Open ANSYS Help > DesignModeler User's Guide > 3D Modeling > Advanced Features and Tools > Symmetry... where you can read this:

The Symmetry feature is a tool used to define a symmetry model. The feature takes either all the bodies or selected bodies of the model as input and accepts up to three symmetry planes. You can choose either full or partial models to work with. If a full model is used, the selected symmetry planes will slice off the model and only a portion of the model will be retained. The valid body types for this feature are surface and solid.

Beam are not supported, so you will have to trim them manually and provide the appropriate boundary conditions manually.