Zhuojin Pipe Fitting Co., LtdPerformance Study of Steel Tube Laminated Viscoelastic Dampers
Literature Overview
This paper by Zhou Yun, Li Jiale, Zhong Genquan (Guangzhou University and Guangdong University of Technology), Zhang Min, Ji Hongen (Jiangsu Rongda Seismic Control Technology Co., Ltd.), and Chen Haobin (Guangzhou University), published in China Civil Engineering Journal (2023, Vol. 56, No. 10, pp. 1–10), investigates the performance of steel tube laminated viscoelastic dampers (VEDs). The study was supported by the National Key R&D Program Key Special Project (2017YFC0703608). Three types of dampers were designed and tested: hollow steel tube laminated viscoelastic damper, solid steel tube laminated viscoelastic damper, and a steel tube damper without viscoelastic material. Low-cycle reciprocating loading tests and finite element simulations were conducted to compare the working mechanisms, failure characteristics, and hysteresis performance of the three damper types.
Core Technical Findings
The study demonstrates that the integration of laminated viscoelastic materials with steel tubes creates an effective seismic energy dissipation device that combines the advantages of viscoelastic damping and steel tube structural capacity.
Damper Performance Comparison
| Performance Indicator | Hollow Steel Tube VED | Solid Steel Tube VED | Steel Tube Damper (No VED) |
|---|---|---|---|
| Hysteresis curve shape | Symmetric and full | Symmetric and full | Not applicable |
| Yield displacement | 1 mm | 1 mm | Higher |
| Equivalent viscous damping ratio at 1 mm | ~10% | ~10% | Lower |
| Equivalent viscous damping ratio at 16 mm | >40% | >40% | Significantly lower |
| Energy dissipation capacity | Higher | Lower than hollow | Lowest |
| Material usage | Less | More than hollow | Moderate |
| Buckling resistance | Good (VED prevents buckling) | Good (VED prevents buckling) | Limited |
| Mechanical model | Bilinear | Bilinear | Not applicable |
Working Mechanism
The laminated viscoelastic material works synergistically with the steel tube to provide energy dissipation through viscous deformation. The viscoelastic material remains in the elastic state throughout the loading cycles, which ensures stable and repeatable energy dissipation performance. The steel tube provides structural capacity and prevents the viscoelastic material from buckling or experiencing excessive deformation.
The hollow steel tube VED outperforms the solid steel tube VED in terms of energy dissipation capacity and efficiency, while using less material. This is because the hollow configuration allows for greater deformation of the viscoelastic material at the same steel tube displacement, resulting in higher energy dissipation per unit of steel tube deformation.
Central Weakening Strategy
The study demonstrates that weakening the steel tube at its midsection concentrates the deformation and energy dissipation at the weakened section, thereby preventing damage at the end connections. This is an important design strategy that ensures the damper can be replaced after a seismic event without requiring repair of the connection details.
Steel Pipe Manufacturing and Welding Implications
The design and fabrication of steel tube laminated viscoelastic dampers involve several critical steel pipe manufacturing and welding considerations:
Steel Tube Fabrication Requirements
| Requirement | Specification | Rationale |
|---|---|---|
| Steel grade | Q345 or equivalent | Adequate yield strength and ductility |
| Tube diameter tolerance | ±1 mm or tighter | Ensures proper fit with viscoelastic material |
| Wall thickness tolerance | ±0.5 mm or tighter | Consistent buckling resistance |
| Surface finish | Clean, free of scale and rust | Prevents premature corrosion and ensures bonding |
| Straightness | ≤ 1/1000 of length | Prevents bending stress during assembly |
| Central weakening | Controlled notch or reduced wall thickness | Concentrates deformation at midsection |
Welding Requirements
The welding of steel tube VEDs requires careful attention to the following aspects:
- End connection welds: The welds connecting the steel tube to the end connection plates must be designed to resist the full seismic load without failure. Full-penetration butt welds or equivalent strength welds should be used.
- Weld metal toughness: The weld metal must have adequate impact toughness to resist brittle fracture under cyclic loading. Charpy V-notch (CVN) impact tests should be performed on weld metal coupons at the expected service temperature.
- HAZ control: The HAZ of the end connection welds must be controlled to prevent excessive hardness and potential brittle fracture. Preheating and interpass temperature control should be implemented based on the carbon equivalent of the base metal.
- Weld inspection: Comprehensive NDT, including ultrasonic testing (UT) and magnetic particle testing (MT), should be performed on all welds to ensure structural integrity.
- Central weakening weld: If the central weakening is achieved through welding (such as a partial-penetration groove weld), the weld quality must be carefully controlled to ensure that the weakening section has the intended capacity and does not become a premature failure point.
Finite Element Analysis and Model Validation
The finite element models developed in this study are validated against the experimental test data. The models capture the key aspects of the damper behavior, including the nonlinear material behavior of the viscoelastic material and the geometric nonlinearity of the steel tube under large deformation.
Bilinear Mechanical Model
The study demonstrates that the mechanical behavior of both the hollow and solid steel tube VEDs can be simplified to a bilinear model. This simplification is valuable for practical design because it allows the use of standard nonlinear dynamic analysis procedures with a simple and well-understood constitutive model.
The bilinear model parameters, including the initial stiffness, post-yield stiffness, and yield force, can be determined from the hysteresis curves obtained from the low-cycle reciprocating loading tests. The equivalent viscous damping ratio is calculated from the hysteresis loop area at each displacement amplitude.
Engineering Application and Design Recommendations
The study provides clear design guidance for the implementation of steel tube laminated viscoelastic dampers in seismic isolation and energy dissipation systems:
- Hollow configuration preferred: The hollow steel tube VED is recommended over the solid configuration due to its superior energy dissipation capacity and material efficiency.
- Central weakening: The central weakening strategy should be implemented to ensure that the damper can be replaced after a seismic event without requiring repair of the connection details.
- Viscoelastic material selection: The viscoelastic material should be selected based on its temperature sensitivity, long-term aging resistance, and mechanical properties at the expected service temperature.
- Connection design: The end connections should be designed with adequate strength and ductility to resist the full seismic load, and the welds should be inspected with comprehensive NDT.
Key Questions and Reflections
A question that arises from this study is the long-term durability of the viscoelastic material under cyclic loading and environmental exposure. The viscoelastic material may experience aging, hardening, or softening over time, which could affect the damper performance. Accelerated aging tests and long-term monitoring data would provide valuable information for design life assessment.
Additionally, the study does not address the effect of temperature on the damper performance. The viscoelastic material properties are temperature-sensitive, and the damper performance may vary significantly between cold and hot conditions. Temperature-dependent testing would provide more comprehensive design data.
Study Insights and Reference Value
This paper provides valuable experimental and analytical data on the performance of steel tube laminated viscoelastic dampers. For steel pipe manufacturers and welding engineers, the key takeaway is that the fabrication quality of the steel tube, including dimensional tolerances, surface finish, and weld quality, directly influences the damper performance. The hollow configuration with central weakening offers the best combination of energy dissipation capacity, material efficiency, and replaceability. The bilinear mechanical model provides a practical tool for structural engineers performing nonlinear dynamic analysis of structures equipped with these dampers. The study's findings support the adoption of steel tube VEDs as a cost-effective and reliable seismic protection measure for buildings and other structures.