Find the direction of the rotating force that produces the maximum stress in the structure without gravity. Maybe it is obvious. For example, in the case of a force at the end of a cantilever beam, the maximum stress is when the force is in the direction of the thin dimension.
Duplicate the Static Structural analysis. I named these Force Up and Force Down.
In each system, use the supports you need, and Standard Earth Gravity, and the rotating force. In the first system the force is defined with components and is a positive value to push up and in the second system the force has a negative value to push down. Insert a Fatigue Tool in each system. In each system make the Loading Type Zero-Based.
Right click on the Model branch and insert a Fatigue Combination.
In the Worksheet, add each force direction.
Insert a Damage result into the Fatigue Combination.
The Damage result is computed from cycling between the stress state of the force going up and the force going down, including the effect of the weight of the structure.
Read the post below by who can correct me if I said something wrong or corroborate if I said it right.