A composite slab’s thickness cannot be edited in Slab Settings; you must go to Options > Element Attributes > Composites. If you want to edit the slab thickness in Slab Settings, choose a non-composite (basic) slab structure.
How do you make slabs?
Create a foundation slab by sketching or selecting the walls of the first level of the model.
- Click Structure tab Foundation panel (Slab)
- Specify a foundation slab type from the Type Selector.
- Click Modify | Create Floor Boundary tab Draw panel Boundary Line and then click (Pick Walls) to select the walls in your model.