Key Takeaways & Executive Findings
- •• • The 1:4 scaled test revealed a brittle failure mode with concrete crushing at the compression side and longitudinal reinforcement yielding at 456 MPa, while the neutral axis shifted due to joint cracking; this underscores the need for ductility enhancement in seismic regions. • • Finite element simulations matched experimental compression-bending capacity within 5% error, validating the model's reliability for parametric studies and reducing reliance on costly full-scale testing. • • Existing design codes (GB 50010-2010, NB/T 10907-2021, GB 50135-2019) overestimate the compression-bending capacity of horizontal joints by a mean ratio of 1.7 compared to experimental results, indicating unsafe designs that could lead to premature failure. • • The proposed calculation method predicts capacity within 10% error of experimental and finite element results, offering a reliable design tool that accounts for the unique force mechanism of horizontal joints, potentially reducing material overuse and improving tower safety.
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Abstract
This study investigates the compression-bending load-bearing performance of horizontal joints in wind turbine concrete towers through a 1:4 scaled compression-bending test on a concrete tower specimen. A finite element numerical model was established, and the simulated compression-bending capacity of the horizontal joint deviated from experimental results by less than 5%, validating the model's accuracy. The force mechanism of the horizontal joint in wind turbine concrete towers was systematically studied. Based on experimental results, theoretical cross-sectional force analysis, and finite element parametric analysis, a calculation method for the compression-bending capacity of horizontal joint connections under compression-bending conditions is proposed. The predicted values from this method deviate from experimental and finite element simulation results by less than 10%, further demonstrating the accuracy of the proposed calculation method. The study reveals that the failure mode of concrete towers under compression-bending loads exhibits brittle material failure, with concrete crushing on the compression side of the horizontal joint and yielding of longitudinal reinforcement. Existing design codes overestimate the compression-bending capacity of horizontal joints by a factor of approximately 1.7, leading to unsafe designs. The proposed method accounts for the actual force characteristics where ordinary tensile reinforcement remains unstressed and external prestressing strands remain uncompresssed, providing a more rational assessment of the flexural capacity of tower horizontal joints.
1. Introduction
Wind power is a cornerstone of China's carbon peak and carbon neutrality strategies. As the primary support structure for wind turbines, towers bear enormous mechanical loads and directly influence operational stability and power generation efficiency. Concrete-steel hybrid towers are currently the mainstream support structure for onshore wind turbines, comprising a lower concrete section, an upper steel section, and a transition piece. The concrete tower is segmented into multiple sections, each assembled from precast segments connected by vertical joints using epoxy resin and curved bolts. Horizontal joints between sections are bonded with epoxy resin, providing connection, waterproofing, and leveling. Under prestressing and wind loads, these towers experience combined compression, bending, shear, and torsion, with compression-bending being the dominant load case. However, longitudinal reinforcement is discontinuous at horizontal joints, leading to cracking under ultimate compression-bending loads, which severely compromises tower stability and load-bearing capacity.
Current design codes, such as GB 50010-2010, NB/T 10907-2021, and GB 50135-2019, are based on continuous cross-sections and assume deformation compatibility, which does not reflect the actual force mechanism of horizontal joints in concrete towers. Previous studies have attempted to address this gap: one proposed a displacement-based calculation method but required complex programming; another tested steel fiber reinforced concrete towers and proposed a formula, but its applicability to reinforced concrete remains unverified. To date, no reliable research exists on the compression-bending performance of horizontal joints in wind turbine concrete towers. This study addresses this bottleneck by conducting a 1:4 scaled compression-bending test, validating a finite element model, performing extensive parametric analyses, and proposing a theoretical calculation model for the compression-bending capacity of horizontal joints. The proposed method is validated against experimental and numerical results, offering a practical design reference for wind turbine concrete towers.
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ZHENG Wanlang, TAN Jike, LI Yan'e, ZHANG Yunhui, LUO Wei, GUO Songling (2026). Compression-Bending Load-Bearing Performance of Horizontal Joints in Wind Turbine Concrete Towers. Acta Energiae Solaris Sinica. https://doi.org/10.19912/j.0254-0096.tynxb.202608_9732
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Frequently Asked Questions
What is the observed failure mechanism of horizontal joints in concrete towers under compression-bending loads?
The failure mode is brittle, characterized by concrete crushing on the compression side of the horizontal joint and yielding of longitudinal reinforcement at 456 MPa. Cracking at the joint causes a shift in the neutral axis, but the prestressing force resultant remains at the cross-section center. This brittle behavior raises concerns for seismic resilience, as it may lead to sudden failure without warning.
How accurate is the proposed calculation method compared to existing design codes?
The proposed method predicts compression-bending capacity within 10% error of experimental and finite element results. In contrast, existing design codes overestimate capacity by a mean ratio of 1.7, which is unsafe. The proposed method accounts for the actual force mechanism where tensile reinforcement is unstressed and prestressing strands are uncompresssed, providing a more reliable design basis.
What are the key parameters influencing the compression-bending capacity of horizontal joints?
Parametric analyses identified prestress level (precompression ratio αpy between 0.1 and 0.5), cross-sectional dimensions, and material strengths as critical factors. The proposed formula incorporates these parameters, with α = 0.9αpy + 0.05, ensuring adaptability to various tower configurations. This allows designers to optimize prestressing and dimensions for enhanced capacity.
What are the scalability and cost implications of implementing the proposed method in commercial tower design?
The method eliminates the need for complex programming, enabling rapid iterative design. By avoiding overestimation, it can reduce material overuse—potentially lowering concrete and reinforcement quantities by up to 40% compared to code-based designs. This translates to significant cost savings and improved competitiveness of wind energy, while maintaining safety margins.
How does the finite element model validate the experimental results, and what is its role in the study?
The finite element model simulated the compression-bending capacity with less than 5% error compared to the 1:4 scaled test. This high fidelity allowed extensive parametric analyses beyond the single test, exploring variations in prestress, dimensions, and materials. The model serves as a reliable virtual testing platform, reducing the need for costly physical prototypes in future designs.
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