Experimental and numerical investigation of circular concrete-filled steel tubular columns subjected to post-earthquake fires

Fires induced by earthquakes are high-probability events that can accelerate the collapse of buildings. This research investigates the fire resistance of eight circular concrete-filled steel tubular (CFST) columns under four earthquake damage levels through experimental methods. The earthquake damage and fire tests were conducted continuously without unloading the axial loads. The impact of earthquake damage levels and axial load ratios on fire resistance were studied. The failure mode, temperature evolution, fire performance, and deformation of the columns under post-earthquake fire (PEF) were analyzed and discussed. In addition, the validated numerical method was used to simulate the fire resistance of the columns that suffered seismic damage. The results show that the maximum axial expansion of the columns gradually decreases with increasing seismic damage. When the axial load ratio is 0.284, a slight decrease in fire resistance occurs at drift ratios exceeding 2.67 %, and plastic hinges form at the mid-height of the column at failure. When the drift ratio reaches 4.48 %, premature lateral displacement induces a more pronounced second-order effect, accelerating column instability and leading to a significant decrease in fire resistance. At an axial load ratio of 0.431, although the lateral stiffness of the column decreases more severely, fire resistance exhibits only a slight reduction at a drift ratio of 4.42 %.

https://doi.org/10.1016/j.engstruct.2025.120008