Mechanical Performance Comparison of Concrete-Filled Steel Tube Lattice Wind Turbine Tower Joints

Literature Overview

This 2020 paper published in the Journal of Chongqing University of Technology (Natural Science) by Li Bin, Zhao Zhenzhong, and Cheng Yachao from Inner Mongolia University of Science and Technology investigates the mechanical performance of concrete-filled steel tube (CFST) lattice wind turbine tower joints. Funded by the National Natural Science Foundation of China (Grant No. 51768056), the study compares two joint connection types: chord-to-chord (K-joint or T-joint style) connections and tube-to-plate connections, under both static and low-cycle cyclic horizontal loading conditions. The research is motivated by the growing demand for cost-effective and durable wind turbine tower structures, where CFST lattice towers offer advantages in stiffness, weight efficiency, and fatigue resistance.

Experimental and Numerical Framework

The authors designed four plane model towers: two with chord-to-chord (chord joint) connections and two with tube-to-plate connections. Each model tower was subjected to both static horizontal loading and low-cycle cyclic horizontal loading tests. Parallel finite element numerical simulations were conducted to complement the experimental results, providing detailed insight into stress distributions, deformation mechanisms, and failure initiation locations. The numerical models were validated against the experimental load-deformation responses, ensuring that the simulation results accurately reflect the physical behavior of the joint connections.

The CFST members in the model towers were fabricated using steel tubes filled with concrete, with the steel tubes welded to form the lattice structure. The joint connections were designed according to common industry practices, with chord-to-chord joints fabricated using flush-cut welds and tube-to-plate joints using gusset plates and fillet welds. The concrete strength and steel grade were selected to represent typical wind turbine tower construction parameters.

Key Technical Findings

Under static horizontal loading, both joint types exhibited failure in the joint zone, with the chord-to-chord joint connection demonstrating higher bearing capacity and greater plastic deformation capacity compared to the tube-to-plate joint connection. Under low-cycle cyclic loading, the failure mode shifted to a combined mechanism involving radial tearing of the parent material at the crossing diagonal brace connection and fracture at the column foot. The chord-to-chord joint connection consistently outperformed the tube-to-plate joint in terms of energy dissipation capacity and ductility.

Engineering Practice Integration

For wind turbine tower design engineers, this study provides a clear recommendation: chord-to-chord (chord joint) connections are preferred over tube-to-plate connections for CFST lattice wind turbine towers. The superior bearing capacity and plastic deformation capacity of chord joints translate to better performance under both static wind loads and dynamic cyclic loads from wind gusts and turbulence. The higher ductility of chord joints is particularly important for fatigue resistance, as wind turbine towers are subjected to millions of load cycles over their service life.

From a fabrication and quality control perspective, chord-to-chord joints require precise cutting and alignment of the intersecting tubes, which demands high-quality CNC cutting equipment and skilled welders. The tube-to-plate joint, while easier to fabricate, introduces stress concentrations at the weld-to-plate transitions and reduces the effective cross-sectional area at the connection. Engineers should ensure that chord joint welds are inspected using ultrasonic testing (UT) or phased array ultrasonic testing (PAUT) to detect internal defects, and that the weld geometry conforms to the applicable standards such as GB/T 150 or ASME B31.3.

Reflections and Implications

This study makes a compelling case for the adoption of chord-to-chord joint connections in CFST lattice wind turbine towers, supported by both experimental and numerical evidence. The superior performance of chord joints in terms of bearing capacity, ductility, and energy dissipation is consistent with the general principle that continuous load paths minimize stress concentrations and provide more uniform strain distribution. The finding that both joint types fail in the joint zone under static loading highlights the critical importance of joint design and detailing in lattice tower structures. Engineers should prioritize joint optimization in the design process, and this study provides a valuable benchmark for comparing new joint concepts and connection details. The practical implications extend beyond wind turbine towers to any CFST lattice structure, including transmission towers, bridge trusses, and industrial frameworks, where the principles of joint performance comparison are directly applicable.