Axial Compression Performance of Multi-Chamber Steel Tube Recycled Concrete Composite Short Columns

Literature Overview

The paper by Deng Xisheng, Xiang Yingming, Chen Yuwen, and Tang Yu, published in Science Technology and Engineering in 2021, presents a numerical investigation of a novel multi-chamber steel tube recycled concrete composite short column. This research, supported by the National Natural Science Foundation of China Youth Science Fund (Project 51808470) and the Guangyuan Urban Investment Group Science and Technology Fund, addresses two pressing challenges in modern construction: the efficient use of recycled concrete aggregates and the structural optimization of concrete-filled steel tube (CFST) columns through multi-chamber design. The study employs ABAQUS finite element analysis to examine failure modes, load-displacement behavior, interaction mechanisms, and axial compression performance degradation.

Innovative Structural Configuration

The multi-chamber steel tube recycled concrete composite short column represents a hybrid structural system that combines three distinct structural elements:

A multi-chamber steel tube outer shell, which divides the cross-section into multiple compartments
A recycled concrete core filling the internal chambers
An external reinforced concrete jacket surrounding the steel tube

This configuration leverages the complementary strengths of each component: the steel tube provides confinement and lateral restraint, the recycled concrete contributes compressive strength while utilizing waste materials, and the external reinforced concrete jacket enhances overall structural integrity and provides additional load-bearing capacity. The use of recycled concrete is particularly significant given the growing global concern about construction and demolition waste disposal and the environmental benefits of aggregate recycling.

Finite Element Analysis Methodology

The ABAQUS-based numerical model incorporated several advanced modeling techniques:

Modeling Aspect	Implementation	Purpose
Material models	Concrete Damage Plasticity (CDP) for recycled concrete; elastic-plastic for steel	Capture nonlinear material behavior including cracking and crushing
Contact pairs	Steel tube to core recycled concrete; steel tube to external RC	Model frictional interaction and load transfer between components
Failure criteria	Concrete cracking and crushing; steel yielding and local buckling	Predict progressive failure mechanisms
Analysis type	Static general with geometric nonlinearity	Account for large deformations and buckling effects

Key Results and Performance Characteristics

Elastic Range and Load-Displacement Behavior

The multi-chamber steel tube recycled concrete composite short column exhibited a notably long elastic range under axial compression, indicating that the composite action between the steel tube, recycled concrete, and external reinforced concrete effectively delays the onset of nonlinear behavior. The ultimate bearing capacity was found to be high relative to conventional CFST columns of similar cross-sectional dimensions, attributed to the enhanced confinement effect provided by the multi-chamber geometry.

Interaction Mechanisms

A critical finding concerns the distribution of contact stresses at the interfaces between structural components:

The contact stress between the steel tube and the core recycled concrete concentrates at the four corners and along the short sides of the chamber cross-section.
The contact stress between the steel tube and the external reinforced concrete similarly concentrates at the corners and short edges.
Along the long sides of the chambers, contact stress is relatively insignificant.

This non-uniform stress distribution has important implications for the design of multi-chamber CFST columns. The concentration of contact stresses at corners and short sides suggests that these regions experience the most intense confinement interaction, while the long sides contribute less to the composite action. This observation is consistent with the general principle that contact pressure between a steel tube and concrete core is highest where the tube curvature is greatest relative to the concrete surface.

Ductility and Stiffness

The composite column maintained good ductility, energy dissipation capacity, and stiffness throughout the loading process. The multi-chamber configuration appears to enhance these properties by providing multiple independent confinement zones that can fail progressively rather than simultaneously, thereby preventing catastrophic structural collapse.

Recycled Concrete Considerations from a Materials Perspective

From a metallurgical and materials engineering standpoint, the use of recycled concrete in structural applications raises several important considerations:

Aggregate quality variability: Recycled aggregates typically exhibit higher water absorption, lower density, and greater variability in mechanical properties compared to natural aggregates. This variability affects the concrete's compressive strength, modulus of elasticity, and durability.
Interfacial transition zone (ITZ): The ITZ between recycled aggregates and the cement paste is generally weaker than in natural aggregate concrete due to residual mortar adhering to the recycled aggregate surface. This weak zone can affect the bond between the recycled concrete and the steel tube.
Long-term durability: Recycled concrete may exhibit accelerated carbonation and chloride ingress due to the porous nature of recycled aggregates and the weaker ITZ. In a CFST column, the steel tube provides some protection, but the external reinforced concrete jacket is exposed to environmental attack.
Creep and shrinkage: Recycled concrete typically shows higher creep and shrinkage values, which can affect the long-term performance of the composite column, particularly the interaction between the steel tube and concrete core.

Engineering Practice Implications

The study provides valuable insights for engineers considering multi-chamber CFST columns with recycled concrete in practical applications:

The multi-chamber design effectively enhances the structural performance of recycled concrete columns, making recycled concrete more viable for structural use despite its generally lower mechanical properties.
The concentration of contact stresses at corners and short sides should be considered in the design of chamber geometries. Optimizing the chamber aspect ratio could potentially distribute contact stresses more uniformly.
The long elastic range and high ultimate capacity make this configuration suitable for applications requiring high load capacity with predictable deformation behavior, such as core columns in high-rise buildings or support columns in industrial facilities.
The use of recycled concrete reduces the environmental impact of construction while maintaining structural performance, aligning with sustainable construction goals.

Study Insights and Reflections

This research demonstrates that innovative structural configurations can effectively compensate for the lower inherent quality of recycled materials, enabling their use in structural applications that would otherwise require virgin materials. The multi-chamber steel tube design creates a synergistic effect where the steel confinement enhances the recycled concrete's performance while the composite action between multiple structural layers provides redundancy and ductility.

The finite element analysis approach used in this study is particularly valuable for exploring design variations that would be prohibitively expensive to test experimentally. The validated numerical model can be extended to investigate different chamber geometries, recycled concrete strengths, steel tube thicknesses, and loading conditions, providing a comprehensive design database for engineering practice.

The study also highlights the importance of understanding interaction mechanisms in composite structures. The non-uniform distribution of contact stresses is a common feature of all CFST systems, but the multi-chamber geometry introduces additional complexity that must be carefully considered in design.

Reference Value and Outlook

The findings contribute to the growing body of knowledge on recycled concrete structural applications and multi-chamber CFST systems. Future research should include experimental validation of the numerical predictions, investigation of long-term durability, and development of simplified design methods. The integration of recycled materials into structural systems through innovative design approaches represents a promising pathway toward sustainable construction, and this study provides a solid technical foundation for advancing this goal.