Mechanical behavior of circular steel-reinforced concrete-filled steel tubular columns under lateral impact after exposure to fire

To study the impact behavior of circular steel-reinforced concrete-filled steel tubular (SRCFST) columns after exposure to fire, a numerical model for the post-fire columns under lateral impact was developed using software ABAQUS. Based on the validated accuracy of the proposed model, the working mechanism of the post-fire columns under lateral impact was analyzed, including the impact response process, the development of sectional internal force and the plastic deformation. Moreover, the influences of key factors such as the fire time, the mass ratio of drop hammer to column and the axial load ratio on the impact resistance of the column were discussed in detail. In addition, the impact resistances of CFST and SRCFST columns after fire were also compared. The results show that the post-fire SRCFST column exhibits a good impact resistance. Comparing with the normal SRCFST column, the maximum mid-span deflection of the post-fire column with 1 h fire time increases by 17%, and the impact force platform value decreases by 12% due to the loss of flexural stiffness. The mass ratio of the drop hammer to the column has a significant influence on the shape of the time history curve of impact force, and the plateau stage of the curve gradually disappears when decreasing the mass ratio to below 3. The existence of axial load can slightly improve the impact force platform value when the axial compression ratio is less than 0.3. However, the impact resistance of the column significantly declines when the axial compression ratio increases to more than 0.3. Comparing the post-fire CFST columns, the SRCFST columns after fire shows a superior impact resistance with an average reduction of 15% in maximum mid-span deflection and an average improvement of 22% in impact force plateau value. © 2021, Editorial Office of Journal of Building Structures. All right reserved.