Experimental investigation on temperature evolution of steel beams in natural fires

Abstract

This paper presents an experimental project of a 3D steel portal frame subjected to a natural fire to investigate the evolution of temperatures of the hot gas layer and the steel beams. Temperature evolution of the steel beams during the test was recorded and compared with those calculated by current design codes, i.e. Eurocode EN 1993-1-2 and Chinese Code CECS200. The experimental results revealed that the temperature of the hot gas gradually decreased with the distance from the fire source, and the temperature variations in the steel beams had obvious hysteresis compared to those of the hot gas. The results calculated according to the equations specified by EN 1993-1-2 and CECS200 were very similar. However, there were noticeable differences between the calculated data and the experimental results after the temperature of the steel beam was higher than 600oC. The calculation for the temperature of steel beams in the hot gas layer does not need additional consideration of the thermal radiation from the flame. Based on the experimental results, this paper improves the equations specified in EN 1993-1-2, using correction coefficients of convection and radiation. It is found that the modified method obtains calculation results in satisfactory agreement with the experimental results, thereby providing a reference for predicting the temperature of steel beams in natural fires.