THE INFLUENCE OF TEMPERATURE DEVIATION IN THE FURNACE FROM THE NOMINAL REGIME ON THE RESULTS OF TESTING STEEL STRUCTURES FOR FIRE RESISTANCE

Abstract

This study is devoted to the evaluation of the time interval until the onset of the limit state of steel structures as a sign of loss of bearing capacity, taking into account the presence of deviation of the actual temperature in the furnace from the nominal regime during their fire resistance test according to national and European standards. The purpose of the study was to identify the dependence between this time interval for such steel structures as beams and columns with a single-layer fire protection system, and the deviation of the actual temperature in the furnace from the nominal regime, as well as to determine the procedure for adjusting the obtained indicators with respect to this time interval to eliminate the influence of the specified deviation temperature on the test results. With the application of the computational experiment method, which is based on solving a direct one-dimensional problem of thermal conductivity, the data on the difference between the values of this time interval, obtained at the minimum and maximum permissible temperatures in the furnace, and the value of this time interval for the nominal temperature regime were determined. Laws have been revealed regarding the influence of the deviation of the actual temperature in the furnace from the nominal regime on the test results of steel structures under the conditions of the standard temperature regime according to EN 1363-1:2020 and DSTU B V.1.1-4-98*. It was established that the difference between the values of the time interval until reaching the critical temperature of 500 °C on the metal surface of a steel structure with a single-layer fire protection system, obtained according to the actual and nominal temperature regimes in the furnace, depends on the time interval of fire exposure and the deviation index between these regimes, and not depends on the thermal properties of the fire protective coating. The largest values of this difference are different for the permissible deviations regulated in national and European standards. For the conditions of the national standard, with an increase in the fire exposure time from 30 min to 240 min, the value of this difference decreases from 14,7% to 3,3%, and for the European standard, it decreases from 6,6% to 2,4%. The procedure for adjusting the indicators obtained during the test regarding the time interval until the onset of the limit state of a steel structure with a single-layer fire protection system based on the loss of load-bearing capacity is determined, which allows to eliminate the influence of the deviation of the actual temperature regime in the furnace from the nominal one on the test results.