Thread: What is the bending strength of 2" OD 304L tube; .065 & .120 wall?

I've been asked to fab a set of 'adult-sized' monkey bars for a Christmas present. The user is 6' 2", 180lbs. They'd like the run to be as long as possible, up to 20' but at least 10'. I've requested a quote for 2" welded 304L round tube in wall thicknesses of .065" and .120". Cross bars will be 1" 304L, .065 wall. The question: What distance can I go between supports for two parallel rails that together must support a 200lb weight in the center without permanent deformation?

I have no idea how to calculate that on a thin-wall SS tube.

SWAGs and personal experience welcome. I'm not going to get it 'engineered' beyond this forum and I don't need liability warnings, etc.

Thanks.

I would say I have seen monkey bars about 10-12 feet long made from 1+1/2" or maybe 2" water pipe. Not sure if it is thick walled or regular wall thickness. i think you have to assume all the weight will be on one side pipe at some times. there is also a goodly dynamic loading requiring quite a safety factor. I think for overhead lifting a safety factor of 5-10 is normal.
You might look at jib crane booms for light cranes such as truck mounted for similar loads.
Bill D

DIY Parkour Gym Equipment: The Ultimate Guide to Pipe Structures | Simplified Building

How about those pipe spears on a forklift to lift rolls of carpet?

GH:

Deflection on a 20'span would be over 10"; on a 10' span it's over 6" with the thin wall tube. With the thicker wall the numbers are about 1.3" and 7/8". This is obviously better, but still too much in my book.

However, if you switch to schedule 40 pipe (2.375" od, 0.157" wall) the deflection is down to about 3/8" and pipe stresses are much more reasonable. It's good practice to limit deflection to L/270 (0.44" for 120" span).

Regards

DB

Thank you, Mr. Bronson. I've suggested sch-40 and powder coat but they're still hoping for SS. If not too much work, could you estimate, say 2 1/2 or 3" thinwall 304 @ 15' span?
Gordon

edit: By the way, are those numbers for single rail deflection, or for splitting the load between two parallel rails?

For something like monkey bars, you should add a impact factor, multiplying that static load of 180lbs by 2-3 times.
Since the owner will likely jump up to the bar, not ease his weight on to it.

Yes, thanks. I don't mind if the deflection is high under such momentary load, I just don't want anything to 'bend' permanently. I have also considered arching the rails, say 6" rise over 10' (12" over 20') but without longitudinal restraints on the end supports that probably won't help.

Originally Posted by D Bronson

...Deflection on a 20'span would be over 10"; on a 10' span it's over 6" with the thin wall tube. With the thicker wall the numbers are about 1.3" and 7/8". This is obviously better, but still too much in my book...

Speaking from experience, I don't think the deflection will be anywhere near that much. Remember you've got two
lengths of tube joined together by rungs or cross-members--they'll have much more strength working together than
as individual members. Yes you'll get some deflection but the tubes will not reach the yield point--not even close.

I'd have no qualms going 17-18 ft. with the .120 wall tubing and you could probably stretch it out to 20 ft. without issues.
If you want to make sure there is no bending weld a small truss to the top of each tube. Another possibility if you have
access to some tube rolls is to put a little Positive --or upward--camber in the tubes before you weld them up...

Edit...I see you mentioned arching the tubes in your post--I must be a slow typer. Having arches will definitely help...

Pipe is available in stainless steel. Probably even 21', use the 2" sch 40 SS pipe, 1 1/2 would probably be fine, unless the guy wants to have chicken fights with his buddies. Second thought just use the 2" sch 40.

Originally Posted by Rob F.

Pipe is available in stainless steel. Probably even 21', use the 2" sch 40 SS pipe, 1 1/2 would probably be fine, unless the guy wants to have chicken fights with his buddies. Second thought just use the 2" sch 40.

A single random of pipe should be 20+ ft.

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Originally Posted by Rob F.

...unless the guy wants to have chicken fights with his buddies...

This is a very good point. Get two (or more) guys swingin' on the thing at the same time and the load goes
up quite a bit. I'm thinkin' the 2" Sched 40 pipe is a better bet...

Originally Posted by LKeithR

This is a very good point. Get two (or more) guys swingin' on the thing at the same time and the load goes
up quite a bit. I'm thinkin' the 2" Sched 40 pipe is a better bet...

Or the guy and his wife? Things could get a little interesting if they have a private back yard...

[Hmm - they want a long run, do they have a bunch of "swinging" friends?]

Thanks for all the info. I"ll check on the cost of sch-40 ss pipe, but I suspect its very high. Another complication is that they want to be able to lower the rails for the kids. Weight-wise the sch-40 pipe might be hard to deal with.

It is all the same price per pound so yes the larger pipe will cost more, since it weighs more. Some place that sells a lot of pipe may get better volume discounts though.

The diameter of the pipe is important regarding holding on. Too big and the monkey wont be able to grip for certain antics. My old college book says a 44mm(1.75") dia is 'the optimum size for human power grip.' It might pay to take them a few off-cuts of varying diameter and see what they are comfortable with.

Originally Posted by gwelo62

The diameter of the pipe is important regarding holding on. Too big and the monkey wont be able to grip for certain antics. My old college book says a 44mm(1.75") dia is 'the optimum size for human power grip.' It might pay to take them a few off-cuts of varying diameter and see what they are comfortable with.

You realize monkey bars are just a ladder laid flat right? The 2" pipe discussed here is not for the "rungs" but the main frame.

Originally Posted by Rob F.

You realize monkey bars are just a ladder laid flat right? The 2" pipe discussed here is not for the "rungs" but the main frame.

Sorry I was thinking of a more general purpose 'jungle-gym' where multiple children hang upside down by their knees.

It is unwise and potentially dangerous to make recommendations for strength, deflection, or material specs without knowing the ANSI/ASTM requirements for playground equipment. Check here first.

ASTM Playground Standards - ANSI Blog

Originally Posted by Illinoyance

It is unwise and potentially dangerous to make recommendations for strength, deflection, or material specs without knowing the ANSI/ASTM requirements for playground equipment. Check here first. ASTM Playground Standards - ANSI Blog

No thanks. If this were being offered to the public for a price, proper documentation would be necessary. But it isn't. From post #1:

Originally Posted by Gordon Heaton

. . . I'm not going to get it 'engineered' beyond this forum and I don't need liability warnings, etc.. . .

I'll test thoroughly, use good judgement, and take responsibility as will the user (family). If it sags, their feet touch the ground and ruin the fun. In the career from which I retired, one of the most tightly regulated industries in the US, I spent countless hours as a manager trying to educate trained professionals not to 'what if' themselves into doing nothing. Damn the lawyers and screwball judges who've convinced this people that they can't pee without a certified toilet, and that if they splash themselves it is someone else's fault.

Why stainless instead of galvanized? Galv pipe used to be in every playground. It is way cheaper and mifht be a tad stiffer than stainless.
I remember as a kid it was a LONG drop from the monkey bars.

Stainless will have corrosion advantages (duh), especially if the welds are passivated. It should also be "smoother" (unless pipe is used), better for swinging grips (rougher would be better for static grips). And galvanized tubing might transfer more metallic elements into the skin, especially when sweaty.

Not to mention that galvanized tube/pipe has issues when welding, and Gordon has to keep his remaining neurons in good shape.

Stiffness should be about the same, and vastly more influenced by diameter and section than by any alloy variation.