Experimental Study on 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 simulated seismic loads. The experiments were conducted in two separate phases, consisting of (1) the quasi-static cyclic tests, followed by (2) fire tests. Three nominally identical column specimens were constructed for these studies. One of the specimens was directly tested under fire to quantify its resistance in an undamaged condition. The other two specimens were first subjected to quasi-static cyclic lateral loads, imposing varying degrees of lateral 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 1.4 and 3.9% for moderate and high damage levels, respectively. The undamaged and damaged columns were then subjected to the same fire tests in accordance with a standard 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. An additional quasi-static cyclic loading test was conducted on the specimen that had been exposed to fire without any prior damage to investigate the behavior of the column subjected to seismic loads after the fire test. Differences in behavior were modest, except for a 5.7% drop in strength attributed to permanent degradation in material properties due to the fire test.