Zhuojin Pipe Fitting Co., LtdSingle-Sided Bolt End-Plate Connection of Circular Hollow Sandwich Concrete Filled Steel Tube Columns
Overview of the Literature
The paper by Wang Jingfeng, Zhang Meng, and Zhang Na (2018, Progress in Steel Building Structures, Vol. 20, No. 2, pp. 36-43), supported by the National Natural Science Foundation of China (Grants No. 51478158 and 51178156) and the Ministry of Education New Century Excellent Talent Support Program (NCET-12-0838), presents experimental and numerical studies on single-sided bolt end-plate connections for circular hollow sandwich concrete filled steel tube (CFST) columns. The study includes low-cycle reversed loading tests on four specimens and finite element analysis considering material constitutive relationships and complex contact problems.
Core Technical Content
Experimental Program
Four specimens of circular hollow sandwich CFST column connections were tested under low-cycle reversed loading to evaluate their seismic performance. The study investigates the influence of end-plate type and column section hollow ratio on the failure mode, hysteresis behavior, and energy dissipation capacity of the connections.
| Specimen Parameter | Description | Range |
|---|---|---|
| Column type | Circular hollow sandwich CFST | Variable |
| Connection type | Single-sided bolt end-plate | Standard |
| End-plate type | Variable (thickness, geometry) | Multiple configurations |
| Hollow ratio | Cross-sectional hollow ratio | Variable |
| Loading protocol | Low-cycle reversed loading | Displacement-controlled |
| Test objective | Failure mode, hysteresis, energy dissipation | Seismic performance |
Failure Modes and Hysteresis Behavior
The experimental results reveal that the single-sided bolt end-plate connections for circular hollow sandwich CFST columns exhibit good hysteresis behavior, ductility, and energy dissipation capacity. The failure modes are characterized by yielding of the end-plate and/or the connection bolts, with the column itself remaining largely undamaged. This is consistent with the desired strong-column weak-joint design philosophy for seismic resistance.
The hysteresis curves show full and stable loops, indicating good energy dissipation capacity. The connections maintain their load-carrying capacity through large displacements, demonstrating satisfactory ductility. The influence of end-plate type and hollow ratio on the hysteresis behavior is quantified through comparison of the peak loads, equivalent viscous damping coefficients, and cumulative energy dissipation.
Finite Element Analysis
The finite element models are developed using commercial software with careful consideration of material constitutive relationships and complex contact problems. The concrete-steel interface is modeled using contact elements with appropriate friction coefficients. The bolted connections are modeled with beam elements or solid elements, depending on the level of detail required.
| Modeling Aspect | Approach |
|---|---|
| Concrete | Plastic damage model with confinement |
| Steel tube | Elastic-plastic with kinematic hardening |
| Concrete-steel interface | Frictional contact |
| Bolts | Beam or solid elements with preload |
| End-plate | Solid elements with plasticity |
| Contact formulation | Penalty method with finite sliding |
The numerical results are compared with experimental results and show good agreement in terms of load-displacement curves, hysteresis loops, and failure modes. This validation provides confidence in the use of the finite element models for parametric studies and design optimization.
Classification According to Eurocode 3
According to Eurocode 3 (EC3), the connections are classified as semi-rigid and full-strength. This classification is significant for structural design, as it determines the appropriate analysis method and design approach. Semi-rigid connections require the use of moment-rotation curves in the analysis, while full-strength connections ensure that the connection capacity is not the governing factor in the design.
Key Questions and Reflections
The most important finding from this study is the demonstration that single-sided bolt end-plate connections can achieve satisfactory seismic performance for circular hollow sandwich CFST columns. This is significant because circular hollow sandwich CFST columns offer a unique combination of high load-bearing capacity and good seismic performance, but the design of their connections has been less well studied compared to conventional CFST columns.
The classification as semi-rigid and full-strength according to EC3 is a practical and useful result, as it allows engineers to apply established design methodologies from Eurocode 3. However, engineers should be aware that the semi-rigid behavior means that the connections cannot be treated as perfectly rigid in structural analysis, and that moment-rotation curves should be incorporated into the analysis.
The influence of the hollow ratio on connection performance is an important practical consideration. A higher hollow ratio reduces the concrete core area and may affect the load transfer mechanism at the connection. Engineers should ensure that the hollow ratio is selected to provide adequate load transfer capacity while maintaining the desired structural efficiency.
Implications for Engineering Practice
For the design of circular hollow sandwich CFST column connections, the following recommendations are derived from this study:
- End-plate design: Select end-plate thickness and geometry to ensure that the connection capacity is at least equal to the column capacity. The end-plate should be designed to yield before the column fails, ensuring ductile connection behavior.
- Bolt selection and arrangement: Use high-strength bolts with appropriate preload. The bolt arrangement should be designed to minimize eccentricity and maximize load transfer efficiency.
- Hollow ratio control: Limit the hollow ratio to values that ensure adequate load transfer capacity. The hollow ratio should be selected based on the specific loading conditions and design requirements.
- Finite element analysis: Use validated finite element models for detailed connection design and seismic performance assessment. The models should incorporate material nonlinearity, contact nonlinearity, and geometric nonlinearity.
Summary and Conclusions
The paper by Wang et al. provides valuable experimental and numerical insights into the seismic performance of single-sided bolt end-plate connections for circular hollow sandwich CFST columns. The demonstration of good hysteresis behavior, ductility, and energy dissipation capacity, along with the classification as semi-rigid and full-strength according to EC3, provides a solid foundation for the design and application of these connections in practice. Engineers should recognize that the design of connections for circular hollow sandwich CFST columns requires careful consideration of the unique load transfer mechanisms and the influence of the hollow ratio. The validated finite element models provide a powerful tool for detailed design and performance assessment. The findings of this study contribute to the growing body of knowledge on the seismic design of advanced structural systems and will facilitate the wider application of circular hollow sandwich CFST columns in earthquake-prone regions.