Side skin reinforcement in beams (ACI 318)
Where h of a beam or joist exceeds 900mm (36 in.), longitudinal skin (side) reinforcement is uniformly distributed along both side faces of the member.
The code requires that skin reinforcement shall extend for a distance h/2 from the tension face. Regardless of this in the current release of Tekla Structural Designer the skin reinforcement is provided to the full height of the beam.