Axial Compression Performance and Capacity Calculation of Recycled Aggregate Concrete Filled Steel Tube Columns

Literature Overview

The study by Chen Zongping, He Tianyu, Xu Jinjun, and Liu Xiang from Guangxi University, published in the Journal of Guangxi University (Natural Science Edition) in 2015, investigates the axial compression performance of circular steel tube recycled aggregate concrete (RAC) columns. The research is funded by the National Natural Science Foundation of China. This work is of considerable practical importance given the global push toward sustainable construction and the increasing use of recycled aggregates in concrete applications.

Core Technical Content

The researchers first validated their numerical simulation approach using ABAQUS finite element software by comparing simulation results with experimental test data. After confirming the feasibility of the numerical method, they extended the analysis by creating 30 additional numerical models to systematically examine the influence of steel ratio, slenderness ratio, and cross-sectional area on the structural behavior of steel tube recycled concrete columns.

The parametric study reveals that increasing the slenderness ratio significantly reduces the ultimate load capacity, while increasing the steel ratio significantly improves ductility and energy dissipation capacity. Increasing the cross-sectional area benefits the load capacity, but the improvement is not pronounced. The study also shows that the current code formulas produce conservative results compared to both experimental and simulated values, indicating that the existing design provisions do not adequately account for the specific behavior of recycled aggregate concrete in steel tube confinement.

Key Technical Parameters and Findings

The researchers introduced the recycled coarse aggregate replacement rate as a correction factor into the existing code formulas. The modified calculation model provides a more accurate prediction of the ultimate load capacity of steel tube recycled concrete columns and offers practical value for design calculations.

Engineering Practice Implications

For the steel tube fabrication and welding aspects, the use of recycled aggregate concrete does not fundamentally change the steel tube manufacturing requirements, but it does introduce additional considerations. The concrete placement in steel tubes filled with recycled aggregate concrete may require more careful compaction due to the potentially coarser and more irregular particle size distribution of recycled aggregates. The steel tube inner surface preparation and the concrete pouring method must ensure full filling and adequate bonding between the steel tube and the recycled concrete core.

The welding quality of the steel tube segments remains critical for the structural performance of the columns. Any weld defects can create stress concentration points that may initiate buckling or fracture under compressive loading. The residual stresses from welding can interact with the compressive stresses in the column, potentially reducing the effective buckling load. Post-weld stress relief treatment may be beneficial for columns subjected to high compressive loads, particularly those with high slenderness ratios where buckling is the governing failure mode.

The modified calculation formulas developed in this study are directly applicable to the design of columns using recycled aggregate concrete. Engineers should note that the replacement rate of recycled aggregates should be considered as a design parameter, and the appropriate correction factor should be applied based on the specific replacement rate used in the project.

Study Insights and Reflections

This research makes a valuable contribution to sustainable construction by providing a reliable design methodology for steel tube recycled aggregate concrete columns. The validation of the numerical model through experimental comparison, followed by systematic parametric analysis, represents a rigorous research methodology. The finding that current code formulas are conservative is encouraging, as it suggests that the use of recycled aggregates does not significantly compromise structural safety when properly designed. However, the study focuses primarily on axial compression, and the behavior of recycled concrete-filled steel tube members under combined loading conditions, including bending and shear, requires further investigation. The work also highlights the importance of incorporating material sustainability factors into structural design formulas, which is a growing trend in modern engineering practice. The modified formulas provide a practical tool for engineers to confidently specify recycled aggregate concrete in steel tube column applications, contributing to waste reduction and resource conservation in the construction industry.