Fire Resistance of Four-Face Heated Reinforced Concrete Columns

Until now, the determination of fire resistance of reinforced concrete (RC) columns has essentially been based on tabulated data. Clearly, a more scientific approach based on an understanding of the fundamental behavior of columns in fire is timely and will be useful to structural engineers. This paper develops a simple and rational method to predict the fire resistance of RC columns subjected to four-face heating. The effects of elevated temperature on material deterioration with regard to the strength and stability of the columns are quantified. Both uniaxial and biaxial bending of columns is considered. The computer code SAFIR, developed at the University of Liege, was used to analyze reported experimental results and to simulate the deformation response. The approach comprises three steps. The first step is to determine the respective strength reduction factors of concrete and steel and the modulus of elasticity at elevated temperature on the basis of numerical simulations using SAFIR. The second step is to calculate the balanced failure point of the column, so as to determine whether the applied load eccentricity is small or large. The third step is to determine the failure load by a trial and error process. This method can be regarded as an extension of the existing American Concrete Institute method for ultimate strength predictions of RC columns at ambient temperature.