Mathematical model of concrete strain diagram under heating

New regulatory documents have been adopted and they have significant differences. Firstly, this is a new concept of calculation, a nonlinear deformation model, and secondly, new approaches to the assessment of reliability, loads and impacts, methods of construction. The calculation consists of two stages. The first begins with the determination of the concrete class at temperature of 20ºC. At the second stage, the calculation is carried out at high temperatures according to Eurocode 2 part 1-2. Comparison of the "stress - strain" diagram of concrete class at compression and temperature of 20ºC by two formulae showed their big gap. There was a need to improve the mathematical model of the ratio of stress-strain of the concrete under elevated temperatures. The method of determination of maximum strain based on energy approach has been developed in the work and allowed to formulate the adjusted dependence of the limit strain on temperature, dependence of maximum strain on temperature, values of the parameters of stress-strain diagram. (paper)