Zhuojin Pipe Fitting Co., LtdLateral Impact Behavior of Hollow Sandwich Concrete-Filled Steel Tube Members
Literature Overview
This paper by Shi Yanli, He Jiaxing, Xian Wei, and Wang Rui from Lanzhou University of Technology and Taiyuan University of Technology (2019) investigates the lateral impact behavior of hollow sandwich concrete-filled steel tube (CFST) members using finite element analysis. The research was supported by the National Natural Science Foundation of China (Grant No. 51768038), the Lanzhou Science and Technology Project (2019-1-61), and the Gansu Provincial Collaborative Innovation Team (2018C-08). It was published in the Journal of Lanzhou University of Technology, Volume 45, Issue 4, pages 132–137. The study employs ABAQUS to model the dynamic impact response of sandwich CFST members with varying hollow ratios, axial compression ratios, and cross-sectional configurations.
Core Technical Content
Sandwich CFST Concept
The hollow sandwich CFST member consists of an outer steel tube, an inner steel tube, and a concrete layer between them, with a hollow core at the center. This configuration offers several potential advantages:
- Reduced self-weight compared to solid CFST members
- Enhanced energy absorption through the hollow core
- Improved impact resistance due to the sandwich structure
- Potential for integration of utility conduits or reinforcement materials in the hollow core
Finite Element Model
The ABAQUS-based finite element model incorporates the following key features:
- Contact relationships between the steel tubes and the falling mass (impactor) and between the steel tubes and the concrete
- Dynamic material models for the inner and outer steel tubes and the concrete, appropriate for high-strain-rate loading
- Validation against experimental data from typical specimens
The material models selected for the dynamic analysis include:
| Component | Material Model | Justification |
|---|---|---|
| Outer steel tube | Johnson-Cook or elastic-plastic with strain rate effect | Captures dynamic hardening |
| Inner steel tube | Johnson-Cook or elastic-plastic with strain rate effect | Captures dynamic hardening |
| Concrete | Concrete damage mechanics (CDM) or Holmquist-Johnson-Cook (HJC) | Captures dynamic crushing and spalling |
| Impactor | Elastic or rigid body | Simplifies contact analysis |
Parametric Analysis
After validating the model against experimental data, a parametric study was conducted to investigate the influence of the following factors on the impact response:
- Hollow ratio (ratio of hollow core area to total cross-sectional area)
- Axial compression ratio
- Cross-sectional configuration (outer circular-inner square vs. double circular tubes)
Key Findings
The parametric analysis reveals the following important trends:
| Parameter | Effect on Impact Response | Magnitude |
|---|---|---|
| Hollow ratio | Significantly affects peak impact force and local deformation | High |
| Axial compression ratio | Significantly affects impact force plateau value and deformation development | High |
| Cross-sectional form | Outer circular-inner square outperforms double circular tubes | Moderate |
Specifically, as the hollow ratio increases, the peak impact force decreases and the local deformation at the impact zone increases. This is because a larger hollow core reduces the effective cross-sectional area available to resist the impact load, leading to greater deformation and lower force capacity.
The axial compression ratio has a significant effect on the impact force plateau value and the progression of deformation. Higher axial compression ratios lead to earlier local buckling of the steel tubes and more rapid deformation development under impact loading.
The cross-sectional configuration comparison shows that the outer circular-inner square sandwich CFST member exhibits superior impact resistance compared to the double circular tube configuration at the same hollow ratio. The square inner tube provides better confinement of the concrete layer and more uniform stress distribution.
Integration with Engineering Practice
The concept of hollow sandwich CFST members has potential applications in several engineering scenarios:
- Bridge pier protection: Sandwich CFST members can be used as protective barriers for bridge piers against vehicle impact. The hollow core provides additional energy absorption capacity while maintaining structural integrity.
- Railway and highway guardrails: The enhanced impact resistance of sandwich CFST members makes them suitable for use in guardrail systems where high-energy impact loads are expected.
- Marine and offshore structures: The reduced self-weight of hollow sandwich CFST members is advantageous for marine applications where buoyancy and weight are critical design considerations.
- Nuclear and defense structures: The enhanced energy absorption and impact resistance of sandwich CFST members can be leveraged for blast-resistant and impact-resistant structures.
From a steel pipe manufacturing perspective, the fabrication of sandwich CFST members requires precise control of the inner and outer tube dimensions, concentricity, and the gap between the tubes for concrete placement. The manufacturing process may involve:
- Precision rolling or forming of both inner and outer tubes
- Assembly of the inner tube within the outer tube with controlled spacing
- Concrete placement through access openings, followed by sealing
- Welding of end plates or connection details
Key Questions and Reflections
A significant question raised by this study is the practical feasibility of manufacturing and constructing hollow sandwich CFST members at scale. The requirement for concentric inner and outer tubes, controlled spacing, and complete concrete fill of the annular space presents significant construction challenges. The quality of the concrete-steel bond in the annular space is critical to the structural performance, and any voids or incomplete fill would significantly degrade the impact resistance.
Another reflection is that the study focuses on lateral impact by a falling mass, which is a simplified representation of real-world impact scenarios. Real impacts may involve oblique loading, multiple impact events, or impacts combined with sustained loads. The dynamic material models used in the analysis may not fully capture the complex failure mechanisms that occur under these more realistic conditions.
A third consideration is the cost-effectiveness of sandwich CFST members compared to conventional solid CFST members. While the sandwich configuration offers enhanced impact resistance, the additional manufacturing complexity and material requirements may not always justify the performance benefits. A comprehensive cost-benefit analysis is needed to determine the optimal application scenarios.
Study Insights and Implications
The most important practical takeaway from this study is that the hollow ratio and axial compression ratio are the dominant parameters governing the impact response of hollow sandwich CFST members, and that the outer circular-inner square cross-sectional configuration provides superior impact resistance compared to the double circular tube configuration. These findings provide a clear basis for the design optimization of sandwich CFST members for impact-resistant applications.
For steel pipe manufacturers, the development of sandwich CFST members represents an opportunity to create specialized products for high-value applications such as bridge protection, marine structures, and defense infrastructure. The manufacturing challenges are significant but manageable with appropriate process development and quality control.
In summary, this study provides valuable insights into the lateral impact behavior of hollow sandwich CFST members through validated finite element analysis, establishing the key design parameters and cross-sectional configurations that optimize impact resistance, and highlighting the potential of this innovative structural concept for applications requiring enhanced energy absorption and impact protection.