Post-earthquake fire resistance of ductile concrete filled double-skin tube columns

Experimental studies were conducted to examine the behavior of concrete filled double-skin tube (CFDST) columns exposed to fire after being subjected to cyclic loads. The experiments were conducted in two separate phases, consisting of the quasi-static cyclic tests followed by fire tests. Three nominally identical column specimens were constructed for these studies. The first specimen was directly tested under fire to quantify its resistance in an undamaged condition. The second and third specimens were first subjected to quasi-static cyclic lateral loads, imposing varying degrees of drift to simulate two different seismic events with moderate and high damage levels before being exposed to fire. Both of the specimens were pushed to the maximum drift of 6-6.5% with different residual drifts of 1.8% and 3.94% for low and high damage levels, respectively. The undamaged and damaged columns were then subjected to the same fire tests following the standard ASTM E119 temperature-time curve while sustaining an axial load until the column failed due to global buckling. Local buckling of the tubes was also observed in the specimens due to the thermal expansion and separation from the concrete. Overall, the results showed marginal differences in the fire resistance of the three specimens, providing evidence for the resilient performance of these columns under post-earthquake fire scenarios.