Zhuojin Pipe Fitting Co., LtdAxial Compression Behaviour of Circular Hollow Interlayer Stainless Steel Pipe Concrete Short Columns
Literature Overview
This paper by Peng Guihan, Song Chunsheng, Luo Huiling, and Wang Jie (Fuzhou University, Fuzhou Institute of Technology, and Bohai Petroleum Equipment Fujian Steel Pipe Co., Ltd.) investigates the axial compressive mechanical properties of circular hollow interlayer stainless steel pipe concrete (HISPC) short columns. Published in Journal of Nanchang University (Engineering Science) in 2020, the work addresses a relatively novel composite structural form that combines an inner stainless steel tube, a concrete infill layer, and an outer stainless steel tube, with a hollow cavity between the inner tube and the concrete. The study is supported by the Fujian Provincial Natural Science Foundation (2018J01769) and the Fujian Provincial Department of Education Middle-aged and Young Teachers Educational Research Project (JAT170791).
Core Technical Content
The research establishes a benchmark finite element solid model calibrated against experimental data, then systematically investigates the influence of key parameters including the hollow ratio, concrete strength, and inner/outer steel tube strength on structural load-bearing capacity. A structural load-bearing capacity correction algorithm is proposed, and the applicability of existing domestic and international codes for calculating the capacity of this structural type is examined.
Key Findings on Parameter Sensitivity
| Parameter | Relationship with Load-Bearing Capacity | Key Observation |
|---|---|---|
| Concrete strength | Linear positive correlation | Higher concrete grade directly increases capacity |
| Outer steel tube strength | Linear positive correlation | Material upgrade of outer tube yields proportional benefit |
| Inner steel tube strength | Linear positive correlation | Similar linear trend as outer tube |
| Hollow ratio | Non-monotonic (increase then decrease) | Optimum at hollow ratio of 0.46 |
The hollow ratio behaviour is particularly noteworthy. Within the investigated range, high-strength inner steel tube hollow interlayer structures consistently outperform solid structures in load-bearing capacity across all hollow ratios examined. The capacity first increases and then decreases as the hollow ratio grows, reaching a peak at a hollow ratio of 0.46. This suggests that an optimal balance exists between the material savings from hollowing and the loss of concrete confinement effectiveness.
Proposed Correction Algorithm and Code Comparison
The proposed structural load-bearing capacity correction algorithm demonstrates good agreement with experimental values, validating the analytical framework. However, the study concludes that current domestic and international code calculation methods for this type of structure are all conservative in their predictions. This is a significant finding from an engineering design perspective, as it implies that designers using existing standards may be over-conservative, potentially leading to unnecessary material usage and cost.
Engineering Practice Implications
From a steel pipe manufacturing and welding quality control standpoint, several critical considerations emerge from this study:
- Stainless steel tube material quality: The linear relationship between steel tube strength and structural capacity underscores the importance of material traceability and mechanical property verification for both inner and outer stainless steel tubes. Any deviation in yield strength or tensile strength from specified values directly translates to structural performance differences.
- Geometric tolerance control: The hollow ratio of 0.46 being optimal means that manufacturing tolerances on inner tube diameter, outer tube diameter, and wall thickness must be tightly controlled. Variations in these dimensions shift the effective hollow ratio away from the design optimum.
- Welding quality at tube junctions: The interlayer design implies that the inner and outer tubes must be connected, likely through welding or mechanical fastening at the column ends. Weld integrity at these connections is critical, as failure of the bond between tubes and concrete would eliminate the composite action that provides the enhanced capacity.
- Concrete placement quality: The hollow interlayer design creates a complex geometry for concrete placement. Ensuring complete, void-free concrete fill between the inner tube and outer tube is essential. Incomplete filling would reduce the effective concrete cross-section and compromise the confinement mechanism.
Study Insights and Reflections
The non-monotonic relationship between hollow ratio and load-bearing capacity is physically intuitive but quantitatively significant. At low hollow ratios, the hollow cavity contributes little material savings but begins to reduce the concrete confinement area. At high hollow ratios, the remaining concrete ring becomes too thin to provide effective confinement to the inner steel tube, and the outer tube may buckle independently. The optimum at 0.46 represents a transition point where the confinement benefit and material efficiency are balanced.
The finding that existing codes are conservative is encouraging for structural designers but raises questions about whether these codes should be updated to accommodate hollow interlayer structures specifically. Until such updates occur, the proposed correction algorithm offers a more rational design basis. For quality control engineers, this means that acceptance criteria derived from existing codes may be unnecessarily stringent for this structural type, and alternative verification methods based on the proposed algorithm could provide more accurate safety assessments.
The involvement of Bohai Petroleum Equipment Fujian Steel Pipe Co., Ltd. in this research is noteworthy, as it suggests industrial relevance and potential for translating laboratory findings into production-scale pipe manufacturing specifications. Stainless steel tubes for this application would need to meet specific dimensional tolerances, surface finish requirements, and mechanical property ranges to ensure consistent structural performance.