CN113933386A

CN113933386A - Ultrasonic pulse energy method for dynamically monitoring concrete damage

Info

Publication number: CN113933386A
Application number: CN202010668421.7A
Authority: CN
Inventors: 王振波; 左建平; 刘畅; 孙鹏
Original assignee: China University of Mining and Technology Beijing CUMTB
Current assignee: China University of Mining and Technology Beijing CUMTB
Priority date: 2020-07-13
Filing date: 2020-07-13
Publication date: 2022-01-14

Abstract

The invention provides an ultrasonic pulse energy method for dynamically monitoring concrete damage, which is characterized in that a monitoring system adopts ultrasonic pulse energy to replace the traditional indexes in the existing monitoring technology, and dynamically identifies and represents the evolution process of the concrete internal damage according to an energy change curve obtained by real-time tracking. The ultrasonic pulse energy parameter is determined by integrating the absolute value of amplitude in a oscillogram with a time axis; the nonlinear initial point of the energy change curve represents damage initiation, the extreme point represents a critical point of crack penetration, and the descending segment directly expresses the evolution process of concrete damage. The ultrasonic pulse energy parameters comprehensively consider the full voltage amplitude of the oscillogram, so that errors caused by manual operation are reduced, the obtained energy change curve can accurately judge key nodes of concrete damage evolution, and the method does not distinguish the pulse vibration direction, is simple and convenient to operate and has a wide application range.

Description

Ultrasonic pulse energy method for dynamically monitoring concrete damage

Technical Field

The invention belongs to the field of concrete structure health monitoring, and particularly relates to a method for dynamically monitoring concrete damage by using ultrasonic pulse energy parameters.

Background

The concrete is an engineering material with complex properties due to the characteristics of various composition materials, long curing time and the like. In an actual service environment, a concrete structure is usually subjected to complex engineering conditions such as stress change, ion erosion, dry-wet cycle and the like, which undoubtedly increases the difficulty of safety monitoring of the existing concrete structure. How internal damage of a concrete structure evolves in the service process and how the safety of the structure is quantitatively evaluated are always very concerned in the field of structural health monitoring.

In the structural health monitoring method, the concrete mechanical strength test relying on-site sampling is direct and reliable, but is easy to cause additional damage to the structure, and the operation process is time-consuming and labor-consuming. Meanwhile, the damage degree of concrete cannot be comprehensively measured by a single strength index. The ultrasonic pulse method is a representative nondestructive testing means and is widely applied to concrete structure health monitoring and internal damage identification. The initial pulse excited by the pulse emitter changes correspondingly after being propagated through the material or the structure, and the pulse acquired by the receiver carries information related to the change of the material/structure. The ultrasonic velocity is easily calculated from the pulse propagation distance and the time when the pulse reaches the receiver, and this parameter is also commonly used in ultrasonic pulse time domain analysis due to its easy acquisition and relative stability.

The previous indoor tests and practices show that the sensitivity of ultrasonic speed to concrete stress and damage crack development obviously depends on the pulse propagation direction, and some cracks in parallel trend are even difficult to identify; the variation amplitude and range of the wave velocity parameters along with the stress are not visual enough, and the quantitative relation between the wave velocity and the damage is not clear. In addition, an artificial factor is usually introduced into the first-arrival time determined by the initial jump point of the waveform, so that the accuracy and reliability of the wave velocity value are reduced. Other information carried by the ultrasonic pulse (e.g., amplitude) is thus utilized to feedback the internal behavior of the material. Unfortunately, most parameters are selected only for the amplitude of the first half cycle or peak amplitude, and the readings appear to be highly discrete as a function of instrument operation.

Disclosure of Invention

In order to solve the problems, the invention provides an ultrasonic pulse energy method for dynamically monitoring concrete damage. According to the method, traditional indexes such as wave velocity and amplitude are replaced by ultrasonic pulse energy parameters, the internal damage evolution process of the concrete material or structure can be tracked in real time, the easy acquireability of indication parameters is reserved, and the monitoring sensitivity is greatly improved.

In particular, the ultrasonic pulse energy is determined as an integral of the absolute value of the amplitude in the waveform plot over the time axis.

The invention provides an ultrasonic pulse energy method for dynamically monitoring concrete damage, which is realized by the following steps:

(1) installing (or pre-embedding) a pulse transmitter and a pulse receiver in opposite directions at a part to be detected of a concrete sample or a structure to be detected, wherein the transmitter and the receiver are connected to a monitoring control system in a wired or wireless mode;

(2) the control system controls the transmitter to excite the ultrasonic pulse at fixed time intervals;

(3) the receiver receives ultrasonic pulses penetrating through a to-be-detected sample or a to-be-detected part of a structure, and transmits pulse waveforms to the control system in real time;

(4) and the control system calculates a corresponding ultrasonic pulse energy index according to the collected pulse waveform, records a change curve of the pulse energy in real time and dynamically monitors the internal damage evolution of the concrete material or structure.

The energy change curve obtained by the ultrasonic pulse energy method can accurately track the evolution process of concrete damage. Before the injury is initiated, energy parameters develop linearly along with the increase of stress, the characteristics of the energy parameters are similar to mechanical linear elasticity, and the initiation point of energy nonlinear change represents the injury initiation; after the damage occurs, the energy change deviates from linearity and shows the characteristic of approximate elastoplasticity; when the damage is completely developed and a crack penetration critical point is about to be reached, the pulse energy reaches an extreme value; and then, along with the penetration and the generation of cracks, the pulse energy curve is rapidly reduced in a Weibull distribution mode, completely accords with the damage change rule described in concrete damage mechanics, and can be directly used for expressing the evolution process of concrete stress damage.

The extreme point of the ultrasonic pulse energy change curve is obviously ahead of the peak stress of the concrete, the advance time is irrelevant to the self attributes of materials such as the strength grade of the concrete, the maintenance age and the like, and the energy method is suitable for early warning the damage of the materials or the structures.

Further, the ultrasonic pulse energy method may use a compression wave (P-wave) or a shear wave (S-wave) as an incident wave, and the monitoring result is not affected by the pulse vibration direction.

Compared with the prior art, the ultrasonic pulse energy method for dynamically monitoring the concrete damage has the following advantages:

(1) the ultrasonic pulse energy parameter is determined by integrating the amplitude with the time axis, the full voltage amplitude of the oscillogram is considered together, the first arrival time does not need to be determined artificially, the artificial factors in the operation process are eliminated, and the obtained result is more objective and reliable;

(2) the positions of key points such as peak points, inflection points and the like on the ultrasonic pulse energy change curve are clear and distinguishable, and the damage evolution process of the concrete is favorably and finely analyzed;

(3) the ultrasonic pulse energy method is not influenced by the pulse vibration direction, and the P wave and S wave energy curves have the same change trend and can be used for representing the evolution process of the internal damage of the concrete;

(4) the ultrasonic pulse energy method can be combined with a wave velocity analysis method, two parameters are read in the same waveform at the same time, and more accurate feedback information of the internal structure of the material can be obtained on the premise of not increasing the monitoring amount.

Drawings

FIG. 1 is a schematic diagram of a concrete damage monitoring system based on an ultrasonic pulse energy method;

FIG. 2 is a graph of typical received waveforms under different strain conditions;

FIG. 3 is a schematic diagram of a method of determining an ultrasonic pulse energy parameter;

FIG. 4 is a graph comparing an ultrasonic pulse energy curve with a concrete stress variation curve

Detailed Description

The invention provides an ultrasonic pulse energy method for dynamically monitoring concrete damage, and in order to more clearly explain the purposes, technical schemes and action effects of the invention, the concrete implementation mode of the invention is further explained by combining a schematic diagram and aiming at an embodiment of a concrete sample. It should be noted that the embodiments described above are only for describing the summary of the invention, and are not intended to limit the invention.

The concrete damage monitoring system based on the ultrasonic pulse energy method is composed of a controller 1, a pulse transmitter 2 and a receiver 3. Wherein the pulse transmitter 2 and the receiver 3 are embedded in the upper pressure head 4 and the lower pressure head 5, respectively, and are connected to the controller 1.

In order to reflect the effect of dynamically tracking the concrete damage evolution of the monitoring system, the embodiment applies a pressure load with a constant strain rate to the concrete sample to be detected 6, and the strain of the sample is collected by the linear displacement sensors 7 arranged on the two sides. In the process, the controller 1 excites the pulse emitter 2 to generate ultrasonic pulses at fixed time intervals, the ultrasonic pulses are collected by the receiver 3 after being transmitted by the concrete sample 6 to be tested, and the recorded waveforms are transmitted to the controller 1 in real time. The

resulting waveforms

8,9 and 10 have significantly different amplitude characteristics under different strain conditions.

The ultrasonic pulse energy parameter 11 is determined by integrating the absolute value of the amplitude in the waveform 12 over the time axis, with the upper integration limit being the pulse travel time 13. An energy change curve 14 is drawn according to the continuously measured ultrasonic pulse energy data, and the curve 14 is highly sensitive to a concrete stress change curve 15.

In the undamaged stage of the concrete, the ultrasonic pulse energy develops linearly to point 16 as the stress increases. The energy change then begins to deviate from linearity until the energy extreme point 17, point 17 corresponding to the most dense state of the concrete sample 6 to be tested. As the crack propagates and coalesces, the ultrasonic pulse energy curve rapidly falls off with a weibull distribution curve 18, but the stress can still increase to a peak point 19. The energy extreme point 17 obviously leads the stress peak point 19 and can be used as a safety early warning for the concrete damage accumulation.

The ultrasonic pulse energy method for dynamically monitoring the concrete damage takes objective and reliable ultrasonic pulse energy parameters as visual indexes for representing the concrete damage, and reduces errors caused by manual operation. The positions of key points such as peak points, inflection points and the like on the energy change curve are clear and distinguishable, and the damage evolution process of the concrete can be accurately described. Meanwhile, the pulses in different vibration directions can be used by a pulse energy method, so that the method is simple and convenient to operate and wide in application range.

It should be noted that the above description is only a preferred embodiment. The scope of the present invention is not limited thereto, and any modifications or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims

1. An ultrasonic pulse energy method for dynamically monitoring concrete damage is characterized in that: the concrete damage monitoring system adopts ultrasonic pulse energy parameters to replace traditional indexes in the existing monitoring technology, tracks the change process of the ultrasonic pulse energy parameters at fixed time intervals, dynamically identifies and represents the evolution process of the internal damage of the concrete according to the obtained ultrasonic pulse energy change curve, and warns the damage of concrete materials or structures.

2. The ultrasonic pulse energy method for dynamically monitoring concrete damage according to claim 1, wherein the ultrasonic pulse energy method comprises the following steps: the ultrasonic pulse energy parameter is determined as an integral of the absolute value of the amplitude in the waveform plot over the time axis.

3. The ultrasonic pulse energy method for dynamically monitoring concrete damage according to claim 1, wherein the ultrasonic pulse energy method comprises the following steps: the monitoring process is realized by the following steps:

(1) an ultrasonic pulse transmitter and a receiver are oppositely arranged at a position to be measured of the concrete, and the transmitter and the receiver are connected to a monitoring control system;

(3) the receiver continuously receives the ultrasonic pulse and transmits the pulse waveform to the control system in real time;

(4) and the control system calculates a corresponding ultrasonic pulse energy index according to the collected pulse waveform, records a change curve of the pulse energy and monitors the internal damage evolution process of the concrete material or structure in real time.

4. The ultrasonic pulse energy method for dynamically monitoring concrete damage according to claim 1, wherein the ultrasonic pulse energy method comprises the following steps: the ultrasonic pulse energy change curve is highly sensitive to the evolution process of concrete damage, the initial point of energy nonlinear change represents damage initiation, the extreme point represents a critical point of crack penetration, and the descending section directly expresses the evolution process of stress damage.

5. The ultrasonic pulse energy method for dynamically monitoring concrete damage according to claim 1, wherein the ultrasonic pulse energy method comprises the following steps: the extreme point of the ultrasonic pulse energy change curve is obviously ahead of the concrete stress peak value, and the advance time is independent of the material property.

6. The ultrasonic pulse energy method for dynamically monitoring concrete damage according to claim 1, wherein the ultrasonic pulse energy method comprises the following steps: compression waves (P waves) or shear waves (S waves) can be used as incident waves, and the monitoring result is not influenced by the pulse vibration direction.

7. The ultrasonic pulse energy method for dynamically monitoring concrete damage according to claim 1, wherein the ultrasonic pulse energy method comprises the following steps: the ultrasonic pulse energy method can be used in combination with a wave velocity analysis method, and more accurate structural information feedback is obtained on the premise of not increasing the monitoring quantity.