Eccentric Compression Performance of Irregular Cross-Section Multi-Cavity CFST Mega Columns

Literature Overview

This study by Cao Wanlin, Wang Ruwei, Yin Fei, Wang Zhihui, and Dong Hongying (Beijing University of Technology, 2020) presents large-scale experimental and analytical research on irregular cross-section multi-cavity concrete-filled steel tube (CFST) mega columns. Funded by the National Natural Science Foundation of China (Grant No. 51578020), the research was published in the Journal of Harbin Institute of Technology, Vol. 52, No. 6, pp. 149-159. The work is directly inspired by mega column designs in two landmark Chinese skyscrapers: the China Zun Tower in Beijing and the Tianjin 117 Tower.

Test Specimens and Prototype Background

The experimental program included four large-scale model specimens representing two distinct mega column configurations:

The specimens underwent uniaxial cyclic eccentric compression loading to evaluate damage evolution, load-bearing capacity, deformation recovery capability, and stiffness degradation characteristics.

Key Experimental Findings

The most significant finding is that incorporating a circular steel tube within the corner cavity of the octagonal 13-cavity mega column effectively retards damage progression and substantially enhances both load-bearing capacity and deformation capacity. This represents a practical strengthening strategy for complex multi-cavity configurations.

Theoretical Analysis and Design Formulas

The authors employed multi-national code provisions and fiber model methods to calculate N-M interaction curves and load-deformation curves for each specimen. The calculated results were generally conservative compared to experimental results.

A key contribution of the study is the proposed simplified correction method for calculating the unified compressive strength (fsc) of multi-cavity CFST columns, building upon:

• The N-M interaction curve calculation method from GB 50936 (Chinese code for CFST structures)
• Han Linhai's CFST constitutive relationship model
• Consideration of multi-cavity specific characteristics

The corrected formulas provide N-M curves and load-bearing capacities that agree well with experimental results, offering a practical design tool for multi-cavity CFST column design.

Steel Pipe and Welding Engineering Considerations

The fabrication of multi-cavity CFST mega columns involves significant steel pipe and welding challenges:

1. Multi-wall tube fabrication: The irregular cross-section requires either formed steel plates welded into shape or specialized tube-rolling technology capable of producing non-circular cross-sections.
2. Internal diaphragm welding: The 13 or 6 internal cavity walls require extensive internal welding, which is technically challenging due to limited access. Robotic welding or specialized welding procedures may be required.
3. Circumferential and longitudinal welds: The outer shell welds must achieve full penetration and maintain geometric accuracy to ensure proper concrete placement and uniform confinement.
4. Corner cavity reinforcement: The addition of circular steel tubes in corner cavities (as in specimen CZ-2) requires precise fitting and welding within confined spaces, demanding high-quality weld procedures.

Standards and Code Compliance

The study references GB 50936 (Code for Design of Concrete-Filled Steel Tubular Structures) as the primary Chinese standard. International standards relevant to multi-cavity CFST design include:

Engineering Practice Integration

The practical implications of this research for steel pipe manufacturing and construction include:

• Multi-cavity CFST mega columns require precision fabrication with tight dimensional tolerances (±2mm for cavity wall positions, ±1mm for wall thickness).
• Welding procedures must be qualified for the specific geometry, with particular attention to internal weld access and inspection.
• The corner cavity reinforcement strategy (circular tube insertion) represents a simple yet effective strengthening method that can be implemented during fabrication.
• Quality control should include full UT coverage of all internal welds, with MT or PT for surface defect detection.

Key Reflections and Study Insights

This research demonstrates that irregular cross-section multi-cavity CFST mega columns can achieve excellent mechanical performance under eccentric compression, with appropriate design considerations. The finding that corner cavity reinforcement significantly improves performance provides a practical and economical strengthening strategy.

From a steel pipe manufacturing perspective, the trend toward mega columns with complex cross-sections drives demand for advanced fabrication capabilities, including robotic welding, precision forming, and comprehensive NDT coverage. The proposed simplified fsc calculation method provides a practical tool for engineers, reducing the complexity of multi-cavity column design while maintaining accuracy.

The study also highlights the importance of scale effects in experimental research. The 1/12 and 1/13 scale ratios used in this study may introduce size effects that should be considered when extrapolating results to full-scale applications. Future research should include full-scale testing or validated numerical models with appropriate size-effect corrections.