Design method for impact resistance of circular concrete-filled double-skin steel tubular members based on dynamic increase factor and equivalent single DoF system

Concrete-filled double-skin steel tubular (CFDST) members are widely employed as load-bearing members in the ultra-high power transmission tower and offshore platform. The impact resistance of this type of members should be considered in the design stage. Based on the previous test results, in total 200 finite element (FE) models considering the coupling of axial and lateral impact loads were established with the ABAQUS software, and the damage mechanism of impact resistance was analyzed. Then, the parametrical studies were carried out to investigate the influences of key factors, including the nominal steel ratio, hollow ratio, cross-sectional diameter and material strength on the impact resistance of the members for the axial load ratio ranging from 0 to 0.7. Finally, the calculation formula for the impact bearing capacity is proposed and the dynamic response at the mid-span was predicted based on the methods of dynamic increase factor and an equivalent single degree-of-freedom model. In this work, the deflection at the mid-span and the plateau impact force were taken as the key indexes to evaluate the impact resistance. Results indicate that the impact resistance of the circular CFDST columns decreaseswith the increasing of axial load ratio. Under lateral impact, the CFDST members with the hollow ratio lower than 0.7 exhibit flexural failure. The interaction between the external steel tube and the inner concrete is stronger than that between the inner steel tube and the outer concrete. In addition, the nominal steel ratio, outer diameter of the cross-section, yield strength of the outer tube, impact velocity and impact mass all play significant roles on the maximum deflection at the mid-span and the plateau impact force when the axial load ratio ranges from 0 to 0.7. Effects of hollow ratio and concrete strength are marginal. The proposed calculation methods can reasonably predict the impact bearing capacity and mid-span displacement response of the CFDST members subjected to an impact. © 2022 Explosion and Shock Waves. All rights reserved.