Goaf site fan foundation horizontal force loading model test device

Abstract

The utility model relates to a goaf site fan foundation horizontal force loading model test device, which comprises a goaf foundation model frame, a fixing device, a loading device, a goaf foundation model and a wind turbine generator model, the front end of an electric cylinder is connected with a loading rod through a spring, and the loading rod is connected with the top of a tower drum in a bolt manner. An adjustable loading system is adopted in the aspect of a wind load loading system, stable output of waveforms such as sine waves, square waves and sawtooth waves can be achieved, and control software can track and correct peak and valley values of controlled variables (such as loads) in the test loading process. The typical value of the dynamic error of each peak value in the whole test process is + / -1% FS, and the adjusting capability is strong; wind loads can be applied to different positions of a goaf site under different engineering geological conditions according to test requirements, and the utilization rate of the test fixing device is improved.

Description

Technical Field

[0001] This utility model relates to a model test of horizontal force loading on a wind turbine foundation, and in particular to a model test device for applying wind loads under different working conditions in a goaf site. Background Technology

[0002] With the long-term mining of coal resources and the rapid development of wind power generation, land for construction projects is becoming increasingly scarce. Some wind farms are forced to consider building in goaf areas, making model testing of wind turbine foundations in goaf sites increasingly important. Current model testing research on wind turbine foundations mainly focuses on general sites, with relatively little research on wind turbine foundations in goaf sites. Therefore, it is necessary to develop a horizontal force loading test device for wind turbine foundations suitable for goaf sites. This device should be able to conduct model tests under different working conditions, which is of great significance for understanding the disaster mechanisms of wind turbine foundations under different geological conditions, wind speeds, and locations.

[0003] The invention patent (ZL 201910467599.2) discloses a test device for vertical and multi-directional horizontal loading of wind turbine foundations, comprising a model box filled with foundation soil, a fixed slide, a loading frame, and a loading device. By processing the slide and loading frame, multi-directional horizontal and vertical loading of the foundation model can be achieved. However, the vertical loading method of this test device restricts the degree of freedom of the tower and cannot reproduce the true displacement of the tower under wind load.

[0004] In addition, invention patent (ZL 201610603317.3) discloses a loading device and method for wind turbine foundation testing. This device includes a tower and a reaction wall located on one side of the tower. The device is relatively short and can simultaneously apply a small horizontal force and a large bending moment to meet the matching loading requirements of a wind turbine foundation model under ordinary laboratory conditions. However, this device is limited to wind turbine foundation model tests in general sites and does not consider the special engineering geological conditions of goaf sites.

[0005] In addition, most ordinary model tests are conducted in general sites and do not involve the special engineering background of goaf areas. Furthermore, most tower models are shorter than the theoretical height, making it impossible to meet the matching of horizontal force and bending moment through single-point loading. Moreover, the loading method of vertical force restricts the degree of freedom at the top of the tower. Utility Model Content

[0006] To address the shortcomings of existing technologies, this utility model provides a horizontal force loading model test device for wind turbine foundations in goaf areas. This new device has a high degree of modularity, allowing for flexible adjustment of the equipment structure according to usage needs, thereby meeting the requirements for equipment operation under different operating environments and greatly improving the flexibility and convenience of experimental operations. Furthermore, during operation, wind loads can be applied to different locations in the goaf area under different engineering geological conditions according to test requirements, improving the utilization rate of the test fixing device.

[0007] To achieve the above objectives, this utility model is implemented through the following technical solution:

[0008] A test device for horizontal force loading of wind turbine foundations in a goaf area includes a model frame, a loading device, a fixing device, a goaf foundation model, and a wind turbine model. The base of the model frame is welded to the columns, and the left and right columns are bolted to the base plate. The base is fixed to the concrete ground with expansion bolts. A baffle is bolted to the columns and can be assembled to the required height according to the test requirements, allowing for easy disassembly. The loading device is bolted to the base, and four long bolts connect the base to two modified channel steels. The channel steels are bolted to the left column of the model frame. To ensure the stability of the channel steels during loading, a fixed crossbeam is added to one cantilever section of the channel steel. The base of the crossbeam is bolted to the channel steel, and both ends of the crossbeam are fixed to the wall with expansion bolts. The loading device adopts a force and displacement dual closed-loop control device, which includes an electric cylinder, a servo, a servo controller, a host and control software. It can achieve the purpose of applying wind load to the wind turbine foundation model test in the goaf area. In addition, the loading system will track and control the test control quantity in real time during the loading process to ensure the accuracy of the output load.

[0009] Furthermore, the base of the model frame includes two steel plates, both of which are drilled with holes according to design requirements for bolt connection to the concrete bottom surface. The thickness of the steel plates is not less than 6mm, and the length of the expansion bolts is not less than 8cm.

[0010] Furthermore, the column comprises two rectangular steel barrels, which are rolled from steel plates with a thickness of not less than 6mm. The outer edge dimensions of the rectangular cross-section are 20cm × 25cm, and the column height is not less than 2m. The joints of the column barrels are fixed by welding. Both columns have holes drilled along their center lines (10cm from the front and rear edges) using laser drilling technology, with a hole spacing of 10cm. Nuts are welded to the back of the bolt holes on the columns for easy bolt connection with the baffle.

[0011] Furthermore, the baffle is made of U-shaped steel that is not easily deformed, and the number of U-shaped steel used is not less than 30. The specifications of the U-shaped steel are 100mm×48mm×53mm and the length is 3m. A bolt hole is reserved at each end of the U-shaped steel 10cm away. During the test, the baffle is fixed to the column by bolts. The baffle of appropriate height can be assembled according to the test requirements.

[0012] Furthermore, the base plate is 2.6m long, 0.25m wide, and 0.2m high. It is made of rolled steel plate with a thickness of not less than 8mm, and the joints are reinforced by welding. The base plate and the columns are bolted together using steel plates, with each column requiring two steel plates. Bolt holes must be pre-drilled in the base plate, columns, and steel plates, and each steel plate requires no fewer than four bolts.

[0013] Furthermore, the two channel steels used in the fixing device are both 140mm×60mm×8mm in size and 1.5m in length. Laser drilling is used to drill holes along the centerline of the channel steel legs at 10cm intervals to allow the loading equipment to move freely horizontally. Additionally, pre-drilling is required at the connection points between the channel steel and the column. Two holes with a 4cm interval are drilled along the waist height of each channel steel at a distance of 10cm from the end. Two bolt holes for connection to the channel steel are drilled every 14cm along the height of the column.

[0014] Furthermore, the loading device requires an L-shaped base to be bolted to a steel plate slide. The L-shaped base is welded from two steel plates, each 8cm long and wide, and 1cm thick. Each steel plate has pre-drilled holes at its four corners. Additionally, a 4cm diameter hole is pre-drilled in the center of the vertical steel plate for assembly with the electric cylinder. The vertical steel plate connects to the front flange of the electric cylinder, while the horizontal steel plate connects to the sliding base. The base measures 25cm x 20cm and is 1cm thick. Two 15cm long bolt holes are pre-drilled along the horizontal direction of the base to allow for minor horizontal adjustments of the electric cylinder. The base is connected to two channel steels with four bolts, each at least 15cm long.

[0015] Furthermore, a force sensor needs to be installed at the piston rod nut at the front end of the electric cylinder. By connecting the force sensor to the controller, the output load can be tracked and corrected in real time. The force sensor should be a high-precision and high-performance sensor to ensure the accuracy of the applied load.

[0016] Furthermore, a high-strength lead screw with a length of 3cm should be installed at the front end of the force sensor. The lead screw is connected to a specially designed stepped bolt tube on its outer side. The bolt tube is 4cm long, with a lower stepped section of 3.5cm and an upper stepped section of 0.5cm. The lower stepped section of the bolt tube is connected to the left side of the spring with a connection length of 3.5cm. The spring wire diameter is 6mm and its length is 10cm. Correspondingly, the right side of the spring is connected to a bolt tube of the same type with a connection length of 3.5cm. The right bolt tube is connected to a loading rod with a length of 8cm. One end of the loading rod is hemispherical to facilitate connection with the tower clamp.

[0017] Furthermore, a clamp should be installed at the height where the wind load is applied to the tower. The selected clamp should be at least 10mm thick, at least 12mm wide, and capable of clamping a diameter of at least 4cm. A hemispherical hole with a diameter of 8mm and a depth of 5mm should be pre-drilled at the center of the outer diameter of the clamp. During loading, the front rod of the electric cylinder should be connected to the hemispherical hole to ensure that the tower's degree of freedom is not restricted, consistent with actual engineering practices.

[0018] Furthermore, the vertical force is applied in the form of a weight, which should be made into a cube shape. A steel pipe with a length of not less than 5cm is welded to the bottom of the weight. The inner diameter of the steel pipe is the same as the outer diameter of the top of the tower, and the wall thickness of the steel pipe is not less than 3mm.

[0019] This new type of structure has a high degree of modularity. On the one hand, the equipment structure can be flexibly adjusted according to usage needs, thereby meeting the requirements of equipment operation in different operating environments and greatly improving the flexibility and convenience of experimental operations. On the other hand, during operation, wind loads can be applied to different locations in the goaf under different engineering geological conditions according to experimental requirements, improving the utilization rate of the test fixing device. (See attached figures for details.)

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments;

[0021] Figure 1 This is a three-dimensional diagram of the model test device of this utility model;

[0022] Figure 2 A 3D drawing of the model fixing device;

[0023] Figure 3 A 3D model of the model frame;

[0024] Figure 4 This is a 3D diagram of the model loading device.

[0025] 1. Column, 2. Goaf foundation model, 3. Channel steel, 4. Crossbeam, 5. Electric cylinder, 6. Steel plate, 7. Long bolt, 8. Expansion bolt, 9. Column base, 10. Baffle, 11. Long bolt hole, 12. L-shaped base, 13. Force sensor, 14. Spring, 15. T-bolt pipe, 16. Loading rod, 17. Model frame base plate, 18. Connecting steel plate, 19. Model frame, 20. Fixing device, 21. Electric servo valve, 22. Servo controller, 23. Main unit, 24. Clamp, 25. Wind turbine upper structure, 26. Loading device, 27. Wind turbine model, 28. Tower. Detailed Implementation

[0026] To facilitate the implementation of the technical means, creative features, objectives, and effects of this utility model, the following description, in conjunction with specific embodiments, further elaborates on this utility model.

[0027] like Figure 1-4 As shown, a horizontal force loading model test device for wind turbine foundation in a goaf area includes a model frame 19, a fixing device 20, a loading device 26, a goaf foundation 2, and a wind turbine model 27.

[0028] The model frame includes columns 1, a base plate 17, and baffles 10. The columns are at least 2m high, and columns 1 are made of rolled steel plates with a thickness of at least 5mm. The joints of the steel plates are reinforced by welding. The bottom steel plates of the columns are connected to the concrete ground by expansion bolts 8, each bolt being at least 10cm long. Each column has at least 8 bolts connecting its bottom steel plate to the ground. The centerlines of the columns are drilled using laser drilling technology to facilitate the assembly of the baffles. Drilling begins 15cm above the bottom of the column and is spaced 10cm apart. Holes are pre-drilled above 1.6m on the left side of the column to facilitate the subsequent assembly of the channel steel 3 used for fixing devices. The drilling interval is 14cm. Each channel steel 3 is fixed to the left side column with two bolts. The base plate is manufactured in the same way as the columns, both being made of rolled steel plates. The base plate connects the two columns, and its width (25cm) is the same as the columns. The base plate is 2.6m long, and both the front and rear sides of the columns are bolted to the base plate, with at least 8 bolts on each side. The baffle is 3m long and 10cm high, made of high-strength U-shaped steel. Both ends of the baffle have pre-drilled bolt holes. When constructing the goaf foundation model, the number of baffles can be assembled according to the experimental requirements, facilitating disassembly and improving the effective utilization rate of the experimental device.

[0029] The fixing device includes channel steel 3, steel plate 6, long bolts 7, L-shaped base 12, and crossbeam 4. The two channel steels are both 140mm × 60mm × 8mm in size and 1.5m in length. Bolt holes are pre-drilled at the connection between channel steel 3 and column 1, with each channel steel requiring two bolts for fixation to the column. Holes are drilled along the centerline of the leg length on the top surface of the channel steel at 10cm intervals to facilitate horizontal movement of the loading device. The steel plate 6 serves as the bottom support for the loading device, supporting it and connecting the channel steel 3. Two bolt holes 11, each at least 10cm long, are pre-drilled along the horizontal direction using laser drilling technology to facilitate localized horizontal movement of the loading device. The steel plate thickness is at least 1cm. Four long bolts 7 are used to connect the steel plate and channel steel, fixing the four corners of the steel plate. The bolt diameter is at least 12mm and the length is at least 15cm, facilitating height adjustment of the loading device. The L-shaped base 12 is used to connect the electric cylinder and the steel plate. The bottom steel plate of the L-shaped base is used to connect the steel plate, and the vertical steel plate is used to connect to the front flange of the electric cylinder. All connections are bolted, with four bolts used to fix each side. The bottom surface of the L-shaped base and the vertical steel plate are connected by welding. A 4cm diameter circular hole needs to be reserved along the center of the vertical steel plate to facilitate connection with the front flange of the electric cylinder. To ensure the stability of the L-shaped base, two triangular steel plates need to be installed between the base steel plate and the vertical steel plate. The thickness of all steel plates used for the L-shaped base is not less than 1cm. The crossbeam is welded from a square tube and a steel plate. The square tube has a side length of not less than 5cm and a wall thickness of not less than 3mm. The steel plate has a thickness of not less than 6mm and a width of not less than 20cm. The steel plate has four bolt holes for connecting to two channel steels respectively. A rectangular steel plate is welded to each end of the square tube. Each steel plate has two long bolt holes. Expansion bolts can be used to fix the crossbeam to the wall through the long bolt holes, thereby limiting the back-and-forth swing of the loading device during the loading process and making the fixing device more secure.

[0030] The loading system includes an electric cylinder 5, a force sensor 13, a T-bolt tube 15, a spring 14, a loading rod 16, an electric servo valve 21, a servo controller 22, and a main unit 23. The electric cylinder 5 is a horizontal force application device. According to the test requirements, a force sensor 13 is installed on the electric cylinder 5 to monitor the output load in real time. To ensure the continuity and stability of the output load curve, a high-stiffness spring 14 is installed at the front end of the force sensor 13. The spring 14 has a wire diameter of not less than 5mm, and both ends of the spring are connected through the T-bolt tube 15 to ensure the spring remains horizontal. The T-bolt tube has pre-drilled screw holes for connection with the bolt at the front end of the force sensor and the loading rod. The front end of the loading rod 16 needs to be modified into a hemispherical shape to facilitate the application of horizontal force. The electric servo controller can precisely control the movement of the electric cylinder according to preset commands, achieving dual closed-loop control of force and displacement through monitoring information from the force sensor and displacement sensor. The electric servo valve 21 can provide feedback on the output load through the sensor and adjust the actuator position or speed according to the error signal to meet the test control requirements.

[0031] The goaf foundation 2 includes a two-dimensional model of each rock stratum 30 between the surface and the bottom of coal seam 29. The goaf foundation model is made of similar materials, and the proportions of each rock stratum are obtained by consulting relevant data. After the foundation model is completed, the front and rear baffles 10 of the model need to be removed, and then coal seam 29 is excavated to form the goaf site. After the goaf site has stabilized, excavation is carried out at a designated location on the surface to lay the fan foundation. During the laying, the flatness of the bottom surface of the fan foundation and the levelness of the foundation should be ensured.

[0032] The wind turbine model 27 includes a wind turbine foundation, a tower 28, clamps 24 and 25, and a superstructure. The wind turbine foundation is manufactured according to the similarity ratio required for the test, and it needs to be prepared in advance, with foundation rings and bolts pre-arranged inside. The tower is manufactured according to the test requirements, and the bottom flange of the tower is connected to the wind turbine foundation. The superstructure is welded from a mass block and steel pipes. The mass block should be made of high-density steel, and the length of the steel pipes should be no less than 5cm, the wall thickness no less than 3mm, and the inner diameter of the steel pipes should be equal to the outer diameter of the top of the tower, thus ensuring a tight connection between the superstructure and the tower. The weight of the superstructure should be based on the vertical load, so that the gravity generated by the self-weight of the superstructure is equal to the magnitude of the vertical load. The clamps need to have a pre-drilled hemispherical hole, the diameter of which is the same as the diameter of the hemispherical end of the loading rod. The end of the loading rod is connected to the clamp hole by a pin, so as not to affect the degree of freedom of the tower. The height of the clamps can be adjusted according to the test requirements to achieve the purpose of applying horizontal forces at different heights.

[0033] In practice:

[0034] The model comprises columns, base plates, baffles, channel steel, movable bases, L-shaped bases, crossbeams, electric cylinders, stepped bolted pipes, springs, clamps, towers, wind turbine foundation models, and goaf foundation models, all connected from top to bottom by bolts. This fully mechanical connection allows for adjustments to the goaf foundation height and horizontal force loading position according to test requirements. The baffles are bolted to the columns; each baffle is 10cm high, and different numbers can be assembled as needed. Both the baffles and columns possess high rigidity and are not easily deformed, avoiding unnecessary test errors caused by model dimensional inaccuracies. The channel steel is bolted to one side of the columns, with each channel steel section secured to the column using two bolts, ensuring its stability. Bolt holes are pre-drilled along the horizontal direction on the upper edge of the channel steel to facilitate horizontal force loading on the wind turbine foundations at different locations within the goaf site. The electric cylinder is bolted to a movable base via an L-shaped base. The movable base has two long bolt holes drilled horizontally, facilitating small-range horizontal adjustments of the electric cylinder. The movable base is fixed to the channel steel with four long bolts, each at least 15cm long, allowing for height adjustment of the electric cylinder according to test requirements. The crossbeam is connected to the channel steel via a steel plate and then fixed with expansion bolts pre-installed in the wall, reinforcing the channel steel and ensuring the electric cylinder does not swing back and forth during loading. A bolted tube and spring are added to the front of the electric cylinder to ensure the accuracy of the output load and the horizontality of the wind load. The loading rod and clamp are connected by a pin-type free connection, ensuring the horizontal force remains horizontal throughout the loading process, and the tower's freedom of movement is unrestricted. The vertical force is fixed to the top of the tower by a weight. This loading method ensures the accuracy of the applied load and saves on test costs. The electric cylinder is connected to the main unit via a controller. The force and displacement sensors configured in the electric cylinder will feed back the output load to the control software in real time. Then, the controller will make real-time corrections to the output load to ensure the stability of the output load.

[0035] In addition, the new type of fixing device can move in any direction within the model frame, and can apply horizontal force to the fan foundation at different locations in the goaf, thus taking into account the impact of different locations in the goaf on the fan foundation disaster.

[0036] This novel structure has a high degree of modularity. On the one hand, the equipment structure can be flexibly adjusted according to usage needs, thereby meeting the requirements of equipment operation in different usage environments, and greatly improving the flexibility and convenience of experimental operations. On the other hand, during operation, wind loads can be applied to different locations in the goaf site under different engineering geological conditions according to experimental requirements, improving the utilization rate of the test fixing device. The above shows and describes the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from the spirit and scope of this utility model, and all such changes and modifications fall within the scope of protection of this utility model. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. A test device for horizontal force loading of a wind turbine foundation in a goaf area, characterized in that, The horizontal force loading model test device for wind turbine foundations in the goaf area includes a model frame, a loading device, a fixing device, a goaf foundation model, and a wind turbine model. The base of the model frame is welded to the columns, and the columns on both sides are connected to the base plate by bolts. The base is fixed to the concrete ground by expansion bolts. The baffle is connected to the columns by bolts. The loading device is fixed to the base by bolts, and the base is connected to two modified channel steels by four long bolts. The channel steels are connected to the left column of the model frame by bolts. At the same time, a fixed crossbeam is added to a section of the cantilever of the channel steel. The crossbeam is connected to the channel steel by bolts, and the two ends of the crossbeam are fixed to the wall by expansion bolts. The loading device adopts a force and displacement dual closed-loop control device, including an electric cylinder, a servo, a servo controller, and a host.

2. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, The base of the model frame consists of two steel plates, both of which are drilled with holes according to design requirements for bolt connection to the concrete bottom surface. The thickness of the steel plates is not less than 6mm, and the length of the expansion bolts is not less than 8cm.

3. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, The column consists of two rectangular steel barrels. The column is made of rolled steel plate with a thickness of not less than 6mm. The outer edge dimension of the rectangular cross section is 20cm×25cm. The column height is not less than 2m. The column barrel joint is fixed by welding. Both columns are drilled with laser drilling technology at 10cm from the center line along the front and rear edges. The drilling spacing is 10cm. Nuts are welded to the back of the bolt holes of the column to facilitate bolt connection with the baffle.

4. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, The baffle is made of U-shaped steel that is not easily deformed. The number of U-shaped steel used is no less than 30. The specifications of the U-shaped steel are 100mm×48mm×53mm and the length is 3m. A bolt hole is reserved at each end of the U-shaped steel 10cm away, and the baffle is fixed to the column by bolts.

5. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, The base plate is 2.6m long, 0.25m wide, and 0.2m high. It is made of steel plate with a thickness of not less than 8mm. The joint gaps are reinforced by welding. The base plate and the column are connected by bolts using steel plates. Each column requires two steel plates for connection. Bolt holes must be reserved in the base plate, column, and steel plates. The number of bolts used for each steel plate is not less than four.

6. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, The two channel steels used for the fixing device are both 140mm×60mm×8mm in size and 1.5m in length. They are drilled with laser drilling technology along the center line of the channel steel legs, with a drilling spacing of 10cm. In addition, holes need to be pre-drilled at the connection between the channel steel and the column. Two holes with a spacing of 4cm are drilled along the waist height direction at 10cm from the end of each channel steel. Two bolt holes for connecting with the channel steel are drilled every 14cm along the height direction on the column.

7. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, The loading device is bolted to the steel plate slide using an L-shaped base. The L-shaped base is made of two welded steel plates, each 8cm long and wide, and 1cm thick. Each steel plate has holes pre-drilled at its four corners. Additionally, a 4cm diameter circular hole is pre-drilled in the center of the vertical steel plate. The vertical steel plate is used to connect to the front flange of the electric cylinder, and the horizontal steel plate is used to connect to the sliding base. The base measures 25cm x 20cm and is 1cm thick. Two long bolt holes, each 15cm long, are pre-drilled along the horizontal direction on the base. The base is connected to two channel steels using four bolts, each at least 15cm long.

8. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 1, characterized in that, A force sensor needs to be installed at the piston rod nut at the front end of the electric cylinder; a high-strength lead screw should be added to the front end of the force sensor. The lead screw is 3cm long and its outer side is connected to a specially made stepped bolt tube. The bolt tube is 4cm long, with a lower stepped section of 3.5cm and an upper stepped section of 0.5cm. The lower stepped section of the bolt tube is connected to the left side of the spring with a connection length of 3.5cm. The spring wire diameter is 6mm and its length is 10cm. The corresponding right end of the spring is connected to a bolt tube of the same type with a connection length of 3.5cm. The right bolt tube is connected to a loading rod with a length of 8cm. One end of the loading rod is hemispherical to facilitate connection with the tower clamp.

9. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 8, characterized in that, A clamp should be installed at the height where the wind load is applied to the tower. The selected clamp should be at least 10mm thick, at least 12mm wide, and have a clamping diameter of at least 4cm. A hemispherical hole with a diameter of 8mm and a depth of 5mm should be pre-drilled at the center of the outer diameter of the clamp.

10. The horizontal force loading model test device for wind turbine foundations in goaf areas according to claim 8, characterized in that, The vertical force is applied in the form of a cube-shaped weight. A steel pipe with a length of not less than 5cm is welded to the bottom of the weight. The inner diameter of the steel pipe is the same as the outer diameter of the top of the tower, and the wall thickness of the steel pipe is not less than 3mm.

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