Eccentric Compression Behavior of Square Concrete-Filled Double-Skin Steel Tubular Columns with Ceramic Recycled Concrete

Literature Overview and Research Background

This paper by Huang Hong et al. (2023), published in Progress in Steel Building Structures (Vol. 25, No. 4, pp. 37-45), investigates the eccentric compression mechanical properties of square concrete-filled double-skin steel tubular (CFDST) columns incorporating ceramic recycled concrete. The research is supported by the National Natural Science Foundation of China (51868020) and was conducted at East China Jiaotong University. The study includes 16 test specimens with varying parameters and corresponding finite element simulations.

From a steel pipe manufacturing perspective, this research addresses an important sustainability challenge: the integration of recycled materials into structural steel pipe applications while maintaining or improving structural performance. Ceramic recycled concrete utilizes waste ceramic fragments as coarse aggregate, offering a circular economy approach to construction materials.

Core Technical Content and Key Findings

Test Matrix and Specimen Configuration

The experimental program included 16 specimens with the following variable parameters:

All specimens exhibited elastoplastic instability failure modes, which is characteristic of slender columns under eccentric loading where buckling governs the failure mechanism rather than pure compression or bending.

Key Performance Findings

1. Ultimate Load Capacity: The ultimate load capacity and flexural stiffness decreased with increasing slenderness ratio and eccentricity, as expected from classical column theory. However, the CFDST specimens demonstrated higher ultimate load capacity compared to their solid counterparts, which is an important finding for design optimization.
2. Ceramic Recycled Concrete Performance: Columns with ceramic recycled concrete exhibited good ductility and deformation capacity, with ultimate load capacity approaching that of columns with ordinary concrete. This is a significant result suggesting that ceramic recycled concrete is a viable substitute for natural aggregate concrete in CFDST applications.
3. Finite Element Validation: The numerical simulations using finite element software produced load-midspan deflection curves that closely matched experimental results, confirming the reliability of the modeling approach.

Design Code Comparison

The authors compared experimental results with predictions from two design standards:

• T/CCES 7-2020 for CFDST specimens
• DB 36/J001-2007 for solid specimens

Both codes provided predictions close to experimental values, indicating that existing design methodologies can be extended to CFDST columns with ceramic recycled concrete with appropriate modifications.

Steel Pipe Manufacturing and Welding Implications

Material Selection for Double-Skin Tubes

The research confirms that double-skin steel tube configurations can effectively utilize recycled concrete while maintaining structural performance. For pipe manufacturers, this opens opportunities to supply specialized double-wall steel tube products for sustainable construction projects. The outer and inner tubes in CFDST columns require careful dimensional control to ensure uniform concrete annular thickness, which directly affects the composite action and load distribution.

Welding Quality Requirements

Square CFDST columns require precise welding at the corners and longitudinal joints of both the outer and inner tubes. The welding quality is particularly critical because:

• Weld defects can initiate stress concentrations under eccentric loading
• The composite action between steel and concrete depends on the integrity of tube connections
• Internal tie bars connecting the outer and inner tubes must be welded with full penetration

Engineers should apply welding quality criteria consistent with standards such as GB 50661 or ISO 3834, with enhanced inspection requirements for internal welds that are difficult to access after assembly.

Residual Stress Considerations

From a welding metallurgy perspective, the residual stresses induced by welding can affect the buckling behavior of CFDST columns under eccentric compression. The interaction between weld-induced residual stresses and the elastoplastic instability failure mode observed in the tests warrants further investigation. Prequalification of welding procedures with attention to residual stress management through post-weld treatment may be beneficial for critical applications.

Study Insights and Engineering Implications

This research demonstrates that ceramic recycled concrete is a technically viable material for CFDST column applications, offering environmental benefits without significant compromise in structural performance. The finding that CFDST configurations outperform solid columns in ultimate load capacity is particularly encouraging, as it suggests that the double-skin concept provides additional structural redundancy.

For the steel pipe industry, this research supports the development of standardized double-wall steel tube products for sustainable construction. Pipe manufacturers should consider offering CFDST-specific tube pairs with matched dimensional tolerances and compatible material grades to facilitate the adoption of this technology. The successful application of existing design codes (with minor adjustments) provides confidence that the transition to CFDST with recycled concrete can proceed without major regulatory barriers.

The elastoplastic instability failure mode observed across all specimens highlights the importance of slenderness ratio control in design. Engineers specifying steel tubes for CFDST applications should carefully evaluate the effective slenderness ratio, accounting for the boundary conditions and the composite action between steel and concrete, to ensure adequate safety margins against buckling failure.