Zhuojin Pipe Fitting Co., LtdEccentric Compression Performance of Steel Tube Recycled Concrete Short Columns
Literature Overview
This study by Zhang Weidong, Wang Zhenbo, and Ding Haijun (2011), published in the Journal of Daqing Petroleum Institute, investigates the eccentric compression behavior of steel tube recycled concrete (STRC) short columns. The research was funded by the Ministry of Housing and Urban-Rural Development of China and the Jiangsu Provincial Department of Education. Fifteen specimens with varying recycled aggregate replacement rates were tested under eccentric loading, and their macroscopic deformation characteristics, load-strain relationships, failure modes, and failure mechanisms were analyzed and compared with conventional steel tube concrete (SRC) columns.
Core Technical Findings
The key finding is that recycled aggregate replacement rate is the primary factor influencing eccentric compression capacity of STRC columns. Under identical conditions, bearing capacity decreases with increasing replacement rate, with a maximum reduction of approximately 20%. The core concrete shrinkage rate increases with higher replacement rates, which reduces the lateral support effect on the steel tube, thereby accelerating local yielding of the steel tube and lowering ultimate bearing capacity.
| Parameter | Conventional SRC | STRC (Low Replacement) | STRC (High Replacement) |
|---|---|---|---|
| Bearing capacity relative to SRC | 100% | 85-95% | 75-80% |
| Core concrete shrinkage | Baseline | Moderate increase | Significant increase |
| Steel tube local yielding onset | Later stage | Slightly earlier | Noticeably earlier |
| Failure mode | Progressive | Similar but accelerated | Accelerated with premature tube yielding |
Failure Mechanism Analysis
The failure mechanism follows a progressive sequence: initial elastic deformation transitions to concrete cracking, followed by steel tube local buckling, and finally composite failure. The critical insight is that recycled concrete's higher shrinkage creates a gap between the core concrete and the inner steel tube surface over time. This gap eliminates the beneficial triaxial confinement that normally develops between steel tube and concrete in conventional SRC members.
From a materials science perspective, recycled coarse aggregate possesses higher porosity and weaker interfacial transition zones compared to natural aggregate. The recycled aggregate retains old mortar films, creating weak interfaces that reduce overall concrete compressive strength and increase shrinkage. This is particularly detrimental in eccentric compression where the confinement effect is already asymmetrically distributed.
Engineering Practice Implications
For engineers specifying steel tube recycled concrete members in practice, the following considerations emerge:
- Replacement rates above 60% should be treated with caution for load-bearing members subjected to eccentric loading
- The 20% capacity reduction must be factored into structural design safety margins
- Shrinkage-induced debonding between steel tube and concrete should be monitored during service life
- Additional confinement measures such as internal spiral reinforcement may partially compensate for the loss of steel tube confinement
The study validates that steel tube recycled concrete remains viable for structural applications but requires careful calibration of design parameters based on the specific replacement rate employed.
Study Insights and Reflections
This research bridges the gap between sustainable construction goals (recycled aggregate utilization) and structural safety requirements. From a pipe manufacturing perspective, the findings reinforce that steel tube geometry and wall thickness play critical roles in composite member performance, and that the interaction between tube and infill material is fundamentally different when the infill material has degraded mechanical properties. Engineers should not assume that replacing natural aggregate with recycled aggregate is a straightforward substitution without corresponding adjustments to design parameters and quality control protocols. The work provides valuable experimental data for calibrating finite element models and for developing practical design guidelines for recycled aggregate steel tube concrete structures.