Development of a Quantitative Relationship between Moment and Unit Curvature

The stress-strain relationship of the reinforcing steel is assumed to be elastoplastic, as determined below and shown in Figure 14.2. The expression for the stress-strain curve of the reinforcement (Equation 15.1) states that the steel stress increases linearly with strain (Es × εs) up to the yield strain εy = fy / Es. After that limit is reached, the steel stress remains constant as strain increases.