Method to obtain Torsion Constant (structural)

In summary: 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
  • #1
Su Solberg
75
0
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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  • #2
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.
 
  • #3
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.
 

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  • #4
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.
 
  • #5
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?
 
  • #6
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.
 
  • #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:
  • #8
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.
 

1. What is the purpose of determining the torsion constant for a structure?

The torsion constant, also known as the second moment of area about the neutral axis, is a measure of a structure's resistance to torsional or twisting forces. It is important in the design and analysis of structural elements such as beams, columns, and shafts.

2. How is the torsion constant calculated?

The torsion constant can be calculated using the formula C = J/R, where C is the torsion constant, J is the polar moment of inertia, and R is the distance from the neutral axis to the outermost point of the cross-sectional area. Alternatively, it can also be calculated by dividing the product of the shear modulus and the cross-sectional area by the distance from the neutral axis to the outermost point.

3. What factors affect the torsion constant?

The torsion constant is influenced by several factors, including the shape and size of the cross-section, the material properties, and the orientation of the cross-section relative to the applied torque. Additionally, any holes or cutouts in the cross-section can significantly change the torsion constant.

4. How is the torsion constant used in structural analysis?

The torsion constant is used to calculate the shear stress and shear strain in a structural element subjected to torsional loading. It is also used to determine the maximum allowable torsional stress, or torsional yield strength, of a material. In structural design, the torsion constant is often compared to the applied torque to ensure that the structure can withstand the expected torsional forces.

5. Can the torsion constant be determined experimentally?

Yes, the torsion constant can be measured experimentally by applying a known torque to a test specimen and measuring the resulting angle of twist. This method is commonly used to verify theoretical calculations and to determine the torsion constant for irregular or complex cross-sections.

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