The relevance of this work is due to the importance of identifying latent defects in building structures of reinforced concrete foundations. The results of the study of defects and damage to reinforced concrete structures are provided. It is proposed to use a telecommunication optical fiber of the G.652 standard as a sensor for identifying mechanical influences for long-haul objects. The optical fiber is placed directly inside a reinforced concrete foundation. As a result, we revealed dependences of the increase in the amount of additional optical losses arising in the fiber located in the concrete beam under varying mechanical stresses and deformations with increasing load. Based on the data obtained, two schemes have been proposed that make it possible to locate local latent defects in the structures of reinforced concrete foundations. New results of measuring the values of mechanical damage and deformation of concrete beams in real time when varying the properties of light passing through an optical fiber of the G.652 standard are obtained.