Post-fire axial impact behavior of columns with hollow section

The objective of this work is the study of the dynamic response of fire-affected hollow steel stub columns subjected to axial impact loadings. Although this issue is of great importance for structural safety against multiple hazards, it has not been adequately considered previously. Dynamic FE models of fire-affected columns subjected to axial impact loading were generated using the ABAQUS/Explicit software package. The effects of material degradation, strain rate sensitivity, and interaction were included in the analysis. The validation process involved comparing results with those obtained experimentally in the literature. High correlations were observed in impact force–time curves, deformation patterns, and failure modes. Later, parametric studies of key factors affecting impact performance were conducted. As observed, thickness and aspect ratio are the key parameters governing the axial impact bearing capacity of rectangular stub columns after fire. More specifically, the increase in thickness from 2 to 6 mm is accompanied by increases in impact capacity of more than 180% and 140% at temperatures of 20 °C and 300 °C, respectively. The increase in aspect ratio from 1.5 to 3.0, in turn, reduces impact capacity by 15–40%. Regarding impact dynamics, the rise in velocity from 3.3 m/s to 10 m/s increases capacity by about 40%, while the increase in hammer mass from 0.4 to 1.5 tons yields less significant gains of 5–14%. At 700 °C, the effect becomes negligible. Thus, changes in section compactness and thickness increase resistance, and impact dynamics must also be considered.