Tubular steel columns under lateral impact: Numerical investigation of the role of axial load, connecting member stiffness, projectile mass, and column length

The present study focuses on investigating the effects of projectile impact on steel tubular columns through finite element (FE) analysis. Initially, an FE model was developed and calibrated against benchmark experiments available in the literature. A Johnson-Cook material model was utilized for these tubular sections and implemented in Abaqus for FE simulations. Numerical analyses were performed with a rigid projectile of mass 100 kg, impacting tubular column at a velocity of 20 m/s. To comprehensively investigate the behavior of the columns, parameters such as axial load level, projectile mass, and unsupported column length were varied in the FE analysis, and their influence on impact forces and permanent deformations of the columns were investigated. Increased axial compressive loading resulted in a reduced maximum impact force and increased deformation of the column. The study also examined the occurrence of negative reaction forces (whiplash effect) at column supports, particularly in columns with longer spans. Displacement profile along the column length was found to have a strong correlation with the whiplash effect. A significant difference between impact force and reaction force was observed when a lower mass projectile impacted the column, compared to a higher mass projectile. Furthermore, the effect of alternate load path on column behavior was modeled using a spring that was connected to the column and represented the stiffness of the neighboring elements connected to the column against column shortening. The results indicated that stiffer connecting members reduce damage to the column by providing an alternate load path after the column loses some of its axial stiffness. However, when the normalized stiffness ratio, which is defined as the ratio of spring stiffness to axial stiffness of the column exceeds 1, no significant increase in impact resistance was observed.