Material properties are defined through certain conventional stress-strain curves both for unconfined concrete and reinforcing steel. In the former a parabolic stress-strain relationship with a softening branch is used, while in the latter a bilinear stress-strain diagram with hardening is implemented. The aforementioned stress – strain curves are depicted in Figure 1.
Figure 1. Stress – Strain diagrams a) for unconfined concrete and b) for reinforcing steel