Multi-Chamber Steel Tube Recycled Concrete Composite Short Column Axial Compression Parameter Analysis

Literature Overview

This paper by Deng Xisheng, Lin Shandong, Chen Yuwen, Yuan Kai, and Tang Yu, published in Science Technology and Engineering (2022, Vol. 22, No. 24), investigates a novel multi-chamber steel tube recycled concrete composite short column designed to address the corner protrusion problem of square-section columns while improving building space utilization. The research is supported by the National Natural Science Foundation of China (Youth Science Fund) and the Guangyuan Urban Investment Group Science and Technology Fund.

The fundamental innovation lies in the use of recycled concrete as the infill material within a multi-chamber steel tube configuration, creating a composite short column that combines the structural advantages of steel tube concrete (SRC) columns with the environmental benefits of recycled aggregate concrete. The multi-chamber configuration, formed by internal steel dividers within the outer steel tube, creates multiple concrete cells that improve the confinement efficiency and reduce the corner protrusion issue inherent in conventional square SRC columns.

Core Technical Content and Finite Element Methodology

The authors employed ABAQUS finite element software to conduct a comprehensive parametric analysis of the proposed composite short column. The numerical model was validated against experimental data from previous studies, ensuring the reliability of the simulation results. The finite element model accounts for the nonlinear material behavior of both the steel tube and the recycled concrete, including the confined concrete constitutive model, the steel tube plasticity model, and the interface interaction between the steel tube and concrete.

The parametric analysis focuses on three key variables: the recycled concrete replacement rate (the ratio of recycled aggregate to natural aggregate in the concrete mix), the recycled concrete compressive strength, and the steel tube wall thickness. For each parameter, multiple values were investigated to establish clear trends in the structural performance of the composite short column.

Parametric Analysis Results

The finite element analysis provides detailed load-displacement curves, ductility indices, and stiffness degradation patterns for each parametric combination. The results reveal important trends that have direct implications for structural design.

The load-bearing capacity of the composite short column increases substantially with both the recycled concrete strength and the steel tube wall thickness, but shows a decreasing trend with increasing replacement rate. This is consistent with the known reduction in compressive strength and elastic modulus of recycled aggregate concrete compared to natural aggregate concrete at equivalent mix designs.

The ductility and stiffness of the composite short column increase with steel tube wall thickness, as the thicker steel tube provides greater confinement pressure on the concrete core. However, both ductility and stiffness decrease with increasing replacement rate and higher recycled concrete strength. The decrease in ductility with higher concrete strength is attributed to the increased brittleness of the concrete material, which reduces the capacity for plastic deformation before failure.

Confinement Mechanism and Multi-Chamber Effect

The multi-chamber configuration introduces an interesting confinement mechanism that differs from conventional single-chamber SRC columns. The internal steel dividers create multiple concrete cells, each of which is confined by the surrounding steel walls. This multi-chamber arrangement provides several advantages:

1. The internal steel dividers act as additional confinement elements, increasing the overall confinement pressure on the concrete core compared to a single large chamber.
2. The reduced chamber dimensions minimize the corner protrusion effect, as the stress concentrations at the corners of each individual chamber are smaller than those in a large square section.
3. The multi-chamber configuration improves the material utilization efficiency, as the concrete is more uniformly confined throughout the cross-section.
4. The steel dividers provide additional load-bearing capacity through direct axial compression resistance.

However, the multi-chamber configuration also introduces challenges in terms of welding quality and construction complexity. The internal steel dividers must be welded to the outer steel tube with full-penetration groove welds to ensure structural integrity. The weld design should follow relevant standards such as GB 50661 or AWS D1.1, with appropriate weld sizing and inspection requirements.

Engineering Practice Considerations

For engineers considering the application of this multi-chamber SRC column in practice, several important considerations must be addressed:

1. The recycled concrete replacement rate should be carefully controlled based on the structural requirements and the availability of recycled aggregate. A replacement rate of 30-50% may provide an acceptable balance between environmental benefits and structural performance.
2. The steel tube wall thickness should be optimized to provide adequate confinement without excessive material usage. The wall thickness-to-diameter ratio should comply with relevant design codes such as GB 50936 or ACI 443.
3. The concrete placement within the multi-chamber configuration requires careful attention to ensure proper compaction in all chambers. The use of self-compacting concrete or appropriate vibration methods is essential to avoid voids and honeycombing.
4. The welding of internal steel dividers to the outer steel tube is a critical construction activity. Preheating may be required for thicker steel sections to prevent cold cracking, and post-weld inspection using ultrasonic testing (UT) or radiographic testing (RT) is mandatory for quality assurance.

Key Questions and Reflections

The research raises several important questions for further investigation. First, the long-term durability of recycled concrete within the steel tube confinement is a concern, particularly regarding the permeability of recycled aggregate concrete and its susceptibility to carbonation and chloride ingress. Second, the seismic performance of the multi-chamber SRC column under cyclic loading has not been investigated in this paper, which is a critical gap for practical application in earthquake-prone regions.

From a materials science perspective, the interfacial transition zone (ITZ) between the recycled aggregate and the cement paste is a critical factor in the mechanical properties of recycled concrete. The ITZ is typically weaker than the ITZ in natural aggregate concrete due to the porous and dusty surface of recycled aggregates, which affects the bond strength and overall concrete performance. The use of supplementary cementitious materials such as fly ash or silica fume may help improve the ITZ quality and enhance the mechanical properties of recycled concrete.

Summary and Study Insights

This paper provides valuable insights into the structural behavior of multi-chamber steel tube recycled concrete composite short columns under axial compression. The parametric analysis clearly demonstrates the influence of recycled concrete replacement rate, concrete strength, and steel tube wall thickness on the load-bearing capacity, ductility, and stiffness of the composite column. The findings offer practical guidance for engineers designing SRC columns using recycled concrete, emphasizing the importance of rational parameter selection to achieve an acceptable balance between environmental sustainability and structural performance. The multi-chamber configuration represents a promising approach to improving the confinement efficiency and space utilization of SRC columns, but further research on seismic performance and long-term durability is needed before widespread practical application.