# Method to obtain Torsion Constant (structural)

by Su Solberg
Tags: constant, method, obtain, structural, torsion
 P: 79 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.
 Sci Advisor HW Helper P: 2,124 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.
P: 79
 Quote by nvn 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.
Attached Thumbnails

 Sci Advisor HW Helper P: 2,124 Method to obtain Torsion Constant (structural) 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.
P: 79
 Quote by nvn 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.