Method to obtain Torsion Constant (structural)

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Discussion Overview

The discussion revolves around the calculation of the torsion constant (J) for plate girders, particularly in the context of full penetration butt welds at connection sections. Participants explore various methods and formulas for determining J, as well as software options for calculation.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants question the validity of using the equation J = Ix + Iy for calculating the torsion constant for plate girders, suggesting it is only applicable to circular tubes and rods.
  • One participant proposes an alternative formula for the torsion constant, K = (1/3)*summation(b*t^3), where b is the length of each plate component and t is the thickness.
  • Another participant expresses uncertainty about the appropriate formula for the cross section, indicating a lack of accurate information.
  • Participants discuss the availability of specialized software for computing torsion and warping constants, with one recommending ShapeDesigner.
  • One participant mentions the Batho-Bredt theory as potentially useful for the calculation, although they do not have the resources to elaborate further.
  • Another participant suggests sharing cross-section dimensions to explore the Bredt-Batho formula collaboratively.

Areas of Agreement / Disagreement

There is no consensus on the appropriate method for calculating the torsion constant, with multiple competing views and formulas presented. Participants express uncertainty and seek further information.

Contextual Notes

Participants note the dependence of the torsion constant calculation on the specific geometry of the cross section, which remains unspecified in some posts. There is also mention of the limitations of available software and resources for accurate computation.

Who May Find This Useful

Individuals interested in structural engineering, particularly those working with plate girders and torsion calculations, may find this discussion relevant.

Su Solberg
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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.
 
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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.
 
nvn said:
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.

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.
 

Attachments

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    sAMPLE.PNG
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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.
 
nvn said:
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.

Thanks for your reply.
I wonder what books/ Software I should find to obtain the J?
 
Su Solberg said:
Thanks for your reply.
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:
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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