Zhuojin Pipe Fitting Co., LtdBending Performance of Circular Stainless Steel Tube Concrete Members with Built-In Steel Sections
Literature Overview
This 2024 paper by Wang Zhibin and colleagues, published in Advances in Steel Building Structures, investigates the pure bending behavior of circular stainless steel tube concrete (SSTC) members with embedded steel sections. The research was supported by the National Natural Science Foundation (grant 52178122), Fujian Provincial Natural Science Foundation (2021J01603), and Quanzhou Science and Technology Program (2021C015R). The study employs finite element modeling validated against experimental data to characterize the enhanced bending capacity and stiffness of this novel composite member type.
Core Technical Findings and Performance Enhancement
The key finding of this research is that the bending capacity of the SSTC member with built-in steel section is 111.33% higher than that of the comparable stainless steel tube concrete member without the embedded steel section. The concrete contribution to the bending moment is 23.31% higher, and the compressive strength of the concrete in the compression zone is approximately 20% higher. The authors attribute this enhancement to the improved confinement effect provided by the combined action of the stainless steel tube and the steel section flanges on the concrete in the compression zone.
| Performance Indicator | SSTC with Built-In Steel Section | SSTC without Built-In Steel Section | Improvement |
|---|---|---|---|
| Bending capacity | Baseline reference | 100% | +111.33% |
| Concrete bending moment contribution | Baseline reference | 100% | +23.31% |
| Compression zone concrete strength | Baseline reference | 100% | +20% |
| Bending stiffness | Increases with parameters | Baseline | Variable |
Parametric Study and Design Guidelines
The parametric study reveals several important relationships governing the bending performance of these composite members. The bending stiffness and capacity both increase with increasing concrete strength, stainless steel section ratio, steel section ratio, and radius-to-thickness ratio. The bending capacity also increases with the yield strength of both the stainless steel tube and the embedded steel section.
| Parameter | Effect on Bending Capacity | Effect on Bending Stiffness |
|---|---|---|
| Concrete compressive strength (fc) | Positive correlation | Positive correlation |
| Stainless steel section ratio | Positive correlation | Positive correlation |
| Steel section ratio | Positive correlation | Positive correlation |
| Radius-to-thickness ratio (D/t) | Positive correlation | Positive correlation |
| Stainless steel yield strength (fy,SS) | Positive correlation | Moderate positive |
| Steel section yield strength (fy,st) | Positive correlation | Moderate positive |
The simplified calculation methods developed by the authors for bending stiffness and bending capacity provide practical design tools for engineers. These methods likely incorporate the confinement enhancement factor for the concrete and the composite action between the steel tube, embedded section, and concrete core.
Manufacturing and Welding Considerations
The fabrication of circular stainless steel tubes with embedded steel sections presents several manufacturing challenges that directly affect the structural performance characterized in this study. The stainless steel tubes are typically manufactured by cold-forming or hot-rolling processes, followed by welding of the longitudinal seam. Common stainless steel grades used include 304 (06Cr19Ni10), 316 (022Cr17Ni12Mo2), and duplex grades such as 2205.
The welding of the longitudinal seam in stainless steel tubes requires careful control of heat input to prevent sensitization and intergranular corrosion in the heat-affected zone. For austenitic stainless steels, the interpass temperature should be kept below 250°C, and the total heat input per pass should be limited to avoid excessive grain growth. The welding filler metal must be carefully selected to match or exceed the corrosion resistance of the base metal, typically using E308L or E316L electrodes for 304 and 316 grades respectively.
The integration of the embedded steel section into the concrete core within the stainless steel tube requires careful consideration of the interface between the carbon steel section and the stainless steel tube. If these are welded together, dissimilar metal welding considerations apply, including the risk of intermetallic compound formation and galvanic corrosion in corrosive environments. The welding procedure must be qualified to address these concerns, potentially using transition weld metals or separation techniques.
Quality Control and Non-Destructive Testing
Given the critical role of the steel tube and embedded section in the bending performance of these composite members, the quality control procedures for their fabrication must be rigorous. Non-destructive testing should include:
- Ultrasonic testing (UT) of the longitudinal weld in the stainless steel tube to detect lack of fusion, cracks, and volumetric defects per ISO 17640 or EN ISO 17637.
- Magnetic particle testing (MT) of the embedded steel section welds to detect surface and near-surface defects per ISO 17638.
- Visual inspection (VT) of all welds for undercut, spatter, and geometric irregularities per ISO 17637.
- Radiographic testing (RT) of critical welds where volumetric defect detection is required per ISO 17636.
The residual stress distribution in the stainless steel tube and the embedded steel section also affects the long-term performance of the member. Residual stresses from welding can be measured using the hole-drilling method per ASTM E837 or the neutron diffraction method, and should be considered in the design to account for their effect on the fatigue and fracture resistance of the member.
Key Reflections and Study Insights
The 111.33% improvement in bending capacity achieved by adding a built-in steel section to the circular stainless steel tube concrete member is a remarkable result that highlights the potential of hybrid composite designs. The confinement mechanism is the key to understanding this enhancement—the steel section flanges provide additional lateral restraint to the concrete in the compression zone, increasing its effective strength and ductility. This is analogous to the confinement effect provided by spiral reinforcement in reinforced concrete columns, but achieved through a more efficient structural arrangement.
From a practical standpoint, the simplified calculation methods developed in this study are essential for widespread engineering adoption. Without such methods, the use of this member type would be limited to research applications where detailed finite element analysis is feasible. The parametric relationships identified in the study provide clear design guidance for optimizing the member proportions, and the emphasis on stainless steel as the outer tube addresses the growing demand for corrosion-resistant structural members in marine and industrial environments. The integration of manufacturing quality control with structural performance prediction is essential for ensuring that the theoretical benefits demonstrated in this study are realized in actual construction applications.