Zhuojin Pipe Fitting Co., LtdBending Performance of Stainless Steel Tube Recycled Concrete Composite Members
Literature Overview
This research by Yang Youfu and Ma Guoliang (2013), published in the Journal of Dalian University of Technology, investigates the flexural behavior of stainless steel tube recycled concrete (RAC) composite members. The study is conducted at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, and is supported by the National Natural Science Foundation of China (Grant 51121005) and the Central University Basic Scientific Research Funds (Grant DUT12ZD215).
Experimental Program and Test Configuration
The test program comprises 14 specimens: 12 stainless steel tube RAC specimens and 2 stainless steel tube normal concrete (NC) comparison specimens. The test matrix examines two primary variables: cross-section type and recycled aggregate replacement rate. All specimens are subjected to four-point bending tests to evaluate flexural capacity, load-deflection behavior, and failure modes.
| Specimen Group | Cross-Section Type | RAC Replacement Rate | Quantity |
|---|---|---|---|
| Comparison | Stainless steel tube + NC | 0% | 2 |
| Test Group A | Stainless steel tube + RAC | 30% | 3 |
| Test Group B | Stainless steel tube + RAC | 50% | 3 |
| Test Group C | Stainless steel tube + RAC | 70% | 3 |
| Test Group D | Stainless steel tube + RAC | 100% | 3 |
Key Technical Findings
The bending performance of stainless steel tube RAC members is fundamentally similar to that of stainless steel tube NC members in terms of failure mode and load-deflection characteristics. However, a progressive reduction in flexural capacity is observed with increasing recycled aggregate replacement rate. The failure modes remain consistent across all specimens, characterized by yielding of the stainless steel tube followed by crushing of the concrete core, with the stainless steel tube providing effective confinement to the RAC core.
The load-deflection curves exhibit elastic, elastic-plastic, and plastic stages, with the transition points shifting slightly with increasing RAC replacement rate. The post-peak behavior demonstrates that the stainless steel tube continues to provide significant load-carrying capacity even after concrete crushing, confirming the ductile nature of the composite system.
Constitutive Modeling and Finite Element Verification
The authors developed a theoretical model based on ABAQUS finite element software to simulate the bending behavior of stainless steel tube RAC members. The constitutive relationships for both the stainless steel and the RAC core were established based on material characterization tests. The finite element model incorporates:
- Shell elements for the stainless steel tube with elastic-plastic material model
- Solid elements for the RAC core with confined concrete model
- Contact interaction between steel tube and concrete core
- Nonlinear geometric and material behavior
The simulation results show good agreement with experimental data, validating the modeling approach and constitutive parameters. This finite element framework can be extended to predict the behavior of stainless steel tube RAC members under various loading conditions and boundary configurations.
Engineering Practice and Material Considerations
From a steel pipe manufacturing perspective, the use of stainless steel tubes for composite members with recycled concrete presents unique challenges and opportunities. Stainless steel tubes, typically fabricated from grades such as 304 or 316L, require specialized welding processes such as GTAW (Tungsten Inert Gas Welding) with appropriate filler metals to maintain corrosion resistance and mechanical properties. The welding procedure specification must account for the higher thermal conductivity and lower thermal diffusivity of stainless steel compared to carbon steel.
The recycled aggregate used in the concrete core must be carefully selected and processed to ensure adequate mechanical properties. Key quality parameters include:
- Crushed recycled aggregate: controlled particle size distribution, low clay content, adequate specific gravity
- Fresh recycled aggregate: high water absorption requiring pre-soaking treatment
- Bond strength: interfacial transition zone between recycled aggregate and cement paste requires optimization through surface treatment or admixture use
The combination of stainless steel tube confinement with recycled concrete offers a sustainable construction solution with good structural performance. The reduction in flexural capacity with increasing RAC replacement rate should be accounted for in design, with appropriate safety factors or material property adjustments. This research supports the feasibility of using recycled materials in composite structural systems without significant compromise in structural performance, provided that design parameters are properly calibrated.