How to define construction stage for composite cross section? 

The above composite section can be defined using Section Property Calculator in Midas having 3 different parts.
The parts of the composite section should be activated in different construction stages. 

Referring to the example above: Create an extra stage between 01_steel+Ab and 02_Composite B. The stage name is '02_Composite A', for example. The duration of the stage should be zero, and no load should not be applied. Using beam load, the self-weight of wet concrete for both sides should be applied at the 01_Steel+Ab stage.

Then, select 02_Composite A for part 2 and 02_Composite B for part 3 as shown below.