Lateral Impact Response of Axially Loaded Steel CHS and SHS Columns by Deformable Projectiles

Abstract This paper presents an experimental investigation on the lateral impact response of axially preloaded steel circular hollow sections (CHS) and square hollow sections (SHS). The study examines the influence of projectile deformability, axial preloading, cross-sectional geometry, and member wall thickness on the impact response of steel tubular members. Ten YSt 310 grade steel columns were tested using a gas-gun facility capable of delivering controlled single-impact loading at an impact velocity of 20 m / s . A disc-spring-based loading assembly was developed to apply a constant axial preload while maintaining simply supported boundary conditions at the column ends. The results showed that, for the same projectile mass and impact velocity, deformable projectiles produced 32.8% and 12.4% lower residual dent depth compared to rigid projectiles in CHS and SHS, respectively. Increasing the wall thickness from 4.8 to 6 mm for CHS and from 6 to 8 mm for SHS significantly enhanced impact resistance, resulting in a 30.2% and 31.4% increase in peak impact force and a reduction in residual dent depth by 41.3% and 40.6%, respectively. Circular columns exhibited higher local stiffness and 17.2% lower mid-span displacement than square columns but caused up to 250% greater projectile deformation due to concentrated contact stresses. Increasing the axial load ratio in CHS from 0.0 to 0.3 resulted in 17.9% reduction in peak impact force, along with 34.6% and 57.6% increase in mid-span displacement and dent depth, respectively. Energy balance analysis confirmed that 67%–80% of the absorbed energy was localized at the impact region, dominated by indentation and projectile deformation.