Zhuojin Pipe Fitting Co., LtdAxial Compression Performance of Circular Hollow CHCCFST Composite Long Columns
Literature Overview
The paper by Ren Qingxin, Wei Qiuyu, Wang Peng, Li Yongjin, and Wang Qinghe from Shenyang Jianzhu University (published in Journal of Shenyang Jianzhu University, Vol. 38, No. 3, 2022, pp. 410–417) investigates the axial compression behaviour of circular hollow circular steel tube concrete filled steel tube (CHCCFST) composite long columns. The research, supported by the National Natural Science Foundation of China (No. 51808351) and several provincial-level funding programmes, establishes finite element models validated against existing experimental data, analyses key parameters affecting structural performance, and proposes simplified calculation formulas for axial compression bearing capacity. This work addresses a novel composite column configuration that combines the benefits of steel tube confinement with the structural efficiency of hollow-core geometry.
Structural Configuration and Design Philosophy
The CHCCFST composite long column represents a hybrid structural element that integrates multiple materials and geometries to optimise load-bearing performance. The configuration typically consists of an outer circular steel tube, an inner circular steel tube, and concrete filling the annular space between them, creating a hollow-core composite column. This design philosophy offers several theoretical advantages:
| Design Feature | Structural Benefit | Engineering Significance |
|---|---|---|
| Outer steel tube | Provides lateral confinement to concrete | Enhances concrete compressive strength through triaxial stress state |
| Inner steel tube | Adds axial load capacity and torsional resistance | Increases overall structural efficiency |
| Annular concrete fill | Fills the gap between tubes, preventing buckling | Creates composite action between steel and concrete |
| Hollow core | Reduces self-weight and material consumption | Improves economic efficiency and constructability |
The hollow-core geometry is particularly attractive for long columns where weight reduction is critical, as it reduces the dead load while maintaining structural integrity through the composite action of the steel tubes and confined concrete.
Finite Element Modelling and Parameter Analysis
The authors developed finite element models that were first validated against existing experimental data to ensure accuracy and reliability. The numerical models then served as a parametric analysis tool to investigate the influence of key parameters on the axial compression performance. The load-versus-mid-column deflection curves were analysed to identify characteristic points that define the structural response under different parameter combinations.
Key Parameters and Their Effects
| Parameter | Variation Range | Effect on Axial Compression Capacity |
|---|---|---|
| Concrete compressive strength (f_cu) | C40 to C60 to C80 | Capacity increase of 42.4% (C40→C60) and 62.8% (C40→C80) |
| Slenderness ratio (λ) | 36 to 30 to 24 | Capacity increase of 31.5% (λ=36→30) and 44.4% (λ=36→24) |
The results demonstrate that both concrete strength and slenderness ratio are critical parameters governing the axial compression performance. The substantial capacity improvement with increasing concrete strength (up to 62.8%) highlights the effectiveness of the steel tube confinement mechanism in utilising high-strength concrete. The slenderness ratio effect (up to 44.4% improvement) reflects the fundamental stability behaviour of long columns, where reduced effective length significantly enhances buckling resistance.
Simplified Calculation Formula Development
Based on the existing stability coefficient φ used in current design codes, the authors proposed a simplified calculation formula for the axial compression bearing capacity of CHCCFST composite long columns. The simplified formula was validated against both finite element analysis results and experimental data, demonstrating good agreement. This is a significant contribution to practical engineering, as it provides designers with a straightforward calculation method that avoids the need for complex numerical analysis in routine design.
The simplified approach builds upon the well-established concept of the stability coefficient, which accounts for the effects of slenderness on column capacity. By calibrating this coefficient against the composite column behaviour, the formula effectively captures the interaction between material strength, geometric properties, and stability effects in a single design expression.
Engineering Practice Considerations
From a fabrication and construction perspective, several practical aspects merit attention:
- The fabrication of CHCCFST composite columns requires precise alignment of the outer and inner steel tubes to ensure uniform annular concrete thickness. Misalignment can create weak zones with reduced confinement effectiveness.
- Concrete placement in the annular space between tubes presents a practical challenge. The relatively narrow annular gap requires specialised pumping techniques and vibration methods to ensure complete filling without voids or honeycombing.
- The welding of steel tube connections at column joints must be designed to accommodate the composite section geometry. Welding access to the inner tube connection may require special fixtures or sequential assembly procedures.
- Quality control of the concrete-concrete-steel interface is essential. The bond strength at this interface directly influences the composite action and load transfer mechanism.
Critical Reflections
The study makes a valuable contribution to the understanding of CHCCFST composite long columns, but several aspects warrant further consideration. The finite element models, while validated, rely on material constitutive models that may not fully capture the complex stress states within the confined concrete under high confinement pressures. The simplified calculation formula, while practical, should be applied within the parameter range studied, and extrapolation to extreme values of concrete strength or slenderness ratio should be approached with caution. Additionally, the study focuses on centred axial compression, whereas real-world columns are subject to eccentric loading and combined bending effects, which may alter the relative contributions of the different structural components.
Summary
This study establishes the axial compression performance of circular hollow CHCCFST composite long columns through validated finite element modelling and parametric analysis, demonstrating that concrete strength and slenderness ratio are the governing parameters with capacity improvements of up to 62.8% and 44.4% respectively. The proposed simplified calculation formula provides a practical design tool that achieves good agreement with both numerical and experimental results. The CHCCFST composite column represents a promising structural solution that combines weight efficiency with high load-bearing capacity, and its application in tall buildings and long-span structures warrants further investigation under more realistic loading conditions.