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  • Square tubing deflection question

    I know there are some really smart foks in here so I will post up my question. Do you know of a site, tool or something that will tell me the deflection of square tubing when cantilevered out with a weight on the end?
    I would like to know how much deflection to figure for distance cantilevered, size and wall thickness of tubing and do not have a clue on how to find out.
    Plain ol Bill

  • #2
    There is a nice little free program that will do it called Beam Boy Analysis Tool. You can download it here:

    http://www.engineering.com/Software/...4/Default.aspx

    It does all sorts of standard beams as well a custom sizes including box sections and round sections including tubing of any size. You need to know the modulus of elasticity which is 30,000 KSI for all types of steel.

    If you want I can calculate it for you.
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      Welcome back, Evan. Yup I can endorse BeamBoy. Very handy so long as you realise its more for confirming wild ass guesses. It's no substitute for actual engineering analysis.

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      • #4
        Thanks for the link to that beam boy calculator. What a great and simple program.

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        • #5
          welcome back
          George from Conyers Ga.
          Remember
          The early bird gets the worm, BUT it's the second mouse that gets the cheese.

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          • #6
            Evan thank you for posting up the link to Beam Boy. I could use a tip on how to use it for a 2"x2" x .250 wall tube. The tube is cantilevered out 120" with an end loading of 500 lbs. If you could tell me how to do this I will run it for all sorts of weights to end up with my design.
            Plain ol Bill

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            • #7
              Originally posted by Forrest Addy View Post
              Welcome back, Evan. Yup I can endorse BeamBoy. Very handy so long as you realise its more for confirming wild ass guesses. It's no substitute for actual engineering analysis.
              My, my...that seems like a pretty severe criticism of a program that seems to do some pretty basic calculations. To claim it is simply useful to confirm "wild ass guesses" essentially means that it has no value, since wild ass guesses are simply that, and have essentially no value of their own.

              Forrest, I was going to ask that you give some specific examples showing how the program is useless (since confirming the useless wild ass guess seems to have little worth) but do not think I will.

              I do not have a horse in the race, but would like to think that the program Evan pointed us to would have more value that just confirming what is useless to begin with...unless one feels that wild ass guesses are useful in engineering.

              Why would you endorse something that is only useful for confirming wild ass guesses? What am I missing?

              Perhaps you intended to say that one should not use the program unless he understands the basics of the calculations it is performing, and can use that understanding to verify the results the program provides?

              I do not post much here, if at all, but after reading a number of your posts the one referred to here seemed different than most...

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              • #8
                I think if you read Forrest's post with EWAG (educated wild ass guess) in place of WAG, it makes perfect sense. In this case, I assumed the E.

                J

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                • #9
                  Originally posted by achtanelion View Post
                  I think if you read Forrest's post with EWAG (educated wild ass guess) in place of WAG, it makes perfect sense. In this case, I assumed the E.

                  J
                  Ha, ha... maybe you are right!

                  Just that in my neck of the woods I have heard of "Wild ass guesses" and " Educated guesses" but... an "Educated Wild Ass Guess" never appeared before...

                  Always willing to live and learn!

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                  • #10
                    Originally posted by Plain ol Bill View Post
                    Evan thank you for posting up the link to Beam Boy. I could use a tip on how to use it for a 2"x2" x .250 wall tube. The tube is cantilevered out 120" with an end loading of 500 lbs.
                    Off the top of my head.....you may be looking at failure rather than deflection with that set up.

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                    • #11
                      Along with BeamBoy you will also want to download a copy of Hollow Structural Sections, Dimensions and Section Properties from the Steel Tube Institute. It lists the Moment of Inertia values for each tube size/wall thickness. You will have to input this value in BeamBoy.

                      If I'm reading BeamBoy correctly, 500 lbs on a 2x2x.250 square tube is near failure at 5.5 feet from the support.

                      I'm not an engineer so I'll defer to those with more knowledge than I.
                      Last edited by TriHonu; 03-06-2013, 10:43 PM.

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                      • #12
                        Originally posted by Bill
                        Evan thank you for posting up the link to Beam Boy. I could use a tip on how to use it for a 2"x2" x .250 wall tube. The tube is cantilevered out 120" with an end loading of 500 lbs. If you could tell me how to do this I will run it for all sorts of weights to end up with my design.
                        Here is a simple to follow tutorial:









                        You can see that with the values you provided the stress is 65 KSI at the support. That is very close to or exceeds the failure stress of ordinary structural steel. It will exceed by a lot the strength of many standard shapes in mild low alloy steel which may be as low as 36 KSI. To withstand that as specified will require a certified high strength alloy with at least 100 KSI bending strength. You should have at least a 50% safety factor and 100% is better. Many steel structures require much higher safety margins, especially in the event of possible application of shock loads.
                        Last edited by Evan; 03-06-2013, 11:58 PM.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Evan,
                          any idea why Beamboy calculates the Moment of Inertia as 0.911 and the Steel Tube Institute lists it as 0.745?

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                          • #14
                            No idea. Safety factor maybe?? BeamBoy is calculating the furthest fibre to the walls rather than the corners. That is about right for the difference. Could just be a simplification in the math or even overlooking the difference from the tube calculation.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              Based upon the design criteria (cantilevered load of 500lbs at the end of a 10ft pc of TS 2x2x1/4) a SWAG (scientific WAG) tells me that this dog will not hunt. A quick calc confirms this. With 50ksi matl you would need TS 4x4x1/4 which would give you a deflection of .67". This would only apply to a stationary load. Dynamic loading will require a much stronger member. Matl with a lower minimum yield will require a stronger member for both stationary and dynamic loading.

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