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Real world prob: bending of 26mT circular plate!

  1. Aug 22, 2011 #1
    Hello all,

    I'd like to check my work on this to make sure a safe lift is done.

    We have an 11m diameter, 35mm thick, 26mT circular steel plate to which we will add two trunions at the ends. The circular plate is welded in 4 parts and once we weld one side we have to flip to weld the other. That is what the trunions are for. The welding for one side will mean the plates are only connected by half their cross section (35mm / 2) before flipping, so this is what I have used for second moment of area and section modulus.

    I kept it simple and used a simply supported beam and calculated both as a center point load (worst case) and uniformly distributed load separately. I'm assuming no correction for dynamic loading and no stress concentration (though there will be I think) due to the other [open] side of the weld as it is a double v joint. I know using the simply supported beam is technically not correct as the theory assumes a constant cross section, so therefore I would like to check with the forum how you would go about solving this! The trunions are another problem altogether but I would first like to check whether we can lift the plate as is or if it needs stiffeners to prevent buckling under own weight.

    Thanks for looking and your solutions. Regards
     
  2. jcsd
  3. Aug 22, 2011 #2
    An important thing you're missing is the stress concentration at the narrow region. You may be able to apply a stress concentration factor from a book like Roark's.
     
  4. Aug 22, 2011 #3
    Thanks for the quick reply. I don't actually have the Roark's book. Is it as simple as taking the max stress at center and applying a multiplier for the region around the trunions, or how would you do it?
     
  5. Aug 22, 2011 #4
    As I understand, your cross-section looks like a straight beam with a v-notch in the middle? You'd find the bending stress with no notch, then apply a factor according to the geometry of the notch.

    A beam model may be even worse since it can try to bend in two directions - like a potato chip.
     
  6. Aug 22, 2011 #5
    hey,

    I'm familiar with using a multiplier for stress concentrations, I just dont know how to calculate the stress at the trunnions as I am calculating it as a simply supported beam where moments are of course zero at supports.

    It's ok though, we have decided to add stiffeners so thanks for your input.
     
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