Dynamic Response and TDOF-Based Analysis of Concrete-Filled Steel Tube Columns Under Lateral Impact

To address the unclear coupling mechanism between local and global responses of concrete-filled steel tube (CFST) columns under lateral impact and the difficulty that conventional single-degree-of-freedom (SDOF) models cannot accurately describe the dynamic response throughout the entire impact process, a finite element model was first developed and validated against existing drop-hammer impact tests. The validated FE analysis shows that the lateral impact response can be divided into local- and global-response stages. During the local-response stage, pronounced inertial effects generate large internal shear forces and give rise to a risk of shear failure. The inertial force distribution was obtained from nodal accelerations, and a dynamic shear-force calculation method was established based on the internal-force relationship at the peak instant. By accounting for stress-wave propagation, local contact, and axial-load effects, a dynamic resistance-function model was reconstructed, and a two-degree-of-freedom (TDOF) theoretical model was employed to solve the impact response of CFST columns. Finally, a simplified analytical procedure was proposed to preliminarily assess the shear-failure risk, predict the deflection response of flexure-dominated members, and identify three steel-tube cracking cases and one axial-compression instability case.