Answer:
The effective depth is calculated using the edge or the centroid of the reinforcement, depending on the reference setting in Window 1.4 – Reinforcement Layout. Furthermore, the minimum height from top or bottom is only applied for one direction. Thus, a surface with a thickness of 180 mm, a concrete cover of 30 mm, and a rebar diameter of 10 mm (basic reinforcement) has an effective depth of either 150 mm (referred to the edge) or 145 mm (referred to the centroid of the reinforcement).
