Zhuojin Pipe Fitting Co., LtdAxial Compression Behavior of Rectangular Hollow Sandwich Steel Tube Concrete Short Columns
Literature Overview
This study by Xie Li, Chen Mengcheng, and Huang Hong from East China Jiaotong University and Nanchang University (published in Industrial Construction, Vol. 43, Issue 5, 2013, pp. 128-131) presents an experimental and numerical investigation of the axial compression behavior of rectangular hollow sandwich steel tube concrete short columns. The research was supported by the National Natural Science Foundation of China (51008122), the 973 Program (2011CB612210), and Jiangxi Provincial scientific research programs.
Core Technical Content
Specimen Configuration
Seven specimens were tested: six rectangular hollow sandwich steel tube concrete short columns and one rectangular solid steel tube concrete short column for comparison. The sandwich configuration consists of an outer rectangular steel tube, an inner rectangular steel tube, and concrete filling the space between the two tubes. This configuration is designed to optimize the use of materials while maintaining structural integrity.
Parametric Variables
The key parametric variable in this study is the aspect ratio (width-to-height ratio) of the inner and outer steel tubes. The specimens were designed with varying combinations of inner and outer tube dimensions to investigate how the cross-sectional geometry influences the axial compression performance.
Experimental Findings
The test results revealed several important trends:
| Comparison Basis | Observation | Mechanism |
|---|---|---|
| Same inner tube, larger outer tube | Slightly higher axial capacity | Increased concrete volume and confinement |
| Same outer tube, larger inner tube | Slightly lower axial capacity | Reduced concrete volume and inner tube local buckling |
| Solid vs. sandwich column | Solid column slightly higher capacity | Continuous concrete confinement without inner tube interference |
Local Buckling of the Inner Tube
A critical finding is that the local buckling of the inner tube contributes to the reduction in axial capacity when the inner tube is enlarged. The inner tube, being unsupported on its inner surface, is susceptible to inward buckling under axial compression. This buckling reduces the effective confinement provided by the inner tube to the concrete and creates a gap between the inner tube and the concrete, which compromises the composite action.
Finite Element Analysis
ABAQUS was used to simulate the full-process axial compression behavior of the specimens. The numerical results were in good agreement with the experimental results, validating the modeling approach. The FEA provided insights into the stress distributions and deformation patterns that are difficult to observe experimentally.
Engineering Practice Integration
Manufacturing Challenges of Sandwich Columns
The sandwich configuration introduces specific manufacturing challenges:
- Inner tube fabrication: The inner tube must be manufactured with precise dimensions to ensure uniform concrete fill between the inner and outer tubes. Any eccentricity between the two tubes would create asymmetric concrete thickness, leading to uneven stress distribution.
- Positioning and fixing: During concrete pouring, the inner tube must be accurately positioned and fixed within the outer tube. This typically requires internal bracing or positioning devices that must be removed after the concrete has hardened.
- Concrete placement: The confined space between the two tubes makes concrete placement and compaction challenging. Vibrators must be designed to fit the narrow gap, and alternative methods such as pumped concrete with low slump may be necessary.
Welding Considerations
If the sandwich column is fabricated from multiple segments, the welding of both inner and outer tubes must be coordinated:
- Outer tube welds should be completed first to ensure structural stability during inner tube welding
- Inner tube welds must be performed with care to avoid distortion of the inner tube, which would compromise the uniformity of the concrete fill
- Welding residual stresses in both tubes should be managed through appropriate welding sequences and, if necessary, post-weld stress relief
Quality Control Measures
The following quality control measures are recommended for sandwich steel tube concrete columns:
- Dimensional inspection of both tubes before assembly
- Positioning accuracy verification before concrete pouring
- Concrete fill verification through internal inspection or ultrasonic testing
- Weld inspection at all tube joints
- Post-hardening inspection for voids or honeycombing
Study Insights and Reflections
The finding that the solid steel tube concrete column has slightly higher axial capacity than the sandwich column is an important design consideration. The sandwich configuration, while offering potential advantages in terms of material efficiency and architectural flexibility, does not fully replicate the performance of a solid column. The reduction in capacity is attributed to the local buckling of the inner tube and the reduced concrete volume, both of which compromise the confinement mechanism that is fundamental to the performance of steel tube concrete members.
The study highlights a fundamental trade-off in sandwich column design: increasing the inner tube size reduces the concrete volume and increases the risk of inner tube local buckling, while decreasing the inner tube size reduces the architectural and material benefits of the sandwich configuration. Designers must carefully balance these competing factors to achieve an optimal design.
A limitation of this study is the focus on short columns only. The behavior of long sandwich columns, where buckling rather than crushing governs the failure, may be different. Additionally, the study does not address the behavior under cyclic or seismic loading, which is critical for structural applications in seismic zones. Future research should extend the investigation to include long columns, combined loading conditions, and fatigue performance.
The practical value of this research lies in its clear identification of the factors that influence the performance of sandwich columns, providing designers with guidance for optimizing the geometry of these members. The ABAQUS modeling approach validated in this study can be adapted for more complex configurations and loading conditions in future design applications.