Fire resistance-effective parameters relationships of slender rectangular and circular RC columns

In literature, few researchers have attempted to describe reasonable relationships between fire resistance of reinforced concrete (RC) columns and the effective parameters. İn general, these relationships have mostly been described by first-order polynomial curves. In this paper, an alternative numerical model is developed to study the relationships between fire resistance of RC columns and the most significant parameters such as load level, slenderness ratio, load eccentricity, concrete cover thickness, shape of cross-section and cross-section size. The model uses Newton-Raphson method as a convergence technique to determine the strain distributions on the heated column cross-section. A powerful methodology is proposed to compute the lateral deflection for slender columns. Comparisons of predicted columns behavior with those observed in fire tests show good agreement for both fire resistance and deformation. An investigation is conducted to determine the accuracy of three simplified calculation methods found in literature in predicting the relationships between different effective parameters and fire resistance. It was found that these relationships should be described using higher-order polynomial curves, rather than using straight lines as most of previous studies predicted. It was also found that in many cases, predictions of the empirical equation incorporated in Eurocode-2 overestimate model predictions.