A power transmission tower stress performance analysis and instability early warning method

Abstract

This invention discloses a method for analyzing the stress performance and predicting instability of power transmission towers, relating to the field of power transmission tower safety technology. The method includes the following steps: S1, collecting structural parameters and mechanical performance indicators of the power transmission tower to be analyzed; S2, performing full-condition static calculations and modal analysis on the power transmission tower using professional tower verification software, locating overloaded members and their control conditions, and obtaining the tower's mode shapes and natural frequencies; S3, establishing a tower analysis model in finite element analysis software, and verifying the accuracy of the model using the mode shapes and natural frequencies obtained in S2. The stress performance analysis and instability prediction method proposed in this invention integrates the full-condition static calculations of professional tower verification software with the collapse simulation and dynamic response analysis of finite element analysis software into the same analysis process. It uses the modal analysis results as a bridge to verify the accuracy of the models between the two software programs, changing the situation where each analysis is independent and the results lack cross-verification.

Description

Technical Field

[0001] This invention relates to the field of power transmission tower safety technology, specifically to a method for analyzing the stress performance of power transmission towers and providing early warning of instability. Background Technology

[0002] This transmission tower is subjected to wind loads, icing loads, and seismic forces during operation. Under repeated loads, the members may experience excessive stress and slenderness ratio, which can lead to buckling instability and even tower collapse in severe cases. Currently, the stress verification of transmission towers mainly relies on specialized tower design software to perform static calculations under various working conditions, which can locate the locations where the stress ratio and slenderness ratio of the members exceed the limits.

[0003] However, specialized software, limited by its analytical framework, cannot simulate the mechanical process of individual buckling of members, gradual structural instability, and eventual collapse of a steel tower under extreme conditions. It also struggles to reflect the actual path of internal force transfer from buckling members to adjacent members. Regarding dynamic loads, some studies use general-purpose finite element software to analyze the pulsating wind or seismic response of steel towers; however, these analytical models are typically not cross-validated with the calculation results from specialized verification software, resulting in a lack of independent verification of model accuracy.

[0004] Meanwhile, there is a lack of systematic connection between static and dynamic analyses. Weak and sensitive areas identified by both analyses are not incorporated into a unified evaluation framework, making it difficult to determine whether statically exceeding limits and significantly amplified dynamic areas point to the same structural location. Furthermore, while there are existing practices combining professional verification software with finite element software, these are limited to a simple chain of modeling with professional software and verification with finite element software, without establishing a closed-loop analysis process from modal verification to constitutive reduction, collapse simulation, and then to dynamic analysis. To address this, we propose a method for analyzing the stress performance and providing early warning of instability in transmission towers. Summary of the Invention

[0005] To address the aforementioned technical problems, a method for analyzing the stress performance and providing early warning of instability of power transmission towers is provided, comprising the following steps: S1. Collect the structural parameters and mechanical performance indicators of the transmission tower to be analyzed; S2. Based on professional tower verification software, perform full-condition static verification and modal analysis on transmission towers, locate over-limit members and their control conditions, and obtain tower vibration modes and natural frequencies. S3. Establish an analysis model of the iron tower in the finite element analysis software. Verify the accuracy of the model using the mode shape and natural frequency obtained in S2. After reducing the constitutive parameters based on the stability coefficient of each member, conduct a collapse simulation for the most unfavorable working condition determined in S2 to determine the starting position and development process of the iron tower instability failure. S4. Based on the finite element model verified in S3, dynamic response analysis was performed by applying pulsating wind load and seismic load respectively to obtain the amplification effect of dynamic load on the tower stress. S5. Based on the over-limit member positioning results of S2 and the instability failure law of S3, determine the weak parts of the structure, and use the dynamic load amplification effect of S4 to determine the dynamic sensitive parts. Output instability early warning information based on the correspondence between the weak parts of the structure and the dynamic sensitive parts.

[0006] Preferably, the structural form, height, span, conductor and ground wire type, hanging point height, and basic design wind speed of the transmission tower are collected as structural parameters, and the steel grade, density, elastic modulus, Poisson's ratio, yield strength, and ultimate strength of the main and auxiliary materials of the tower are collected as mechanical performance indicators.

[0007] Preferably, the static verification under all working conditions in S2 includes: A multi-condition verification system covering strong winds, icing, line breakage, installation, and anchoring is constructed. The stress calculation of all members of the tower under each condition is performed, and the slenderness ratio and stress ratio of each member are statistically analyzed. Members with slenderness ratios exceeding the allowable slenderness ratio and stress ratios exceeding the allowable stress ratio are marked as over-limit members. The maximum stress ratio condition corresponding to each over-limit member is recorded as its control condition.

[0008] Preferably, the modal analysis in S2 includes: The transmission tower's first few vibration modes and corresponding natural frequencies are calculated using professional tower verification software. These vibration modes include bending modes along the horizontal line direction, bending modes along the vertical line direction, and torsional modes.

[0009] Preferably, the tower analysis model established in S3 includes: In finite element analysis software, beam elements are used to simulate the main and auxiliary materials of the iron tower to establish a linear element analysis model. Rigid connection constraints are set at the bottom, and the conductor load is applied to the hanging point as a concentrated load. Using the first few modes and natural frequencies obtained from S2 as a reference, when the mode natural frequencies of the finite element model and the results of the professional verification software meet the following verification conditions: the relative deviation of the natural frequencies of the first two bending modes does not exceed the frequency verification threshold; the relative deviation of the natural frequencies of higher-order modes does not exceed the higher-order frequency verification threshold, the model verification is confirmed to be successful.

[0010] Preferably, the reduction of constitutive parameters based on the stability coefficient of each member in S3 includes: Based on the stability coefficient φ of each member obtained from the S2 static verification, the buckling critical stress of each member is calculated. The buckling critical stress is used to replace the yield strength in the original constitutive parameters of the member as the reduced yield stress, so that each member in the finite element model enters the yield state when the stress reaches the buckling critical stress.

[0011] Preferably, the collapse process simulation in S3 includes: The structural self-weight, tower wind load divided by wind pressure section, and conductor and ground wire load are combined and applied to the reduced finite element model. The static analysis method is used to gradually apply the load, record the stress distribution of the members, nodal displacement, and member yield sequence at each load stage, and determine the starting member position of the tower instability failure, the development process of instability from the starting member to the adjacent members, and the final failure mode.

[0012] Preferably, the dynamic response analysis of the pulsating wind load in S4 includes: Based on the Davenport spectrum, a random pulsating wind field is generated. The wind speed time history curves and corresponding wind load time history curves of each wind pressure section of the tower are calculated. The wind load time history is applied to the main material nodes of the verified finite element model to perform explicit dynamic analysis. The tower top displacement time history and tower leg base shear time history are obtained to determine the amplification factor of pulsating wind on tower displacement, member stress and base shear.

[0013] Preferably, the dynamic response analysis of seismic load in S4 includes: applying multidimensional and multi-point seismic excitation considering traveling wave effect, partial coherence effect and local site effect to the finite element model of the tower, performing dynamic response analysis, and obtaining the stress distribution of the tower members, the change of node displacement and the failure status of the members under seismic action.

[0014] Preferably, the location of the over-limit member is compared with the location of the member that initiates instability and failure determined by the collapse simulation. When the two locations are consistent, the member is marked as the primary warning location among the weak parts of the structure. Member segments with amplification factors exceeding the amplification factor threshold and member segments that fail in the seismic response are marked as dynamically sensitive locations. The instability control condition is determined based on the overlap between the primary warning location and the dynamically sensitive location, and instability warning information including the warning location, control condition, and sensitive location is output.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The stress performance analysis and instability early warning method proposed in this invention integrates the full-condition static verification of professional tower calculation software with the collapse simulation and dynamic response analysis of finite element analysis software into the same analysis process. Modal analysis results serve as a verification bridge for the accuracy of the models between the two software programs, changing the situation in existing technologies where the two software programs analyze independently and lack cross-verification of results. By using a method of reducing constitutive parameters through member stability coefficients, the buckling critical stress of the compressed member is taken as the reduced yield stress, so that the yielding of the member in the finite element model corresponds to the occurrence of buckling instability in a mechanical sense, providing an operable constitutive treatment method for simulating the entire process of tower collapse. Dynamic load amplification factors are obtained through pulsating wind and seismic dynamic response analysis, and the locations of dynamically sensitive parts and statically exceeding limits are compared. When the two coincide, they are identified as the primary early warning location, providing a judgment basis combining static and dynamic analysis for instability early warning. Attached Figure Description

[0016] Figure 1 This is a flowchart of the stress performance analysis and instability early warning method of the present invention. Detailed Implementation

[0017] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0018] Reference Figure 1 As shown, a method for analyzing the stress performance and predicting instability of power transmission towers includes the following steps: S1. Collect the structural parameters and mechanical performance indicators of the transmission tower to be analyzed; S1 includes: collecting the structural form, height, span, conductor and ground wire type, hanging point height and design basic wind speed of the transmission tower as structural parameters, and collecting the steel grade, density, elastic modulus, Poisson's ratio, yield strength and ultimate strength of the main and auxiliary materials of the tower as mechanical performance indicators.

[0019] Structural parameters are used to determine the spatial geometry and external load conditions of the tower. Among them, the structural form and height determine the overall stiffness distribution and windward area of ​​the tower, the span and conductor type determine the magnitude of the conductor tension load, the hanging point height determines the distribution of the load application location, and the design basic wind speed is the reference input for wind load calculation.

[0020] Mechanical performance indicators are used to define the material constitutive relations of each member in finite element analysis. The use of different steel grades for the main material and auxiliary material reflects the difference in load-bearing capacity between the two components in actual engineering. Density is used to calculate the self-weight of the structure. Elastic modulus and Poisson's ratio define the stress-strain relationship in the elastic stage, while yield strength and ultimate strength define the constitutive behavior in the plastic stage.

[0021] S2. Based on professional tower verification software, perform full-condition static verification and modal analysis on transmission towers, locate over-limit members and their control conditions, and obtain tower vibration modes and natural frequencies. The full-condition static verification in S2 includes: constructing a multi-condition verification system covering strong winds, icing, broken wires, installation, and anchor wires at different wind angles; performing stress calculations on all members of the tower under each condition; statistically analyzing the slenderness ratio and stress ratio of each member; marking members with slenderness ratios exceeding the allowable slenderness ratio and stress ratios exceeding the allowable stress ratio as over-limit members; and recording the maximum stress ratio condition corresponding to each over-limit member as its control condition.

[0022] The high wind conditions with different wind angles cover the range from 0° to 315°. This is because the stress state of each member of the tower is significantly different under different wind angles. Some members only experience stress exceeding the limit under specific wind angles. Comprehensive coverage of wind angles is necessary to avoid missing control conditions.

[0023] The allowable value for slenderness ratio is determined based on the limitations imposed on compression members in the "Technical Regulations for Structural Design of Overhead Transmission Line Towers". The physical basis for this limitation is that compression members with excessively large slenderness ratios will experience elastic instability and lose their load-bearing capacity before reaching the material's yield strength. The allowable value for stress ratio is 1.0. When the stress ratio exceeds 1.0, it indicates that the calculated stress of the member under that working condition has exceeded its allowable stress, and the load-bearing capacity does not meet the design requirements.

[0024] The modal analysis in S2 includes: calculating several modes of vibration and their corresponding natural frequencies of the transmission tower using professional tower verification software. The modes of vibration include bending modes along the horizontal line direction of the tower, bending modes along the vertical line direction, and torsional modes.

[0025] The mode shapes and natural frequencies obtained from modal analysis reflect the inherent vibration characteristics of the tower. The natural frequencies corresponding to the bending modes in the transverse and longitudinal directions characterize the overall stiffness of the tower along its two principal axes, while the torsional mode shapes reflect the tower's torsional stiffness. These modal parameters serve as the benchmark for subsequent finite element model verification and also provide a basis for determining the resonance between the load frequency and the structure's natural frequency in dynamic response analysis.

[0026] S3. Establish an analysis model of the iron tower in the finite element analysis software. Verify the accuracy of the model using the mode shape and natural frequency obtained in S2. After reducing the constitutive parameters based on the stability coefficient of each member, conduct a collapse simulation for the most unfavorable working condition determined in S2 to determine the starting position and development process of the iron tower instability failure. The establishment of the tower analysis model in S3 includes: using beam elements to simulate the main and auxiliary materials of the tower in the finite element analysis software to establish a line element analysis model, setting rigid connection constraints at the bottom, and applying the conductor and ground wire load as a concentrated load to the hanging point position. Using the first few modes and natural frequencies obtained from S2 as a reference, when the relative deviation between the natural frequencies of the first two bending modes of the finite element model and the results of the professional verification software does not exceed the frequency verification threshold and the relative deviation between the natural frequencies of the higher-order modes does not exceed the higher-order frequency verification threshold, the model verification is confirmed to be successful.

[0027] The rigid connection constraint at the bottom is based on the fact that the transmission tower is connected to the foundation via anchor bolts, which can be approximated as a fixed-end constraint in the bending plane. The frequency verification threshold is set as follows: the first two bending modes are the most direct reflection of the overall stiffness of the tower, and their natural frequencies are most sensitive to model parameters, requiring strict verification standards; higher-order modes are affected by local modes, and their frequencies are less sensitive to model details, allowing for a moderate relaxation. For example, the relative deviation of the natural frequencies of the first two bending modes should not exceed 1%, and the relative deviation of the natural frequencies of higher-order modes should not exceed 10%.

[0028] The reduction of constitutive parameters based on the stability coefficient of each member in S3 includes: calculating the buckling critical stress of each member based on the stability coefficient φ of each member obtained from the static verification in S2, and replacing the yield strength in the original constitutive parameters of the member with the buckling critical stress as the reduced yield stress, so that each member in the finite element model enters the yield state when the stress reaches the buckling critical stress.

[0029] The physical meaning of the stability coefficient φ is the ratio of the critical buckling stress to the yield strength of the material in a compression member after considering factors such as initial bending, residual stress, and plastic development. The value of φ is determined according to the stability coefficient table of axially compressed members in the "Standard for Design of Steel Structures" based on the slenderness ratio of the member and the strength grade of the steel.

[0030] The mechanical basis for using the buckling critical stress as the reduced yield stress is that the instability failure of transmission tower members is essentially buckling instability rather than material yielding. When the stress in the member section reaches the buckling critical stress, the member loses its load-bearing capacity. Therefore, the yield point in the constitutive model is set as the buckling critical stress, so that the "yielding" of the member in the finite element model corresponds to the occurrence of buckling instability in a mechanical sense, thereby reproducing the real process of member buckling one by one and the structure gradually becoming unstable in the collapse simulation.

[0031] The collapse process simulation in S3 includes: combining the structure's self-weight, tower wind load divided by wind pressure section, and conductor load into a reduced finite element model; applying the load step by step using static analysis method; recording the stress distribution of members, nodal displacements, and member yielding sequences at each load stage; determining the starting member location of the tower's instability failure, the development process of instability from the starting member to adjacent members, and the final failure mode.

[0032] The basis for dividing the wind pressure sections is as follows: along the height of the iron tower, the wind speed increases with the height, and the wind pressure changes accordingly. The iron tower is divided into several wind pressure sections along its height. The wind load is calculated by taking the wind pressure value at the representative height of each section, so that the load distribution approximates the gradient change of the actual wind pressure along the height.

[0033] The conductor load takes into account both the conductor's own weight and the wind force on the conductor, and is applied as a concentrated force at the attachment point.

[0034] During the collapse, the first member to reach the critical buckling stress is the initiating member for instability and failure. After the buckling of this member, the load it bears is transferred to the adjacent members, causing the stress of the adjacent members to increase and buckle successively, forming a development process from local instability to overall collapse.

[0035] S4. Based on the finite element model verified in S3, dynamic response analysis was performed by applying pulsating wind load and seismic load respectively to obtain the amplification effect of dynamic load on the tower stress. The dynamic response analysis of pulsating wind load in S4 includes: generating a random pulsating wind field based on the Davenport spectrum, calculating the wind speed time history curves and corresponding wind load time history curves for each wind pressure section of the tower, applying the wind load time history to the main material nodes of the verified finite element model, performing explicit dynamic analysis, obtaining the tower top displacement time history and tower leg base shear time history, and determining the amplification factor of pulsating wind on tower displacement, member stress and base shear.

[0036] The Davenport spectrum is a mathematical model describing the power spectral density of fluctuating wind speed in the atmospheric boundary layer. Its physical meaning is the distribution characteristics of fluctuating wind energy at different frequencies. This spectrum reflects the characteristic of natural wind having large energy in low-frequency components and small energy in high-frequency components.

[0037] The basis for using the Davenport spectrum to generate random fluctuating wind fields is that the "Code for Design of Building Structures" lists the Davenport spectrum as the recommended model for fluctuating wind power spectrum in wind vibration analysis, which is suitable for calculating the wind-induced dynamic response of structures under general terrain conditions in my country.

[0038] The wind speed time history curve is calculated as follows: Using the design basic wind speed as the average wind speed at a height of 10m, the average wind speed at that height is calculated based on the wind speed profile at the representative height of each wind pressure segment. The pulsating component generated by the Davenport spectrum is then superimposed on this average wind speed to obtain the wind speed time history curve for each wind pressure segment. The amplification factor is calculated as follows: The maximum displacement at the tower top, the maximum stress in the members, and the maximum shear force at the base obtained from the dynamic analysis are compared with the corresponding response values ​​under static wind loads. The ratio of the dynamic response value to the static response value is the amplification factor.

[0039] The dynamic response analysis of seismic load in S4 includes: applying multi-dimensional, multi-point seismic excitation considering traveling wave effect, partial coherence effect and local site effect to the finite element model of the tower, performing dynamic response analysis, and obtaining the stress distribution of the tower members, the change of node displacement and the failure of the members under seismic action.

[0040] The traveling wave effect refers to the phase difference in the arrival time of the ground motion at different support points of a tower when the seismic wave propagates at a finite wave speed. For a long-span tower-line system, this phase difference causes the legs of the tower to be subjected to asynchronous seismic excitation, resulting in torsional and differential settlement effects. The partial coherence effect refers to the fact that due to the scattering and reflection of seismic waves in the propagation path, the ground motion at different support points is not completely correlated. The coherence decreases as the distance between support points increases. This effect causes the excitation waveforms of each leg of the tower to be different. Local site effects refer to the differences in seismic motion spectrum characteristics caused by varying soil conditions at different support points of the tower, resulting in inconsistencies in the seismic excitation amplitude and spectral composition at each support. When the tower is located in a region with undulating terrain or spans different geological units, the effects of the above three factors are more significant and must be considered simultaneously to obtain dynamic response results that approximate reality.

[0041] S5. Based on the over-limit member positioning results of S2 and the instability failure law of S3, determine the weak parts of the structure, and use the dynamic load amplification effect of S4 to determine the dynamic sensitive parts. Output instability early warning information based on the correspondence between the weak parts of the structure and the dynamic sensitive parts.

[0042] S5 includes: comparing the location of the over-limit member with the location of the member that initiates instability and failure determined by the collapse simulation; when the two locations are consistent, the member is marked as the primary warning location among the weak parts of the structure; the member segments with the amplification factor of the pulsating wind exceeding the amplification factor threshold and the member segments that fail in the seismic response are marked as dynamic sensitive locations; the instability control condition is determined based on the overlap between the primary warning location and the dynamic sensitive location; and the instability warning information including the warning location, the control condition, and the sensitive location is output.

[0043] The consistency between the location of the overloaded member and the location of the member at the onset of instability indicates that the weak link identified by the static analysis coincides with the instability starting point revealed by the collapse simulation. This part is the first to lose its bearing capacity under extreme conditions and has the highest warning priority.

[0044] The threshold for the amplification factor of pulsating wind is set based on the following: when the amplification factor exceeds the threshold, the proportion of the additional response caused by the dynamic load in the total response has reached a level that cannot be ignored. Designing only according to static load will underestimate the actual stress state of this part.

[0045] The overlap between the primary warning location and the dynamically sensitive location indicates that this location is a weak point under both static and dynamic loads. The corresponding control conditions represent the combination of conditions most likely to cause instability in the tower and should be the core focus of instability warning. For example, the threshold for the pulsating wind amplification factor is set to 1.5, meaning that a member segment whose dynamic response exceeds 50% of its static response is marked as a dynamically sensitive location.

[0046] The following detailed description of the stress performance analysis and instability early warning method for power transmission towers according to the present invention is provided in conjunction with specific implementation steps. This embodiment is only used to explain the present invention and is not intended to limit the scope of protection of the present invention.

[0047] Implementation Step 1: Basic Parameter Review. Collect the basic parameters of the transmission tower to be analyzed, including the tower structure as a double-circuit straight-line tower, tower height Hm, total height H1m, and spans L1m and L2m; conductor and ground wire models are LGJ-300 / 40, JL / G1A-300 / 40 (conductor), and GJ-50 (ground wire), respectively; ground wire suspension point height H2m; conductor suspension point heights are H3m, H4m, and H5m, respectively; design basic wind speed Vm / s; the main material is Q345B steel, and the auxiliary material is Q235B steel. The mechanical properties of the steel, such as density, elastic modulus, Poisson's ratio, yield strength, and ultimate strength, are taken according to national standards.

[0048] Step 2: Static and modal analysis, the specific operations are as follows: 1. Setting up execution standards and control information: Based on relevant standards such as the "Technical Regulations for the Design of Overhead Transmission Line Tower Structures", "Code for Design of Steel Structures", and "Code for Loads on Building Structures", the calculation basis is set to determine the calculation control information such as the tower voltage level, number of tower bodies, number of connecting legs, and total number of working conditions. The calculation of the starting and ending connecting legs and working conditions covers the entire range.

[0049] 2. Construction and Screening of Working Condition System: Construct a multi-working condition system including strong winds (different wind angles: 0°, 45°, 60°, 90°, 135°, 180°, 225°, 270°, 315°), icing, wire breakage (break of ground wire, breakage of different conductors), installation and lifting, installation of anchor wires, minimum temperature, long-term load, etc. Valid working conditions are screened out through software calculations, and invalid working conditions are eliminated.

[0050] 3. Modal analysis: The first three and above vibration modes and natural frequencies of the tower are obtained by software calculation. The main vibration modes of the tower are identified as X-direction bending, Y-direction bending, torsion and local vibration modes. The distribution law of vibration modes and natural frequencies is analyzed.

[0051] 4. Stress Calculation and Over-Limit Analysis of Tower Members: Perform stress calculations for all tower members under various effective working conditions. Compile statistics on the specifications, bolt types, calculated length, radius of gyration, calculated slenderness ratio, allowable slenderness ratio, stability coefficient, maximum pressure, calculated stress, allowable stress, and stress ratio of each member. Determine whether any member exceeds the slenderness ratio or stress ratio limit, locate the members exceeding the limit, and clarify the control conditions for each member exceeding the limit (such as 60° wind, 225° wind, anchor line installation, etc.).

[0052] Implementation Step 3: Model Validation and Collapse Process Simulation, the specific operations are as follows: 1. Finite element model establishment: Beam elements (B31) are used to simulate the main and auxiliary materials of the tower. Based on the tower structure drawings, a line element analysis model is established in the software. Rigid constraints are set at the bottom of the tower to simulate the fixed supports in actual engineering. According to the load calculation results of the conductor and ground wire, the conductor and ground wire loads are applied to the corresponding hanging points of the tower in the form of concentrated loads. Material properties are defined. The main material Q345B and the auxiliary material Q235B are both adopted with bilinear reinforced constitutive models. The density, elastic modulus, Poisson's ratio, yield strength, ultimate strength and other parameters of the steel are input.

[0053] 2. Model accuracy verification: Modal analysis was performed on the established finite element model to calculate the first six modes and natural frequencies of the tower. The results were compared with the modal analysis results. The error of the natural frequency of the first two modes (X-direction and Y-direction bending) was required to be controlled within 1%, and the error of the higher-order modes was required to be controlled within 10%, thus verifying the accuracy of the model.

[0054] 3. Selection of the most unfavorable working condition: Based on the results of the analysis of the tower members exceeding the limit, the working condition with the most severe stress ratio exceeding the limit is selected as the most unfavorable working condition (such as a strong wind condition with a wind direction angle of 60° and the design basic wind speed).

[0055] 4. Constitutive model reduction: Based on the calculated stability coefficient φ of each member, the constitutive model of each member in the finite element model is reduced, and the critical stress of buckling instability of the member is taken as the yield stress of the member to simulate the buckling instability characteristics of the member.

[0056] 5. Load setting: Considering the combined effect of structural self-weight, tower wind load and conductor load, the tower wind load is divided into wind pressure sections, the wind load value of each section is calculated and applied evenly to each node of the main material of the wind pressure section; the conductor load considers the combined effect of self-weight and wind load.

[0057] 6. Collapse process simulation: Using static analysis, loads are applied step by step to simulate the stress process and the entire collapse process of the tower under the most unfavorable working conditions. The stress distribution, displacement changes, and member yielding conditions of the tower at different load stages are recorded to clarify the starting position of the tower instability failure (such as the second main section above the tower leg), the development process (buckling instability of the main member → stress increase of the diagonal member → lateral tilting of the superstructure) and the final failure mode, and to verify the analysis results of the over-limit members.

[0058] Implementation Step 4: Dynamic Response Characteristics Analysis of Transmission Towers 1. Analysis of the pulsating wind effect: 1.1 In accordance with the "Code for Design of Building Structures", the Davenport spectrum is used as the wind power spectrum model to generate a random pulsating wind field. The wind speed at a height of 10m is taken as the basic design wind speed Vm / s, the load duration is T=100s, and the time interval is Δt=0.01s.

[0059] 1.2 Calculate the wind speed time history curves at each wind pressure section of the tower, calculate the corresponding wind load time history curves based on the wind speed time history curves, and apply them to the main material nodes of the tower finite element model; at the same time, apply the structural self-weight and conductor / ground wire loads as static loads to the corresponding positions.

[0060] 1.3 Select typical wind angles (such as 90°) to carry out explicit dynamic analysis, obtain the time history curves of tower top displacement and tower leg column base reaction force (shear force), analyze the wind-induced vibration characteristics of the tower, and statistically analyze the amplification factor of pulsating wind on tower displacement, stress and base shear force, and clarify the influence of pulsating wind effect on the stress performance of the tower.

[0061] 2. Seismic motion effect analysis: Considering the spatial distribution effect of the transmission tower-conductor-ground wire system, the traveling wave effect, partial coherence effect, and local site effect are introduced. Typical seismic waves are selected and amplitude-modulated according to specifications. Multidimensional and multi-point seismic excitation is applied to the finite element model of the tower, and dynamic response analysis is carried out to obtain the stress distribution, displacement change, and member failure of the tower under seismic action. The failure mode and dynamic response law of the tower under seismic action are analyzed, and the influence of seismic motion on the stress performance of the tower is clarified.

[0062] Implementation Step 5: Formulation of Instability Early Warning and Prevention Measures 1. Weaknesses Identification: Based on the results of static analysis, collapse simulation and dynamic response analysis, identify the weak members of the tower (members with excessive slenderness ratio and excessive stress ratio), instability control conditions (most unfavorable wind conditions, installation conditions, etc.), and sensitive points to dynamic loads (areas with significant amplification effects of pulsating wind and areas with strong seismic response).

[0063] 2. Instability early warning measures: Develop instability early warning indicators for weak members and control conditions. For example, when the design basic wind speed is 80%, conduct real-time stress monitoring on members exceeding the limit; issue tower instability risk warnings before extreme weather such as strong winds and earthquakes, and take temporary reinforcement measures.

[0064] 3. Structural optimization scheme: For members with excessive slenderness ratio, shorten the effective length of the member and reduce the slenderness ratio by adding intermediate supports and changing support conditions; for members with excessive stress ratio, optimize the member specifications (increase the cross-sectional size) and adjust the structural form to improve the load-bearing capacity of the member.

[0065] 4. Operation, maintenance and emergency response plan: Identify key inspection areas of the tower (segments containing oversized members) and develop regular inspection and testing plans; develop emergency response plans for tower collapse accidents, clarify emergency response procedures, repair measures and line restoration plans, and improve emergency response capabilities.

[0066] Implementation Notes: During the implementation of this invention, the model establishment of professional verification software and finite element analysis software must be strictly based on the actual structural parameters of the tower to ensure that the model is consistent with the actual structure.

[0067] During modal analysis, it is necessary to ensure that the calculation boundary conditions and material parameters of the finite element model are consistent with those of the professional verification software to improve the accuracy of model verification.

[0068] In the collapse simulation, the reduction of the constitutive model of the members must be strictly based on the stability coefficient of the members to ensure that the simulation results can truly reflect the buckling instability characteristics of the tower.

[0069] In dynamic response analysis, the generation of pulsating wind fields and the selection of seismic waves must comply with relevant national standards to ensure the rationality and accuracy of dynamic loads.

[0070] The stress performance analysis and instability early warning method for power transmission towers of the present invention can be widely applied to stress performance analysis, design optimization, operation and maintenance and instability early warning of various types of power transmission towers of 35kV and above. It has the characteristics of simple operation, accurate calculation and comprehensive analysis, and can effectively improve the structural safety of power transmission towers and the operational reliability of power transmission lines.

[0071] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for analyzing the stress performance and predicting instability of power transmission towers, characterized in that, Includes the following steps: S1. Collect the structural parameters and mechanical performance indicators of the transmission tower to be analyzed; S2. Based on professional tower verification software, perform full-condition static verification and modal analysis on transmission towers, locate over-limit members and their control conditions, and obtain tower vibration modes and natural frequencies. S3. Establish an analysis model of the iron tower in the finite element analysis software. Verify the accuracy of the model using the mode shape and natural frequency obtained in S2. After reducing the constitutive parameters based on the stability coefficient of each member, conduct a collapse simulation for the most unfavorable working condition determined in S2 to determine the starting position and development process of the iron tower instability failure. S4. Based on the finite element model verified in S3, dynamic response analysis was performed by applying pulsating wind load and seismic load respectively to obtain the amplification effect of dynamic load on the tower stress. S5. Based on the over-limit member positioning results of S2 and the instability failure law of S3, determine the weak parts of the structure, and use the dynamic load amplification effect of S4 to determine the dynamic sensitive parts. Output instability early warning information based on the correspondence between the weak parts of the structure and the dynamic sensitive parts.

2. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, S1 includes: The structural form, height, span, conductor and ground wire type, hanging point height, and basic design wind speed of the transmission tower are collected as structural parameters. The steel grade, density, elastic modulus, Poisson's ratio, yield strength, and ultimate strength of the main and auxiliary materials of the tower are collected as mechanical performance indicators.

3. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, The static verification under all working conditions in S2 includes: A multi-condition verification system covering strong winds, icing, line breakage, installation, and anchoring is constructed. The stress calculation of all members of the tower under each condition is performed, and the slenderness ratio and stress ratio of each member are statistically analyzed. Members with slenderness ratios exceeding the allowable slenderness ratio and stress ratios exceeding the allowable stress ratio are marked as over-limit members. The maximum stress ratio condition corresponding to each over-limit member is recorded as its control condition.

4. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, The modal analysis in S2 includes: The transmission tower's first few vibration modes and corresponding natural frequencies are calculated using professional tower verification software. These vibration modes include bending modes along the horizontal line direction, bending modes along the vertical line direction, and torsional modes.

5. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, The tower analysis model established in S3 includes: In finite element analysis software, beam elements are used to simulate the main and auxiliary materials of the iron tower to establish a linear element analysis model. Rigid connection constraints are set at the bottom, and the conductor load is applied to the hanging point as a concentrated load. Using the first few modes and natural frequencies obtained from S2 as a reference, when the mode natural frequencies of the finite element model and the results of the professional verification software meet the following verification conditions: the relative deviation of the natural frequencies of the first two bending modes does not exceed the frequency verification threshold; the relative deviation of the natural frequencies of higher-order modes does not exceed the higher-order frequency verification threshold, the model verification is confirmed to be successful.

6. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 5, characterized in that, The constitutive parameters in S3, which are reduced based on the stability coefficients of each member, include: Based on the stability coefficient φ of each member obtained from the S2 static verification, the buckling critical stress of each member is calculated. The buckling critical stress is used to replace the yield strength in the original constitutive parameters of the member as the reduced yield stress, so that each member in the finite element model enters the yield state when the stress reaches the buckling critical stress.

7. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 6, characterized in that, The collapse process simulation in S3 includes: The structural self-weight, tower wind load divided by wind pressure section, and conductor and ground wire load are combined and applied to the reduced finite element model. The static analysis method is used to gradually apply the load, record the stress distribution of the members, nodal displacement, and member yield sequence at each load stage, and determine the starting member position of the tower instability failure, the development process of instability from the starting member to the adjacent members, and the final failure mode.

8. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, The dynamic response analysis of the pulsating wind load in S4 includes: Based on the Davenport spectrum, a random pulsating wind field is generated. The wind speed time history curves and corresponding wind load time history curves of each wind pressure section of the tower are calculated. The wind load time history is applied to the main material nodes of the verified finite element model to perform explicit dynamic analysis. The tower top displacement time history and tower leg base shear time history are obtained to determine the amplification factor of pulsating wind on tower displacement, member stress and base shear.

9. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, The dynamic response analysis of seismic load in S4 includes: applying multi-dimensional, multi-point seismic excitation considering traveling wave effect, partial coherence effect and local site effect to the finite element model of the tower, performing dynamic response analysis, and obtaining the stress distribution of the tower members, the change of node displacement and the failure of the members under seismic action.

10. The method for analyzing the stress performance and predicting instability of a power transmission tower according to claim 1, characterized in that, S5 includes: comparing the location of the over-limit member with the location of the member that initiates instability and failure determined by the collapse simulation; when the two locations are consistent, the member is marked as the primary warning location among the weak parts of the structure; the member segments with the amplification factor of the pulsating wind exceeding the amplification factor threshold and the member segments that fail in the seismic response are marked as dynamic sensitive locations; the instability control condition is determined based on the overlap between the primary warning location and the dynamic sensitive location; and the instability warning information including the warning location, the control condition, and the sensitive location is output.

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