The dissertation is dedicated to solving the current scientific and technical problem of revealing the regularities of the formation of through holes in fire-resistant plasterboard cladding of steel beams during its local destruction due to fire and the associated loss of its fire-resistant ability depending on the time of the fire as a scientific basis for improving the method of calculating the assessment of their fire resistance. The introduction provides a general description of the dissertation, justifies the relevance of the research topic, formulates the goal, objectives, determines the object and subject of the study, indicates the scientific novelty and practical significance of the results obtained, reveals the connection of the work with scientific programs, plans and topics, determines the personal contribution of the applicant, provides data on testing, publications, structure and scope of work.
The first section analyzes statistical data on the number and characteristics of fires in buildings with steel structures and provides basic information on the standardization of fire safety of steel beams. The behavior of steel beams during the thermal impact of fire and methods for increasing the fire resistance of steel beams are described. Experimental methods for assessing the fire resistance of steel beams, the procedure for conducting fire tests of steel beams for fire resistance, and experimental methods for determining the fire protection ability of fire protection systems of steel beams are presented.
Based on the results of the analysis, the purpose and main tasks of the work were formed.
The second section is devoted to the description of the experimental equipment for studying thermal processes in steel samples with fire-retardant plasterboard cladding during their fire tests and the methods of manufacturing, preparing samples for testing, conducting fire tests of samples of fragments of steel beams. The main experimental equipment is a plant consisting of a fire furnace with gas burners that provide the appropriate temperature regime of the fire in the chamber of the fire furnace. A scheme for the location of thermocouples and the conditions for their use is proposed. The experiment was performed during the control time, which corresponds to the time of the occurrence of the limit state in terms of loss of bearing capacity for steel beams.
The third section presents the results of fire tests of fragments of steel beams with an I-section with gypsum board fireproof cladding under the influence of a standard fire temperature regime and the obtained temperature test data in the tested samples. It was established that as a result of high-temperature heating for 60 min under a standard temperature regime, complete destruction of samples with one layer of gypsum board fireproof cladding and partial destruction of samples with two-layer and three-layer cladding occurred, which indicates a negative thermal effect on the integrity of the fireproof cladding and the ability to maintain fireproofing ability. A generalized dependence of the thermal conductivity coefficient of gypsum board fireproof cladding on temperature in tabular form was obtained, which can be used to calculate the temperature in steel beams with this type of fire protection.
The fourth section presents mathematical modeling of the thermal impact of fire on the behavior of a steel beam with a gypsum board fireproof cladding. Based on the results of the conducted research, the behavior of a steel beam with a gypsum board fireproof cladding during the thermal impact of fire is described. The conditions for the occurrence of a state of loss of fire resistance beyond the limit state of loss of bearing capacity of a steel beam with a gypsum board fireproof cladding are determined and it is shown that the opening of a through defect between the beam and parts of the gypsum board fireproof cladding more than 25 mm is recorded earlier than the occurrence of the limit state of loss of bearing capacity, which must be taken into account in the relevant calculations.
The fifth section presents a method for assessing the fire resistance of steel beams with gypsum plasterboard fireproofing, taking into account its loss of fireproofing ability. Based on the established regularities, nomograms are constructed for calculating the time of loss of the fireproofing ability of steel beams by gypsum plasterboard cladding, depending on their section coefficient and load level at three values of the thickness of the gypsum plasterboard fireproofing, and a computational method for assessing the fire resistance of steel beams with gypsum plasterboard fireproofing is proposed using the time of loss of the fireproofing ability by gypsum plasterboard cladding, determined according to the proposed nomograms.
