Axial Compression Behavior of Combined Cross-Shaped Steel Tube Concrete Columns

Literature Overview

This research by Xie Li, Fang Xu, Chen Mengcheng, Yang Chao, and Huang Hong from East China Jiaotong University proposes a novel composite column design combining square steel tubes and channel steel welded to form a multi-chamber cross-shaped steel tube concrete (STC) column. Published in Industrial Construction, Volume 53, Issue 2, 2023, the study was supported by the National Natural Science Foundation of China (Grant No. 51378206) and the Jiangxi Provincial Natural Science Foundation (Grant No. 20171BAB216044).

Core Technical Findings

The authors designed and tested five specimens with varying lengths and cross-sectional forms to evaluate the axial compression performance of this innovative column type. The combined cross-shaped STC column was inspired by the design philosophy of reinforced concrete irregular columns, adapted here for steel tube concrete applications.

The final failure mode of the specimens was characterized by multiple small bulges distributed along the column length, rather than a single localized failure. This distributed buckling pattern indicates effective confinement by the steel tube on the core concrete.

Technical Interpretation

The multi-chamber configuration created by welding square steel tubes with channel steel provides several structural advantages. Each chamber acts as an independent confined concrete unit, yet the overall section behaves as a unified structural member. The cross-shaped geometry offers improved biaxial bending resistance compared to conventional rectangular STC columns, which is particularly beneficial for columns subjected to combined axial and flexural loading.

The confinement mechanism in this composite section is more complex than in a simple circular or rectangular STC column. The channel steel members provide additional lateral restraint at the junction regions, while the square steel tubes confine the concrete within their respective chambers. This dual confinement system delays the onset of concrete crushing and enhances post-peak deformation capacity.

Standards and Design Formula Development

The authors proposed an axial compression capacity calculation formula based on existing code provisions, adapted for the combined cross-shaped geometry. The theoretical values obtained from this formula showed good agreement with experimental results, suggesting that the formula can serve as a practical design tool. The formula likely incorporates the confined concrete strength enhancement factor, adjusted for the multi-chamber geometry, and accounts for the contribution of both the steel tube and channel steel components.

A key consideration in applying such formulas is the effective confinement pressure distribution. Unlike a circular STC column where confinement is uniform, the combined cross-shaped section exhibits non-uniform confinement, with higher confinement at the central junction region and lower confinement at the outer limbs. The proposed formula must adequately capture this non-uniformity to maintain accuracy.

Engineering Practice Implications

For structural engineers designing multi-story buildings or bridge piers, this combined cross-shaped STC column offers a promising alternative to conventional column sections. The improved capacity-to-weight ratio and enhanced ductility make it suitable for seismic design applications where energy dissipation through plastic deformation is desired. The multi-chamber design also facilitates formwork and concrete placement, as each chamber can be cast independently or sequentially.

However, practical fabrication challenges must be addressed. The welding of square steel tubes to channel steel members introduces residual stresses and potential weld defects that could affect the overall structural performance. Quality control during fabrication, including weld inspection and dimensional verification, is essential to ensure the as-built column matches the design assumptions.

Reflection and Key Questions

The study raises important questions about the long-term durability of the multi-chamber STC column, particularly regarding corrosion protection at the weld interfaces and the potential for differential concrete shrinkage between chambers. Additionally, the seismic performance under cyclic loading was not investigated, which limits the applicability of the findings to seismic design without further research. The interaction between the channel steel and the concrete during large deformations also warrants more detailed study, as the channel steel may experience local buckling of its web or flanges before the full confinement capacity is realized.

Concluding Remarks

This research presents a creative and technically sound approach to enhancing the performance of steel tube concrete columns through geometric innovation. The combination of square steel tubes and channel steel to form a multi-chamber cross-shaped section demonstrates significant potential for improving both capacity and ductility. The proposed design formula provides a practical basis for engineering applications, though further research on cyclic loading behavior, fatigue performance, and long-term durability would strengthen the foundation for widespread adoption in seismic regions.