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Method to obtain Torsion Constant (structural)

  1. Jan 19, 2010 #1
    Hi every one.

    I just wonder whether using Ix+Iy = J is a suitable method to calculate the Torsion Constant of a plate girders (full penetration butt weld at connection section)

    Since, as stated at wiki, the polar moment of inertia is only identical to J for circle tube and rod.

    p.s. is there any software/calculation method that i can obtain the J and Ixx,Iyy immediately.

    Thanks for your kind help in advence.
  2. jcsd
  3. Jan 19, 2010 #2


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    No, J = Ix + Iy is not suitable, in this case. In this case, torsional constant (sometimes called K, instead of J) is K = (1/3)*summation(b*t^3), where b = length of each plate component in the cross section, and t = thickness of each plate component.
  4. Jan 19, 2010 #3
    Thanks for your quick reply, brother nvn.
    But i think that's for opened thin tube.

    The J that I would like to find is as attached.
    Btw, could you suggest some notable book name/web-site that I can refer to ?

    Thanks again for your kind assistance.

    Attached Files:

  5. Jan 19, 2010 #4


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    Due to post 1, I thought your cross section was open, but now from post 3 I see it is not. I do not have an accurate formula now.
  6. Jan 20, 2010 #5
    Thanks for your reply.
    I wonder what books/ Software I should find to obtain the J?
  7. Sep 17, 2010 #6
    There are a few specialized software to compute the torsion and warping constant. Just Google "torsion constant software". I have successfully used ShapeDesigner in a previous job.
  8. Sep 18, 2010 #7
    i did a search for "Solidworks torsion constant" to see if there was a way to do it with solidworks/add-ins. i didn't find a way to do it with solidworks but the first hit is to another forum where they discuss it including many programs others have used for that purpose. i don't know if the moderators care if i link to another forum so i will let you find it with that search.

    also it seems that the Batho-Bredt theory could be helpful. i don't have the resources or know how to help with that though. there is a google books link that talks about it (5.6 and beyond): http://books.google.com/books?id=hG...&resnum=3&ved=0CBsQ6AEwAg#v=onepage&q&f=false

    another also, i have access to the book: Advanced Applied Stress Analysis by C.T.F. Ross; it talks about the torsional constant and batho-bredt theory.
    Last edited: Sep 18, 2010
  9. Sep 19, 2010 #8


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    Nice find, Lazer57. Su Solberg, if you post the dimensions of your cross section, we could play around with it, and try the Bredt-Batho formula.
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