Post-heating response of concrete-filled circular steel columns

Concrete-Filled Steel Tubular (CFST) columns are increasingly becoming popular for carrying heavy loads. One of the major concerns for such columns has always been the exposure to fire and subsequent cooling for which different methods are adopted. This study investigates the effect of cooling regimes after exposure to elevated temperature of 600oC for three hours on axial compression behavior of concrete-filled circular stub columns. The experimental program involves the testing of thirty columns consisting of two sizes of outer steel tube. Double skin columns were also considered for the bigger diameter column. The cooling regimes considered in the study were annealing and water quenching. The columns were tested for two possible modes of load transfer viz. core loaded and composite loaded. The behavior of columns was studied in terms of ultimate load capacity, load-deformation pattern and stresses in the materials. The ductility of concrete-filled columns was higher than that of the steel tube alone. The confinement offered by outer steel tube was less in composite loaded columns as compared to core loaded columns. The annealing was found to be slightly better than water quenching for post-fire cooling of columns.