Method to obtain Torsion Constant (structural)

  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. nvn

    nvn 2,124
    Science Advisor
    Homework Helper

    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. 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. nvn

    nvn 2,124
    Science Advisor
    Homework Helper

    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. Thanks for your reply.
    I wonder what books/ Software I should find to obtain the J?
  7. 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. 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):

    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. nvn

    nvn 2,124
    Science Advisor
    Homework Helper

    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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