Lateral Impact Tests and Finite Element Analysis of Hollow Sandwich Stainless Steel Tube Concrete Members

Literature Overview

The paper by Jiang Shan and Wang Rui (2016, published in Industrial Construction, Vol. 46, No. 11, pp. 161-167) presents experimental and numerical investigations on the lateral impact behavior of hollow sandwich stainless steel tube concrete (SSC) members. The research was supported by the National Natural Science Foundation of China (51379290). This study is particularly relevant to the growing interest in stainless steel composite structures for applications where corrosion resistance, durability, and impact resistance are critical requirements.

Technical Background

The hollow sandwich SSC member is a composite structural element that combines the advantages of stainless steel with concrete, while incorporating a hollow core to reduce weight and improve impact energy absorption. The configuration consists of:

• An outer stainless steel tube that provides structural integrity and corrosion protection.
• An inner stainless steel tube that creates the sandwich configuration.
• A concrete layer between the two steel tubes that contributes to compressive strength and energy absorption.
• A hollow core that reduces self-weight and provides a controlled deformation zone during impact.

This configuration is particularly suited for applications such as bridge piers, marine structures, and protective structures where impact loading (vehicle impact, blast loading, falling objects) is a design consideration. In my experience with impact-resistant design, the hollow core concept is an effective strategy for energy absorption because it allows controlled local deformation without compromising the overall structural integrity.

Experimental Program

Six groups of specimens were tested under three different impact conditions using a DHR9401 drop-weight impact testing machine. The test matrix included variations in:

The experimental measurements included:

• Impact force time-history curves
• Overall residual deformation
• Local deformation patterns
• Failure modes

Key Experimental Findings

Effect of Impact Height (Energy)

As the impact height (and therefore impact energy) increased, the following trends were observed:

1. Platform force value increased: The steady-state impact force (platform value) increased with impact energy, indicating that the member's resistance to deformation increased with the severity of loading.
2. Impact duration increased: Higher impact energy resulted in longer impact duration, as more energy needed to be dissipated through plastic deformation.
3. Overall deformation increased: Both global and local deformations increased with impact energy, as expected.

These trends are consistent with the general behavior of impact-loaded structures and confirm that the hollow sandwich SSC member responds in a predictable manner across the tested energy range.

Effect of Hollow Ratio

The hollow ratio (the ratio of the hollow core cross-sectional area to the total cross-sectional area) had a significant influence on impact performance:

1. Low hollow ratio: The member exhibited stable platform behavior with a distinct peak force phase, indicating good energy absorption capacity.
2. Medium hollow ratio: The platform behavior remained relatively stable, but the peak force phase became less pronounced.
3. High hollow ratio: The platform behavior became unstable, the peak force phase gradually disappeared, and the overall impact resistance decreased significantly.

This finding highlights the critical role of the concrete layer thickness in impact resistance. As the hollow ratio increases, the concrete layer becomes thinner, reducing its ability to absorb impact energy and maintain stable force response. In practical design, this suggests that the hollow ratio should be limited to ensure adequate concrete layer thickness for impact resistance.

Failure Modes

The failure modes observed in the tests included:

• Local buckling of the outer stainless steel tube at the impact point
• Concrete crushing in the concrete layer
• Progressive deformation of the hollow core region
• Potential inner tube deformation for high-energy impacts

The stainless steel's ductility and corrosion resistance contributed to the member's ability to absorb energy through plastic deformation without catastrophic failure.

Finite Element Analysis

A finite element model was developed using ABAQUS to simulate the lateral impact behavior of the hollow sandwich SSC members. The model incorporated:

• Nonlinear material models for stainless steel (capturing strain hardening and strain-rate effects)
• Concrete damage plasticity model for the concrete layer
• Appropriate contact definitions between the steel tubes and concrete
• Dynamic explicit analysis for impact simulation

Model Validation

The finite element analysis results were compared with the experimental results, and good agreement was observed between the calculated and experimental impact force time-history curves, residual deformations, and failure modes. This validation confirms the reliability of the finite element model for predicting the impact behavior of hollow sandwich SSC members.

Engineering Practice Implications

Design Guidelines

Based on the experimental and numerical findings, the following design guidelines can be derived:

1. Hollow ratio limitation: The hollow ratio should be limited to ensure a minimum concrete layer thickness that provides adequate impact resistance. The specific limit depends on the expected impact energy and the structural importance of the member.
2. Stainless steel grade selection: The stainless steel grade should be selected to balance ductility (for energy absorption) with strength (for load-carrying capacity). Common grades such as 304, 316, and duplex stainless steels offer different combinations of these properties.
3. Concrete mix design: The concrete should be designed to provide adequate compressive strength and ductility. High-strength concrete may be used for the outer layers, while a more ductile concrete mix may be appropriate for the core region.

Application Scenarios

The hollow sandwich SSC member is particularly suitable for:

• Marine structures: Where corrosion resistance and impact resistance (from vessels, waves) are required.
• Bridge piers: Where vehicle impact protection is a design requirement.
• Protective structures: Where blast or impact loading is a design consideration.
• Offshore platforms: Where corrosion resistance and impact resistance are both critical.

Critical Assessment

While the research provides valuable insights into the impact behavior of hollow sandwich SSC members, several aspects warrant further investigation. First, the study focuses on single-impact loading, whereas practical structures may be subjected to repeated impact events. The effect of cyclic or repeated impact on the member's residual strength and deformation capacity should be investigated. Second, the study does not address the effect of corrosion on the impact performance, which is particularly relevant for marine applications where the stainless steel's corrosion resistance is a primary design driver. Third, the finite element model validation is based on a limited number of test specimens, and further validation across a wider range of parameters would increase confidence in the model's predictive capability.

Summary

This paper presents a systematic investigation of the lateral impact behavior of hollow sandwich stainless steel tube concrete members through both experimental testing and finite element analysis. The findings demonstrate that the hollow sandwich configuration provides effective impact energy absorption, with the hollow ratio playing a critical role in determining the member's impact performance. The validated finite element model offers a reliable tool for predicting the impact behavior of these members under various loading conditions and geometric configurations. For engineers designing impact-resistant composite structures, particularly in marine and infrastructure applications, this research provides valuable guidance on the design of hollow sandwich SSC members that balance corrosion resistance, structural efficiency, and impact protection. The work contributes to the growing body of knowledge on stainless steel composite structures and supports the development of more resilient and durable infrastructure systems.