a. following yielding of the internal tension steel reinforcement the concrete crushes in the compression zone, as the strain in the top fiber exceeds Ɛcu2 (3,5‰ for fck ≤ 50MPa).
b. following yielding of the internal tension steel reinforcement the FRP reaches a limiting strain, Ɛf,lim (this is a simplified way to prevent debonding of the FRP in areas where flexure dominates the response, e.g. mid-span of simply supported beams.