Pile foundation damage indirect identification and evaluation method based on high pier vibration test

Abstract

The invention discloses a high pier vibration test-based pile foundation damage indirect identification and evaluation method. The method comprises the following steps of S1, carrying out early-stage preparation and planning; s2, measuring points are arranged on the high pier, the high pier is made to vibrate in an environment excitation mode, and related data in the vibration process are collected; s3, processing and analyzing the acquired data; s4, establishing an intact finite element model of the damaged pile foundation of the high pier according to related materials and the collected data, and calculating a corresponding theoretical flexibility matrix; s5, the change rate of the actually-measured structure flexibility matrix of the high pier relative to the pier pile finite element model flexibility matrix with the intact damaged pile foundation of the high pier is calculated; and S6, analysis is conducted according to the obtained change rate, whether the pile foundation is damaged or not is recognized, and the integrity of the pile body is evaluated. According to the pile foundation damage indirect identification and evaluation method based on the high pier vibration test, the modal vibration characteristics of the pier can be tested in an environment excitation mode, the cost of excitation equipment is saved, and the safety of the pier structure can be guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of bridge pile foundation damage detection, and in particular relates to an indirect identification and evaluation method for pile foundation damage based on high pier vibration testing. Background Art

[0002] In the field of construction engineering, pile foundation is an important part of the supporting structure, and its stability and safety are directly related to the safety and durability of the overall project. As structures such as bridges and high-rise buildings develop towards higher and more complex directions, the application of high pier structures is becoming more and more extensive. However, due to its own characteristics such as high flexibility, high slenderness ratio, and complex structural dynamic characteristics, high pier structures are easily affected by various factors during operation, resulting in damage to the pile foundation, which in turn affects the stability and safety of the overall structure.

[0003] Traditional pile foundation damage identification methods mostly rely on direct means such as direct observation, static load test or local detection. Although these methods can evaluate the damage status of pile foundations to a certain extent, they usually require artificial excitation, which not only requires expensive excitation equipment, but also easily causes local damage to the pier structure, thus having limitations such as high detection cost and potential damage to the structure. Especially for high pier structures, due to their increased height and complexity, the above traditional detection methods are often difficult to comprehensively and accurately evaluate the damage status of pile foundations. Therefore, in order to save costs and ensure the safety of pier structures, a method that can indirectly identify and evaluate pile foundation damage is needed. The present invention solves this technical problem. Summary of the invention

[0004] The present invention provides an indirect identification and assessment method for pile foundation damage based on high pier vibration testing, which can test the modal vibration characteristics of piers by means of environmental excitation, save the cost of excitation equipment, ensure the safety of the pier structure, and comprehensively and accurately identify and assess the damage of the pile foundation.

[0005] An indirect identification and assessment method for pile foundation damage based on high pier vibration test includes the following steps:

[0006] S1. Carry out preliminary preparation and planning, clarify the test objectives and collect relevant materials, and design the plan according to the actual situation;

[0007] S2. Arrange measurement points on the high pier, make the high pier vibrate by environmental excitation, and collect relevant data during the vibration process;

[0008] S3, process and analyze the collected data;

[0009] S4. Based on the relevant materials and collected data, a finite element model of the intact high pier damaged pile foundation is established, and the corresponding theoretical flexibility matrix is ​​calculated;

[0010] S5, calculating the change rate of the measured structural flexibility matrix of the high pier relative to the flexibility matrix of the finite element model of the pier pile with intact damaged pile foundation;

[0011] S6. Analyze the obtained change rate to identify whether the pile foundation is damaged and evaluate the integrity of the pile body.

[0012] Further, the step S4 includes the following steps:

[0013] S41. Establish the initial pier and pile finite element model of high pier and pile foundation according to relevant materials;

[0014] S42, based on the collected high pier data, modifying the pier elastic modulus of the initial pier pile finite element model to obtain a pier pile finite element model with intact high pier damaged pile foundation;

[0015] S43. Calculate the theoretical flexibility matrix of the intact finite element model of the damaged pile foundation of the high pier.

[0016] Furthermore, in step S42, the process of correcting the elastic modulus of the bridge pier of the initial pier pile finite element model is as follows:

[0017] S421. Based on the vibration frequency of the high pier, the square sum of the relative errors between the first two calculated frequencies and the measured frequencies of the initial pier pile finite element model is used as the objective function, the relative errors between the first two calculated frequencies and the measured frequencies are used as the state variables, and the design variables are the elastic modulus of the high pier;

[0018] S422, wherein the design variables are expressed in the following manner:

[0019] x=(x1,x1,…,x n ) T

[0020] Among them, x i represents the i-th design variable, T represents the transpose operation of the vector, and n represents the number of design variables;

[0021] S423, the objective function is expressed as:

[0022]

[0023]

[0024] u i ≤q i ≤l i , i=1,2,…,m

[0025] Among them, F obj is the objective function, n is the modal order, f ai To calculate the frequency, f ei is the measured frequency, and the constraints are: U ai with U ei represent the calculated frequency and the measured frequency, respectively, and b i represents the i-th error, q i represents the i-th parameter to be corrected, u i and l i Represents the upper and lower limits of the i-th parameter to be corrected. The objective function continues to decrease under the constraints and eventually converges. The parameter values ​​when the objective function converges are the optimal solution.

[0026] Furthermore, in step S421, the state variable is calculated as follows:

[0027] S4211. The state variable is expressed as:

[0028] E=(f c -f m ) / f m

[0029] Among them, f c The frequency value for the first two vertical bending calculations, f m is the measured frequency value of the first two-order vertical bending, and its constraint condition is set to ±10%, that is, the range of E is [-0.1, 0.1], so there are two state variables;

[0030] S4212, set the objective function J as follows:

[0031]

[0032] E in the formula i Corresponding to two state variables, is the weight factor of each state variable:

[0033]

[0034] because And the corresponding frequency error E i It is proportional to the square of , so that each optimization iteration process can proceed in the direction of rapidly decreasing objective function value, which can improve the optimization efficiency.

[0035] Furthermore, in step S42, the matching between the modified finite element model of the pier pile and the actual test modal vibration mode of the bridge pier is calculated and analyzed, and the modal correlation criterion MAC can be used to characterize it. The calculation expression of MAC is as follows:

[0036]

[0037] In the formula, represents the calculated mode shape vector, They represent the measured vibration mode vectors respectively. The higher the MAC value, the better the correlation between the vibration modes.

[0038] Furthermore, in step S43, the modal flexibility of the high pier structure can be expressed as:

[0039]

[0040] In the formula, [F d ] is the structural modal flexibility, To identify the structural vibration mode, is the normalized vibration shape, n represents the total order of the identified modes, ω r is the rth order natural frequency of the structure;

[0041] From the above formula, we can see that due to the 1 / ω of the high-order frequency 2 The value is small, and the flexibility matrix is ​​mainly determined by the low-order modal parameters. Therefore, as long as the low-order modes of the pier are identified, a more accurate flexibility matrix can be obtained.

[0042] Furthermore, the step S5 comprises:

[0043] S51, calculating the difference in diagonal element flexibility between the measured structural flexibility matrix of the high pier and the theoretical flexibility matrix of the finite element model of the pier with intact damaged pile foundation;

[0044] S52. Calculate the flexibility change rate of the diagonal elements of the measured structural flexibility matrix of the high pier relative to the theoretical flexibility matrix of the finite element model of the pier with intact damaged pile foundation.

[0045] Furthermore, the step S3 includes:

[0046] S31, performing preprocessing operations including denoising and filtering on the collected vibration signal to improve signal quality;

[0047] S32. Use modal analysis technology to extract the modal parameters of high piers including natural frequency, damping ratio and vibration mode.

[0048] Furthermore, the step S2 comprises:

[0049] S21. Select representative measuring points on the high pier;

[0050] S22. Install a sensor for detecting vibration at the selected measuring point, ensuring that the sensor is firmly fixed and can accurately capture the vibration signal;

[0051] S23. According to the test plan, the high pier is vibrated by using environmental excitation;

[0052] S24. Start the data acquisition system to record the acceleration response data of the high pier during vibration.

[0053] Furthermore, the step S1 includes:

[0054] S11. Clarify the specific objectives of the test, including identifying the specific damage location of the pile foundation and assessing the extent of the damage;

[0055] S12. Collect relevant information including design drawings of high piers and their pile foundations, geological survey reports, and historical maintenance records;

[0056] S13. Design a reasonable vibration test plan based on the actual situation of the target and high pier, including measurement point layout, test equipment selection, and test time.

[0057] The technical effects of the present invention are as follows:

[0058] (1) The indirect identification and evaluation method of pile foundation damage based on high pier vibration test provided by the present invention only needs to install an acceleration sensor on the high pier, then obtain the frequency vibration mode and measured flexibility matrix of the high pier tested under environmental excitation, and establish an initial finite element model of the high pier and pile foundation, then correct the pier elastic modulus of the initial pier-pile finite element model according to the measured frequency of the high pier, obtain the pier-pile finite element model of the high pier damaged pile foundation and intact, and calculate the theoretical flexibility matrix of the finite element model of the high pier damaged pile foundation and intact, and finally calculate the change rate of the measured flexibility matrix relative to the theoretical flexibility matrix of the high pier damaged pile foundation and intact model, so as to comprehensively and quantitatively evaluate the pile foundation condition, thereby eliminating the need to interrupt the bridge deck traffic, knock on the pier pile foundation and other structures for testing, and thus will not cause any damage to the pile foundation, and there is no need to use excitation equipment, thus saving costs and improving the safety of the structure;

[0059] (2) This scheme uses environmental excitation to excite the high pier structure and analyzes the collected data without the need for artificial excitation using excitation equipment, thereby making up for the shortcomings of existing pile foundation damage detection technology, improving the efficiency and convenience of non-destructive testing of pile foundation integrity, and providing a new method and basis for determining the specific type of pile foundation damage in non-destructive testing;

[0060] (3) This scheme adopts environmental excitation. It only needs to measure the pier response caused by environmental excitations such as traffic load, wind, and water flow to identify the modal parameters of the high pier. There is no need to use artificial excitation. While ensuring the safety of the structure, there is no need to close the traffic for testing, which improves the practicality of this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1Flow chart of the correction process of the present invention.

[0062] Figure 2 This is a picture of the high pier at the test site.

[0063] Figure 3 Finite element model diagram for pier and pile.

[0064] Figure 4 This is the layout diagram of the high pier measurement points for the test plan.

[0065] Figure 5 This is the finite element model diagram of pier damage and pile damage.

[0066] Figure 6 It is the acceleration time history curve.

[0067] Figure 7 This is the measured vibration mode diagram of the high pier.

[0068] Figure 8 Schematic diagram of the theoretical frequency of the finite element model of good pier and good pile and the measured frequency of the finite element model of damaged pier and damaged pile.

[0069] Fig. 9 Schematic diagram of parameter correction value and change rate.

[0070] Fig.10 This is a comparison chart of the frequency correction value of the good finite element model of the pier damaged pile and the measured value of the finite element model of the pier damaged pile.

[0071] Fig.11 Schematic diagram of the theoretical flexibility matrix of the modified finite element model of damaged piles.

[0072] Fig.12 Schematic diagram of the measured flexibility matrix of the pier pile.

[0073] Fig.13 Schematic diagram of the diagonal element difference and diagonal element change rate of the flexibility matrix. DETAILED DESCRIPTION

[0074] 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. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the present invention and its application or use. 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. Unless otherwise specifically stated, the relative arrangement of the components and steps, expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention.

[0075] At the same time, it should be understood that for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technologies, methods and devices known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods and devices should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0076] An indirect identification and assessment method for pile foundation damage based on high pier vibration test includes the following steps:

[0077] S1. Carry out preliminary preparation and planning, clarify the test objectives and collect relevant materials, and design the plan according to the actual situation;

[0078] S2. Arrange measurement points on the high pier, make the high pier vibrate by environmental excitation, and collect relevant data during the vibration process;

[0079] S3, process and analyze the collected data;

[0080] S4. Based on the relevant materials and collected data, a finite element model of the intact high pier damaged pile foundation is established, and the corresponding theoretical flexibility matrix is ​​calculated;

[0081] S5, calculating the change rate of the measured structural flexibility matrix of the high pier relative to the flexibility matrix of the finite element model of the pier pile with intact damaged pile foundation;

[0082] S6. Analyze the obtained change rate to identify whether the pile foundation is damaged and evaluate the integrity of the pile body.

[0083] A positive flexibility change rate indicates that the pile foundation is damaged and the lateral stiffness of the pile foundation cannot meet the design requirements. A larger positive flexibility change rate indicates a greater degree of damage to the pile foundation. A negative flexibility change rate indicates that the lateral stiffness of the pile foundation meets the design requirements. This allows a comprehensive assessment of whether the actual pile foundation meets the design requirements and forms a test report.

[0084] Further, the step S4 includes the following steps:

[0085] S41. Establish the initial pier and pile finite element model of high pier and pile foundation according to relevant materials;

[0086] S42, based on the collected high pier data, modifying the pier elastic modulus of the initial pier pile finite element model to obtain a pier pile finite element model with intact high pier damaged pile foundation;

[0087] S43. Calculate the theoretical flexibility matrix of the intact finite element model of the damaged pile foundation of the high pier.

[0088] In actual engineering, the theoretical calculation values ​​of the bridge finite element model established according to drawings, specifications and other standards are often far from the measured values ​​obtained through experiments, and even cannot meet the accuracy required by actual engineering. That is, the established finite element model cannot reflect the actual working state of the structure. Therefore, in order to make the calculated values ​​of the structural finite element model parameters consistent with the measured values, it is very necessary to correct the established structural finite element model.

[0089] This solution applies a dynamic-based finite element model correction method, specifically a parametric correction method. The parametric correction method refers to correcting some parameters in the model so that the calculated value of the corrected model is close to the measured value. The correction parameters generally select elastic modulus, density, and boundary conditions. The parametric correction method is similar to the structural optimization theory. The error of dynamic information under the same excitation is constructed as the objective function, and then a part of the physical parameters in the finite element model is changed to minimize the objective function for correction. Because the objective function is generally nonlinear, an iterative optimization algorithm is often selected during the optimization calculation.

[0090] Since the order of the measured modal parameters of the bridge pier is limited, and the larger the order, the larger the modal error of the identification, in order to avoid the morbid problem caused by the error in the correction solution process, the target value of the correction should select the modal parameter with smaller error. In the process of modal parameter identification, the accuracy of frequency is higher than that of vibration mode and damping ratio. In this paper, the elastic modulus of high pier concrete is selected as the parameter to be corrected.

[0091] Furthermore, in step S42, the process of correcting the elastic modulus of the bridge pier of the initial pier pile finite element model is as follows:

[0092] S421. Based on the vibration frequency of the high pier, the square sum of the relative errors between the first two calculated frequencies and the measured frequencies of the initial pier pile finite element model is used as the objective function, the relative errors between the first two calculated frequencies and the measured frequencies are used as the state variables, and the design variables are the elastic modulus of the high pier;

[0093] S422, wherein the design variables are expressed in the following manner:

[0094] x=(x1,x1,…,x n ) T

[0095] Among them, x i represents the i-th design variable, T represents the transpose operation of the vector, and n represents the number of design variables; the design variable x i The constraints are in, x i and They represent the design variables x i The upper and lower limit constraints;

[0096] S423, the objective function is expressed as:

[0097]

[0098] u i ≤q i ≤l i , i=1,2,…,m

[0099] Among them, F obj is the objective function, n is the modal order, f ai To calculate the frequency, f ei is the measured frequency, and the constraints are: U ai with U ei represent the calculated frequency and the measured frequency, respectively, and b i represents the i-th error, q i represents the i-th parameter to be corrected, u i and l i Represents the upper and lower limits of the i-th parameter to be corrected. The objective function continues to decrease under the constraints and eventually converges. The parameter values ​​when the objective function converges are the optimal solution.

[0100] In engineering and physics, calculating the first two natural frequencies of a system usually refers to modal analysis, which is especially common in mechanical, civil and aerospace engineering. It is usually performed through specialized finite element analysis software, such as ANSYS, ABAQUS or NASTRAN. These software provide powerful computing power and user-friendly interface, which can effectively handle complex engineering problems. This part belongs to the existing technology known to technicians in this field and will not be described in detail here.

[0101] Furthermore, in step S421, the state variable is calculated as follows:

[0102] S4211. The state variable is expressed as:

[0103] E=(f c -f m ) / f m

[0104] Among them, f c The frequency value for the first two vertical bending calculations, f m is the measured frequency value of the first two-order vertical bending, and its constraint condition is set to ±10%, that is, the range of E is [-0.1, 0.1], so there are two state variables;

[0105] S4212, set the objective function J as follows:

[0106]

[0107] E in the formulai Corresponding to two state variables, is the weight factor of each state variable:

[0108]

[0109] because And the corresponding frequency error E i It is proportional to the square of , so that each optimization iteration process can move in the direction of rapidly decreasing the objective function value, which can improve the optimization efficiency. The coefficient 10000 is to increase the objective function value.

[0110] Furthermore, in step S42, the matching between the modified finite element model of the pier pile and the actual test modal vibration mode of the bridge pier is calculated and analyzed, and the modal correlation criterion MAC can be used to characterize it. The calculation expression of MAC is as follows:

[0111]

[0112] In the formula, represents the calculated mode shape vector, They represent the measured vibration mode vectors respectively. The higher the MAC value, the better the correlation between the vibration modes, that is, the smaller the difference. The lower the MAC value, the greater the difference. Through the evaluation of the MAC criterion, the difference between the modified finite element model and the actual test results can be quantified, helping engineers evaluate the accuracy and reliability of the model.

[0113] Furthermore, in step S43, the modal flexibility of the high pier structure can be expressed as:

[0114]

[0115] In the formula, [F d ] is the structural modal flexibility, To identify the structural vibration mode, is the normalized vibration shape, n represents the total order of the identified modes, ω r is the rth order natural frequency of the structure;

[0116] From the above formula, we can see that due to the 1 / ω of the high-order frequency 2 The value is small, and the flexibility matrix is ​​mainly determined by the low-order modal parameters. Therefore, as long as the low-order modes of the pier are identified, a flexibility matrix with high accuracy can be obtained. The establishment of the flexibility matrix belongs to the prior art known to those skilled in the art and will not be described in detail here.

[0117] Furthermore, the step S5 comprises:

[0118] S51, calculating the difference in diagonal element flexibility between the measured structural flexibility matrix of the high pier and the theoretical flexibility matrix of the finite element model of the pier with intact damaged pile foundation;

[0119] S52. Calculate the flexibility change rate of the diagonal elements of the measured structural flexibility matrix of the high pier relative to the theoretical flexibility matrix of the finite element model of the pier with intact damaged pile foundation.

[0120] Specifically, the diagonal element flexibility change rate can be obtained by:

[0121] Extract diagonal elements from the measured flexibility matrix and the finite element model flexibility matrix respectively. These diagonal elements usually represent the displacement response under the unit load on each degree of freedom;

[0122] For each diagonal element, calculate the change rate of its measured value relative to the theoretical value of the finite element model. The change rate can be calculated by the following formula:

[0123]

[0124] Among them, Δ measured represents the diagonal elements of the measured flexibility matrix, Δ FEM are the diagonal elements of the flexibility matrix of the finite element model;

[0125] Then, the change rate of the diagonal elements at each degree of freedom is analyzed to evaluate the impact of the damage on the structural flexibility. A higher change rate may indicate that the structure has more severe damage at that degree of freedom.

[0126] Furthermore, the step S3 includes:

[0127] S31, performing preprocessing operations including denoising and filtering on the collected vibration signal to improve signal quality;

[0128] S32. Use modal analysis technology to extract the modal parameters of high piers including natural frequency, damping ratio and vibration mode.

[0129] Furthermore, the step S2 comprises:

[0130] S21. Select representative measuring points on the high pier, usually including the pier top, different heights of the pier body, and key locations that may be affected by pile foundation damage;

[0131] S22. Install a sensor for detecting vibration at the selected measuring point, ensuring that the sensor is firmly fixed and can accurately capture the vibration signal. Specifically, a horizontal vibration pickup or an acceleration sensor may be used;

[0132] S23. According to the test plan, use environmental excitation methods (such as wind, traffic load, etc.) to make the high pier vibrate;

[0133] S24, start the data acquisition system to record the acceleration response data of the high pier during the vibration process. The data acquisition system (DAS) is a prior art and will not be described in detail here.

[0134] Furthermore, the step S1 includes:

[0135] S11. Clarify the specific objectives of the test, including identifying the specific damage location of the pile foundation and assessing the extent of the damage;

[0136] S12. Collect relevant information including design drawings of high piers and their pile foundations, geological survey reports, and historical maintenance records;

[0137] S13. Design a reasonable vibration test plan based on the actual situation of the target and high pier, including measurement point layout, test equipment selection, and test time.

[0138] Specifically, the specific testing process of this embodiment is as follows:

[0139] See also Figure 1 In order to establish a reasonable finite element model, it is necessary to modify the dynamic model of the initial pier and pile finite element model so that the modified model can better and comprehensively reflect the overall dynamic and static performance of the structure. According to the actual situation, a suitable method can be selected. The process adopted in this embodiment is as follows: Figure 1 As shown in the figure, first, based on the APDL language, parametric modeling and nonlinear dynamic and static force analysis of the high pier structure are carried out, and post-processing is performed to extract the analysis results; then the calculated value obtained by analysis is compared with the measured value to determine whether correction is needed; when the calculated value is significantly different from the measured value and correction is needed, it is necessary to select the parameters to be corrected based on the eigenvalue sensitivity analysis and ignore the parameters with lower sensitivity; then enter the optimization module, OPT (Opt) iStruct is a finite element software with an optimization module; then refer to the nonlinear static analysis results to determine the upper and lower limit constraints of the parameters to be modified (design variables); then declare the state variables: specify the calculated value of the natural frequency of the structure as the state variable, and determine its reasonable constraints based on the measured values; define the objective function: specify the relative error between the calculated and measured values ​​of the natural frequency of the structure (high pier) as the objective function, and use a weighted method to consider the degree of fit required by different orders; specify the first-order algorithm as the optimization algorithm, and select an appropriate optimization iteration process control method; then start the optimization analysis and save the result file of each optimization iteration process; then analyze the final optimization result and judge whether the optimization result is reasonable. When the difference between the optimized calculated value and the measured value is small, the optimization result is considered reasonable. The specific process in the above content will be mentioned below;

[0140] See also Figure 2The bridge of a highway project is a high-pier three-span continuous beam bridge. Its superstructure is composed of 6 small box beams. The span of each main beam is 40m and the width is 3.04m. The 11th pier on the right side of the bridge contains 3 piers. The cross section of the pier is a circular cross section with a diameter of 2.2m. The center point distance between two adjacent piers is 7.448m. From left to right, the heights of these three piers (excluding the cap beam) are 25.227m, 25.268m and 25.309m respectively. The pile foundation length is 48m and the pile diameter is 2.2m.

[0141] See also Figure 3 , according to the bridge design drawings, the initial finite element model of the high pier pile foundation is established, that is, the initial finite element model of the pier pile with good pier. The current bridge foundation specification considers the pile as a beam supported on an elastic foundation and satisfies the Winkler assumption. Therefore, according to the elastic foundation beam theory, the pile foundation can be simulated by a beam unit, and the interaction between the pile and the soil is simulated by setting the soil spring according to the m method. The lateral horizontal force of the soil on the pile can be simulated by a group of horizontal springs, and the pile bottom support reaction can be simulated by a group of vertical springs.

[0142] See also Figure 4 According to the detection plan, three acceleration sensors are arranged vertically along the high pier, and they are numbered in sequence from left to right and from top to bottom. The measurement point arrangement is as follows: Figure 4 The longitudinal horizontal acceleration time history response data of the high pier was collected under environmental excitation. To ensure the accuracy of the collected data, two sets of data were collected, each lasting 30 minutes, and the sampling frequency was set to 500 Hz;

[0143] See also Figure 5 In order to make full use of the finite element software to simulate the damage of the actual bridge, the unit cross-sectional area within the upper 5-15m range of the pile foundation of the finite element model of pier and pile is reduced by 30% to achieve the effect of simulating pile foundation damage. Similarly, the unit cross-sectional area within the upper 15-25m range of the high pier of the finite element model of pier and pile is reduced by 30% to achieve the effect of simulating high pier damage, thereby establishing a finite element model of pier damage and pile damage, such as Figure 5 As shown in the figure, the finite element model can fully simulate the high piers and pile foundations of actual projects, and its vibration response is the vibration response of the actual pier-pile structure;

[0144] See also Figure 6 , a Gaussian white noise with a duration of 150s and a mean of 0 is applied to the finite element model of pier damage and pile damage to simulate the effects of environmental excitations such as ground pulsation, and the horizontal acceleration response of each measuring point of the finite element model of pier damage and pile damage under environmental excitation is extracted;

[0145] See also Figure 7, using SSI, EFDD and other modal parameter identification methods to analyze the vibration acceleration time history response data of the finite element model of pier damage and pile damage under white noise excitation, identify the frequency, vibration mode and other modal characteristics of the finite element model of pier damage and pile damage, and identify the first two frequencies of the pier pile structure as 0.65Hz and 4.517Hz;

[0146] In order to improve the efficiency of optimization correction, it is necessary to select reasonable parameters to be corrected. Based on the eigenvalue sensitivity analysis, insensitive parameters are removed, and the elastic modulus of the high pier unit of the finite element model of good pier and good pile is selected as the parameter to be corrected. The finite element model of good pier and good pile is corrected. Here, mainly based on engineering experience, the upper and lower limits of the design parameters are set to ±10%, that is, the high pier design elastic modulus E0 = 35GPa, then its allowable variation range is [0.9E0, 1.1E0], that is, [31.5, 38.5]. Eigenvalue sensitivity analysis is a prior art known to those skilled in the art and will not be described in detail here.

[0147] See also Figure 8 The theoretical frequency of the finite element model of good piles and good piers for the first two stages and the measured frequency of the finite element model of damaged piers and damaged piles are as follows: Figure 8 As shown, it can be seen that the frequency of the initial finite element model of the pier pile is very different from that of the measured pier. The initial finite element model of the pier pile cannot represent the actual pier and pile foundation. It is necessary to correct the model to obtain a good finite element model of the pier pile with good pier damage. The first-order optimization method of finite element model correction is adopted. The measured pier frequency of the finite element model of the pier damage pile is used as the state variable to construct the optimization objective function.

[0148] See also Fig. 9 , Fig.10 , the correction value and change rate of the pier elastic model parameters are as follows: Fig. 9 As shown in the figure, the relative error between the theoretical frequency and the measured frequency after the first two corrections of the pier pile structure is as follows: Fig.10 As shown in the figure, it can be seen that the relative error between the measured value and the corrected value is 5.5% at most and 2.4% at least; the frequency value of the finite element model of the pier pile after correction is closer to the measured value, so the damage state of the pier is taken into account in the finite element model of the damaged pier pile, and the finite element model of the damaged pier pile can be used as the original design model of the pile foundation;

[0149] See also Fig.11 , Fig.12, the first two frequencies and first two vibration modes of the measured bridge are identified to calculate the flexibility matrix of the finite element model of the damaged pier pile. The flexibility matrix is ​​the flexibility matrix of the measured pier pile in the engineering application. Then, the theoretical frequency vibration mode of the good finite element model of the damaged pier pile is obtained by the finite element model correction method to calculate the theoretical flexibility matrix of the good finite element model of the damaged pier pile. The change rate of the measured flexibility matrix of the pier pile and the theoretical flexibility matrix of the good finite element model of the damaged pier pile are compared to analyze whether the pile foundation is damaged and evaluate the integrity of the pile body, and judge whether the actual pile length meets the design requirements;

[0150] See also Fig.13 , calculate the difference between the measured flexibility matrix of the pier pile and the theoretical flexibility matrix of the modified finite element model of the damaged pier pile and the change rate of the diagonal elements of the flexibility matrix, according to Fig.13 It can be seen that the change rate of the measured flexibility matrix of the pier pile has a significant change compared with the theoretical flexibility matrix of the finite element model of the optimized pier damaged pile. In particular, the flexibility change rate of measuring points 3, 6, and 9 at the pier-column connection is relatively large, with a change rate of 34%-36%, indicating that the test pile foundation may have defects such as broken piles, necking, and insufficient pile length. Therefore, the indirect identification and evaluation method of pile foundation damage based on high pier vibration test can comprehensively evaluate the integrity and pile length of the inspected pile foundation, form a reliable test report, greatly reduce the time cost of batch pile foundation testing, with high accuracy and strong reliability, and more economical, practical and convenient testing.

[0151] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for indirect identification and assessment of pile foundation damage based on high pier vibration test, characterized in that: The following steps are involved: S1. Carry out preliminary preparation and planning, clarify the test objectives and collect relevant materials, and design the plan according to the actual situation; S2. Arrange measurement points on the high pier, make the high pier vibrate by environmental excitation, and collect relevant data during the vibration process; S3, process and analyze the collected data; S4. Based on the relevant materials and collected data, a finite element model of the intact high pier damaged pile foundation is established, and the corresponding theoretical flexibility matrix is ​​calculated; S5, calculating the change rate of the measured structural flexibility matrix of the high pier relative to the flexibility matrix of the finite element model of the pier pile with intact damaged pile foundation; S6. Analyze the obtained change rate to identify whether the pile foundation is damaged and evaluate the integrity of the pile body.

2. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 1 is characterized in that: The step S4 comprises the following steps: S41. Establish the initial pier and pile finite element model of high pier and pile foundation according to relevant materials; S42, based on the collected high pier data, modifying the pier elastic modulus of the initial pier pile finite element model to obtain a pier pile finite element model with intact high pier damaged pile foundation; S43. Calculate the theoretical flexibility matrix of the intact finite element model of the damaged pile foundation of the high pier.

3. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 2 is characterized in that: In step S42, the process of correcting the elastic modulus of the bridge pier of the initial pier pile finite element model is as follows: S421. Based on the vibration frequency of the high pier, the square sum of the relative errors between the first two calculated frequencies and the measured frequencies of the initial pier pile finite element model is used as the objective function, the relative errors between the first two calculated frequencies and the measured frequencies are used as the state variables, and the design variables are the elastic modulus of the high pier; S422, wherein the design variables are expressed in the following manner: x=(x1, x1,…, x n ) T Among them, x i represents the i-th design variable, T represents the transpose operation of the vector, and n represents the number of design variables; S423, the objective function is expressed as: u i ≤q i ≤l i ,i=1,2,…,m Among them, F obj is the objective function, n is the modal order, f ai To calculate the frequency, f ei is the measured frequency, and the constraints are: U ai with U ei represent the calculated frequency and the measured frequency respectively, b i represents the i-th error, q i represents the i-th parameter to be corrected, u i and l i Represents the upper and lower limits of the i-th parameter to be corrected. The objective function continues to decrease under the constraints and eventually converges. The parameter values ​​when the objective function converges are the optimal solution.

4. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 3 is characterized in that: In step S421, the state variable is calculated as follows: S4211. The state variable is expressed as: E=(f c -f m ) / f m Among them, f c The frequency value for the first two vertical bending calculations, f m is the measured frequency value of the first two-order vertical bending, and its constraint condition is set to ±10%, that is, the range of E is [-0.1, 0.1], so there are two state variables; S4212, set the objective function J as follows: E in the formula i Corresponding to two state variables, is the weight factor of each state variable: because And the corresponding frequency error E i It is proportional to the square of , so that each optimization iteration process can proceed in the direction of rapidly decreasing objective function value, which can improve the optimization efficiency.

5. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 4 is characterized in that: In step S42, the matching between the modified finite element model of the pier and the actual test modal vibration mode of the pier is calculated and analyzed, which can be characterized by the modal correlation criterion MAC. The calculation expression of MAC is as follows: In the formula, represents the calculated mode shape vector, They represent the measured vibration mode vectors respectively. The higher the MAC value, the better the correlation between the vibration modes.

6. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 2 is characterized in that: In step S43, the modal flexibility of the high pier structure can be expressed as: In the formula, [F d ] is the structural modal flexibility, To identify the structural vibration mode, is the normalized vibration shape, n represents the total order of the identified modes, ω r is the rth order natural frequency of the structure; From the above formula, we can see that due to the 1 / ω of the high-order frequency 2 The value is small, and the flexibility matrix is ​​mainly determined by the low-order modal parameters. Therefore, as long as the low-order modes of the pier are identified, a more accurate flexibility matrix can be obtained.

7. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 2 is characterized in that: The step S5 comprises: S51, calculating the difference in diagonal element flexibility between the measured structural flexibility matrix of the high pier and the theoretical flexibility matrix of the finite element model of the pier with intact damaged pile foundation; S52. Calculate the flexibility change rate of the diagonal elements of the measured structural flexibility matrix of the high pier relative to the theoretical flexibility matrix of the finite element model of the pier with intact damaged pile foundation.

8. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 1 is characterized in that: The step S3 comprises: S31, performing preprocessing operations including denoising and filtering on the collected vibration signal to improve signal quality; S32. Use modal analysis technology to extract the modal parameters of high piers including natural frequency, damping ratio and vibration mode.

9. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 1 is characterized in that: The step S2 comprises: S21. Select representative measuring points on the high pier; S22. Install a sensor for detecting vibration at the selected measuring point, ensuring that the sensor is firmly fixed and can accurately capture the vibration signal; S23. According to the test plan, the high pier is vibrated by using environmental excitation; S24. Start the data acquisition system to record the acceleration response data of the high pier during vibration.

10. The indirect identification and assessment method for pile foundation damage based on high pier vibration test according to claim 1, characterized in that: The step S1 comprises: S11. Clarify the specific objectives of the test, including identifying the specific damage location of the pile foundation and assessing the extent of the damage; S12. Collect relevant information including design drawings of high piers and their pile foundations, geological survey reports, and historical maintenance records; S13. Design a reasonable vibration test plan based on the actual situation of the target and high pier, including measurement point layout, test equipment selection, and test time.

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