Performance of circular concrete filled steel tubes after fire exposure: Experiments

Abstract

This study investigated the performance of postfire concrete-filled steel tubes (CFSTs) to obtain some information on fire safety of CFST structures. To achieve this aim, 18 CFST specimens that were divided into six groups were used in the tests. One group represented the control group, and five groups were exposed to fire for 15, 30, 45, 60, and 75 min. After the fire exposure, these specimens were axially loaded until failure. The results indicated that 15 to 45 min of fire caused damage in the form of swelling of the steel tubes, whereas longer fire caused explosive failure. Explosive failure resulted in zero load-carrying capacity, leading to the collapse of CFST structures. Fire shifted the global buckling of control specimens to the local buckling of postfire specimens under axial loading. Fire detrimentally affected the loadxdisplacement behavior of the CFST specimens. After exposure to fire for 15–45 min, the ultimate load of the postfire CFST specimens was reduced by 6.0 %−55.3 %, the yield load was reduced by 13.8 %−66.0 %, and the stiffness was reduced by 15.1 %−36.3 % compared with those of the control specimens. An analytical model to predict the load-carrying capacity of postfire CFST columns was proposed. This model could be a useful tool for evaluating postfire CFST columns with short fire durations.