Answer:
The "RF‑MAT NL" add-on module for RFEM 5 allows you to use the nonlinear material model "Isotropic Damage 2D/3D" in RFEM to define the stress-strain diagram for steel fiber concrete. The internal forces and deformation can be determined in the subsequent nonlinear FE calculation.
The two links of the FAQ contain two interesting technical articles about steel fiber concrete.
