The problem of estimation of fire resistance of steel frame structures with intumescent coatings is considered. It implies that both physical properties of a covering (its thickness and structure) and mechanical properties of a metal structure change critically at heating. All above changes should be considered to maintain the standard values of fire resistance of a construction at calculation. Usually, known technical characteristics of fire resistance of intumescent coverings are used for estimation of fire resistance of steel structures with intumescent coverings. Importance of taking into account the influence of strength loss time at heating of a steel structure on calculation of fire resistance limit of system “intumescent fireproof coating steel structure” is shown in the article. On an example of calculation of heating time to the critical temperature of steel columns and beams protected by intumescent coating, it is shown that own heating time of steel structures before they lose strength makes 10 to 16 % from a settlement limit of fire resistance. This fact should be considered at the forecast of fire resistance of steel frame structures with intumescent coatings.

The study is aimed at surface strengthening of jewelry tools. Samples in the form of a tool with a flat and curved surface profile are considered. Macrophotographs of jewelry korneisen at different stages of wear, as well as after restoration and strengthening are given. The results of the influence of chemical-thermal and thermo-friction treatments on the structure and properties of U7 and U8A steels used for jewelry tools are presented. The methodology of experimental researches is given. The equipment used for each of the hardening methods investigated in this work is considered. Auxiliary media and features of sample preparation for the experiment are also described. Photos of samples and some equipment at different stages of the study are given. Data on the distribution of microhardness, photographs of microstructures in cross section of samples after different types of hardening are presented. A comparison of the strengthening efficiency of the samples after the use of different processing methods is performed.

Calculations on the example of a steel column showed that with the combined effect of an explosion that causes deformation and subsequent fire, even without damaging the fire-retardant coat, there is a significant decrease in the fire resistance of the structure due to a decrease in the critical temperature. It is shown that, on the basis of the methodology proposed in this work, for hazardous operations industrial facilities, it is possible to predict the stability of steel columns in crash explosions followed by fire, as well as to recommend the values ​​of workloads and parameters of fire-retardant coats providing the necessary stability. It is also shown that when calculating the fire resistance limit of a steel structure with intumescent fire-retardant coat, it is necessary to take into account the proper heating time of steel structures until they lose strength.

The results of estimative calculations of bearing capacity, critical temperatures, and fire resistance ratings of reinforced concrete bending elements based on fiber concrete with disperse reinforcement of steel, basalt and synthetic fiber are presented. The calculations carried out on the example of a reinforced concrete rectangular beam both taking into account the percentage of reinforcement of each element and at a constant load corresponding to the condition of calculation adequacy showed that disperse reinforcement of a reinforced concrete bending element with steel, basalt and synthetic fiber increases its bearing capacity, but slightly affects critical temperature and fire resistance rating. Despite the fact that concrete with basalt fiber is the least sensitive to heat, concrete with steel and synthetic fibers turned out to be comparable in this indicator with ordinary concrete. The presented results of evaluative calculations allow predicting the use of bending reinforced concrete elements based on concrete with disperse fibers in conditions of increased fire hazard, depending on the percentage of reinforcement and on the workload.

No abstract