A simplified approach for predicting fire resistance of reinforced concrete columns under biaxial bending

Reinforced concrete (RC) columns, when exposed to fire, are often subjected to biaxial bending arising from eccentricity in loading, 1-, 2-, 3-side fire exposure or due to non-uniform spalling. Effect of such biaxial bending and spalling is not taken into consideration in evaluating fire resistance of RC columns in current design codes. In this paper a set of numerical studies were carried out to quantify the effect of various factors on fire induced biaxial bending in RC columns. Results from parametric studies are utilized to develop a simplified equation for evaluating the fire resistance of RC columns under biaxial bending conditions. The proposed equation accounts for the effects of fire-induced spalling, 1-, 2-, 3-, or 4-sided fire exposure, bi-eccentric loading and design fire scenarios. The validity of the equation is established by comparing the predictions from the equation with results from finite element analysis and test data. The applicability of the proposed equation to fire resistance design of RC columns is illustrated through a numerical example.