Zhuojin Pipe Fitting Co., LtdWorking Mechanism of Stainless Steel Pipe Concrete Members Under Explosion Loading
Literature Overview
This paper by Tan Qinghua, Han Linhai, Jia Shaogang, and Jiang Zhigang, published in China Civil Engineering Journal (2024, Vol. 57, No. 6), presents experimental and numerical investigations into the dynamic response of stainless steel pipe concrete (SSC) members subjected to blast loading. The research is supported by the National Natural Science Foundation of China (52220105005) and the Hunan Provincial Natural Science Foundation (2018JJ2470). The study compares circular and square stainless steel pipe concrete specimens with and without concrete infill, examining damage patterns, dynamic response, and energy dissipation characteristics.
Core Technical Points
Experimental Configuration
| Parameter | Values Tested | Purpose |
|---|---|---|
| Section shape | Circular, Square | Compare geometric effects on blast resistance |
| Concrete infill | With, Without | Isolate contribution of concrete core |
| Scaled distance | Multiple values (near to far field) | Cover elastic to failure regimes |
| Steel grade | Stainless steel (nominal yield strength matched with carbon steel) | Compare with conventional CFST |
Damage Progression with Scaled Distance
The research reveals a clear damage evolution pattern:
- Far-field (large scaled distance): Elastic deformation dominates; no permanent damage observed.
- Intermediate field: Bending failure initiates at mid-span with yielding of the stainless steel tube.
- Near-field (small scaled distance): Progressive transition from bending to shear failure; local buckling and tearing of the tube wall become prominent.
Three Failure Modes Identified
| Failure Mode | Characteristic | Governing Mechanism |
|---|---|---|
| Bending failure | Hinged at two locations, large lateral displacement | Flexural yielding of tube and concrete |
| Bending-shear failure | Combined hinge and shear zone | Interaction of flexure and shear forces |
| Shear failure | Sudden collapse with limited displacement | Diagonal tension cracking and tube rupture |
Numerical Analysis and Validation
Finite Element Model Features
The validated FE model incorporates:
- Dynamic explicit analysis with mass scaling for computational efficiency
- Johnson-Cook constitutive model for stainless steel to capture strain rate effects
- Concrete damaged plasticity model for infill concrete
- Contact algorithms with friction to simulate tube-concrete interface behavior
- Blast loading applied via pressure-time curves derived from Hopkinson-Cranz scaling
The model successfully reproduces experimental peak displacements within 10% deviation and captures the correct failure mode sequence across the tested scaled distance range.
Energy Dissipation Comparison
A critical finding is that concrete infill significantly enhances energy absorption capacity. The mechanism involves:
- Concrete constraining the tube against local buckling, allowing the tube to develop greater plastic deformation before failure
- Interfacial friction between tube and concrete contributing additional damping
- Concrete crushing absorbing significant kinetic energy in near-field scenarios
Integration with Engineering Practice
Blast Protection Design Considerations
For engineers designing blast-resistant structures incorporating steel pipe concrete members:
- Stainless steel offers superior corrosion resistance compared to carbon steel, which is advantageous in harsh environments (marine, chemical processing, military installations).
- The ductility of stainless steel provides enhanced post-yield deformation capacity, which is critical for blast protection where energy absorption is the primary design objective.
- The higher cost of stainless steel must be justified by the combined benefits of corrosion resistance and improved blast performance.
Comparison: Stainless Steel vs. Carbon Steel CFST
| Property | Stainless Steel CFST | Carbon Steel CFST |
|---|---|---|
| Corrosion resistance | Excellent | Requires protective coating |
| Blast energy absorption | Superior | Baseline |
| Cost | 3-5× higher | Baseline |
| Post-blast repairability | Better (no corrosion damage) | Coating damage requires repair |
| Long-term maintenance | Minimal | Regular inspection and recoating |
Design Recommendations
Based on the findings, the following recommendations emerge:
- For critical blast protection applications where long-term service life and minimal maintenance are required, stainless steel pipe concrete members represent a technically superior solution.
- The concrete infill should not be treated as merely a structural enhancement but as an integral component of the blast energy dissipation system.
- Section shape selection should consider the specific threat scenario: circular sections perform better in pure bending scenarios, while square sections may offer advantages in shear-dominated failure modes due to their flatter faces.
Key Questions and Reflections
- How does the strain rate sensitivity of different stainless steel grades (e.g., duplex vs. austenitic) affect the blast performance predictions?
- What is the optimal concrete strength for maximizing blast energy absorption—does higher strength always translate to better performance?
- Can the findings be extended to consider multi-blast loading scenarios, which are relevant for certain threat environments?
The research demonstrates that stainless steel pipe concrete members offer a compelling solution for blast protection, combining the proven structural advantages of composite construction with the corrosion resistance and ductility of stainless steel. The validated numerical model provides a powerful tool for parametric optimization of member geometry and material selection for specific threat scenarios.