A method for upgrading and retrofitting existing wind turbine towers and the resulting wind turbine towers

Abstract

This invention relates to the field of upgrading and retrofitting existing wind turbine towers, and discloses a method for upgrading and retrofitting existing wind turbine towers and the resulting wind turbine towers. The method involves excavating multiple new foundation pits along the circumferential direction of the existing wind turbine tower foundation; pouring plain concrete into the new foundation pits; constructing anchor bolts within each new foundation pit; hoisting multiple prefabricated auxiliary tower leg foundations into the corresponding new foundation pits. Each auxiliary tower leg foundation includes a foundation cap and a column. During hoisting, a predetermined space is reserved between the inner ring of the foundation cap and the edge of the original foundation. The pre-drilled holes on the foundation cap are aligned with the anchor bolts, and grouting is performed to ensure complete gripping between the anchor bolts and the auxiliary tower leg foundations. Then, the top of the anchor bolts is mechanically connected to the foundation cap. Circumferential and vertical reinforcing bars are inserted into the predetermined space, followed by formwork and pouring concrete to integrate the auxiliary tower leg foundations with the original foundation. Finally, the auxiliary tower structures are connected sequentially from bottom to top according to the designed height.

Description

Technical Field

[0001] This invention relates to the field of upgrading and retrofitting existing wind turbine towers, specifically to a method for upgrading and retrofitting existing wind turbine towers and the resulting wind turbine towers. Background Technology

[0002] The wind turbine tower is the core supporting structure of a wind turbine generator set. It supports the massive nacelle and rotor to a height of nearly 100 meters, providing a platform for capturing more stable and powerful wind energy, and is crucial for the safe and stable operation of the entire wind turbine generator set. However, existing wind turbine tower structures still have the following problems: 1. Limited load-bearing capacity: The bending moment of the base of the first-generation all-steel wind turbine tower can only withstand about 50,000 kN·m, which cannot meet the load requirements of tens of thousands of kN·m required by high-power wind turbines of 6 MW and above, and is difficult to adapt to the power upgrade needs of the wind power industry.

[0003] 2. Serious waste of resources: Traditional renovation requires the complete demolition of the original foundation, foundation ring and tower, resulting in a huge waste of resources in the early stage of construction, and the reconstruction cost is high and the construction period is long.

[0004] 3. Insufficient structural stability: The rigidity of a single tower structure is limited, and it is prone to excessive displacement under the coupled effects of earthquakes and wind disasters, resulting in poor disaster resistance.

[0005] 4. Low wind energy utilization efficiency: The first-generation tower has a fixed height, which cannot meet the wind energy capture needs in low wind speed areas. In addition, on-site construction requires a large number of rolled steel pipes, and the processing accuracy and environmental protection need to be improved.

[0006] 5. Weak pull-out and overturning resistance of the foundation: The original foundation only relies on the ring concrete foundation, which is insufficient in pull-out and overturning resistance under the large horizontal load of high-power wind turbines. Summary of the Invention

[0007] In order to solve the technical problems existing in the prior art, the present invention discloses a method for upgrading and retrofitting existing wind turbine towers and the resulting wind turbine towers.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, this invention proposes a method for upgrading and retrofitting existing wind turbine towers, comprising the following steps: Multiple new foundation pits were excavated along the circumferential direction of the existing wind turbine tower foundations; Roughen the edges of the original base; Plain concrete was poured into the newly added foundation pit and the pit was leveled. Install anchor bolts in each new foundation pit; Multiple prefabricated auxiliary tower leg foundations are hoisted into the corresponding new foundation pits. The auxiliary tower leg foundations include a pile cap and a column. Holes are reserved on the pile cap, and anchor bolts are pre-embedded on the column. During hoisting, ensure that a predetermined space is reserved between the inner ring of the pile cap and the edge of the original foundation. Align the reserved holes on the pile cap with the anchor bolts and grout them to ensure that the anchor bolts are fully gripped with the auxiliary tower leg foundations. Then, mechanically connect the top of the anchor bolts to the pile cap. Within the reserved space, circumferential and vertical reinforcing bars are inserted, and then formwork is erected and the auxiliary tower leg foundation is cast together with the original foundation. Connect the prefabricated first-layer auxiliary tower leg to the auxiliary tower leg foundation, and then connect the first-layer auxiliary tower leg to the second-layer auxiliary tower leg. Next, connect the ring constraint assembly and the radial connection assembly to the second-layer auxiliary tower leg. The radial connection assembly is connected to the existing tower. Connect the remaining auxiliary tower legs in sequence from bottom to top according to the designed height position. After each layer of auxiliary tower legs is connected, install the ring constraint assembly and the radial connection assembly.

[0009] As a further technical solution, the circumferential constraint assembly includes an upper circumferential steel pipe and a lower circumferential steel pipe, as well as diagonal bars welded between adjacent auxiliary tower legs in the annular shape.

[0010] As a further technical solution, the diameter and wall thickness of the circumferential steel pipe decrease synchronously from bottom to top along the height direction of the existing tower.

[0011] As a further technical solution, the radial connection assembly includes several horizontal connecting rods arranged at a set angle, and the horizontal connecting rods, the tower tube, and the auxiliary tower legs form a triangular structure.

[0012] As a further technical solution, the multi-layer auxiliary tower legs are arranged in a tapered shape that is wider at the bottom and narrower at the top along the existing tower height direction.

[0013] As a further technical solution, along the existing tower height direction, the auxiliary tower legs of adjacent layers are connected by flanges and bolts.

[0014] As a further technical solution, the circumferential steel pipe can be replaced by a lattice truss ring.

[0015] As a further technical solution, the anchor bolt can be replaced with steel strand.

[0016] As a further technical solution, horizontal bracing is installed between the intersecting diagonal braces.

[0017] As a further technical solution, the first-layer auxiliary tower leg is connected to the anchor bolts on the pedestal.

[0018] As a further technical solution, the diameter of the auxiliary tower leg gradually decreases from bottom to top along the height direction of the existing tower.

[0019] Secondly, the present invention provides a wind turbine tower, which is obtained through the above-mentioned method for upgrading and transforming existing wind turbine towers.

[0020] The method for upgrading and retrofitting existing wind turbine towers and the resulting wind turbine towers proposed in this invention have the following beneficial effects: This invention fully preserves the existing wind turbine tower's foundation, foundation ring, and main tower section, upgrading it only by adding a conical expanded-base composite foundation, prestressed auxiliary components, and extension sections. This results in high resource utilization and significantly reduced retrofit costs. Construction is convenient and environmentally friendly: the tower auxiliary structure and auxiliary tower leg foundations are all prefabricated in the factory, shortening the overall construction period and improving assembly efficiency. Simultaneously, the load-bearing capacity is significantly improved; the base bending moment of the upgraded structure can be increased to tens of thousands of kN·m. The prestressed auxiliary tower legs, with their expanded bottom diameter and upward-convex tapered arrangement, balance the load through negative stress, making them suitable for 6-9 MW high-power wind turbines, meeting power upgrade requirements. It also boasts excellent disaster resistance. The existing tower section is assembled with conical tapered prestressed auxiliary tower legs and a composite foundation lattice-type conical truss combination structure. Combined with horizontal partitions controlled by slenderness ratio to enhance overall stiffness, the structure's response remains within the elastic range under the coupled effects of earthquakes and wind disasters. The multi-legged annular radial conical layout and symmetrical arrangement significantly improve the structure's torsional resistance, while the triangular grid significantly enhances geometric stability and shear stiffness, resulting in outstanding stability. By extending the tower height and combining it with a full-tower tapered variable cross-section design, along with new hubs and blades, the wind energy capture efficiency in low-wind-speed areas is effectively improved. The hollowed-out pure cross-bracing system reduces the drag coefficient, optimizes wind vibration response, and enhances aerodynamic stability; multiple sets of rock anchor composite foundations significantly improve pull-out and overturning resistance, making them suitable for mountainous rock geological conditions. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1 This is a schematic diagram of the overall modified structure of the present invention; Figure 2 This is a schematic diagram of the reinforced tower structure of the present invention; Figure 3 This is a schematic diagram of the cross-sectional distribution of the reinforcement device; Figure 4 This is a schematic diagram of the fully prefabricated basic structure of the present invention; Figure 5 This is a schematic diagram of the prefabricated foundation structure of the present invention; The diagram exaggerates the spacing or dimensions between parts to show their positions; the diagram is for illustrative purposes only.

[0023] 1. Existing foundation; 2. Precast auxiliary tower leg foundation; 21. Pier cap; 22. Column; 23. Anchor bolt; 24. Anchor bolt; 25. Steel plate; 26. Mechanical connector; 27. Vertical reinforcement; 28. Circumferential reinforcement; 29. ​​Roughening treatment; 3. Auxiliary tower structure; 31. First-level auxiliary tower leg; 32. Circumferential steel pipe; 33. Diagonal brace; 34. Horizontal connecting rod; 4. Existing tower structure; Detailed Implementation It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. For ease of description, the words "up," "down," "left," and "right" appearing in this invention only indicate that they are consistent with the up, down, left, and right directions of the accompanying drawings themselves, and do not limit the structure. They are merely for the purpose of facilitating the description of this invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] As described in the background section, existing technologies have shortcomings. To address these technical problems, this invention proposes a method for upgrading and retrofitting existing wind turbine towers, and the resulting wind turbine tower. The method includes the following steps: excavating multiple new foundation pits along the circumferential direction of the existing wind turbine tower foundation; roughening the edges of the original foundation; pouring plain concrete into the new foundation pits and leveling them; constructing anchor bolts in each new foundation pit; hoisting multiple prefabricated auxiliary tower leg foundations into the corresponding new foundation pits, wherein each auxiliary tower leg foundation includes a pier and a column, with pre-drilled holes on the pier and anchor bolts pre-embedded in the column; during hoisting, ensuring a predetermined space is left between the inner ring of the pier and the edge of the original foundation; ensuring that the space reserved on the pier... The holes and anchor bolts are aligned and grouting is performed to ensure that the anchor bolts are fully bonded to the auxiliary tower leg foundation. Then, the top of the anchor bolts is mechanically connected to the foundation. Circumferential and vertical reinforcing bars are inserted into the reserved space, and then formwork is erected and the auxiliary tower leg foundation is cast together with the original foundation. The prefabricated first-layer auxiliary tower leg is connected to the auxiliary tower leg foundation, and then the first-layer auxiliary tower leg is connected to the second-layer auxiliary tower leg. Then, the annular constraint assembly and radial connection assembly are connected to the second-layer auxiliary tower leg. The radial connection assembly is connected to the existing tower tube. The remaining auxiliary tower legs are connected sequentially from bottom to top according to the designed height position. After each layer of auxiliary tower legs is connected, the annular constraint assembly and radial connection assembly are installed.

[0026] This invention fully preserves the existing wind turbine tower's foundation, foundation ring, and main tower section, upgrading it only by adding a conical expanded-base composite foundation, prestressed auxiliary components, and extension sections. This results in high resource utilization and significantly reduced retrofit costs. Construction is convenient and environmentally friendly: the tower auxiliary structure and auxiliary tower leg foundations are all prefabricated in the factory, shortening the overall construction period and improving assembly efficiency. Simultaneously, the load-bearing capacity is significantly improved; the base bending moment of the upgraded structure can be increased to tens of thousands of kN·m. The prestressed auxiliary tower legs, with their expanded bottom diameter and upward-convex tapered arrangement, balance the load through negative stress, making them suitable for 6-9 MW high-power wind turbines, meeting power upgrade requirements. It also boasts excellent disaster resistance. The existing tower section is assembled with conical tapered prestressed auxiliary tower legs and a composite foundation lattice-type conical truss combination structure. Combined with horizontal partitions controlled by slenderness ratio to enhance overall stiffness, the structure's response remains within the elastic range under the coupled effects of earthquakes and wind disasters. The multi-legged annular radial conical layout and symmetrical arrangement significantly improve the structure's torsional resistance, while the triangular grid significantly enhances geometric stability and shear stiffness, resulting in outstanding stability. By extending the tower height and combining it with a full-tower tapered variable cross-section design, along with new hubs and blades, the wind energy capture efficiency in low-wind-speed areas is effectively improved. The hollowed-out pure cross-bracing system reduces the drag coefficient, optimizes wind vibration response, and enhances aerodynamic stability; multiple sets of rock anchor composite foundations significantly improve pull-out and overturning resistance, making them suitable for mountainous rock geological conditions.

[0027] Example 1 This embodiment targets 2-3 MW first-generation all-steel wind turbine towers. Through a combination of multiple auxiliary tower legs arranged in a tapered, gradually changing pattern and a graded circumferential truss steel pipe structure, it significantly improves tower stiffness, torsional resistance, and load-bearing capacity, making it suitable for upgrading and retrofitting 6-9 MW high-power wind turbines. For example... Figure 1 As shown in the figure, this embodiment provides a construction method for upgrading and retrofitting existing wind turbine towers, including the following steps: (1) Positioning and excavation: The center points of the eight new foundation pits were laid out using a total station. The excavation dimensions of the foundation pits should be 300-500mm larger than the outer contour of the precast components to allow space for formwork and manual operation. Excavation should be carried out to the bottom elevation of the existing foundation 1, and over-excavation is strictly prohibited. If over-excavation is necessary, plain concrete should be used to fill the gaps.

[0028] (2) Interface roughening treatment 29: The edge of the original foundation 1 is roughened 29, the surface laitance and loose layer are removed to expose the solid stones, and the depth is not less than 40mm. Before hoisting, it is cleaned with high pressure water and the interface is kept moist before pouring to enhance the bonding strength between the old and new concrete.

[0029] (3) Leveling of pit bottom cushion layer: Pour a 100mm C30 plain concrete cushion layer and level it with a scraper. The surface flatness is controlled within ±3mm. The elevation difference of each pit bottom shall not exceed 10mm.

[0030] (4) Construction of anchor bolt 24: After the drilling rig for anchor bolt 24 is in place, the hole is drilled. After drilling, high-pressure air must be used to thoroughly blow away the accumulated powder in the hole. Rock anchor bolt 24 is inserted, and non-shrink grout is injected using the bottom grouting method.

[0031] (5) Lifting of prefabricated auxiliary tower leg foundation 2: The crane lifts the prefabricated block and uses the positioning frame to ensure that it maintains a design distance of 200mm from the edge of the original foundation 1; the prefabricated auxiliary tower leg foundation 2 includes a foundation 21 and a column 22. Holes are reserved on the foundation 21 and anchor bolts 23 are pre-embedded on the column 22. (6) Grouting of anchor holes in precast auxiliary tower leg foundation 2: First, check the alignment of the reserved holes in the precast block with the anchor bars, and then grout. The grout should have micro-expansion properties to ensure that the anchor bars and the precast block are completely bonded.

[0032] (7) Reinforcement binding and post-pouring of connecting section: Within the 200mm reserved space, insert circumferential reinforcement 28 and vertical reinforcement 27 according to the design drawings. If the original foundation 1 has exposed reinforcement. Then install the lateral formwork and use a small vibrator to strengthen the vibration at the interface to ensure compaction.

[0033] (8) Installation and mechanical connection of steel plate 25: Inspect the embedded parts on the top of the precast block and grind the surface if necessary. Install the connecting steel plate 25 and use a torque wrench to initially tighten and finally tighten the mechanical connector 26 to ensure smooth stress transmission.

[0034] (9) Demolding and cement-soil backfilling: Demolding is carried out after the concrete strength of the post-cast section reaches 75%. Cement-soil (recommended ratio 8%-12%) is used for backfilling. It is compacted in layers, with each layer not exceeding 250mm in thickness to ensure strength.

[0035] (10) Connection and overall coordination of auxiliary tower structure 3: Connect the prefabricated first-layer auxiliary tower leg 31 to the prefabricated auxiliary tower leg foundation 2; then connect the first-layer auxiliary tower leg 31 to the second-layer auxiliary tower leg 31; then connect the annular constraint assembly and the radial connection assembly on the second-layer auxiliary tower leg 31. The radial connection assembly is connected to the existing tower 4. Connect the remaining auxiliary tower legs in sequence from bottom to top according to the designed height position. After each layer of auxiliary tower legs is connected, the annular constraint assembly and the radial connection assembly are installed. When tightening the anchor bolts 23, the principle of "symmetrical connection and step-by-step tightening" must be followed. After completion, check the stress state of the 8 support points to ensure that the new reinforcement system and the original system form a closed and coordinated stress condition.

[0036] In this embodiment, the circumferential constraint assembly of each auxiliary tower leg 31 includes an upper circumferential steel pipe and a lower circumferential steel pipe, as well as diagonal bars welded between adjacent circumferential auxiliary tower legs; In this embodiment, eight sets of conical expanded-base composite foundations are evenly arranged radially along the original tower 4, corresponding one-to-one with the first-layer auxiliary tower legs 31. The auxiliary structure of the tower forms a gradually changing circumferential constraint truss. Specifically, circumferential steel pipes 32 are arranged in layers along the height of the tower. Each layer of circumferential steel pipes 32 simultaneously surrounds the eight conical auxiliary tower legs 31 and is rigidly connected (welded) to the central main tower 4 and the eight auxiliary tower legs 31. The circumferential steel pipes 32 adopt a design in which the pipe diameter and wall thickness gradually change synchronously with the conical convergence of the tower, forming a gradient bearing system of "strong constraint at the bottom, medium constraint in the middle, and weak constraint at the top", which solves the defects of traditional single towers that have no circumferential constraint and poor torsional performance. The distance between the bottom connection point of the lower circumferential steel pipe 32 and the auxiliary tower leg 31 is ≤1.5m, and the distance between the top connection point of the upper circumferential steel pipe 32 and the auxiliary tower leg 31 is ≤1.5m, to ensure uniform constraint. The slenderness ratio of the transverse diaphragm components (circumferential steel pipe, horizontal connecting rod) is controlled to ≤150.

[0037] Furthermore, the auxiliary tower leg 31 adopts pure cross diagonal bracing 33 to form a stable triangular grid.

[0038] Furthermore, to address the wind energy capture needs in low-wind-speed areas, a Q460 steel conical variable cross-section extension section, 50m high, can be added to the top of the existing central tower 4. The slope of the extension section's tapering is perfectly matched with that of the lower auxiliary tower leg 31, forming an integrated conical force-bearing system for the entire tower. This solves the problems of insufficient stiffness and large wind vibration response after extension of a traditional single-section tower. The extension section is connected to the flange of the existing tower 4 via a transition main plate, with pre-reserved hub and blade connection interfaces at the top.

[0039] Furthermore, in this embodiment, the arrangement parameters of the auxiliary tower legs 31 are as follows: 8 auxiliary tower legs 31 are evenly distributed radially around the central existing tower tube 4. The center of the height of the bottom first layer of auxiliary tower legs 31 is 4m away from the center of the central existing tower tube 4, and the center of the height of the topmost auxiliary tower leg 31 is 2m away from the center of the central existing tower tube 4, forming a 1:0.5 tapered gradient layout that is wider at the bottom and narrower at the top, which thoroughly optimizes the bending moment distribution of the traditional single tower tube. Furthermore, in this embodiment, the node construction parameters are as follows: adjacent auxiliary tower legs 31 nodes adopt single-ring rigid nodes with a node ring wall thickness ≥16mm and the length of each auxiliary tower leg 31 ≤1.2m to ensure uniform constraint of the conical structure.

[0040] Furthermore, in this embodiment, the height of the extension section is 50m, the bottom diameter is consistent with the top diameter of the central tower, the top diameter is narrowed to match the top layout of the auxiliary tower leg 31, and the slope of the narrowing is completely consistent with that of the auxiliary tower leg 31, forming an integrated conical force-bearing system for the entire tower, with a total tower height of up to 140m, solving the problem of insufficient rigidity after the extension of the traditional single tower.

[0041] The integrated wind turbine tower structure of this invention, consisting of a central main tower and an outer conical lattice auxiliary load-bearing system, completely solves the industry pain points of traditional single towers—such as concentrated bending moments at the bottom, insufficient stiffness, weak overturning resistance, and wasted resources in traditional retrofitting—through the radial expansion and upward convergence of eight auxiliary tower legs 31. Combined with a pure cross-braced 33 triangular lattice system, single-ring rigid nodes, and a conical expanded-base radial foundation, it achieves a comprehensive improvement in load-bearing capacity, disaster resistance, and wind energy utilization efficiency without altering the traditional core force transmission path of the tower. It is suitable for 6-9 MW high-power wind turbines and wind power development needs in low-wind-speed areas.

[0042] This invention relates to a tapered, gradually changing auxiliary tower leg system 31 with a pure cross-bracing 33 grid system: the eight auxiliary tower legs 31 adopt a radial tapered layout that is wider at the bottom and narrower at the top. The grid system uses a pure cross-bracing 33 design, completely eliminating horizontal bracing and forming a stable triangular grid, which significantly improves the shear stiffness and geometric stability of the structure, while reducing the structure's self-weight and wind resistance coefficient. Built-in prestressing tendons achieve tensile stress compensation, optimize the bending moment distribution along the height, and solve the defects of concentrated bending moment at the bottom and insufficient shear stiffness in traditional single towers. The key protection features are the tapered, gradually changing tower leg layout design, the pure cross-bracing 33 triangular grid structure, and the prestressing compensation design.

[0043] This invention relates to a gradually changing circumferentially constrained truss and a single-ring hoop node: circumferential trusses with synchronously varying pipe diameters and wall thicknesses are arranged in layers along the tower height, forming a gradient load-bearing system. This connects the central tower and auxiliary tower legs 31 into an integrated structure, improving overall torsional stiffness. The nodes employ single-ring hoop rigid nodes, simplifying construction, alleviating stress concentration, and improving node fatigue life, thus solving the problems of traditional single-tower structures lacking circumferential constraints, having poor torsional performance, and experiencing stress concentration at nodes. The key protection focuses on the gradient design of the gradually changing circumferential truss, the construction of the single-ring hoop node, and the standard control of connection point spacing.

[0044] The present invention features a conical, expanded-base radial foundation system: the auxiliary tower legs 31 adopt a column-foot-direct-landing independent foundation, the radial arrangement expands the anti-overturning moment arm, eliminates the traditional single-tower ring-shaped integral foundation, significantly reduces the amount of concrete used, improves the foundation's pull-out and overturning resistance, and is suitable for complex geological conditions.

[0045] This invention features an integrated design for a tapered variable cross-section extension section: the extension section adopts a tapered variable cross-section design that matches the slope of the auxiliary tower leg 31, forming an integrated tapered force-bearing system for the entire tower. This solves the problems of insufficient stiffness and large wind vibration response after extension of a traditional single-section tower, thus improving wind energy capture efficiency in low-wind-speed areas. The key protection focuses on the slope-matching design of the tapered extension section and the reinforced structure of the transition main plate.

[0046] The principles of moment optimization and load sharing are as follows: Traditional single-tower structures bear all wind loads on their own, resulting in highly concentrated bending moments at the bottom and susceptibility to fatigue failure. This invention utilizes an external conical lattice-type auxiliary load-bearing system to evenly distribute wind and turbine loads across the central tower and eight auxiliary tower legs 31. The tapered, gradually changing layout ensures a smooth distribution of bending moments along the height, reducing the bottom bending moment by more than 30% compared to traditional single-tower structures. Furthermore, the prestressed compressive stress within the auxiliary tower legs 31 counteracts the bending tensile stress in the concentrated tensile stress areas at the bottom, achieving reasonable load distribution and stress balance, significantly improving the structure's load-bearing capacity and fatigue life.

[0047] The principles of stiffness enhancement and vibration resistance optimization are as follows: Traditional single towers are hollow cantilever beams with limited overall stiffness and large wind vibration response. This invention connects the central tower and auxiliary tower legs 31 into an integrated spatial structure through a conical lattice truss system. The pure cross diagonal braces 33 and triangular webs significantly improve the shear stiffness of the structure, with the overall stiffness being more than twice that of traditional single towers. The hollow lattice structure reduces the wind drag coefficient, optimizes the structure's natural frequency, and avoids resonance with the wind vibration frequency. Under the coupled effects of earthquakes and wind disasters, the structural response always remains within the elastic range, resulting in excellent disaster resistance performance.

[0048] The basic principle of overturning resistance strengthening is as follows: Traditional single-tower foundations rely on a ring-shaped integral foundation, which has a limited overturning moment arm and insufficient resistance to uplift and overturning. This invention adopts a conical, expanded-base, radially arranged independent foundation. The radial layout significantly expands the overturning moment arm, more than doubling it compared to traditional single-tower foundations. The direct-ground design of the column bases enables direct force transmission. Furthermore, it allows for flexible selection of foundation types such as monopiles and rock anchors based on geological conditions, adapting to complex geological conditions and enhancing the foundation's resistance to uplift and overturning.

[0049] The principles governing connection reliability and ease of construction are as follows: Traditional single-tower connections rely solely on flanges, resulting in limited torsional and fatigue resistance at the joints. This invention employs a single-ring rigid joint, simplifying the structure, alleviating stress concentration, and improving joint fatigue life. All components are prefabricated in the factory and assembled on-site with bolts, eliminating the need for on-site steel pipe rolling. This reduces the construction cycle by more than 50% compared to traditional single-tower modifications, aligning with the trend of green and low-carbon construction.

[0050] The principle behind improving wind energy utilization efficiency is as follows: Traditional single-tower structures are limited in height and lack sufficient rigidity after extension, making them unsuitable for wind energy capture in low-wind-speed areas. This invention achieves a total tower height upgrade to 140m through a tapered variable-section extension section. Simultaneously, the tapered layout optimizes wind load distribution, improving wind energy capture efficiency in low-wind-speed areas. It can be adapted to 6-9 MW high-power wind turbines, meeting the power upgrade needs of the wind power industry.

[0051] Furthermore, the 31 prestressed tendons of the auxiliary tower legs can be replaced with steel strands with a tensile strength of 1770MPa instead of 1860MPa. The prestress can be adjusted to 12-18MPa to meet the stress requirements of conical tower legs of different power wind turbines. Compared with the traditional single tower design without prestress, this improves the structural safety reserve.

[0052] Furthermore, alternatives to the web member system: In areas with extremely strong winds, local horizontal bracing can be added to the pure cross-bracing 33 web members, retaining the triangular core structure of the web members, further improving the local shear stiffness, without changing the overall conical lattice layout, and significantly improving wind resistance compared to the traditional single tower structure without web members.

[0053] Furthermore, alternative foundation options: When geological conditions are excellent, rock anchors 24 can be eliminated. In soft soil foundation areas, bored piles can be used instead of precast piles, which are suitable for the foundation requirements of radial conical layouts and have greater adaptability compared to traditional single-tower ring foundations.

[0054] Furthermore, a circumferential truss alternative: In scenarios sensitive to self-weight, a lattice truss ring can be used instead of a solid steel pipe ring. The angle of the web members can be adjusted according to the tapered layout, which can further reduce the self-weight of the structure while ensuring stiffness. Compared with the traditional single tower without circumferential constraints, the stiffness is significantly improved.

[0055] Furthermore, the no-extension retrofit solution: For the retrofit of existing traditional single towers, the extension section can be eliminated, and only a conical lattice auxiliary load-bearing system can be added to improve the load-bearing capacity, adapt to the power upgrade requirements of existing wind turbines, without the need to demolish the original tower, and the resource utilization rate exceeds 90%.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for upgrading and retrofitting existing wind turbine towers, characterized in that, Includes the following steps: Multiple new foundation pits were excavated along the circumferential direction of the existing wind turbine tower foundations; Roughen the edges of the original base; Plain concrete was poured into the newly added foundation pit and the pit was leveled. Anchor bolts were installed in each new foundation pit; Multiple prefabricated auxiliary tower leg foundations are hoisted into the corresponding new foundation pits. The auxiliary tower leg foundations include a pile cap and a column. Holes are reserved on the pile cap, and anchor bolts are pre-embedded on the column. During hoisting, ensure that a predetermined space is reserved between the inner ring of the pile cap and the edge of the original foundation. Align the reserved holes on the pile cap with the anchor bolts and grout them to ensure that the anchor bolts are fully gripped with the auxiliary tower leg foundations. Then, mechanically connect the top of the anchor bolts to the pile cap. Within the reserved space, circumferential and vertical reinforcing bars are inserted, and then formwork is erected and the auxiliary tower leg foundation is cast together with the original foundation. Connect the prefabricated first-layer auxiliary tower leg to the auxiliary tower leg foundation, and then connect the first-layer auxiliary tower leg to the second-layer auxiliary tower leg. Next, connect the ring constraint assembly and the radial connection assembly to the second-layer auxiliary tower leg. The radial connection assembly is connected to the existing tower. Connect the remaining auxiliary tower legs in sequence from bottom to top according to the designed height position. After each layer of auxiliary tower legs is connected, install the ring constraint assembly and the radial connection assembly.

2. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, The circumferential constraint assembly includes an upper circumferential steel pipe and a lower circumferential steel pipe, as well as diagonal bars welded between adjacent auxiliary tower legs in the annular shape.

3. The method for upgrading and retrofitting existing wind turbine towers as described in claim 2, characterized in that, The diameter and wall thickness of the circumferential steel pipe decrease synchronously from bottom to top along the height direction of the existing tower.

4. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, The radial connection assembly includes several horizontal connecting rods arranged at a set angle, forming a triangular structure with the tower and auxiliary tower legs.

5. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, The multi-layer auxiliary tower legs are arranged in a tapered shape that is wider at the bottom and narrower at the top along the height of the existing tower.

6. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, Along the existing tower height direction, the auxiliary tower legs of adjacent floors are connected by flanges and bolts.

7. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, The anchor bolts mentioned above can be replaced with steel strands.

8. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, The first auxiliary tower leg is connected to the anchor bolts on the pedestal.

9. The method for upgrading and retrofitting existing wind turbine towers as described in claim 1, characterized in that, The diameter of the auxiliary tower leg gradually decreases from bottom to top along the height direction of the existing tower.

10. A wind turbine tower, characterized in that, It is obtained through the method of upgrading and retrofitting existing wind turbine towers as described in any one of claims 1-9.

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