I'm having trouble identifying the mass participating in the general torsion mode.
I have a rectangular shaped steel structure of 16.00 x 4.00 x 3.50 meters.
I attached the top view of the modal deformed shape for modes 1, 2, 3;
Also you can see in the modal analysis table that RZ mass is 0 for mode 3 which is general torsion.
I'm guessing that I missed something somewhere,
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