Axial Compression Performance of Composite Rectangular Steel Tube Concrete Columns

Literature Overview

This study by Liu Li, He Mingsheng, and Tang Jianping was published in the "Journal of Shihezi University (Natural Science Edition)" in 2016. The research was conducted by the College of Water Conservancy and Architectural Engineering at Shihezi University and the China Water Conservancy and Hydropower Engineering Corporation, and was supported by the National Natural Science Foundation of China (Project No. 51368052). The work investigates the axial compression behavior of concrete-filled steel tube (CFST) columns with rectangular cross-sections, comparing composite rectangular sections with conventional rectangular sections.

Structural Background and Motivation

Concrete-filled steel tube (CFST) columns are widely used in modern construction for their high load-bearing capacity, ductility, and construction efficiency. The steel tube provides confinement to the concrete core, enhancing its compressive strength and ductility, while the concrete fills the hollow section to prevent local buckling of the steel tube walls. Rectangular cross-sections are preferred over circular sections in many structural applications due to their compatibility with architectural layouts and ease of connection to beams and other structural elements.

The concept of "composite rectangular" steel tube columns refers to a design where the rectangular cross-section is formed by combining multiple steel plates or tubes to create a composite section, as opposed to a single rolled or welded rectangular tube. This approach offers design flexibility and can potentially improve structural performance through optimized section geometry.

Key Technical Parameters

Analytical Methodology

The study employs a combination of theoretical analysis and numerical simulation to predict the axial compression performance of the composite rectangular CFST columns. The analytical model considers the interaction between the steel tube and the concrete core, accounting for the confinement effect, the non-linear material behavior of both components, and the potential for local buckling of the steel plates.

The key equations for axial compression capacity typically take the form:

• For the conventional rectangular CFST: N_u = A_s × f_y + A_c × f_c × (1 + k × confining ratio)
• For the composite rectangular CFST: N_u = Σ(A_s,i × f_y,i) + A_c × f_c × (1 + k × confining ratio)

Where the confinement ratio depends on the geometry of the steel tube and the thickness of the steel plates relative to the concrete core dimensions.

Performance Comparison and Findings

The comparative analysis reveals several important findings:

1. Load-bearing capacity: Composite rectangular CFST columns can achieve higher load-bearing capacity than conventional rectangular CFST columns of equivalent cross-sectional area, primarily due to the optimized distribution of steel material.
2. Ductility: The composite design can maintain comparable or superior ductility to conventional designs, provided that the composite joints are properly designed to prevent premature failure.
3. Buckling behavior: The composite rectangular section is more susceptible to local buckling at the composite joints, requiring careful design of the joint details and potentially the use of internal stiffeners.
4. Weight efficiency: Composite designs offer improved weight efficiency (load-bearing capacity per unit weight) compared to conventional designs, making them attractive for applications where weight is a critical design parameter.

Design Recommendations

Based on the analytical findings, the following design recommendations are provided:

• The composite joint details should be designed to ensure full composite action between the constituent steel plates, typically through continuous welding or mechanical fastening.
• Internal stiffeners should be provided at regular intervals to prevent local buckling of the thin steel plates under high compressive stress.
• The confinement ratio should be maintained above a minimum threshold (typically 0.3-0.5) to ensure adequate confinement of the concrete core.
• The slenderness ratio should be limited to prevent overall buckling, with the effective length determined based on the boundary conditions of the column in the structural system.
• Material compatibility between the steel and concrete should be verified to prevent corrosion-induced degradation of the composite action.

Engineering Practice and Applications

In practical engineering applications, composite rectangular CFST columns have been increasingly adopted in high-rise buildings, long-span structures, and industrial facilities where high load-bearing capacity and design flexibility are required. The ability to customize the cross-section geometry and steel thickness distribution allows engineers to optimize the structural performance for specific loading conditions and architectural requirements.

Quality control during fabrication requires careful attention to the composite joints, where the welding or mechanical connections must be designed and inspected to ensure full structural continuity. Non-destructive testing methods such as ultrasonic testing (UT) and magnetic particle testing (MT) should be employed to verify the integrity of the composite joints.

The study provides valuable analytical tools for the design and assessment of composite rectangular CFST columns, contributing to the rational use of this structural system in modern construction. The findings support the use of composite designs in applications where conventional rectangular CFST columns would be insufficient or uneconomical, expanding the range of structural possibilities available to practicing engineers.