# Custom 6x6 Post Swing Set Design - need to execute tomorrow



## keymaster (Jul 28, 2015)

Are you having concrete delivered or mixing yourself?


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## Daniel Holzman (Mar 10, 2009)

You say the project is deliberately over engineered. What exactly do you mean by this? To a structural engineer, this would mean that you calculated the maximum anticipated forces on the structure, applied a reasonable safety factor, and sized the elements and joints to safely handle the forces. This would account for all possible modes of failure, which in this case would include torsion, buckling, compression and tension failure, bending failure, and pullout. An engineer would check all the elements and all the connections to make sure that each component was engineered to at least the minimum required safety factor.

Other people use the term "engineered" much more loosely. Some mean they designed to a specific code. Some mean they copied someone else's design. Some mean they guessed the required size of a member, then made it bigger than they thought they needed. The reason this discussion is important in this case is that there is no indication this structure was pre-engineered by a manufacturer, or that it was built to a specific code. So what would the basis be for determining how large a hole you need, what strength concrete you require, and how much embedment is required?


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## nicolask (Sep 4, 2015)

keymaster said:


> Are you having concrete delivered or mixing yourself?


If I need more than I can mix, I will have it delivered...


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## nicolask (Sep 4, 2015)

Daniel Holzman said:


> You say the project is deliberately over engineered. What exactly do you mean by this? To a structural engineer, this would mean that you calculated the maximum anticipated forces on the structure, applied a reasonable safety factor, and sized the elements and joints to safely handle the forces. This would account for all possible modes of failure, which in this case would include torsion, buckling, compression and tension failure, bending failure, and pullout. An engineer would check all the elements and all the connections to make sure that each component was engineered to at least the minimum required safety factor.
> 
> Other people use the term "engineered" much more loosely. Some mean they designed to a specific code. Some mean they copied someone else's design. Some mean they guessed the required size of a member, then made it bigger than they thought they needed. The reason this discussion is important in this case is that there is no indication this structure was pre-engineered by a manufacturer, or that it was built to a specific code. So what would the basis be for determining how large a hole you need, what strength concrete you require, and how much embedment is required?


Thanks Daniel. No I am not an engineer. 

I should have said "overdesign" instead of over-engineer I realize now :smile:

I took into consideration a lot of the aspects you mentioned by looking at park equipments, speaking to an architect who is not an engineer, and to a experimented construction project manager and by simulating the swinging of three adults in my head. I also took in consideration specifications from a park structure builder. They use "12 bags" of concrete for such installations but I do not know if they use sonotubes or pour directly into the ground or which shape the "footing" has. They also use laminated 4x6 (2 pieces) to make the posts but it is made of white cedar which is more robust. That is why I used two 6x6. Also the steel bracket is an addition I thought of, to prevent the horizontal post to fall on people if it breaks at the joint. 1/4 inch makes it massive. I did not make any calculations. I would love to know how to do that !

Here is what information I based my design on : 

http://www.jeuxmodulair.com/outdoor-playset-the-luxury-swing.php

The PDF has some spécifications.


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## keymaster (Jul 28, 2015)

nicolask said:


> If I need more than I can mix, I will have it delivered...



My point was about the type of concrete--I should have been more clear. What is available for delivery is often standardized by region, and concrete suppliers can tell you what you need for your area and application. If there is a permit involved (possibly for the footings) then you should talk to the building dept. about what they require. Concrete strength and footing diameter are general code requirements. (Swing sets don't usually have footings, they are self supported; your design requires them.) 

The issues are strength, and how quickly a mix achieves its rated strength--which might affect your decision, depending on how soon you want to use it. If you are concerned about uplift due to frost, then a design with a sonotube that allows the concrete to "mushroom" below the tube will be best.


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## Knucklez (Oct 21, 2007)

this message board gets such great advice! we are grateful for the expert advice


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## keymaster (Jul 28, 2015)

nicolask said:


> H
> 
> I am wondering what type of concrete to use and how much of it ?


The IRC minimum is 2500 psf for foundations, with min. 3500 psf for concrete that will be highly exposed.

The post size, and possibly soil conditions, would determine footing size, not static load. The load requirements are minimal, even doubling your numbers. 

The issues are how deep the built-up 12"x6" post needs to be embedded in concrete, and how large does the footing need to be to stabilize the post, while resisting cracking and other forces. You plan on 4' embedment, 1/3rd to 2/3rds; the post is plenty stout. The code (IRC) says nothing on a problem like this--it's usually something for an engineer. 

The AWC prescriptive deck guide would prescriptively require an 18" min. footing. However, that prescription is based on factors which don't apply (the load, a deck, 1500 psf soil bearing capacity).

It wouldn't hurt to discuss this with the building department.


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## ron45 (Feb 25, 2014)

http://diy.stackexchange.com/questions/19994/what-is-the-allowable-span-of-2-stacked-6x6s


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## keymaster (Jul 28, 2015)

ron45 said:


> http://diy.stackexchange.com/questions/19994/what-is-the-allowable-span-of-2-stacked-6x6s



Ron, that's an entertaining link. Do we really need to design for 450 lb children? Really? (Swinging in sync, attaining 90 degrees of elevation.) 

It's the reciprocal of Nicolask's design, which is a 6x6 beam of unspecified span, supported by 6x12 posts. (In the discussion you posted, 6x6 posts support a 6x12 beam.) I figured the 6x6 beam was sufficient, but didn't take into account the span, the species, or any 450 lb kids. (Species of wood, not child.)


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## Daniel Holzman (Mar 10, 2009)

Engineering of a swingset requires accounting for dynamic loads. As it happens, the maximum vertical force exerted by a swinging child occurs at the bottom of the arc due to the combination of gravity and centripetal acceleration, and can be up to twice the weight of the child. So the actual total vertical force from a 100 lb child on the chain is 200 lbs. Add in a typical dynamic safety factor of 1.8, and the design load becomes 360 lbs. Account for fatigue due to repetitive motion, and the 450 lb figure is not so out of sight as it may initially appear.


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## keymaster (Jul 28, 2015)

Daniel Holzman said:


> Engineering of a swingset requires accounting for dynamic loads. As it happens, the maximum vertical force exerted by a swinging child occurs at the bottom of the arc due to the combination of gravity and centripetal acceleration, and can be up to twice the weight of the child. So the actual total vertical force from a 100 lb child on the chain is 200 lbs. Add in a typical dynamic safety factor of 1.8, and the design load becomes 360 lbs. Account for fatigue due to repetitive motion, and the 450 lb figure is not so out of sight as it may initially appear.



I'm better with static loads. I knew I could pull you into this discussion. (Engineers and humor are like moths to candles.) Better keep the 900 lb kids off it then. It's not over-engineering when an engineer does it? 

If this is a swing set kit that you purchase, its intended use would be made apparent by it being _child sized_. (And it would have a maximum load warning.) If you make it tall, and make it look sturdy, and use big steel plates and heavy chain it had better be strong. 

(Western red cedar, 12' span and grade one (Fb of 725) doesn't pass the one large adult test when using your load & safety factors. I don't know if the OP's span is 12 feet.)


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## nicolask (Sep 4, 2015)

Span is 10" 

I hope 3 adults can use it safely simultaneously

I found the concrete shape that goes with the commercial model swing set I based my set on : the reference model uses a steel pipe for horizontal support

the concrete shape consists of an upside down "T" with 3/8 steel reinforcements bars (armatures) the slab is 2'x3' and a 12" sonotube on top

unfortunately the 12" sonotube don't appear to work with the 6x12 post I might to make a custom frame for the concrete:smile:


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## nicolask (Sep 4, 2015)

Span is 10' (foot) sorry

bars must be bent at the "T" junction

currently digging 2'x3' x 4'1/2 holes in the ground...


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## nicolask (Sep 4, 2015)

I will not allow any adult over 250lbs to use it alone or else

the slab I mentione previously is 6 to 8 inches think (will make it 8 or more)


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## keymaster (Jul 28, 2015)

nicolask said:


> Span is 10'
> 
> I hope 3 adults can use it safely simultaneously
> 
> ...



Keep proper spacing between the swings, for safety. It looks like you have 18" between each? (Check with a swing manufacturer.) Make sure your beam to swing connections are made using proper hardware. The manufacturer's site to which you linked may be able to supply engineered fittings.

The concrete footings obviously need to be larger than the maximum post dimensions, with a safe margin on all sides. The size and need for reinforcement is something that can only be answered by engineering. (I'm not sure what you mean by "concrete shape," the "slab," etc.) I would use a cylindrical footing to below frost. Earth-forming may work depending on how cohesive your soil is, but will almost certainly use more concrete. At minimum you should form the top 24"-30" to get the post properly centered on the footing, and plumb.

Think about how you will join the two posts together. The more they act like one, the better.


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## ron45 (Feb 25, 2014)

Something to consider and the reason for the link.

Two maybe three children on one swing.
two adults on one swing.
Two on each swing.
All synchronized swinging.

Sounds like snap, crackle, pop, and that's not rice crispies either.


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## nicolask (Sep 4, 2015)

ron45 said:


> Something to consider and the reason for the link.
> 
> Two maybe three children on one swing.
> two adults on one swing.
> ...


The weight limit I am concerned with is 3 adults weighting no more than 250 lbs each. I want it to be strongly built but not that strong (somewhat more than enough, is good to me).

From the previous posts, I understand it will be fine. Commercial playground equipment is another story and another budget !

Most residential swings would fail in your scenario. Two people on each swing is not something I want to proof my installation from.

I will post the hardware I am using and that would not be the problem. The point of failure in any event would be the "pinching" effet on the horizonral beam center swing I would think. 

But even then, it would break but would not fall on people : that is one of the reason for the steel brace I added. The other reason being that if the beam to post junction fails, the beam must remain in the air and not on people's heads.


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## nicolask (Sep 4, 2015)

keymaster said:


> Keep proper spacing between the swings, for safety. It looks like you have 18" between each? (Check with a swing manufacturer.) Make sure your beam to swing connections are made using proper hardware. The manufacturer's site to which you linked may be able to supply engineered fittings.
> 
> The concrete footings obviously need to be larger than the maximum post dimensions, with a safe margin on all sides. The size and need for reinforcement is something that can only be answered by engineering. (I'm not sure what you mean by "concrete shape," the "slab," etc.) I would use a cylindrical footing to below frost. Earth-forming may work depending on how cohesive your soil is, but will almost certainly use more concrete. At minimum you should form the top 24"-30" to get the post properly centered on the footing, and plumb.
> 
> Think about how you will join the two posts together. The more they act like one, the better.


Pretty sure it is 20", spacing is good from what I read, the minimum being 12". 
http://www.all4thekids.com/Swing-Set-Swing-Spacing.pdf

Swings I bought with manufacturer chains
http://www.jeuxmodulair.com/product.php?product=28

Spring clips 
http://www.jeuxmodulair.com/product.php?product=94

Supports 
http://www.jeuxmodulair.com/produit.php?produit=91

I have 3/8 zinc plated "Machine Screws" to attach the support to the beam... 4 of them per swing.


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## nicolask (Sep 4, 2015)

keymaster said:


> The concrete footings obviously need to be larger than the maximum post dimensions, with a safe margin on all sides. The size and need for reinforcement is something that can only be answered by engineering. (I'm not sure what you mean by "concrete shape," the "slab," etc.) I would use a cylindrical footing to below frost. Earth-forming may work depending on how cohesive your soil is, but will almost certainly use more concrete. At minimum you should form the top 24"-30" to get the post properly centered on the footing, and plumb.
> 
> Think about how you will join the two posts together. The more they act like one, the better.


For the posts joining it is 1/2" machine screws with bolts. 3 of them, 1 in the center, 1 on top (two if you count the one that goes thgough the beam) and one on bottom. I would have put construction glue but I thought it would not be necessary or is it ? It's not too late to change that even though assembly is done it is not in the ground/concrete yet ! I think I would have needed to plane the wood to achieve a good bond.

Also thanks for your thoughts on the concrete footing this is my main concern now. I have not yet found the solution other than to build a rectangular frame. I could not find larger than 12" sonotubes, is there larger ones and if so how big should it be to achieve the safe margin you mentioned ?


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## nicolask (Sep 4, 2015)

keymaster said:


> My point was about the type of concrete--I should have been more clear. What is available for delivery is often standardized by region, and concrete suppliers can tell you what you need for your area and application. If there is a permit involved (possibly for the footings) then you should talk to the building dept. about what they require. Concrete strength and footing diameter are general code requirements. (Swing sets don't usually have footings, they are self supported; your design requires them.)
> 
> The issues are strength, and how quickly a mix achieves its rated strength--which might affect your decision, depending on how soon you want to use it. If you are concerned about uplift due to frost, then a design with a sonotube that allows the concrete to "mushroom" below the tube will be best.


 I plan to use 30 MPa concrete. Definitely going for a such footing shape.


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## keymaster (Jul 28, 2015)

nicolask said:


> Span is 10"
> 
> I hope 3 adults can use it safely simultaneously


If it were me, and I wanted this to be safe for children and adults, I would use a deeper beam--and wouldn't use red cedar.

Do you know the grade of red cedar? 

If it is select structural grade (Fb=1100 PSI): 

1) Using three 250 lbs adults, 900 lb load x 3, treating the beam as uniformly loaded, maximum moment is 3375 ft-lbs; required section is 36.8 in^3, section modulus is 36. The beam is insufficient.

2) Using two 250 lb adults, two concentrated 900 lb loads at equal thirds, the required section is 32.7, sufficient. 

3) Using three 200 lb adults, a uniform load of 2160 lbs, the required section is 29.5, sufficient. 

4) Using Red Cedar No. 1 (Fb = 825), _all insufficient._

I'm not an engineer. The results are mixed enough that I would want to strengthen the beam. If the grade is other than select structural, it is insufficient. Factors which would result in a reduction in performance due to moisture weren't applied. It's important that you verify the grade of lumber with the supplier.


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## nicolask (Sep 4, 2015)

keymaster said:


> If it were me, and I wanted this to be safe for children and adults, I would use a deeper beam--and wouldn't use red cedar.
> 
> Do you know the grade of red cedar?
> 
> ...


Wow thanks for these. I will lower the maximum adult weight to 200lbs. I think I had maybe once a adult over 200lbs visit my house and he was not the swinging type..

I had a feeling that the red cedar beam would be rather weak. I can upgrade that eventually. Any recommendation on the exterior wood type that would fit well with my installation ? If I use a steel pipe later on I will have to replace hanging hardware.


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## nicolask (Sep 4, 2015)

keymaster said:


> It's important that you verify the grade of lumber with the supplier.


 
Here is the cedar I purchased : 

http://www.canac.ca/fr/product/mate...cedre-noueuxbr-6-po-x-6-po-x-12-pi_31635.aspx

"Knotty cedar beam, planed on 4 sides (not dried natural wood, untreated) . Cedar west of fine quality, ideal for patio , railing, flower box , swings , etc."


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## nicolask (Sep 4, 2015)

keymaster said:


> If it were me, and I wanted this to be safe for children and adults, I would use a deeper beam--and wouldn't use red cedar.



If you take the problem the another way around, what is the total maximum weight considering the materials and swing repartition ? 

My hanging hardware already has a 250lbs weight limit per pair so this so my limit for 1 swing. If the total weight is 600lbs, I do not think I would ever exceed that.

All I have to do is to affix the weight limitation on the swing post so that the "insurance" aspect is covered (in case someone over 250lbs sneaks in my backyard to use the swings).


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## nicolask (Sep 4, 2015)

See the attached drawing for the planned footing :

:vs_cool: (my daughter selected this Smilie)


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## nicolask (Sep 4, 2015)

bottom slab size is 2'x3' and 8" thick


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## keymaster (Jul 28, 2015)

nicolask said:


> Here is the cedar I purchased :
> 
> http://www.canac.ca/fr/product/mate...cedre-noueuxbr-6-po-x-6-po-x-12-pi_31635.aspx
> 
> "Knotty cedar beam, planed on 4 sides (not dried natural wood, untreated) . Cedar west of fine quality, ideal for patio , railing, flower box , swings , etc."


That does not sound like a structural grade. I would confirm with the supplier, as I stated. Structural grade is usually free of knots and checks. (It is hard to say with cedar, however.) That could be grade 1, in which case the lower performance applies.


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## ron45 (Feb 25, 2014)

Daniel said, " Engineering of a swingset requires accounting for dynamic loads. As it happens, the maximum vertical force exerted by a swinging child occurs at the bottom of the arc due to the combination of gravity and centripetal acceleration, and can be up to twice the weight of the child. So the actual total vertical force from a 100 lb child on the chain is 200 lbs. Add in a typical dynamic safety factor of 1.8, and the design load becomes 360 lbs. Account for fatigue due to repetitive motion, and the 450 lb figure is not so out of sight as it may initially appear.

Now picture 3 adults, all swinging at the same time, all at the same height, as in perfect alignment, synchronized swinging.

Also, What would be the stress factor for one post.?
Swing sets usually have two post on each end angled to meet the stress load.

Are your timbers cut to support vertical or lateral loads.


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## nicolask (Sep 4, 2015)

keymaster said:


> That does not sound like a structural grade. I would confirm with the supplier, as I stated. Structural grade is usually free of knots and checks. (It is hard to say with cedar, however.) That could be grade 1, in which case the lower performance applies.


Will do and report back thanks. In worst case some beams are almost 100% knot free I'll keep one for the horizontal beam.

I could switch it for structural treated wood..


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## nicolask (Sep 4, 2015)

nicolask said:


> Will do and report back thanks. In worst case some beams are almost 100% knot free I'll keep one for the horizontal beam.
> 
> I could switch it for structural treated wood..




I would like to say a big thanks for all the precious advice you guys have posted. I should complete the project by mid-week and will post pictures.

Stiil having uncertainty for the 18" sonotube but if I find 20" I will take that just to be sure.


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## Daniel Holzman (Mar 10, 2009)

I would like to make a clarification to my previous post on loads. The maximum load on the swing is the sum of dead weight plus centripetal force. The dead weight is simply the weight of the person plus the swing and chain. The centripetal force depends on the arc swung by the person. The worst case is a 180 degree arc, from horizontal to horizontal, which is difficult to achieve for most people.

In the most severe realistic case (180 degree arc), the centripetal force is equal to twice the weight of the person swinging, and is directed downward when the person is at the bottom of the arc. The centripetal force adds to the weight, so the worst possible case is a total of three times the weight of the person. For a 100 pound person, the load would be 300 lbs, which needs to be multiplied by a safety factor, hence the previously quoted figure of 450 lbs design load, which is not a bad estimate. Of course, if you have someone 200 lbs swinging, the design load can easily approach 1000 lbs (including safety factor). If you have multiple people swinging simultaneously, you would in theory have to account for the possibility that all three simultaneously achieve 180 degree arcs, and are synchronized at the bottom. That can lead to very high loads, probably beyond any realistic wood beam size, but possible.

It is also possible that you have an Olympic class gymnast in your backyard, and they push the swing higher than the support bar (beyond 180 degrees). I have never seen anyone do this in person, but on Mythbusters or some similar show, there was a video of someone getting close to a 360 degree arc, hard to fathom really. That would exert substantially higher load than the 180 degree case, a little hard to actually compute, since the chain will probably go slack, but there may be additional dynamic loads when the swing snaps the chain tight. Potential for breaking the chain or the support I suppose.

For a three swing set, to analyze the beam, you would need to compute bending stress due to three point loads, assuming the swings are attached as point loads, which is likely the case. This will generate surprisingly large forces.

PS: I built a swingset in my backyard many years ago, using my treehouse as the support for the swings. I never designed it for a 200 lb person swinging 180 degrees, so it is likely that the set would fail if two 200 lbs gymnasts performed acrobatics on it (it is a two swing set).

Good luck with the project.


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## nicolask (Sep 4, 2015)

ron45 said:


> Are your timbers cut to support vertical or lateral loads.


 I want to answer : both !


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## nicolask (Sep 4, 2015)

Daniel Holzman said:


> I would like to make a clarification to my previous post on loads. The maximum load on the swing is the sum of dead weight plus centripetal force. The dead weight is simply the weight of the person plus the swing and chain. The centripetal force depends on the arc swung by the person. The worst case is a 180 degree arc, from horizontal to horizontal, which is difficult to achieve for most people.
> 
> In the most severe realistic case (180 degree arc), the centripetal force is equal to twice the weight of the person swinging, and is directed downward when the person is at the bottom of the arc. The centripetal force adds to the weight, so the worst possible case is a total of three times the weight of the person. For a 100 pound person, the load would be 300 lbs, which needs to be multiplied by a safety factor, hence the previously quoted figure of 450 lbs design load, which is not a bad estimate. Of course, if you have someone 200 lbs swinging, the design load can easily approach 1000 lbs (including safety factor). If you have multiple people swinging simultaneously, you would in theory have to account for the possibility that all three simultaneously achieve 180 degree arcs, and are synchronized at the bottom. That can lead to very high loads, probably beyond any realistic wood beam size, but possible.
> 
> ...


Ok so basically I need to make sure mostly the beam (and rest of the installation) can sustain an intermittent 1800 lbs load split in 3 points to achieve 200lbs * 3 weight limit specifications. Did I understand correctly ?


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## nicolask (Sep 4, 2015)

nicolask said:


> Will do and report back thanks. In worst case some beams are almost 100% knot free I'll keep one for the horizontal beam.
> 
> I could switch it for structural treated wood..


I contacted the wood beam supplier and he said "no" to structural grade. However, I asked what is the load bearing capacity for a bad piece that would have multiple knots, he answered 5000 lbs without any problem with the 10' span including if the total load is centered on the beam. He mentioned 20000 lbs as a support beam if the weight is uniform.

He mentioned that aesthetically, the beam would in time curve somewhat and the only way to work around that is to have it rectangular shaped (wood type is not the factor). I asked if inside square angles would help and he said yes.

How does that sound to you guys ? does sound reasonable for the 1800 lbs I understood for 3, 200 lbs adults ?


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## ron45 (Feb 25, 2014)

It's taking awhile but by golly your getting there.

If you don't wish to use metal (hint) or more then one post per end (no sway support)
I would check into a manufactured beam.


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## keymaster (Jul 28, 2015)

Daniel Holzman said:


> I would like to make a clarification to my previous post on loads. In the most severe realistic case (180 degree arc), the centripetal force is equal to twice the weight of the person swinging, and is directed downward when the person is at the bottom of the arc. The centripetal force adds to the weight, so the worst possible case is a total of three times the weight of the person. For a 100 pound person, the load would be 300 lbs, which needs to be multiplied by a safety factor, hence the previously quoted figure of 450 lbs design load, which is not a bad estimate. Of course, if you have someone 200 lbs swinging, the design load can easily approach 1000 lbs (including safety factor). If you have multiple people swinging simultaneously, you would in theory have to account for the possibility that all three simultaneously achieve 180 degree arcs, and are synchronized at the bottom. That can lead to very high loads, probably beyond any realistic wood beam size, but possible.
> 
> For a three swing set, to analyze the beam, you would need to compute bending stress due to three point loads, assuming the swings are attached as point loads, which is likely the case. This will generate surprisingly large forces.


A few things to clarify my approach. I was "ballparking" due to concerns about species and grade (using your dynamic load factors). I had serious concerns about the use of red cedar, as 6x6 red cedar is most readily available for decorative purposes, and often as posts. The description the OP provided confirms my suspicions. "Knotty" and "pretty" are rarely used structural terms. 

I didn't feel the need to include dead load, as it is negligible in this case, only carrying itself. I was trying to illustrate that all supposed results are meaningless if the most basic assumptions they are based on such as grade can't be known. If allowable fiberstress is 825 psf, for example, it was already failing. That's where I wanted to leave it. I was concerned that the OP might take any passing value as validation--when in reality I was trying to demonstrate that it was unsafe. (Indeed, that is what he has done, fixing on a value of 200 lbs live load as safe--when it fails at many grades of cedar. *Edit:* 200 lbs leading to up to 1080 lbs dynamic loads.)

I was using the analogy of a uniformly loaded header for estimation purposes. (Load calcs being based on assumptions, as you know, but others may not.) There are six chains/ropes for the three swings, each 15-16 inches apart with a 17" separation (Graphic Standards, avg. chair width, 15-1/2"). A ten foot header span would carry seven joists at 16" o.c. or five rafters at 24" o.c. The conditions are similar. If the beam won't bear the uniform load, it won't bear more concentrated loads--all other things being equal. Understandably, a 250 lb person can sit in one swing, while another carries a 100 lb child, just as rafters and joists uniformly spaced can be unevenly loaded. I wasn't trying to model all loads, I was most concerned with demonstrating the difference in bearing capacity by grade.

If the OP wants to make that beam truly safe, he should consider adding steel angle (one each side, below).


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## nicolask (Sep 4, 2015)

Hi all I am very proud of the result ! I used 960 KG of concrete. I will post pictures later on today (forgot my USB cable in the car). Forms remain underground. We use it daily with adults and kids.

It is very strong and feels commercially made. So far the horizontal beam is neither bending nor showing weakness. It feels like this will last for many many years. 

I used thick vapor barrier to wrap the posts before pouring the concrete and thermoplactic to prevent water from entering the joint between post and concrete. This was a temporary solution I had nothing else and weather was not good when I finished the project. Will replace with Sika silicone to match color and will eventually waterproof the top of concrete cylinders.


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## 123pugsy (Oct 6, 2012)

Glad to hear it.

Looking forward to the pics.


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## nicolask (Sep 4, 2015)

Here it is from automn, will do the finishing touches soon : 

- If anyone wants to do Something similar, use bigger than 18" sonotubes because concrete did crack at 2 corners for each posts even though I used rebars. It is merely cosmetic but still frustrating.

- When you see it though it does seem a bit overdesign for the needs but people enjoy it and that is what counts. Maybe not so overdesign after all.


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## 123pugsy (Oct 6, 2012)

Very nice.
That's not going anywhere.


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## nicolask (Sep 4, 2015)

Thank you. Other improvements would be : 

- To use circle shaped rebars since squares corners are too close to the side
- Removing the shapes rather than leaving them underground : I read something about sonotube collapse and wanted to backfill as I poured which I did but I am pretty sure it would have been fine without backfilling
- Also I drilled partial holes and used pieces of rebars to anchor the underground part of the posts in the concrete before pouring 
- used 6-8 inches of gravel under slab for drainage


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## Njdad (Jul 18, 2020)

Hi Nicolask. I am think of a similar project for my backyard and would love to know how your project has held up. Unfortunately the picture of your completed project are not showing up. Would you mind reposting?

I am not an engineer/architect/handyman.... Here is what I am envisioning. 

Two vertical 6x6 12ft tall pressure treated posts set in concrete (3ft plus another foot or so for stones at the bottom) placed 8ft apart. A 12ft 6x6 post will sit on top of the vertical posts with a 3.5ft overhang. I intend to have a climbing rope on the 4 foot section. For the 8 foot section between the two vertical posts, I want the flexibility to have a swinging bench, or swings or a swinging tire on rope. My idea is to have the corresponding holes drilled on the horizontal beam and change the fixtures as need be. I intend to use the same precautions that you have taken with rebars set in concrete and the top of the concrete sloping away from the beams. To make this even more complicated I am planning to have another 6 x 6 post set in ground perpendicular to one of the two vertical beams about 6ft away. The idea is to have an L shape structure. A 6x6 post will sit on top and I plan to have a pull up bar installed between these two vertical beams. The reason for the top post so that I can hand the tire to swing to this side when we have the larger side being used for a bench. My dilemma is how to support the top post on the smaller 6ft section. One end will not be an issue since there is a 6x6 vertical post there. However on the other end, the vertical beam there is already supporting the 12ft horizontal beam. 

Any thoughts, suggestions, criticism to the plan?

Thank you!


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## chandler48 (Jun 5, 2017)

It's a 5 year old thread. Maybe the moderators could start your own thread with a reference back to the older one for clarity.


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## nicolask (Sep 4, 2015)

Njdad said:


> Hi Nicolask. I am think of a similar project for my backyard and would love to know how your project has held up. Unfortunately the picture of your completed project are not showing up. Would you mind reposting?
> 
> I am not an engineer/architect/handyman.... Here is what I am envisioning.
> 
> ...


Still brand new today ! Nothing moved and the horizontal beam did not bend at all. I understand the photos have been lost in the forum I will add some this week-end for you.

Everyone who visits my backyard compliments my custom swing set and now two kids play daily in them and more on thw week-ends.

When I have heavier men (220lbs+) swing, there is some perceptible torsion movement at the angles where the steel braces are, but an architect tells me it is normal for a wood construction.

Can you draw your project and post the drawing ? I think that would help a lot for others who may be reading.


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