Safety assessment method for initial defect of concrete filled steel tube intersecting welded joint

Abstract

The invention discloses a safety assessment method for initial defects of a concrete filled steel tube intersecting welded joint, which comprises the following steps of: classifying the initial defects, and establishing an initial discrimination standard of the initial defects through finite element analysis and calculation; performing a fatigue test on the steel pipe concrete joint with the initial defect, determining the fatigue performance and influence factors of the steel pipe concrete joint, and verifying the initial judgment standard to obtain a comprehensive evaluation standard of the initial defect; according to the comprehensive evaluation standard of the initial defect, fatigue life evaluation parameters of the initial defect are obtained, and meanwhile, a prediction evaluation system of the fatigue life of the welded joint is constructed through the fatigue performance and influence factors of the steel pipe concrete joint. According to the method, potential defects can be found before the welding joint is put into use through initial defect evaluation, so that measures can be taken in time to repair or replace the welding joint, and sudden failure caused by the defects in the using process is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of structural engineering, and in particular to a safety assessment method for initial defects of steel tube concrete intersecting welded joints. Background Art

[0002] With the acceleration of urbanization and the growth of traffic demand, steel tube concrete structures have been widely used in modern construction projects, especially bridge construction, due to their excellent mechanical properties, construction convenience and economy. Steel tube concrete structures are composed of steel tubes and concrete filled inside, which fully utilizes the bending resistance of steel tubes and the compressive resistance of concrete, making the structure light and strong, with high bearing capacity and good seismic performance.

[0003] In steel tube concrete structures, welded joints, as key parts of connecting components, bear the heavy responsibility of transmitting internal forces and maintaining the integrity of the structure. The quality of welding directly affects the safety and durability of the entire structure. Especially in steel tube concrete intersecting welded joints, the quality of welds is particularly important for the fatigue performance of the structure, because these joints are often subjected to complex stress states, especially under the frequent action of vehicle loads, fatigue cracks are prone to occur, which in turn threatens the safety of the structure.

[0004] During the welding process, due to the influence of various factors such as material properties, welding process, environmental conditions, etc., some defects such as cracks, pores, and lack of fusion are inevitable. These defects will not only reduce the mechanical properties of the welded joint, but also become the starting point for the initiation and expansion of fatigue cracks under repeated loads. Especially in the toe and toe transition zone of the intersecting welded joints of steel tube concrete, due to the serious stress concentration phenomenon, even a small initial defect may lead to serious fatigue damage, thus greatly affecting the service life and safety of the structure.

[0005] The Chinese invention with publication number CN105628373A provides a method for calculating fatigue damage of welded steel structures, the method comprising: establishing a full-space curve model for fatigue resistance of welding details; calculating the real time-history stress of the welding detail structure based on the welding residual stress at the welding details and the time-history stress of the welding detail structure under vehicle load; processing the real time-history stress using the rain flow counting method, and calculating the equivalent stress amplitude and the total stress cycle number based on the processing result; calculating the fatigue life corresponding to the equivalent stress amplitude using the established full-space curve model; calculating the fatigue damage of the welded steel structure based on the calculated fatigue life and the total stress cycle number. The fatigue damage calculation method for a welded steel structure provided in the embodiment of the application can accurately calculate the fatigue damage under different loads and welding residual stress levels.

[0006] The above and similar fatigue damage calculation methods are difficult to accurately and reasonably simulate the corresponding initial defects in the process of simulating the initial defect shape and size, and quickly determine the influence mechanism of the initial defects on the fatigue performance of the steel tube concrete intersecting welded joints, because the key factors such as the type, position and spatial geometry of the initial defects are highly random. Summary of the invention

[0007] The purpose of the present invention is to provide a safety assessment method for initial defects of intersecting welded joints of steel tube concrete, so as to solve the problems raised in the above-mentioned background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: a safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes, the safety assessment method comprising:

[0009] Initial defect discrimination criteria: Classify initial defects and establish initial defect discrimination criteria through finite element analysis and calculation;

[0010] Fatigue verification test: Fatigue test is performed on the steel tube concrete node with initial defects to determine the fatigue performance and influencing factors of the steel tube concrete node, and the initial judgment standard is verified to obtain the comprehensive evaluation standard of the initial defects;

[0011] Fatigue life assessment system: According to the comprehensive assessment standard of the initial defect, the fatigue life assessment parameters of the initial defect are obtained. At the same time, the fatigue performance and influencing factors of the steel tube concrete node are used to construct a prediction and assessment system for the fatigue life of the welded joint, specifically:

[0012] Determining strain parameters, temperature parameters, humidity parameters and defect parameters corresponding to the initial defect through the comprehensive evaluation criteria of the initial defect and the sensor data;

[0013] The parameters of the dynamic prediction model are determined according to the strain parameter, temperature parameter, humidity parameter and defect parameter, and the dynamic prediction model is updated to obtain the fused total damage.

[0014] Furthermore, the initial criteria for determining the initial defects are established, including:

[0015] Classifying the initial defects according to the type, location, size and shape corresponding to the initial defects;

[0016] Through finite element analysis and calculation, the stress distribution of the welded joint under different defect conditions is determined;

[0017] According to the stress distribution of the weld joint under the different defect conditions, the initial judgment standard of the initial defect is determined, and the initial judgment standard is specifically:

[0018] Minor defects: allowed to exist;

[0019] Minor flaws: need to be monitored;

[0020] Moderate defect: needs to be repaired;

[0021] Big flaw: Must be fixed.

[0022] Furthermore, the stress distribution of the welded joint under different defect conditions is determined, including:

[0023] According to the physical properties and mechanical properties of the steel tube concrete intersecting welded joint, a three-dimensional geometric model of the steel tube concrete intersecting welded joint is established, and the three-dimensional geometric model is meshed;

[0024] Through the classified initial defects, finite element analysis is performed on the three-dimensional geometric model after meshing to obtain the fatigue life corresponding to each defect type, and an SN curve is constructed to determine the stress distribution of the welded joint under different defect conditions, specifically: the larger the stress amplitude, the smaller the fatigue life.

[0025] Furthermore, when establishing the three-dimensional geometric model of the steel tube concrete intersecting welded joint, the properties of the steel, the properties of the concrete and the geometric parameters of the initial defects are defined. The properties of the steel include elastic modulus, Poisson's ratio and yield strength. The properties of the concrete include elastic modulus, Poisson's ratio and compressive strength. The geometric parameters of the initial defects include steel tube diameter, steel tube wall thickness, concrete core diameter, weld thickness and weld length.

[0026] Furthermore, the initial discrimination criteria are verified, including:

[0027] Fatigue tests were conducted on concrete-filled steel tube node specimens with different initial defects to obtain verification results of the fatigue tests;

[0028] According to the verification results of the fatigue test, the stress concentration factor and fatigue life of each concrete-filled steel tube node specimen are obtained, specifically:

[0029] ;

[0030] in: is the fatigue life of the initial defect under different stress amplitudes, , is the material constant, is the stress amplitude, is the stress concentration factor, is the maximum stress value, is the stress value without defects;

[0031] The comprehensive evaluation standard of the initial defect is obtained through the stress concentration factor and fatigue life.

[0032] Furthermore, a comprehensive evaluation of the initial defect is obtained through the stress concentration factor and fatigue life, and the comprehensive evaluation includes strength evaluation, stiffness evaluation and fatigue life evaluation, specifically:

[0033] Strength assessment: the influence of pores on the strength of welded joints is less than the influence of slag inclusions on the strength of welded joints. The influence of incomplete penetration on the strength of welded joints is less than the influence of undercut on the strength of welded joints.

[0034] Stiffness evaluation: the influence of pores on the stiffness of welded joints is less than the influence of slag inclusions on the stiffness of welded joints. The influence of undercuts on the stiffness of welded joints is less than the influence of incomplete penetration on the stiffness of welded joints.

[0035] Fatigue life assessment: the impact of porosity on the fatigue life of welded joints < the impact of slag inclusion on the fatigue life of welded joints < the impact of incomplete penetration on the fatigue life of welded joints < the impact of undercut on the fatigue life of welded joints.

[0036] Furthermore, the total damage after the fusion is obtained, including:

[0037] Determine the parameters of the dynamic prediction model: determine the material constants through the SN curve, determine the hot spot stress parameters through finite element analysis, and determine the damage accumulation model parameters through the linear damage accumulation model;

[0038] Update the dynamic prediction model: Update and adjust the damage accumulation process and damage evolution equation of the welded joint at different stress levels, specifically:

[0039] ;

[0040] in: is the total damage after the k+1th cycle, is the total damage after the kth cycle, is the remaining life after the k+1th cycle, is the remaining life after the kth cycle, is the actual number of cycles in the k+1th cycle, is the stress amplitude Fatigue life under is the stress amplitude after the k+1th cycle;

[0041] Fusion dynamic prediction model: The SN curve model, hot spot stress method model and damage accumulation model are integrated to obtain the total damage after integration.

[0042] Furthermore, the material constants are determined by the SN curve, specifically:

[0043] ;

[0044] in: is the fatigue life, is the stress amplitude, , is the material constant;

[0045] The damage accumulation model parameters are determined by the linear damage accumulation model, specifically:

[0046] ;

[0047] in: is the total damage, is the actual number of cycles loaded at level i, is the stress amplitude Fatigue life under is the stress amplitude of the i-th level loading, The index of the number of loads.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] First, the present invention can detect potential defects in the welded joint before it is put into use through initial defect assessment, so that timely measures can be taken to repair or replace it, avoiding sudden failure caused by defects during use. At the same time, through a comprehensive assessment of initial defects, structural failure caused by welded joint defects can be effectively prevented, thereby reducing the occurrence of safety accidents.

[0050] Second: Based on the evaluation results of initial defects, the present invention can optimize the design of welded joints, improve their durability and reliability, and thus extend the service life of the entire structure. At the same time, by evaluating the initial defects, a reasonable maintenance plan can be formulated, and necessary inspections and repairs can be carried out in a timely manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of the process of the safety assessment method of the present invention;

[0052] Figure 2 It is a curve diagram between fatigue life and coped amplitude of the present invention;

[0053] Figure 3A schematic diagram of a process for establishing an initial determination standard for initial defects of the present invention;

[0054] Figure 4 A schematic diagram of a process for obtaining a comprehensive evaluation standard for initial defects of the present invention;

[0055] Figure 5 The present invention is a schematic diagram of the process of constructing a prediction and evaluation system for the fatigue life of welded joints. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] When evaluating the fatigue performance of steel tube concrete intersecting welded joints by conventional safety assessment methods, it relies on the way of detecting initial defects and roughly simulating the initial defects, so it is difficult to accurately and reasonably simulate the corresponding initial defects. The technical solution provided by this application first establishes the initial defect discrimination standard, and then tests the established initial defect discrimination standard through multiple fatigue tests to obtain the comprehensive evaluation standard of the initial defects. Finally, the fatigue life evaluation parameters of the initial defects are obtained through the comprehensive evaluation standard of the initial defects, and a prediction and evaluation system for the fatigue life of the welded joint is constructed, so that potential defects can be discovered in advance before the welded joint is put into use, avoiding sudden failure caused by defects during use, and effectively preventing structural failure caused by defects in the welded joint, reducing the occurrence of safety accidents.

[0058] refer to Figure 1-Figure 5 This embodiment provides a safety assessment method for initial defects of steel tube concrete intersecting welded joints, and the safety assessment method includes the following steps:

[0059] Step S1: Establish the initial defect discrimination standard. That is, classify the initial defects according to the type, location, size, shape and other factors corresponding to the initial defects, and analyze and calculate the classified initial defects in combination with finite element analysis and calculation to obtain the initial discrimination standard of the initial defects. The details are as follows:

[0060] Step S1.1: Obtain the initial defects that may occur at the toe and toe transition zone of the intersecting welded joint of steel tube concrete through technical research, actual bridge investigation and literature data. At the same time, record the type (such as pores, slag inclusions, incomplete penetration), location (such as weld toe, weld root, saddle, transition zone), size (such as length, depth) and shape (such as circular, linear) of each initial defect.

[0061] At the same time, they are classified according to the type, size, location and shape of the initial defects, specifically:

[0062] Classification by type: Porosity, slag inclusions, lack of penetration and undercut.

[0063] Classification by location: weld toe, weld root, saddle, transition zone.

[0064] Classification by size: tiny defects (<1mm), small defects (1-3mm), medium defects (3-5mm) and large defects (>5mm). It is worth noting that in the process of classifying the size in this embodiment, only this data is used as an example, and it can be specifically defined according to the actual application scenario. Therefore, when classifying by size, it is not unique.

[0065] Classified by shape: circular, oval and linear.

[0066] Step S1.2: Use finite element analysis software such as ANSYS and ABAQUS to perform finite element analysis and calculation on the classified initial defects to determine the effects of different types and degrees of initial defects on the welded joint. The details are as follows:

[0067] Step S1.2.1: Establish a finite element model, that is, establish a three-dimensional geometric model of the steel tube concrete intersecting welded joint through finite element analysis software such as ANSYS and ABAQUS, define the physical and mechanical properties of the steel tube concrete intersecting welded joint, and mesh the established three-dimensional geometric model to ensure the accuracy of subsequent data calculations. Finally, the actual working conditions are simulated by combining the established three-dimensional geometric model with the determined boundary conditions and loads.

[0068] In this embodiment, the geometric parameters of the initial defects (steel pipe diameter, steel pipe wall thickness, concrete core diameter, weld thickness and weld length) are defined by finite element analysis software such as ANSYS and ABAQUS, and a geometric model of the steel pipe and concrete core is established. It is worth noting that in the process of establishing the geometric model of the steel pipe and concrete core, a weld needs to be added to the geometric model according to the defined geometric parameters of the initial defects to ensure that the position, thickness and length of the weld conform to the actual engineering situation.

[0069] Furthermore, the properties of steel and concrete are defined, where the properties of steel include elastic modulus (e.g. 210 GPa), Poisson's ratio (e.g. 0.3) and yield strength (e.g. 350 MPa), and the properties of concrete include elastic modulus (e.g. 30 GPa), Poisson's ratio (e.g. 0.17) and compressive strength (e.g. 30 MPa).

[0070] Furthermore, in this embodiment, the above-established geometric model is meshed by tetrahedral or hexahedral meshes. It is worth noting that in the process of meshing, a denser mesh is required for high stress concentration areas such as weld toes to ensure mesh quality and avoid excessively distorted units.

[0071] Step S1.2.2: According to the initial defects classified in step S1.1, initial defects of different types and degrees are introduced into the three-dimensional geometric model established in step S1.2.1 to perform finite element analysis, that is, to obtain the stress distribution of the weld joint under different defect conditions.

[0072] In the process of specific implementation, the data corresponding to the welding joint in this embodiment are shown in the following table, which includes the initial defect type, location, size, shape and maximum stress amplitude, specifically:

[0073] Table 1: Welding joint data table:

[0074] ;

[0075] Furthermore, the above data is used to construct the SN curve to determine the fatigue life corresponding to each defect type. Specifically, by constructing the SN curve, the calculation formula for the fatigue life corresponding to the defect type is obtained, which is:

[0076] ;

[0077] in: is the fatigue life of the initial defect under different stress amplitudes, , is the material constant, is the stress amplitude.

[0078] In this embodiment, the constant A is 10 8 , constant B is 3, and the minimum stress is 0 MPa, so the stress amplitudes corresponding to the above initial defects are:

[0079] The stress amplitude of pores is 120 MPa, the stress amplitude of slag inclusions is 150 MPa, the stress amplitude of incomplete penetration is 200 MPa, and the stress amplitude of undercut is 250 MPa.

[0080] In other words, the fatigue life corresponding to the above initial defect is:

[0081] The fatigue life of pores is 5.79×10 3 times, the fatigue life of slag inclusion is 2.96×10 3 times, the fatigue life of incomplete penetration is 1.25×10 3 times, the fatigue life of the undercut is 6.40×10 2 Second-rate.

[0082] According to the data obtained above, we can get the following Figure 2 The curve graph shown, Figure 2 is a curve diagram between stress amplitude and fatigue life in this embodiment. Figure 2 It can be seen that with the increase of stress amplitude, the fatigue life decreases significantly.

[0083] Step S1.3: According to the relationship between the stress amplitude and fatigue life obtained in step S1.2.2, the initial judgment criteria for initial defects are determined, specifically:

[0084] Minor defects (<1mm): do not affect fatigue life and are allowed to exist.

[0085] Small defects (1-3mm): Slightly affect fatigue life and need to be monitored.

[0086] Medium defects (3-5mm): moderately affect fatigue life and need to be repaired.

[0087] Large defects (>5mm): seriously affect fatigue life and must be repaired.

[0088] Step S2: Fatigue verification test. That is, fatigue test is performed on the steel tube concrete node with initial defects to verify the initial judgment standard and obtain the fatigue performance and influencing factors of the steel tube concrete node. The details are as follows:

[0089] Step S2.1: Fatigue test verification is performed on steel tube concrete node specimens with different initial defects to obtain fatigue test results. In this embodiment, multiple steel tube concrete node specimens are set, each of which contains different types of initial defects (such as pores, slag inclusions, incomplete penetration and undercuts). At the same time, initial defects of different sizes and shapes are artificially introduced into each specimen to ensure that the geometric shape of the defects is consistent with the actual engineering situation. Each specimen is numbered one by one to facilitate recording the type, size and shape of the defects.

[0090] Furthermore, the load parameters in the fatigue test are set, including the maximum stress, minimum stress, stress amplitude and loading frequency, and the environmental conditions of the test are set, including temperature, humidity and loading waveform, to simulate actual working conditions.

[0091] In the process of specific implementation, the maximum stress is determined according to the maximum stress value in the actual project, and the minimum stress is usually set to 0 MPa or a negative value, which depends on the actual working conditions. The loading frequency is selected according to the capacity of the testing machine and the characteristics of the specimen, and is usually set to 5-10 Hz. The humidity keeps the test environment temperature at room temperature (for example, 20-25°C), the humidity keeps the test environment humidity at about 50% relative humidity, and the loading waveform selects a sine wave or trapezoidal wave loading waveform to simulate the actual working conditions.

[0092] Furthermore, each specimen is fixed on the loading device and ensured that it does not slide or loosen during the test. At the same time, during the test, the crack initiation and expansion process of the specimen is observed in real time through equipment such as high-speed cameras and microscopes. It is worth noting that during fatigue testing, when obvious cracks or failures occur in the specimen, the test will be terminated and its fatigue life will be recorded.

[0093] Step S2.2: Obtain the stress concentration factor and fatigue life of each steel tube concrete node specimen through the data from the fatigue test in step S2.1. The formula for obtaining the stress concentration factor is as follows:

[0094] ;

[0095] in: is the stress concentration factor, is the maximum stress value, is the stress value in the absence of defects.

[0096] In the process of specific implementation, the data in the following table can be obtained, specifically:

[0097] Table 2: Welding joint data Table 2:

[0098] ;

[0099] According to the data in the above table, a comprehensive evaluation of initial defects can be obtained, including strength evaluation, stiffness evaluation and fatigue life evaluation. Specifically:

[0100] Strength assessment: The influence of pores on the strength of welded joints is less than the influence of slag inclusions on the strength of welded joints. The influence of incomplete penetration on the strength of welded joints is less than the influence of undercut on the strength of welded joints.

[0101] Stiffness assessment: the effect of pores on the stiffness of welded joints is less than the effect of slag inclusions on the stiffness of welded joints. The effect of undercut on the stiffness of welded joints is less than the effect of incomplete penetration on the stiffness of welded joints.

[0102] Fatigue life assessment: the impact of porosity on the fatigue life of welded joints < the impact of slag inclusion on the fatigue life of welded joints < the impact of incomplete penetration on the fatigue life of welded joints < the impact of undercut on the fatigue life of welded joints.

[0103] That is to say, combined with the initial determination criteria of the initial defect obtained in step S1.3, the comprehensive determination criteria of the initial defect is:

[0104] Pores: Pores with a diameter less than 1 mm have little effect on strength and stiffness and are allowed to exist.

[0105] Slag inclusion: has a great impact on strength and stiffness and needs to be repaired.

[0106] Incomplete penetration: has a great impact on strength and stiffness and needs to be repaired.

[0107] Undercut: It has a serious impact on strength and stiffness and must be repaired.

[0108] Step S3: Fatigue life assessment system. That is, according to the comprehensive assessment standard of the initial defect determined in step S2.2 and the sensor data obtained in real time, the fatigue life assessment parameters of the initial defect are determined, and through the fatigue performance and influencing factors of the steel tube concrete node, a dynamic prediction model is constructed to predict the fatigue life at different stages. The details are as follows:

[0109] Step S3.1: According to the comprehensive evaluation criteria of the initial defect determined in step S2.2, the strain parameters corresponding to the initial defect, i.e., the stress concentration factor and the stress amplitude, are determined. At the same time, the temperature parameters, humidity parameters, and defect parameters corresponding to the initial defect are obtained by acquiring the sensor data in real time. The temperature parameters are the fatigue performance parameters of the material, the humidity parameters are the corrosion rate and fatigue life of the material, and the defect parameters are the defect position, size, and shape.

[0110] Specifically, the strain of the weld joint is measured by strain sensors (such as resistance strain gauges, optical fiber strain sensors), the ambient temperature is monitored by temperature sensors (such as thermocouples, thermistors), the ambient humidity is monitored by humidity sensors (such as capacitive humidity sensors), the vibration of the weld joint is monitored by vibration sensors (such as accelerometers), and surface defects are detected by visual sensors (such as high-definition cameras, infrared cameras). In other words, strain sensors and temperature sensors are deployed at key parts of the weld joint (such as the weld toe). Temperature sensors and humidity sensors are deployed around the weld joint to monitor environmental conditions. Visual sensors are deployed on the surface of the weld joint to take images regularly and detect surface defects.

[0111] Furthermore, the obtained sensor data is preprocessed, that is, filtered, denoised and calibrated, and then feature data is extracted. At the same time, the temperature parameter, humidity parameter and defect parameter are adjusted accordingly according to the extracted feature data.

[0112] During the implementation process, the strain data shown in the following table were collected, specifically:

[0113] Table 3: Strain data table:

[0114] ;

[0115] Specifically, the initial stress concentration factor is 1.5, when the strain exceeds 70με, the stress concentration factor increases by 0.01, and when the strain is less than 50με, the stress concentration factor decreases by 0.01. That is to say, according to the data in the above table, the time points when the strain exceeds 70με are 2 s, 3 s and 4 s, so the stress concentration factor increases by 0.03, that is, the final stress concentration factor is 1.53.

[0116] Further, the stress amplitude is determined based on the strain data. According to the data in the above table, the maximum strain is 90με and the minimum strain is 50με. The elastic modulus of the material in this embodiment is 210GPa, so the stress amplitude in this embodiment is 8.4MPa.

[0117] During the specific implementation process, the temperature data shown in the following table was collected, specifically:

[0118] Table 4: Temperature data table:

[0119] ;

[0120] Specifically, when the temperature exceeds 30°C, the material constants A and B increase by 10%, and when the temperature is below 20°C, the material constants A and B decrease by 10%. According to the data in the above table, the time points when the temperature exceeds 30°C are 2 s, 3 s, and 4 s, so the material constants A and B increase by 30% each. The initial material constants A and B are 10 8 and 3.5, that is, the final material constants A and B are 1.3×10 8 and 4.55.

[0121] During the implementation process, the humidity data shown in the following table was collected, specifically:

[0122] Table 5: Humidity data table:

[0123] ;

[0124] Specifically, when the humidity exceeds 60%, the corrosion rate increases by 0.001, and when the humidity is below 50%, the corrosion rate decreases by 0.001. According to the data in the above table, the time points when the humidity exceeds 60% are 2 s, 3 s, and 4 s, so the corrosion rate increases by 0.003. The initial corrosion rate is 0.01, that is, the final corrosion rate is 0.013.

[0125] Further, the fatigue life is determined based on the above corrosion rate. The initial fatigue life in this embodiment is 10 6 Therefore, according to the data in the above table, the final fatigue life is 987,000 times.

[0126] During the implementation process, the defect data shown in the following table was collected, specifically:

[0127] Table 6: Defect data table:

[0128] ;

[0129] According to the data in the above table, the defect position detected by the visual sensor is the weld toe, the defect sizes are 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm and 2.5 mm, and the defect shapes are circular and linear.

[0130] Step S3.2: According to the strain parameters, temperature parameters, humidity parameters and defect parameters obtained in step S3.1, a dynamic prediction model is constructed and the dynamic prediction model is updated. The details are as follows:

[0131] Step S3.2.1: Determine the parameters of the dynamic prediction model, wherein the material constants are determined by the SN curve, the hot spot stress parameters are determined by finite element analysis, and the damage accumulation model parameters are determined by the linear damage accumulation model.

[0132] In this embodiment, the fatigue test in step S2.1 can simulate actual working conditions, including different load levels, loading frequencies, and ambient temperatures, and can also obtain the maximum stress amplitude, minimum stress value, fatigue life, etc.

[0133] In the process of specific implementation, the stress amplitude-fatigue life data shown in the following table can be obtained, specifically:

[0134] Table 7: Stress amplitude-fatigue life data table:

[0135] ;

[0136] Furthermore, the stress amplitude and fatigue life satisfy the following relationship:

[0137] ;

[0138] in: is the fatigue life, is the stress amplitude, , is the material constant.

[0139] Therefore, the material constants can be obtained by linear regression method and logarithmic data. and The logarithmic size of the material constant is then obtained through calculation using the least squares method and linear regression model. and The actual size of the material constant. That is, in this embodiment, and The sizes are: 1.32×107 and 3.5 respectively.

[0140] In this embodiment, static and dynamic stress analysis is performed using the finite element model established in step S1.2.1 to obtain stress distribution of key parts such as the weld toe.

[0141] In the process of specific implementation, the following finite element analysis results can be obtained, specifically:

[0142] The stress concentration factors at the weld toe are 4.5, 6.0 and 7.0, and the nominal stress value is 100 MPa.

[0143] In this embodiment, through the fatigue test in step S2.1, the stress level, loading times, cumulative damage, etc. of each loading are obtained to obtain the fatigue damage accumulation under multi-level loading, specifically:

[0144] ;

[0145] in: is the total damage, is the actual number of cycles loaded at level i, is the stress amplitude Fatigue life under is the stress amplitude of the i-th level loading, The index of the number of loads.

[0146] In the process of specific implementation, the following stress level-fatigue life-actual loading times data can be obtained, specifically:

[0147] Table 8: Stress level-fatigue life-actual loading times data table:

[0148] ;

[0149] According to the data in the above table, the total damage is 0.4.

[0150] Furthermore, the total damage and material constants , The following relationship is satisfied:

[0151] ;

[0152] in: is the total damage, , is the material constant, is the stress amplitude.

[0153] Therefore, according to the data in the above table, we can know that: material constant , The sizes are: 1×10 -6 and 4.0.

[0154] Step S3.2.2: Based on the parameters of the dynamic prediction model determined in step S3.2.1, the damage accumulation process and damage evolution equation of the weld joint at different stress levels are updated and adjusted.

[0155] In this embodiment, the damage accumulation process of the weld joint at different stress levels is updated, that is, the state equation is updated. The state equation is specifically:

[0156] ;

[0157] in: is the total damage after the k+1th cycle, is the total damage after the kth cycle, is the remaining life after the k+1th cycle, is the remaining life after the kth cycle, is the actual number of cycles in the k+1th cycle, is the stress amplitude Fatigue life under is the stress amplitude after the k+1th cycle.

[0158] In the process of specific implementation, there are time-stress amplitude and cycle number data as shown in the following table, specifically:

[0159] Table 9: Time-stress amplitude and number of cycles data table:

[0160] ;

[0161] Furthermore, according to the data in the above table:

[0162] In the initial state:

[0163] Total damage after cycle 0 0, the remaining life after the 0th cycle is 1,000,000 times.

[0164] During the first loop:

[0165] Stress amplitude after the first cycle The actual number of cycles for the first cycle is 100 MPa. is 1000 times.

[0166] That is, the stress amplitude Fatigue life under Total damage after the first cycle is 1,000,000 times 0.001, the remaining life after the first cycle 999000 times.

[0167] During the second loop:

[0168] Stress amplitude after the second cycle The actual number of cycles for the second cycle is 120 MPa. is 500 times.

[0169] That is, the stress amplitude Fatigue life under 500,000 times, total damage after the second cycle 0.002, the remaining life after the second cycle It is 998500 times.

[0170] During the third cycle:

[0171] Stress amplitude after the third cycle The actual number of cycles is 150MPa, the third cycle is 200 times.

[0172] That is, the stress amplitude Fatigue life under 200,000 times, total damage after the third cycle The remaining life after the second cycle is 0.003. It is 998300 times.

[0173] During the fourth cycle:

[0174] Stress amplitude after the 4th cycle The actual number of cycles for the 4th cycle is 200 MPa. For 100 times.

[0175] That is, the stress amplitude Fatigue life under 50,000 times, total damage after the 4th cycle 0.005, the remaining life after the 4th cycle It is 998200 times.

[0176] In this embodiment, the damage evolution equation is updated, that is, the damage accumulation process of the material at different stress levels is updated.

[0177] In the process of specific implementation, there are time-stress amplitude and damage data as shown in the following table, specifically:

[0178] Table 10: Time-stress amplitude and damage data table:

[0179] ;

[0180] Furthermore, according to the data in the above table:

[0181] In the initial state:

[0182] Material constants , The sizes are: 1×10 -6 and 4.0.

[0183] During the first loop:

[0184] Stress amplitude after the first cycle The total damage after the first cycle is 100 MPa. is 0.001, at which point the material constant The size is: 1×10 -6 .

[0185] During the second loop:

[0186] Stress amplitude after the second cycle The total damage after the second cycle is 120MPa. is 0.002, at which point the material constant The size is: 1.16×10 -6 .

[0187] During the third cycle:

[0188] Stress amplitude after the third cycle The total damage after the third cycle is 150MPa. is 0.003, at which point the material constant The size is: 1.37×10 -6 .

[0189] During the fourth cycle:

[0190] Stress amplitude after the 4th cycle The total damage after the fourth cycle is 200 MPa. is 0.005, at which point the material constant The size is: 1.56×10 -6 .

[0191] Step S3.2.3: According to the updated and adjusted state equation and damage evolution equation in step S3.2.2, the SN curve model, hot spot stress method model and damage accumulation model are integrated.

[0192] In the process of carrying out the specific embodiment, there are time-stress amplitude, number of cycles and damage data as shown in the following table, specifically:

[0193] Table 11: Time-stress amplitude, number of cycles and damage data table:

[0194] ;

[0195] Furthermore, according to the data in the above table:

[0196] During the first loop:

[0197] Stress amplitude after the first cycle The actual number of cycles for the first cycle is 100 MPa. is 1000 times.

[0198] In other words, the damage under the SN curve model is:

[0199] ;

[0200] The damage under the hot spot stress method model is:

[0201] ;

[0202] The damage under the damage accumulation model is:

[0203] ;

[0204] During the second loop:

[0205] Stress amplitude after the second cycle The actual number of cycles for the second cycle is 120 MPa. is 500 times.

[0206] In other words, the damage under the SN curve model is:

[0207] ;

[0208] The damage under the hot spot stress method model is:

[0209] ;

[0210] The damage under the damage accumulation model is:

[0211] ;

[0212] During the third cycle:

[0213] Stress amplitude after the third cycle The actual number of cycles is 150MPa, the third cycle is 200 times.

[0214] In other words, the damage under the SN curve model is:

[0215] ;

[0216] The damage under the hot spot stress method model is:

[0217] ;

[0218] The damage under the damage accumulation model is:

[0219] ;

[0220] During the fourth cycle:

[0221] Stress amplitude after the 4th cycle The actual number of cycles for the 4th cycle is 200 MPa. For 100 times.

[0222] In other words, the damage under the SN curve model is:

[0223] ;

[0224] The damage under the hot spot stress method model is:

[0225] ;

[0226] The damage under the damage accumulation model is:

[0227] ;

[0228] It is worth noting that the total damage after fusion is calculated as:

[0229]

[0230] in: is the total damage after fusion, is the corresponding weight of the SN curve model, is the damage corresponding to the SN curve model, is the weight corresponding to the hot spot stress method model, is the damage corresponding to the hot spot stress method model, is the weight corresponding to the damage accumulation model, is the damage corresponding to the damage accumulation model.

[0231] In the specific operation and implementation process, the SN curve model corresponds to the weight , weights corresponding to the hot spot stress method model , the weight corresponding to the damage accumulation model The sizes of are set to 0.4, 0.3 and 0.3 respectively. That is, the total damage after fusion in this embodiment is It is 0.0031.

[0232] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is limited by the attached embodiments and their equivalents.

Claims

1. A safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes, characterized in that: The safety assessment method includes: Initial defect discrimination criteria: Classify initial defects and establish initial defect discrimination criteria through finite element analysis and calculation; Fatigue verification test: Fatigue test is performed on the steel tube concrete node with initial defects to determine the fatigue performance and influencing factors of the steel tube concrete node, and the initial judgment standard is verified to obtain the comprehensive evaluation standard of the initial defects; Fatigue life assessment system: According to the comprehensive assessment standard of the initial defect, the fatigue life assessment parameters of the initial defect are obtained. At the same time, the fatigue performance and influencing factors of the steel tube concrete node are used to construct a prediction and assessment system for the fatigue life of the welded joint, specifically: Determining strain parameters, temperature parameters, humidity parameters and defect parameters corresponding to the initial defect through the comprehensive evaluation criteria of the initial defect and the sensor data; The parameters of the dynamic prediction model are determined according to the strain parameter, temperature parameter, humidity parameter and defect parameter, and the dynamic prediction model is updated to obtain the fused total damage.

2. A safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 1, characterized in that: Establishing the initial criteria for the initial defects includes: Classifying the initial defects according to the type, location, size and shape corresponding to the initial defects; Through finite element analysis and calculation, the stress distribution of the welded joint under different defect conditions is determined; According to the stress distribution of the weld joint under the different defect conditions, the initial judgment standard of the initial defect is determined, and the initial judgment standard is specifically: Minor defects: allowed to exist; Minor flaws: need to be monitored; Moderate defect: needs to be repaired; Big flaw: must be fixed.

3. A safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 2, characterized in that: Determine the stress distribution of the welded joint under different defect conditions, including: According to the physical properties and mechanical properties of the steel tube concrete intersecting welded joint, a three-dimensional geometric model of the steel tube concrete intersecting welded joint is established, and the three-dimensional geometric model is meshed; Through the classified initial defects, finite element analysis is performed on the three-dimensional geometric model after meshing to obtain the fatigue life corresponding to each defect type, and an SN curve is constructed to determine the stress distribution of the welded joint under different defect conditions, specifically: the larger the stress amplitude, the smaller the fatigue life.

4. The safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 1 is characterized in that: When establishing the three-dimensional geometric model of the steel tube concrete intersecting welded joint, the properties of the steel, the properties of the concrete and the geometric parameters of the initial defects are defined. The properties of the steel include elastic modulus, Poisson's ratio and yield strength. The properties of the concrete include elastic modulus, Poisson's ratio and compressive strength. The geometric parameters of the initial defects include steel tube diameter, steel tube wall thickness, concrete core diameter, weld thickness and weld length.

5. A safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 1 or 2, characterized in that: Verifying the initial discrimination criteria includes: Fatigue tests were conducted on concrete-filled steel tube node specimens with different initial defects to obtain verification results of the fatigue tests; According to the verification results of the fatigue test, the stress concentration factor and fatigue life of each concrete-filled steel tube node specimen are obtained, specifically: ； in: is the fatigue life of the initial defect under different stress amplitudes, , is the material constant, is the stress amplitude, is the stress concentration factor, is the maximum stress value, is the stress value without defects; The comprehensive evaluation standard of the initial defect is obtained through the stress concentration factor and fatigue life.

6. A safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 5, characterized in that: Through the stress concentration factor and fatigue life, a comprehensive evaluation of the initial defect is obtained, wherein the comprehensive evaluation includes strength evaluation, stiffness evaluation and fatigue life evaluation, specifically: Strength assessment: the influence of pores on the strength of welded joints is less than the influence of slag inclusions on the strength of welded joints. The influence of incomplete penetration on the strength of welded joints is less than the influence of undercut on the strength of welded joints. Stiffness evaluation: the influence of pores on the stiffness of welded joints is less than the influence of slag inclusions on the stiffness of welded joints. The influence of undercuts on the stiffness of welded joints is less than the influence of incomplete penetration on the stiffness of welded joints. Fatigue life assessment: the impact of porosity on the fatigue life of welded joints < the impact of slag inclusion on the fatigue life of welded joints < the impact of incomplete penetration on the fatigue life of welded joints < the impact of undercut on the fatigue life of welded joints.

7. The safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 1 is characterized in that: The total damage after the fusion is obtained, including: Determine the parameters of the dynamic prediction model: determine the material constants through the SN curve, determine the hot spot stress parameters through finite element analysis, and determine the damage accumulation model parameters through the linear damage accumulation model; Update the dynamic prediction model: Update and adjust the damage accumulation process and damage evolution equation of the welded joint at different stress levels, specifically: ； in: is the total damage after the k+1th cycle, is the total damage after the kth cycle, is the remaining life after the k+1th cycle, is the remaining life after the kth cycle, is the actual number of cycles in the k+1th cycle, is the stress amplitude Fatigue life under is the stress amplitude after the k+1th cycle; Fusion dynamic prediction model: The SN curve model, hot spot stress method model and damage accumulation model are integrated to obtain the total damage after integration.

8. A safety assessment method for initial defects of intersecting welded joints of concrete-filled steel tubes according to claim 7, characterized in that: The material constants are determined by the SN curve, specifically: ； in: is the fatigue life, is the stress amplitude, , is the material constant; The damage accumulation model parameters are determined by the linear damage accumulation model, specifically: ； in: is the total damage, is the actual number of cycles loaded at level i, is the stress amplitude Fatigue life under is the stress amplitude of the i-th level loading, The index of the number of loads.

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