A method for calculating the bearing capacity of the borehole wall of a single bolt connection node in a power transmission tower

Abstract

This invention discloses a method for calculating the bearing capacity of the borehole wall in a single-bolt connection node of a power transmission tower, comprising the following steps: calculating a first independent variable, a second independent variable, and a third independent variable based on the bearing strength of the connecting member, the yield strength of the connecting member, the bolt end distance, the bolt edge distance, and the bolt hole diameter; establishing a fitting model for the edge distance bearing capacity influence coefficient with the ratio of the second independent variable to the first independent variable as the abscissa and the edge distance bearing capacity influence coefficient as the ordinate; establishing a fitting model for the end distance bearing capacity influence coefficient with the third independent variable as the abscissa and the end distance bearing capacity influence coefficient as the ordinate; calculating the borehole wall bearing capacity based on the bolt diameter, connecting plate thickness, tensile strength of the connecting member, edge distance bearing capacity influence coefficient, and end distance bearing capacity influence coefficient. This invention overcomes the limitations of traditional standard methods, which consider only one parameter and ignore coupling effects, providing a scientific basis and technical support for the safe, economical, and reliable design of power transmission towers.

Description

Technical Field

[0001] This invention belongs to the technical field of power transmission tower structure design, specifically relating to a method for calculating the bearing capacity of the borehole wall of a single bolt connection node in a power transmission tower. Background Technology

[0002] Single-bolt connections are a common type of connection used for diagonal and auxiliary members in transmission towers. The bearing capacity of the borehole wall at these connections directly affects the safety of the local structure and the overall reliability of the structure. Under extreme loads such as strong winds and icing, the connection may fail due to insufficient bearing capacity, leading to member failure or even tower instability, posing a serious threat to the safe operation of the power grid. Therefore, accurately calculating the bearing capacity of single-bolt connections is of great significance for the safe design and reliable operation and maintenance of transmission towers.

[0003] Currently, the calculation of the bearing capacity of single-bolt connection nodes on transmission towers in engineering mainly relies on domestic and international design standards such as China's DL / T5486-2020, the US ASCE, and Europe's EN 1993-1-8. Each standard uses empirical formulas or simplified calculation methods based on bolt diameter, connecting plate thickness, and material strength. However, existing methods have significant limitations: firstly, the US ASCE and China's DL / T... The existing standards use fixed coefficients for calculation, failing to fully consider the geometric effects of bolt hole end distance (load direction) and edge distance (perpendicular to load direction), thus decoupling the bearing capacity from the geometric parameters of the node edge. Secondly, while the 2005 version of the European standard EN1993-1-8 introduced end distance and edge distance reduction factors, their values ​​were conservative. The 2024 version of this standard went even further, completely eliminating the influence of edge distance on bearing capacity, oversimplifying the complex failure mechanics of the node. Thirdly, existing standards do not systematically consider the coupling effect of end distance and edge distance, nor do they establish damage control criteria based on the hole wall deformation threshold. This leads to conservative calculation results under certain working conditions, resulting in material waste or failing to accurately reflect the true stress state of the node, posing potential safety hazards. Furthermore, although refined finite element simulation or full-scale testing can be used to determine the bearing capacity of the node, these methods are usually complex in modeling, costly in calculation, or time-consuming, and require high levels of equipment and expertise, making them unsuitable for rapid design and verification in engineering sites. Therefore, there is currently a lack of an accurate and practical method for calculating the bearing capacity of the borehole wall of a single bolted connection node that can comprehensively consider the effects of multi-parameter coupling and is easy for engineering designers to apply directly. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the incompleteness of the parameter system in existing standard formulas, thus resolving the issue that they cannot accurately and continuously reflect the influence of key geometric arrangement parameters of bolts; existing methods for calculating the bearing capacity of borehole walls in single-bolt angle steel connection nodes of transmission towers do not fully consider the coupling effect of end distance and edge distance, resulting in large differences in calculation results between standards, and some methods are overly conservative or pose safety hazards; furthermore, refined simulation / experimental methods are difficult to adapt to rapid engineering applications, and there is a lack of damage control criteria based on borehole wall deformation, making it impossible to achieve accurate and efficient calculation and design optimization of node bearing capacity. This invention aims to solve the above technical problems by proposing a more accurate and widely applicable method for calculating the bearing capacity of bolted angle steel connection nodes in transmission towers, thereby providing a theoretical basis for the safety and economic optimization of node design.

[0005] According to the technical solution of the present invention, the present invention provides a method for calculating the bearing capacity of the borehole wall of a single bolt connection node in a power transmission tower, comprising the following steps: Step S1: Calculate the first independent variable β, the second independent variable α, and the third independent variable γ using the following formulas: (Formula 1), (Formula 2), (Formula 3), in, f represents the compressive strength of the connecting component. y The yield strength of the connecting component is given by e1, the bolt end distance is given by e2, the bolt edge distance is given by d0, and the bolt hole diameter is given by d0. Step S2, using the ratio of the second independent variable α to the first independent variable β as the abscissa, the edge distance bearing capacity influence coefficient β... b Using the vertical axis as the ordinate, establish the edge distance bearing capacity influence coefficient β. b The fitting model; Step S3, with the third independent variable γ as the abscissa, the influence coefficient β of the end distance bearing capacity. d Using the vertical axis as the ordinate, establish the influence coefficient β of the end-distance bearing capacity. d The fitting model; Step S5, calculate the bearing capacity N of the borehole wall using the following formula: (Formula 7), (Formula 8), Where, N u The bearing capacity of the hole wall of a single bolted connection node on a power transmission tower is given by: d is the bolt diameter, t is the thickness of the connecting plate, and f is the bearing capacity of the hole wall. u This refers to the tensile strength of the connecting component.

[0006] In some implementations, in step S2, a cubic polynomial is used to fit the scattered data to establish the edge bearing capacity influence coefficient β according to the following formula. b Fitting model: (Formula 5), Among them, A b B is the first fitting intercept. b C is the coefficient of the linear term. b D is the coefficient of the quadratic term. b The coefficient of the cubic term.

[0007] In some implementations, A b =0.287, B b =1.828, C b = 1.576, D b =0.431.

[0008] In some implementations, in step S3, a nonlinear polynomial is used as the fitting basis function to fit the scattered data, and the end-distance bearing capacity influence coefficient β is established according to the following formula. d Fitting model: (Formula 6), Among them, A d B is the second fitting intercept. d C is the first fitting coefficient. d is the second fitting coefficient.

[0009] In some implementations, A d =1.252、B d =-0.001、C d =1.316.

[0010] In some implementations, step S4 is further included between step S3 and step S5; Step S4 is to verify the validity of the parameters in the following way: Ensure the tensile strength f of the connecting components y , compressive strength of connecting components The values ​​of e1 / d0 conform to the requirements of the transmission tower specifications and satisfy e1 / d0 = 1.0~3.5 and e2 / d0 = 1.2~5.0.

[0011] In some implementations, step S5 is followed by step S6; Step S6 involves comparing the borehole wall bearing capacity N calculated in step S5 with the actual load F on the node. If N / F ≥ 1, the borehole wall bearing capacity meets the design requirements. If N / F < 1, the values ​​of α / β and / or γ are adjusted, the borehole wall bearing capacity N is recalculated, and step S6 is repeated until the design requirements are met.

[0012] In some implementations, in step S6, if N / F < 1, then the bolt edge distance e1 and / or bolt edge distance e2 are adjusted.

[0013] In some implementations, β = 1.5.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention proposes a method for calculating the bearing capacity of single-bolt connection nodes in power transmission towers. This method overcomes the limitations of traditional standard methods, which consider only a single parameter and neglect coupling effects. It systematically considers the combined influence of multiple key parameters, such as bolt hole edge distance, end distance, connection plate thickness, and component material strength. By establishing a coupling relationship model between parameters, it achieves a refined evaluation of the node's bearing capacity from both geometric constraints and material properties perspectives. The calculation process is clear, and the formulas are explicit, requiring no complex finite element modeling or large-scale experiments, making it easy for engineering designers to understand and apply. Applying this method to the design and safety verification of power transmission tower nodes can, while ensuring structural safety, avoid material waste caused by overly conservative design. It can also effectively identify and prevent potential risks arising from insufficient bearing capacity calculations, providing a scientific basis and technical support for the safe, economical, and reliable design of power transmission towers. Attached Figure Description

[0015] Figure 1 This is a flowchart of a calculation method according to an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of a single-bolt connection node structure of a power transmission tower.

[0017] Figure 3 This is a scatter plot of the fitting curve of the bearing capacity influence coefficient of the angle steel bolt node edge distance in this invention.

[0018] Figure 4 This is a scatter plot of the fitting curve of the influence coefficient of the bearing capacity of the angle steel bolt node end distance in this invention. Detailed Implementation

[0019] This invention provides a method for calculating the bearing capacity of the borehole wall of a single-bolt connection node in a power transmission tower. Specifically, it is a multi-parameter coupled method for calculating the bearing capacity of the borehole wall of a single-bolt connection node in a power transmission tower. The multi-parameter coupling essentially represents a comprehensive mechanism in which multiple key parameters, such as bolt hole edge distance, end distance, connecting plate thickness, and component material strength, interact and jointly influence the node's bearing capacity. This method is applicable to the design and verification of the bearing capacity of single-bolt angle steel nodes in power transmission towers and similar lattice steel structures. Overall, this method includes the following steps: dimensionless processing of foundation design parameters; calculation based on the key design parameters using an established multi-parameter coupling model; node failure mode judgment and parameter validity verification; calculation of the bearing capacity of the borehole wall; bearing capacity verification and node design optimization. The key point is that, firstly, the design parameters of the connection node's edge distance, end distance, connecting plate thickness, and component strength are obtained; then, a coupling model between the above-mentioned multiple parameters and the node's ultimate bearing capacity is established; based on this model, the comprehensive bearing capacity design value of the node is calculated. This invention overcomes the limitation of traditional methods that consider only one parameter, and realizes the refined calculation of the bearing capacity of the hole wall of a single bolt connection node, providing a reliable basis for the safe design and optimization of transmission tower nodes.

[0020] Please refer to the following first. Figure 2 A bolted joint refers to a structural connection point in a power transmission tower formed by bolts connecting connecting components (such as steel plates or angle steel). The bolt hole diameter d0 refers to the diameter of the bolt hole (round hole) pre-drilled (or stamped) on the connecting component (such as steel plate or angle steel) for installing the bolt. The bolt end distance e1 refers to the distance from the center of the bolt hole to the edge of the angle steel end along the direction of force. The bolt edge distance e2 refers to the distance from the center of the bolt hole to the edge of the angle steel along the direction perpendicular to the direction of force. The connecting plate thickness t refers to the thickness of a single connecting plate of the connecting component penetrated by the bolt; the connecting plate refers to the plate portion connected to the bolt, such as a steel plate or angle steel leg. The yield strength f of the connecting component... y This refers to the yield strength of the steel used in the connecting components. The compressive strength of the connecting components. This refers to the smaller of the design compressive strength values ​​of the bolt hole wall and the bolt shank in a connecting component. The borehole wall bearing capacity refers to the ability of the bolt hole wall material to resist plastic deformation and tearing failure when compressed by the bolt shank. Furthermore, Figure 2 p1 represents the bolt hole spacing (center distance).

[0021] Currently, angle steel is the most important component in transmission tower structures due to its simple cross-sectional shape, high material utilization, convenient connection, and mature processing technology. Most of these angle steel components are connected by bolts to form load-bearing nodes, and the reliability and load-bearing capacity of these connections directly determine the mechanical performance, safety margin, and economy of the entire tower structure. Bolted connection nodes exhibit various failure modes, mainly including bolt shear failure, tensile failure of the connected angle steel's net cross-section, bolt bearing failure, and borehole bearing failure. Borehole bearing failure is a complex process of local yielding and tearing: under the compression of the bolt shank, the material in front of the borehole wall undergoes plastic deformation accompanied by shear slip, eventually tearing along a controlled direction (such as the end, edge, or along the line connecting the centers of the borehole group). For single-bolted angle steel nodes widely used in transmission towers, because the angle steel limbs are relatively thin, their ultimate bearing capacity often does not depend on the shear or bearing strength of the bolt itself, nor is it controlled by the net cross-sectional strength of the component, but is mainly determined by the borehole bearing strength. Therefore, borehole wall bearing failure is usually the key failure mode controlling the ultimate bearing capacity of this type of node.

[0022] To guide engineering design, countries worldwide have established corresponding steel structure design code systems. my country's current "Technical Specification for Design of Overhead Transmission Line Tower Structures" (DL / T 5486-2020) and earlier versions primarily adopt simplified formulas proven through long-term engineering practice for calculating the bearing capacity of bolt joint hole walls; these formulas are essentially semi-theoretical and semi-empirical in nature. Internationally, standards such as European standards (EN 1993-1-8) and American AISC standards also provide their own calculation methods. These standards generally use the following common form: Fb = C×fu×d×t, where C is a comprehensive influence coefficient. Chinese standards typically simplify C to an empirical constant or piecewise value indirectly related to parameters such as bolt end distance e1 and bolt edge distance e2, while European and American standards attempt to more explicitly relate parameters such as bolt end distance e1 and bolt edge distance e2 through some coefficients. However, existing standard formulas still have the following common limitations: First, the formulas in American standards AISC 360-22 and ASCE 10-15 mainly consider the independent influence of single parameters, lacking explicit expression of the coupled effects of multiple parameters such as end distance and edge distance; second, European standard EN 1993-1-8:2024 completely ignores the influence of edge distance on bearing capacity, while European standard EN 50341-2012 does not distinguish the difference in bearing capacity between intermediate bolts and end bolts; finally, the Chinese standard DL / T 5486-2020 is essentially a semi-theoretical and semi-empirical formula, and its bearing capacity formula cannot reflect the explicit relationship with geometric parameters. Overall, domestic methods lack the necessary parametric mathematical framework and cannot support refined design; while advanced foreign parametric models, due to their inherent mismatch, are difficult to directly apply to Chinese engineering practice. Neither can meet the new requirements for structural design safety, economy, and digitalization in the context of high-quality development in China's power transmission industry. This contradiction constitutes the core problem that this invention aims to solve. These shortcomings make it difficult for existing standards to meet the urgent needs of current power transmission engineering construction for refined design and life-cycle cost optimization.

[0023] In recent years, with the development of computational mechanics and experimental technology, the academic and engineering communities have deepened their research on the performance of bolted connections. Numerous refined finite element analyses (FEA) and full-scale tests have shown that the bearing capacity of a joint is not simply determined by a single minimum parameter, but rather is a complex function of the continuous and synergistic effects of multiple parameters such as end distance, edge distance, center distance, material strength, bolt diameter, and plate thickness. The "minimum value" or piecewise linear approach commonly used in existing standards, while ensuring design safety (usually leaning towards conservatism), essentially encloses a continuous physical response surface in several discrete, polygonal, conservative planes. This method experiences a sharp drop in prediction accuracy at parameter boundaries and fails to reflect the true increase or decrease in bearing capacity when parameters continuously change within the "safe zone," leading to either overly rough and conservative design results, increasing material costs, or unrecognized risks in non-standard layouts. Currently, my country's high-voltage transmission facility construction is at a critical stage of simultaneously emphasizing "high-speed growth" and "high-quality development." Faced with the practical needs of optimizing life-cycle costs, conserving resources, and implementing digital and intelligent design, there is an urgent need to develop a method for calculating bearing capacity that can accurately and continuously characterize the influence of geometric parameters. This is not only an important improvement to the existing theoretical system, but also a key technological support for promoting the refinement and economy of power transmission structure design.

[0024] Please see Figure 1 The present invention provides a method for calculating the bearing capacity of the borehole wall of a single bolt connection node in a power transmission tower. The method mainly uses the deformation threshold of the bolt hole wall as the damage control criterion, comprehensively considers the coupling effect of end distance and edge distance as well as the influence of material strength, and achieves refined calculation of the bearing capacity of the borehole wall through dimensionless processing, fitting model establishment, and failure mode judgment. The method includes the following steps.

[0025] Step S1: Dimensionless processing is performed on the basic parameters.

[0026] Among them, the basic parameters refer to the core influencing parameters of a single bolt connection node on a transmission tower, including: bolt hole diameter d0, bolt end distance e1, bolt edge distance e2, and yield strength f of the connecting member. y , compressive strength of connecting components Then, the first independent variable β, the second independent variable α, and the third independent variable γ are calculated using the following formulas: (Formula 1), (Formula 2), (Formula 3).

[0027] In this scheme, the ratio of the bearing capacity of the connecting member to its yield strength is taken as the dimensionless first independent variable β, as shown in Formula 1. To improve the engineering applicability and calculation efficiency of the bearing capacity fitting formula, while considering both calculation accuracy and engineering practical value, β is approximated as a constant value of 1.5. The correlation between bolt hole diameter d0, bolt end distance e1, and bolt edge distance e2 is dimensionlessized to obtain the second independent variable α and the third independent variable γ, as shown in Formulas 2 and 3. Furthermore, the actual bearing capacity of the single bolt connection node / the ultimate bearing capacity of the node is taken as the normalized dependent variable β. b (i.e., the influence coefficient of edge distance bearing capacity) and β d The product of (i.e., the end distance bearing capacity influence coefficient) (see Formula 8 below) achieves dimensionless processing of the parameters, eliminating the influence of dimensions on the calculation results.

[0028] Step S2, using the ratio of the second independent variable α to the first independent variable β (α / β) as the abscissa, the edge distance bearing capacity influence coefficient β... b Using the vertical axis as the ordinate, establish the edge distance bearing capacity influence coefficient β. b The fitting model.

[0029] For example, in step S2, based on the mechanical test and numerical simulation data of a single-bolt connection node, the ratio of the second independent variable α to the first independent variable β is used as the abscissa, and the edge distance bearing capacity influence coefficient β is used as the abscissa. b (Using the normalized dependent variable) as the ordinate, plot a scatter plot, such as... Figure 3 As shown in the figure (the horizontal axis represents the substituted and simplified α / β), a cubic polynomial is used to fit the scattered data to establish a fitting model for the influence coefficient of the edge bearing capacity; as shown in Formulas 4 and 5: (Formula 4), (Formula 5), Among them, A b B is the first fitting intercept. b C is the coefficient of the linear term. b D is the coefficient of the quadratic term. b The coefficients are cubic terms; the coefficient values ​​were determined by fitting experimental data: A b =0.287, B b =1.828, C b = 1.576, D b =0.431. The coefficient of determination R of the fitted model is... 2 =0.85129, adjusted coefficient of determination Adj.R 2 =0.84987, the sum of squared residuals is 0.46505, indicating high fitting accuracy and precise reflection of α / β and β. b The quantitative relationship.

[0030] Step S3, with the third independent variable γ as the abscissa, the influence coefficient β of the end distance bearing capacity. d Using the vertical axis as the ordinate, establish the influence coefficient β of the end-distance bearing capacity. d The fitting model.

[0031] For example, in step S3, based on the mechanical test and numerical simulation data of a single-bolt connection node, the dimensionless third independent variable γ is used as the abscissa, and the end distance bearing capacity influence coefficient β is used. d (Using the normalized dependent variable) as the ordinate, plot a scatter plot, such as... Figure 4 As shown in Equation 6, a nonlinear polynomial is used as the fitting basis function, and the scattered data is fitted by regression using the ordinary least squares method to establish a fitting model for the influence coefficient of the end distance bearing capacity. (Formula 6), Among them, A d B is the second fitting intercept. d C is the first fitting coefficient. d The second fitting coefficient; after fitting and calibration with experimental and simulation data, the values ​​of each coefficient are: A d =1.252、B d =-0.001、C d =1.316. The model's coefficient of determination R0 is 1.316. 2 =0.86525, adjusted coefficient of determination Adj.R 2 =0.86437, the sum of squared residuals is 0.02701, the fitting accuracy is excellent, and it can accurately characterize γ and β. d The quantitative relationship.

[0032] Preferably, there is a step S4, which verifies the validity of the parameters in the following way: Ensure the tensile strength f of the connecting components y , compressive strength of connecting components The values ​​should conform to the material specifications for angle steel and bolts of transmission towers, and the parameter ranges should meet e1 / d0=1.0~3.5 and e2 / d0=1.2~5.0, which are suitable for calculating single-bolt connection nodes of conventional transmission towers. If they do not meet the requirements, adjustments should be made to satisfy them.

[0033] Step S5: Calculate the bearing capacity of the borehole wall.

[0034] Based on the fitting model established in step S2, the calculated values ​​of the dimensionless independent variables α / β are substituted to obtain the edge distance bearing capacity influence coefficient β. b Based on the fitting model established in step S3, the calculated value of the dimensionless independent variable γ is substituted to obtain the influence coefficient β of the end distance bearing capacity. d; combined with the ultimate bearing capacity N of the borehole wall of the single bolt connection node of the transmission tower u (As shown in Formula 7), calculate the borehole wall bearing capacity N (full name: actual single bolt connection node borehole wall bearing capacity considering multi-parameter coupling and edge distance effects), as shown in Formula 8: (Formula 7), (Formula 8), Where d is the bolt diameter, t is the connecting plate thickness, and f u This refers to the tensile strength of the connecting component.

[0035] Preferably, the method further includes step S6, bearing capacity verification and node design optimization (comparing the borehole wall bearing capacity N calculated in step S5 with the actual load F on the node to verify the safety of the node design): If N / F≥1, then the bearing capacity of the node hole wall meets the design requirements; If N / F < 1, the bolt distance can be adjusted according to the fitted model, and the values ​​of α / β and / or γ can be adjusted to a reasonable range. The borehole wall bearing capacity N is then recalculated, and step S6 is repeated until the design requirements are met. Further, the values ​​of α / β and / or γ can be adjusted by adjusting the bolt distance e1 and / or bolt distance e2. The borehole wall bearing capacity is recalculated and the node design is optimized until the safety requirements are met. Optimizing the node design specifically includes, for example, increasing the bolt distance e2 and / or increasing the bolt distance e1.

[0036] Furthermore, in this invention, the bolt end distance is the distance from the center of the bolt hole to the end of the angle steel in the direction of load application, and the bolt edge distance is the distance from the center of the bolt hole to the edge of the angle steel in the direction perpendicular to the direction of load application; the bolt hole wall deformation threshold d0 / 6 is a node damage control criterion, corresponding to approximately 70% of the node's ultimate load, and is matched with the net section yield bearing capacity, taking into account both the node's safety performance and deformation control requirements.

[0037] The following description, in conjunction with a specific embodiment, provides further details.

[0038] This embodiment takes the angle steel single bolt connection node of a power transmission tower as the calculation object. The node adopts L90×8 angle steel of material S355 and is connected by M20 bolts of grade 8.8. The bolt end distance is 20mm and the bolt edge distance is 20mm. The bearing capacity of the hole wall is calculated.

[0039] Step 1: Determine the basic calculation parameters and perform dimensionless processing; Based on the node details, the thickness of the connecting member is t=8mm, the bolt hole diameter is d0=21.5mm, and the bearing capacity of the connecting member is... (In this embodiment, the design value of the bearing strength of the angle steel hole wall) = 510MPa, and the yield strength of the connecting member f y (In this embodiment, the yield strength of the angle steel is 355 MPa, bolt end distance e1 = 20 mm, bolt edge distance e2 = 20 mm, and the tensile strength of the connecting member f is... u (In this embodiment, this refers to the tensile strength of the angle steel) = 470 MPa; therefore, the following values ​​are calculated: β = 1.5, α = 0.925, γ = 0.930, N u =075.2kN.

[0040] Step 2: Substitute the values ​​into the fitting model to calculate the influence coefficient of the edge distance bearing capacity; Calculate α / β = 0.925 ÷ 1.5 = 0.617, substitute it into the fitting model of the edge distance bearing capacity influence coefficient, and calculate β. b ≈0.916.

[0041] Step 3: Substitute the values ​​into the fitting model to calculate the influence coefficient of end distance bearing capacity; Substituting γ=0.930 into the fitting model for the influence coefficient of end distance bearing capacity, β is calculated. d ≈1.170.

[0042] Step 4: (After verifying the validity of the parameters) Determine the failure mode; In this calculation, α / β = 0.617. At this point, the effective tensile bearing capacity of the angle steel edge is slightly lower than the ultimate bearing capacity of the bolt hole wall. The joint is in the critical transition stage between tensile failure of the angle steel edge and bearing failure of the bolt hole wall. During this stage, the bolt distance remains a key parameter affecting the ultimate bearing capacity of the joint. The edge distance bearing capacity influence coefficient β obtained by the cubic polynomial fitting model established in this invention is... b This allows for precise quantification of the load-bearing capacity reduction effect caused by insufficient edge distance during the transition phase.

[0043] Step 5: Calculate the bearing capacity of the borehole wall; The borehole wall bearing capacity is calculated to be 80.57 kN according to Formula 8.

[0044] Step 6: Bearing capacity verification; The actual load on the node is F=65kN. The calculated bearing safety factor N / F=80.57 / 65=1.24≥1. It is determined that the bearing capacity of the hole wall of the node meets the design safety requirements. There is no need to adjust the end distance and edge distance parameters. The node design is reasonable.

[0045] If the actual load on the node is F=85kN, then N / F=80.57 / 85=0.948<1, the node bearing capacity is insufficient, and the design needs to be optimized: the bolt edge distance e2 can be increased (e.g., adjusted to 40mm), and the α value can be recalculated, or the bolt edge distance e1 can be increased (e.g., adjusted to 30mm), and the γ value can be recalculated, until N / F≥1, which meets the safety requirements.

[0046] In the specific embodiments of the present invention, all calculation parameters are derived from experimental measurements and numerical simulation data. The fitting model has been verified by a large number of experiments and simulations, and has high accuracy and strong reliability. The calculation steps are clear and the parameter adjustment direction is well-defined. It can be directly applied to the design, verification and optimization of single-bolt angle steel connection nodes of transmission towers. Under the premise of ensuring structural safety, it effectively avoids material waste and improves the economy and accuracy of transmission tower design.

[0047] In summary, the key core concepts of this invention include abandoning the existing domestic standard practice of conservatively estimating the influence of geometric parameters by "taking the minimum value," and instead adopting a continuous function model to directly and continuously describe the mathematical relationship between bolt end distance, edge distance, and bearing capacity coefficient. Specifically, this involves reconstructing the coefficients in the European standard formulas using parametric functions, specifically by defining them using linear or nonlinear functions containing variables such as α and γ. Furthermore, the technical support of this invention includes the calibration of specific coefficients in the parametric functions based on a combination of finite element numerical analysis and physical test data to ensure the reliability and accuracy of the model. The advantages of this invention are rooted in its complete technical chain established for practical engineering in my country, from "mechanism research" to "model construction" and then to "engineering application." Its superiority can be explained through the following rigorous cause-effect reasoning: First, because: This invention is based on refined numerical simulation and physical experiments, and constructs a computational kernel that reflects the real failure mechanism of materials in China.

[0048] Refined Numerical Simulation: In performing finite element analysis, this invention does not use the simplified elastoplastic model commonly used in traditional design, but instead introduces an advanced constitutive model capable of simulating material damage and fracture processes. This model can more realistically simulate the complete fracture process of domestically produced steel under bolt compression, from the nucleation, growth, and aggregation of microscopic cavities near the hole wall, ultimately leading to the initiation and propagation of macroscopic cracks.

[0049] Systematic physical testing: This invention is not purely theoretical derivation, but is based on systematic full-scale node tests covering a range of key parameters. These tests strictly adopted domestic standard materials, mainstream processing techniques, and typical structural details, thereby obtaining first-hand data reflecting the actual performance of domestic nodes and constructing a reliable database to support model development.

[0050] Results: This makes the underlying mechanical mechanisms of the parameterized formula proposed in this invention clearer, elevating the prediction of bearing capacity from "macro-empirical fitting" to "micro-mechanism-driven." Compared with traditional methods, it can more accurately predict the limit state and failure mode of node failure, especially for bearing behavior under complex stress states, significantly improving the physical reliability and theoretical accuracy of the calculation results.

[0051] Secondly, because the parameterized model of this invention is directly calibrated by domestic experimental and simulation data, the localization of the model's "genes" is ensured.

[0052] The determination of all key coefficients in the formula (such as bolt end distance e1 and bolt edge distance e2 mentioned above) is based entirely on the finite element analysis results and physical test data based on domestic conditions. Through data-driven methods such as regression analysis and machine learning, the output of the formula is optimally fitted to the "real domestic bearing capacity".

[0053] Consequence: Therefore, this invention completely overcomes the "incompatibility" problem caused by directly applying foreign standards. Its parameterized relationships naturally incorporate the performance characteristics of domestically produced steel, the influence of deviations in domestic processing techniques, and the effects of common structural details. There is no longer a "systematic error" between the calculation model and the engineering object, fundamentally guaranteeing the prediction accuracy and reliability of this method in the design scenario of Chinese power transmission towers.

[0054] Third, because: This invention combines a complete parametric mathematical framework with a localized model, forming a tool that can be directly used for design.

[0055] While ensuring accuracy, this invention ultimately provides a mathematical function with a clear form and continuous variables. Key geometric parameters required for design (bolt end distance e1, bolt edge distance e2, etc.) appear directly as independent variables in the formula, and their influence is continuously and quantitatively characterized.

[0056] Result: This has brought revolutionary convenience and value to domestic design practices.

[0057] It achieves truly refined design: designers can clearly quantify the specific benefits of adjusting a structural parameter on load-bearing capacity, thereby proactively seeking the optimal and most economical layout scheme within safety regulations, changing the passive design mode that relied on "minimum structural requirements" in the past.

[0058] Perfectly adapted to digital and intelligent design processes: The parametric formula itself is a natural, computable "objective function." It can be seamlessly integrated into parametric modeling, topology optimization, and artificial intelligence algorithms, driving automated design, intelligent optimization, and life-cycle cost analysis, greatly improving design efficiency and unlocking optimization potential.

[0059] Combining advanced technology, safety, and economy: This method not only incorporates the advanced features of parameterized fine analysis, but also ensures safety and reliability through localized data calibration. At the same time, its optimization guidance can directly bring significant economic benefits such as material savings and cost reduction.

[0060] Conclusion: Through innovations in three aspects—depth of mechanism research (fracture constitutive simulation), reliability of data support (localized testing), and applicability of model construction (parametric localized calibration)—this invention demonstrates a comprehensive advantage of high precision, strong applicability, ease of optimization, and intelligence, effectively meeting the new era's demands for high-quality development in my country's power transmission industry.

[0061] 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 them; obviously, the described embodiments are some embodiments of the present invention, but not all embodiments; based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention; in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the bearing capacity of the borehole wall of a single-bolt connection node in a power transmission tower, characterized in that, Includes the following steps: Step S1: Calculate the first independent variable β, the second independent variable α, and the third independent variable γ using the following formulas: (Official 1), (Official 2), (Official 3), in, f represents the compressive strength of the connecting component. y The yield strength of the connecting component is given by e1, the bolt end distance is given by e2, the bolt edge distance is given by d0, and the bolt hole diameter is given by d0. Step S2, using the ratio of the second independent variable α to the first independent variable β as the abscissa, the edge distance bearing capacity influence coefficient β... b Using the vertical axis as the ordinate, establish the edge distance bearing capacity influence coefficient β. b The fitting model; Step S3, with the third independent variable γ as the abscissa, the influence coefficient β of the end distance bearing capacity. d Using the vertical axis as the ordinate, establish the influence coefficient β of the end-distance bearing capacity. d The fitting model; Step S5, calculate the bearing capacity N of the borehole wall using the following formula: (Official 7), (Official 8), Where, N u The bearing capacity of the hole wall of a single bolted connection node on a power transmission tower is given by: d is the bolt diameter, t is the thickness of the connecting plate, and f is the bearing capacity of the hole wall. u This refers to the tensile strength of the connecting component.

2. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a transmission tower according to claim 1, characterized in that, In step S2, a cubic polynomial is used to fit the scattered data to establish the edge bearing capacity influence coefficient β according to the following formula. b Fitting model: (Official 5), Among them, A b B is the first fitting intercept. b C is the coefficient of the linear term. b D is the coefficient of the quadratic term. b The coefficient of the cubic term.

3. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a transmission tower according to claim 2, characterized in that, A b =0.287,B b =1.828,C b = 1.576,D b =0.431。 4. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a power transmission tower according to claim 1, characterized in that, In step S3, a nonlinear polynomial is used as the fitting basis function to fit the scattered data, and the end-distance bearing capacity influence coefficient β is established as follows: d Fitting model: (Official 6), Among them, A d B is the second fitting intercept. d C is the first fitting coefficient. d is the second fitting coefficient.

5. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a power transmission tower according to claim 4, characterized in that, A d =1.252、B d =-0.001、C d =1.316。 6. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a power transmission tower according to claim 1, characterized in that, Step S4 is also included between step S3 and step S5; Step S4 is to verify the validity of the parameters in the following way: Ensure the tensile strength f of the connecting components y , compressive strength of connecting components The values ​​of e1 / d0 conform to the requirements of the transmission tower specifications and satisfy e1 / d0 = 1.0~3.5 and e2 / d0 = 1.2~5.

0.

7. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a power transmission tower according to claim 1, characterized in that, Step S5 is followed by step S6; Step S6 involves comparing the borehole wall bearing capacity N calculated in step S5 with the actual load F on the node. If N / F ≥ 1, the borehole wall bearing capacity meets the design requirements. If N / F < 1, the values ​​of α / β and / or γ are adjusted, the borehole wall bearing capacity N is recalculated, and step S6 is repeated until the design requirements are met.

8. The method for calculating the bearing capacity of the hole wall of a single bolt connection node in a transmission tower according to claim 7, characterized in that, In step S6, if N / F < 1, then adjust the bolt edge distance e1 and / or bolt edge distance e2.

9. The method for calculating the bearing capacity of the borehole wall of a single bolted connection node in a transmission tower according to any one of claims 1 to 8, characterized in that, β=1.5。

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