Zhuojin Pipe Fitting Co., LtdAxial Compression Bearing Capacity of Built-in Steel Section Steel Tube Concrete Members
Literature Overview
The paper by Mao Wenjing, Shi Yanli, and Wang Wenda (2021), published in Progress in Steel Building Structures, addresses the axial compression behavior of a relatively novel composite structural member: the built-in steel section steel tube concrete (BSS-SC) column. This member type combines the advantages of conventional steel tube concrete (CFST) columns with the additional strength and stiffness provided by an internal steel section, aiming to meet the demands of modern structures trending toward greater heights, heavier loads, and larger spans. The research was supported by the National Natural Science Foundation of China (Grant Nos. 51468037 and 51768038).
Numerical Modeling and Validation
The authors employed ABAQUS finite element software to develop a full-process numerical model of built-in steel section circular steel tube concrete short columns under axial compression. The model was validated against existing experimental data on the bearing capacity of such members. The numerical analysis captures the complete stress-strain behavior, including the stress distribution across the cross-section and the interaction forces between the constituent components.
Key Parameters Investigated
| Parameter | Influence on Bearing Capacity | Influence on Strain Behavior |
|---|---|---|
| Concrete strength | Significant positive effect | Moderate effect |
| Steel tube steel ratio | Significant positive effect | Moderate effect |
| Built-in steel section steel ratio | Moderate positive effect | Small effect |
| Steel section cross-sectional form | Moderate positive effect | Small effect |
Stress-Strain Behavior and Component Interaction
The study reveals several important mechanical behaviors:
- The built-in steel section exerts a dual confinement effect on the core concrete, resulting in an increase in concrete strength beyond what would be achieved by the steel tube alone.
- The coordinated action between the steel section, concrete, and steel tube effectively enhances both the bearing capacity and ductility of the column.
- The steel ratio of the built-in steel section and the cross-sectional form of the steel section have relatively small effects on strain variation.
Simplified Bearing Capacity Formula
A simplified calculation formula for the axial compression bearing capacity of built-in steel section circular steel tube concrete short columns was proposed. The formula results showed good agreement with experimental data. This is of significant practical value, as it provides engineers with a straightforward design tool that does not require complex finite element analysis for routine design calculations.
Metallurgical and Materials Considerations
From a materials engineering perspective, the dual confinement effect is of considerable interest. The steel tube provides external confinement, while the built-in steel section provides internal confinement. This dual-confinement mechanism can significantly enhance the compressive strength and ductility of the core concrete, particularly under high confining pressures. However, the effectiveness of this mechanism depends critically on the bond between the steel section and the concrete, which in turn depends on the surface treatment of the steel section, the concrete mix design, and the construction quality.
The selection of steel grades for both the steel tube and the built-in steel section must be carefully considered. Higher strength steel grades (such as Q345 or Q390) for the steel tube can provide greater confinement, while the built-in steel section may be selected based on the overall strength requirements. The compatibility of steel grades between different components is important to ensure uniform deformation behavior and avoid premature failure at material interfaces.
Welding and Fabrication Considerations
The fabrication of built-in steel section steel tube concrete columns involves several critical welding operations:
- The connection between the built-in steel section and the steel tube, if any, must be designed to ensure adequate load transfer.
- Girth welds of the steel tube must be inspected to ensure full penetration and absence of defects.
- The longitudinal welds of the built-in steel section, if applicable, must meet the same quality standards as the steel tube welds.
The heat input during welding can affect the local microstructure of the steel tube and steel section, potentially reducing toughness in the heat-affected zone. Post-weld heat treatment may be necessary for high-strength steel grades to restore adequate toughness.
Summary
This paper makes a valuable contribution to the understanding of built-in steel section steel tube concrete columns, providing both a validated numerical model and a practical simplified bearing capacity formula. The dual confinement mechanism identified in the study opens new possibilities for designing more efficient composite columns. The research findings suggest that the built-in steel section is most effective in enhancing bearing capacity rather than ductility, while the steel tube continues to play the primary role in providing confinement and ductility. Engineers designing such members should carefully consider the interaction between all three components and ensure that the construction details adequately realize the theoretical performance predicted by the proposed formula.