How to model Flat slab with drop panels in physical modeler

Hi All,

I've been trying to import a 3d model from revit to staad physical model, using ISM revit plugin.

The model contains column and wall drops, therefore the region within the drop is modelled as opening, and then another slab with reduced thickness is generated.

In physical model it shows error as two surfaces overlap each other...but one is opening and the other is physical slab.

kindly let me know, how to model a flat slab with drops.