Method for calculating maximum bending moment of main member of power transmission tower after displacement of multiple legs

Abstract

The present application relates to a kind of power transmission tower multi-leg displacement occurs main material maximum bending moment calculation method, comprising: the bending stiffness of the main material of power transmission tower on the first layer diaphragm and equivalent axial force bar stiffness are calculated;Get the area ratio μ of cross member and equivalent axial force bar;Solving the axial force of each equivalent axial force bar of main material equivalent plane structure, establish the bending moment calculation theoretical model of main material and solve the expression of main material bending moment;The deformation of the equivalent axial force bar of each main material along two directions r, θ is substituted into the expression of main material bending moment, respectively, the maximum bending moment of each main material two directions r, θ is obtained.The rod in space structure is converted into the rod of plane by certain simplification and stiffness equivalent method in the present application, simplifies the difficulty of calculation, need not to establish the finite element calculation of corresponding tower real model for different towers, just need to know the height of the lower two layers of cross-shaped leg tower and the material properties of main material, can quickly find out the bending moment of tower main material and the change rule of foundation horizontal displacement.

Description

Technical Field

[0001] This invention relates to the field of power transmission line structure technology, and in particular to a method for calculating the maximum bending moment of the main material of a power transmission tower after multiple legs have been displaced. Background Technology

[0002] When a self-supporting transmission tower is located in an area with unfavorable geological or topographical conditions, its foundation may experience horizontal displacement. This can alter the relative distance between the tower legs, causing changes in the stress on the tower's steel structural members. Consequently, the tower members may fail, become unstable, or collapse entirely, affecting the safe and stable operation of the transmission line. However, current foundation design specifications do not explicitly define the amount of horizontal displacement at the top of the foundation columns. Nevertheless, as the foundation displacement increases, the maximum bending moment of the main tower members also increases accordingly. Therefore, deriving an expression relating the foundation displacement and the maximum bending moment of the main tower members is crucial for the safety assessment and reinforcement of the tower.

[0003] Qianjin Shu established a finite element analysis model of a 500kV high-voltage transmission tower, simulating and analyzing the tower's failure under single and complex operating conditions. The results showed that tension on the foundation is more dangerous than compression, and horizontal displacement of the foundation is the main factor leading to tower instability. Yuan Guanglin studied the influence of various surface deformations on the internal forces and deformations of the transmission tower, using support displacement at material yield as a standard for judging the safety of the transmission tower. The study showed that the lower members are mainly affected by horizontal surface deformation, while the upper members are mainly affected by vertical deformation, and the axial force variation in the bottom members is greater than that in the upper members. Huang Feilong established a finite element model of the transmission tower, simulating the influence of different displacements of the tower leg foundation supports on tower deformation and material failure. Studies have shown that the upper tower members are minimally affected by foundation support displacement, while the internal force changes are greatest in the bottom tower legs, diagonal members, and transverse diaphragm members on the upper side of the tower legs, leading to failure before the upper tower members. Liu Zhengwei established a pile-soil-transmission tower finite element coupled model, considering four combinations of foundation displacements, and studied the influence of foundation horizontal displacement on the internal force changes of various transmission tower members. Based on the strength and stability requirements of the specifications, he gave the allowable horizontal displacement values ​​for two typical transmission towers.

[0004] As can be seen, most of the aforementioned studies on the horizontal displacement of transmission tower foundations focus on finite element simulations of specific problems to determine the allowable displacement of the transmission tower foundation under different operating conditions. However, this calculation method requires establishing different tower models for different towers, making the calculation process cumbersome. Currently, no literature provides a calculation expression for the relationship between the horizontal displacement of the transmission tower foundation and the bending moment of the main structure. Therefore, providing the variation law of the bending moment of the main structure of the transmission tower under the action of horizontal displacement of the foundation is of great significance for the safety assessment and reinforcement of the tower. Summary of the Invention

[0005] To address the problem that existing technologies require the creation of different tower models for different towers, resulting in cumbersome calculation processes, the present invention aims to provide a method for calculating the maximum bending moment of the main material of a transmission tower after displacement of multiple legs, which simplifies the calculation process by eliminating the need to create corresponding real tower models for finite element calculations for different towers.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for calculating the maximum bending moment of the main structure of a transmission tower after multiple legs have shifted, the method comprising the following sequential steps:

[0007] (1) Starting from the rightmost leg of the transmission tower, number the legs clockwise as a, b, c, d, and calculate the bending stiffness k and equivalent axial stiffness k0 of the main material of the transmission tower on the first layer of the transverse diaphragm.

[0008] (2) By taking advantage of the fact that the bending stiffness k of the main material on the first layer of transverse diaphragm is equal to the stiffness k0 of the equivalent axial force bar, and the area relationship between the main material and the transverse material, the area ratio μ of the transverse material and the equivalent axial force bar can be obtained.

[0009] (3) Let the area ratio μ of the cross member and the equivalent axial member be infinite, solve for the axial force of each equivalent axial member of the planar structure after the main member is equivalent, and decompose the axial force of each equivalent axial member into the stiffness k0 of the equivalent axial member and the deformation of the equivalent axial member.

[0010] (4) Establish the main material bending moment calculation model and solve the main material bending moment calculation model to obtain the expression of the main material bending moment;

[0011] (5) Substitute the deformation of the equivalent axial force bar of each main member along the two directions r and θ into the expression of the bending moment of the main member to obtain the maximum bending moment M of each main member in the two directions r and θ. r and M θ .

[0012] Step (1) specifically includes the following steps:

[0013] (1a) The formula for calculating the bending stiffness k is as follows:

[0014]

[0015] In the formula: h1 and h2 are the height of the tower leg and the height between the second section, respectively; E1 is the elastic modulus of the main material; I1 is the moment of inertia of the main material section along the bending direction.

[0016] (1b) The formula for calculating the equivalent axial stiffness k0 is as follows:

[0017]

[0018] In the formula: A0 is the equivalent area of ​​the equivalent axial force bar; s is the root opening of the transmission tower.

[0019] Step (2) specifically includes the following steps:

[0020] (2a) By setting the bending stiffness k of the main material on the first transverse diaphragm to be equal to the stiffness k0 of the equivalent axial member, the ratio of the area of ​​the main material to the equivalent area of ​​the equivalent axial member is obtained:

[0021]

[0022] In the formula: A1 is the area of ​​the main material, A0 is the equivalent area of ​​the equivalent axial force member; i is the radius of inertia of the main material; s is the root opening of the transmission tower; h1 and h2 are the height of the tower leg and the height of the second section, respectively.

[0023] (2b) The ratio of the area of ​​the main material of the transmission tower to the area of ​​the crossbar is 4 to 7 times. Combining the ratio of the area of ​​the main material to the equivalent area of ​​the equivalent axial force bar obtained in step (2a), the area ratio μ of the crossbar and the equivalent axial force bar is obtained as μ > 50.

[0024] Step (3) specifically refers to: fixing the tower leg d of the transmission tower, and assuming that tower legs a, b, and c are displaced respectively. Then, the area ratio μ of the cross member and the equivalent axial force member is set to ∞ to obtain the axial force of each equivalent axial force member in the equivalent structure:

[0025]

[0026]

[0027]

[0028]

[0029] In the formula, N a″x This represents the axial force along the x-direction in the equivalent axial force member after the tower leg a is equivalently positioned; N a″y N represents the axial force along the y-direction of the equivalent axial force member after the tower leg a is equivalently positioned; b″x N represents the axial force along the x-direction of the equivalent axial force member after the tower leg b is equivalent; b″y This represents the axial force along the y-direction of the equivalent axial force member after the tower leg b is equivalent; N c″x This represents the axial force along the x-direction of the equivalent axial force member after the tower leg c is equivalent; N c″y N represents the axial force along the y-direction of the equivalent axial force member after the tower leg c is equivalent; d″x This represents the axial force along the x-direction of the equivalent axial force member after the tower leg d is equivalent; N d″yThe axial force of the equivalent axial force member along the y direction is represented by d; k0 is the tensile and compressive stiffness of the equivalent axial force member; the coefficient before k0 in each of the above formulas is the deformation of the corresponding equivalent axial force member; draw a ray from the center point O of the tower to each tower leg, the direction of the ray is the direction of the displacement r of each tower leg, and the θ direction is the direction of the displacement 90° counterclockwise from the r direction; Let be the displacement of tower leg a along the r direction. Let be the displacement of tower leg a along the θ direction. Let be the displacement of tower leg b along the r direction. Let be the displacement of tower leg b along the θ direction. Let c be the displacement of the tower leg along the r direction. Let c be the displacement of the tower leg along the θ direction.

[0030] In step (3), the equivalent planar structure specifically refers to: on the first layer of the transverse diaphragm of the transmission tower, by taking into account the equal bending stiffness of the main members of each tower leg at that height and the equivalent axial stiffness of the main members, each main member is equivalent to an equivalent axial stiffness along the r and θ directions, for a total of 8 members. The planar structure formed by these 8 axial stiffness members and the transverse members on the first layer of the transverse diaphragm is the equivalent planar structure.

[0031] Step (4) specifically includes the following steps:

[0032] (4a) Establish a bending moment calculation model for the main material of the transmission tower: Take the tower leg height h1 and the second section height h2 of the transmission tower. Use the cantilever beams of the three nodes corresponding to the tower leg height h1 and the second section height h2 to simulate the bending situation of a certain main material of the tower. The three nodes are the upper node a′, the middle node a″ and the lower node a. The upper node is completely fixed, the middle node a″ is constrained in the horizontal direction, and the lower node a is free.

[0033] (4b) Apply a horizontal force P to the lower node a. Using structural mechanics methods, the displacement u at this point is:

[0034]

[0035] In the formula: κ is the slope of the main material; h1 and h2 are the height of the tower leg and the height between the second section, respectively; E1 is the elastic modulus of the main material; I1 is the moment of inertia of the section of the main material along the bending direction.

[0036] (4c) The bending moment at the section at intermediate node a″ is:

[0037]

[0038]

[0039] In the formula: I r The moment of inertia of the main material about the r direction; Iθ The moment of inertia of the main material about the θ direction; M r The bending moment of the main material about the r direction; M θ The bending moment of the main material about the θ direction;

[0040] (4d) Because κ 2 <<1, M in step (4c) r M θ The simplified expression for the bending moment of the main material is as follows:

[0041] M r =m r u,M θ =m θ u

[0042] In the formula: κ is the slope of the main material.

[0043] Step (5) specifically refers to substituting the deformation of the equivalent axial force bar obtained in step (3) into the expression for the bending moment of the main material, thereby obtaining the bending moment expressions for each main material:

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] In the formula: This represents the bending moment of tower leg a about the direction r. Let represent the bending moment of tower leg a about the direction θ. This represents the bending moment of the tower leg b about the direction r. This represents the bending moment of the tower leg b about the direction θ. This represents the bending moment of the tower leg c about the direction r. Let c represent the bending moment of the tower leg about the direction θ. This represents the bending moment of the tower leg d about the direction r. Let d represent the bending moment of the tower leg about the direction θ; h1 and h2 represent the height of the tower leg and the height between the second and third sections, respectively; E1 is the elastic modulus of the main material; I1 is the moment of inertia of the main material section along the bending direction; I r The moment of inertia of the main material about the r direction; I θ The moment of inertia of the main material about the θ direction;

[0050] exist Choose the maximum value as the maximum bending moment M in direction r. r ,exist Choose the maximum value as the maximum bending moment M in direction θ. θ .

[0051] As can be seen from the above technical solution, the beneficial effects of the present invention are as follows: First, the present invention uses an equivalent concept to transform the rods in the spatial structure into planar rods through certain simplification and stiffness equivalence methods, simplifying the calculation difficulty and facilitating the obtaining of the expression for the bending moment of the main material after the horizontal displacement of the foundation of the cross-leg transmission tower; Second, for towers of different sizes, the present invention does not require the establishment of corresponding real tower models for finite element calculations for different towers. It only needs to know the height of the bottom two floors of the cross-leg transmission tower and the material properties of the main material to quickly find the bending moment of the main material of the tower and the variation law of the horizontal displacement of the foundation; Third, since the current foundation design specifications do not have a clear provision on the displacement of the top of the tower foundation column, but obviously the foundation displacement will affect the safety performance of the tower, the present invention can provide an important reference for the safety assessment and reinforcement of the tower after the horizontal displacement of the foundation of the cross-leg overhead transmission tower. Attached Figure Description

[0052] Figure 1 This is a flowchart of the method of the present invention;

[0053] Figure 2 This is a schematic diagram showing the direction of tower leg displacement;

[0054] Figure 3 This is a schematic diagram of the bending moment theory calculation model;

[0055] Figure 4 This is a schematic diagram showing the equivalent stiffness of the main material on the transverse diaphragm. Detailed Implementation

[0056] like Figure 1 As shown, a method for calculating the maximum bending moment of the main structure of a transmission tower after multiple legs have shifted is described. This method includes the following sequential steps:

[0057] (1) Starting from the rightmost leg of the transmission tower, number the legs clockwise as a, b, c, d, and calculate the bending stiffness k and equivalent axial stiffness k0 of the main material of the transmission tower on the first layer of the transverse diaphragm.

[0058] (2) By taking advantage of the fact that the bending stiffness k of the main material on the first layer of transverse diaphragm is equal to the stiffness k0 of the equivalent axial force bar, and the area relationship between the main material and the transverse material, the area ratio μ of the transverse material and the equivalent axial force bar can be obtained.

[0059] (3) Let the area ratio μ of the cross member and the equivalent axial member be infinite, solve for the axial force of each equivalent axial member of the planar structure after the main member is equivalent, and decompose the axial force of each equivalent axial member into the stiffness k0 of the equivalent axial member and the deformation of the equivalent axial member.

[0060] (4) Establish the main material bending moment calculation model and solve the main material bending moment calculation model to obtain the expression of the main material bending moment;

[0061] (5) Substitute the deformation of the equivalent axial force bar of each main member along the two directions r and θ into the expression of the bending moment of the main member to obtain the maximum bending moment M of each main member in the two directions r and θ. r and M θ .

[0062] Step (1) specifically includes the following steps:

[0063] (1a) The formula for calculating the bending stiffness k is as follows:

[0064]

[0065] In the formula: h1 and h2 are the height of the tower leg and the height between the second section, respectively; E1 is the elastic modulus of the main material; I1 is the moment of inertia of the main material section along the bending direction.

[0066] (1b) The formula for calculating the equivalent axial stiffness k0 is as follows:

[0067]

[0068] In the formula: A0 is the equivalent area of ​​the equivalent axial force bar; s is the root opening of the transmission tower.

[0069] Step (2) specifically includes the following steps:

[0070] (2a) By setting the bending stiffness k of the main material on the first transverse diaphragm to be equal to the stiffness k0 of the equivalent axial member, the ratio of the area of ​​the main material to the equivalent area of ​​the equivalent axial member is obtained:

[0071]

[0072] In the formula: A1 is the area of ​​the main material, A0 is the equivalent area of ​​the equivalent axial force member; i is the radius of inertia of the main material; s is the root opening of the transmission tower; h1 and h2 are the height of the tower leg and the height of the second section, respectively.

[0073] (2b) The ratio of the area of ​​the main material of the transmission tower to the area of ​​the crossbar is 4 to 7 times. Combining the ratio of the area of ​​the main material to the equivalent area of ​​the equivalent axial force bar obtained in step (2a), the area ratio μ of the crossbar and the equivalent axial force bar is obtained as μ > 50.

[0074] Step (3) specifically refers to: such as Figure 2 As shown, the tower leg d of the transmission tower is fixed, and the tower legs a, b, and c are assumed to undergo displacement. Then, the area ratio μ of the cross member and the equivalent axial force member is set to ∞ to obtain the axial force of each equivalent axial force member in the equivalent structure:

[0075]

[0076]

[0077]

[0078]

[0079] In the formula, N a″x This represents the axial force along the x-direction in the equivalent axial force member after the tower leg a is equivalently positioned; N a″y N represents the axial force along the y-direction of the equivalent axial force member after the tower leg a is equivalently positioned; b″x N represents the axial force along the x-direction of the equivalent axial force member after the tower leg b is equivalent; b″y This represents the axial force along the y-direction of the equivalent axial force member after the tower leg b is equivalent; N c″x This represents the axial force along the x-direction of the equivalent axial force member after the tower leg c is equivalent; N c″y N represents the axial force along the y-direction of the equivalent axial force member after the tower leg c is equivalent; d″x This represents the axial force along the x-direction of the equivalent axial force member after the tower leg d is equivalent; N d″y The axial force of the equivalent axial force member along the y direction is represented by d; k0 is the tensile and compressive stiffness of the equivalent axial force member; the coefficient before k0 in each of the above formulas is the deformation of the corresponding equivalent axial force member; draw a ray from the center point O of the tower to each tower leg, the direction of the ray is the direction of the displacement r of each tower leg, and the θ direction is the direction of the displacement 90° counterclockwise from the r direction; Let be the displacement of tower leg a along the r direction. Let be the displacement of tower leg a along the θ direction. Let be the displacement of tower leg b along the r direction. Let be the displacement of tower leg b along the θ direction. Let c be the displacement of the tower leg along the r direction. Let c be the displacement of the tower leg along the θ direction.

[0080] In step (3), the equivalent planar structure specifically refers to: such as Figure 4 As shown, on the first layer of the transverse diaphragm of the transmission tower, the bending stiffness and equivalent axial stiffness of the main members of each tower leg at this height are equal. Each main member is equivalent to an equivalent axial stiffener along the r and θ directions, for a total of 8 members. The planar structure formed by these 8 axial stiffeners and the transverse members on the first layer of the transverse diaphragm is the equivalent planar structure. Figure 4In the diagram, a″b″c″d″ correspond to the nodes of tower legs a, b, c, and d at the height of the first-layer transverse diaphragm, respectively.

[0081] Step (4) specifically includes the following steps:

[0082] (4a) Establish a calculation model for the bending moment of the main material of the transmission tower: such as Figure 3 As shown, the height of the tower leg h1 and the height of the second section h2 are taken. The cantilever beams of the three nodes corresponding to the height of the tower leg h1 and the height of the second section h2 are used to simulate the bending situation of a certain main material of the tower. The three nodes are the upper node a′, the middle node a″ and the lower node a. The upper node is completely fixed, the middle node a″ is constrained in the horizontal direction, and the lower node a is free. By applying a force P to the lower node a and calculating the displacement of the lower node a, the relationship between the displacement of the lower node a and the bending moment of the middle node a″ can be found.

[0083] (4b) Apply a horizontal force P to the lower node a. Using structural mechanics methods, the displacement u at this point is:

[0084]

[0085] In the formula: κ is the slope of the main material; h1 and h2 are the height of the tower leg and the height between the second section, respectively; E1 is the elastic modulus of the main material; I1 is the moment of inertia of the section of the main material along the bending direction.

[0086] (4c) The bending moment at the section at intermediate node a″ is:

[0087]

[0088]

[0089] In the formula: I r The moment of inertia of the main material about the r direction; I θ The moment of inertia of the main material about the θ direction; M r The bending moment of the main material about the r direction; M θ The bending moment of the main material about the θ direction;

[0090] (4d) Because κ 2 <<1, M in step (4c) r M θ The simplified expression for the bending moment of the main material is as follows:

[0091] M r =m r u,M θ =m θ u

[0092] In the formula: κ is the slope of the main material.

[0093] Step (5) specifically refers to substituting the deformation of the equivalent axial force bar obtained in step (3) into the expression for the bending moment of the main material, i.e., the displacement u, to obtain the bending moment expressions for each main material:

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] exist Choose the maximum value as the maximum bending moment M in direction r. r ,exist Choose the maximum value as the maximum bending moment M in direction θ. θ ;

[0100] In the formula: This represents the bending moment of tower leg a about the direction r. Let represent the bending moment of tower leg a about the direction θ. This represents the bending moment of the tower leg b about the direction r. This represents the bending moment of the tower leg b about the direction θ. This represents the bending moment of the tower leg c about the direction r. Let c represent the bending moment of the tower leg about the direction θ. This represents the bending moment of the tower leg d about the direction r. Let d represent the bending moment of the tower leg about the direction θ; h1 and h2 represent the height of the tower leg and the height between the second and third sections, respectively; E1 is the elastic modulus of the main material; I1 is the moment of inertia of the main material section along the bending direction; I r The moment of inertia of the main material about the r direction; I θ The moment of inertia of the main material about the θ direction.

[0101] Example 1

[0102] Taking a certain ultra-high voltage transmission tower as an example, finite element analysis was performed for verification. The results show that as the tower displacement increases, the bending moment expression of the main material in this invention consistently matches the finite element results well.

[0103] Comparison results of the main material bending moment expression and finite element values:

[0104] Foundation displacement loading conditions for power transmission towers: A total of 10 power transmission tower cases were calculated. All power transmission towers have the same material parameters, elastic modulus E = 206 GPa, Poisson's ratio ν = 0.3. The displacement conditions shown in Table 1 were applied to the tower leg supports, and the magnitude of the applied displacement was the same.

[0105] Table 1. Basic Displacement Loading Conditions

[0106]

[0107]

[0108] Finite element calculation process:

[0109] Finite element simulation was used to calculate the transmission towers, with Case 1 showing the constraint method for the transmission tower as follows: Figure 2 As shown in Table 1, apply the loads shown in Table 1 and record the magnitudes of the bending moments in the r and θ directions of the transmission tower.

[0110] The results calculated by this invention are compared with those obtained by finite element analysis. In this case, a steel pipe tower, the resultant bending moment (M) can be obtained by summing the squares of the bending moments in both directions of each tower leg and then taking the square root. FEM M represents the result of the maximum resultant bending moment calculated using finite element methods, while M represents the result of the maximum resultant bending moment calculated using this invention. This formula for calculating the maximum combined bending moment only applies when the cross-section of the main material, such as the steel pipe tower, is circular; it is not applicable when the cross-section of the main material is not circular. Table 2 shows that the larger the horizontal displacement of the tower legs, the larger the calculated bending moment. The calculated moment is largest when tower legs a, b, and c simultaneously experience horizontal displacement in the r direction. Column 4 of Table 2 presents the error analysis between the bending moment expression and the finite element calculation results. It can be seen that the expression result is too large, leaning towards a safer approach.

[0111] Table 2 Comparison of Finite Element Values ​​and Main Material Bending Moment Expressions

[0112]

[0113] In summary, this invention employs an equivalent approach, transforming the rods in a spatial structure into planar rods through simplification and stiffness equivalence. This simplifies calculations and facilitates the deriving of the expression for the bending moment of the main structure of a cross-legged overhead transmission tower after horizontal displacement of the tower leg foundation. For towers of different sizes, this invention does not require establishing corresponding real tower models for finite element analysis. Knowing only the height of the bottom two stories of the cross-legged tower and the material properties of the main structure is sufficient to quickly identify the bending moment of the main structure and the variation of the foundation's horizontal displacement. Since current foundation design specifications do not explicitly define the displacement at the top of the tower foundation columns, but foundation displacement clearly affects the tower's safety performance, this invention provides an important reference for the safety assessment and reinforcement of cross-legged overhead transmission towers after horizontal displacement of the tower leg foundation.

Claims

1. A method for calculating the maximum bending moment of the main structure of a transmission tower after displacement of multiple legs, characterized in that: The method includes the following steps in sequence: (1) Starting from the rightmost leg of the transmission tower, number the legs clockwise as a, b, c, d, and calculate the bending stiffness of the main material of the transmission tower on the first transverse diaphragm. and equivalent axial stiffness ; (2) Utilizing the bending stiffness of the main material on the first layer of transverse diaphragm and equivalent axial stiffness By considering the equality of the main members and the area relationship between the cross members, we can obtain the area ratio of the cross members and the equivalent axial force members. ; (3) Let the area ratio of the cross member and the equivalent axial member be... To find the axial force of each equivalent axial member in the equivalent planar structure after the main material is considered to be infinite, decompose the axial force of each equivalent axial member into the equivalent axial member stiffness. And the deformation of the equivalent axial force rod; (4) Establish the main material bending moment calculation model and solve the main material bending moment calculation model to obtain the expression of the main material bending moment; (5) Arrange each main material along two directions , Substituting the deformation of the equivalent axial force bar into the expression for the bending moment of the main member, we obtain the bending moment of each main member in two directions. , Maximum bending moment and ; In step (3), the equivalent planar structure specifically refers to: on the first layer of the transverse diaphragm of the transmission tower, the bending stiffness of each main tower leg member at that height is equal to the equivalent axial stiffness of the member, and each main member is arranged along... , Each direction is equivalent to an equivalent axial force bar, for a total of 8 bars. The planar structure formed by these 8 axial force bars and the cross members on the first layer of transverse partition is the equivalent planar structure. Step (4) specifically includes the following steps: (4a) Establish the bending moment calculation model for the main material of the transmission tower: take the height of the tower leg. Second Intersection Height The height of the transmission tower legs Second Intersection Height The cantilever beam with three corresponding nodes simulates the bending condition of a main member of the iron tower. The three nodes are the upper nodes. Intermediate nodes and next node In this context, the top node is completely fixed, and the middle node... Constrain horizontal displacement, lower node free; (4b) In the next node Apply a force along the horizontal direction at the point The displacement at that point was obtained using structural mechanics methods. for: ； In the formula: The slope of the main material; These refer to the height of the tower legs and the height between the second and second sections of the transmission tower, respectively. The elastic modulus of the main material; The moment of inertia of the main material's cross section along the bending direction; (4c) Intermediate node The bending moment at the section is: ； In the formula: Main material Moment of inertia in the direction; Main material Moment of inertia in the direction; Main material Bending moment in the direction; Main material Bending moment in the direction; (4d) Because In step (4c) , The simplified expression for the bending moment of the main material is as follows: ； In the formula: The slope of the main material.

2. The method for calculating the maximum bending moment of the main structure of a transmission tower after displacement of multiple legs, as described in claim 1, is characterized in that: Step (1) specifically includes the following steps: (1a) The bending stiffness The calculation formula is as follows: ； In the formula: These refer to the height of the tower legs and the height between the second and second sections of the transmission tower, respectively. The elastic modulus of the main material; The moment of inertia of the main material's cross section along the bending direction; (1b) Equivalent axial stiffness The calculation formula is as follows: ； In the formula: This represents the equivalent area of ​​the equivalent axial force bar; This is the root opening of the transmission tower.

3. The method for calculating the maximum bending moment of the main structure of a transmission tower after displacement of multiple legs, as described in claim 1, is characterized in that: Step (2) specifically includes the following steps: (2a) Let the bending stiffness of the main material on the first layer diaphragm be... and equivalent axial stiffness The ratio of the area of ​​the main material to the equivalent area of ​​the equivalent axial force member is obtained by comparing the two: ； In the formula: Main material area This represents the equivalent area of ​​the equivalent axial force bar; The radius of inertia of the main material; For the root opening of the transmission tower; These refer to the height of the tower legs and the height between the second and second sections of the transmission tower, respectively. (2b) The ratio of the area of ​​the main material to the area of ​​the transverse cross member of the transmission tower is 4 to 7 times. Combining the ratio of the area of ​​the main material to the equivalent area of ​​the equivalent axial member obtained in step (2a), the area ratio of the cross member to the equivalent axial member is obtained. .

4. The method for calculating the maximum bending moment of the main structure of a transmission tower after displacement of multiple legs, as described in claim 1, is characterized in that: Step (3) specifically refers to: the tower legs of the transmission tower Fixed, with tower legs , , Displacement occurs respectively , , , , , Then, the area ratio of the horizontal member and the equivalent axial member is calculated. Take as The axial forces of each equivalent axial member in the equivalent structure are obtained as follows: ； In the formula, Indicates tower legs The equivalent axial force of the rod along the x-direction after the conversion; Indicates tower legs The axial force along the y-direction of the equivalent axial force rod after the equivalent axial force is obtained; They represent the tower legs respectively. The equivalent axial force of the rod along the x-direction after the conversion; Indicates tower legs The axial force along the y-direction of the equivalent axial force rod after the equivalent axial force is obtained; Indicates tower legs The equivalent axial force of the rod along the x-direction after the conversion; Indicates tower legs The axial force along the y-direction of the equivalent axial force rod after the equivalent axial force is obtained; Indicates tower legs The equivalent axial force of the rod along the x-direction after the conversion; Indicates tower legs The axial force along the y-direction of the equivalent axial force rod after the equivalent axial force is obtained; This represents the tensile and compressive stiffness of the equivalent axially loaded bar; in each of the above formulas... The coefficient before the line represents the deformation of the corresponding equivalent axial force member; a ray is drawn from the center point O of the tower to each leg, and the direction of the ray represents the displacement of each leg. direction, Direction is Rotate 90° counterclockwise. For tower legs along Displacement in direction, For tower legs along Displacement in direction, For tower legs along Displacement in direction, For tower legs along Displacement in direction, For tower legs along Displacement in direction, For tower legs along Displacement in direction.

5. The method for calculating the maximum bending moment of the main structure of a transmission tower after displacement of multiple legs, as described in claim 1, is characterized in that: Step (5) specifically refers to substituting the deformation of the equivalent axial force bar obtained in step (3) into the expression for the bending moment of the main material, thereby obtaining the bending moment expressions for each main material: ； ； In the formula: Indicates that the tower leg a is wrapped around Bending moment in the direction, Indicates that the tower leg a is wrapped around Bending moment in the direction, Indicates that the tower leg b is wrapped around Bending moment in the direction, Indicates that the tower leg b is wrapped around Bending moment in the direction, Indicates that the tower leg is wrapped around the base. Bending moment in the direction, Indicates that the tower leg is wrapped around the base. Bending moment in the direction, Indicates the tower leg d around Bending moment in the direction, Indicates the tower leg d around Bending moment in the direction, These are the tower leg height and the second section height of the transmission tower, respectively. The elastic modulus of the main material; The moment of inertia of the main material's cross section along the bending direction; Main material Moment of inertia in the direction; Main material Moment of inertia in the direction; exist , , , Choose the maximum value as the direction. Maximum bending moment ,exist , , , Choose the maximum value as the direction. Maximum bending moment .

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