Calculation of the residual strength of steel-concrete composite columns under standard fire conditions

In this paper the fire behaviour of composite columns in hollow square and circular sections infilled with concrete was studied by the method of calculation of the EC4 wich is a summation method that uses equations to determine the temperature field and residual strength of composite hollow sections subjected to a conventional fire, and then a comparison was made between residual resistances calculated by this method and those calculated by a formula from the literature. Calculations have shown that the fire resistance of the columns is very sensitive to the variation of the transverse dimension of the profile and the thickness of the tube. As for the comparison between the fire resistances of square profiles and those of circular sections, it is noted that whatever the area of the section, the resistance of circular profiles is greater than that of square profiles especially during the first hour of fire, and this is because of the large circumference of the square sections compared to the circular ones. And finally the index of residual resistance calculated by Eurocode 4 (IRREC4) remains lower than that calculated by the literature formula (IRRHan) up to certain values of the section dimension and the buckling length beyond which it will be the opposite.