Experimental studies of multilevel formation of normal cracks in reinforced concrete elements

Abstract

This article is devoted to the study of the real process of gradual formation and disclosure of normal cracks in reinforced concrete elements and structures from the standpoint of accumulation of concrete and reinforcement mutual displacements. It is emphasized that the process of normal cracks formation is in fact multilevel and is accompanied by a gradual disruption of the interaction of reinforcement with concrete. It is pointed out that in most methods of calculating the fracture toughness of reinforced concrete elements and structures, the Thomas hypothesis finds declarative rather than real application. A critical analysis of recent studies devoted to the development of methods and ways for calculating the crack opening width in reinforced concrete elements by their multilevel formation is given. At the same time, special attention is paid to the methods of modeling the processes of reinforcement with concrete coupling. The validity and regularity of the use in the calculations of linear coupling between the average adhesion stresses of reinforcement with concrete and the average values of normal stresses in the reinforcing rod over the entire range of reinforced concrete element deformation are analyzed. The most important problems that need to be solved in the course of the experimental studies are outlined to reveal the real influence of the forces and average stresses of reinforcement with concrete adhesion on the step and width of the normal cracks opening in reinforced concrete elements. The program and methodology of experimental studies, design of prototypes and installations, the main characteristics of concrete and reinforcement used for their manufacture are presented. The basic results of testing of prism elements and reinforced concrete beams are illuminated. The experimental values of the studied parameters are compared with the results of theoretical calculations. The most important conclusions from the conducted researches are given and their further perspectives are indicated.