The scientific work is dedicated to the theoretical generalization and to the new solution of the scientific problem on the need to analyze the appearance of technological cracks and the reasons for their emergence in concrete structures at the micro and macro levels, studying the impact of injuries on the stress-strain state, crack, deformation and durability of structures during operation.
The forecasting of a failure of the responsible engineering systems and construction elements represents an important practical problem, the analysis of which in theoretical, as in applied aspects is paid much attention. For the rational reinforced concrete constructions and their structures design it is necessary to improve calculation method, that entails more detailed study of concrete properties and reinforced concrete constructions’ work under load. Thus, one of the concrete’s features that has been identified recently, is its damage by technological cracks.
The results of the experimental-theoretical researches of technologically damaged bending elements are given. The stress-strain state of reinforced concrete beams, when acting of a low cycle load, was investigated. The character of cracks formation, cracks development and beams destruction in dependence on the technological damage of concrete was determined. With the increase of the technological damage coefficient in reinforced concrete samples the degree of cracks formation in the process of experiments increases. It is experimentally proved that all the cracks in the prototypes were developed by the technological defect that makes it possible to forecast the location of their appearance and direction development.
It has experimentally been established that residual deformations increase with the load increase up to 0.3 of the fracture load.
It was found that the methods of non-destructive testing without changing the quality, parameters and characteristics of the product, allow to detect the hidden defects, or reveal such features that entail the potentially products’ unreliability by the indirect secondary features.
Ultrasound examinations showed the presence of invisible (technological) hair cracks were that were present in the samples that were tested in the absence of the action of bending moment.
The model of determination of depth of technological cracks in bending elements before loading was received. This enables to predict the occurrence of force cracks in bending elements and the growth of inclined cracks in the zone of joint action of moment and transverse force, as well as to predict grafting of old concrete with new during reconstruction of port facilities, adhesion, normal and tangential stresses in the contact zone.
An asymptotic study of stress fields in the vicinity of the tip of a force crack, taking into account the mixed stress, is an important task of nonlinear fracture mechanics, and in particular, taking into account the presence of a scattered damage field. Therefore, the study of the stress and strain field near the crack tip under tensile and shear loads is of particular relevance when calculating the bearing capacity and deformability of structures.
The asymptotic analysis of a stress-strain state and the fields of continuity at a crack top of a normal break away in the medium with the damage in a linked task set ("elasticity–damage") for a flat stressed state are presented in the dissertation. The composition of asymptotic task solution, based on the decomposition method by its own functions is given.
The mathematical model of the description and the algorithm of numerical determination of the stress-deformed state near the crack top of the normal separation in the reinforced concrete elements that are bended under mixed load conditions is proposed .
Following the algorithm, it is possible to obtain eigenvalues for constructing a multiscale, multilevel description of fracture processes in the vicinity of the crack tip that lead to loosening of the material, crack growth, and structural failure.
