When generating new ISM repositories to be used in analysis applications such as STAAD or SACS, we've found that some of the elements we've placed in AECOsim Building Designer are not being translated. These seem to be our plate and deck components that we've created using tools from the Solid Modeling task group, such as Slab Solid or Solid By Extrusion. These elements are important for our analysis process.
Unfortunately regular MicroStation solids will not export to ISM format. However, you can use the Place Slab, Place Linear Form or Place Free Form tools from the Form Modeling task group and add Structural attributes after the fact as shown below. These elements will be translated to ISM for use as Plates or Decks.
And in CONNECT Edition:
Note that AECOsim Building Designer Ss4 or later does include a dedicated Deck tool that includes both Steel and Concrete sub-components. You could also place a short length steel Column using a rectangular profile to represent a plate, or create a custom DataGroup Catalog Type and apply it to a Slab Form.