On the effect of the duration of operation of metal structures on their fire resistance
Introduction. The solution of the issue of assessing the fire resistance limit of metal structures under the influence of prolonged mechanical stress and environmental factors, as well as an objective assessment of their behavior in fire conditions should be inextricably linked with the aging process, leading to changes in the physical and chemical, mechanical properties of metals. The analysis of scientific works in the field of fire resistance of metal structures indicates that the aging process of metals is not actually taken into account when considering the issue of assessing the limits of fire resistance of these structures. It is not clear to what extent the aging factor of metals can influence the behavior of metal structures in fire conditions. In this regard, it is undoubtedly necessary to develop scientific ideas about the behavior of metal structures in fire conditions, taking into account the duration of their operation, the relationship of this behavior with processes occurring under prolonged exposure to environmental factors, as well as obtaining new experimental data on the limits of fire resistance of metal structures of various service life. Aims and purposes. Formation of scientific opinion on the peculiarities of the influence of the duration of operation of metal structures on their fire resistance. Methods. The article used the method of analytical research based on the results of the analysis of works in the field of metal aging processes, taking into account the prolonged impact of mechanical stress and various environmental factors. Results and their discussion. Based on the results of the analysis of theoretical and experimental studies, it is suggested that the fire resistance of metal structures may decrease as a result of their prolonged operation. The possibility of reducing the fire resistance of metal structures is based on the research results of many authors, whose works revealed characteristic changes in the chemical composition, structural elements, properties of metals as a result of prolonged operation of metal structures. Conclusion. The result of the analysis of scientific papers shows that the long-term operation of metal structures and the impact of various environmental factors can lead to a decrease in the limits of their fire resistance. The possibility of reducing the fire resistance of metal structures as a result of their long-term operation, which was not previously taken into account in regulatory documents and the calculation methodology for assessing fire resistance, is considered.