Response of circular hollow steel tubes under simultaneous high temperatures and impact loading

Hollow steel tubes have been widely employed in engineering structures, and their performance under accidental loading throughout their lifecycle deserves careful attention. During service, they may experience coupled effects such as fire and impact. However, studies on their response under combined high-temperature and impact loading remain limited. Therefore, this study experimentally and numerically examined the impact response of circular hollow steel tubes subjected to coupled high-temperature and impact load. Eleven specimens were tested using a drop-weight impact device coupled with a high-temperature furnace to examine the effects of temperature, impact energy, and tube thickness on their impact resistance. The experiments captured failure patterns, impact force and deformation responses. Results showed that all specimens experienced coupled global flexural and local indentation at the impact location. With the temperature increasing from 200 °C to 800 °C, the plateau impact force decreased by 56.4%, whereas the peak mid-span deflection and residual local deformation increased by 496.2% and 79.6%, respectively. Finite element (FE) models were established and verified against the test data, then used to elucidate the underlying mechanisms and conduct a parametric study of key factors affecting impact performance at elevated temperatures. Finally, a two-degree-of-freedom (TDOF) model was proposed to predict the local deformation of hollow steel tubes under combined high-temperature and impact loading, providing a practical tool for their design and assessment under extreme conditions.