Alternative approaches to the estimation of corrosion-damaged beams stiffness with regard for localization of corrosion focus and distribution of corrosion damages in concrete on the basis of layered model are considered. The following methods of determining displacements in corrosion-damaged reinforced concrete beams of rectangular cross-section have been considered. In the first one, the stiffness of the beam in determining the deflection is considered constant. In this case, the corrosion-damaged deflections values may be underestimated due to failure to take into account the actual work of reinforced concrete. In the second, the deflection is calculated considering the height of the concrete compression zone that varies along the length of the beam. For these approaches, stiffness reduction in the beam sections in the presence of corrosion damage to the concrete of the compressed zone is modeled. It is shown that in the presence of corrosion damage, the deflections of the structure can significantly increase, which requires mandatory consideration in the life cycle of load-bearing structures of structures when assessing their mechanical safety. The necessity of obligatory registration of corrosion damages in the implementation of algorithms of optimal design of reinforced concrete structures has been revealed.