Simplified method for evaluating the biaxial capacity of rectangular reinforced concrete columns during fire.

For design situations in case of ambient temperature, both EN1992-1-1 and ACI318 provide guidelines for the design of columns, and for evaluating the structural capacity in case of biaxial bending. However, the effect of fire on these columns subjected to biaxial bending is not mentioned in the provisions. Hence, it is important to evaluate the mechanical behavior of columns in case of biaxial bending combined with fire and to provide guidelines for fire resistance design. In this paper, first a simplified method proposed by Bresler is presented for design under ambient temperature in order to predict the interaction curves of concrete columns subjected to biaxial bending and axial loading, based on a calculation of the uniaxial bending capacity. In order to verify whether this method can be adopted in case of fire, a cross-sectional calculation tool is introduced and validated with experimental data. Further, the results from the simplified method are compared with those obtained with the calculation tool. Subsequently, the simplified method is elaborated further in order to take into account the effect of an ISO 834 standard fire for a column loaded by a symmetrical biaxial load. Finally, the results of a parametric study are presented. Suggestions are given for implementing this method for design of relatively short concrete columns subjected to biaxial bending in case of an ISO 834 fire. [ABSTRACT FROM AUTHOR]