Minimum area of surface reinforcement As,surfmin
Eurocode 2 part 1-1: Design of concrete structures J.1 (2) - Annex J (informative)
The area of surface reinforcement As,surf should be not less than As,surfmin in the two directions parallel and orthogonal to the tension reinforcement in the beam.
The recommended value of the reinforcement area As,surfmin is 0,01Act,ext, where Act,ext is the area of the tensile concrete external to the links (cf. Figure J.1).