It is known that the relationship between stresses and deformations in reinforced concrete is significantly different for the stage of its work with and without cracks. In practical calculations of reinforced concrete structures at the stage of work without cracks, the influence of the nonlinearity of deformations on the behavior of the structure is insignificant, and the properties of reinforced concrete can be assumed to be isotropic. At the stage of work of the structure with cracks, the nonlinearity manifests itself very significantly. To take into account the nonlinear properties of reinforced concrete, in addition to creating more complex programs based on the methodology given in it is necessary to pay attention to a more accurate assessment of the fundamental properties of reinforced concrete that determine its behavior under load.