Eccentric Compression Performance of Steel Tube High-Strength Recycled Concrete Composite Columns

Literature Overview

The paper by Niu Haicheng, Shang Tianyu, Li Bohan, and Huang Minghui, published in the journal "Progress in Steel Building Structures" in 2024, presents an experimental and analytical investigation of the eccentric compression behavior of steel tube concrete composite columns incorporating high-strength recycled concrete. Funded by the National Natural Science Foundation of China and Henan Provincial Key R&D programs, this study represents a timely contribution to the field of sustainable structural engineering, addressing the dual challenges of structural performance optimization and waste material utilization. The authors conducted eccentric compression tests on six composite columns with varying concrete types and eccentricity ratios, and validated their findings against calculation formulas from the Technical Specification for Steel Tube Concrete Composite Columns (T/CECS 188-2019).

Experimental Program and Test Results

The experimental program comprised six composite columns tested under eccentric compression loading, with concrete type and eccentricity ratio serving as the primary test parameters. The columns incorporated both ordinary concrete and high-strength recycled concrete as the core fill material, enclosed within steel tube outer shells that provided lateral confinement. The test results revealed that both recycled concrete composite columns and ordinary concrete composite columns exhibited three distinct loading stages: elastic stage, cracked stage, and failure stage. The failure characteristics included crushing and spalling of the outer concrete cover, buckling of longitudinal reinforcement, and outward bulging of stirrups.

The key finding regarding recycled concrete was that while the initial stiffness and deformation capacity were somewhat reduced compared to ordinary concrete columns, the ultimate bearing capacity was slightly higher. This counterintuitive result can be attributed to the different stress-strain behavior of recycled concrete under confinement, where the aggregate interlock and interface transition zone characteristics influence the post-peak behavior differently than in unconfined conditions.

Bearing Capacity Calculation Model

The authors validated the bearing capacity of sixteen steel tube concrete composite columns against calculation formulas from T/CECS 188-2019 and related scholarly proposals. The analysis revealed that the eccentric compression bearing capacity calculation must account for both the inherent bearing capacity of the steel tube itself and the confining effect of the steel tube on the core concrete. As the eccentricity ratio increases, the initial stiffness and bearing capacity decrease rapidly, while the displacement ductility coefficient increases significantly. The neutral axis shifts progressively toward the compression zone, and the agreement with the plane section assumption diminishes as the eccentricity grows.

The practical implication of this finding is that existing calculation models may need modification to accurately predict the behavior of recycled concrete composite columns, particularly at higher eccentricity ratios where the nonlinear interaction between the steel tube, concrete core, and reinforcing steel becomes more pronounced. The confining effect of the steel tube, which is a well-established mechanism in conventional concrete-filled steel tube columns, appears to interact differently with recycled concrete due to the altered aggregate properties and interfacial characteristics introduced by the recycling process.

Engineering Practice and Sustainability Implications

The use of recycled concrete in composite columns represents a significant step toward sustainable construction practices, diverting construction and demolition waste from landfills and reducing the demand for virgin aggregate materials. However, the engineering community must ensure that the structural performance of recycled concrete composite members meets or exceeds that of conventional alternatives. The findings of this study provide encouraging evidence that high-strength recycled concrete can be successfully employed in composite column applications, with bearing capacity comparable to or slightly exceeding that of ordinary concrete counterparts.

For quality control purposes, the production and inspection of recycled concrete require additional attention to aggregate quality, water-cement ratio control, and mix proportion optimization. The interface transition zone between recycled aggregate and cement paste is a critical region that influences the mechanical properties of the concrete and, consequently, the performance of the composite column. Non-destructive testing methods such as ultrasonic pulse velocity testing and rebound hammer testing should be employed during construction to monitor the quality of the concrete placement and identify potential defects that could compromise the structural integrity.

Study Insights and Outlook

This research contributes valuable experimental data and analytical insights to the growing body of knowledge on recycled concrete composite structures. The finding that recycled concrete columns can achieve comparable or slightly superior bearing capacity, despite reduced initial stiffness, challenges the prevailing perception that recycled materials inherently compromise structural performance. For engineers designing sustainable structures, this work provides the technical justification to incorporate recycled concrete into composite column systems, subject to appropriate design modifications and quality assurance measures. Future research should address long-term durability, including carbonation resistance, chloride ingress, and freeze-thaw performance of recycled concrete under steel tube confinement, as these factors will ultimately determine the service life and maintenance requirements of such structures in aggressive environments.