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.