Polar moment of area offset axis

[blckwtr]

Is Jp always Ixx+Iyy? I have two square steel sections offset from y-axis, the x-axis goes through neutral axis on both. I want to find the second moment of area, and I'm a bit unsure...

 

[rb1957]

if "the x-axis goes through neutral axis on both" then Iyy is the self MoI of the two squares (no shift term)
and Ixx and Iyy are principal MoI (Ixy = 0)

what you are seeing is that torque is reacted by an Fy couple, shear at each square).

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