CN106932485A - Prestressed tendon corrosion depth monitoring method based on piezoelectric intelligent aggregate - Google Patents

Abstract

The invention discloses a prestressed tendon corrosion depth monitoring method based on piezoelectric intelligent aggregate, which adopts wavelet packet energy to carry out analysis and judgment, takes the wavelet packet energy after wavelet packet decomposition as a variable and calculates RMSD values of stress wave energy in different states and stress wave energy in a healthy state. The method has the advantages of low cost, simple and convenient operation, almost no influence of external factors on the monitoring process, capability of accurately determining the internal corrosion depth of the prestressed concrete and providing reliable basis for structural safety assessment.

Description

A method for monitoring the corrosion depth of prestressed tendons based on piezoelectric intelligent aggregates

technical field

The invention relates to the technical field of health monitoring of civil engineering structures, in particular to a method for monitoring the corrosion depth of prestressed concrete structures based on piezoelectric intelligent aggregates.

Background technique

Due to the use of high-strength steel wire, prestressed concrete has been widely used in practical engineering due to its advantages of light weight, high rigidity, and good anti-seismic and crack resistance. However, in recent decades, there have been many failure accidents of prestressed concrete structures. Most of the reasons are due to durability failure, and the corrosion of prestressed tendons is the main mode leading to the durability failure of prestressed concrete. When the prestressed concrete structure is in a corrosive environment for a long time, the steel strands will be corroded, and the corrosion products will adhere to the surface of the steel bars, and the volume can reach 2 to 6 times the original volume, and the mechanical properties such as the strength and elongation of the steel strands will decrease. Degradation due to corrosion, thus affecting structural safety.

At present, the health monitoring methods of prestressed concrete mainly include ultrasonic method, acoustic emission method, and grating method. Disadvantages such as environmental impact and monitoring location within reach. The most critical thing is that these monitoring methods are mainly aimed at concrete cracks, and their scope of application is limited.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for monitoring the corrosion depth of prestressed tendons based on piezoelectric intelligent aggregates in view of the deficiencies in the prior art.

In order to solve the above technical problems, the technical solution adopted in the present invention is: a method for monitoring the corrosion depth of prestressed tendons based on piezoelectric intelligent aggregates, comprising the following steps:

1) Pre-embed smart aggregates to the corresponding positions of the prestressed tendons and lead out the data transmission line, starting from the smart aggregate closest to the anchor end of the prestressed tendons, and number the smart aggregates in sequence;

2) The inner diameter is d, the outer diameter is D, and the circular prestressed corrugated pipe with the nominal value of wall thickness is H. The prestressed tendons are stretched, grouted, naturally cured, and concrete is poured after anchoring to make concrete for the beam body. member;

3) Seal the anchoring end of the beam member, paste the piezoelectric ceramic sheet on the end of the prestressed tendon, and use the piezoelectric ceramic sheet as a driver for signal excitation;

4) After the beam member made in step 3) reaches the design strength, connect the pre-embedded intelligent aggregate and the piezoelectric ceramic sheet pasted on the end of the prestressed tendon to the multi-functional data acquisition device through the BNC connector, and at the same time connect the computer Connect with multi-function data acquisition equipment;

5) The multifunctional data acquisition device drives the piezoelectric ceramic sheet to send a sinusoidal frequency sweep signal, and at the same time the multifunctional data acquisition device collects the signal sent by the piezoelectric ceramic sheet received by the smart aggregate;

6) Carry out wavelet packet energy analysis on the signal received by the smart aggregate, and the obtained result is used as the initial energy value E _h,j ;

7) When the beam member needs to be tested, collect the signal according to the method of step 4) to step 6), and use the signal to calculate the energy E _i,j when it needs to be tested, and then calculate the damage index I:

When I approaches 0, it means that the prestressed tendons are not corroded; on the contrary, when I approaches 1, the degree of corrosion is more serious; N is the series of wavelet packet decomposition;

8) Analyze and calculate the damage index I of each intelligent aggregate arranged longitudinally along the beam member, determine the corrosion status of the prestressed tendon between the piezoelectric ceramic sheet and the intelligent aggregate, thereby determine the corrosion depth of the prestressed tendon.

In step 1), the inner diameter d is 60 mm, the outer diameter D is 73 mm, and the nominal wall thickness H is 2.5 mm.

In step 1), the diameter of the prestressed tendon is 15.2mm.

In step 3), after pasting the piezoelectric ceramic sheet on the end of the prestressing tendon, cover it with the piezoelectric ceramic sheet of AB glue.

In step 5), the frequency of the sine sweep signal is 100Hz-150kHz, and the amplitude is 10V.

Compared with the prior art, the beneficial effects of the present invention are: the present invention is low in cost, simple and convenient in operation, the monitoring process is almost not affected by external factors, and can accurately determine the internal corrosion depth of prestressed concrete. Safety assessment provides a reliable basis.

Description of drawings

Fig. 1 is a structural diagram of the monitoring system of the present invention;

Fig. 2 is a schematic diagram of the monitoring principle of the linear bellows of the present invention;

Fig. 3 is the monitoring principle diagram of the curved bellows of the present invention;

Fig. 4 is a large sample diagram of the piezoelectric ceramic sheet of the present invention pasted on the prestressed rib;

Fig. 5 is the large sample diagram after the corrosion of the prestressed tendon of the present invention;

Among them, ①-intelligent aggregate; ②-piezoelectric ceramic sheet; ③-end anchor; ④-prestressed pipe; ⑤-concrete; ⑥-prestressed tendon; ⑦-grouting material;

detailed description

In prestressed concrete, the corrosion of prestressed tendons usually starts from the end anchor and extends from the outside to the inside. This is because once the grouting fluid sealing measures taken at the end anchor fail or cracks, oxygen and moisture in the air It reacts chemically with the prestressed tendons and rusts, and this corrosion will develop from the outside to the inside along the gap between the steel strands. Therefore, the layout of the first piezoelectric smart aggregate is selected at a distance of 1 cm from the anchor end to the concrete surface, and the other piezoelectric smart aggregates are distributed along the longitudinal direction of the bellows at a distance of 5 cm. The lower side of the piezoelectric smart aggregate is close to the front of the prestressed pipe. Above, these piezoelectric smart aggregates are used as piezoelectric sensors to receive signals. After the tensioning and anchoring of the prestressed tendon is completed, a piezoelectric ceramic sheet is pasted on the end of the prestressed tendon. After the pasting is completed, the piezoelectric ceramic sheet is covered with AB glue. The piezoelectric ceramic sheet is used as a piezoelectric driver to generate signals. The piezoelectric intelligent aggregate used as a sensor is respectively connected to the NI6363 multifunctional data acquisition device through wires; the piezoelectric ceramic sheet used as a driver is also connected to the NI6363 multifunctional data acquisition device through wires. The NI6363 multifunctional data acquisition device is connected to the computer through a USB data cable. The specific working form of the system is to control the multifunctional data acquisition equipment NI6363 to send high-frequency signals through the supporting software LabVIEW of the multifunctional acquisition equipment on the computer, and the signal excites the piezoelectric ceramic chip as the driver. The signal generated by the piezoelectric ceramic sheet is received by the piezoelectric smart aggregate as a sensor, and the received signal is transmitted to the multifunctional data acquisition device NI6363 through a wire, and finally the collected signal is transmitted to the computer by the NI6363.

When the prestressed tendon between the piezoelectric ceramic sheet and the piezoelectric smart aggregate is not corroded, the signal energy index analyzed by the computer is basically consistent with the initial signal energy index. When the prestressed tendon is corroded, the corrosion product adheres to the surface of the prestressed tendon to form a gap, resulting in a change in the medium between the piezoelectric ceramic sheet and the piezoelectric smart aggregate, and the qualitative change of the signal energy analyzed by the computer will be smaller than the initial signal energy index .

According to the analysis based on wavelet packet energy in the present invention, since there are three kinds of media in the propagation path of the stress wave, i.e. prestressed tendons, concrete and prestressed pipes, the process is relatively complicated. Existence makes the stress wave propagation process more complicated. The amplitude of the collected signal is the embodiment of the signal energy. The piezoelectric ceramic sheet as the driver vibrates under the action of the electric signal to generate a high-frequency stress wave. When the stress wave propagates inside the concrete, it will be reflected and refracted on the damaged section. Such phenomena lead to changes in the stress wave signal passing through the corresponding position, thereby showing the change of the electrical signal output by the piezoelectric smart aggregate. By comparing the change, the identification of the corrosion of the prestressed tendon is realized.

Adopt wavelet packet energy to analyze and judge among the present invention, take the wavelet packet energy after the wavelet packet decomposition as variable, calculate the RMSD (root mean square deviation) value of the stress wave energy under different states and the stress wave energy under the healthy state, RMSD is A suitable damage indicator that compares the difference between the signals of the healthy state and the damaged state.

Definition of damage indicators:

The sensor signal is decomposed into 2 ^N signal groups {X ₁ ,X ₂ ···X ₂ ⁿ } by an N-level wavelet packet. E _i,j is the energy of the decomposed signal in the damaged state, the expression is And X _j =[X _j,1 ,X _j,2 ···X _j,m ], where i is the time index, j is the frequency band (j=1,2,···2 ⁿ ), m is the sampling data number; E _h,j is the energy index in a healthy state.

In the present invention, the piezoelectric signal of the prestressed tendon in the component can be selected as the initial energy index E _h,j under the state of corrosion. In the later monitoring process, if the obtained E _i,j is similar to E _h,j , the damage index I is close to 0, it means that the prestressed tendon in this area is not corroded; on the contrary, if the prestressed tendon is corroded in the monitoring area, E _i,j will be less than E _h,j , and the more serious the corrosion, the more the damage index tends to be 1.

The concrete realization process of the present invention is as follows

Step 1. As shown in Figure 2 and Figure 3, the inner diameter d is 60mm, the outer diameter D is 73mm, and the nominal wall thickness is 2.5mm, and the prestressed tendons with a nominal diameter of 15.2mm are stretched inside the circular prestressed bellows , grouting, natural curing, pouring C50 concrete after anchoring.

Step 2. Before the concrete pouring of the component, pre-embed the intelligent aggregate to the corresponding setting position and lead out the data transmission line. The layout of the first piezoelectric smart aggregate is selected at a distance of 1 cm from the anchor end to the concrete surface. The other piezoelectric smart aggregates are distributed along the longitudinal direction of the bellows at a distance of 5 cm. The lower side of the piezoelectric smart aggregate is close to the front of the prestressed pipe. above. Starting from the smart aggregate closest to the anchor end of the prestressed tendon, the smart aggregates are numbered sequentially, and these smart aggregates are used as sensors for signal reception.

Step 3: Stretching and grouting the prestressed tendons of the member, and sealing the anchoring end after the grout has reached strength. Paste the piezoelectric ceramic sheet on the end of the prestressed tendon, cover and protect it with the AB glue piezoelectric ceramic sheet after pasting, so as not to be affected by the external environment. The piezoelectric ceramic sheet is used as a driver for signal excitation.

Step 4. After the component reaches the design strength, connect the pre-embedded piezoelectric smart aggregate and the piezoelectric ceramic sheet attached to the end of the prestressed tendon to the NI 6363 multifunctional data acquisition device through the BNC connector, and at the same time connect the computer through The USB communication line is connected with the NI 6363 multifunction data acquisition device.

Step 5. With the help of the supporting software LabVIEW of the multifunctional acquisition equipment, the NI6363 drives the piezoelectric ceramic chip to send out a 100Hz-150kHz sinusoidal frequency sweep signal, and the amplitude of the signal is 10V.

Step 6. At the same time, NI6363 collects the signal received by the smart aggregate as a sensor, and saves the collected data to the computer.

Step 7: Perform wavelet packet energy analysis on the collected signal data with the Matlab wavelet analysis program, and use it as the initial energy value E _h,j .

Step 8. When the component needs to be detected, the signal is collected according to the method of step 4 to step 6, and the energy E _i,j of the energy at this time is calculated by Matlab, and the calculated damage index I,

Among them, E _i,j is the energy of the decomposed signal in the damaged state, and E _h,j is the energy index in the healthy state. When I is close to 0, it means that the prestressed tendons are not corroded. On the contrary, when I is close to 1, the degree of corrosion is more serious.

Step 9. By analyzing and calculating the damage index I of each piezoelectric intelligent aggregate arranged longitudinally along the beam length, the corrosion status of the prestressed tendon between the piezoelectric ceramic sheet and the piezoelectric intelligent aggregate can be determined, thereby determining the prestressed Corrosion depth of ribs.

Claims (5)

1. a kind of presstressed reinforcing steel corrosion penetration monitoring method based on piezoelectric intelligent aggregate, it is characterised in that comprise the following steps：

1) to the relevant position of presstressed reinforcing steel and draw data line by intelligent aggregate is pre-buried, from apart from presstressed reinforcing steel anchor end most Near intelligent aggregate starts, to intelligent aggregate number consecutively；

2) it is d in internal diameter, external diameter is D, wall thickness nominal value is the circular prestressing force bellows inner stretch-draw prestressing force muscle of H, mud jacking, from So maintenance, sealing off and covering anchorage after-pouring concrete makes concrete and is used as beam body component；

3) sealing off and covering anchorage is carried out to beam body member anchoring end, piezoelectric ceramic piece is pasted on presstressed reinforcing steel termination, the piezoelectric ceramic piece is made For driver carries out signal excitation；

4) in step 3) after the beam body component that makes reaches design strength, pre-buried intelligent aggregate and presstressed reinforcing steel end will be pasted on The piezoelectric ceramic piece of head is connected by BNC connector with multifunctional data acquiring equipment, while computer is adopted with multi-functional data Collection equipment is connected；

5) multifunctional data acquiring device drives piezoelectric ceramic piece sends sine sweep signal, while multifunctional data acquiring equipment The signal that the piezoelectric ceramic piece that collection intelligent aggregate is received sends；

6) signal received to intelligent aggregate carries out wavelet-packet energy analysis, and the result for obtaining is used as initial energy value E_h,j；

7) beam body component need detection when, according to step 4)~step 6) method collection signal, and utilize the signal of change Go out ENERGY E when needing detection_i,j, then calculate damage criterion I：

$I=\sqrt{\frac{\underset{j=1}{\overset{2^N}{\Σ}}{(E_{i,j}-E_{h,j})}^2}{\underset{j}{\overset{2^N}{\Σ}}{\left(E_{h,j}\right)}^2}};$

When I levels off to 0, illustrate that presstressed reinforcing steel does not occur corrosion, conversely, when I levels off to 1, corrosion degree is more serious；N is small echo Wrap the series for decomposing；

8) the damage criterion I of each intelligent aggregate that analytical calculation is longitudinally arranged along beam body component, it is determined that piezoelectric ceramic piece with The corrosion situation of presstressed reinforcing steel between intelligent aggregate, so that it is determined that the corrosion penetration of presstressed reinforcing steel.

2. the presstressed reinforcing steel corrosion penetration monitoring method based on piezoelectric intelligent aggregate according to claim 1, its feature exists In step 2) in, internal diameter d is 60mm, and outer diameter D is 73mm, and wall thickness nominal value H is 2.5mm.

3. the presstressed reinforcing steel corrosion penetration monitoring method based on piezoelectric intelligent aggregate according to claim 1, its feature exists In step 2) in, a diameter of 15.2mm of presstressed reinforcing steel.

4. the presstressed reinforcing steel corrosion penetration monitoring method based on piezoelectric intelligent aggregate according to claim 1, its feature exists In step 3) in, after piezoelectric ceramic piece is pasted on into presstressed reinforcing steel termination, covered with AB rubber cements piezoelectric ceramic piece.

5. the presstressed reinforcing steel corrosion penetration monitoring method based on piezoelectric intelligent aggregate according to claim 1, its feature exists In step 5) in, sine sweep signal frequency is 100Hz-150kHz, and amplitude is 10V.