A method for calculating the bearing capacity of a main member of a power transmission tower considering bolt connection

Abstract

The application discloses a kind of transmission tower main material bearing capacity calculation methods considering bolt connection, which is used to solve the problem that the bearing capacity calculation of main material of transmission tower containing bolt connection is not accurate enough, gives the modeling method for calculating the bearing capacity of main material component containing bolt connection using finite element method, calculates the nonlinear buckling load of main material of transmission tower containing bolt connection, and obtains the load deformation process of main material of transmission tower considering bolt connection.The method considers the influence of additional bending moment caused by the existence of bolt node in the transmission tower, reduces the error between the calculated bearing capacity of main material of transmission tower and the actual situation, so as to more accurately simulate the bearing condition of main material of transmission tower.

Description

Technical Field

[0001] This invention belongs to the field of power transmission tower technology and relates to a method for calculating the bearing capacity of the main material of a power transmission tower considering bolted connections under axial load. Background Technology

[0002] Transmission towers, as a crucial component of the power system, play a vital role in the safe operation of the power grid. Currently, the vast majority of transmission towers are constructed from equilateral angle steel connected by bolts. As a highly flexible structure, the main steel members are one of the primary load-bearing components of the transmission tower. For ease of construction and transportation, these main steel members are typically assembled in sections, making the bolted connections crucial for ensuring the tower's load-bearing capacity. To guarantee the strength and rigidity of these bolted connections, a relatively large number of bolts are usually required. The outer steel cladding of the transmission tower is generally larger than that of the main steel members. At the bolted connection, due to the difference in size between the two main steel members, their axes are not aligned, causing eccentricity. When the main steel members bear loads, additional bending moments are generated, thus affecting the stress characteristics of the main steel members at the bolted connection.

[0003] Numerous full-scale tower tests have shown that many transmission tower failures are related to the instability of the main structural members, sometimes even occurring before the design load is reached. Therefore, research on the load-bearing capacity of the main structural members of transmission towers is crucial to ensuring good load-bearing performance. Ignoring bolted connections means neglecting the effect of additional bending moments caused by component eccentricity, which may lead to significant discrepancies between the calculated load-bearing capacity and the actual situation. Therefore, research on the load-bearing capacity of the main structural members of transmission towers considering bolted connections is of great significance. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for calculating the bearing capacity of the main material of transmission towers considering bolted connections. This method addresses the problem that many transmission tower collapse accidents are caused by damage to the main material, and the location of the damage is close to the node. With the help of finite element analysis software, a method for calculating the bearing capacity of the main material of transmission towers considering bolted connections is proposed. This method can effectively simulate the deformation process of the main material of transmission towers and can effectively calculate the bearing capacity of the main material of transmission towers.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for calculating the bearing capacity of the main material of a power transmission tower considering bolted connections, comprising the following steps:

[0006] S1. Establish a three-dimensional solid model of the main material of the power transmission tower, including bolted connections;

[0007] S2, set the properties of the main materials and bolt connections in the 3D solid model;

[0008] S3, mesh the main material and bolted connections and establish contact constraints between the bolts and the main material;

[0009] S4, Application of boundary conditions;

[0010] S5, Solving for the load-bearing capacity of the main material;

[0011] S6. Modify the fit parameters of the main material and bolt connection in the three-dimensional solid model, and repeat steps 4 and 5. Based on the solution results, analyze the influence of the slenderness ratio of the main material, bolt size, bolt preload, number of loose bolts, and assembly clearance parameters of the main material on the ultimate bearing capacity of the main material.

[0012] Based on the above scheme, the three-dimensional solid model includes two main materials of different types, outer steel, two end plates and bolts. One end of the two main materials is covered by the outer steel, and the outer steel is connected to the main materials by multiple bolts. The other end of the two main materials is provided with end plates.

[0013] Based on the above scheme, the three-dimensional solid model is created by using three-dimensional design software to model the main material, outer steel, end plate and bolts, assemble them, and then import the assembled components into finite element analysis software.

[0014] Based on the above scheme, in S2, the properties of the main material, outer steel, end plate and bolts are set based on finite element analysis software, and it is assumed that the three-dimensional solid model is an elastic-strengthened bilinear material model.

[0015] Based on the above scheme, in S3, the three-dimensional solid model adopts C3D8R elements to mesh the main material, outer steel, end plate and bolt one by one to form a finite element model of the main material component containing bolts. In the part where the main material, outer steel and bolts are in contact, surface contact connection is established and the friction coefficient is set.

[0016] Based on the above scheme, the boundary conditions are as follows: on the end plate outside one of the main materials, the node located at the minimum axis of the main material is fully constrained; on the end plate outside the other main material, the node located at the minimum axis of the main material is constrained to have its displacement perpendicular to the length direction of the main material; and at the centroid node of the main material, a displacement load is applied along the length direction of the main material and pointing inward; and a bolt preload is applied to each bolt.

[0017] Based on the above scheme, in S5, linear buckling analysis is performed on the three-dimensional solid model to obtain the first buckling mode of the component; 1 / 1000 of the deformation result of the first buckling mode is taken as the initial defect, and nonlinear buckling analysis is performed on the two main materials to obtain the bearing capacity of the main material of the transmission tower.

[0018] Based on the above scheme, both main materials and the outer steel are equilateral angle steel, the bolts are standard hexagonal bolts, and the number of bolts connecting the outer steel to the two main materials is equal and arranged in a single row.

[0019] Based on the above scheme, when the bolts are non-standard bolts, the total shear capacity of the non-standard bolts shall not be lower than the design value of the original standard bolts, and the number of non-standard bolts n l Determined according to the following formula

[0020]

[0021] In the formula, F Q The design shear force is given by n; the number of standard bolts is given by d; the diameter of the standard bolt is given by τ; and the shear stress of the standard bolt is given by τ. l d represents the number of non-standard bolts. l This refers to the diameter of non-standard bolts used on power transmission towers.

[0022] Based on the above scheme, the attribute settings include the material, elastic modulus, Poisson's ratio, and yield strength of the main material, outer steel and end plate.

[0023] Based on the above scheme, the bolts used are 6.8 grade M20 standard hex bolts, and the bolt preload is taken as 60% of the bolt's ultimate bearing capacity.

[0024] The beneficial effects of adopting the above technical solution are as follows:

[0025] (1) In view of the problem that a large number of power transmission tower collapse accidents are caused by the damage to the main material and the damage location is close to the node location, the present invention proposes a method for calculating the bearing capacity of the main material of the power transmission tower considering bolted connection with the help of finite element analysis software. This method can effectively simulate the deformation process of the main material of the power transmission tower and can effectively calculate the bearing capacity of the main material of the power transmission tower.

[0026] (2) Compared with the previous model of main material of transmission tower, the present invention takes into account the influence of the additional bending moment caused by the presence of bolt nodes in the transmission tower, thereby reducing the error between the calculated bearing capacity of the main material of the transmission tower and the actual situation.

[0027] (3) The transmission tower main material model considering bolted connection proposed in this invention can also analyze the influence of parameters such as slenderness ratio, bolt size, bolt preload, number of loose bolts and main material assembly gap on the ultimate bearing capacity of the component. Attached Figure Description

[0028] Figure 1 It includes the component model and geometric dimensions of the main materials connecting the transmission tower;

[0029] Figure 2It shows the distribution and numbering of bolts connecting the main components of the power transmission tower;

[0030] Figure 3 It is a stress cloud diagram of the component;

[0031] Figure 4 shows the load-displacement curves for models with different slenderness ratios;

[0032] Figure 5 These are the load-displacement curves for models with different bolt diameters;

[0033] Figure 6 These are the load-displacement curves for different bolt preload models;

[0034] Figure 7 These are load-displacement curves for models with different numbers of loose bolts;

[0035] Figure 8 These are the load-displacement curves of assembly gap models for different main materials;

[0036] In the diagram: 1. Main material 1, 2. Main material 2, 3. Outer steel, 4. Bolt, 5. End 1, 6. End plate 2. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0038] Numerous full-scale tower tests have shown that many transmission tower failures are related to instability at the bolted connections of the main structural members, sometimes even occurring before the design load is reached. In a full-scale tower test of a 220kV ZMC2 type transmission tower, the main structural members failed, and the failure location was relatively close to the node. The applied load at the time of main structural member instability was only 95% of the design load. Therefore, to ensure good load-bearing performance of transmission towers, research on the load-bearing capacity of main structural members with bolted connections is crucial.

[0039] This invention relates to a method for calculating the bearing capacity of the main material of a power transmission tower considering bolted connections. This method addresses the problem of numerous power transmission tower collapses where the main material fails close to nodes. Utilizing finite element analysis software, a method for calculating the bearing capacity of the main material considering bolted connections is proposed. This method can effectively simulate the deformation process of the main material and calculate its bearing capacity. To solve the above technical problems, the technical solution includes the following steps: First, taking the main material at the failure location of a 220kV ZMC2 type power transmission tower as the research object, a three-dimensional solid model of the main material including bolted connections is established using CREO software, and the assembled components are imported into the finite element analysis software. Then, the properties of each component are set, meshed, and boundary conditions are applied. Finally, nonlinear buckling analysis is performed on the component to obtain its bearing capacity.

[0040] The main steps of the method for calculating the bearing capacity of the main material of a power transmission tower considering bolted connections, as described in 1, are as follows:

[0041] Step 1: Establishing a 3D solid model of the main components of the power transmission tower, including bolted connections.

[0042] As attached Figure 1 The diagram shows a schematic of the main components of a power transmission tower with bolted connections. Main component 1 is an L100×10 equilateral angle steel, main component 2 is an L110×10 equilateral angle steel, the outer sheathing steel is an L110×10 equilateral angle steel, and the bolts are standard M20×40 hexagonal bolts of grade 6.8. Ten bolts are used to connect the outer sheathing steel to the main components, arranged in a single row with a spacing of 60mm between them. For ease of study, the length of main component 1 is taken as l, the length of main component 2 as h, the length of the outer sheathing steel as w, and the assembly gap between main component 1 and main component 2 as j. The bolts are numbered, as detailed in the attached diagram. Figure 2 As shown, solid models of each part were created using Creo software, and then assembled. The assembled components were then imported into finite element analysis software.

[0043] Step 2: Setting the properties of the 3D solid model

[0044] The properties of each component were set in the finite element analysis software. An elastic-strengthened bilinear material model was applied. The main material, outer steel, and end plate were all made of Q345 steel. The elastic modulus of Q345 was taken as 206 GPa, Poisson's ratio as 0.3, and yield strength as 345 MPa. The elastic modulus of the 6.8 grade M20 bolts was taken as 206 GPa, Poisson's ratio as 0.3, and yield strength as 480 MPa.

[0045] Step 3: Mesh generation and establishment of contact between components

[0046] The model uses C3D8R elements to mesh each component individually, resulting in a finite element model of the main component containing bolts. There is some interaction between the components, requiring the establishment of contact between them. The contact method is surface-to-surface contact with a friction coefficient of 0.3.

[0047] Step 4: Applying boundary conditions

[0048] On end plate 2, the node located at the minimum axis of the angle steel is fully constrained. On end plate 1, the displacement in the X and Y directions of the node located at the minimum axis of the angle steel is constrained, and a displacement load is applied in the Z direction at the centroid node of the angle steel. The ultimate bearing capacity of the 6.8 grade M20 bolt is 150.8 kN, and the bolt preload is taken as 60% of the ultimate bearing capacity of the bolt, that is, the magnitude of the bolt preload is 90.2 kN.

[0049] Step 5: Solving for the bearing capacity of the component

[0050] First, linear buckling analysis is performed on the component to obtain its first buckling mode. Then, 1 / 1000 of the deformation result of the linear buckling mode is taken as the initial imperfection. Subsequently, nonlinear buckling analysis is performed on the main material to obtain the bearing capacity of the transmission tower's main material.

[0051] Example 1:

[0052] First, taking the component at the failure location of a 220kV ZMC2 type transmission tower as the research object, a three-dimensional solid model of the main components of the transmission tower with bolted connections was established using CREO software. As shown in Appendix 1, the main component model of the transmission tower with bolted connections consists of main component 1, main component 2, outer steel cladding, end plate 1, end plate 2, and bolts. The bolt preload was taken as 60% of the ultimate bearing capacity of the bolts. Nonlinear buckling analysis was then performed on the component to obtain its bearing capacity. The influence of parameters such as slenderness ratio, bolt size, bolt preload, number of loose bolts, and assembly clearance of the main components on the ultimate bearing capacity of the component was analyzed.

[0053] To analyze the influence of parameters such as slenderness ratio, bolt size, bolt preload, number of loose bolts, and assembly clearance of main materials on the ultimate bearing capacity of components, five sets of parametric models were established, namely models with different slenderness ratios, different bolt diameters, different bolt preloads, different numbers of loose bolts, and different assembly clearances.

[0054] Table 1 Models with different slenderness ratios

[0055]

[0056] To investigate the effect of slenderness ratio on the load-bearing capacity of components, studies were conducted on the main members of transmission towers with boltless connections and bolted connections, with slenderness ratios of 80, 100, 120, and 140, respectively. Detailed parameters of the components are shown in Table 1.

[0057] To investigate the influence of bolt diameter on the load-bearing capacity of structural members, the main components of transmission towers with bolted connections, bearing bolt diameters of 16mm, 20mm, and 24mm, were studied and designated B1, B2, and B3, respectively. Table 2 shows the parameters for the different bolt diameter models studied. When the bolt diameter is 16mm, the number of bolts is 16; when the bolt diameter is 24mm, the number of bolts is 8. The bolt spacing was kept constant at 60mm when designing the outer steel casing length. Theoretical calculations showed that the outer steel casing lengths for M16 and M24 bolts are 826mm and 656mm, respectively.

[0058] Table 2 Models with different bolt diameters

[0059]

[0060] The number of bolts of different diameters is determined by formula (1) to ensure that the total shear resistance of the bolts is not lower than the original design value.

[0061]

[0062] In the formula, F Q n represents the shear force; n represents the number of standard bolts; d represents the diameter of the standard bolt type; n1 represents the number of bolts of other specifications; d1 represents the diameter of other commonly used bolt types for power transmission towers.

[0063] To ensure the connection strength and rigidity of the main materials, a specified preload is usually applied to the bolts. For a 6.8 grade M20 bolt, the ultimate bearing capacity is 150.8 kN. To study the effect of bolt preload on the bearing capacity of the component, as shown in Table 3, the preload is taken as 20%, 40%, 60%, and 80% of its ultimate bearing capacity S0, i.e., 30.2 kN, 60.3 kN, 90.5 kN, and 120.6 kN respectively, and numbered C1, C2, C3, and C4 respectively.

[0064] Table 3 Models of different bolt preload forces

[0065]

[0066] Table 4 Models with different numbers of loose bolts

[0067]

[0068] When transmission towers operate for extended periods, bolts may loosen or fatigue, leading to a reduction or even loss of preload. To address the issue of bolts becoming ineffective due to loosening, bolts lacking preload are removed during finite element analysis. To study the impact of the number of loose bolts on the load-bearing capacity of the structure, only bolts on main member 1 are considered for loosening, and the model is divided into three groups. The first group contains bolts 1-7, 1-8, 1-9, and 1-10, representing 40% of the bolts on main member 1 in the standard structure. The second group contains bolts 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10, representing 60% of the bolts on main member 1 in the standard structure. The third group contains bolts 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10, representing 80% of the bolts on main member 1 in the standard structure. The original model, the first group of models, the second group of models, and the third group of models, whose bolts were not loose, are numbered D1, D2, D3, and D4, respectively. The specific parameters are shown in Table 4.

[0069] When assembling main materials, there is usually a certain assembly gap at the ends of the main materials, such as... Figure 2 As shown in Table 5, to study the influence of assembly gaps on the load-bearing capacity of components, assembly gaps j were taken as 0 mm, 10 mm, 40 mm, and 60 mm, and numbered F1, E2, E3, and E4 respectively. The maximum assembly gap was taken as 6 times the standard gap. The model parameters for different assembly gaps are shown in Table 5.

[0070] Table 5 Models with different assembly gaps

[0071]

[0072] As attached Figure 3 The image shows the stress contour plot of the component. (Attached) Figure 3 The deformation of the middle component is roughly the same as that of the main material in the real tower test of the 220kV ZMC2 type transmission tower, and the maximum stress occurs at the buckling part, with a maximum stress of 345MPa.

[0073] To investigate the load-deformation process of the component influenced by slenderness ratio, the load-deformation curve at end plate 1 was extracted. The results are shown in Figure 4. In the figure, the horizontal axis represents the Z-direction displacement at the minimum axis of end plate 1, and the vertical axis represents the axial compressive load of the component. Table 6 was also prepared, showing the ultimate bearing capacity statistics of the model when the slenderness ratios are 80, 100, 120, and 140. Table 6 shows that when the slenderness ratios of the main members (excluding bolt connections) are 80, 100, 120, and 140, the ultimate bearing capacities of the components are 506 kN, 357 kN, 255 kN, and 190 kN, respectively. It is evident that for main members without bolt connections, the ultimate bearing capacity of the member gradually decreases with increasing slenderness ratio. When the slenderness ratios of main members with bolt connections are 80, 100, 120, and 140, the ultimate bearing capacities of the members are 303 kN, 229 kN, 174 kN, and 135 kN, respectively. This shows that the ultimate bearing capacity of the member gradually decreases with increasing slenderness ratio, and the variation law of the ultimate bearing capacity of main members with bolt connections is the same as that of main members without bolt connections. At the same slenderness ratio, the ratios of the ultimate bearing capacity of members with bolt connections to those without are 59.9%, 64.0%, 68.2%, and 71.1%, respectively. Therefore, the presence of bolted joints reduces the ultimate bearing capacity of the main member by approximately 35% compared to that without bolt connections, and the smaller the slenderness ratio, the greater the decrease in the ultimate bearing capacity of the main member.

[0074] As attached Figure 5The load-displacement curves of the main structural members, shown in models B1, B2, and B3, are calculated for bolt sizes M16, M20, and M24, respectively. As shown in Table 2, assuming model B2 is used as a reference, in the reference member, there are 10 M20 bolts, the outer steel length is 670 mm, and the ultimate bearing capacity is 229 kN. In model B1, there are 16 M16 bolts, the outer steel length is 826 mm, and the ultimate bearing capacity is 233 kN, only 1.7% higher than the standard member. In model B3, there are 8 M24 bolts, the outer steel length is 656 mm, and the ultimate bearing capacity remains essentially unchanged compared to the standard member. Therefore, the bolt size commonly used in transmission towers has little impact on the ultimate bearing capacity of the structural members.

[0075] Table 6. Statistical table of ultimate bearing capacity of models with different slenderness ratios

[0076]

[0077] As attached Figure 6 The C1, C2, C3, and C4 models shown are the load-displacement curves of the main structural member calculated when the bolt's ultimate bearing capacity is 20%, 40%, 60%, and 80%, respectively. (See attached...) Figure 6 It can be seen that when the preload is 40%, 60%, and 80% of the bolt's ultimate bearing capacity, the load-displacement curves basically coincide, and the ultimate bearing capacity of the component is 229 kN in all cases. When the preload is 20% of the bolt's ultimate bearing capacity, the ultimate bearing capacity of the component is 227 kN, which is only 0.8% lower than that of the standard component. Therefore, when the bolt preload varies within a certain range, the magnitude of the bolt preload has little effect on the ultimate bearing capacity of the component. When the preload is 20% of the bolt's ultimate bearing capacity, bolt slippage occurs, with a slippage distance of approximately 2 mm. If the bolt slippage distance is too large, the bolt shank will come into direct contact with the outer steel sheath, and the stress in both the bolt and the outer steel sheath may increase. The shank is in contact with the inner wall of the bolt hole, and is subjected to shearing action, which can easily lead to stress concentration. When the preload is increased to 40% of the bolt's ultimate bearing capacity, the bolt slippage disappears. Therefore, increasing the bolt preload can effectively reduce bolt slippage, thereby avoiding stress concentration.

[0078] As attached Figure 7 The D1, D2, D3, and D4 models shown are the load-displacement curves of the main structural member calculated when the number of loose bolts is 0, 4, 6, and 8, respectively. (See attached...) Figure 7It can be seen that the load-displacement curves of the reference model with no loose bolts and the model with 40% loose bolts are basically the same, and the ultimate bearing capacity of the components is approximately 229 kN in both cases, meaning that the strength and stiffness of the components have not changed. For the component with 60% of the bolts loosened on main material 1, bolt slippage occurred when the load reached 170 kN, and the ultimate bearing capacity of the component was 210 kN, a decrease of 7.8% compared to the original model with no loose bolts. For the component with 80% of the bolts loosened on main material 1, bolt slippage also occurred when the load reached 72 kN, and the ultimate bearing capacity of the component was 190 kN, a decrease of 17% compared to the original model with no loose bolts. Therefore, when the number of loose bolts is less than 40%, the ultimate bearing capacity of the main material is unaffected; when the number of loose bolts exceeds 40%, the ultimate bearing capacity of the main material gradually decreases with the increase in the number of loose bolts.

[0079] As attached Figure 8 The E1, E2, E3, and E4 models shown are the load-displacement curves of the main material components calculated when the assembly clearance of the main material is 0mm, 10mm, 40mm, and 60mm, respectively. (See attached...) Figure 8 It can be seen that the slopes and ultimate loads of different load-displacement curves are slightly different, indicating that the size of the assembly gap between the main materials has a slight impact on the stiffness and ultimate load of the component. As the assembly gap gradually increases from 0 to 60 mm, the slope of the load-displacement curve of the component decreases slightly, indicating that as the assembly gap between the main materials increases, the stiffness of the entire main material connection component decreases accordingly. When the assembly gap is 0 mm, 10 mm, 40 mm, and 60 mm, the corresponding ultimate bearing capacities of the component are 238 kN, 229 kN, 225 kN, and 220 kN, respectively, and the variation of the ultimate bearing capacity of the component relative to the standard component is 3.9%, 0%, 1.7%, and 3.9%. When the assembly gap is 6 times the standard gap, the ultimate bearing capacity of the component decreases by only 3.9%, indicating that the assembly gap of the main materials has a small impact on the ultimate bearing capacity of the main materials.

[0080] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0081] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0082] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0083] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit its scope of protection. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading the present invention, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, but these changes, modifications or equivalent substitutions are all within the scope of protection of the pending claims of the invention.

Claims

1. A method for calculating the bearing capacity of the main material of a power transmission tower considering bolted connections, characterized in that... Includes the following steps: S1. Establish a three-dimensional solid model of the main components of the power transmission tower, including bolted connections. The three-dimensional solid model includes two main components of different types, outer steel, two end plates, and bolts. One end of each main component is covered by the outer steel, and the outer steel is connected to the main component by multiple bolts. The other end of each main component is equipped with an end plate. The three-dimensional solid model is created by using three-dimensional design software to solid model the main components, outer steel, end plates, and bolts, assembling them, and then importing the assembled components into finite element analysis software. S2 sets the properties of the main material and bolt connections in the 3D solid model; based on the finite element analysis software, sets the properties of the main material, outer steel, end plate and bolts, and assumes that the 3D solid model is an elastic-strengthened bilinear material model; S3, mesh the main material and bolt connection and establish contact constraints between the bolt and the main material; the three-dimensional solid model uses C3D8R elements to mesh the main material, outer steel, end plate and bolt one by one to form a finite element model of the main material component containing bolts, and establish surface contact connection at the part where the main material, outer steel and bolts are in contact, and set the friction coefficient; S4, Application of boundary conditions: The boundary conditions are as follows: on the end plate outside one of the main members, the node located at the minimum axis of the main member is fully constrained; on the end plate outside the other main member, the node located at the minimum axis of the main member is constrained to have its displacement perpendicular to the length direction of the main member; and at the centroid node of the main member, a displacement load is applied along the length direction of the main member and pointing inward; and a bolt preload is applied to each bolt. S5, Solving the bearing capacity of the main material: Perform linear buckling analysis on the three-dimensional solid model to obtain the first buckling mode of the component; take 1 / 1000 of the deformation result of the first buckling mode as the initial defect, and perform nonlinear buckling analysis on the two main materials to obtain the bearing capacity of the main material of the transmission tower. S6. Modify the fit parameters of the main material and bolt connection in the three-dimensional solid model, and repeat steps 4 and 5. Based on the solution results, analyze the influence of the slenderness ratio of the main material, bolt size, bolt preload, number of loose bolts, and assembly clearance parameters of the main material on the ultimate bearing capacity of the main material.

2. The method for calculating the bearing capacity of the main material of a transmission tower considering bolted connections according to claim 1, characterized in that... Both main materials and the outer steel are equilateral angle steel, and the bolts are standard hexagonal bolts. The number of bolts connecting the outer steel to the two main materials is equal and arranged in a single row.

3. The method for calculating the bearing capacity of the main material of a transmission tower considering bolted connections according to claim 2, characterized in that... When the bolts are non-standard bolts, the total shear capacity of the non-standard bolts shall not be lower than the design value of the original standard bolts, and the number of non-standard bolts shall be... n l Determined according to the following formula In the formula, F Q To design shear force; n The standard number of bolts; d The diameter is for the standard bolt type. τ The shear stress of a standard bolt; n l This refers to the number of non-standard bolts. d l This refers to the diameter of non-standard bolts used in power transmission towers.

4. The method for calculating the bearing capacity of the main material of a power transmission tower considering bolted connections according to claim 1, characterized in that... The attribute settings include the material, elastic modulus, Poisson's ratio, and yield strength of the main material, outer steel, and end plate.

5. The method for calculating the bearing capacity of the main material of a transmission tower considering bolted connections according to claim 1, characterized in that... The bolts used are 6.8 grade M20 standard hex bolts, and the bolt preload is 60% of the bolt's ultimate bearing capacity.

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