Wind Vibration Response Analysis of Rectangular Steel Tube Concrete Bundle Wind Turbine Tower

Literature Overview and Structural Innovation

The paper by Gao Xiang, Guo Hongchao, Guo Pinzhang, and Liang Gang from Xi'an University of Technology, published in Earthquake Engineering and Engineering Dynamics (Volume 44, Issue 2, 2024, pp. 98-107), presents a novel structural concept for wind turbine towers: the rectangular steel tube concrete bundle tower. This research is supported by multiple funding sources including the National Natural Science Foundation of China (Grant No. 51978571), Shaanxi Provincial Key R&D Programs, and the China Postdoctoral Science Foundation. The innovation addresses the growing challenge of developing wind energy in low-wind-speed regions, where traditional circular steel towers become economically and structurally inefficient due to the need for excessive height and blade length.

The rectangular steel tube concrete bundle tower is composed of multiple rectangular steel tube concrete units assembled into a larger structural section. This configuration offers several theoretical advantages:

• High strength: The composite action between steel tubes and concrete cores provides high axial and flexural capacity.
• Large stiffness: The rectangular geometry provides greater second moment of area per unit weight compared to circular sections.
• Strong energy dissipation: The interface between steel tubes and concrete provides additional damping through friction and micro-slip mechanisms.

Wind Load Simulation and Dynamic Time-History Analysis

The wind load simulation methodology employed in this study follows established practices in wind engineering:

• Kaimal gust wind speed power spectrum: The Kaimal spectrum is used to characterize the statistical properties of turbulent wind, providing a realistic representation of the frequency content of wind fluctuations.
• Harmonic synthesis method: The wind load time-history curve is generated using the harmonic synthesis method, which constructs a random time series with the desired power spectrum characteristics.
• Dynamic time-history analysis: The generated wind load time histories are applied to the structural model in a dynamic time-history analysis, capturing the full dynamic response of the tower.

The analysis computes the wind vibration coefficient and equivalent static wind loads, which are essential parameters for serviceability and ultimate limit state design. The wind vibration coefficient accounts for the amplification of static response due to dynamic effects, while the equivalent static wind load provides a simplified representation of the dynamic response for use in routine design calculations.

Key Results and Structural Performance

The results of the dynamic analysis provide valuable insights into the structural performance of the rectangular steel tube concrete bundle tower:

The displacement angle of 1/154 is particularly significant, as it falls well within the typical code requirement of 1/50 to 1/100 for wind turbine towers. This indicates that the rectangular steel tube concrete bundle configuration provides sufficient stiffness to limit wind-induced deflections even under extreme loading conditions. The component strength results show that all structural elements have substantial safety margins, suggesting that the design could potentially be optimized for material efficiency without compromising safety.

Methodological Comparison: Gust Load Factor vs. Inertial Wind Load Method

The paper compares two methods for computing equivalent static wind loads: the displacement-equivalent gust load factor method and the inertial wind load method. The findings reveal that:

• The gust load factor method yields a relatively low wind vibration coefficient, indicating that the tower's dynamic response is not significantly amplified by vortex shedding or other resonance phenomena at the frequencies of interest.
• The inertial wind load method produces equivalent static loads that are consistent with the results of the full random vibration analysis, validating the use of this simplified approach for practical design.

This methodological comparison is important for engineering practice, as it demonstrates that simplified wind load calculation methods can be reliably used for the preliminary design of rectangular steel tube concrete bundle towers, while full dynamic analysis should be reserved for final design verification and detailed assessment of critical components.

Study Insights and Engineering Implications

The development of the rectangular steel tube concrete bundle tower represents a promising structural innovation for the wind energy industry, particularly for applications in challenging wind resource environments. The key insight from this research is that the bundle configuration provides a favorable balance between stiffness, strength, and damping, resulting in a structurally efficient tower design. For engineers involved in wind turbine tower design, the findings suggest that rectangular steel tube concrete bundles should be considered as a viable alternative to traditional circular steel towers, particularly for large-capacity turbines in low-wind-speed regions. The research also highlights the importance of dynamic analysis in the design of tall, slender structures, as the dynamic response can significantly influence the design wind loads and overall structural safety. The validation of simplified wind load calculation methods provides practical guidance for engineers seeking to balance computational efficiency with analytical rigor in the design process.