You can add custom blocks to the display of a structural member as a component in a display representation. For example, you can add stiffener plates to beams as a custom blocks or add clip angles to members as a custom blocks.
Adding stiffener plates to a beam
Custom blocks can be either 2D or 3D. When you add a custom block, you can specify several rules for positioning and scaling the new component. Each custom block also appears in the display properties component list so that you can control its layer, color, and linetype.
Be sure to set the properties of the objects used to create your custom blocks to ByBlock. Otherwise, you cannot control these objects through the display properties.