Impact response of hybrid FRP-concrete-steel double-skin tubular bridge piers with fixed-simply supported boundary conditions: Experimental study and FE analysis

Hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) have emerged as an innovative type of hollow-section bridge pier, particularly suitable for use in corrosive environments, and have recently been applied in practical bridge engineering projects. Vehicle collisions are a leading cause of bridge pier failures, making impact resistance a critical performance factor for ensuring the structural safety of bridges. However, the existing studies about the impact performance of DSTCs have significant limitations. For instance, the void ratio φ (0.42–0.47) and the column diameter D (114–168 mm) studied are considerably smaller than those typically found in practical bridge structures. To address this gap, this study investigated six DSTCs with large void ratios (φ = 0.73 or 0.82) and section diameters (D = 300 mm), where the lower end was fixed and the upper end was simply supported. These columns were subjected to impact loading using a horizontal vehicle impact system to examine the influences of impact velocity, number of impacts, FRP thickness, steel thickness, and DSTC void ratio. The experimental results demonstrated the following: (1) due to the constraint at the upper end, DSTC specimens exhibited small overall lateral displacement but more pronounced localized concave deformation after the impact; (2) increasing the void ratio resulted in reduced impact force, decreased global lateral displacement, and increased localized concave deformation; (3) contact stiffness and flexural stiffness increased with steel thickness, leading to higher impact force, decreased global lateral displacement, and smaller local dent deformation. Subsequently, utilizing LS-DYNA, an FE model was used to simulate the dynamic responses of DSTC specimens. A parameter analysis was performed to study the influences of impactor mass, steel yield strength, impactor height, and axial compression ratio.