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Pull up bar specification

  1. Feb 19, 2012 #1
    Hello,

    I am looking to install a pull up bar in my home.
    I have a 6' 4" span. I weigh 200lb.
    I'd like the bar to have a round cross section so that I can grip it directly. Ideally the outside diameter of the pipe should be 1.25".
    I don't want there to be too much spring or give in the pipe.

    What pipe should I look for for this task?

    Thanks,
    -A-
     
  2. jcsd
  3. Feb 20, 2012 #2
    I think the span is going to be your biggest challenge. If you can add one support bracket in the middle of the span, that would solve any concern regarding the deflection that you refer to.

    I am at a loss to think of a tubular metal that wouldn't have noticeable deflection at that span. However, I have a solid (and likely hardened) steel bar in my garage that I am told was a driveshaft for some sort of vehicle. It's probably 1" around and very stiff, but also very heavy...

    Have you tried visiting your local metal supplier or fabrication shop to ask what the best type of metal pipe would be?

    I may be wrong, but I believe you can use the term "deflection" to describe the sagging/bending that you want to avoid. A higher deflection ratio = less bending.

    Good luck.
     
  4. Feb 20, 2012 #3
    Thank you so much for taking the time to reply.

    My request about no deflection may be too literal. It can have some give, so long as it doesn't permanently deform over time.

    I will also take you advice and try to figure out a middle support but it's not looking promising.

    Thanks again,
    -A-
     
  5. Feb 20, 2012 #4

    Q_Goest

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    Hi ablefire, welcome to the board. A 1" schedule 80 steel pipe would have an OD of 1.315" and wall thickness of 0.179". Made of steel, it can support your weight with a stress of roughly 24 ksi and deflect just over 1/2". Increasing the wall thickness to schedule 160, 0.250", results in the stress dropping to 20 ksi and the deflection dropping to just under 1/2". Either pipe would work fine and not permanently deform.
     
  6. Feb 20, 2012 #5

    OldEngr63

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    For a uniform bar with simply supported ends and a single point load at mid-span, the maximum deflection occurs at mid-span and is

    ymax=W L3/(48 E I)

    where
    W = load, lb
    L = span length, in
    E = Young's modulus, psi
    I = area moment of inertia, in4

    The maximum bending moment occurs at the same location, so the maximum bending stress is there as well

    σbend=M c/I = W L c/(2 I)

    With these equations, it is evident that the longer you make your bar, the larger the center span deflection and the maximum bending stress become. These are the factors that limit the acceptable/unacceptable performance of any particular bar.
     
  7. Feb 21, 2012 #6
    Thank you for the timely and helpful response complete with equations.
    I am not sure what the Young's modulus of the materials at my hardware store are so I'll have to make some educated guesses.

    Another approach that I am favoring now is to use a beam as a support and to hang rings off it thereby eliminating any restrictions imposed on the diameter by the need to grip it directly.

    Any thoughts on what specs would suffice if I go with larger diameter or even a square cross-section?

    Thanks again,
    -A-
     
  8. Feb 21, 2012 #7
    OldEngr63: I found a 1 3/8" pipe made of 7 gauge 1008 carbon steel.
    7 gauge is 0.1793" and 1008 steel has a Young's modulus of 30 x 10^6.

    Using your formula, and using 65" as the length and 200 lb as the load, I obtain a deflection of 0.0317 inches which seems good. Almost too good ...

    Am I missing something or will this pipe do the job?

    Thanks,
    -A-
     
  9. Feb 21, 2012 #8

    nvn

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    ablefire: Do you want this round bar to be steel, or aluminum? I currently assumed steel. I think you need to use a yield factor of safety of FSy = 2.0, relative to the static (dead) load, to allow for a moderate amount of dynamic amplification. Therefore, unless you have a material specification stating otherwise, the allowable bending stress is currently Sba = 120 MPa (or an absolute maximum of 124 MPa).

    Therefore, a round bar having the outside diameter (OD) you suggested in post 1 would be inadequate and overstressed. Steel or aluminum round tubes or pipes having the following OD (d2) and wall thickness (t) currently appear adequate for your application stated in post 1 (with no midspan support).

    (1) d2 = 34.9250 mm, t = 9.525 mm.
    (2) d2 = 36.5125 mm, t = 7.230 mm.
    (3) d2 = 38.1000 mm, t = 5.760 mm.​
     
    Last edited: Feb 21, 2012
  10. Feb 21, 2012 #9

    Q_Goest

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    In the OP you said the span was 6' 4" (76").

    Not sure how you got the numbers you did because OldEngr didn't provide the equation for I which is: (Pie) / 64 * (Do4 - Di4)

    For the pipe in question, and assuming a 76" span, I get a stress of 21 ksi and delfection of almost 1/2". I think you'll be fine with that. For a 65" span, the deflection drops to around 0.31". Perhaps your calculation shifted a decimal?

    Hi nvn. Personally, I wouldn't be concerned with the dynamic part, but you're right, I think if you were to drop quickly to arms length, there would be a significant increase in stress. At least in this case, this increase in stress will simply result in the bar bending a bit if the stress exceeds yield. The values I calculate provide at least a factor of safety of 1.5 to yield. Bending obviously isn't a desired result, but I can't imagine anyone getting hurt.
     
  11. Feb 22, 2012 #10
    Nobody will be doing a pull-up spread out to 76 inches....or even 60 inches........but I do understand the need to use a wide grip.

    I would compute loads using 60 inches for length and assume the load is in the center but most of my bars have been standard pipe from home depot threaded on the ends.

    I screw flanges onto the ends, measure length, and bolt them to a wooden subframe that mounts to the house.

    You can get some more strength by putting another piece of pipe inside the bar.
     
    Last edited: Feb 22, 2012
  12. Feb 22, 2012 #11

    nvn

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    ablefire: Post 8 and a few other posts apply to the span length stated in post 1. If the span length requirement has now changed, let us know, because then you would get a different set of answers.
     
  13. Feb 23, 2012 #12
    Use thicker than you believe is needed. When going for max pullups you WILL kick your legs and be bouncing around a bit. I would be using a 1.250 x .250 wall DOM minimum. Make your mounting points rock solid or it will get torn out.
     
  14. Feb 27, 2012 #13
    Thank you all for such gentlemanly and scholarly responses.

    To clarify, the span is 6' 4" which happens to be the distance between 2 walls in my home. My grip width is in the 24-36" range. I'd like to minimize deflection.

    I have found this tube which is 1 3/8 diameter with 3/8 wall thickness. This corresponds to the first combination that nvn kindly provided?

    Will this do the job?

    Also, this tube is a little expensive for me and any less expensive alternatives would be welcome.

    Again, many thanks for the patient and informative responses,
    -A-
     
  15. Feb 27, 2012 #14
  16. Feb 27, 2012 #15

    OldEngr63

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    The item quoted at the URL given by jacko jeebus is for 1-1/4 OD tube, not 1-3/8 tube. It had a 3/8 wall thickness.
     
  17. Feb 28, 2012 #16
    Jaco and OldEng,
    Thank you both.

    Jaco, are you suggesting the 1-1/4 tube with the 3/8 wall thickness?
    Also I'm having trouble finding .375 thickness ERW so DOM may have to do.
     
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