Numerical evaluation of post fire capacity of reinforced concrete columns

This study employs finite element modelling to investigate the behaviour of reinforced concrete (RC) columns subjected to fire including cooling phase. Although previous experimental studies have observed the response of RC columns subjected to fire, still there remains a need of numerical research for systematically identifying the critical range of axial loads that may lead to structural collapse throughout the cooling phase and after the structure has cooled. The effects of fire are simulated through thermal loading applied to the column surfaces exposed to fire. Heat transfer is modelled through conduction, convection and radiation mechanisms, while the variation of concrete and steel properties is incorporated with respect to temperature. A water-cooling method is adopted to cool the column. The outcomes of numerical modelling are examined with respect to fire resistance, failure loads, peak temperatures attained and temperature distribution contours. The resistance of the column during the heating phase shows strong agreement with the results of standard furnace tests reported in previous experimental studies, proving the accuracy and consistency of the developed model. Numerical modeling results is then compared for cooling zone with previous numerical study using similar modeling approach and comparison results demonstrated consistency. A parametric study has been done by validated model, with various clear cover, load ratio and slenderness ratio to detect the potential critical axial load range capable of triggering structural collapse. It has been observed that the number of cases of delayed collapse is high for shorter fires and delayed collapse is particularly critical for RC columns with a slenderness ratio of 28.87 or less.