A method for measuring strain modal parameters of a beam structure

Abstract

The application discloses a kind of strain modal parameter measurement methods of beam structure, comprising the following steps: in beam structure determines signal generation point;In signal generation point, specify signal sampling point;In signal sampling point, build series full-bridge structure, according to series full-bridge structure configuration calculation model;The output signal of test sampling point is obtained, and the strain modal parameter of beam structure is calculated.According to the above technical scheme, the strain modal parameter of beam structure under different working conditions can be accurately identified and measured, the accuracy of identification and measurement results can be improved, the measured modal parameter is closer to the actual situation, and the nonlinear error caused by structural mutation can be effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of bridge health monitoring, and more specifically, to a method for measuring the strain modal parameters of a beam structure. Background Technology

[0002] With the rapid development of my country's modern industry, highways, and railways, especially the development of truss, steel, and beam structure industries, more and more buildings and other fields are adopting beam structures for construction. These are often the first choice, or even the only choice, for critical structures in key national engineering projects. Currently, common detection methods for damage identification and vibration fatigue testing of beam structures include ultrasonic testing, infrared testing, acoustic emission, spontaneous potential detection, and impact echo detection. These methods can perform structural health checks on the appearance and structural characteristics of beam structures.

[0003] Damage assessment of key structural components and nodes in beam structures is difficult to reflect using the above detection methods. Therefore, for beam structures, a systematic and comprehensive technical solution is needed to evaluate the overall structural health, safety level, and remaining lifespan. This technical solution obtains the natural frequency, damping, and corresponding structural mode shapes of the structural system through the identification, measurement, and processing of strain modal parameters of the beam structure, providing a scientific means for damage identification and structural health monitoring of beam structures. Summary of the Invention

[0004] To achieve the above objectives, this application provides a method for measuring the strain modal parameters of a beam structure, comprising the following steps:

[0005] Determine the signal generation point in a beam structure;

[0006] Specify the signal sampling point at the signal generation point;

[0007] A series full-bridge structure is built at the signal sampling points, and a calculation model is configured based on the series full-bridge structure.

[0008] Acquire the output signals from the test sampling points and calculate the strain modal parameters of the beam structure;

[0009] The construction of the series full bridge structure includes: installing resistance strain gauges on the four surfaces of the beam, forming four sets of bridge arms, which are defined as the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm.

[0010] 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.

[0011] The second bridge arm is formed by connecting two fixed resistors with the same resistance value as the first bridge arm end to end.

[0012] The third bridge arm consists of a strain gauge located on the left side of the beam and a strain gauge located on the bottom side of the beam, connected end to end to form an electric bridge.

[0013] The fourth bridge arm is formed by connecting two fixed resistors with the same resistance value as the first or third bridge arm end to end to form a bridge circuit.

[0014] Furthermore, the series full-bridge structure refers to connecting the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm end to end to form a series bridge.

[0015] Furthermore, the setting of resistance strain gauges refers to: arranging strain gauges along the length of the beam structure and connecting them to fixed resistors of equal resistance.

[0016] The calculation model also includes: a variable voltage source, an impact hammer, a dynamic strain signal amplifier, and a data processing system;

[0017] A variable voltage source is used to power the series full-bridge structure;

[0018] The impact hammer is used to strike at the signal generation point, providing hammering excitation to the series full-bridge structure;

[0019] Dynamic strain signal amplifiers are used to amplify the strain response of a structure under hammer excitation.

[0020] The data processing system is connected to the circuit output of the series full-bridge structure and is used to calculate the corresponding calculation model of the output input of the full-bridge structure in order to calculate the recognition results in each direction.

[0021] Furthermore, acquiring the output signals of the test sampling points includes: acquiring the resistance parameters of four sets of resistance strain gauges, the Wheatstone bridge voltage, and the sensitivity coefficient of the strain gauges. The resistance parameters also include: the resistance R on the right side of the beam structure. R The left-side resistance R of the beam structure L The top surface resistance R of the beam structure T The bottom resistance R of the beam structure B ;

[0022] The output voltage of a full-bridge strain gauge is calculated as follows:

[0023]

[0024] Among them, U B U0 is the output voltage of the full-bridge strain gauge, R is the resistance of the strain gauge, and ΔR is the change in resistance of the strain gauge.

[0025] The strain modal parameters include: longitudinal strain on each surface of the beam structure, calculated as follows:

[0026]

[0027] Where ε represents the longitudinal strain on each surface of the beam structure, and its value is the sum of the strain responses of the four surfaces of the beam structure.

[0028] Furthermore, the output signal of the test sampling point refers to:

[0029] The strain signal generated by the impact excitation of an impact hammer at the signal generation point of a beam structure;

[0030] The strain signal has been amplified by a dynamic strain signal amplifier.

[0031] Nine signal generation points are set in one of the beam structures, and the nine signal generation points are evenly distributed in the beam structure.

[0032] According to the present invention, the strain modal parameters of beam structures under different working conditions can be accurately identified and measured, thereby improving the accuracy of identification and measurement results, making the modal parameters closer to the actual situation, and effectively avoiding nonlinear errors caused by structural abrupt changes. Attached Figure Description

[0033] Figure 1 This is a step diagram of the method for measuring strain modal parameters of a beam structure according to an embodiment of the present invention;

[0034] Figure 2 This is a diagram of a series full-bridge structure provided according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the location of resistance strain gauges according to an embodiment of the present invention. Detailed Implementation

[0036] The specific implementation of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] This invention is used to detect the characteristics of key structural components of beam structures. Resistance strain gauges are installed at designated positions on their surfaces to form a multi-faceted series combination. This combination is then used in conjunction with a variable voltage source, an impact hammer, a dynamic signal amplifier, and a data acquisition system to acquire the amplified signal after the strain response and calculate the strain modal parameters.

[0038] Figure 1 The method for measuring the strain modal parameters of the beam structure in this application is illustrated in the figure, which includes the following steps:

[0039] Step S100: Determine the signal generation point in the beam structure;

[0040] The method provided in this application identifies nine hammer impact points on the beam as signal generation points, such as... Figure 3 As shown, the nine signal generation points are evenly distributed in the beam structure.

[0041] Step S110: Specify the signal sampling point in the signal generation point:

[0042] In step S100, a signal generation point is selected as the signal sampling point, such as... Figure 3 In the middle, point 2 is selected as the signal sampling point, and a series full bridge is arranged at the signal sampling point.

[0043] Step S120: Construct a series full-bridge structure at the signal acquisition location and configure the calculation model according to the series full-bridge structure;

[0044] The beam structure constructed in this step is a series full-bridge structure. First, four sets of resistance strain gauges are set on the four surfaces of the beam. The four sets of resistance strain gauges form four bridge arms, which are defined as the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm.

[0045] The first bridge arm consists of a strain gauge placed on the top surface of the beam and a strain gauge placed on the right side of the beam, connected end to end to form an electric bridge.

[0046] The second bridge arm is formed by connecting two fixed resistors with the same resistance value as the first bridge arm end to end.

[0047] The third bridge arm consists of a strain gauge located on the left side of the beam and a strain gauge located on the bottom side of the beam, connected end to end to form an electric bridge.

[0048] The fourth bridge arm is formed by connecting two fixed resistors with the same resistance value as the first or third bridge arm end to end to form a bridge circuit.

[0049] When the transverse section of the beam structure is quadrilateral, the first surface is the right surface, the third surface is the top surface, and the second and fourth surfaces are the left surface and the bottom surface, respectively. That is, among the right surface, left surface, top surface and bottom surface, the first and third resistance strain gauges, the second and fourth resistance strain gauges are arranged parallel to the longitudinal direction of the beam structure.

[0050] like Figure 2 As shown, the series-connected full-bridge structure includes: two longitudinal resistance strain gauges on the right and top surfaces connected in series to form the first bridge arm; two longitudinal resistance strain gauges on the left and bottom surfaces connected in series to form the third bridge arm; external fixed resistors of equal resistance connected end to end to form the second and fourth bridge arms; and the bridge arms containing the first, second, third, and fourth bridge arms are connected end to end to form a series-connected bridge.

[0051] In practical applications, the longitudinal material properties of each surface of a beam structure are non-uniform. The difference in longitudinal material properties will lead to different strain effects on each surface. Therefore, this application designs the position of the strain gauges, that is, at the center of the four surfaces in the middle of the beam structure, strain gauges and external fixed resistors of equal resistance are arranged along the length of the structure to form a multi-arm series full bridge. That is, setting up resistance strain gauges means that on each bridge arm, strain gauges are arranged along the length of the beam structure and external fixed resistors of equal resistance are connected to form resistance strain gauges.

[0052] Strain gauges can reflect the amount of surface deformation of the test piece. By adjusting the position of the strain gauges, the difference in strain influence on the surface material can be reduced, effectively avoiding nonlinear errors caused by structural abrupt changes.

[0053] The method for arranging strain gauges is to attach and fix them to the surface of the beam structure.

[0054] After the series full-bridge structure is determined, the calculation model is configured. The calculation model also includes: a variable voltage source, an impact hammer, a dynamic strain signal amplifier, and a data processing system.

[0055] A variable voltage source is used to power the series full-bridge structure;

[0056] Impact hammers are used to provide hammering excitation to tandem full-bridge structures to generate strain signals;

[0057] Dynamic strain signal amplifiers are used to amplify the strain signals generated by a structure under hammer excitation in order to improve the accuracy of identification and measurement results and make the measured modal parameters closer to the actual situation.

[0058] The data processing system is connected to the circuit output of the series full-bridge structure and is used to calculate the corresponding calculation model of the output input of the full-bridge structure in order to calculate the recognition results in each direction.

[0059] Step S130: Obtain the output signal of the test sampling point and calculate the strain modal parameters of the beam structure;

[0060] Figure 3 The figure shows a schematic diagram of the location of resistance strain gauges. Nine impact points were determined on the beam. In this application, an impact hammer was designed to strike different impact points in sequence, and sampling was performed at point 2 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.

[0061] In this step, the resistance parameters of four sets of resistance strain gauges, the Wheatstone bridge voltage, and the sensitivity coefficient of the strain gauges are obtained; for example... Figure 2 As shown in the diagram, in the strain gauge arrangement, the right side R of the beam structure RArranged longitudinally along the beam structure; R on the left side of the beam structure L Arranged longitudinally along the beam structure; top surface R of the beam structure T Arranged longitudinally along the beam structure; bottom surface R of the beam structure B Arranged longitudinally along the beam structure.

[0062] The output voltage of a full-bridge strain gauge is calculated as follows:

[0063]

[0064] Among them, U B U0 is the output voltage of the full-bridge strain gauge, R is the resistance of the strain gauge, and ΔR is the change in resistance of the strain gauge.

[0065] This calculation method can be written as: Where K is the sensitivity coefficient of the strain gauge;

[0066] The method for calculating the output voltage can be modified as follows: Where ε is the sum of the strain responses of the four surfaces of the beam structure, and ε1, ε2, ε3 and ε4 are the longitudinal strain responses measured on the four surfaces of the beam structure, respectively.

[0067] Let: ε1 = ε T1 ;ε2=ε R1 ;ε3=ε B1 ;ε4=ε L1 ;

[0068] Modal parameters include: longitudinal strain on each surface of the beam structure, calculated as follows:

[0069]

[0070] Where ε is the sum of the strain responses of the four surfaces of the beam structure, and ε1, ε2, ε3 and ε4 are the longitudinal strain responses measured on the four surfaces of the beam structure, respectively.

[0071] Then the output voltage:

[0072] Transformed into:

[0073] According to ε=ε1+ε2+ε3+ε4 we can get:

[0074] In this step, the accurate strain response value of the structure is identified by the full bridge and used as input for one row or one column of the strain frequency response function matrix.

[0075] The method provided by this invention can accurately identify and measure the strain modal parameters of beam structures under different working conditions, which can improve the accuracy of identification and measurement results. The measured modal parameters are closer to the actual situation and can effectively avoid nonlinear errors caused by structural abrupt changes.

[0076] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the present invention is not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method of measuring strain modal parameters of a beam structure, characterized by, The method comprises the following steps: determining a signal generation point in a beam structure; designating a signal sampling point in the signal generation point; building a series full-bridge structure in the signal sampling point, and configuring a calculation model according to the series full-bridge structure; obtaining an output signal of the signal sampling point, and calculating a strain modal parameter of the beam structure; wherein the building of the series full-bridge structure comprises: arranging a resistance strain gauge on four direction surfaces of the beam, forming four bridge arms through the resistance strain gauges, and defining the four bridge arms as a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm; the series full-bridge structure refers to connecting the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm in series to form a series electric bridge; the arranging of the resistance strain gauges refers to arranging strain gauges along the length direction of the beam structure, and connecting constant-value resistors with equal resistance values; the positions of the strain gauges are the center positions of the four surfaces in the middle of the beam structure; the four surfaces refer to a right surface, a top surface, a left surface and a bottom surface; wherein the two resistance strain gauges on the right surface and the top surface are connected in series to form the first bridge arm, and the two resistance strain gauges on the left surface and the bottom surface are connected in series to form the third bridge arm; the output signal of the signal sampling point is calculated based on the longitudinal strain responses measured on the four surfaces of the beam structure; 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 in series to form an electric bridge; the second bridge arm is formed by connecting two constant-value resistors with equal resistance values in series and connecting the two constant-value resistors in series with the first bridge arm; 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 in series to form an electric bridge; the fourth bridge arm is formed by connecting two constant-value resistors with equal resistance values in series and connecting the two constant-value resistors in series with the first bridge arm or the third bridge arm to form an electric bridge.

2. The strain modal parameter measurement method of claim 1, wherein, the calculation model further comprises: a variable voltage source, an impact force hammer, a dynamic strain signal amplifier and a data processing system; the variable voltage source is used to supply power to the series full-bridge structure; the impact force hammer is used to hammer 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 the hammering excitation; the data processing system is connected to the circuit output of the series full-bridge structure, and is used to calculate the corresponding calculation model of the output quantity input of the full-bridge structure to obtain the identification results in each direction.

3. The strain modal parameter measurement method of claim 1, wherein, the obtaining of the output signal of the signal sampling point comprises: Obtaining resistance parameters of the four groups of resistance strain gauges, Wheatstone bridge voltage, sensitivity coefficient of the strain gauge, the resistance parameters further include: beam structure right face resistance R R , beam structure left face resistance R L , beam structure top face resistance R T , beam structure bottom face resistance R B ; the calculation method of the output voltage of the full-bridge structure is: ， wherein, is the bridge voltage of the Wheatstone circuit, is the output voltage of the full-bridge strain gauge, R is the resistance of the strain gauge, is the change in resistance of the strain gauge.

4. The strain modal parameter measurement method of claim 3, wherein, the strain modal parameter comprises: the longitudinal strain of each surface of the beam structure, and the calculation method is: , wherein, the output signal of the signal sampling point refers to: S is the sum of the strain responses of the four faces of the beam structure, the strain signal generated by the impact force hammer at the signal generation point of the beam structure under hammering excitation; 1、 the strain signal is amplified by the dynamic strain signal amplifier. 2、 nine signal generation points are arranged in the beam structure, and the nine signal generation points are evenly distributed in the beam structure. 3 and ​ 4 are the longitudinal strain responses measured on the four surfaces of the beam structure, respectively, and K is the sensitivity coefficient of the strain gauge.

5. The strain modal parameter measurement method of claim 1, wherein, ​ ​ ​ 6. The strain modal parameter measurement method of claim 1, wherein, ​

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