Bashynskyi O. Creation and operation criteria for structural models of steel beams with fire protection. – Qualifying scientific work on the rights of the manuscript. The thesis on conferment of a scientific degree of the Doctor of philosophy on a specialty 192 – Building and civil engineering, area of knowledge 19 – Architecture and building. – Kyiv National University of Construction and Architecture. Ministry of Education and Science of Ukraine, Kyiv, 2024. The main content of the thesis. The thesis is aimed at developing numerical methods for assessing the fire resistance limit of steel structures by taking into account the uneven temperature distribution along the height of the section, nonlinear changes in the thermophysical properties of materials and fireproof coatings. Based on the results of the analysis of national and foreign scientific sources and regulatory documents, as well as numerous finite element and experimental studies: - it has been found that national and foreign documents and manuals describe only simplified analytical methods for assessing the fire resistance limit of steel structures; there are experimental methods for assessing the fire resistance limit, but they are not universal and do not allow for quick and convenient assessment of the fire resistance of any structure; - the numerical finite element method was adapted and used to solve the problem of nonstationary heat conduction for the thermotechnical analysis of the cross-section of a steel floor beam; - patterns that led to an uneven temperature distribution along the height of the cross-section of a steel floor beam were established; - the reliability of the results obtained by using the numerical finite element method in comparison with the experimental method was established; - it was found that the thermotechnical analysis of a steel floor beam, taking into account the nonlinear change in the thermal and physical characteristics of materials, opens up additional reserves of the bearing capacity of steel beams at high temperatures; - a methodology and algorithm for steel floor beams with fire protection analysis with implementation in the LIRA-FEM software was created. From the point of view of philosophy, the scientific and technological development of mankind is growing exponentially. The latest technologies allow for accurate, safe, convenient and fast surveys that allow for the consideration of numerous factors and criteria for the operation of building structures that could not be taken into account before. This research is aimed at increasing structural safety, environmental friendliness, and energy efficiency, which in turn affects the safety of human life, which is currently a very important factor. In the first section, the current state of fire safety in the country and methods for assessing the fire resistance limit of building structures were analyzed. The methods of fire protection of building structures were described and a number of the most common fire protection materials were presented. Modern experimental, analytical and numerical methods for assessing the fire resistance limit of steel structures, namely steel floor beams, were analyzed. Experimental methods are the most effective, but not universal, and analytical methods do not take into account the key criteria for the operation of heat-loaded structures, so it is necessary to build a universal method for assessing the fire resistance limit of structures on the basis of analytical and numerical methods. In the second section the solution of the problem of nonstationary thermal conductivity using the numerical finite element method was described in detail. A numerical experiment of the effect of a fire on a steel floor beam on which a reinforced concrete floor slab rests was carried out in the LIRA-FEM software. Two types of analyses were performed: thermotechnical, in which the distribution of temperature fields at each point of the beam cross-section at each minute of the fire was determined; and static, in which the strength characteristics of the cross-section and the elastic-deformation characteristics of steel were preliminarily reduced according to the average temperature in the beam cross-section at a fixed time. The results of the thermotechnical analysis were compared with the results of a similar analysis performed in the ANSYS FLUENT software and described in the regulatory document. In the third section the algorithm for determining the nonlinear properties of structural materials and fireproof coatings was described. A thermotechnical analysis of the steel floor beam was performed with consideration of the fire protection material. The analysis results were compared with the results of the experimental research. The results confirmed the reliability of the methodological approaches to determining the cross-sectional temperature developed in this thesis.
