Safe Pull-up Bar Span for 124" - Advice?

[Justin Bishop]

Hello smart physicists!

I'm hoping to run a span of 124" for a pull up bar, with a support in the middle at the 62" point (so 3 supports total). I'm using the Rogue P-5V Pull-Up Bar Brackets (https://www.roguefitness.com/rogue-p-5v-garage-pullup-system). The brackets call for a tube with a 1.25" OD.

I'd love to be able to use this aluminum tube: https://www.onlinemetals.com/merchant.cfm?pid=7003&step=4&showunits=inches&id=71&top_cat=60

Since it's roughly 7x cheaper than something like this steel equivalent: https://www.onlinemetals.com/merchant.cfm?pid=14781&step=4&showunits=inches&id=312&top_cat=1

I'm open to any recommendation. Please help? I just want to make sure I don't get something that leaves me concussed on the floor after an aggressive pull up maneuver. :) Thanks in advance!

 

[anorlunda]

Use an online calculator such as https://www.roguefab.com/tube-calculator/

When I tried it on your specified tube with a 400 pound load, it said your selection was more than 10x too weak.

The same calculator said that the 1.25" x 60" 6061 aluminum tube with a 0.2" wall thickness would do it. The one you linked has 0.011" wall thickness.

Edit: I said 400 pounds as double the weight of the heaviest person. Are you thinking of more than one person at a time?

 

[Justin Bishop]

thanks Anor. It would just be one person at a time. I must be missing something, because it appears both tubes I linked have a wall thickness of 0.25", not 0.011" ?

 

[Justin Bishop]

The roguefab site is useful. If I'm understanding right, does this mean the 6061-T6 Aluminum tube I linked to will just barely work at 400lbs?

 

[anorlunda]

I must be missing something, because it appears both tubes I linked have a wall thickness of 0.25", not 0.011" ?

You're correct. When I went there, I read the wall thickness tolerance, not the actual dimension.

 

[JBA]

Due to the potential for a jerk at the start pf a pull up, which can double or more the bar loading of a 200 lb individual, the 376 lbs yield point that I calculated your selected Al tube is not safe for your application.

 

[Justin Bishop]

Due to the potential for a jerk at the start pf a pull up, which can double or more the bar loading of a 200 lb individual, the 376 lbs yield point that I calculated your selected Al tube is not safe for your application.

thanks JBA for your input. When I plug in the numbers for the 62" 6061-T6 Aluminum Tube with 1.25" OD and 0.25" wall thickness at https://www.roguefab.com/tube-calculator/ I get a computed load of about 425lbs. Am I doing something differently?

Also, what would you recommend? I'm open to any ideas.

 

[Justin Bishop]

Would it be at all possible to use a strong species of hardwood as a 1.25" dowel?

 

[JBA]

The short answer is "no". Have you seen the size and cost of the the wooden rails for parallel bars for gymnastics? They are composite wooden structures and you don't even want to know their cost. A 1.25" diameter wooden dowel wouldn't come anywhere close to having a safe strength for you application.

 

[Justin Bishop]

Thanks JBa. So do you recommend the steel rod then, or what? Also I won’t be doing anyone handed pull ups so my load will be distributed a bit and roguefab says 435lbs. I also weigh less than 180lbs. You definitely think the aluminum wouldn’t cut it?

 

[Justin Bishop]

Would this work? https://www.onlinemetals.com/merchant.cfm?pid=12668&step=4&showunits=inches&id=192&top_cat=60

 

[JBA]

That would probably work, but that does not come with any guarantee, only a registered certified engineer can provide that.

The bending stress for a 200 lb load would be reduced to 16ksi and the ASM published min yield for that alloy is 73ksi (twice that of the 6061 T6); so, for a 200 lb load the safety factor = 73/16 = 4.5 which is more in the safe range needed. Also, there is no risk of a buckling failure with the solid bar as opposed the tubing and the amount of bar center droop and spring board effect will also be substantially reduced.

Edit: go to http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6 for complete material properties for that bar material

 

[Justin Bishop]

That would probably work, but that does not come with any guarantee, only a registered certified engineer can provide that.

The bending stress for a 200 lb load would be reduced to 16ksi and the ASM published min yield for that alloy is 73ksi (twice that of the 6061 T6); so, for a 200 lb load the safety factor = 73/16 = 4.5 which is more in the safe range needed. Also, there is no risk of a buckling failure with the solid bar as opposed the tubing and the amount of bar center droop and spring board effect will also be substantially reduced.

Edit: go to http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6 for complete material properties for that bar material

thanks a lot JBA, I'm going to give it a shot :)

 

[Mark44]

I'm hoping to run a span of 124" for a pull up bar, with a support in the middle at the 62" point (so 3 supports total).

Why such a long span? That's 10' 4". Can't you use a shorter bar of, say, 24", with a support at each end? Some years ago I made a pullup bar out of a wood dowel about 1 -1/4" or 1 - 1/2", with a hole drilled at each end. I screwed eye-bolts into a a couple of rafters on my porch, and hung short pieces of stout woven rope from the eye-bolts down through the dowel, with figure-8 knots keeping the dowel in place. It worked great.