Impact Resistance of Large Hollow Ratio Hollow Sandwich Steel Tube Concrete Members

Literature Overview

This paper by Shi Yanli, Wei Ran, Wang Wenda, and Ji Sunhang from Lanzhou University of Technology, published in 2023 in Progress in Steel Building Structures, Volume 25, Issue 2, investigates the impact resistance of large hollow ratio hollow sandwich steel tube concrete (HSTC) members. The research was supported by the National Natural Science Foundation of China (52168020, 52168021) and the Lanzhou City Science and Technology Plan Project (2019-1-61). The study employs finite element analysis using ABAQUS software to establish lateral impact models of HSTC members considering initial geometric defects. The hollow ratio range investigated is 0.2 to 0.9, with a particular focus on the effects of initial geometric defects on the impact response of members with a hollow ratio of 0.8. The study also provides a simplified prediction formula for the impact force-local deformation relationship under lateral impact loading.

Core Technical Findings

The study demonstrates that the impact resistance of large hollow ratio HSTC members is significantly influenced by initial geometric defects, and that the effects of these defects become more pronounced as the hollow ratio increases. The key findings are summarized below.

Effect of Initial Geometric Defects

The study compares the impact performance of HSTC members with and without initial geometric defects. The results show that the consideration of initial geometric defects leads to a reduction in the impact force plateau value and an increase in local deformation. Specifically, when the hollow ratio reaches 0.8, the adverse effects of geometric defects are most pronounced: the impact force plateau value decreases by 10.6%, and the mid-span local deformation increases by 20.4%. This significant degradation in impact performance is attributed to the reduced structural stability of the hollow sandwich configuration at high hollow ratios, which makes the member more sensitive to initial imperfections.

Influence of Design Parameters

The parametric analysis reveals the following influence patterns on the impact response of large hollow ratio HSTC members:

• Nominal steel ratio: Increasing the nominal steel ratio effectively reduces the adverse influence of initial geometric defects on the impact performance. A higher steel ratio provides greater structural stiffness and stability, which compensates for the geometric imperfections and maintains the impact force plateau value at a higher level.
• Inner steel tube diameter-thickness ratio: Reducing the inner steel tube diameter-thickness ratio (i.e., using a thicker wall) effectively reduces the adverse influence of initial geometric defects. A thicker inner tube wall provides greater local stability and reduces the susceptibility to local buckling, which is a critical failure mode for large hollow ratio members under impact loading.
• Material strength: Changing the material strength has a relatively small influence on the impact performance of large hollow ratio HSTC members. This finding suggests that the impact resistance of these members is more sensitive to geometric parameters than to material properties, which is an important consideration for the optimization of the design.

Simplified Prediction Formula

Based on the parametric analysis results and the static load-local indentation relationship, the authors developed a simplified prediction formula for the impact force-local deformation curve of large hollow ratio HSTC members under lateral impact loading. The formula can predict the impact response of both defect-free and defective members, providing a practical tool for the preliminary design and assessment of the impact performance of HSTC members. The formula accounts for the influence of the hollow ratio, initial geometric defects, and other key design parameters, and its prediction accuracy is validated against the finite element results.

Technical Parameters and Design Guidelines

Hollow Ratio and Impact Performance