FIRE RESISTANCE OF STEEL BUILDING BEAMS

Приведены экспериментальные и численные исследования несущей способности стальных балок из сталей классов С255 и С355 при воздействии стандартного температурного режима пожара. Цель исследования - уточнение метода расчета предела огнестойкости изгибаемых стальных балок с учетом неравномерного распределения температуры в поперечном сечении, что позволит повысить точность расчетов и безопасность таких конструкций в практике строительства.
 The disadvantage of calculation and analytical methods for determining the fire resistance limits of building metal structures is the lack of practical information on the features of changes in the strength characteristics of the most common building steels at high exposure temperatures and the results of experimental studies to determine the bearing capacity of steel structures under fire exposure. For this purpose there were carried out studies of the strength characteristics of steels with rolled metal samples of C255 and C355 strength classes as well as empirical dependences of the change in the yield strength in the temperature range 20 °C < t < 700 °C were determined, which are necessary to calculate building metal structures for fire resistance. Experiments to determine the actual fire resistance of beams were carried out with class C255 rolled I-beams and class C355 welded I-beams. As controlled characteristic areas of steel temperature change there were taken the following items: the lower flange, the middle of the wall and the upper flange of the average I-section. Graphs of deformation (deflection) in the middle section of the beam under fire exposure are constructed. The calculation of fire resistance limit of bent steel beams was carried out taking into account the uneven distribution of temperature in the cross section. Comparison of experimental data and calculation results by means of the developed model, which takes into account the uneven heating of the section, showed their good agreement (up to 15 %) in terms of the loss of bearing capacity during three-sided heating under standard fire conditions.