be appropriate for that span, but I sure as heck would err generously on the side of over-building it.

A) when thinking about who would be using it, I wouldn't even want to imagine it failing, but on the non-emotional side… 
B) when thinking about the loads that it's going to see, consider that we're not talking about static loads, we're talking about absorbing and redirecting the kinetic energy of multiple children dropping from a height of 4 or 5 feet once every second or so.


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## patcollins (Jul 22, 2010)

Your corner braces will do a little bit for the flexing of the top beam, but not a lot. Where they will help is in the racking motion side to side.

I am afraid the other guys are right about the postholes. The swing set at my grandfathers house did not have this problem but its uprights were telephone poles (he was a pole man for the local power company and acquired them some how along with the truck auger to put them in …..)


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## Goose22j (Mar 2, 2015)

MrUnix and Maker of Sawdust… were your holes traditional post holes or…? As I mentioned, mine are about 40 inches down and pretty wide…i used a total of 23 bags of 50-pound post hole cement.


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## MakerofSawdust (Mar 28, 2011)

My post holes were 36-40" deep in SOLID clay. They were 12" in diameter. I seriously questioned if the concrete we put in the holes was going to be harder or softer than the clay. I suggest keeping your posts and adding A-frames to them, all the way to the top. It appears you have some room to at least get a decent A-frame. Your posts probably won't move right away, but over time.


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## knotscott (Feb 27, 2009)

I'd definitely try to shore that beam up some more. We had a 4×6 main beam with a 2×4 screwed in as a top plate (like what you show as figure "I") holding 3 swings across an 11' span. I also added diagonal supports like you show as "H". Little kids are fine, but when the kids got bigger, the beam flexed enough to concern my wife, though I was fairly sure it wasn't gonna break. In hind sight, I wonder if a third 2×6 along the side of the first two might actually be more effective than addimg a 2×4 as a top plate. Bigger kids will swing as high as they can possible go. Even when your kids aren't huge, some of the neighborhood kids might be. Ours stood for about 13 years without a problem, but it always drove my wife crazy watching it….I told her to stop watching. 
;-)


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## Goose22j (Mar 2, 2015)

MakerofSawdust-good to know…mine are about 24 inches in diameter at the widest and probably closer to 16-18 at the narrowest (widest is front to back). Hoping that is enough of an increase to make a difference…
as far as the A frame, there is room in front of the swing but only 2-3 feet behind the swing. unfortunately an A-frame would defeat the aesthetic purpose of building it how we did…and also force us to build (or possibly anchor) on the artificial turf, which is why i'm hoping to avoid it. what do you think of the added footing support in the picture I added (item J)

KnotScott - thanks for the feedback, good to know!


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## bondogaposis (Dec 18, 2011)

A swing set is a dynamic load. I think the span is way too long for any of your solutions. You really need to beef up the top I'm not sure if 2×12's would be adequate, but I know that 2×6"s will be way over stressed even w/ a 2×4 on top. I also think you will have to guy wire the uprights to front and back sides to achieve any kind of stability.


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## Goose22j (Mar 2, 2015)

KnotScott-what happened after 13 years . I'm assuming you moved or took it down? what was your vertical support? A-Frame or Vertical Posts like mine?
were your diagonals at a 45 degree angle, and how long were they (i.e., how long was the unsupported span?)

Thanks!


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## patcollins (Jul 22, 2010)

The greatest force put on the beam should be when the kid is at the bottom starting their upward motion.

Silly question here, is there enough room behind the swingset so the kids on the outside don't hit the wall?


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## MakerofSawdust (Mar 28, 2011)

I don't think the added stuff at the bottom of the posts will help enough. The place to limit movement is at the top of the posts. The good part though is that it likely won't fail soon or suddenly. You'll have lots of time to watch for movement of the posts.


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## Goose22j (Mar 2, 2015)

Thanks Bondo-
I know tone doesn't convey well in text, so please know i mean this respectfully: On what are you basing the conclusion that the 2×6s will be way over stressed even with the 2×4? What about with the diagonals? Based on engineering background, employment experience, other structures you've built, etc?

The reason I ask is that I just got in touch with a civil engineer family member, who believes the diagonal supports will assist greatly…

Again, please know I mean this with the utmost respect-i'm just trying to filter in all the information I'm getting and determine which suggestions to implement, etc.

Thanks!!


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## Goose22j (Mar 2, 2015)

Pat - Good questions! 
Yes, which is (unfortunately why the beam is so long). there is, at the shortest point, nearly nine and a half feet behind the swing. figuring the angles of trajectory, considering upper body, etc, i figured 7.5 - 8 feet was more than sufficient…and then I added a couple feet


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## patcollins (Jul 22, 2010)

> Thanks Bondo-
> I know tone doesn t convey well in text, so please know i mean this respectfully: On what are you basing the conclusion that the 2×6s will be way over stressed even with the 2×4? What about with the diagonals? Based on engineering background, employment experience, other structures you ve built, etc?
> 
> The reason I ask is that I just got in touch with a civil engineer family member, who believes the diagonal supports will assist greatly…
> ...


Don't want o speak for Bondo but the corner braces effectiveness depends greatly on implementation and how well they do what they are supposed to. They have to be quite rigid and attached at both points very well to do their job which is to shorten the effective span of the top beam. Knowing how "outdoor wood" is with shrinking, drying out etc I just wouldn't count on being able to make them super rigid and them stay that way for long.

I will say that I am pretty conservative in structure analysis because I do it for aircraft, most of my experience is with metal.


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## dhazelton (Feb 11, 2012)

Put another post in the middle of that setup. That beam will sag, and in my opinion, a lot. And in my experience concrete does nothing for a post that deep except make it really hard to replace if and or when the wood rots or splits. Well tamped gravel and soil would have been better. When the kids outgrow that you'll want to take it down and you'll be cursing yourself and that concrete. If you put another post in the center then any lateral forces on that top beam when swinging will be minimized. Still the whole structure may rack sideways without corner bracing.

You also have placement issues. What if a kid falls off the back of a swing and flies into that block wall? Do you plan on putting down some type of soft barrier under it in both directions like rubber chips or mulch? I think you should have consulted this group or an expert before you did any construction.


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## knotscott (Feb 27, 2009)

Ours had A-frame sides. The kids got lost interest, the swing set got old, and I got tired of trimming around it!

p.s. Build a fort area, climbing walls, slide, etc, add whatever you can too it….our kids lived on it. The house that's the most fun is where the kids will be….

p.s.s: Another option to brace that beam would be to build a fort struct around one of the upright supports, and effectively shorten the span that the swings would hang from. This pic is crude, but shows the idea:


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## patcollins (Jul 22, 2010)

Thinking about it I would put an A-frame in the center, and the corner bracing.

I can't say I ever remember a kid falling off a swing and going backwards, I just remember them going straight down more or less.


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## dhazelton (Feb 11, 2012)

If you have forward or backward momentum you don't fall straight down. Also, who's to say they won't get on the swing from the side where your camera is and fly off into the wall? There's a reason parks and playgrounds took out all the swings. At the very least you should remove the stone around the perimeter and what looks like a soldiers course of brick and put down a 6 inch layer of soft material. I'm not trying to bust your chops, it just looks like the wrong spot for a swing set and you should eliminate the hazards before a neighbor kid get's a concussion hitting his head on the ground (is that astroturf?) or the wall or the stone mulch.


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## MrUnix (May 18, 2012)

Forts are cool, kids love them and you can place it next to the fence where they can't swing anyway. Most common plans I've seen use an A-frame on one end, a fort on the other, and a 4×6 minimum for up to a 12 foot span, with a swing on each end closest to the supports and a ladder or chin bar in the middle. Longer spans use larger beams.

The swings on the ends are to minimize the force applied to the center of the span where it is weakest; unfortunately, it looks like yours will have to be in the middle.

Cheers,
Brad


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## bondogaposis (Dec 18, 2011)

On what are you basing the conclusion that the 2×6s will be way over stressed even with the 2×4?

My assumptions are based on what would be considered adequate for home construction. In home construction 2×6 floor joists are not adequate to even span ten feet. Here you have 20 feet, sure you sistered two of them together and may add another 2×4 giving you the equivalent of 2 2×8's. Once again in home construction 2×8 floor joists are only adequate for a 10' span. That is for floor joists that are 16" apart across a whole floor. You have only 2 with double that span. I'm not an engineer but I believe that three kids going at once on that swing is going to provide a lot more stress than someone walking across a floor.

Here is a calculator for floor joist spans if you want to play around.

The reason I ask is that I just got in touch with a civil engineer family member, who believes the diagonal supports will assist greatly…

Absolutely it will help, the question is, will it be enough to prevent failure? I know you have invested a lot of work in this already and are looking for an easy fix. I think the key will be trying to break that span in half somehow. Someone mentioned supporting the center with an A frame that seems like a good idea.


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## patcollins (Jul 22, 2010)

> If you have forward or backward momentum you don t fall straight down.
> 
> - dhazelton


I think most swing accidents are kids (and adults) rolling backwards off the seat because unless the seat breaks it is what prevents them from going backwards or forwards with momentum.


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## dhazelton (Feb 11, 2012)

It's your project. Your property. Your children. Do what you want and Godspeed.


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## Goose22j (Mar 2, 2015)

1) I'm considering the A-frame in the middle, but the problem is I am not able/willing to sink it in or pin it to the ground because it is artificial turf and it will ruin it (not cheap stuff).
Would an A-frame in the middle be effective it it just rested on the ground, not pinned down at all?

2) 2nd alternative, what if I just added an additional 4×4 in the middle that went straight down and rested on the ground (i.e., not an a-frame). This would certainly address the downward sag of the top beam, would it also help with the forces of swing, simply by virtue of being more weight and another source that could take some pressure? Or useless?

3) 3rd alternative… what if I add sort of a half-size, half A frame. in other words, if i put a diagonal 4×4 from halfway up the back 4×4 on each side to the ground about 3 feet behind. Here's an image: https://www.dropbox.com/s/qldthwomv30xfct/alternativefix.jpg.










Thought is I would anchor it in shallow concrete, about 12-18 inches, since when kids were swinging back, the force would be pushing on it, and when kids were swinging forward, the pull force wouldn't be sufficient to pull it out of the ground because it was held in place by the vertical 4×4 (and the minimal movement of that post would not exert an inordinate amount of pressure.) did that make any sense whatsoever, and would that be a big help?

4) 4th idea, what if instead of (or in addition to) adding diagonal kickers (item H in the above-linked pictures), I added two more 2×6s to the cross beam. basically a mini pergola This is what I'm thinking: https://www.dropbox.com/s/hyqu1fmidcqe1ga/pergola.jpg?dl=0. 









I would imagine that would go a long way to addressing the crossbeam sag, and also the forces of swing on the crossbeam, though I'm guessing that wouldn't do much if anything to help relieve pressure off the vertical posts. Thoughts on this? What would make a bigger difference, this or the diagonal kickers running from the vertical posts to the crossbeam?

thanks again guys!


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## patcollins (Jul 22, 2010)

1) I think it could especially if it conformed to the ground well and was weighted down.

2) It would help, the amount it would help though wouldn't be that great but about a 50% improvement over what you had, the question would be "is that enough?"

3) That would also help, the question would be by how much again.

4) would be very strong in the direction that you increased the dimension, it would also add strength in the other direction just not nearly as much. A non-engineer explanation: Doubling the width of a beam will double its strength in the downward direction, but doubling the height of the beam will yield an 8x strength improvement, this assumes that the weight of the additional wood doesn't play that much into things.


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