PSC structure grouting void rate quantification method based on frequency mixing combined harmonic waves

Abstract

The invention discloses a PSC structure grouting void rate quantification method based on frequency mixing combined harmonics, and belongs to the technical field of grouting void detection.The PSC structure grouting void rate quantification method comprises the following steps that pearl wool is wound on the surface of a steel strand to simulate void, the axial length is kept unchanged, and the circumferential winding range is changed to adjust the void rate; ultrasonic guided wave sensors are installed on the sections of the two ends of the steel strand, and guided wave signals are excited and received in a one-transmitting and one-receiving mode; applying a sine frequency mixing signal which is modulated by a Hanning window and of which the center frequency is sum to the excitation sensor, and recording an ultrasonic guided wave signal of the receiving sensor; converting the time domain signal into a frequency domain signal; recording amplitudes at the second harmonic frequency and the combined harmonic frequency; calculating a damage index DI according to the amplitude; and establishing a relationship between the DI value and the void ratio thereof under different void ratios. The method needs baseline data and is not influenced by nonlinearity of an instrument, the proposed damage index is sensitive to the change of the void rate, and the void rate can be sensitively monitored.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of grouting void detection, and particularly relates to a PSC structure grouting void rate quantification method based on mixed combination harmonics. BACKGROUND

[0002] In a prestressed concrete (PSC) structure, grouting compactness is a key factor to ensure that the steel strand and the surrounding concrete work cooperatively, prevent corrosion, and prevent structural failure. However, construction process defects or long-term environmental erosion can easily cause voids to occur at the interface between the grouting layer and the steel strand, and early detection and quantitative evaluation of such defects are crucial to structural safety. Traditional detection methods such as the knocking method and linear ultrasonic parameter-based guided wave technology have significant limitations: the knocking method relies on the experience of the operator and cannot be quantitatively analyzed; the linear ultrasonic guided wave technology (such as amplitude attenuation and wave velocity change) is not sensitive enough to small voids, and is affected by the non-uniformity of the concrete material, the multiple reflections at the steel strand-grouting interface, and the boundary effect, making it difficult to accurately quantify the length of the voids.

[0003] Therefore, there is an urgent need for a PSC structure grouting void rate quantification method based on mixed combination harmonics to solve the above problems. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a PSC structure grouting void rate quantification method based on mixed combination harmonics, which does not require baseline data and is not affected by instrument nonlinearity. The proposed damage index is sensitive to changes in void rate and can sensitively monitor the development of voids.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions: The present application provides a PSC structure grouting void rate quantification method based on mixed combination harmonics, comprising the following steps: S1: wrapping pearl wool around the surface of the steel strand to simulate voids, keeping the axial length unchanged and changing the circumferential wrapping range to adjust the void rate; S2: installing ultrasonic guided wave sensors at the cross sections of both ends of the steel strand, and exciting and receiving guided wave signals in a one-transmit-one-receive manner; S3: applying a sinusoidal mixed signal with a center frequency of and Hz modulated by a Hanning window to the excitation sensor, and recording the ultrasonic guided wave signal of the receiving sensor; S4: converting the time-domain signal to a frequency-domain signal by fast Fourier transform; S5: recording the amplitudes at the second harmonic frequency and the combination harmonic frequency, and repeating steps S3, S4 and S5; S6: calculating the damage index DI according to the amplitudes recorded in step S5; S7: Establishing the linear fitting equation of the value and its void ratio to calculate the void ratio DI .

[0006] Further, in step S5, the combined harmonic frequency includes: .

[0007] Further, the frequency and the frequency satisfy: The ratio of is not an integer, and the second harmonic and the combined harmonic frequency do not overlap in the frequency domain.

[0008] Further, in step S6, the calculation formula of the damage index DI is ： In the formula, and represent the amplitude at the fundamental frequency, and represent the amplitude at the multiple frequency, and represent the amplitude at the second-order combined sum and difference frequency, and represent the amplitude at the third-order combined sum frequency.

[0009] Further, in step S7, the linear fitting equation is: In the formula, is the intercept; is the slope, representing the proportional coefficient of the value DI with the change of the void ratio .

[0010] Further, in step S3, the window function length L of the Hanning window satisfies: In the formula, is the propagation speed of the guided wave in the steel strand.

[0011] Further, in step S7, the environmental temperature error compensation is introduced to calculate the void ratio : In the formula, is the correction amount caused by the environmental temperature, , ​​​​Temperature coefficient, T is the measured ambient temperature.

[0012] The beneficial effects of the present application are: 1. The present application solves the problem of traditional methods relying on baseline data and being susceptible to instrument nonlinear interference through mixed frequency harmonic detection technology 2. The present application overcomes the limitation of requiring intact state comparison data in traditional methods, and the mixed frequency harmonic is sensitive to structural damage but not sensitive to instrument inherent nonlinearity, and through the cooperative response of multiple order harmonics, it can capture small changes in the void rate; 3. Fusion of 6 types of harmonic components (fundamental frequency, frequency multiplication, second-order combination, third-order combination); through normalization processing (such as ), the influence of excitation signal fluctuation is suppressed, and the nonlinear change of the material is focused; the third-order term ( ) enhances the sensitivity to early micro-voids and improves the detection accuracy.

[0013] Other advantages, objects, and features of the present application will be set forth in the following specification and, in part, will be apparent to those skilled in the art from the present application, or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and obtained by the following description. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to make the purpose, technical scheme and beneficial effects of the present application clearer, the present application provides the following drawings for illustration: Figure 1 Flowchart of an embodiment of the present application. DETAILED DESCRIPTION

[0015] As shown in Figure 1 , the present application provides a PSC structure grouting void rate quantification method based on mixed frequency harmonic, comprising the following steps: S1: wrapping pearl wool on the surface of the steel strand to simulate void, keeping the axial length unchanged and changing the circumferential winding range to adjust the void rate, wherein the void rate is the percentage of the circumferential void area to the total area, ranging from 0 to 100%; S2: installing ultrasonic guided wave sensors on the cross section of both ends of the steel strand, and exciting and receiving guided wave signals in a one-to-one manner; S3: applying a sine mixed frequency signal modulated by a Hanning window to the excitation sensor, the center frequency of which is and , and recording the ultrasonic guided wave signal of the receiving sensor; Wherein, the frequency is and There is no multiple relationship between the frequencies, and the second harmonic and the combined harmonic frequency do not overlap in the frequency domain; Wherein, the window function length L of the Hanning window satisfies: In the formula, The propagation speed of the guided wave in the steel strand; S4: Convert the time-domain signal into a frequency-domain signal using Fast Fourier Transform; S5: Record the second harmonic frequency ( and ) and combined harmonic frequencies ( , , , Find the amplitude at point S3, S4 and S5, and repeat steps S3, S4 and S5. Wherein, the frequency is and The ratio is not an integer, and z and z; S6: Calculate the damage index based on the amplitude recorded in step S5. DI ; Among them, damage indicators DI The calculation method is as follows: In the formula, and This represents the amplitude at the fundamental frequency. and This indicates the amplitude at the octave. and These represent the amplitudes at the sum and difference frequencies of the second-order combination, respectively. and This represents the amplitude of the third-order combined harmonics at the specified frequency. S7: Establishing different emptying rates DI The linear fitting equation between the value and its emptying rate is used to calculate the emptying rate. ; In the formula, The intercept; The slope represents DI Value varies with emptying rate The proportionality coefficient of change; Among these methods, environmental temperature error compensation can be incorporated to calculate the air removal rate. : In the formula, This is the correction amount due to ambient temperature. , Here, T represents the temperature coefficient, and T is the measured ambient temperature.

[0016] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for quantifying the grouting void ratio of PSC structure based on mixing combination harmonics, characterized in that, Comprising the following steps: S1: wrapping pearl wool on the surface of the steel strand to simulate the void, keeping the axial length unchanged and changing the circumferential winding range to adjust the void rate; S2: installing ultrasonic guided wave sensors on the cross section of both ends of the steel strand, and exciting and receiving guided wave signals in a one-transmitting-one-receiving mode; S3: Apply to the excitation sensor a sinusoidal mixing signal modulated by a Hann window with a center frequency of and ultrasonic guided wave signals to the receiving sensor; S4: converting the time domain signal into a frequency domain signal through fast Fourier transform; S5: recording the amplitude at the second harmonic frequency and the combined harmonic frequency, and repeating steps S3, S4 and S5; S6: Calculate the damage index according to the amplitude recorded in step S5 DI ; S7: Establishing the linear fitting equation of the value and its void fraction under different void fractions DI The linear fitting equation of the value and its void fraction was calculated .

2. The method according to claim 1, wherein the method is characterized by: In step S5, combining the harmonic frequencies comprises: , , , .

3. The method according to claim 1, wherein the method is characterized by, frequency and frequency satisfies: and the ratio of the frequencies is not an integer, and the second harmonic and the combination harmonic frequencies do not overlap in the frequency domain.

4. The method according to claim 1, wherein the method is characterized by: In step S6, the damage index DI The calculation formula of the damage index is ： wherein and denotes the amplitude at the fundamental frequency, and denotes the amplitude at the second harmonic frequency, and denotes the amplitude at the second combination sum and difference frequencies, respectively, and denotes the amplitude at the third combination harmonic and sum frequencies.

5. The method according to claim 1, wherein the method is characterized by: In step S7, the linear fitting equation is: wherein is the intercept; is the slope, representing DI the proportionality factor of the value as a function of the void fraction. the proportionality factor of the value as a function of the void fraction.

6. The method according to claim 1, wherein the method is characterized by: In step S3, the window function length L of the Hanning window satisfies: In the formula, is the propagation speed of the wave in the steel strand.

7. The method according to claim 1, wherein the method is characterized by: In step S7, an ambient temperature error compensation is introduced to calculate the void fraction : wherein is the correction for ambient temperature, , is the temperature coefficient, T is the measured ambient temperature.

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