Zhuojin Pipe Fitting Co., LtdAxial Compression Capacity of Steel Tube Basalt Fiber Concrete Short Columns
Literature Overview
This paper by Wang Xinzong, Li Chuanxi, Xie Heliang, Ling Jinyu, and Li Yongsuo investigates the axial compression behavior of concrete-filled steel tube (CFST) short columns incorporating basalt fiber-reinforced concrete (BFRC) as the core material. Published in the Bulletin of the Chinese Ceramic Society in 2018, the study was supported by the National Natural Science Foundation of China (Grant 51678226), the Ministry of Science and Technology 973 Program (2015CB057700), and a national-level college student innovation project (201611527001). The work directly addresses the question of whether replacing conventional concrete with basalt fiber-reinforced concrete improves the load-bearing capacity and ductility of CFST columns.
Experimental Program and Specimen Configuration
The study involved a comparative test program in which CFST short columns with ordinary concrete cores were tested alongside identical columns with basalt fiber-reinforced concrete cores. The specimens were subjected to monotonic axial compression until failure. The key variables included the steel tube parameters (diameter, wall thickness, and steel grade), the concrete compressive strength, and the basalt fiber dosage and length.
From a steel pipe manufacturing standpoint, the steel tubes used in such experiments are typically seamless tubes or longitudinally welded tubes conforming to GB/T 8162 or GB/T 17395. The wall thickness uniformity and the quality of any longitudinal welds are critical because they directly influence the confining pressure exerted on the concrete core. Any local thinning or weld defect in the steel tube wall would reduce the confinement effectiveness and potentially lead to premature local buckling.
Key Test Results
The experimental results demonstrate several important trends:
| Performance Indicator | Ordinary CFST Column | CFST Column with Basalt Fiber Concrete | Improvement |
|---|---|---|---|
| Ultimate axial load capacity | Baseline | Higher | Up to 10.1% increase |
| Elastic stage duration | Shorter | Longer | Significant extension |
| Ductility coefficient | Lower | Higher | Increases with steel ratio |
| Sensitivity to fiber length variation | Not applicable | Minimal effect | Fiber length has small influence on capacity |
The maximum improvement in load-bearing capacity of 10.1% is achieved at lower steel ratios, and the improvement diminishes as the steel ratio increases. This trend can be explained by the fact that at higher steel ratios, the steel tube contributes a proportionally larger share of the total load capacity, thereby diluting the relative benefit of the fiber-reinforced concrete.
Mechanism of Improvement
The basalt fibers contribute to the enhanced performance through several mechanisms:
- Crack bridging: Basalt fibers bridge microcracks in the concrete, delaying crack propagation and maintaining load-carrying capacity beyond the conventional concrete cracking point.
- Improved post-peak ductility: The fibers maintain tensile resistance across cracks, preventing sudden concrete fragmentation and allowing the steel tube to continue confining the damaged concrete core.
- Enhanced elastic stage: The fiber reinforcement increases the stiffness and elastic range of the concrete, extending the linear portion of the load-strain curve.
From a welding and fabrication perspective, the improved ductility of the composite column is beneficial because it provides a more forgiving response to any residual stresses or minor defects introduced during the steel tube manufacturing and welding process. A column with greater ductility can accommodate localized imperfections without catastrophic failure.
Engineering Practice Considerations
| Consideration | Recommendation |
|---|---|
| Basalt fiber dosage | Optimal dosage should be determined through trial mixes; excessive dosage may cause workability issues during concrete placement inside the steel tube |
| Fiber length | The study indicates minimal influence on capacity; standard lengths of 12–25 mm are acceptable |
| Steel tube welding quality | Maintain strict quality control on longitudinal welds; even minor weld defects can reduce confinement effectiveness |
| Concrete placement method | Use tremie method or pump with low slump to ensure full concrete fill without voids inside the steel tube |
| Quality inspection | Perform hydrostatic testing after concrete curing to verify structural integrity and absence of internal voids |
Study Insights and Reflections
The 10.1% improvement in load-bearing capacity, while modest in absolute terms, represents a meaningful engineering gain, particularly in applications where weight optimization or space constraints are critical. The finding that the improvement diminishes with increasing steel ratio suggests that basalt fiber-reinforced concrete is most beneficial in CFST columns with moderate steel ratios, where the concrete core contributes a significant share of the total capacity. For engineers involved in steel pipe supply and welding for CFST column fabrication, this work reinforces the importance of ensuring high-quality steel tubes with uniform wall thickness and sound welds, as these factors directly govern the confinement effectiveness that enables the full benefits of fiber-reinforced concrete to be realized.