Dynamic response of cross steel reinforced concrete filled steel tubular columns under impact under fire

To explore the impact response of cross steel-reinforced concrete-filled steel tubular (CSRCFST) columns under fire, a finite element model using ABAQUS software was generated. After validation against test results, para-metric studies were carried out to investigate the effects of impact load as well as time of fire exposure on the impact resistance of CSRCFST columns. The numerical results show that the impact behavior of post-fire CSRCFST columns can be divided into three stages: peak stage, plateau stage, and softening stage. For CSRCFST columns, the peak and plateau stages are important, which absorbed 32.4% and 67.6% of the impact kinetic energy, respectively. After two hours of fire exposure, the stiffness and peak impact load of the column decreased by 93.7% and 71.7%, respectively. However, the peak mid-span deflection and residual deflection increased by 6.5% and 20.1%, respectively. When the drop weight tripled, the maximum deflection and residual deformation of the midspan increased by 2.8 and 3.2 times, respectively. However, the peak impact load in-creases only by 14.5%. When the impact energy is the similar, the maximum midspan deflection of the specimen is almost identical, whereas a larger impact momentum reduces the peak impact force but increases the impact force at the plateau stage. By increasing fire duration, the behaviors of the column deteriorate seriously, with 85% reductions in peak impact force and 39% increase in maximum midspan deflection. In addition, the effects of impact velocity are also significant regarding each stage.