Click Concrete Design > Cracking Factors to open the Cracking Factors dialog.

This dialog provides a way to specify cracking factors that will apply to the bending stiffness of selected members and/or shells. A value of 0 implies completely cracked. A value of 1.0 implies completely uncracked.
Tip: Regardless of how Cracking Factors have been set, they will only be considered if the option to "Use cracked section properties" has been selected in Analysis > Analysis Options.