Method for identifying the strength characteristics of concrete of a reinforced concrete crossbar during heating under conditions of fire

Abstract

This paper proposes a method that makes it possible to study the patterns of changes in the concrete strength of rein- forced concrete crossbars depending on the heating temperature under fire con- ditions by interpreting the results of their standard fire tests. For the implementa- tion of this method, it is proposed to use similar data obtained using mathemati- cal modeling based on the finite element method and given material properties, including the curve of concrete strength reduction recommended by the guide- lines, as data included in the set of mea- surement results during fire tests depend- ing on temperature. Such data are time dependences of temperature indicators at individual cross-section points and time dependence of the maximum deflection of the crossbar. The article proposes an interpolation method that makes it possi- ble to set the temperature at any point of the section based on the approximation of the isotherms by parabolas with a vari- able indicator of their power. A method based on the mathematical interpretation of temperature indicators obtained using the proposed interpolation method and the curve of the dependence of the maxi- mum deflection on time using a deforma- tion model for describing the stress-strain state is proposed to identify the depen- dence of the concrete strength of rein- forced concrete crossbars. The work also shows that the results obtained using the proposed method of identifying concrete strength reduction coefficients are adequate as their rela- tive error is on average no more than 7 %. Based on the results, the possibility of its application to study the regularities of the decrease in the strength of reinforced concrete crossbars under fire conditions has been proven