There are two kinds of simulations that are possible, but they have different objectives.
One kind is an extremely detailed model that tries to replicate the physics of concrete fracture, fiber breakage, fiber-concrete bond failure, fiber friction, etc to model at a very fine level what is happening to the components in the material under load. The model tries to predict what the experimental data will be, even before it is measured. This is the type of simulation a material researcher might build.
Another kind of simulation is much simpler, taking an existing mathematical material model with some adjustable parameters, and attempting a best fit of those parameters to the experimental data of a three point bending test, so that other more complicated shapes of reinforced concrete structure can be modeled and predictions made for the load carrying capability of those shapes that were never tested. The model of the three point test is going to reproduce the previously measured three point experimental data when the values of the parameters have been properly chosen. This is the type of simulation a structural engineer might build.
Which type of model are you trying to build?
If it is the the second type, then there are several plasticity models that have parameters you can adjust to match your experimental data.