Behavior of circular reinforced concrete columns under fire conditions

Anumerical model was developed for tracing the behavior of circular reinforced concrete (RC) columns over the entire range of loading from pre-fire conditions to collapse under fire. The macroscopic finite element based model utilizes time dependant momentcurvature relations of various column segments and the analysis is carried out in three stages; namely, establishing fire temperatures, calculating the heat transfer through the structure, and then carrying out strength analysis. The model, which accounts for high temperature nonlinear material properties, is capable of predicting the fire resistance of circular RC columns under realistic fire scenarios, loading conditions, and failure criteria. The validity of the model is established by comparing predictions from the computer program with results from full-scale fire resistance tests. The validated model is applied to undertake a set of parametric studies to quantify the effect of column size, load level, load eccentricity, and concrete strength on the fire resistance of RC columns. Results generated from parametric studies are utilized to develop a simplified equation for evaluating the fire resistance of circular RC columns. Fire resistance predictions from the proposed equation are in good agreement with those obtained from fire tests and nonlinear finite element analysis.