If you are using the fifth version of ATENA you can use GiD as pre-processor commercial software to make your model. GiD 11.0.7 and GiD 11.0.8 are compatible with ATENA. So, you can go to the following address to model different types and shapes of FRP:

data-Materials-Solid Concrete- Reinforced Concrete.

If you go as above a window will be open with 7 tabs. You can define your FRPs here. The mechanical properties of FRPs can be defined in this section. For instance, the direction, the elastic modulus,the elongation of FRPs and other parameters such as Poisson ratio can be defined using these tabs. I hope the information would be handy and useful.