Zhuojin Pipe Fitting Co., LtdTransverse Local Compression Performance of Square Hollow Sandwich Steel Tube Concrete
Literature Overview
This paper by Yang Youfu and Meng Chunyuan, published in Journal of Architecture and Civil Engineering (2015, Vol. 32, No. 4), investigates the transverse local compression behavior of square hollow sandwich steel tube concrete (SHSSTC) members. The research is funded by the Liaoning Provincial Natural Science Foundation (2013020125) and combines experimental testing of six specimens with nonlinear finite element analysis using ABAQUS. The study focuses on understanding the load-bearing mechanism and failure characteristics when local transverse loads are applied to the sandwich composite section.
Core Technical Points
Square Hollow Sandwich Steel Tube Concrete Configuration
The SHSSTC section consists of an outer square steel tube, an inner hollow core, and concrete infill between the outer and inner tubes. This sandwich configuration offers:
- Reduced self-weight compared to solid CFST while maintaining structural efficiency
- Improved thermal and acoustic insulation from the hollow core
- Enhanced local buckling resistance from the sandwich action
- Potential for integration of utility conduits within the hollow core
Experimental Parameters
| Parameter | Symbol | Values Tested | Description |
|---|---|---|---|
| Load-to-depth ratio | a/h | 0.15, 0.20, 0.25 | Transverse local load width relative to section depth |
| Hollow ratio | φ | 0.3, 0.4, 0.5 | Ratio of inner hollow area to total cross-sectional area |
| Number of specimens | - | 6 | Parametric test matrix |
Failure Mode Analysis
The transverse local compression induces complex stress states including:
- Local denting: Direct compression beneath the load plate causing local wall deformation
- Web crippling: Diagonal compression failure of the concrete between outer and inner tubes
- Tension buckling: Opposite face experiencing tension-induced buckling
- Concrete crushing: Progressive crushing of the sandwich concrete layer
The hollow ratio significantly influences the failure mode transition:
- Low hollow ratio (φ = 0.3): Behavior approaches conventional CFST with concrete crushing as primary failure
- Medium hollow ratio (φ = 0.4): Combined web crippling and local denting
- High hollow ratio (φ = 0.5): Dominant local denting with limited concrete contribution
Finite Element Modeling and Validation
Model Configuration
The ABAQUS nonlinear FE model incorporates:
- Elastic-plastic material models for steel tubes and concrete
- Contact elements with friction to simulate tube-concrete interaction
- Geometric nonlinearity for large deformation analysis
- Progressive damage model for concrete crushing
- Rigid load plate with appropriate friction conditions
Results Comparison
| Comparison Metric | FE vs. Experiment | Deviation |
|---|---|---|
| Peak load | Good agreement | Within 10% |
| Load-displacement curve shape | Captures elastic, plastic, and post-peak phases | Within 12% |
| Strain distribution | Matches measured strain gauge data | Within 15% |
| Failure mode | Correctly predicts primary failure mechanism | Qualitative match |
Integration with Engineering Practice
Application Scenarios
SHSSTC members are particularly suitable for:
- Bridge columns and piers: Where reduced self-weight is important for seismic performance
- Marine platform structures: Where hollow cores can accommodate utility routing
- Industrial structures: Where thermal insulation requirements are significant
- High-rise building columns: Where weight optimization reduces foundation costs
Design Considerations
For practical design of SHSSTC members under transverse local compression:
- The load-to-depth ratio a/h is the primary geometric parameter governing capacity; designers should target a/h values within the tested range for reliable predictions
- The hollow ratio should be selected to balance weight reduction against capacity loss; a hollow ratio of 0.3-0.4 appears optimal for most applications
- Local reinforcement (e.g., internal stiffeners or increased concrete strength at loaded regions) can significantly enhance capacity for critical connections
- Weld quality between outer and inner tubes is critical; any discontinuity in the tube-to-tube weld will concentrate stresses and reduce capacity
Quality Control Requirements
| Inspection Item | Method | Acceptance Criteria |
|---|---|---|
| Tube-to-tube weld integrity | UT/RT | No planar defects exceeding code limits |
| Concrete density and strength | Core sampling | ≥ Design strength at 28 days |
| Hollow core dimensional accuracy | Survey | Within ±3 mm tolerance |
| Coating continuity | Visual/PT | No bare metal exposure |
| Section flatness and squareness | Measurement | Within 1:500 of nominal |
Key Questions and Reflections
- How does the transverse local compression behavior change when the hollow ratio exceeds 0.5, approaching a thin-walled sandwich structure?
- What is the effect of concrete strength grade on the load-bearing mechanism—does higher strength concrete shift the failure mode from concrete crushing to steel yielding?
- Can the findings be extended to consider combined transverse local compression with axial load, which is more representative of actual structural loading?
The research establishes that square hollow sandwich steel tube concrete members possess favorable mechanical properties under transverse local compression, with the FE model providing a reliable predictive tool for design. The parametric study demonstrates that both the load-to-depth ratio and hollow ratio significantly influence capacity and failure mode, providing engineers with clear guidance for section optimization. The validated numerical approach can serve as a basis for developing simplified design formulas suitable for practical engineering applications.