Experimental studies on the impacts of strain and loading modes on the formation of concrete 'stress-strain' relations

摘要

"Stress-strain" relations obtained through experimental studies are used for strain calculations. Relations at constant rates of stress changes and constant rates of strain changes are known. In the latter case, relations with a descending section are obtained. Such relations have been introduced into the standards and recommendations for structural calculations in different countries. The article contains experimental studies in variable concrete loading and strain modes under uniaxial and biaxial compression. Uniaxial and biaxial compression tests were carried out on a special device [32], in which it is possible to control the strain mode by changing rigidity characteristics. These tests are necessary as in statically indeterminate systems concrete is strained with a synchronous change in loading and strain rates; taking this phenomenon into account makes it possible to give a more accurate description of strain diagrams. We obtained the data on the basis of which we built the stress-strain relations for different strain and loading modes. We identified specific features of concrete strain, accumulation of internal damages, and changes in the values of ultimate strains. We established the appearance of "critical states" depending on the strain mode during the accumulation of internal damages. We propose determining the ultimate strain value under uniaxial and biaxial compression at the moment the "critical state" occurs. As the experimental setup represents a once statically-indeterminate system with rigidity characteristics control, it is assumed that the obtained results can be used to analyze the methods for calculating statically-indeterminate systems. (C) 2019 Elsevier Ltd. All rights reserved.