Fire resistance of building structures made of rolled steel with increased heat resistance indicators

Introduction. The paper is devoted to experimental and analytical study of the load-bearing capacity of bending structures made of ordinary and fire-resistant rolled steel under standard temperature conditions. Fire tests were carried out with rolled I-beams No. 20B1 manufactured according to GOST R 57837–2017 from steels of strength classes C255, C390 and welded I-beams 180 × 90 × 10 from steels C355, C390, C355P, C390P with the length of 3,500 mm. Experiments on determination of high-temperature mechanical properties of new steel grades were carried out.

Materials and methods. The values of actual fire resistance limits of beams obtained experimentally are determined according to GOST 30247.1–94 and GOST 30247.0–94. The thermotechnical part of the calculation of the temperature in the cross-section of steel beams was performed in the ANSYS Mechanical programme complex. The calculation of bearing capacity was carried out according to the developed method and the registered programme for computer. Experiments on determination of mechanical properties of rolled metal products under high-temperature heating were carried out on small-sized specimens in accordance with GOST 9651–84.

Results and discussion. Experimentally obtained values of actual fire resistance limits for I-beams made of ordinary and fire-resistant rolled steel. The averaged values of coefficients of change of yield strength at elevated temperatures of construction rolled steel, including fire-resistant steel, which can be used in calculation models of fire resistance assessment of steel structures, were determined. A programme complex for calculation of fire resistance limit taking into account non-uniform temperature distribution in the cross-section of the structure was developed. The results of calculations of fire resistance limits according to the proposed model are close to the experimental data obtained on I-beams made of building steels, including fire-resistant ones.

Conclusions. The fire resistance limit of beams made of fire-resistant rolled steel C355P, C390P at standard temperature regime occurs 10–15 minutes later than beams made of ordinary construction steel. The results of experimental and analytical studies of fire resistance limits of structures made of new types of fire-resistant steels confirm the increase in the time of metal heating from the beginning of fire exposure to the achievement of critical temperature in the design cross-section, which allows to justify their use in the design of buildings and structures in accordance with the requirements of standardized documents on fire safety, as well as to reduce the use of fireproof materials, reduce the metal intensity and cost of construction.

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