Dear Ibrahim, you can find the right answer for your question in the answers of this question:

https://www.researchgate.net/post/Does_anyone_know_how_to_model_fiber_reinforced_concrete_in_Abaqus

interesting

I think you should take fibers into account in the material modeling(use stress stain curve and other parameters for steel fiber concrete ), but it's so difficult to distribute fibers in concrete

Dear Ibrahim,

It's possible using a Matlab code and excel spread sheet to do the distribution in any 3D CAD Software and then import to ABAQUS. But the solution will take long time due to the large numbers of fibers. The program will have to solve for each single fiber which will take very long time.

For concrete simulation you don't model the aggregate inside. Here is the same issue, you don't have to model the fibers inside. Just input the experimental stress strain curve (after changing to true stress and plastic strain) to your FE software and do a best fit to calibrate your FEM.

Unless you want to study the fibers it self in the solution (stresses, deformations...etc of fibers) you don't have to model the fibers separately. But if you want to go in details here's two links where the distribution is done in details but for ansys spaceclaim.

Link-1

http://studentcommunity.ansys.com/thread/modelling-material-random-distribution-in-ansys-wb/

Link-2

http://studentcommunity.ansys.com/thread/mesh-design-issues-for-sc-static-structural/