Cover to Reinforcement (ACI 318)
The nominal concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (including ties and surface reinforcement where relevant) and the nearest concrete surface.
You are required to set a minimum value for the nominal cover, cnom, u for each member in the member properties.
These values are then checked against the nominal limiting cover, cnom,lim
If cnom,u < cnom,lim then a warning is displayed in the calculations.