Through model of R / C elements in 2D ATENA i have failed to get a good agreement with experiment, where i have used as initial data the experimental results on constituens (concrete cube strength). Although I noticed that I need to use the initial modulus of elasticity rather than secant, it was not enough to achieve the same slope of the force in relation to the displacement. Curve that I have obtained by calculation is still much weaker. So I tried to change the parameters of the concrete as it is the case of confined concrete, because of the influence and the amount of transverse reinforcement. I wonder if ATENA2D itself has already taken the effect of confined concrete into account. Since I have very good experimental data about the reinforcement properties is it possible that on any other way to increase the initial stiffness of the model and have a good physical explanation. Please explain me about confined concrete.

P.S. I have used EC2 formulas for confined concrete (page 36) but still in my model there is not enough initial stiffness, since probably because confined concrete affects strength and deformation, but other parameters remain unchanged (elastic modulus).
Kind regards and thank you for your support