CN115683035A - A Method for Measuring Strain Modal Parameters of Beam Structures - Google Patents

Abstract

The invention discloses a method for measuring strain modal parameters of a beam type structure, which comprises the following steps: determining a signal generation point in a beam structure; designating a signal sampling point in the signal generating points; building a serial full-bridge structure at the signal sampling point, and configuring a calculation model according to the serial full-bridge structure; and acquiring an output signal of the test sampling point, and calculating the strain modal parameter of the beam type structure. According to the technical scheme, the strain modal parameters of the beam type structure under different working conditions can be accurately identified and measured, the accuracy of identification and measurement results can be improved, the measured modal parameters are closer to the actual conditions, and the nonlinear error caused by structure mutation can be effectively avoided.

Description

A Method for Measuring Strain Modal Parameters of Beam Structures

technical field

The invention relates to the field of bridge health monitoring, in particular to a method for measuring strain modal parameters of beam structures.

Background technique

With the rapid development of my country's modern industry, highways, and railways, especially the development of the rack, steel, and beam structure industries, more and more buildings and other fields are constructed using beam structures. It is the first choice, even the only choice, for key structures of key engineering projects. At present, the commonly used detection methods for damage identification and vibration fatigue of beam structures include ultrasonic testing, infrared testing, acoustic emission, natural potential testing, impact echo testing, etc. These testing methods can analyze the appearance and structural characteristics of beam structures. Perform structural health checks.

The damage judgment of the key structural components and nodes of the beam structure is difficult to reflect through the above detection methods. Therefore, for the beam structure building, the overall structural health, safety, remaining life, etc. need a technical solution to carry out a systematic and comprehensive The evaluation of this technical scheme is to obtain the natural frequency, damping and corresponding structural mode shape of the structural system through the identification, measurement and processing of the strain modal parameters of the beam structure, which provides a basis for damage identification and structural health monitoring of the beam structure. scientific means.

Contents of the invention

In order to achieve the above purpose, the present application provides a method for measuring strain modal parameters of a beam structure, comprising the following steps:

Determine the signal occurrence point in the beam structure;

Specify the signal sampling point in the signal generation point;

Build a series full bridge structure at the signal sampling point, and configure the calculation model according to the series full bridge structure;

Obtain the output signal of the test sampling point and calculate the strain modal parameters of the beam structure;

Among them, building a series full-bridge structure includes: setting resistance strain gauges on the surface of the beam in four directions, and forming four groups of bridge arms through the resistance strain gauges. The four groups of bridge arms are defined as the first bridge arm, the second bridge arm, the third bridge arm bridge arm and the fourth bridge arm.

Wherein, the first bridge arm is composed of a strain gauge arranged on the top surface of the beam and a strain gauge arranged on the right side of the beam connected end to end to form an electric bridge;

The second bridge arm is composed of two fixed-value resistors connected end-to-end with the same resistance value as the first bridge arm;

The third bridge arm is composed of a strain gauge arranged on the left side of the beam and a strain gauge arranged on the bottom surface of the beam connected end to end to form an electric bridge;

The fourth bridge arm is composed of an externally connected two fixed-value resistors with the same resistance value as the first bridge arm or the third bridge arm and connected end to end to form an electric bridge.

Further, the series full bridge structure refers to connecting the bridge arms where the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm are located end to end to form a series bridge.

Further, setting the resistance strain gauge refers to arranging strain gauges along the length direction of the beam structure, and externally connecting fixed-value resistors of equal resistance.

Among them, the calculation model also includes: variable voltage source, impact hammer, dynamic strain signal amplifier and data processing system;

A variable voltage source is used to power the series full bridge structure;

The impact hammer is used for hammering at the signal generation point to provide hammering excitation to the series full bridge structure;

The dynamic strain signal amplifier is used to amplify the strain response of the structure under hammer excitation;

The data processing system is connected to the circuit output of the series full bridge structure, and is used to calculate the output of the full bridge structure and input it into the corresponding calculation model to calculate and obtain the recognition results in all directions.

Further, obtaining the output signal of the test sampling point includes: obtaining the resistance parameters of the four groups of resistance strain gauges, the Wheatstone circuit bridge voltage, and the sensitivity coefficient of the strain gauge. The resistance parameters also include: the resistance R _R on the right side of the beam structure, the beam structure Left resistance R _L , beam structure top resistance R _T , beam structure bottom resistance R _B ;

The output voltage of the full-bridge strain gauge is calculated as:

Among them, U _B is the Wheatstone circuit bridge voltage, U ₀ is the output voltage of the full-bridge strain gauge, R is the resistance of the strain gauge, and ΔR is the variation of the strain gauge resistance.

Among them, the strain modal parameters include: the longitudinal strain of each surface of the beam structure, and the calculation method is:

Among them, ε is the longitudinal strain of each surface of the beam structure, and its value is the sum of the strain responses of the four surfaces of the beam structure.

Further, the output signal of the test sampling point refers to:

The strain signal generated by the impact hammer at the signal generation point of the beam structure;

The strain signal has been amplified by a dynamic strain signal amplifier.

Nine signal generation points are set in one beam structure, and the nine signal generation points are evenly distributed in the beam structure.

According to the present invention, it is possible to accurately identify and measure the strain modal parameters of the beam structure under different working conditions, improve the accuracy of the identification and measurement results, make the modal parameters closer to the actual situation, and effectively avoid abnormal effects caused by structural mutations. linearity error.

Description of drawings

1 is a step diagram of a method for measuring strain modal parameters of a beam structure provided according to an embodiment of the present invention;

2 is a structural diagram of a series full bridge provided according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of the arrangement of resistance strain gauges according to an embodiment of the present invention.

Detailed ways

The specific implementation of the present invention will be described in detail below in conjunction with the accompanying drawings.

The invention is used to detect the characteristics of the key structural components of the beam structure. Resistive strain gauges are arranged at designated positions on the surface to form a multi-faceted series combination, which is combined with variable voltage sources, impact hammers, dynamic signal amplifiers and The data acquisition system cooperates to collect the amplified signal after the strain response and calculate the strain modal parameters.

Fig. 1 provides the step diagram of the method for measuring the strain modal parameters of the beam structure in the present application, as shown in the figure, including the following steps:

Step S100: Determine the signal generation point in the beam structure;

In the method provided by the present application, nine hammering points are determined on the beam as signal generation points. As shown in FIG. 3 , the nine signal generation points are evenly distributed in the beam structure.

Step S110: Specify the signal sampling point in the signal generation point:

From the signal generation point provided in step S100, select a point as the signal sampling point, as shown in Figure 3, select the second point as the signal sampling point, and lay out a series full bridge at the signal point sampling point.

Step S120: Build a serial full-bridge structure at the signal collection position, and configure a calculation model according to the serial full-bridge structure;

The beam structure built in this step is a series full bridge structure. First, four groups of resistance strain gauges are arranged on the four directions of the beam, and four groups of bridge arms are formed by the four groups of resistance strain gauges. The arms are defined as a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm;

The first bridge arm is composed of a strain gauge arranged on the top surface of the beam and a strain gauge arranged on the right side of the beam connected end to end to form an electric bridge;

The second bridge arm is composed of two fixed-value resistors connected end-to-end with the same resistance value as the first bridge arm;

The third bridge arm is composed of a strain gauge arranged on the left side of the beam and a strain gauge arranged on the bottom surface of the beam connected end to end to form an electric bridge;

The fourth bridge arm is composed of an externally connected two fixed-value resistors with the same resistance value as the first bridge arm or the third bridge arm and connected end to end to form an electric bridge.

When the transverse section of the beam structure is a quadrilateral, the first surface is the right surface, the third surface is the top surface, the second surface and the fourth surface are respectively the left surface and the bottom surface; that is, the right surface, the left surface, On the top surface and the bottom surface: the first resistance strain gauge and the third resistance strain gauge, the second resistance strain gauge and the fourth resistance strain gauge are arranged parallel to the longitudinal direction of the beam structure.

As shown in Figure 2, the series full-bridge structure includes: two longitudinal resistance strain gauges on the right surface and the top surface are connected in series to form the first bridge arm; two longitudinal resistance strain gauges on the left surface and the bottom surface are connected in series to form the third bridge arm. Bridge arm; external fixed-value resistors of equal resistance are connected end to end to form the second bridge arm and the fourth bridge arm. connected to form a series bridge.

In practical applications, the properties of the longitudinal material on each surface of the beam structure are inhomogeneous, and the difference in the properties of the longitudinal material will lead to different effects of strain on each surface. At the center of the four surfaces in the middle of the structure, strain gauges and external fixed-value resistors of equal resistance are arranged along the length of the structure to form a multi-arm series full bridge. , the strain gauges are arranged along the length direction of the beam structure, and fixed-value resistors of equal resistance are externally connected to form a resistance strain gauge.

The strain gauge can reflect the surface deformation of the tested piece. Through the setting method of the position of the strain gauge, the difference of the strain effect of the surface material can be reduced, and the nonlinear error caused by the structural mutation can be effectively avoided.

The operation method of arranging the strain gauges can paste and fix the strain gauges on the surface of the beam structure.

After the series full bridge structure is determined, continue to configure the calculation model, which also includes: variable voltage source, impact hammer, dynamic strain signal amplifier and data processing system;

A variable voltage source is used to power the series full bridge structure;

The impact hammer is used to provide hammer excitation to the tandem full bridge structure to generate strain signals;

The dynamic strain signal amplifier is used to amplify the strain signal generated by the structure under hammer excitation, so as to improve the accuracy of identification and measurement results, and make the measured modal parameters closer to the actual situation;

The data processing system is connected to the circuit output of the series full bridge structure, and is used to calculate the output of the full bridge structure and input it into the corresponding calculation model to calculate and obtain the recognition results in all directions.

Step S130: Obtain the output signal of the test sampling point, and calculate the strain modal parameters of the beam structure;

Figure 3 is a schematic diagram of the location of the resistance strain gauges. As shown in the figure, nine hammering points are determined on the beam. In this application, the order of different hammering points in the hammering points is designed by using the impact hammer. Sampling is carried out at 2 points to realize the measurement and identification of one row and one column of the strain frequency response function matrix of the beam structure, which is used to measure the strain modal parameters of the beam under different working conditions.

In this step, the resistance parameters of the four sets of resistance strain gauges, the bridge voltage of the Wheatstone circuit, and the sensitivity coefficient of the _strain gauges, etc. are obtained; Layout; the left side R _L of the beam structure is arranged longitudinally along the beam structure; the top surface R _T of the beam structure is arranged longitudinally along the beam structure; the bottom surface R _B of the beam structure is arranged longitudinally along the beam structure.

The output voltage of the full-bridge strain gauge is calculated as:

Among them, U _B is the Wheatstone circuit bridge voltage, U ₀ is the output voltage of the full-bridge strain gauge, R is the resistance of the strain gauge, and ΔR is the variation of the strain gauge resistance;

其中，K为应变计的灵敏度系数；This calculation can be written as:

Among them, K is the sensitivity coefficient of the strain gauge;

其中，ε为梁式结构四个面的应变响应之和,ε₁、ε₂、ε₃和ε₄分别为梁式结构四个表面测得的纵向应变响应；The calculation method of the output voltage can be transformed into:

Among them, ε is the sum of the strain responses of the four surfaces of the beam structure, and ε ₁ , ε ₂ , ε ₃ and ε ₄ are the longitudinal strain responses measured on the four surfaces of the beam structure respectively;

Order: ε ₁ = ε _T1 ; ε ₂ = ε _R1 ; ε ₃ = ε _B1 ; ε ₄ = ε _L1 ;

The modal parameters include: the longitudinal strain of each surface of the beam structure, and the calculation method is:

Among them, ε is the sum of the strain responses of the four surfaces of the beam structure, and ε ₁ , ε ₂ , ε ₃ and ε ₄ are the longitudinal strain responses measured on the four surfaces of the beam structure, respectively.

Then the output voltage:

transforms into:

According to ε＝ε ₁ +ε ₂ +ε ₃ +ε ₄ :

In this step, the accurate strain response value of the structure is identified through the full bridge, which is used as the input of one row or one column of the strain frequency response function matrix.

Through the method provided by the invention, the strain modal parameters of the beam structure under different working conditions can be accurately identified and measured, the accuracy of identification and measurement results can be improved, and the measured modal parameters are closer to the actual situation, which can effectively avoid Non-linear errors caused by structural mutations.

The above disclosures are only a few specific embodiments of the present invention, however, the present invention is not limited thereto, and any changes conceivable by those skilled in the art shall fall within the protection scope of the present invention.

Claims (9)

1. A method for measuring a strain modal parameter of a beam structure is characterized by comprising the following steps:

determining a signal generation point on the beam structure;

designating a signal sampling point among the signal generation points;

building a serial full-bridge structure at the signal sampling point, and configuring a calculation model according to the serial full-bridge structure;

acquiring an output signal of the test sampling point, and calculating a strain modal parameter of the beam type structure;

wherein, build serial-type full-bridge structure includes: resistance strain gauges are arranged on the surfaces of the beam in four directions, four groups of bridge arms are formed by the resistance strain gauges, and the four groups of bridge arms are defined as a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm.

2. The method of measuring a strain mode parameter of claim 1, wherein:

the first bridge arm is formed by connecting a strain gauge arranged on the top surface of the beam and a strain gauge arranged on the right surface of the beam end to form a bridge;

the second bridge arm is formed by connecting two constant value resistors which are connected with the first bridge arm in an equal resistance manner end to end;

the third bridge arm is formed by connecting a strain gauge arranged on the left surface of the beam and a strain gauge arranged on the bottom surface of the beam end to form a bridge;

the fourth bridge arm is formed by connecting two constant value resistors with the same resistance value as the first bridge arm or the third bridge arm end to form a bridge.

3. The method according to claim 1, wherein the series full bridge structure is characterized in that: and connecting the bridge arms of the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm end to form a series bridge.

4. The method according to claim 1, wherein the setting of the resistance strain gauge means: and strain gauges are arranged along the length direction of the beam type structure, and are externally connected with constant-value resistors with equal resistance values.

5. The method of strain modal parameter measurement of claim 1, wherein the computational model further comprises: the device comprises a variable voltage source, an impact hammer, a dynamic strain signal amplifier and a data processing system;

the variable voltage source is used for supplying power to the series full-bridge structure;

the impact hammer is used for hammering at a signal generation point to provide hammering excitation for the serial full-bridge structure;

the dynamic strain signal amplifier is used for amplifying the strain response generated by the structure under the hammering excitation;

and the data processing system is connected with the circuit output of the serial full-bridge structure and used for calculating the output quantity of the full-bridge structure and inputting the output quantity into the corresponding calculation model so as to calculate and obtain each identification result.

6. The method according to claim 1, wherein the obtaining the output signal of the sampling point comprises:

acquiring resistance parameters of the four groups of resistance strain gauges, wheatstone circuit bridge voltage and sensitivity coefficients of the strain gauges, wherein the resistance parameters further comprise: beam structure right resistance R _R Left resistance R of beam structure _L Roof resistor R with beam structure _T Bottom surface resistance R of beam structure _B ；

The output voltage of the full-bridge strain gauge is calculated in the following mode:

wherein, U _B Is a Wheatstone circuit bridge voltage, U ₀ The output voltage of the full-bridge strain gauge, R, the resistance of the strain gauge, and Δ R, the variation of the strain gauge resistance.

7. The method of measuring a modal strain parameter of claim 6, wherein the modal strain parameter comprises: the longitudinal strain of each surface of the beam structure is calculated in the following way:

wherein epsilon is the longitudinal strain of each surface of the beam structure, and the value of epsilon is the sum of the strain responses of four surfaces of the beam structure.

8. The method according to claim 1, wherein the output signals of the test sampling points refer to:

strain signals generated by point hammering excitation of the impact force hammer on the signals of the beam type structure;

the strain signal has been amplified by a dynamic strain signal amplifier.

9. The method of measuring strain modal parameters of claim 1 wherein 9 signal generating points are provided in one of the beam structures, the 9 signal generating points being evenly distributed in the beam structure.

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