Method of Identification of Mechanical Characteristics of Concrete of Reinforced Concrete Crossbars according to the Results of Fire Tests

Abstract

The article substantiates the method of identifying the mechanical characteristics of concrete of reinforced concrete beams based on the results of fire tests. The idea of the work is to improve the calculation approach to assessing the fire resistance of reinforced concrete beams by clarifying the mechanical characteristics of concrete during its heating under the conditions of exposure to the standard fire temperature regime. The proposed method of identifying the mechanical characteristics of concrete is based on the reproduction of temperature distributions in the cross-sections of reinforced concrete beams based on the results of point temperature measurements during fire tests and the application of equilibrium equations compiled using the deformation mathematical model of the stress-strain state. As a result of the obtained experimental data, the temperature distributions were reproduced using the proposed interpolation method. According to the obtained temperature distributions and the proposed mathematical apparatus, the coefficient of reduction in the concrete strength of reinforced concrete beams during fire tests was identified, the maximum deflection of two sample reinforced concrete beams was determined, and using a deformation model based on the use of equilibrium systems of internal layers in the cross section of reinforced concrete beams, the coefficient of reduction of strength of concrete under the condition of exposure to the standard fire temperature regime was specified.. The presented curves of the value of the coefficient of reduction of concrete strength according to the proposed method and according to the recommendations of Eurocode 2 indicate the presence of a deviation between these indicators. Therefore, the refined dependence of the coefficient of reduction of concrete strength for reinforced concrete crossbars will allow to significantly increase the accuracy of the calculation method of fire resistance assessment for structural elements of this type.