Zhuojin Pipe Fitting Co., LtdDesign Parameters for Lattice Steel Tube Concrete Wind Turbine Towers
Literature Overview
This paper by Li Bin, Zhang Qunhui, Yi Kuaikai, and Gao Chunyan from Inner Mongolia University of Science and Technology and Zhejiang Zhongnan Construction Group presents a nonlinear finite element analysis of lattice-type steel tube concrete (STC) wind turbine towers. Published in the Journal of Inner Mongolia University of Science and Technology, Vol. 33, No. 3, 2014, pp. 259-263, the work was supported by the National Natural Science Foundation of China (Grant 51068021) and the Inner Mongolia Natural Science Foundation (Grant 2012MS0711).
Research Objective and Methodology
The study employs nonlinear static finite element analysis to reveal the complete loading process, failure modes, and ultimate bearing capacity of lattice STC towers. Four key geometric and stiffness parameters are systematically investigated:
- Tower aspect ratio (λ) — the ratio of tower height to base width
- Web member configuration — the arrangement and type of diagonal and vertical members
- Tower column diameter-to-thickness ratio (γ) — governing local buckling resistance
- Stiffness ratio of web members to tower columns (β) — governing the load-sharing mechanism between components
Key Results and Design Recommendations
The finite element analysis produced clear quantitative relationships between parameters and structural performance:
| Parameter | Effect on Ultimate Capacity | Effect on Failure Mode |
|---|---|---|
| Aspect ratio λ increase | Capacity increases | Shifts toward web buckling |
| Column d/t ratio γ decrease | Capacity increases | Shifts toward column yielding |
| Stiffness ratio β increase | Capacity increases | Shifts toward column yielding |
| Web member form | Minimal influence | Minimal influence |
The recommended design parameters are:
- Tower aspect ratio λ: controlled at approximately 1/9
- Bottom-layer web member form: re-braced (subdivided) configuration
- Upper-layer web member form: conventional configuration acceptable
- Column diameter-to-thickness ratio γ: less than 30
- Web-to-column stiffness ratio β: less than 0.05
The recommendation that β should be less than 0.05 is particularly significant from a structural integrity standpoint. This constraint ensures that web members do not become disproportionately stiff relative to the tower columns, which would cause premature column failure before the web system reaches its capacity. In essence, this is a ductility-based design philosophy applied to lattice structures — the weaker component should fail first in a controlled manner, allowing the structure to redistribute loads before catastrophic collapse.
Engineering Practice Considerations
The finding that web member configuration has minimal influence on ultimate capacity is practically valuable. It implies that designers have considerable freedom in selecting web member forms based on constructability, fabrication cost, and aesthetic considerations without significantly compromising structural performance. However, the recommendation to use re-braced configurations at the bottom layer reflects the reality that base-level members experience the highest stresses and benefit from enhanced local stability.
The diameter-to-thickness ratio limit of 30 aligns with established local buckling criteria for steel tubes under compression. For wind turbine towers subjected to combined axial, bending, and torsional loading, this limit ensures adequate reserve against local instability. In practice, this may require thicker-walled tubes than would be selected based on global strength alone, representing a trade-off between material efficiency and structural reliability.
Study Insights
This research demonstrates the power of parametric finite element analysis in establishing design guidelines for complex structural systems. The systematic identification of dominant parameters and their interaction effects provides engineers with actionable design targets rather than vague qualitative observations. The lattice STC tower concept represents an innovative structural solution that leverages the composite action of steel tubes and concrete to achieve favorable strength-to-weight ratios for tall, slender wind turbine support structures. The recommended parameter ranges should serve as initial design targets, subject to refinement based on site-specific wind loading, soil conditions, and turbine characteristics.