# Method to obtain Torsion Constant (structural)

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.

nvn
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.

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.
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.

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nvn
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.

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.
I wonder what books/ Software I should find to obtain the J?

I wonder what books/ Software I should find to obtain the J?
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.

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:
nvn