Zhuojin Pipe Fitting Co., LtdPrefabricated Hollow Steel Tube Concrete Support Technology for Subway Stations
Literature Overview
The paper by Ouyang Dong, Luo Huiping, Chen Jianwei, Han Xu, Chen Zhijun, and Duan Siyuan from China Railway Siyuan Survey and Design Institute Group, published in Urban Rapid Rail Transit (2023, Vol. 36, No. 4, pp. 107-113), presents a novel prefabricated hollow steel tube concrete (HSTC) support system developed under the dual-carbon strategy. The research was funded by National Key R&D Program projects (Grants 2018YFC0808702 and 2019YFC0605100).
Background and Motivation
Deep foundation pit support systems in subway station construction traditionally use either:
- Cast-in-place reinforced concrete supports (high carbon footprint, long construction time)
- Prefabricated steel pipe supports (lower carbon but higher material cost)
The proposed hollow STC support combines the advantages of both approaches by utilizing a hollow steel tube as the primary structural element with partial concrete infill, achieving reduced carbon emissions while maintaining structural capacity.
Specimen Design and Testing
Two full-scale hollow STC support specimens were fabricated and subjected to axial compression testing:
| Parameter | Description |
|---|---|
| Number of specimens | 2 |
| Scale | Full-size (full-scale) |
| Loading method | Axial compression |
| Failure mode | Concrete crushing |
| Analysis tool | Abaqus finite element analysis |
| Analysis type | Material and geometric nonlinearity |
Both specimens failed by concrete crushing, indicating that the steel tube contributed to overall structural stability while the concrete provided the primary compressive resistance.
Finite Element Analysis Validation
The nonlinear finite element model incorporating both material nonlinearity (stress-strain relationships for steel and concrete) and geometric nonlinearity (large deformation effects) showed good agreement with experimental results, validating the analytical approach for design purposes.
Performance Comparison
| Performance Indicator | Cast-in-place RC Support | Prefabricated Steel Pipe Support | Hollow STC Support |
|---|---|---|---|
| Carbon emissions | Highest | Moderate | Significantly lower |
| Economic cost | Moderate | Higher | Lower |
| Construction speed | Slow | Fast | Fast |
| Structural capacity | High | High | Meets design requirements |
The hollow STC support was successfully applied in the Tangma Interval No. 2 Air Shaft project, demonstrating practical engineering viability.
Technical Analysis from Steel Pipe Fabrication Perspective
Several aspects of this technology are directly relevant to steel pipe fabrication and welding professionals:
- Hollow tube design: The hollow section reduces concrete volume while maintaining structural integrity. The tube wall thickness must be designed to resist local buckling under the eccentric loads that develop when only partial concrete infill is present.
- Concrete infill methodology: Unlike fully filled STC columns, the hollow STC support requires controlled partial concrete placement. This introduces challenges related to:
- Concrete segregation prevention
- Void detection and prevention
- Interface bond development at partially filled sections
- Welding of prefabricated segments: The prefabricated nature of the support requires butt welding or bolted connections between segments. Weld quality is critical as these joints must transfer full axial loads and resist potential bending moments during installation.
- Surface treatment for bond: The internal surface of the steel tube requires appropriate treatment to ensure adequate bond with the concrete. Shot blasting or mechanical roughening of the internal surface is recommended.
Quality Control Considerations
For the successful implementation of hollow STC supports, the following quality control measures are essential:
| QC Activity | Method | Acceptance Criteria |
|---|---|---|
| Weld inspection (butt joints) | UT + MT | No cracks, full penetration |
| Concrete placement quality | UT of infill zone | No voids exceeding specified size |
| Dimensional accuracy | Surveying | Within ±3 mm for critical dimensions |
| Steel tube surface quality | Visual + MT | No surface defects at weld zones |
| Load test (if required) | Hydraulic loading | Meets design capacity |
Carbon Reduction Quantification
The dual-carbon strategy context is particularly relevant in the current engineering environment. The hollow STC support achieves carbon reduction through:
- Reduced concrete volume (lower cement production emissions)
- Prefabricated construction (reduced on-site energy consumption)
- Optimized steel usage (thinner walls than fully filled STC)
- Reduced construction time (lower equipment fuel consumption)
Study Insights and Engineering Implications
This research represents a significant advancement in sustainable deep foundation pit support technology. The combination of prefabricated hollow steel tubes with partial concrete infill offers a practical solution that balances structural performance, economic efficiency, and environmental responsibility. For steel pipe manufacturers and welders, this technology creates new requirements for:
- Precision fabrication of hollow tubes with controlled internal surface finish
- Welding procedures qualified for the specific joint configurations used in prefabricated support systems
- Quality assurance systems capable of verifying both the steel tube manufacturing quality and the subsequent concrete infill quality
The successful application at the Tangma Interval project demonstrates that this technology has moved beyond the laboratory stage and is ready for wider implementation in urban subway construction projects. As the dual-carbon strategy drives innovation in construction materials and methods, the hollow STC support technology represents a promising direction that leverages traditional steel pipe fabrication expertise while addressing contemporary sustainability challenges.