ANALYSIS OF DETERMINATION METHODS OF STRESS-STRAIN STATE OF CONCRETE STRUCTURES UNDER TEMPERATURE INFLUENCES

Abstract

The scientific work is dedicated to the analysis of existing methods for calculating the total value of concrete deformation under the simultaneous influence of mechanical load and elevated temperatures. During the operation of buildings and structures, it has been proven that the influence of temperature loads, especially in combination with force loads, leads to a significant change in the operational qualities of both individual structural elements and buildings as a whole. The relationship between stress, deformation and temperature of materials should be clearly defined during research of the structures operation under the influence of high temperatures. A so-called “rheological approach” is used to account for these interrelated effects, and the related effects between stress and expansion behavior are taken into account by introducing load-induced thermal strain into the calculation. In the conducted analysis, the results of experimental studies of foreign scientists and normative values, given in EC2 and ENV-1992, were taken into account. It was established that the distribution of stresses and deformations in concrete structures cannot be correctly determined exclusively by applying the corresponding recommended Eurocode 2 curves. Values of deformations, corresponding to compressive concrete strength at specified temperatures, are given without transparent justification of the way of taking into account the related effects between stress and expansion of the material. Thus, the σ-ε curves of concrete in EC2 should be used only for the heating phase, however, they are not used for the cooling phase. As further ways of improvement, on the basis of the existing EC2 methodology, the development of the mathematical “stress-strain-temperature” relationship is proposed for the research of interrelated effects between stress and expansion of concrete. To account for the interrelated effects between stress and expansion in concrete subjected to simultaneous heating and loading, an equation is proposed to calculate the strain value, corresponding to the compressive strength. Keywords: stress-strain state, concrete, temperature, calculation, analysis.