The cross section is analyzed as cracked. This analysis is somewhat more conservative than the gross section calculation suggested in the code.
The concrete compressive stresses are limited to 0.5 fcp for all cases.
If the limit stress is exceeded then reinforcement is added as required to limit the concrete stress; depending on the bending moment and axial forces, either compression reinforcement, tension reinforcement or both will be added.
For sections with multiple concrete strengths, the section limiting stress is reported as the smallest (absolute value) stress limit of all of the individual concrete areas.