Bridge guardrail multifunctional operation platform safety evaluation method and system based on finite elements

Abstract

The application provides a bridge guardrail multifunctional operation platform safety evaluation method and system based on finite elements, relates to the technical field of safety evaluation methods, and comprises the following steps: constructing a three-dimensional finite element model of a bridge guardrail target platform to obtain wind load data of grid nodes of each three-dimensional finite element model; calculating temperature field distribution data of the whole structure in a preset evaluation time period to extract equivalent stress time histories of key regions; correcting stress amplitudes by adopting a Goodman average stress correction method; calculating total cumulative fatigue damage degrees of the key regions in the preset evaluation time period by adopting a Miner linear cumulative damage method; calculating dynamic safety margin indexes of the three-dimensional finite element model, and grading and evaluating the dynamic safety margin indexes. The wind pressure coefficient is calculated through a fluid domain and is mapped to the finite element model, so that the stress and temperature distribution of the structure in an actual environment can be truly simulated, and the evaluation result is closer to the engineering practice.

Description

Technical Field

[0001] This invention relates to the field of safety assessment methods, specifically to a safety assessment method and system for a multi-functional working platform for bridge railings based on the finite element method. Background Technology

[0002] The multi-functional working platform for bridge railings is an important auxiliary facility suspended on the outside of bridge railings for bridge inspection, maintenance, and cleaning operations. During service, the platform simultaneously bears various complex loads, including wind loads, temperature loads, its own weight, and operational live loads. Among these, wind loads exhibit significant spatiotemporal variability, temperature loads cause uneven thermal stress distribution in the structure, and cyclic loads lead to fatigue accumulation damage at critical connection points. Traditional safety assessments often employ static design verification methods, simplifying wind loads to uniformly distributed static pressure, which fails to reflect the actual pressure distribution characteristics generated by wind flow around the platform components, resulting in inaccurate wind load application. Most assessment methods only consider the single effect of wind loads or temperature loads, neglecting the synergistic effect of structural stress under the coupling of wind and thermal multi-physics fields.

[0003] In the prior art, document CN112417728A proposes a method to form an automated, reasonable, and reliable operational safety assessment calculation and analysis process through an automated module, using optimization algorithms to generate an operational safety assessment and analysis result database that can cover more parameter combinations, and connecting the platform client and the shore-based computing center through an information transmission system to form a complete operational safety assessment system. However, this scheme still uses a relatively simplified equivalent static method for wind load processing and fails to achieve non-uniform, dynamic, and accurate mapping of the wind pressure coefficient on the structural surface through CFD fluid dynamics analysis. In terms of temperature field analysis, it does not consider solar radiation, long-wave radiation, and the windward and sunward sides. The comprehensive impact of differentiated convective heat transfer neglects the synergistic effect of wind-thermal multi-physics coupling on structural stress. In terms of fatigue assessment, it lacks a refined calculation process based on actual stress time history data, including rainflow counting, Goodman correction, and Miner linear cumulative damage. Furthermore, although this scheme achieves operational safety assessment through database pre-setting and remote calculation, it fails to construct a digital twin model and integrate real-time monitoring data such as ultrasonic thickness measurement. It cannot dynamically update the remaining bearing capacity of the structure and calculate the real-time safety margin index, thus making it difficult to achieve dynamic graded early warning of the structural safety status throughout its entire life cycle. Therefore, there is an urgent need for a safety assessment method and system for a multi-functional operating platform for bridge railings based on the finite element method.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a safety assessment method and system for a multi-functional working platform for bridge guardrails based on the finite element method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: S1: Construct a three-dimensional finite element model of the target bridge guardrail multi-functional operation platform and complete the mesh generation. Perform fluid dynamics analysis on the three-dimensional finite element model to construct the corresponding fluid domain. Calculate the wind pressure coefficient of each node in the fluid domain within the preset evaluation time period. Map the wind pressure coefficient to the mesh nodes of the three-dimensional finite element model and solve for the wind load data of each mesh node. S2: Apply convective heat transfer boundary conditions to the three-dimensional finite element model, calculate the temperature field distribution data at each moment within the preset evaluation time period, perform transient structural analysis on the temperature field distribution data and wind load data, and extract the equivalent stress time history of the key areas of the model. S3: Decompose the equivalent stress time history of the key area to obtain stress cycles. After correcting the stress amplitude of the stress cycles by average stress, calculate the total cumulative fatigue damage of the key area within the preset evaluation time period. S4: Construct digital twin models of key areas, obtain corresponding real-time load data based on the digital twin models and obtain the maximum equivalent stress value of key areas, calculate the remaining bearing capacity of each key area in combination with the total cumulative fatigue damage; calculate the dynamic safety margin index of the entire three-dimensional finite element model based on the remaining bearing capacity and the maximum equivalent stress value, and complete the safety status classification assessment of the target platform based on the dynamic safety margin index.

[0007] Furthermore, a three-dimensional finite element model of the target platform is constructed, specifically as follows: Based on the engineering drawings, a three-dimensional solid model of all load-bearing components, including main beams, columns, cross braces, platform plates, and connecting plates, is constructed at a 1:1 scale. The geometric dimensions of each load-bearing component are defined as the input parameters of the three-dimensional solid model to form a parametric model. The elastic modulus, Poisson's ratio, density, and yield strength of the material of each load-bearing component are used as the mechanical properties of the parametric model to construct a three-dimensional finite element model of the platform. Mesh the completed 3D solid model: Use the mesh generation module in the finite element software to divide all load-bearing components into discrete mesh elements of tetrahedral solid elements, automatically generating a continuous mesh layout. The connection points between all mesh elements in this mesh layout are the mesh nodes.

[0008] Furthermore, wind load data for each grid node is obtained, specifically: Set the preset evaluation time period as ,in Indicates the start time of the evaluation. Indicates the end time of the assessment; This represents the index of the evaluation time within the preset evaluation time period, satisfying... ; First, the surface of the fluid domain is meshed: the three-dimensional finite element model is imported into the CFD software, and a cuboid fluid domain is created around the three-dimensional finite element model. The distance from the inlet of the fluid domain to the front edge of the three-dimensional finite element model structure is set to 5 times the structure width, and the distance from the outlet of the fluid domain to the rear edge of the three-dimensional finite element model structure is set to 10 times the structure width. The height and width of the domain are both 5 times the maximum three-dimensional finite element model structure size. The maximum three-dimensional finite element model structure size is defined as the maximum geometric span of the three-dimensional finite element model in the X, Y, and Z directions. The surface of the fluid domain is divided into fluid meshes to generate a fluid domain mesh on the surface of the fluid domain, and discrete points on the fluid domain mesh are marked as fluid nodes; The following formula is used to calculate the fluid nodes on the surface of the fluid domain at the evaluation time. Wind pressure coefficient: in, Indicates the first Each fluid node at the evaluation time The wind pressure coefficient; Indicates the first Each fluid node at the evaluation time The absolute value of the fluid pressure was obtained from CFD simulation; Indicates the static pressure reference value; Indicates air density; Indicates reference wind speed; Indicates the fluid node index; The wind pressure coefficient of each fluid node is dynamically mapped to the mesh nodes of the three-dimensional finite element model using the radial basis function interpolation method. Then, the wind load data of each mesh node of the three-dimensional finite element model is obtained according to the following formula: in, in, Indicates the first The coordinates of each fluid node; Indicates the first The coordinates of each grid node, Indicates the index of a mesh node in a three-dimensional finite element model; Indicates the first Each grid node at the evaluation time Wind load data; Represents radial basis functions; Indicates the first Each grid node at the evaluation time The wind pressure coefficient; Indicates the first The weight coefficients of each fluid node are solved by the LU decomposition method; This indicates the total number of fluid nodes.

[0009] Furthermore, the temperature field distribution data of the entire three-dimensional finite element model within the preset evaluation time period are calculated, specifically as follows: A convective heat transfer boundary condition is applied to the three-dimensional finite element model. Finite element software is then used to solve for the temperature field distribution data of the entire three-dimensional finite element model at any time within a preset evaluation period. Specifically, the convective heat transfer boundary condition is as follows: Select all external surfaces of the 3D finite element model, set the ambient air temperature to the ambient fluid temperature of the external surfaces, and divide the external surfaces into windward and sunward sides. For the windward side, determine the ambient wind speed... The convective heat transfer coefficient is defined according to the following formula: This represents the convective heat transfer coefficient of the windward side; For the sunny side, Take 0.3 times the ambient wind speed, that is: This represents the convective heat transfer coefficient on the sun-facing side; The initial temperature of the three-dimensional finite element model is set at the start of a preset evaluation period. Based on the actual materials of each load-bearing component of the target platform, the thermal conductivity and specific heat capacity of each component are defined. A heat flux density varying with time is applied to the sun-facing surface directly exposed to sunlight during the preset evaluation period. in, Indicates the evaluation time The total solar radiation intensity was obtained from the local meteorological database; Indicates the evaluation time The shadow coefficient is automatically output by CFD software using a solar radiation model; Indicates the sunny side at the time of assessment Solar radiation heat flux density; Indicates the surface solar radiation absorptivity; The surface emissivity of the outer surface material of the three-dimensional finite element model was measured using an emissivity meter, while a long-wave radiation heat transfer boundary condition was applied to the outer surface. The calculation formula used is as follows: in, The emissivity of the outer surface of the three-dimensional finite element model; This represents the Stefan-Boltzmann constant; The equivalent radiation temperature of the sky; The outer surface temperature of the three-dimensional finite element model; This represents the relationship between the outer surface of the three-dimensional finite element model and the sky at the evaluation time. Long-wave radiation heat transfer.

[0010] Furthermore, the equivalent stress time history of key regions is extracted, specifically: The method for calibrating the key area is as follows: apply standard loads under standard working conditions to the three-dimensional finite element model and perform static analysis to calculate the static equivalent stress distribution of the three-dimensional finite element model; mark the area formed by mesh nodes whose static equivalent stress value is greater than 30% of the material yield strength as the high stress area; All mesh nodes in the high-stress zone are sorted from largest to smallest according to their static equivalent stress values, and the connected regions containing the top 5% of the sorted mesh nodes are selected as the first type of critical region. Geometric discontinuities are marked as the second type of critical areas. These discontinuities include welded joints between the main beam and the column, welds where the cross brace meets the platform plate, and areas where the platform plate cross section changes abruptly or where there are openings. The union of the first type of critical region and the second type of critical region is identified as the final critical region; Transient structural analysis was performed on temperature field distribution data and wind load data to extract the equivalent stress time history of key regions. Time synchronization processing was performed on the wind load data and temperature field distribution data. If the time points of the two types of data did not overlap, linear interpolation was used to unify them to the same time point. The wind load data from the 3D finite element model was used as the boundary condition, and the temperature field distribution data was imported as the temperature load. The thermal expansion coefficient of the material was defined, and the time step was set in the finite element software, with its time axis aligned with the time points of the temperature field distribution data and wind load data. The total stress tensor of each mesh node was calculated. The total stress tensor of each mesh node was processed using finite element software, and the curves of the von Mises equivalent stress of all mesh nodes as a function of time were output. The curve corresponding to the maximum value of the von Mises equivalent stress of each mesh node was taken as the equivalent stress time history of the key region.

[0011] Furthermore, the equivalent fully reversible stress amplitude is obtained, specifically: The equivalent stress time history is decomposed using the rainflow counting method to obtain stress cycles, and the stress amplitude and average stress of each stress cycle are output: The equivalent stress time history is preprocessed by traversing the entire equivalent stress time history, retaining all peaks and troughs, and deleting all points in monotonically increasing or decreasing processes, resulting in a sequence of extreme points consisting of alternating peaks and troughs. Then, using three adjacent extreme points as an analysis window, if the stress range formed by the middle extreme point within the window relative to the two extreme points on the left and right is contained by the stress range formed by the two extreme points on the outer side, a complete cycle is extracted, and the middle point is deleted. The stress amplitude of this cycle is half of the von Mises equivalent stress difference of the trough, and the average stress is the average value of the von Mises equivalent stress of the trough. This process is repeated until no more can be extracted. Finally, the remaining extreme point sequences are connected end to end to form the maximum stress cycle. In each stress cycle, if the average stress in the critical region is greater than or equal to the tensile strength of the material, static failure has occurred, and the critical region is deemed to have failed. If the average stress in the critical region is less than the tensile strength of the material, the stress amplitude is corrected using the Goodman average stress correction method to obtain an equivalent fully reversible stress amplitude. in, Indicates the first The equivalent completely reversed stress amplitude of one stress cycle; Indicates the first Stress amplitude of one stress cycle; Indicates the first Average stress over one stress cycle; Indicates the tensile strength of the material; Indicates the index of the stress cycle.

[0012] Furthermore, the total cumulative fatigue damage in the key area during the preset evaluation period is calculated, specifically as follows: Based on the complete reversal stress amplitude, the Miner linear cumulative damage method is used to calculate the total cumulative fatigue damage in the critical area over the preset evaluation time period: in, Indicates the first The total number of stress cycles within a day; Indicates the critical area to the assessment time. Total cumulative fatigue damage; Indicates the first Tianzhongdi The equivalent completely reversed stress amplitude of one stress cycle; Indicates a day index; This indicates the time from the start of the preset evaluation period to the evaluation time. Total number of days experienced It is an integer; Indicates the stress amplitude at complete reversal The number of cycles required to run until fatigue failure is obtained from the SN curve of the material.

[0013] Furthermore, the dynamic safety margin index of the three-dimensional finite element model is calculated as follows: Constructing a digital twin model of the key area: Extracting the range of a local sub-model containing the key area from the 3D finite element model, and converting the element type of the local sub-model, that is, converting the main beams, columns, and cross braces into beam elements, and the platform plate and connecting plate into shell elements. During the conversion process, the cross-sectional shape and size of the beam elements, the thickness of the shell elements, and the connection relationship between the load-bearing components are preserved, and the elastic modulus, Poisson's ratio, density, and yield strength of the load-bearing components in the key area are fully mapped to the corresponding beam elements and shell elements. Based on the digital twin model, the key area is further subdivided into multiple key parts, namely... Extract the static equivalent stress values ​​of all mesh nodes within the critical region, sort them from largest to smallest, and select the locations corresponding to the top 10% of mesh nodes as critical parts. Simultaneously, geometric discontinuities, including welded connections between the main beam and column, welds at the junction of the cross brace and platform plate, and areas where the platform plate cross-section undergoes abrupt changes or has opening edges, are also considered critical parts. The locations of these two types of critical parts are merged and deduplicated to form the final set of critical parts, denoted as […]. , Indexes representing key parts; Indicates the total number of key parts; Simultaneously, real-time load data for the key area is obtained, and further, the maximum equivalent stress value for the key area is obtained, specifically: Real-time data on wind speed, ambient temperature, and structural strain in key areas are collected. After time-synchronized preprocessing, the effective load parameters at the current moment are extracted. These parameters are then input into the digital twin model for forward solving to calculate the von Mises equivalent stress of all beam and shell elements in the key area. The maximum von Mises equivalent stress value among all beam and shell elements is taken as the value of the key area at the evaluation time. The maximum equivalent stress value is denoted as ; Based on ultrasonic thickness measurement data, calculate the thickness loss rate of the key area section: in, Indicates the critical region section at the evaluation time. Thickness loss rate; Indicates the first Initial thickness of the sheet metal in key components; Indicates the time of evaluation The thickness was monitored by ultrasonic thickness measurement. Current thickness of key components; Calculate the remaining bearing capacity based on the total cumulative fatigue damage: in, Indicates the key area at the time of assessment The remaining bearing capacity; Indicates the initial bearing capacity of the critical area; Calculate the dynamic safety margin index based on the remaining bearing capacity and maximum equivalent stress value of the key area: in, Indicates the key area at the time of assessment The maximum equivalent stress value; Indicates the evaluation time The dynamic safety margin index.

[0014] Furthermore, the dynamic safety margin index is assessed in a tiered manner, specifically as follows: When the dynamic safety margin index is greater than the upper limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a safe state; when the dynamic safety margin index is not greater than the lower limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a dangerous state and an alarm is issued; when the dynamic safety margin index is greater than the lower limit of the preset threshold but not greater than the upper limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a state to be monitored. At this time, the evaluation time interval is shortened, and if the dynamic safety margin index shows a downward trend for three consecutive evaluations, it is upgraded to a dangerous state and an alarm is issued.

[0015] The present invention also provides a safety assessment system for a multi-functional bridge railing work platform based on the finite element method. This system is used to perform the aforementioned safety assessment method for a multi-functional bridge railing work platform based on the finite element method, and includes: Data acquisition module: used to construct a three-dimensional finite element model of the target bridge guardrail multi-functional operation platform and complete the mesh generation, perform fluid dynamics analysis on the three-dimensional finite element model to construct the corresponding fluid domain, calculate the wind pressure coefficient of each node in the fluid domain within the preset evaluation time period, map the wind pressure coefficient to the mesh nodes of the three-dimensional finite element model, and solve for the wind load data of each mesh node. Data calculation module: used to apply convective heat transfer boundary conditions to the three-dimensional finite element model, calculate the temperature field distribution data at each time within the preset evaluation time period, perform transient structural analysis on the temperature field distribution data and wind load data, and extract the equivalent stress time history of key areas of the model; Correction module: used to decompose the equivalent stress time history of the key area to obtain stress cycles, and after correcting the stress amplitude of the stress cycles by average stress, calculate the total cumulative fatigue damage of the key area within the preset evaluation time period. The overall assessment module is used to construct digital twin models of key areas, obtain corresponding real-time load data based on the digital twin models and obtain the maximum equivalent stress value of the key areas, and calculate the remaining bearing capacity of each key area in combination with the total cumulative fatigue damage. Based on the remaining bearing capacity and the maximum equivalent stress value, the dynamic safety margin index of the entire three-dimensional finite element model is calculated, and the safety status classification assessment of the target platform is completed based on the dynamic safety margin index.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes CFD fluid dynamics analysis and radial basis function interpolation technology to accurately map the wind pressure coefficient of the fluid domain grid nodes to each grid node of the finite element model, achieving non-uniform and dynamically accurate application of wind loads on the structural surface, significantly improving the accuracy of wind load calculation. Simultaneously applying wind loads and convective heat transfer boundary conditions, and obtaining the equivalent stress time history under wind-heat coupling through transient structural analysis, overcomes the deficiency of existing technologies that neglect multi-physics synergistic effects. Based on this, using the rainflow counting method combined with Goodman correction and Miner's linear cumulative damage theory, fatigue cumulative damage assessment is performed based on real stress time history data, greatly improving the reliability of fatigue life prediction. By constructing a digital twin model and integrating real-time monitoring data such as ultrasonic thickness measurement, the remaining bearing capacity can be dynamically updated and the dynamic safety margin index can be calculated, achieving a leap from periodic checkups to real-time health monitoring of the work platform. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall method flow of the present invention; Figure 2 This is a graph showing the relationship between the total cumulative fatigue damage and the remaining bearing capacity of the corresponding critical area. Figure 3 This is a schematic diagram of the overall system structure of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0019] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] Example: Please see Figures 1-2 The present invention provides a technical solution: The safety assessment method for a multi-functional work platform for bridge guardrails based on the finite element method includes the following steps: S1: Construct a three-dimensional finite element model of the target bridge guardrail multi-functional operation platform and complete the mesh generation. Perform fluid dynamics analysis on the three-dimensional finite element model to construct the corresponding fluid domain. Calculate the wind pressure coefficient of each node in the fluid domain within the preset evaluation time period. Map the wind pressure coefficient to the mesh nodes of the three-dimensional finite element model and solve for the wind load data of each mesh node. The three-dimensional finite element model of the target platform is constructed as follows: Based on the engineering drawings, a three-dimensional solid model of all load-bearing components, including main beams, columns, cross braces, platform plates, and connecting plates, is constructed at a 1:1 scale. The geometric dimensions of each load-bearing component are defined as the input parameters of the three-dimensional solid model to form a parametric model. The elastic modulus, Poisson's ratio, density, and yield strength of the material of each load-bearing component are used as the mechanical properties of the parametric model to construct a three-dimensional finite element model of the platform. Mesh the completed 3D solid model: Use the mesh generation module in the finite element software to divide all load-bearing components into discrete mesh elements of tetrahedral solid elements, automatically generating a continuous mesh layout. The connection points between all mesh elements in this mesh layout are the mesh nodes.

[0021] In the above process, by constructing three-dimensional solid models of all load-bearing components, including main beams, columns, cross braces, platform plates, and connecting plates, at a 1:1 scale based on engineering drawings, complete geometric consistency between the simulation model and the actual structure was ensured. The geometric dimensions of each load-bearing component were defined as input parameters of the three-dimensional solid model, forming a parametric model. This allows the entire three-dimensional finite element model to be quickly updated simply by modifying the corresponding parameters when the dimensions of a component of the work platform change, without the need for remodeling. This significantly improves model reusability and design iteration efficiency. The elastic modulus, Poisson's ratio, density, and yield strength of the materials of each load-bearing component were used as mechanical properties of the parametric model, ensuring the physical authenticity and calculation accuracy of structural stiffness, mass distribution, and strength verification in subsequent finite element analyses. Based on this, all load-bearing components are divided into discrete mesh elements using tetrahedral solid elements, which can automatically adapt to complex geometries such as the intersection of the main beam and connecting plate, and the weld transition zone, without the need for manual geometric subdivision or simplification, thus significantly reducing the preprocessing workload of mesh generation. Tetrahedral solid elements have good geometric flexibility, which can naturally densify the mesh in critical areas with large stress gradients, while maintaining a relatively sparse mesh layout in areas with gentle stress changes, thus achieving a balance between computational accuracy and computational efficiency.

[0022] Obtain wind load data for each grid node, specifically as follows: Set the preset evaluation time period as ,in Indicates the start time of the evaluation. Indicates the end time of the assessment; This represents the index of the evaluation time within the preset evaluation time period, satisfying... ; First, the surface of the fluid domain is meshed: the three-dimensional finite element model is imported into the CFD software, and a cuboid fluid domain is created around the three-dimensional finite element model. The distance from the inlet of the fluid domain to the front edge of the three-dimensional finite element model structure is set to 5 times the structure width, and the distance from the outlet of the fluid domain to the rear edge of the three-dimensional finite element model structure is set to 10 times the structure width. The height and width of the domain are both 5 times the maximum three-dimensional finite element model structure size. The maximum three-dimensional finite element model structure size is defined as the maximum geometric span of the three-dimensional finite element model in the X, Y, and Z directions. In the above process, setting the distance from the fluid domain inlet to the leading edge of the structure to 5 times the structure width, the distance from the outlet to the trailing edge of the structure to 10 times the structure width, and both the domain height and width to 5 times the maximum structure size are to achieve a balance between computational accuracy and computational resources. Too close an inlet distance would cause non-physical disturbances to the structure before the incoming flow boundary layer has fully developed, while a width of 5 times ensures that the airflow has formed a stable velocity profile before reaching the structure. Too short an outlet distance would artificially truncate the downstream wake, causing distortion of the recirculation zone and errors in pressure calculations, while a width of 10 times allows the wake to fully develop and return to the incoming flow conditions. Setting the domain height and width to 5 times the maximum structure size effectively eliminates the blocking effect of the wall on the flow field's shape, avoiding artificial acceleration of the airflow and changes in pressure distribution due to the computational domain boundary being close to the structure.

[0023] The surface of the fluid domain is divided into fluid meshes to generate a fluid domain mesh on the surface of the fluid domain, and discrete points on the fluid domain mesh are marked as fluid nodes; In the above process, when dividing the fluid domain surface into fluid meshes, five prism-layer boundary layer meshes are first generated at the structural wall to accurately capture the drastic changes in velocity and pressure gradients near the wall. The height of the prism layer increases in a geometric progression, and the height of the first layer is usually calculated based on the wall y+ value requirement, typically y+≈30~300. The core region far from the wall is filled with tetrahedral or hexahedral unstructured meshes.

[0024] The following formula is used to calculate the fluid nodes on the surface of the fluid domain at the evaluation time. Wind pressure coefficient: in, Indicates the first Each fluid node at the evaluation time The wind pressure coefficient; Indicates the first Each fluid node at the evaluation time The absolute value of the fluid pressure was obtained from CFD simulation; Indicates the static pressure reference value; Indicates air density; Indicates reference wind speed; Indicates the fluid node index; In the above process, static pressure reference value The far-field static pressure at the inlet boundary of the fluid domain, undisturbed by structural forces, is typically determined based on a standard ambient atmospheric pressure value, such as 101325 Pa, with reference to wind speed. The reference height for the structure at the inlet of the fluid domain is usually taken as the average wind speed at the top of the platform or the centroid of the windward side. Its value can be determined based on the basic wind speed of the return period in the meteorological statistics of the bridge location or converted according to the wind speed profile formula at different heights in the "Code for Wind Resistance Design of Highway Bridges". In actual engineering applications, the reference wind speed can also be directly taken as the average value of the measured wind speed data within the preset evaluation period or the design reference wind speed.

[0025] Dependent variable Indicates the first Each fluid node at the evaluation time The wind pressure coefficient has the following technical effect: the wind pressure coefficient is a dimensionless parameter that characterizes the ratio of the actual wind pressure at the fluid node to the incoming flow pressure. It can eliminate the influence of wind speed and air density changes on the absolute value of pressure, making the wind pressure distribution law of the same structure under different wind speed conditions comparable, and providing a normalized data basis for mapping the fluid domain calculation results to the finite element model. Dependent variable With independent variable , , , This is relevant because the physical essence of the wind pressure coefficient is the difference between the gauge pressure (absolute pressure) at the fluid node and the static pressure reference value, and the incoming flow pressure. The ratio of, where This reflects the absolute pressure level calculated from the flow field at that node. It provides a static pressure reference for undisturbed airflow in the far field. and These four independent variables together determine the magnitude of the dynamic pressure of the incoming flow, and together they determine the value of the dimensionless wind pressure coefficient at this node. when Increase or When decreasing, The wind pressure coefficient tends to increase as the absolute pressure at the fluid node increases or the ambient static pressure decreases. Increase or When the denominator increases, Increase The wind pressure coefficient shows a decreasing trend, meaning that the higher the air density or the greater the reference wind speed, the smaller the wind pressure coefficient becomes under the same pressure difference, reflecting the normalization characteristic of the wind pressure coefficient as a dimensionless parameter.

[0026] The wind pressure coefficient of each fluid node is dynamically mapped to the mesh nodes of the three-dimensional finite element model using the radial basis function interpolation method. Then, the wind load data of each mesh node of the three-dimensional finite element model is obtained according to the following formula: in, in, Indicates the first The coordinates of each fluid node; Indicates the first The coordinates of each grid node, Indicates the index of a mesh node in a three-dimensional finite element model; Indicates the first Each grid node at the evaluation time Wind load data; Represents radial basis functions; Indicates the first Each grid node at the evaluation time The wind pressure coefficient; Indicates the first The weight coefficients of each fluid node are solved by the LU decomposition method; This indicates the total number of fluid nodes.

[0027] In the above process, the dependent variable Indicates the first Each grid node at the evaluation time The wind load data has the following technical effect: by using radial basis function interpolation, the wind pressure coefficient on the fluid domain node is converted into the direct load value on the finite element mesh node, realizing high-precision cross-mesh data transfer from the fluid domain mesh to the structural mesh, and providing accurate mechanical boundary conditions applied to each mesh node for subsequent transient structural analysis. Dependent variable With independent variable , , Directly related, among which It itself also through Weighting coefficients of each fluid node Radial basis functions Fluid node coordinates and grid node coordinates This is relevant because the wind pressure coefficient at the fluid node needs to be weighted and summed using radial basis functions with distance as the variable in order to interpolate the wind pressure coefficient at any grid node location. The weighting coefficients... The physical meaning of this is determined by solving the linear equations using the LU decomposition method; it is the degree of contribution of each fluid node to the wind pressure coefficient of the target grid node. When air density Increase or refer to wind speed When it increases, The trend is increasing, meaning that the higher the air density or the greater the wind speed, the greater the wind load applied to the grid nodes; when the interpolated wind pressure coefficient... When it increases, The two also show an increasing trend, and are positively correlated; during radial basis function interpolation, when the grid node coordinates With fluid node coordinates distance As it increases, the radial basis function value The influence typically decreases, which reduces the contribution of the fluid node to the wind pressure coefficient of the target grid node, reflecting the spatial correlation characteristic that the influence weakens with increasing distance. The process of dynamically mapping the wind pressure coefficient of each fluid node to the mesh nodes of the three-dimensional finite element model using the radial basis function interpolation method is as follows: First, using the coordinates of all fluid nodes... As the center points of the radial basis functions, construct a matrix containing the radial basis functions. It reflects the spatial distance relationship between fluid nodes and the polynomial enhancement matrix. its first Behavior A system of linear equations; in, Represent a A symmetric matrix whose elements Indicates the first The grid node and the first Radial basis function values ​​between fluid nodes; Represent a The matrix whose first... Behavior That is, the first column is a constant 1, and the subsequent columns are the values ​​of the first, second, third, and fourth columns respectively. fluid nodes Coordinate components; Represents a length of A column vector whose elements are , indicating the first The weighting coefficients corresponding to each fluid node; Let represent a column vector of length 4, whose elements are Lagrange multipliers, used as auxiliary unknowns and... Solve simultaneously; Represents a length of A known column vector, whose elements are This indicates that all fluid nodes are at the evaluation time. Wind pressure coefficient calculated by CFD; This represents the total number of fluid nodes on the surface of the fluid domain; The system of equations is solved using the LU decomposition method to obtain the weighting coefficients for each fluid node. and Lagrange multiplier vectors Finally, for any mesh node coordinate in the three-dimensional finite element model... According to the formula Calculate the interpolated wind pressure coefficient at this grid node, where the radial basis function... Using the distance between the grid node and each fluid node as the independent variable, the weighting coefficients are... This determines the contribution of each fluid node to the wind pressure coefficient of the current mesh node, thereby achieving a continuous, smooth, and accurate spatial mapping of the wind pressure coefficient from the fluid domain mesh to the structural finite element mesh through known data points.

[0028] In the above process, Lagrange multiplier vectors are introduced. To ensure the accuracy of the interpolation polynomial, its value is obtained by solving the matrix equation, which can accurately solve for the weighting coefficient of each fluid node. This system of equations is expressed in matrix form, which represents the spatial relationships between fluid nodes. In The completeness condition of linear polynomials is expressed through and By incorporating a unified solution framework, the interpolation results are ensured to have good smoothness while accurately reconstructing the known wind pressure coefficient vectors at all fluid nodes. This means achieving accurate pass-through of the interpolation function.

[0029] S2: Apply convective heat transfer boundary conditions to the three-dimensional finite element model, calculate the temperature field distribution data at each moment within the preset evaluation time period, perform transient structural analysis on the temperature field distribution data and wind load data, and extract the equivalent stress time history of key regions of the model; calculate the temperature field distribution data of the entire three-dimensional finite element model within the preset evaluation time period, specifically: A convective heat transfer boundary condition is applied to the three-dimensional finite element model. Finite element software is then used to solve for the temperature field distribution data of the entire three-dimensional finite element model at any time within a preset evaluation period. Specifically, the convective heat transfer boundary condition is as follows: Select all external surfaces of the 3D finite element model, set the ambient air temperature to the ambient fluid temperature of the external surfaces, and divide the external surfaces into windward and sunward sides. For the windward side, determine the ambient wind speed... The convective heat transfer coefficient is defined according to the following formula: This represents the convective heat transfer coefficient of the windward side; For the sunny side, Taking 0.3 times the ambient wind speed, the convective heat transfer coefficient is defined according to the following formula: This represents the convective heat transfer coefficient on the sun-facing side; In the above process, the division between the windward and sun-facing sides is a reasonable and fixed division based on the structural characteristics and dominant environmental conditions of the bridge railing multi-functional work platform, rather than a dynamic change over time. The windward side is defined as the outer surface of the bridge railing multi-functional work platform that directly bears the impact of the incoming flow in the prevailing wind direction, usually the prevailing wind direction or the most unfavorable design wind direction in the area where the bridge is located, such as the vertical panel near the outside of the bridge facing the direction of the incoming flow; the sun-facing side is defined as the outer surface that is directly exposed to sunlight under the effect of solar radiation during the day, usually the outer surface of the upper surface of the platform. The reason for this fixed division is that for the work platform suspended on the outside of the bridge railing, its geometry and installation orientation have a clear and fixed orientation. At the same time, based on the conservative principle of safety assessment, the windward side is the surface with the most unfavorable wind direction and the sun-facing side is the surface with the largest cumulative radiation during the day, such as the platform panel, which can cover the most severe wind-heat coupling conditions. about The calculation is based on the following formula: This formula is used to calculate the convective heat transfer coefficient of the windward side; where the constant 5.7 represents the basic heat transfer capacity of air under natural convection conditions. When the ambient wind speed... As the coefficient approaches zero, the airflow no longer scours the surface, and heat exchange is primarily driven by the density difference of the air. At this point, the heat transfer coefficient converges to a lower limit. Based on the summarization of a large amount of experimental data on natural air convection, this lower limit is typically within a certain range. The magnitude of the heat transfer is 5.7, which is a representative constant in this range, reflecting the basic intensity of heat exchange between the surface and the air in a windless environment. The constant 3.8 represents the enhancement effect coefficient of forced convection on heat transfer, quantifying the linear influence of wind speed on heat transfer capacity. The value of 3.8 comes from systematic measured regression analysis of the heat transfer characteristics of flat plates or building exterior surfaces under forced airflow conditions in the field of engineering thermophysics, indicating that for every increase in wind speed... The convective heat transfer coefficient increases linearly. This reflects the physical law that the greater the flow velocity, the more intense the surface heat exchange; for the windward side, since it directly faces the incoming wind direction, the actual wind speed acting on the surface is approximately equal to the ambient wind speed. Therefore, this formula can be used directly to calculate the convective heat transfer coefficient of the windward side; about The calculation is based on the following formula, which is used to calculate the convective heat transfer coefficient of the sun-facing side. The sun-facing side is typically located on the leeward side of the platform or is obstructed by the platform's main beams, columns, or other structural components. The actual airflow velocity reaching this surface is significantly reduced. If the ambient wind speed is used directly... This would significantly overestimate its convective heat transfer intensity; taking the actual wind speed acting on the sun-facing side as 0.3 times the ambient wind speed is an engineering simplification based on wind field flow characteristics and structural shading effects. In wind field studies of bridges and ancillary facilities, the average wind speed on the leeward side or in the shaded area typically decreases to a fraction of the incoming wind speed. The factor of 0.3 is a conservative middle value within this range, reflecting both the weakening effect of shading on airflow speed and not excessively underestimating the convective heat dissipation capacity of the sun-facing side. Therefore, substituting 0.3 times the ambient wind speed into the empirical formula, we get... This ensures that the heat transfer coefficient of the sun-facing side is lower than that of the windward side, thus reasonably reflecting the temperature gradient between the windward and sun-facing sides due to the difference in wind speed in the temperature field calculation, and avoiding the temperature field calculation deviation caused by a uniform heat transfer coefficient.

[0030] By defining different convective heat transfer coefficients for the windward and sun-facing sides, the temperature field calculation deviation caused by applying the same heat transfer coefficient to the entire outer surface in traditional methods is avoided. A higher convective heat transfer coefficient is used for the windward side. It can accurately simulate the physical process of rapid heat loss from the surface under strong wind conditions; the sun-facing side uses a lower convective heat transfer coefficient. This reasonably reflects the characteristics of reduced airflow and weakened heat transfer in the shaded area. The combined effect of these two factors makes the temperature gradient between the windward and sunward sides in the subsequent temperature field distribution data more realistic, thus providing accurate thermal boundary condition input for transient structure analysis. Ultimately, this differentiated heat transfer boundary condition, together with the subsequently applied solar radiation heat flux density and long-wave radiation heat transfer boundary conditions, forms the basis for wind-thermal multiphysics coupling analysis.

[0031] The initial temperature of the three-dimensional finite element model is set at the start of a preset evaluation period. Based on the actual materials of each load-bearing component of the target platform, the thermal conductivity and specific heat capacity of each component are defined. A heat flux density varying with time is applied to the sun-facing surface directly exposed to sunlight during the preset evaluation period. in, Indicates the evaluation time The total solar radiation intensity was obtained from the local meteorological database; Indicates the evaluation time The shadow coefficient is automatically output by CFD software using a solar radiation model; Indicates the sunny side at the time of assessment Solar radiation heat flux density; Indicates the surface solar radiation absorptivity; In the above process, the surface solar radiation absorptivity The value typically ranges from 0 to 1, and its specific value depends on the material's color, surface roughness, and material type. Generally speaking, the darker the color or the rougher the surface of the material, the higher the absorption rate. For example, the absorption rate of black or dark-colored paint can reach over 0.9, while the absorption rate of lighter-colored or metallic materials is lower. For example, the absorption rate of silver paint is about 0.25, and the absorption rate of polished aluminum plates can be as low as 0.12. about The precise determination of the value typically employs a spectrophotometric method: First, samples are taken from the actual structure of the target platform according to the national standard "Spectrophotometer Test Method for Measuring Solar Transmittance and Solar Absorption Ratio of Materials" (GB / T 25968-2010); then, the reflectance of the sample at different wavelengths is measured using a spectrophotometer, and the final solar radiation absorption coefficient is calculated based on a weighted integral of a standard solar spectrum such as ASTM G173. ; Total solar radiation intensity Indicates the evaluation time The total solar radiation reaching the Earth's surface comprises both direct and diffuse radiation, and its value varies with geographical location, date, and time. This parameter is obtained from local meteorological databases, such as commercial solar radiation databases like Solargis. Shadow coefficient Indicates the time of evaluation The solar radiation intensity received by the sun-facing surface of the 3D finite element model is the ratio between the theoretical maximum solar radiation intensity (i.e., the direct radiation assuming no obstruction). Its value ranges from 0 to 1, where 0 represents complete obstruction and 1 represents no obstruction. This parameter is automatically obtained by CFD software using a solar radiation model. Specifically, after activating the solar radiation calculation model in CFD software such as Ansys Fluent or Star-CCM+, the user first needs to define the latitude, longitude, time zone, and specific date range corresponding to the evaluation period of the target platform's geographical location. The software's built-in celestial algorithm automatically calculates the solar altitude angle and azimuth angle based on the date and time. Combining this with the spatial geometric relationships between load-bearing components such as main beams, columns, and cross braces in the 3D finite element model, the software uses ray tracing or discrete coordinate methods to solve for the direct solar radiation on the structural surface and the multiple scattering processes after reflection from the surrounding environment, such as guardrails and the main bridge structure. Finally, in the CFD software output, the shadow flag is first defined as a continuous value representing the proportion of partial occlusion, such as 0.3 indicating that 30% of the area is occluded. For each mesh node on the sunlit side, the software outputs the shadow flag as it changes over time, and this output is used as the shadow coefficient. ; By increasing the surface solar radiation absorption rate Total solar radiation intensity and shading coefficient Multiply, with Applying heat flux density in a time-varying manner can accurately reflect the intensity variation of solar radiation from sunrise to sunset throughout the day, while utilizing... The shading effect of the platform's main beam, columns, cross braces, and other components on different surfaces is captured. The technical effect of this processing method is that it makes the heating process of the sun-facing side in the temperature field distribution data match the actual solar radiation conditions, avoiding the problem of overestimation or underestimation of the temperature field caused by using a constant heat flux density.

[0032] The surface emissivity of the outer surface material of the three-dimensional finite element model was measured using an emissivity meter, while a long-wave radiation heat transfer boundary condition was applied to the outer surface. The calculation formula used is as follows: in, The emissivity of the outer surface of the three-dimensional finite element model; This represents the Stefan-Boltzmann constant; The equivalent radiation temperature of the sky; The outer surface temperature of the three-dimensional finite element model; This represents the relationship between the outer surface of the three-dimensional finite element model and the sky at the evaluation time. Long-wave radiation heat transfer.

[0033] During the above process, the outer surface of the bridge railing multi-functional work platform receives solar radiation heat flux density. In addition to convective heat exchange with the air, heat is also exchanged with the sky through long-wave radiation. This heat load can even become the dominant factor at night or on cloudy days; ignoring it will lead to serious distortion of temperature field distribution data. The surface emissivity of the outer surface material of the three-dimensional finite element model was measured using an emissivity meter. And combined with the Stefan-Boltzmann constant Sky equivalent radiation temperature and the external surface temperature calculated by finite element software ,by Applying long-wave radiation heat transfer boundary conditions in this manner can accurately describe the radiation heat transfer process between the structure surface and the sky based on the fourth-power temperature difference law. This allows the physical process of the outer surface cooling down at night due to long-wave radiation and warming up during the day due to the superposition of long-wave radiation and solar radiation to be fully presented in the temperature field distribution data, in conjunction with the aforementioned solar radiation heat flux density. and convective heat transfer coefficient , Together, they constitute the full thermal load boundary conditions of convection, solar shortwave radiation, and longwave radiation, significantly improving the physical authenticity and computational accuracy of the temperature field distribution data input in transient structural analysis.

[0034] Extracting the equivalent stress time history of key regions, specifically: The method for calibrating the key area is as follows: apply standard loads under standard working conditions to the three-dimensional finite element model and perform static analysis to calculate the static equivalent stress distribution of the three-dimensional finite element model; mark the area formed by mesh nodes whose static equivalent stress value is greater than 30% of the material yield strength as the high stress area; All mesh nodes in the high-stress zone are sorted from largest to smallest according to their static equivalent stress values, and the connected regions containing the top 5% of the sorted mesh nodes are selected as the first type of critical region. Geometric discontinuities are marked as the second type of critical areas. These discontinuities include welded joints between the main beam and the column, welds where the cross brace meets the platform plate, and areas where the platform plate cross section changes abruptly or where there are openings. The union of the first type of critical region and the second type of critical region is identified as the final critical region; In the above process, performing equivalent stress time history extraction and fatigue damage calculation on all mesh nodes of the entire three-dimensional finite element model would result in a massive computational scale, low computational efficiency, and be unnecessary. By first applying standard loads under standard working conditions to the three-dimensional finite element model and performing static analysis to calculate the static equivalent stress distribution, the region formed by mesh nodes whose static equivalent stress value is greater than 30% of the material yield strength is marked as a high-stress zone, which can initially screen out areas with heavy loads. Furthermore, the connected regions containing the top 5% of mesh nodes with static equivalent stress values ​​within the high-stress zone are designated as the first type of critical region, which can focus on the local area with the highest stress and avoid the critical region being too large due to setting the threshold too low. At the same time, geometric discontinuities such as the welded connection points between the main beam and the column, the weld joints at the intersection of the cross brace and the platform plate, and areas where the platform plate cross section changes abruptly or the edges of openings are marked as the second type of critical region. This is because even if the static equivalent stress value does not meet the above 30% threshold, stress concentration and fatigue cracks are likely to occur at geometric discontinuities under cyclic loading, and they cannot be overlooked. Finally, the union of the first and second critical regions was defined as the final critical region, which takes into account both the high-stress-dominated failure mode and the fatigue-sensitive locations caused by geometric discontinuities, thus achieving a balance between computational accuracy and computational efficiency.

[0035] Transient structural analysis was performed on temperature field distribution data and wind load data to extract the equivalent stress time history of key regions: Time synchronization processing was performed on wind load data and temperature field distribution data. If the time points of the two types of data did not coincide, linear interpolation was used to unify them to the same time point. The wind load data of the three-dimensional finite element model was used as the boundary condition, and the temperature field distribution data was imported as the temperature load. The thermal expansion coefficient of the material was defined, and the time step was set in the finite element software with its time axis aligned with the time points of the temperature field distribution data and wind load data. The total stress tensor of each mesh node was calculated, and the total stress tensor of each mesh node was processed using the finite element software to output the von Mises equivalent stress curve of all mesh nodes as a function of time. The curve corresponding to the maximum von Mises equivalent stress of each mesh node was used as the equivalent stress time history of the key region.

[0036] In the above process, the coefficient of thermal expansion of the material can be obtained by consulting authoritative material handbooks or databases, such as mechanical design handbooks, ASME standards, Mitcalc material databases, etc. These handbooks have provided reference values ​​for the coefficient of thermal expansion of commonly used engineering materials that have undergone rigorous testing. Wind load data and temperature field distribution data originate from different physical processes, and their time sampling points are usually inconsistent. Directly performing transient structural analysis would lead to time axis misalignment and the inability to apply boundary conditions synchronously. By synchronizing the two types of data and using linear interpolation to unify them to the same time point when the time points do not overlap, it is ensured that within each calculation time step, the same mesh node of the 3D finite element model simultaneously bears the correct wind load data and temperature load. By applying the wind load data as boundary conditions to the structural surface and importing the temperature field distribution data as temperature load and defining the thermal expansion coefficient of the material, the finite element software can simultaneously calculate mechanical stress (caused by wind load) and thermal stress (caused by temperature gradient). The sum of these two values ​​yields the total stress tensor for each mesh node. Finally, finite element method software was used to output the von Mises equivalent stress curves over time for all mesh nodes. The curve corresponding to the maximum von Mises equivalent stress of each mesh node was taken as the equivalent stress time history of the key region. The technical effect is that the extracted equivalent stress time history reflects the most severe stress state of the key region under the coupling of wind and heat multiphysics fields, which provides a basis for subsequent decomposition, stress cycle calculation, and total cumulative fatigue damage using the rainflow counting method. It provides physically accurate and representative basic data.

[0037] S3: Decompose the equivalent stress time history of the key area to obtain stress cycles. After correcting the stress amplitude of the stress cycles by average stress, calculate the total cumulative fatigue damage of the key area within the preset evaluation time period. The equivalent fully reversible stress amplitude is obtained as follows: The equivalent stress time history is decomposed using the rainflow counting method to obtain stress cycles, and the stress amplitude and average stress of each stress cycle are output: The equivalent stress time history is preprocessed by traversing the entire equivalent stress time history, retaining all peaks and troughs, and deleting all points in monotonically increasing or decreasing processes, resulting in a sequence of extreme points consisting of alternating peaks and troughs. Then, using three adjacent extreme points as an analysis window, if the stress range formed by the middle extreme point within the window relative to the two extreme points on the left and right is contained by the stress range formed by the two extreme points on the outer side, a complete cycle is extracted, and the middle point is deleted. The stress amplitude of this cycle is half of the von Mises equivalent stress difference of the trough, and the average stress is the average value of the von Mises equivalent stress of the trough. This process is repeated until no more can be extracted. Finally, the remaining extreme point sequences are connected end to end to form the maximum stress cycle. In the above process, the equivalent stress time history obtained directly from transient structural analysis is an irregular continuous time series, which cannot be directly used for fatigue damage calculation. It must be decomposed into several complete stress cycles with definite stress amplitudes and mean stresses. By preprocessing the equivalent stress time history, traversing the entire sequence and retaining all peaks and troughs while deleting points in monotonically rising or falling processes, a sequence of extreme points consisting of alternating peaks and troughs is obtained. This process eliminates intermediate transition points that do not constitute complete cycles, reducing the amount of subsequent calculations. Then, taking three adjacent extreme points as an analysis window, it is determined whether the stress range formed by the middle extreme point in the window relative to the two extreme points on the left and right is included by the stress range formed by the two extreme points on the outside. If the inclusion condition is met, a complete cycle is extracted and the middle point is deleted. The stress amplitude of this cycle is half of the difference between the von Mises equivalent stress of the peak and the trough, and the average stress is the average of the von Mises equivalent stress of the peak and the trough. This process is repeated until no more can be extracted. Finally, the remaining extreme point sequence is connected end to end to form the maximum stress cycle. The core of this algorithm is that it can extract complete stress cycles one by one from complex random load time histories without missing any load fluctuations that contribute to fatigue damage.

[0038] In each stress cycle, if the average stress in the critical region is greater than or equal to the tensile strength of the material, static failure has occurred, and the critical region is deemed to have failed. If the average stress in the critical region is less than the tensile strength of the material, the stress amplitude is corrected using the Goodman average stress correction method to obtain an equivalent fully reversible stress amplitude. The specific formula is as follows: in, Indicates the first The equivalent completely reversed stress amplitude of one stress cycle; Indicates the first Stress amplitude of one stress cycle; Indicates the first Average stress over one stress cycle; Indicates the tensile strength of the material; Indicates the index of the stress cycle.

[0039] In the above process, the original stress cycle is an asymmetric cycle with tensile mean stress, which is determined by the stress amplitude. and average stress Common characterization; using the Goodman mean stress correction method, this asymmetric cycle is equivalently transformed into a stress ratio. The standard stress cycle is characterized by a mean stress of zero; after the above conversion, the equivalent quantity obtained is the complete reversal stress amplitude corresponding to the standard cycle. ; Its technical advantage lies in enabling stress cycles under different average stress conditions to be uniformly mapped onto a standard material SN curve for fatigue life assessment, thus avoiding fatigue damage calculation errors caused by directly using the original stress amplitude. Dependent variable With independent variable , , This is relevant because the physical essence of the Goodman correction method is to convert the average stress components in the actual stress cycle into a completely reversible stress amplitude under equal life conditions through linear interpolation. This reflects the intensity of the alternating load during the cycle. This reflects the average load level during the cycle. It provides a normalized benchmark of mean stress for the ultimate tensile strength of materials. These three independent variables together determine the value of the equivalent fully reversible stress amplitude. When the stress amplitude When it increases, The trend is increasing, meaning that the larger the alternating load, the larger the equivalent complete reversal stress amplitude; when the tensile strength of the material... When the denominator increases, Increase The trend is decreasing, meaning that the higher the material strength, the smaller the equivalent complete reversal stress amplitude; when the average stress When the denominator increases, Decrease The trend is increasing, meaning that the greater the average tensile stress, the greater the equivalent complete reversal stress amplitude, reflecting the adverse effect of the average tensile stress on fatigue life.

[0040] The total cumulative fatigue damage in the key area is calculated over the preset evaluation period, specifically as follows: Based on the complete reversal stress amplitude, the Miner linear cumulative damage method is used to calculate the total cumulative fatigue damage in the critical area within a preset evaluation time period. The specific formula used is as follows: in, Indicates the first The total number of stress cycles within a day; This indicates the critical area as of the assessment time. Total cumulative fatigue damage; Indicates the first Tianzhongdi The equivalent completely reversed stress amplitude of one stress cycle; Indicates a day index; This indicates the time from the start of the preset evaluation period to the evaluation time. Total number of days experienced It is an integer; Indicates the stress amplitude at complete reversal The number of cycles required to run until fatigue failure is obtained from the SN curve of the material.

[0041] In the above process, the equivalent complete reversal stress amplitude corresponding to each stress cycle obtained by the rainflow counting method and the Goodman correction method The damage is discrete and varies in magnitude, making it impossible to directly assess the overall fatigue damage degree of the critical area under multi-level variable amplitude loads. Therefore, it is necessary to use linear cumulative damage theory to superimpose these cyclic damages of different amplitudes and employ the Miner linear cumulative damage method to calculate the total cumulative fatigue damage degree of the critical area within a preset assessment time period. Its core assumption is that each stress cycle independently consumes a portion of the material's fatigue life, and that damage can be linearly superimposed. Indicates the first Tianzhongdi The proportion of fatigue damage caused by each stress cycle, which is obtained by referring to the material's SN curve. The number of fatigue damage cycles Taking the reciprocal, the damage share of all stress cycles is accumulated day by day and cycle by cycle, thus obtaining the result from the start time of the preset assessment period to the current assessment time. Total cumulative fatigue damage .

[0042] S4: Construct digital twin models of key areas, obtain corresponding real-time load data based on the digital twin models and obtain the maximum equivalent stress value of key areas, calculate the remaining bearing capacity of each key area in combination with the total cumulative fatigue damage; calculate the dynamic safety margin index of the entire three-dimensional finite element model based on the remaining bearing capacity and the maximum equivalent stress value, and complete the safety status classification assessment of the target platform based on the dynamic safety margin index.

[0043] The dynamic safety margin index of the three-dimensional finite element model is calculated as follows: Constructing a digital twin model of the key area: Extracting the range of a local sub-model containing the key area from the 3D finite element model, and converting the element type of the local sub-model, that is, converting the main beams, columns, and cross braces into beam elements, and the platform plate and connecting plate into shell elements. During the conversion process, the cross-sectional shape and size of the beam elements, the thickness of the shell elements, and the connection relationship between the load-bearing components are preserved, and the elastic modulus, Poisson's ratio, density, and yield strength of the load-bearing components in the key area are fully mapped to the corresponding beam elements and shell elements. Based on the digital twin model, the critical area is further subdivided into multiple critical parts. Specifically, the static equivalent stress values ​​of all grid nodes within the critical area are extracted, sorted from largest to smallest, and the locations corresponding to the top 10% of grid nodes are selected as critical parts. Simultaneously, geometric discontinuities, including welded connections between the main beam and column, welds at the junction of the cross brace and platform plate, and areas where the platform plate cross-section undergoes abrupt changes or has opening edges, are also considered critical parts. The locations of these two types of critical parts are merged and deduplicated to form the final set of critical parts, denoted as […]. , Indexes representing key parts; Indicates the total number of key parts; In the above process, by extracting local sub-models containing key regions from the 3D finite element model and converting their element types—that is, converting the main beam, columns, and cross braces into beam elements, and the platform plate and connecting plates into shell elements—the cross-sectional shape and dimensions of the beam elements, the thickness of the shell elements, and the connection relationships between load-bearing components are preserved. The elastic modulus, Poisson's ratio, density, and yield strength of the materials are fully mapped to the corresponding beam and shell elements. This significantly reduces the number of elements and degrees of freedom while maintaining the accuracy of the mechanical response in the key regions, thus significantly improving the forward solution speed of the digital twin model. Based on this, the static equivalent stress values ​​of all mesh nodes within the key regions are extracted. After sorting them from largest to smallest, the locations corresponding to the top 10% of mesh nodes are selected as key parts. Geometric discontinuities, such as the welded connection points between the main beam and columns, the welds at the intersections of the cross braces and the platform plate, and areas where the platform plate cross-section undergoes abrupt changes or has openings, are also considered key parts. These two types of locations are merged and deduplicated to form the final set of key parts. Its technical effect is that it focuses on the local position with the highest stress level by using the first 10% static equivalent stress threshold, and covers the sensitive position that is prone to fatigue cracks even if the static equivalent stress is not high by using geometric discontinuities.

[0044] Simultaneously, real-time load data for the key area is obtained, and further, the maximum equivalent stress value for the key area is obtained, specifically: Real-time data on wind speed, ambient temperature, and structural strain in key areas are collected. After time-synchronized preprocessing, the effective load parameters at the current moment are extracted. These parameters are then input into the digital twin model for forward solving to calculate the von Mises equivalent stress of all beam and shell elements in the key area. The maximum von Mises equivalent stress value among all beam and shell elements is taken as the value of the key area at the evaluation time. The maximum equivalent stress value is denoted as ; In the above process, the digital twin model needs to be driven by real-time monitoring data to reflect the true stress state of the key area at the current moment, and cannot rely solely on historical wind load data and temperature field distribution data within a preset evaluation period. By collecting raw data on wind speed, ambient temperature, and structural strain in the key area in real time, and performing time-synchronized preprocessing to ensure that data collected by different sensors correspond to the same physical moment, the effective load parameters at the current moment are extracted. These effective load parameters are then input into the digital twin model for forward solving to calculate the von Mises equivalent stress of all beam and shell elements in the key area. Finally, the maximum value among all beam and shell elements is taken as the stress of the key area at the evaluation moment. Maximum equivalent stress value ,make It can reflect the most severe stress level in key areas under the current environmental load in real time.

[0045] Based on ultrasonic thickness measurement data, calculate the thickness loss rate of the key area section: in, Indicates the critical region section at the evaluation time. Thickness loss rate; Indicates the first Initial thickness of the sheet metal in key components; Indicates the time of evaluation The thickness was monitored by ultrasonic thickness measurement. Current thickness of key components; In the above process, the dependent variable Indicates the critical region section at the evaluation time. The thickness loss rate, its technical effect is: using the most unfavorable part as the evaluation benchmark, avoids underestimating the weakening effect of local severe corrosion on the bearing capacity due to averaging treatment; dependent variable With independent variable and This is relevant because the physical essence of thickness loss rate is the relative thinning ratio of each key component, among which... Provided the first The initial thickness of the plate material in key components is used as a reference value. This reflects the current thickness of the critical component as monitored by ultrasonic thickness measurement at the current assessment moment, and the difference between the two values. This is the absolute thinning amount, which is then divided by the initial thickness. That is, the relative thickness loss rate of the critical part is obtained, and then the maximum value is taken for all critical parts to obtain the thickness loss rate of the entire critical area section. When the Thickness of key components When it decreases, the difference Increase As it increases, the operation of taking the maximum value may lead to... The greater the thickness reduction, the higher the thickness loss rate; when the first... Initial thickness of key components When the thickness increases, under the same absolute thinning amount The trend is decreasing, meaning that the larger the initial thickness, the smaller the relative loss rate, reflecting the normalization characteristic of thickness loss rate as a relative indicator.

[0046] Calculate the remaining bearing capacity based on the total cumulative fatigue damage: in, Indicates the key area at the time of assessment The remaining bearing capacity; Indicates the initial bearing capacity of the critical area; In the above process, the initial bearing capacity of the key area It can be obtained directly from the design documents of the target platform. Specifically, it is necessary to consult the structural design calculation book or construction drawings of the platform to find the ultimate bearing capacity design value or standard bearing capacity value for key areas. This value is usually determined by the design unit through theoretical calculations before the platform leaves the factory, based on relevant specifications such as the "Steel Structure Design Standard" GB 50017, and is entered into the platform's initial technical file as a benchmark parameter for structural safety assessment. Dependent variable Indicates the key area at the time of assessment The remaining bearing capacity, which means the initial bearing capacity Multiply by fatigue damage reduction factor respectively and thickness loss reduction factor The current load-bearing capacity is obtained after comprehensively considering fatigue cumulative damage and cross-sectional corrosion thinning. Dependent variable With independent variable , , This is relevant because the physical essence of residual bearing capacity is the remaining value after the initial bearing capacity has been weakened by fatigue damage and cross-sectional loss. It provides an initial benchmark for load-bearing capacity. This reflects the degree of internal fatigue degradation caused by cyclic loading. This reflects the degree of weakening of the external cross-section caused by corrosion or wear, and the three factors together determine the magnitude of the remaining load-bearing capacity; for When the initial bearing capacity When it increases, The total cumulative fatigue damage shows an increasing trend; Increase or thickness loss rate When it increases, or Decrease The trend is decreasing, meaning that the more severe the fatigue damage or the more severe the thickness reduction, the smaller the remaining load-bearing capacity.

[0047] In the above embodiments, 20 sets of data on the total cumulative fatigue damage and the remaining bearing capacity of the corresponding critical area are given to reflect the change of the remaining bearing capacity of the critical area with the change of the total cumulative fatigue damage, as shown in Table 1: Table 1: Relationship between total cumulative fatigue damage and the remaining bearing capacity of the corresponding critical area Table 1 above provides... , It can be seen that when the total cumulative fatigue damage... Increase The remaining load-bearing capacity tends to decrease as fatigue damage becomes more severe.

[0048] Calculate the dynamic safety margin index based on the remaining bearing capacity and maximum equivalent stress value of the key area: in, Indicates the key area at the time of assessment The maximum equivalent stress value; Indicates the evaluation time The dynamic safety margin index.

[0049] In the above process, the dependent variable Indicates the evaluation time The dynamic safety margin index, which means the remaining bearing capacity The maximum equivalent stress value at the current moment The ratio. Its technical effect lies in: reducing historical cumulative degradation, i.e., fatigue damage. and thickness loss rate With real-time load response, i.e., maximum equivalent stress value By incorporating everything into a single safety margin index, a dynamic safety assessment of the entire chain of bridge railing multi-functional work platforms is achieved, considering both past damage accumulation and current load requirements; dependent variable With independent variable and This is relevant because the physical essence of the safety margin index is the ratio of the structure's resistance to the load effect; for When the remaining bearing capacity When it increases, The trend is increasing, meaning that the greater the structural resistance, the higher the safety margin; when the maximum equivalent stress value When it increases, The trend is decreasing, meaning that the larger the current load, the lower the safety margin.

[0050] The dynamic safety margin index is assessed in a tiered manner, specifically as follows: When the dynamic safety margin index is greater than the upper limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a safe state; when the dynamic safety margin index is not greater than the lower limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a dangerous state and an alarm is issued; when the dynamic safety margin index is greater than the lower limit of the preset threshold but not greater than the upper limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a state to be monitored. At this time, the evaluation time interval is shortened, and if the dynamic safety margin index shows a downward trend for three consecutive evaluations, it is upgraded to a dangerous state and an alarm is issued.

[0051] In the above process, the preset threshold upper limit is usually set to a value of According to the design requirements for the ultimate limit state of bearing capacity in the "Steel Structure Design Standard", the safety factor of structural members under standard load combinations is generally not less than [a certain value]. Meanwhile, considering the spatiotemporal variability of wind and temperature loads, calculation errors in the finite element model, the difference between the actual and nominal strength of materials, and unforeseen overload situations that may occur during long-term service, the upper limit of the dynamic safety margin index is set at [value missing]. It can provide sufficient safety reserves for the operating platform; The preset threshold lower limit is usually set to a value of In theory, when the dynamic safety margin index This indicates that the remaining load-bearing capacity is exactly equal to the current maximum equivalent stress value, and the structure is in a state of limit equilibrium. Any tiny load increment could trigger failure. However, due to the combined effects of finite element model analysis errors, real-time monitoring data noise, and load prediction uncertainties, the actual... exist There is a risk of misjudgment when the price fluctuates nearby; therefore, the lower limit of the preset threshold is set to... ,in Additional value added to the theoretical failure threshold. As a safety buffer zone; Shortening the assessment interval specifically means: when the dynamic safety margin index When the monitored area falls between the lower and upper limits of the preset threshold for the first time, the original regular evaluation interval, such as once every 24 hours or once a week, is shortened to an encrypted evaluation interval, such as once every 6 hours or once every 12 hours.

[0052] Please see Figure 3 The present invention also provides a safety assessment system for a multi-functional bridge railing work platform based on the finite element method. This system is used to perform the aforementioned safety assessment method for a multi-functional bridge railing work platform based on the finite element method, and includes: Data acquisition module: used to construct a three-dimensional finite element model of the target bridge guardrail multi-functional operation platform and complete the mesh generation, perform fluid dynamics analysis on the three-dimensional finite element model to construct the corresponding fluid domain, calculate the wind pressure coefficient of each node in the fluid domain within the preset evaluation time period, map the wind pressure coefficient to the mesh nodes of the three-dimensional finite element model, and solve for the wind load data of each mesh node. Data calculation module: used to apply convective heat transfer boundary conditions to the three-dimensional finite element model, calculate the temperature field distribution data at each time within the preset evaluation time period, perform transient structural analysis on the temperature field distribution data and wind load data, and extract the equivalent stress time history of key areas of the model; Correction module: used to decompose the equivalent stress time history of the key area to obtain stress cycles, and after correcting the stress amplitude of the stress cycles by average stress, calculate the total cumulative fatigue damage of the key area within the preset evaluation time period. The overall assessment module is used to construct digital twin models of key areas, obtain corresponding real-time load data based on the digital twin models and obtain the maximum equivalent stress value of the key areas, and calculate the remaining bearing capacity of each key area in combination with the total cumulative fatigue damage. Based on the remaining bearing capacity and the maximum equivalent stress value, the dynamic safety margin index of the entire three-dimensional finite element model is calculated, and the safety status classification assessment of the target platform is completed based on the dynamic safety margin index.

[0053] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0054] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0055] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0056] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A safety assessment method for a multi-functional working platform for bridge railings based on the finite element method, characterized in that, include: S1: Construct a three-dimensional finite element model of the target bridge guardrail multi-functional operation platform and complete the mesh generation. Perform fluid dynamics analysis on the three-dimensional finite element model to construct the corresponding fluid domain. Calculate the wind pressure coefficient of each node in the fluid domain within the preset evaluation time period. Map the wind pressure coefficient to the mesh nodes of the three-dimensional finite element model and solve for the wind load data of each mesh node. S2: Apply convective heat transfer boundary conditions to the three-dimensional finite element model, calculate the temperature field distribution data at each moment within the preset evaluation time period, perform transient structural analysis on the temperature field distribution data and wind load data, and extract the equivalent stress time history of the key areas of the model. S3: Decompose the equivalent stress time history of the key area to obtain stress cycles. After correcting the stress amplitude of the stress cycles by average stress, calculate the total cumulative fatigue damage of the key area within the preset evaluation time period. S4: Construct digital twin models of key areas, obtain corresponding real-time load data based on digital twin models and obtain the maximum equivalent stress value of key areas, calculate the remaining bearing capacity of each key area in combination with the total cumulative fatigue damage; calculate the dynamic safety margin index of the entire three-dimensional finite element model based on the remaining bearing capacity and the maximum equivalent stress value, and complete the safety status classification assessment of the target platform based on the dynamic safety margin index. The wind pressure coefficient of each fluid node on the surface of the computational fluid domain at each moment during the preset evaluation time period is as follows: Obtain the absolute pressure value of the CFD simulation fluid at the corresponding moment of the fluid node, and subtract the static pressure reference value from the absolute pressure value to obtain the pressure difference; The ratio of half the air density to the square of the reference wind speed is calculated as the first ratio. The wind pressure coefficient at the corresponding fluid node at the corresponding moment is obtained based on the pressure difference and the first ratio. The radial basis function interpolation method is used to dynamically map the wind pressure coefficient of each fluid node onto the mesh nodes of the three-dimensional finite element model, specifically as follows: The weight coefficients of each fluid node are solved by LU decomposition, and the wind pressure coefficients corresponding to each grid node are calculated by combining the radial basis function. By multiplying half the air density, the square of the reference wind speed, and the wind pressure coefficient corresponding to the grid node, the wind load data of each grid node at the corresponding time moment in the three-dimensional finite element model can be obtained.

2. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 1, characterized in that, The three-dimensional finite element model of the target platform is constructed as follows: Based on the engineering drawings, a three-dimensional solid model of all load-bearing components, including main beams, columns, cross braces, platform plates, and connecting plates, is constructed at a 1:1 scale. The geometric dimensions of each load-bearing component are defined as the input parameters of the three-dimensional solid model to form a parametric model. The elastic modulus, Poisson's ratio, density, and yield strength of the material of each load-bearing component are used as the mechanical properties of the parametric model to construct a three-dimensional finite element model of the platform. Mesh the completed 3D solid model: Use the mesh generation module in the finite element software to divide all load-bearing components into discrete mesh elements of tetrahedral solid elements, automatically generating a continuous mesh layout. The connection points between all mesh elements in this mesh layout are the mesh nodes.

3. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 2, characterized in that, Obtain wind load data for each grid node, specifically as follows: Set the preset evaluation time period as ,in Indicates the start time of the evaluation. Indicates the end time of the assessment; This represents the index of the evaluation time within the preset evaluation time period, satisfying... ; First, the surface of the fluid domain is meshed: the three-dimensional finite element model is imported into the CFD software, and a cuboid fluid domain is created around the three-dimensional finite element model. The distance from the inlet of the fluid domain to the front edge of the three-dimensional finite element model structure is set to 5 times the structure width, and the distance from the outlet of the fluid domain to the rear edge of the three-dimensional finite element model structure is set to 10 times the structure width. The domain height and domain width are both 5 times the maximum three-dimensional finite element model structure size, which is defined as the maximum geometric span of the three-dimensional finite element model in the X, Y, and Z directions.

4. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 1, characterized in that, Calculate the temperature field distribution data of the entire three-dimensional finite element model within a preset evaluation time period, specifically as follows: A convective heat transfer boundary condition is applied to the three-dimensional finite element model. Finite element software is then used to solve for the temperature field distribution data of the entire three-dimensional finite element model at any time within a preset evaluation period. Specifically, the convective heat transfer boundary condition is as follows: Select all external surfaces of the 3D finite element model, set the ambient air temperature to the ambient fluid temperature of the external surfaces, and divide the external surfaces into windward and sunward sides. For the windward side, determine the ambient wind speed... The convective heat transfer coefficient is defined according to the following formula: This represents the convective heat transfer coefficient of the windward side; For the sunny side, Take 0.3 times the ambient wind speed, that is: This represents the convective heat transfer coefficient on the sun-facing side; The initial temperature of the three-dimensional finite element model is set at the start of a preset evaluation period. Based on the actual materials of each load-bearing component of the target platform, the thermal conductivity and specific heat capacity of each component are defined. A heat flux density varying with time is applied to the sun-facing surface directly exposed to sunlight during the preset evaluation period. in, Indicates the evaluation time The total solar radiation intensity was obtained from the local meteorological database; Indicates the evaluation time The shadow coefficient is automatically output by CFD software using a solar radiation model; Indicates the sunny side at the time of assessment Solar radiation heat flux density; Indicates the surface solar radiation absorptivity; The surface emissivity of the outer surface material of the three-dimensional finite element model was measured using an emissivity meter, while a long-wave radiation heat transfer boundary condition was applied to the outer surface. The calculation formula used is as follows: in, The emissivity of the outer surface of the three-dimensional finite element model; This represents the Stefan-Boltzmann constant; The equivalent radiation temperature of the sky; The outer surface temperature of the three-dimensional finite element model; This represents the relationship between the outer surface of the three-dimensional finite element model and the sky at the evaluation time. Long-wave radiation heat transfer.

5. The safety assessment method for a multi-functional bridge railing work platform based on finite element method according to claim 4, characterized in that, Extracting the equivalent stress time history of key regions, specifically: The method for calibrating the key area is as follows: apply standard loads under standard working conditions to the three-dimensional finite element model and perform static analysis to calculate the static equivalent stress distribution of the three-dimensional finite element model; mark the area formed by mesh nodes whose static equivalent stress value is greater than 30% of the material yield strength as the high stress area; All mesh nodes in the high-stress zone are sorted from largest to smallest according to their static equivalent stress values, and the connected regions containing the top 5% of the sorted mesh nodes are selected as the first type of critical region. Geometric discontinuities are marked as the second type of critical areas. These discontinuities include welded joints between the main beam and the column, welds where the cross brace meets the platform plate, and areas where the platform plate cross section changes abruptly or where there are openings. The union of the first type of critical region and the second type of critical region is identified as the final critical region. Transient structural analysis was performed on temperature field distribution data and wind load data to extract the equivalent stress time history of key regions: Time synchronization processing was performed on wind load data and temperature field distribution data. If the time points of the two types of data did not coincide, linear interpolation was used to unify them to the same time point. The wind load data of the three-dimensional finite element model was used as the boundary condition, and the temperature field distribution data was imported as the temperature load. The thermal expansion coefficient of the material was defined, and the time step was set in the finite element software, with its time axis aligned with the time points of the temperature field distribution data and wind load data. The total stress tensor of each mesh node was calculated, and the total stress tensor of each mesh node was processed using the finite element software to output the curves of the von Mises equivalent stress of all mesh nodes as a function of time. The curve corresponding to the maximum value of the von Mises equivalent stress of each mesh node was used as the equivalent stress time history of the key region.

6. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 5, characterized in that, The equivalent fully reversible stress amplitude is obtained as follows: The equivalent stress time history is decomposed using the rainflow counting method to obtain stress cycles, and the stress amplitude and average stress of each stress cycle are output: The equivalent stress time history is preprocessed by traversing the entire equivalent stress time history, retaining all peaks and troughs, and deleting all points in monotonically increasing or decreasing processes, resulting in a sequence of extreme points consisting of alternating peaks and troughs. Then, using three adjacent extreme points as an analysis window, if the stress range formed by the middle extreme point within the window relative to the two extreme points on the left and right is contained by the stress range formed by the two extreme points on the outer side, a complete cycle is extracted, and the middle point is deleted. The stress amplitude of this cycle is half of the von Mises equivalent stress difference of the trough, and the average stress is the average value of the von Mises equivalent stress of the trough. This process is repeated until no more can be extracted. Finally, the remaining extreme point sequences are connected end to end to form the maximum stress cycle. In each stress cycle, if the average stress in the critical region is greater than or equal to the tensile strength of the material, static failure has occurred, and the critical region is deemed to have failed. If the average stress in the critical region is less than the tensile strength of the material, the stress amplitude is corrected using the Goodman average stress correction method to obtain an equivalent fully reversible stress amplitude. in, Indicates the first The equivalent completely reversed stress amplitude of one stress cycle; Indicates the first Stress amplitude of one stress cycle; Indicates the first Average stress over one stress cycle; Indicates the tensile strength of the material; Indicates the index of the stress cycle.

7. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 6, characterized in that, The total cumulative fatigue damage in the key area is calculated over the preset evaluation period, specifically as follows: Based on the complete reversal stress amplitude, the Miner linear cumulative damage method is used to calculate the total cumulative fatigue damage in the critical area over a preset evaluation period: in, Indicates the first The total number of stress cycles within a day; Indicates the critical area to the assessment time. Total cumulative fatigue damage; Indicates the first Tianzhongdi The equivalent completely reversed stress amplitude of one stress cycle; Indicates a day index; This indicates the time from the start of the preset evaluation period to the evaluation time. Total number of days experienced It is an integer; Indicates the stress amplitude at complete reversal The number of cycles required to run until fatigue failure is obtained from the SN curve of the material.

8. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 7, characterized in that, The dynamic safety margin index of the three-dimensional finite element model is calculated as follows: Constructing a digital twin model of the key area: Extracting the range of a local sub-model containing the key area from the 3D finite element model, and converting the element type of the local sub-model, that is, converting the main beams, columns, and cross braces into beam elements, and the platform plate and connecting plate into shell elements. During the conversion process, the cross-sectional shape and size of the beam elements, the thickness of the shell elements, and the connection relationship between the load-bearing components are preserved, and the elastic modulus, Poisson's ratio, density, and yield strength of the load-bearing components in the key area are fully mapped to the corresponding beam elements and shell elements. Based on the digital twin model, the key area is further subdivided into multiple key parts, namely... Extract the static equivalent stress values ​​of all mesh nodes within the critical region, sort them from largest to smallest, and select the locations corresponding to the top 10% of mesh nodes as critical parts. Simultaneously, geometric discontinuities, including welded connections between the main beam and column, welds at the junction of the cross brace and platform plate, and areas where the platform plate cross-section undergoes abrupt changes or has opening edges, are also considered critical parts. The locations of these two types of critical parts are merged and deduplicated to form the final set of critical parts, denoted as […]. , Indexes representing critical parts Indicates the total number of key parts; Simultaneously, real-time load data for the key area is obtained, and further, the maximum equivalent stress value for the key area is obtained, specifically: Real-time data on wind speed, ambient temperature, and structural strain in key areas are collected. After time-synchronized preprocessing, the effective load parameters at the current moment are extracted. These parameters are then input into the digital twin model for forward solving to calculate the von Mises equivalent stress of all beam and shell elements in the key area. The maximum von Mises equivalent stress value among all beam and shell elements is taken as the value of the key area at the evaluation time. The maximum equivalent stress value is denoted as ; Based on ultrasonic thickness measurement data, calculate the thickness loss rate of the key area section: in, Indicates the critical region section at the evaluation time. Thickness loss rate; Indicates the first Initial thickness of the sheet metal in key components; Indicates the time of evaluation The thickness was monitored by ultrasonic thickness measurement. Current thickness of key components; Calculate the remaining bearing capacity based on the total cumulative fatigue damage: in, Indicates the key area at the time of assessment The remaining bearing capacity; Indicates the initial bearing capacity of the critical area; Calculate the dynamic safety margin index based on the remaining bearing capacity and maximum equivalent stress value of the key area: in, Indicates the key area at the time of assessment The maximum equivalent stress value; Indicates the evaluation time The dynamic safety margin index.

9. The safety assessment method for a multi-functional bridge railing operation platform based on finite element method according to claim 8, characterized in that, The dynamic safety margin index is assessed in a tiered manner, specifically as follows: When the dynamic safety margin index is greater than the upper limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a safe state; when the dynamic safety margin index is not greater than the lower limit of the preset threshold, it indicates that the bridge railing multi-functional work platform is in a dangerous state and an alarm is issued. When the dynamic safety margin index is greater than the lower limit of the preset threshold but not greater than the upper limit of the preset threshold, it indicates that the bridge railing multi-functional operation platform is in a state of waiting for monitoring. At this time, the evaluation time interval is shortened. If the dynamic safety margin index shows a downward trend in three consecutive evaluations, it is upgraded to a dangerous state and an alarm is issued.

10. A finite element method-based safety assessment system for a multi-functional bridge railing work platform, wherein the finite element method-based safety assessment system for a multi-functional bridge railing work platform is used to implement the finite element method-based safety assessment method for a multi-functional bridge railing work platform as described in claims 1-9, characterized in that: Data acquisition module: used to construct a three-dimensional finite element model of the target bridge guardrail multi-functional operation platform and complete the mesh generation, perform fluid dynamics analysis on the three-dimensional finite element model to construct the corresponding fluid domain, calculate the wind pressure coefficient of each node in the fluid domain within the preset evaluation time period, map the wind pressure coefficient to the mesh nodes of the three-dimensional finite element model, and solve for the wind load data of each mesh node. Data calculation module: used to apply convective heat transfer boundary conditions to the three-dimensional finite element model, calculate the temperature field distribution data at each time within the preset evaluation time period, perform transient structural analysis on the temperature field distribution data and wind load data, and extract the equivalent stress time history of key areas of the model; Correction module: used to decompose the equivalent stress time history of the key area to obtain stress cycles, and after correcting the stress amplitude of the stress cycles by average stress, calculate the total cumulative fatigue damage of the key area within the preset evaluation time period. The overall assessment module is used to construct digital twin models of key areas, obtain corresponding real-time load data based on the digital twin models and obtain the maximum equivalent stress value of the key areas, and calculate the remaining bearing capacity of each key area in combination with the total cumulative fatigue damage. Based on the remaining bearing capacity and the maximum equivalent stress value, the dynamic safety margin index of the entire three-dimensional finite element model is calculated, and the safety status classification assessment of the target platform is completed based on the dynamic safety margin index.

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