A damage and deformation identification method for multi-anchor cable anti-sliding piles suitable for shaking table tests

Abstract

The present invention discloses a method for identifying damage and deformation of multi-anchor cable anti-sliding piles suitable for shaking table tests. The method starts with shaking table test data, adopts B-spline fitting algorithm and Hilbert-Huang transform (HHT) means, identifies damage and deformation of multi-anchor piles under reciprocating seismic loads from the perspective of energy transfer characteristics, and explains the evolution process of earthquake damage and catastrophic changes of multi-anchor piles by combining the distribution trend of pile peak marginal spectrum (PMSA) and macroscopic deformation signs of slope. In addition, by applying the B-spline fitting algorithm to the baseline correction processing of acceleration data, the shortcomings of traditional baseline correction methods such as FIR filtering, least squares fitting, and wavelet transform are made up.

Description

Technical Field

[0001] The invention belongs to the field of earthquake resistance technology, and in particular relates to a damage and deformation identification method for multi-anchor cable anti-sliding piles suitable for shaking table tests. Background Art

[0002] The retaining structure is one of the most widely used and effective measures in slope reinforcement construction, and the pile-anchor retaining structure is currently the most economical, fast, safe and reliable slope support solution. Its design level directly affects the stability of the slope. The slope is generally the weakest earthquake resistance area of ​​the line. Once landslides and other problems occur, the consequences are often immeasurable.

[0003] Retaining structures are generally designed for earthquake resistance through theoretical calculations. When the structure is very complex and the existing calculation theory cannot satisfactorily solve the problem, researchers often use shaking table model tests to directly observe the seismic response and damage form of the structure to evaluate the overall earthquake resistance of the structure. As a key device for structural earthquake resistance testing in earthquake engineering research, the earthquake simulation shaking table can be used to simulate earthquake environments, determine the dynamic characteristics and earthquake resistance of various retaining structures, and test the earthquake resistance of the structure and its damage mechanism under the action of earthquake forces, thereby improving the earthquake resistance design theory and methods.

[0004] Multi-anchor cable anti-slide piles (hereinafter referred to as multi-anchor piles) are one of the effective measures used in the field of geotechnical engineering reinforcement. A survey conducted after the 2008 Wenchuan earthquake showed that this retaining structure showed good seismic performance in earthquakes. However, there is little engineering experience with multi-anchor piles at home and abroad. The earliest proposal and use of multi-anchor piles was in the large-scale complex landslide control project of Beijing Jietai Temple. Some scholars have made a comparative analysis of multi-anchor piles and single-anchor piles, and concluded that multi-anchor piles have great advantages in force, deformation control and economy. However, the current research on damage and deformation of multi-anchor piles is mostly based on the displacement and deformation monitoring of the top of the pile body in model tests or numerical analysis, and has not been studied from the characteristic parameters of the multi-anchor piles themselves and the physical quantities monitored inside the pile body.

[0005] At present, although there are some methods to identify structural damage, such as wavelet analysis and intrinsic modal analysis, these methods have different defects, the main reason being that their analysis results depend on the selected basis functions. When describing non-stationary signals in the time-frequency domain, HHT has excellent time-frequency resolution and can overcome the limitations of traditional signal processing methods. In addition, due to its outstanding time-frequency positioning ability, HHT has been widely used in structural damage detection, marine engineering, earthquake landslide damage identification and other fields. In general, the HHT method has good adaptability and high efficiency in processing seismic signals. However, there is limited research on the identification of seismic damage and deformation of multi-anchor piles using the energy transfer characteristic method, especially the applicability of seismic Hilbert energy spectrum and marginal spectrum to the overall or local damage and deformation of multi-anchor piles needs further discussion.

[0006] The acceleration time course measured in the test is affected by the test conditions and data acquisition, and will contain some noise components, resulting in distortion of the measured data. Distorted acceleration data often manifests as: ① The baseline of the acceleration time course deviates from the zero line (i.e., the baseline when there is no signal); ② The velocity time course obtained after one integration of the measured acceleration time course does not return to zero after the excitation ends. Therefore, before analyzing the acceleration data measured in the test, it is necessary to preprocess the measured acceleration data. The processing methods mainly include filtering and baseline correction. The current baseline correction methods include FIR filtering, least squares fitting, wavelet transform, polynomial fitting, piecewise polynomial fitting, etc. These methods can achieve baseline correction of acceleration data to a certain extent, but they also have their own problems. FIR filtering can easily lead to significant amplitude-frequency distortion; the least squares fitting method needs to predict the type of trend term (DC component, linear component, exponential function, power function, etc.) in advance when fitting the signal. As the complexity of the trend term increases, the difficulty of fitting also increases, which is not suitable for complex actual signals; the selection of wavelet basis functions and the determination of wavelet orders in wavelet transform need to be predicted in advance; polynomial fitting and piecewise polynomial fitting both have the problem of difficulty in determining the fitting order, which leads to underfitting or overfitting. Using the B-spline fitting algorithm for acceleration data baseline correction can not only overcome the problem of difficulty in determining the fitting order and achieve better fitting results, but also has low calculation amount and complexity. Summary of the invention

[0007] Based on the analysis of the acceleration data of the multi-anchor pile test in the shaking table test, combined with the B-spline fitting algorithm and the HHT method, this invention proposes a multi-anchor pile damage deformation identification method suitable for the shaking table test, the purpose of which is to fully identify the earthquake damage deformation of the multi-anchor pile under the action of the earthquake, and infer the disaster evolution process of the multi-anchor pile. The specific technical scheme of the invention is as follows:

[0008] A method for identifying damage and deformation of multi-anchor cable anti-sliding piles suitable for shaking table tests comprises the following steps:

[0009] 1) Design the layout plan of multi-anchor pile acceleration sensors, and arrange the acceleration sensors on the multi-anchor cable anti-sliding piles according to the layout plan;

[0010] 2) Construct a shaking table test model, load multi-level seismic waves according to the test process, and obtain the acceleration response data of multi-anchor piles;

[0011] 3) Filtering: Write a Chebyshev II bandpass filter program in MATLAB software to filter the acceleration data obtained in step 2);

[0012] 4) Baseline correction: Write a B-spline fitting algorithm in MATLAB software to perform baseline correction on the acceleration data processed in step 3);

[0013] 5) Acceleration data after filtering and baseline correction X ( t ) to perform empirical mode decomposition (EMD) and obtain X ( t ) is a series of intrinsic mode function (IMF) components;

[0014] 6) Perform Hilbert transform on each IMF to obtain the instantaneous frequency spectrum curve and Hilbert spectrum curve of each IMF;

[0015] 7) Combining the Hilbert spectrum curves of each IMF in step 6, we get X ( t )'s Hilbert spectrum H ( t,ω ) ；

[0016] 8) Hilbert spectrum H ( t,ω ) is integrated on the time axis, and we get X ( t ) h ( t,ω );extract X ( t ) is the marginal spectrum peak value, denoted as PMSA;

[0017] 9) Identify the seismic damage and deformation of multi-anchor piles based on the distribution of PMSA along the pile body: If PMSA increases with the increase of pile elevation, it indicates that the multi-anchor pile has no dynamic damage; on the contrary, if PMSA at a certain position of the pile body shows a downward trend, it indicates that damage and deformation have occurred at that position of the pile body;

[0018] 10) Draw a distribution cloud map of the PMSA of the pile body changing with seismic excitation, and use the cloud map to determine the damage and deformation development process of multi-anchor piles under multi-level seismic wave excitation.

[0019] Furthermore, in the step 2), the seismic wave loading waveform is EL Centro wave, and the loading system of the multi-level seismic wave is: 0.1g→0.15g→0.2g→0.3g.

[0020] The principle of B-spline fitting algorithm is as follows:

[0021] Assume that there is a spectral data point sequence in two-dimensional space , and the nodes in the x direction are represented by symbol t. Considering x j Usually an increasing sequence, remember:

[0022] (1)

[0023] by t o and t n+1 As the boundary node, the region R = [a, b] is divided internally and expanded externally to obtain a non-decreasing node sequence containing internal nodes, boundary nodes and external nodes { t i};

[0024] (2)

[0025] Where N is the number of internal nodes, k is the order of the B-spline function.

[0026] After the node sequence is determined, x of k Step or k -1 degree B-spline basis function

[0027] It can be recursively calculated by DeBoor-Cox definition

[0028] (3)

[0029] Then, about x of k Step or k -1 degree B-spline curve can be uniquely represented as , where {c j} is the column vector of control coefficients. Here, k It is usually taken as 4.

[0030] Substitute the sample data points Concurrently , we get the matrix form of linear equations

[0031] (4)

[0032] in,

[0033] is the fitting error.

[0034] Usually the number of B-spline basis functions is selected to be smaller than the number of sample data point groups, that is, N+k < n , then equation (4) is an overdetermined system of equations, so the least squares method is used to solve the control coefficients, and the control coefficients can be obtained C n The least squares estimate of .

[0035] (5)

[0036] The B-spline fitting algorithm is used for baseline correction of seismic wave acceleration data. The process is as follows: Figure 2 As shown in the figure. This principle uses the B-spline fitting algorithm to continuously approach the baseline of the acceleration data through a cyclic iteration method. The basic steps are as follows:

[0037] (1) Input the original filtered acceleration data S 0 (m-dimensional vector), and let it be the fitted signal u 0 The initial value of u 0 = S 0 ;

[0038] (2) Yes u 0 Perform B-spline fitting to obtain the fitting curve u n ;

[0039] (3) Comparison u 0 and u n The size of each item is calculated by finding its minimum value and assigning it u 0 ;

[0040] (4) Calculation u n right u 0 If the relative error is greater than the threshold , then return to step 2 and continue the loop; otherwise, end the loop and obtain the baseline u n ;

[0041] (5) Set the baseline u n From the raw acceleration data S 0 Subtract it from the acceleration data to obtain the corrected acceleration data. X(t) .

[0042] The beneficial effects of the present invention are as follows: In the past, the damage and deformation identification of multi-anchor piles was mostly based on the displacement and deformation monitoring of the top of the pile body in model tests or numerical analysis, and failed to start from the characteristic parameters of the multi-anchor piles themselves and the physical quantities monitored inside the pile body; the present invention is based on the acceleration response data of the shaking table model test, and effectively identifies the earthquake damage and deformation of the multi-anchor piles from the perspective of the energy transfer characteristics of the pile body itself. In addition, by applying the B-spline fitting algorithm to the baseline correction processing of acceleration data, the shortcomings of traditional baseline correction methods such as FIR filtering, least squares fitting, and wavelet transform are made up. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic flow chart of the identification method of the present invention;

[0044] Figure 2 It is a schematic diagram of the acceleration baseline correction process by B-spline fitting in step 4) of the present invention;

[0045] Figure 3 This is a schematic diagram of filling the shaking table test model in step 2) of the present invention;

[0046] Figure 4 yes Figure 3 The main view;

[0047] Figure 5 It is a cross-sectional view of the arrangement of the multi-anchor pile acceleration sensor of the present invention;

[0048] Figure 6 It is the EL Centro wave acceleration time history curve diagram of the present invention;

[0049] Figure 7 It is the Fourier spectrum of EL Centro wave acceleration of the present invention;

[0050] Figure 8 is the IMF1-residual of the S01' measuring point under the action of 0.1g seismic wave of the multi-anchor pile of the present invention;

[0051] Fig. 9 is the instantaneous frequency corresponding to each IMF of the present invention;

[0052] Fig.10 It is the marginal spectrum of each measuring point of the pile body under the action of 0.1g seismic wave;

[0053] Fig.11 It is the curve of the marginal spectrum of the pile body measuring point changing with the relative elevation;

[0054] Fig.12 This is the distribution cloud diagram of PMSA of pile body under 0.15g earthquake with earthquake excitation;

[0055] Fig.13 This is the distribution cloud diagram of PMSA of pile body under 0.2g earthquake with earthquake excitation;

[0056] Fig.14 It is the distribution cloud diagram of PMSA of pile body changing with earthquake excitation under 0.3g earthquake. DETAILED DESCRIPTION

[0057] In this case, the shaking table test method is used to study the seismic damage and deformation identification of multi-anchor piles of a tunnel crossing a landslide area under earthquake action. The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0058] 1) First, design the layout plan of the multi-anchor pile acceleration sensor, and arrange the acceleration sensor on the pile body according to the design plan. The acceleration sensor is fixed on the front side of the multi-anchor pile with 302 glue. The acceleration sensor layout is as follows: Figure 5 shown.

[0059] 2) According to the acceleration sensor layout plan, build the vibration table test model. The completed test model is as follows: Figure 3 and 4 As shown. Loading seismic wave test to obtain multi-anchor pile acceleration data. The seismic wave loading waveform is EL Centro wave, and the loading system is: 0.1g→0.15g→0.2g→0.3g.

[0060] 3) Filtering: The acceleration data obtained in step 2) is filtered by programming a Chebyshev II bandpass filter in MATLAB software.

[0061] 4) Baseline correction: The acceleration data processed in step 3) is baseline corrected by writing a B-spline fitting algorithm in MATLAB software. The time course curve of the acceleration data of the input table after filtering and baseline correction is as follows: Figure 6 As shown, the Fourier spectrum is Figure 7 shown.

[0062] 5) Perform empirical mode decomposition (EMD) on the filtered and baseline-corrected data of the time history curve of the pile acceleration measurement point to convert the original signal X ( t ) is decomposed into several IMF components.

[0063] 6) Perform Hilbert transform on each IMF to obtain the instantaneous frequency spectrum and Hilbert spectrum corresponding to each IMF.

[0064] 7) Combining the Hilbert spectra of all IMFs, we can get X ( t )'s Hilbert spectrum H ( t,ω ). The acceleration time history curve of the S01' measurement point under the action of 0.1g EL Centro wave is subjected to EMD decomposition to obtain its corresponding instantaneous spectrum as shown in Figure 8 and 9 shown.

[0065] 8) Hilbert spectrum in the time domain H ( t,ω ) to get X ( t ) h ( t,ω ), where the marginal spectrum of each measuring point of the pile under the action of 0.1g seismic wave is h ( t,ω )as follows Fig.10 9) Extract the peak marginal spectrum amplitude (PMSA) of each measuring point, and draw the curve of the change of PMSA of each measuring point along the relative elevation of the pile under different earthquake intensity excitation as follows Fig.11 shown.

[0066] 9) According to the PMSA variation curve of the pile body measurement point ( Fig.11 ) To identify the damage and deformation of multiple anchor points: It can be seen that when the seismic excitation is 0.1g, the PMSA changes almost steadily with the increase of relative elevation, and there is no obvious decline, indicating that under the action of 0.1g seismic motion, the multi-anchor piles do not have obvious deformation damage. Subsequently, when the seismic excitation is 0.15g and 0.2g, below the relative height of 0.42 (S03'), the PMSA of the multi-anchor piles maintains a nearly linear growth trend. When the relative height exceeds 0.42 (S03'), the PMSA shows a nearly linear decreasing trend, which indicates that the pile body is damaged and deformed at a relative height of 0.42 (S03'). In addition, when the input earthquake intensity is 0.3g, the PMSA of the S02' measuring point drops precipitously. Therefore, under the action of earthquake motion intensity, the damage and deformation of the multi-anchor pile first appeared at a relative height of 0.42 (S03'). As the earthquake motion intensity increased to 0.3g, the pile damage further developed to a relative height of 0.22 (S02').

[0067] 10) Identification of the evolution process of earthquake damage of multi-anchor piles: The surfer10 software is used to draw the distribution cloud diagram of the PMSA of the pile body with earthquake excitation, as shown below Fig.12As shown in step 9, the pile body does not show obvious deformation damage under the 0.1g earthquake intensity, so the 0.1g working condition is not analyzed. Fig.12 It can be seen that the PMSA of the multi-anchor pile under the action of 0.15g earthquake intensity shows a local amplification effect in the middle of the pile body. That is, the PMSA in the pile top area is smaller than that in the middle of the pile body, indicating that the pile top area has been damaged and deformed, resulting in abnormal energy transfer near the pile top. However, due to the low intensity of the earthquake, the pile body was not damaged and still maintained a certain degree of pile body integrity. Fig.13 As shown in Figure 2, when the input earthquake intensity is 0.2g, the damage position of the multi-anchor pile changes from the middle of the pile body to the top of the pile. Fig.14 As shown in the figure, then under the action of 0.3g earthquake wave, the damaged part of the pile body extends downward to the bottom area of ​​the pile, that is, the evolution process of earthquake damage disaster of multi-anchor pile is the progressive cumulative damage from the middle of the pile body to the top of the pile to the bottom of the pile. Under the action of different levels of earthquake motion intensity, multi-anchor piles show the spatial coupling deformation continuity effect of regional damage.

Claims

1. A method for identifying damage and deformation of multi-anchor cable anti-sliding piles suitable for shaking table tests, characterized in that: The following steps are involved: 1) Design the layout plan of multi-anchor pile acceleration sensors, and arrange the acceleration sensors on the multi-anchor cable anti-sliding piles according to the layout plan; 2) Construct a shaking table test model, load multi-level seismic waves according to the test process, and obtain the acceleration response data of multi-anchor piles; 3) Filtering: Write a Chebyshev II bandpass filter program in MATLAB software to filter the acceleration data obtained in step 2); 4) Baseline correction: Write a B-spline fitting algorithm in MATLAB software to perform baseline correction on the acceleration data processed in step 3); 5) Acceleration data after filtering and baseline correction X(t) Perform empirical mode decomposition (EMD) and get X(t) A series of intrinsic mode function (IMF) components of ; 6) Perform Hilbert transform on each IMF to obtain the instantaneous frequency spectrum curve and Hilbert spectrum curve of each IMF; 7) Combining the Hilbert spectrum curves of each IMF in step 6, we get X ( t )'s Hilbert spectrum H ( t,ω ) ； 8) Hilbert spectrum H ( t,ω ) is integrated on the time axis, and we get X ( t ) h ( t,ω );extract X ( t ) is the marginal spectrum peak value, denoted as PMSA; 9) Identify the seismic damage and deformation of multi-anchor piles based on the distribution of PMSA along the pile body: If PMSA increases with the increase of pile elevation, it indicates that the multi-anchor piles have no dynamic damage; On the contrary, if the PMSA at a certain position of the pile body shows a downward trend, it indicates that damage and deformation have occurred at that position of the pile body; 10) Draw a distribution cloud map of the PMSA of the pile body changing with seismic excitation, and use the cloud map to determine the damage and deformation development process of multi-anchor piles under multi-level seismic wave excitation.

2. The damage and deformation identification method for multi-anchor cable anti-sliding piles suitable for shaking table test according to claim 1 is characterized in that: In the step 2), the seismic wave loading waveform is EL Centro wave, and the loading system of the multi-level seismic wave is: 0.1g→0.15g→0.2g→0.3g.

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