Study on the fire resistance of concrete-filled steel tubular column to composite beam joints after earthquake damage

Background: Post-earthquake fire is one of the secondary disasters caused by the earthquake; many earthquakes around the world have brought about severe fires and led to enormous losses. It is of great significance to study the fire resistance of structures after earthquake to improve the level of urban disaster prevention and reduce the fire loss. Methods: A nonlinear finite element model of composite joints subjected to post-earthquake fires is established based on ABAQUS software. The state after the earthquake damage is imported into the thermal-stress analysis model through the restart request in ABAQUS, and considered as the initial state of the thermal-stress analysis model. Results: It is noticed that when the damage index is less than 0.517, the damage level shows significant effect on the fire resistance, but the influence is no longer significant when the damage index reaches 0.781. When only the column is exposed to fire, the column showed obvious local buckling and overall bending deformation. Meanwhile, when the joint area below the concrete slab is exposed to fire, the joint shows a mixed failure mode of the excessive vertical displacement of beam end and column instability. Conclusion: The fire resistance of the composite joint decreases gradually with the increase of seismic damage level. The fire condition has a significant effect on the fire resistance of the composite joints; with the increase of fire area, the fire resistance of composite joints with same damage degrees decreases gradually.