Anti-loose composite nut structure for iron tower and construction method

Abstract

The invention relates to the technical field of iron tower construction, and discloses an anti-loose composite nut structure for an iron tower and a construction method.The anti-loose composite nut structure for the iron tower comprises connecting plates arranged on an iron tower connecting part and used for connection, a bolt penetrates through the position between every two adjacent connecting plates, and a screw of each bolt is sleeved with a first flat washer and a second flat washer; the first flat washer and the second flat washer are distributed on the sides, away from each other, of the two connecting plates and located between the head of the bolt and the adjacent connecting plate. Through the inclined washer between the lower nut and the upper nut, the friction coefficient between the upper nut and the lower nut is reduced and stabilized, a thread difference is formed between the upper nut and the lower nut, synchronous rotation of the upper nut and the lower nut is prevented, and the site construction management difficulty is reduced; a plurality of contact surfaces are formed between a nut thread and a bolt thread, so that the anti-loosening performance of the nut is improved; a plurality of reverse contact surfaces of threads of the upper nut and the lower nut abut against each other, so that the anti-loosening performance is further enhanced; a reliable double-nut self-locking anti-loosening structure is formed only through the inclined gasket, special assemblies and machining processes are avoided, and the anti-loosening cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of iron tower construction, and in particular to an anti-loosening composite nut structure for an iron tower and a construction method. Background Art

[0002] In the field of iron towers, the existing truss towers currently have round steel pipe components that are mostly connected by flanges, and angle steel components that are mostly connected by shear bolt nodes. Regardless of flange or shear bolt nodes, during use, due to the lack of effective maintenance for a long time, a considerable number of bolts and nuts have loosened or fallen off. While node tightening relies on manual work, if there is a lack of effective supervision, there will be major safety hazards. Especially for shear bolt nodes, since the relevant design and construction acceptance standards for iron towers have low requirements for bolt preload, friction-type connections cannot be formed, and the node plates are in a sliding state when the nodes are sheared. According to the research results of scholars at home and abroad, compared with node bolts (flange bolts) that bear alternating tension and compression loads, node bolts (shear bolts) that bear reciprocating lateral loads are more likely to loosen or even fall off, affecting structural safety.

[0003] The severity of bolt loosening is mainly affected by the node processing accuracy, the initial preload of the bolt, the roughness of the contact surface, the local wind conditions (including wind speed and turbulence), etc. However, in essence, under the action of wind load, the bolts are subjected to reciprocating tension and compression loads or lateral loads, the preload gradually decays and the nut rotates, so a composite nut structure and construction method for preventing loosening of iron towers are proposed. Summary of the invention

[0004] In order to solve the technical problems existing in the prior art, the present invention provides an anti-loosening composite nut structure for an iron tower and a construction method.

[0005] The present invention is implemented by the following technical scheme: a composite nut structure for preventing loosening of an iron tower, a connecting plate for connection arranged at a connecting part of an iron tower, bolts passing through adjacent connecting plates, a flat washer 1 and a flat washer 2 provided on the screw rod of the bolt, flat washer 1 and flat washer 2 are distributed on the side away from each other of two groups of connecting plates, flat washer 1 is located between the bolt head and the adjacent connecting plate, a lower nut, an oblique washer and an upper nut are sequentially provided on the side away from the connecting plate of flat washer 2, the lower nut and the upper nut are threadedly sleeved with the screw rod of the bolt, and the oblique washer is sleeved on the outer ring of the screw rod of the bolt.

[0006] As a further improvement of the above solution, one side of the inclined washer is a plane, and the other side of the inclined washer is an inclined surface.

[0007] As a further improvement of the above solution, the angle of the inclined surface is 1° to 3°.

[0008] As a further improvement of the above solution, the plane of the inclined washer contacts the upper nut, and the inclined surface of the inclined washer contacts the lower nut.

[0009] As a further improvement of the above solution, the torque ratio of the upper nut and the lower nut during installation is: 1:0.2-0.9.

[0010] As a further improvement of the above solution, the front face of the first flat washer contacts the bolt head, and the front face of the second flat washer contacts the lower nut.

[0011] A construction method for an anti-loosening composite nut structure for an iron tower comprises the following steps:

[0012] Step S1, making a connection plate with mounting holes on the tower connection parts, and bringing the tower connection parts close to each other so that adjacent connection plates collide with each other and enter a waiting state for installation;

[0013] Step S2, insert the flat washer into the bolt, and pass the bolt through the connecting plate;

[0014] Step S3, installing the flat washer and the lower nut, and applying torque to the lower nut;

[0015] Step S4: Install the oblique gasket and the upper nut on the bolt, and apply torque to the upper nut to complete the installation.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention reduces and stabilizes the friction coefficient between the upper and lower nuts through the inclined washer between the lower nut and the upper nut, and forms a thread difference between the upper and lower nuts to prevent the upper and lower nuts from rotating synchronously, thereby reducing the difficulty of on-site construction management.

[0018] 2. Multiple contact surfaces are formed between the nut thread and the bolt thread of the present invention, and the number of superstatics is higher, which is beneficial to improving the mechanical bite force between the threads and improving the anti-loosening performance of the nut.

[0019] 3. The present invention utilizes multiple reverse contact surfaces of the upper and lower nut threads to press against each other, forming a reliable thread self-locking structure, further enhancing the anti-loosening performance.

[0020] 4. The present invention only uses inclined washers to form a reliable double-nut self-locking anti-loosening structure, avoids the use of special components and mechanical processing technology, and has a low anti-loosening cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic structural diagram of a composite nut structure for preventing loosening of an iron tower provided by the present invention;

[0022] Figure 2 An exploded view of a composite nut structure for preventing loosening of an iron tower provided by the present invention;

[0023] Figure 3 A schematic diagram of the structure of the connection node provided by the present invention;

[0024] Figure 4 A comparison diagram of bolt loosening results under different amplitudes in Example 5 provided by the present invention;

[0025] Figure 5 A comparison diagram of bolt loosening results at different frequencies in Example 5 provided by the present invention;

[0026] Figure 6 A comparison diagram of bolt loosening results under different pre-tightening forces in Example 5 provided by the present invention;

[0027] Figure 7 A comparison diagram of bolt loosening results at different gasket inclination angles in Example 5 provided by the present invention;

[0028] Figure 8 A diagram showing the loosening of the two-nut three-washer anti-loosening bolts in Example 5 provided by the present invention;

[0029] Fig. 9 A diagram showing the loosening of the composite nut (1.5°) anti-loosening bolt in Example 5 provided by the present invention;

[0030] Fig.10 A diagram showing the loosening of the composite nut (3°) anti-loosening bolt in Example 5 provided by the present invention;

[0031] Fig.11 This is a diagram showing the loosening of the ring groove rivet in Example 5 provided by the present invention.

[0032] Description of main symbols:

[0033] 1. Connecting plate; 2. Bolt; 3. Lower nut; 4. Upper nut; 5. Two flat washers; 6. Angled washers; 7. One flat washer. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0035] Embodiment 1:

[0036] Please combine Figure 1-Figure 3, a composite nut structure and construction method for preventing loosening of an iron tower according to the present embodiment, a connecting plate 1 for connection is arranged at the connecting part of the iron tower, bolts 2 are penetrated between adjacent connecting plates 1, the screw rods of the bolts 2 are sleeved with flat washers 1 and flat washers 2 5, the flat washers 1 7 and flat washers 2 5 are distributed on the side away from each other of the two groups of connecting plates 1, the flat washer 1 7 is located between the head of the bolt 2 and the adjacent connecting plate 1, and the side of the flat washer 2 5 away from the connecting plate 1 is sequentially provided with a lower nut 3, an oblique washer 6 and an upper nut 4, the lower nut 3 and the upper nut 4 are sleeved with the screw rod threads of the bolt 2, and the oblique washer 6 is sleeved on the outer ring of the screw rod of the bolt 2.

[0037] One side of the inclined washer 6 is a plane, and the other side of the inclined washer 6 is an inclined surface.

[0038] The included angle of the inclined surface is 1° to 3°.

[0039] The plane of the inclined washer 6 contacts the upper nut 4 , and the inclined surface of the inclined washer 6 contacts the lower nut 3 .

[0040] The torque ratio of the upper nut 4 and the lower nut 3 during installation is: 1:0.2-0.9.

[0041] The front side of the flat washer 7 contacts the head of the bolt 2, and the front side of the flat washer 2 5 contacts the lower nut 3.

[0042] During the installation process, it is not allowed to apply lubricating grease to the contact surfaces of bolt 2, lower nut 3, upper nut 4, flat washer 1 5, flat washer 2 7 and angled washer 6.

[0043] Among them, the inclined washer 6 is used to change the thread contact state so that the lower nut 3 and the upper nut 4 form a reliable double-nut self-locking structure to prevent loosening; the flat washer 7 is used to protect the chamfer of the root of the bolt 2; a flat washer 5 is provided between the connecting plate 1 and the lower nut 3 to reduce and stabilize the friction coefficient;

[0044] Embodiment 2:

[0045] A construction method for an anti-loosening composite nut structure for an iron tower comprises the following steps:

[0046] Step S1, making a connection plate 1 with a mounting hole on the tower connection component, and bringing the tower connection parts close to each other so that adjacent connection plates 1 collide with each other and enter a waiting state for installation;

[0047] Step S2, insert the flat gasket 7 into the bolt 2, and pass the bolt 2 through the connecting plate 1;

[0048] Step S3, installing the flat washer 6 and the lower nut 3, and applying torque to the lower nut 3;

[0049] Step S4, installing the inclined washer 6 and the upper nut 4 on the bolt 2, and applying torque to the upper nut 4 to complete the installation.

[0050] Embodiment 3:

[0051] Construct the test group:

[0052] According to the test requirements, six test groups were constructed, including one female and two washers conventional bolt connection pair, two female and two washers bolt connection pair, two female and three washers anti-loosening bolt, composite nut (two female and two flat washers and one 1.5° inclined washer), composite nut (two female and two flat washers and one 3° inclined washer) and ring groove rivet. Each group was divided into three groups for testing. The group test contents are shown in Table 1.

[0053] Table 1 is a detailed list of 6 test groups:

[0054]

[0055]

[0056] Embodiment 4:

[0057] Lateral vibration test:

[0058] Test conditions: The test is carried out in accordance with the "Fastener Transverse Vibration Test Method" GB / T10431-2008 standard, using the Ambunec fastener transverse vibration tester to perform the transverse vibration test operation;

[0059] Experimental test results:

[0060] (1) The first group of tests (S1-1\S1-2\S1-3) is for bolts + flat washers + nuts. The test frequency is 12.5 Hz, the amplitude is ±2 mm, the lubrication condition is engine oil, the vibration number is 1500 times, and the number of valid tests is 2. The test results are shown in Table 2.

[0061] Table 2 shows the S1 lateral vibration test results:

[0062]

[0063] (2) The second group of tests (S2-1\S2-2\S2-3) was conducted on bolts + flat washers + nuts + nuts. The test frequency was 12.5 Hz, the amplitude was ±2 mm, the lubrication condition was engine oil, the number of vibrations was 1500, and the number of valid tests was 3. The test results are shown in Table 3.

[0064] Table 3 shows the S2 lateral vibration test results:

[0065]

[0066]

[0067] (3) The third group of tests (S3-1\S3-2\S3-3) is composed of bolt + flat washer + nut + flat washer + nut. The test frequency is 12.5 Hz, the amplitude is ±2 mm, the lubrication condition is engine oil, the vibration number is 1500 times, and the number of valid tests is 3. The test results are shown in Table 4.

[0068] Table 4 shows the S3 lateral vibration test results:

[0069]

[0070] (4) The fourth group of tests (S4-1\S4-2\S4-3) is composed of bolt + flat washer + nut + bevel washer (1.5° + nut. The test frequency is 12.5 Hz, the amplitude is ±2 mm, the lubrication condition is engine oil, the vibration number is 1500 times, and the number of valid tests is 3. The test results are shown in Table 5.

[0071] Table 5 shows the lateral vibration test results of the 1.5° inclined washer in S4:

[0072]

[0073] (5) The fourth group of tests (S4-1\S4-2\S4-3) is composed of bolt + flat washer + nut + bevel washer (3° + nut, the test frequency is 12.5 Hz, the amplitude is ±2 mm, the lubrication condition is engine oil, the vibration number is 1500 times, the number of valid tests is 3, and the test results are shown in Table 6;

[0074] Table 6 shows the lateral vibration test results of the 3° inclined washer in S4:

[0075]

[0076] (6) The sixth group of tests (S5-1\S5-2\S5-3) was conducted on ring groove rivets. The test frequency was 12.5 Hz, the amplitude was ±2 mm, the lubrication condition was engine oil, the number of vibrations was 1500 times, and the number of valid tests was 1. The test results are shown in Table 7.

[0077] Table 7 shows the results of the S6 lateral vibration test:

[0078]

[0079] Embodiment 5:

[0080] Tower flange anti-loosening bolt test:

[0081] 1. Experimental purpose: It is divided into two stages, and the respective purposes are as follows:

[0082] (1) The looseness of the conventional bolted connection with one nut and two gaskets at the flange node under different test parameters (amplitude, frequency, preload, gasket inclination angle) under reciprocating external load;

[0083] (2) The anti-loosening effect of three types of anti-loosening bolts (two-nut three-washer anti-loosening bolts, composite nuts, and ring groove rivets) under the action of reciprocating external loads.

[0084] 2. Test conditions: The test uses a high-performance actuator to reciprocate and load the specimen with horizontal force based on a certain frequency and amplitude. The absolute values ​​of thrust and tension are equal during the reciprocating loading.

[0085] The test is a full-scale test. The test object (test piece) is a 12.5m high communication single pipe, which consists of 3 tower sections. The tower sections are connected by flanges and are processed and installed to make the test piece compatible with the workbench of the test equipment. The tooling includes bottom production, loading head, and loading point connection flange.

[0086] The loading point is located above the top flange of the second tower section. Therefore, the bending moment of the top flange of the second tower section is small, and the bolts will not loosen. The flange (F2) connecting the first tower section and the second tower section actually bears the tension and compression alternating reciprocating load. Therefore, it is only necessary to monitor the preload of the flange bolts in real time. At the same time, although the bottom flange foundation anchor bolts are not the subject of the test research, they should be inspected and maintained during the test to prevent loosening from affecting the structural stiffness.

[0087] The bolt preload is monitored in real time through an annular pressure sensor, and the data is collected and saved by the data acquisition instrument. An annular pressure sensor is arranged on the bolts of the flange (F2) connecting the first tower section and the second tower section. The bolt facing the actuator is defined as bolt No. 1, and the bolt facing away from the actuator is defined as bolt No. 2. Bolts No. 1 and No. 2 should be monitored simultaneously;

[0088] 3. Analysis of test subjects

[0089] (1) Structural natural frequency

[0090] The test object model is established and the natural frequency of the structure is calculated. It is assumed that the tower bottom is a fixed support and the tower sections are rigidly connected.

[0091] The first three natural frequencies of the above structural model are 3.86Hz, 15.23Hz, and 35.81Hz.

[0092] Before the first phase of the test, the acceleration time history curve of the specimen was obtained by the tapping method, and the acceleration time history curve was subjected to Fourier transform to obtain the acceleration frequency domain curve of the structure. The three peak points of the curve were 2.90Hz, 12.79Hz, and 30.36Hz, corresponding to the first three natural frequencies of the structure.

[0093] The natural frequencies of each order of the model are greater than the measured natural frequencies because the model does not take into account the foundation stiffness and the overall stiffness of the model is greater than the actual one. The foundation bending stiffness is estimated to be 4.0e+7Nm / rad. The foundation stiffness is corrected in the model. The first three natural frequencies of the corrected model are 2.99Hz, 12.67Hz, and 30.73Hz, which are close to the measured results. It can be judged that the model stiffness is consistent with the actual one. The actuator excitation frequency should be staggered by more than 10% from the structural natural frequency, as shown in Table 8;

[0094] Table 8 is a table showing the differences in structural natural frequencies:

[0095] Model Measured difference Hz Hz ％ First-order natural frequency 2.99 2.9 3.103448 Second-order natural frequency 12.67 12.79 -0.93823 The third-order natural frequency 30.73 30.36 1.218709

[0096] (2) F2 bolt force

[0097] Based on the structural stiffness obtained in the above process, the stiffness at the loading point is calculated to be 267N / mm. The maximum loading amplitude in the first phase of the test is ±50mm, and the horizontal force is estimated to be approximately ±13.35kN. The distance between the loading point and F2 is 4.25m, that is, the bending moment on F2 is approximately 56.74kNm.

[0098] The flange stress is calculated, and the stress ratios of various parts are shown in Table 9, all of which are less than 1, so there is no risk of extreme damage to the node.

[0099] Table 9 is the verification result of flange ultimate load capacity:

[0100] Bolt tension Bolt stress ratio Flange plate stress ratio Stress ratio of vertical weld of stiffener Stress ratio of horizontal weld of stiffener Ft ratio1 ratio2 ratio3 ratio4 kN [-] [-] [-] [-] 32.63 0.23 0.1 0.33 0.27

[0101] Although there is no risk of extreme failure of the nodes, each set of tests should be carefully inspected before conducting to pay attention to the presence of fatigue cracks.

[0102] 4. Experimental group and parameter settings

[0103] The experimental group settings are shown in Table 10;

[0104] Table 10 is a list of test groups:

[0105]

[0106]

[0107] The bolt preload is generally controlled by torque. The torque values ​​are shown in Table 11. The bolt preload should be kept basically consistent between the tests of each group of bolts at the same point.

[0108] Table 11 shows the nut torque values ​​of the test group:

[0109]

[0110]

[0111] 5. Experimental results:

[0112] Phase I Trial:

[0113] The first phase of the test mainly studied the influence of different test conditions (amplitude, frequency, preload, gasket inclination angle) on the loosening of conventional bolted connection pairs with one nut and two gaskets. The final installation torque was 180Nm and the number of vibrations was 3000 times.

[0114] (1) Comparison of bolt loosening results under different amplitudes, as shown in Table 12 and Figure 4 As shown;

[0115] Table 12 shows the bolt loosening under different amplitudes:

[0116]

[0117] (2) Comparison of bolt loosening results at different frequencies, as shown in Table 13 and Figure 5 As shown;

[0118] Table 13 shows the bolt loosening conditions at different frequencies:

[0119]

[0120] (3) Comparison of bolt loosening results under different preload forces, as shown in Table 14 and Figure 6 As shown;

[0121] Table 14 shows the loosening of bolts under different preload forces:

[0122]

[0123] (4) Comparison of bolt loosening results under different washer inclination angles, as shown in Table 15 and Figure 7 As shown;

[0124] Table 15 Bolt loosening at different washer inclination angles:

[0125]

[0126] Phase II Trial:

[0127] The second phase of the test mainly studies the anti-loosening effect of three types of anti-loosening bolts (two-nut three-washer anti-loosening bolts, composite nuts, and ring groove rivets). The final tightening torque is 180Nm and the vibration number is 3000 times.

[0128] (1) The loosening of the two-nut three-washer anti-loosening bolts is shown in Table 16 and Figure 8 As shown;

[0129] Table 16 shows the loosening situation of two-nut three-washer anti-loosening bolts:

[0130] Experimental Group Before test / KN After test / KN Residual preload / % Installation torque DT1 30.3 23.4 77.2 25％+100％ DT2 29.6 22.6 76.3 50％+100％ DT3 29.8 19.8 66.4 80％+100％

[0131] (2) Loosening of composite nut (1.5°) anti-loosening bolts, as shown in Table 17 and Fig. 9 As shown;

[0132] Table 17 shows the loosening of compound nut (1.5°) anti-loosening bolts:

[0133]

[0134]

[0135] (3) Loosening of compound nut (3°) anti-loosening bolt, as shown in Table 18 and Fig.10 As shown;

[0136] Table 18 shows the loosening of compound nut (3°) anti-loosening bolts:

[0137] Experimental Group Before test / KN After test / KN Residual preload / % Installation torque DX4 29.5 25.5 86.1 25％+100％ DX5 30.6 24.7 80.7 50％+100％ DX6 29.3 22.2 75.8 80％+100％

[0138] (4) Looseness of the ring groove rivets, as shown in Table 19 and Fig.11 As shown;

[0139] Table 19 shows the looseness of the ring groove rivets:

[0140] Experimental Group Before test / KN After test / KN Residual preload / % Installation torque HM1 98 84.4 86.1 [-]

[0141] The above lateral vibration test and tower flange anti-loosening bolt test show that:

[0142] Loosening prevention of bolts subjected to reciprocating shear loads

[0143] (1) Anti-loosening effect: ring groove rivet > composite nut (3°) anti-loosening bolt > two-nut three-washer anti-loosening bolt > conventional double nut anti-loosening structure > single nut bolt;

[0144] (2) The double nut anti-loosening structure commonly used in iron towers is prone to the phenomenon of the lower nut following the rotation in actual applications. Most of the double nuts do not produce effective tightening force, but only increase the contact area between the nut thread and the bolt thread, which greatly reduces the anti-loosening effect. This method achieves an ideal anti-loosening effect, but has high requirements for installation process management;

[0145] (3) Two-nut three-washer anti-loosening bolts can solve the problem that the lower nut is easy to rotate in the conventional double-nut anti-loosening structure. During use, the installation torque of the upper nut should be greater than the installation torque of the lower nut, and an effective tightening force should be generated between the double nuts to form a double-nut self-locking structure;

[0146] Anti-loosening of bolts subjected to alternating tension and compression loads

[0147] (1) Anti-loosening effect: ring groove rivet > composite nut (3°) anti-loosening bolt > composite nut (1.5°) anti-loosening bolt > two-nut three-washer anti-loosening bolt > single nut bolt;

[0148] (2) To achieve an ideal and stable anti-loosening effect with two-nut and three-washer anti-loosening bolts, the installation torque of the upper nut must be greater than the installation torque of the lower nut, and an effective tightening force must be generated between the two nuts to form a double-nut self-locking structure.

[0149] The present invention reduces and stabilizes the friction coefficient between the upper and lower nuts through the oblique washer between the lower nut and the upper nut, forms a thread difference between the upper and lower nuts, prevents the upper and lower nuts from rotating synchronously, and reduces the difficulty of on-site construction management; multiple contact surfaces are formed between the nut thread and the bolt thread, and the hyperstatic number is higher, which is beneficial to improving the mechanical bite force between the threads and improving the anti-loosening performance of the nut; multiple reverse contact surfaces of the upper and lower nut threads are used to tighten each other to form a reliable thread self-locking structure, which further enhances the anti-loosening performance; only oblique washers are used to form a reliable double-nut self-locking anti-loosening structure, which avoids the use of special components and mechanical processing technology, and has a low anti-loosening cost.

[0150] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A composite nut structure for preventing loosening of an iron tower, which is provided at a connecting plate for connecting at a connecting portion of an iron tower, characterized in that: Bolts are passed through between adjacent connecting plates, and the screw sleeves of the bolts are provided with flat washers 1 and 2. Flat washers 1 and 2 are distributed on the side of the two groups of connecting plates away from each other. Flat washer 1 is located between the bolt head and the adjacent connecting plate. The side of flat washer 2 away from the connecting plate is provided with a lower nut, an inclined washer and an upper nut in sequence. The lower nut and the upper nut are threadedly sleeved with the screw threads of the bolts, and the inclined washer is sleeved on the outer ring of the screw of the bolt.

2. The anti-loosening composite nut structure for an iron tower as claimed in claim 1, characterized in that: One side of the inclined washer is a plane, and the other side of the inclined washer is an inclined surface.

3. The anti-loosening composite nut structure for an iron tower as claimed in claim 2, characterized in that: The included angle of the inclined surface is 1° to 3°.

4. The anti-loosening composite nut structure for an iron tower as claimed in claim 2, characterized in that: The plane of the inclined washer contacts the upper nut, and the inclined surface of the inclined washer contacts the lower nut.

5. The anti-loosening composite nut structure for an iron tower as claimed in claim 1, characterized in that: The torque ratio of the upper nut and the lower nut during installation is 1:0.2-0.

9.

6. The anti-loosening composite nut structure for an iron tower as claimed in claim 1, characterized in that: The front face of the first flat washer contacts the bolt head, and the front face of the second flat washer contacts the lower nut.

7. A construction method for a composite nut structure for preventing loosening of an iron tower as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: Step S1, making a connection plate with mounting holes on the tower connection parts, and bringing the tower connection parts close to each other so that adjacent connection plates collide with each other and enter a waiting state for installation; Step S2, insert the flat washer into the bolt, and pass the bolt through the connecting plate; Step S3, installing the flat washer and the lower nut, and applying torque to the lower nut; Step S4: Install the oblique gasket and the upper nut on the bolt, and apply torque to the upper nut to complete the installation.

Images