Zhuojin Pipe Fitting Co., LtdSeismic Performance Test Study of Steel Pipe Recycled Concrete Frame
Literature Overview and Sustainable Construction Context
This paper by Meng Ercong, Wu Xiaoping, Yang Zhen, and Su Yisheng, published in the Journal of Guangxi University (Natural Science Edition) in 2016, investigates the seismic performance of steel pipe recycled concrete (SPRC) frame structures. The research was supported by the National Natural Science Foundation of China (Grant No. 51468003), the Doctoral Program Special Research Fund of Ministry of Education (20134501110001), and the Guangxi Science Research and Technology Development Project (Gui Ke Zhuan 14124005-1-2). The study addresses an important intersection of sustainable construction and seismic engineering: the use of recycled concrete in steel pipe concrete frame structures.
Test Specimens and Experimental Setup
The authors designed and fabricated two one-bay, one-story frames with 100% recycled concrete replacement rate, consisting of square steel pipe recycled concrete columns and reinforced recycled concrete beams. The beam cross-sectional height was the variable parameter, with two different heights used to investigate its influence on seismic performance.
| Specimen Parameter | Specimen 1 | Specimen 2 |
|---|---|---|
| Beam height | Smaller | Larger |
| Column type | Square steel pipe recycled concrete | Square steel pipe recycled concrete |
| Beam type | Reinforced recycled concrete | Reinforced recycled concrete |
| Recycled concrete replacement rate | 100% | 100% |
| Loading protocol | Low-cycle cyclic loading | Low-cycle cyclic loading |
The low-cycle cyclic loading test was conducted to simulate the inelastic behavior of the frame under seismic loading. The loading was applied at the beam midspan, with displacement-controlled loading to capture the full hysteretic behavior.
Key Experimental Results
The test results revealed several important characteristics of the SPRC frame seismic performance:
| Performance Indicator | Result | Assessment |
|---|---|---|
| Hysteresis loop shape | Full spindle-shaped | Good energy dissipation |
| Equivalent viscous damping coefficient (hue) | > 0.22 at failure | Excellent energy dissipation |
| Story drift angle at failure | ~1/39 | Good collapse resistance |
| Effect of beam height on capacity | Increases with beam height | Expected trend |
| Effect of beam height on initial stiffness | Increases with beam height | Expected trend |
| Effect of beam height on ductility | Decreases with beam height | Trade-off effect |
| Effect of beam height on energy dissipation (pre-peak) | Increases with beam height | Beneficial |
| Effect of beam height on energy dissipation (post-peak) | Decreases with beam height | Detrimental |
| Effect of beam height on residual stiffness | Minor influence | Not critical |
The hysteresis loops exhibited a full spindle shape, indicating good energy dissipation capacity. The equivalent viscous damping coefficients at failure were all above 0.22, which is considered excellent for seismic-resistant structures. The story drift angles at failure were approximately 1/39, demonstrating good collapse resistance and ductility.
Recycled Concrete and Steel Pipe Interaction
The use of 100% recycled concrete in the steel pipe columns and beams introduces several technical considerations that are relevant to the structural performance:
- Recycled aggregate properties: Recycled concrete aggregate (RCA) typically has higher water absorption and lower density compared to natural aggregate. This can affect the concrete strength, stiffness, and durability. The steel pipe confinement helps to mitigate some of these adverse effects by providing lateral restraint to the concrete core.
- Steel pipe-concrete bond: The bond between the steel pipe and the recycled concrete is critical for the composite action of the SRC column. Recycled concrete may have a slightly reduced bond strength due to the higher water absorption of RCA, but the confinement effect of the steel pipe compensates for this.
- Material nonlinearity: The recycled concrete exhibits a different stress-strain behavior compared to conventional concrete, with potentially lower peak strength but similar post-peak ductility when confined by the steel pipe. This material nonlinearity should be properly accounted for in nonlinear analysis.
Engineering Practice Implications
The study provides valuable insights for the application of recycled concrete in seismic-resistant steel pipe concrete structures:
- Beam height optimization: The results show that increasing beam height improves capacity and initial stiffness but reduces ductility. Engineers must balance these competing objectives based on the specific seismic design requirements. A moderate beam height that provides adequate capacity while maintaining good ductility is generally preferred.
- Energy dissipation mechanism: The SPRC frame exhibits good energy dissipation through inelastic deformation of the beam and column. The steel pipe confinement in the columns enhances the energy dissipation capacity by delaying concrete crushing and maintaining post-peak load-carrying capacity.
- Collapse resistance: The story drift angle of 1/39 at failure indicates good collapse resistance, which is essential for life-safety objectives in seismic design. This performance level meets or exceeds the requirements of most seismic design codes.
Study Insights and Reflections
This study is significant for promoting sustainable construction practices in seismic zones. The use of recycled concrete reduces the demand for natural aggregate, decreases construction waste, and contributes to a circular economy. The demonstration that SPRC frames with 100% recycled concrete replacement can achieve excellent seismic performance is encouraging for the widespread adoption of recycled materials in structural applications.
From my perspective as a welding and metallurgy specialist, the square steel pipe columns in these frames require careful attention to welding quality at the column-beam connections and at any field splices. The welding of square steel pipes involves the same metallurgical considerations as round steel pipes, including HAZ softening, residual stress, and distortion control. The use of recycled concrete does not directly affect the welding process, but it does influence the overall structural behavior that the welded connections must accommodate. Engineers should ensure that the welded connections have sufficient ductility to accommodate the inelastic deformations expected during seismic events, particularly at the column-beam joints where plastic hinge formation is expected.
Reference Value and Outlook
This work provides experimental evidence that steel pipe recycled concrete frames can achieve excellent seismic performance, supporting the use of recycled concrete in seismic-resistant structures. Future research could extend to multi-story frames, investigate the effects of partial recycled concrete replacement (e.g., 30%, 50%, 70%), and explore the long-term durability of recycled concrete under cyclic loading. The findings are relevant to seismic design codes such as GB 50011, ACI 318, and Eurocode 8, which could be updated to include provisions for recycled concrete in steel pipe concrete structures. Engineers designing sustainable seismic-resistant structures should consider the SPRC frame as a viable option, supported by the experimental evidence presented in this study.