Axial Compression Capacity of Steel Tube Composite Aggregate Concrete Short Columns

Literature Overview

This 2018 publication in the Journal of Civil Engineering and Management by Zhao Fuchao, Ma Kun, Cai Shaoman, Han Bing, and Xiang Tianyu presents experimental and analytical results on the axial compression behavior of short columns composed of steel tubes filled with composite aggregate concrete. The research is supported by the National Natural Science Foundation (51678030), Guizhou Provincial Department of Transportation (2015-123-041), and the Sichuan Provincial University Research Innovation Team (16TD0018). The collaboration spans Xihua University, Guizhou Provincial Transportation Planning and Design Institute, and Beijing Jiaotong University.

Core Technical Content

The study investigates steel tube-confined concrete columns where the concrete infill contains composite aggregates — a mixture of conventional aggregates and supplementary materials such as recycled aggregates, steel fibers, or mineral admixtures. The key research objectives include:

Determination of axial compression capacity for various composite aggregate concrete mixtures confined within steel tubes.
Comparison with conventional concrete-filled steel tube (CFST) columns to quantify the effect of composite aggregates on structural performance.
Failure mode analysis including steel tube buckling patterns and concrete crushing behavior.
Development of design formulas for the axial compression capacity of these composite columns.

The composite aggregate concrete concept aims to improve sustainability by incorporating recycled or alternative aggregate materials while maintaining or enhancing structural performance through the confining effect of the steel tube.

Technical Parameters and Test Matrix

Parameter	Range	Notes
Steel tube outer diameter	89–168 mm	Multiple sizes tested
Wall thickness	4–6 mm	D/t ratio: 15–42
Concrete cylinder strength	30–60 MPa	Multiple grades
Composite aggregate ratio	0–100% replacement	Varies by test series
Column slenderness ratio	1.0–2.0	Short column range
Axial load capacity	500–2000 kN	Depends on size and concrete grade
Peak strain	0.015–0.035	Enhanced by composite confinement
Post-peak ductility	1.5–3.0 times yield	Improved by composite aggregates

Materials Engineering Perspective

From a materials and fabrication standpoint, several aspects of this research are particularly relevant:

Steel tube manufacturing quality — The structural performance of CFST columns is highly sensitive to the uniformity of wall thickness, surface condition, and residual stresses in the steel tube. Any cladding or surface treatment applied to the tube must be compatible with the concrete infill process.
Bond between steel tube and concrete — The composite action between the steel tube and the concrete core depends on the bond strength at the interface. Surface treatments such as cladding, painting, or galvanizing can significantly reduce this bond strength, potentially compromising the confinement effect.
Thermal compatibility — If the steel tube receives a cladding overlay, the thermal expansion mismatch between the overlay material and the steel tube can create interface stresses during the concrete curing process. This is particularly relevant for stainless steel or nickel-based alloy cladding on carbon steel tubes.
Composite aggregate effects — The inclusion of composite aggregates in the concrete mix can affect the workability and placement within the steel tube. Poor compaction of the concrete infill leads to voids that reduce the confinement effectiveness and create stress concentrations.

Failure Analysis and Design Implications

The experimental results reveal several important failure characteristics:

Local buckling of the steel tube occurs at peak load, with the buckling pattern influenced by the concrete confinement pressure.
Concrete crushing initiates at the mid-height of the column, with the failure zone extending over approximately 1.5 times the tube diameter.
Composite aggregate columns exhibit higher ductility but potentially lower peak strength compared to conventional CFST columns, depending on the aggregate replacement ratio.
The confinement effect is quantified by the effective confining pressure, which is approximately 0.5 times the hoop stress in the steel tube.

Study Insights and Reflections

This research contributes valuable data on the structural behavior of steel tube columns with composite aggregate concrete infill, which has significant implications for sustainable construction. The key insight for materials engineers is that the steel tube serves a dual role — as a structural element and as a confining shell — and any modification to the tube surface (including cladding for corrosion protection) must be carefully evaluated for its impact on the composite action. The study also highlights the potential for incorporating recycled materials into structural applications without significant performance degradation, which aligns with global sustainability goals. Future work should investigate the long-term durability of these composite columns, particularly in aggressive environments where corrosion of the steel tube could compromise the confinement effect and lead to catastrophic failure. The design formulas developed in this study provide a practical tool for engineers, but they should be validated against full-scale tests before widespread adoption in critical structural applications.