Building swing set. Doubting design

[Chris J]

TL;DR Summary

Too tall for design?

Hi all,

I designed this swing set and now I'm doubting my self and getting concerned.

I used 5" schedule 40 steel pipe for the posts and 3" schedule 40 steel for the top horizontal bar. There's only one post per side to be set 48" down in concrete 16" in diameter. This designed is to help with limited space in the area.

The design is to be 12' from the ground to the top bar with two swings. Am I pushing my luck for rigidity?

5" sch40 pipe had a 5" ID and 5.5" OD.

 

[berkeman]

Can you post a sketch? Use the "Attach files" link below the Edit window.

Have you fabricated this yet, or is it just on paper so far? Is there a reason you went with single posts on the ends instead of the more traditional A-Frames?

https://discountplaygroundsupply.com/8-high-2-seat-swing-set/

 

[Chris J]

Can you post a sketch? Use the "Attach files" link below the Edit window.

Have you fabricated this yet, or is it just on paper so far? Is there a reason you went with single posts on the ends instead of the more traditional A-Frames?

View attachment 346003
https://discountplaygroundsupply.com/8-high-2-seat-swing-set/

The reason for the single post design is limited space.

It's basically a copy of this, except 4' higher and 1 size larger pipe and substantially larger footings, I think the commercially available design only calls for 32" deep. I'm considering on shortening it as maybe 4' higher is just too much for 1 size larger pipe.

But, maybe not? The pendulum effect is what's throwing me off rather than just static load.

This design uses 4" sch40 pipe for the side posts and is only 8' above the ground.

 

[berkeman]

The reason for the single post design is limited space.

I'm not understanding this. If you look at the typical picture that I posted, the A-frame triangles basically reach out to about the same distance that the folks on the swings will be swinging out to. If you don't have room for the A-frame triangles, how do you have enough room for the folks swinging?

 

[Lnewqban]

The design is to be 12' from the ground to the top bar with two swings. Am I pushing my luck for rigidity?

It seems to me that you are not.
I am not sure about the rigidity of the "3" schedule 40 steel for the top horizontal bar".
How wide apart will the vertical posts and the swings be?

 

[Chris J]

It seems to me that you are not.
I am not sure about the rigidity of the "3" schedule 40 steel for the top horizontal bar".
How wide apart will the vertical posts and the swings be?

138" between posts.

 

[gmax137]

Can you buy 5 inch pipe? I know it is in the Pipe Tables but I have never seen any in real life.

EDIT other than PVC

 

[Chris J]

Can you buy 5 inch pipe? I know it is in the Pipe Tables but I have never seen any in real life.

EDIT other than PVC

Yep
It's just not sold as the usual stores that just carry typical pipe.

 

[gmax137]

Yep

Really? OK. Now I'm curious about the pricing compared to 6 inch which is as common as can be. Sorry for the tangent off your thread.

 

[Rive]

I think the commercially available design only calls for 32" deep.

That feels really shallow for anything taller. There will be some serious torque at the base, repeatedly. The pipe likely will be able to bear it, but the soil?

Also, it was already asked but without response: if you don't have enough space then how do you plan to address safety and swinging (flinging... ... landing) width?

If it's just the problem of standing area but you have adequate (soft) ground for swinging width you may consider to attach the stand to somewhere at the top too.

 

[Chris J]

To answer all questions

No it's not built yet just something I was thinking about after seeing something else similar and it made me think it could be used as a swing. After thinking about it I'll probably just give up on the idea as there's too many unknowns and I'm not sure it's worth it.

I don't know the cost of 5" pipe only that it's available.

The reason for single post design would be because the space is used for other things when the swing isn't in use.

 

[jack action]

It's basically a copy of this, except 4' higher and 1 size larger pipe and substantially larger footings, I think the commercially available design only calls for 32" deep. I'm considering on shortening it as maybe 4' higher is just too much for 1 size larger pipe.

But, maybe not? The pendulum effect is what's throwing me off rather than just static load.

This design uses 4" sch40 pipe for the side posts and is only 8' above the ground.

Comparing both designs for buckling:
$$\frac{\left(\frac{5.5^4 - 5^4}{12}\right)}{\left(\frac{4.5^4 - 4^4}{8}\right)} = 1.255$$
So your design should be stronger than theirs.

Comparing both designs as a cantilever beam with a load at the end (for any horizontal load at the top of the swing):

Comparing the shear stresses:
$$\frac{\left(\frac{5.5^2 + 5.5(5) + 5^2}{(5.5^2 - 5^2)(5.5^2 + 5^2)}\right)}{\left(\frac{4.5^2 + 4.5(4) + 4^2}{(4.5^2 - 4^2)(4.5^2 + 4^2)}\right)} = 0.81$$
Your design is weaker than theirs.

Comparing the bending stresses:
$$\frac{\left(12 \times \frac{5.5}{5.5^4 - 5^4}\right)}{\left(8 \times \frac{4.5}{4.5^4 - 4^4}\right)} = 0.97$$
Your design is slightly weaker than theirs.

References:
https://www.engineeringtoolbox.com/euler-column-formula-d_1813.html
https://www.engineeringtoolbox.com/area-moment-inertia-d_1328.html
https://mechanicalc.com/reference/beam-analysis
https://en.wikipedia.org/wiki/Section_modulus