Test Method for Damage Identification of Precast Assembled Beam Bridges Based on Strain Curves

Abstract

This invention relates to the field of bridge testing and inspection technology, specifically disclosing a test method for damage identification of precast assembled beam bridges based on strain curves. The method includes: arranging multiple strain test points on the precast assembled beam bridge to be tested; applying a moving load and collecting strain data from the strain sections; extracting the strain data from each strain section and performing noise reduction processing on the strain data to obtain the strain influence lines for each strain section; determining the longitudinal damage location: determining the longitudinal damage location based on the changes in the intersection positions of strain influence lines at different spans. This invention uses strain influence lines at different spans of the longitudinal beams of the precast assembled beam bridge to correct errors caused by residual strain influence and reduce noise in the test data, reducing errors caused by equipment and environmental factors. Changes in the intersection points of the strain influence lines enable longitudinal damage identification of the precast assembled beam bridge. The test is short, has minimal impact on bridge traffic, reduces test costs, and improves economic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of bridge testing and inspection technology, and specifically relates to a test method for damage identification of precast assembled beam bridges based on strain curves. Background Technology

[0002] Bridges are a crucial component of transportation infrastructure, serving as vital arteries for transportation and playing a critical role in promoting social and economic development. Precast beam bridges, as a common bridge structure, are highly adaptable to crossing obstacles of medium and small spans and constitute a significant portion of my country's total bridge fleet. During their service life, with the increasing duration of service, various natural environmental factors and traffic conditions combine to cause some beam bridges to gradually deteriorate and age, resulting in reduced strength, decreased load-bearing capacity, and reduced reliability. In severe cases, this can even endanger pedestrian and vehicular safety. For precast beam bridges, beam damage, represented by concrete cracking, breakage, and carbonation, is a significant factor jeopardizing bridge safety. Timely and effective damage identification is essential for the safe operation of precast beam bridges.

[0003] Load testing is the most commonly used method for bridge damage diagnosis. Traditional load testing employs a step-by-step application of static loads, resulting in a cumbersome process that requires prolonged traffic closures, causing significant disruption to normal traffic and making it uneconomical. Furthermore, traditional load testing methods rely solely on calibration coefficients to diagnose the overall health of the bridge, leading to a single diagnostic indicator and coarse, inaccurate results. Researching a longitudinal damage identification test method for precast assembled beam bridges, enabling rapid identification of damage location and extent, is crucial for effectively preventing bridge safety accidents. Summary of the Invention

[0004] The purpose of this invention is to provide a test method for damage identification of precast assembled beam bridges based on strain curves, which can effectively identify the location and extent of longitudinal damage in precast assembled beam bridges and improve the accuracy of the test.

[0005] To achieve the above objectives, this invention provides a test method for damage identification of precast assembled beam bridges based on strain curves, comprising the following steps:

[0006] (1) Arrange strain test points: Arrange multiple strain test points on the precast assembled beam bridge to be tested. The multiple strain test points are respectively set at the spans L / 4, L / 2 and L3 / 4 of the middle beam C, the side beam A and the side beam E.

[0007] (2) Applying moving load: Apply moving load to the beam bridge by moving the loading vehicle at a constant low speed along the bridge deck from the end of the bridge to the end of the bridge, and collect strain data of the strain section at the spans L / 4, L / 2 and L3 / 4 of the side beams and middle beams through the data acquisition and analysis system.

[0008] (3) Data extraction and processing: Extract strain data of each strain section, and perform noise reduction processing on the strain data to obtain the strain influence line of each strain section;

[0009] (4) Determination of longitudinal damage location: The longitudinal damage location is determined by the change in the position of the intersection of the strain influence lines at span L / 4 and L / 2 and the intersection of the strain influence lines at span L / 4 and L3 / 4 with the corresponding intersection of the strain influence lines in the undamaged state.

[0010] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, the acquisition and analysis system includes a dynamic signal acquisition instrument, a switch, and a computer; the dynamic acquisition instrument is connected to the switch via a network cable, the switch is connected to the computer via a network cable, and the dynamic acquisition instrument is connected to the strain gauge.

[0011] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridge based on strain curve, in step (2), the moving load is applied by means of positive load or eccentric load.

[0012] Preferably, in the above-mentioned test method for damage identification of prefabricated assembled beam bridges based on strain curves, the loading vehicle is a three-axle or four-axle heavy-duty vehicle.

[0013] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, the following algorithm is used to correct the error caused by residual strain:

[0014]

[0015] Among them, B p The measured strain A p The corrected strain value, A p To influence the strain value at point p in the online time history, m is the time history coordinate corresponding to the peak point, T is the effective time history, and ε is the strain value at point T.

[0016] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, the noise reduction processing of strain data in step (3) is as follows: preliminary fitting and preliminary noise reduction are performed using the "balance shift" method, with a balance distance of 30 numerical points, specifically:

[0017]

[0018]

[0019]

[0020] Where K is the number of equilibrium numerical points, m is the total number of data points collected by the data acquisition and analysis system, and A n B represents the measured strain value on the strain influence line when the time history is n. n The measured strain value is given by the strain influence line after initial fitting when the time history is n; p represents a time point in the time period, which is a number from 1 to 15; Q represents a time point in the time period, which is a number from m to 15.

[0021] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, the influence lines obtained from the initial noise reduction undergo secondary noise reduction processing: a polynomial piecewise fitting method is used for secondary fitting, dividing the initially fitted ε-t influence lines into 8 equal parts, and fitting them using the least squares method. The fitting principle is as follows:

[0022] Preset n-term polynomial y n (x), and the number of fitting iterations is N = n + 1.

[0023] y n =A0+A1x+A2x 2 +...+A n (5)

[0024] Wherein, error a n for:

[0025] a n =Y i -y i =Y i -A0-A1x-A2x 2 -...-A n (6)

[0026] Where Y n y represents the measured strain value. n Let be the fitted strain value. The total average error of the polynomial is δ.

[0027]

[0028] The coefficients A0, A1, A2...A can be obtained by combining equation (6) with the measured strain influence line. n These coefficients satisfy the following analytical expression:

[0029]

[0030] Rearrange equation (6).

[0031]

[0032] Equation (7) is finally transformed into the following form:

[0033]

[0034] Since equation (10) is an ill-conditioned system of equations, rounding errors during the solution process will cause the calculated A to be affected. n There is a large error, and the error increases with the degree n of the polynomial, so n should be less than 7.

[0035] The negative correlation coefficient E is used as an indicator of the correlation between the fitted influence line and the measured influence line, and its expression is as follows:

[0036]

[0037] In the formula, y i Let be the measured strain at the i-th sampling point. Let be the fitted strain at the i-th acquisition point. This represents the average measured strain. The closer E is to 1, the higher the fitting accuracy.

[0038] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, the fitting accuracy needs to meet the following requirement: the difference between the envelope area of ​​the second-fit strain influence line and the first-fit influence line is less than 5%.

[0039] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, a temperature compensation block is attached next to the strain section.

[0040] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridges based on strain curves, the strain influence line at the L / n section on the longitudinal beam N and the strain influence line at the L / m section are intersected at point N. L / n-L / m The form numbering, when the strain influence line intersection point C L / 4-L / 2 and C L / 4-L / 2 Compared to the intersection of the strain influence lines in the undamaged state, the ordinate value decreases, indicating damage to the middle beam; when the intersection of the strain influence lines is C... L / 4-L / 2 and C L / 4-3L / 4 The vertical coordinate value increases compared to the intersection of the strain influence lines in the undamaged state, indicating damage to the side beam.

[0041] Preferably, in the above-mentioned test method for damage identification of precast assembled beam bridge based on strain curves, when the middle beam and the side beam are damaged, the intersection point of the strain influence line of the damaged longitudinal beam section moves towards the damage location compared to the intersection point in the undamaged state, and the movement range increases with the increase of damage. The damage location and damage range are determined according to the movement direction and movement range of the intersection point of the strain influence line.

[0042] Preferably, in the above-mentioned test method for damage identification of prefabricated assembled beam bridges based on strain curves, the corresponding strain influence line in the undamaged state is determined by finite element calculation.

[0043] Compared with existing technologies, the present invention has the following advantages:

[0044] This invention presents a test method for damage identification of precast assembled beam bridges based on strain curves. It tests the strain influence lines of cross-sections at different spans of the longitudinal beams of precast assembled beam bridges. By correcting for errors caused by residual strain and reducing noise in the test data, it minimizes errors caused by equipment and environmental factors, thereby improving test accuracy. Damage identification of precast assembled beam bridges is achieved by observing the changes in the intersection points of strain influence lines at different spans. The test is short, has minimal impact on bridge traffic, avoids prolonged traffic interruptions, reduces test costs, and improves economic efficiency. It can provide a basis for extending the service life of bridges and formulating maintenance plans, and has significant significance and practical value. Attached Figure Description

[0045] Figure 1 This is a data processing flowchart in an embodiment of the present invention.

[0046] Figure 2 This is an elevation view of the model in the experimental example of the present invention (unit of dimensions: mm).

[0047] Figure 3 This is a cross-sectional view of the model in the experimental example of this invention (unit: mm).

[0048] Figure 4 This is a physical image of the T-beam model used in the experimental examples of this invention.

[0049] Figure 5 This is a schematic diagram of the connection between the model and the experimental instrument in the experimental example of this invention.

[0050] Figure 6 This is a schematic diagram of the vertical cracks in the longitudinal beam of a bridge component in the experimental example of this invention.

[0051] Figure 7 The following are schematic diagrams (unit: mm) of damage to bridge components under various working conditions in the test examples of this invention: (a) Schematic diagram of damage location under working condition 1; (b) Schematic diagram of damage location under working condition 2; (c) Schematic diagram of damage location under working condition 3.

[0052] Figure 8 This is a diagram showing the arrangement of the sensors in the experimental examples of this invention.

[0053] Figure 9 The following are the load path diagrams for the test examples of this invention: (a) normal load path; (b) off-center load path.

[0054] Figure 10 Images of the loading test sites in the test examples of this invention: (a) normal load test; (b) off-center load test.

[0055] Figure 11In the test example of this invention, C was tested under normal load without damaging bridge components. L / 2 (At the mid-span of the beam) Strain influence line of the section: (a) before noise reduction; (b) preliminary noise reduction; (c) secondary noise reduction treatment.

[0056] Figure 12 This is an elevation view of the finite element model of the T-beam component in the experimental example of this invention.

[0057] Figure 13 The location of the intersection of the strain influence lines of the positive load path section in the experimental example of this invention: (a) Intersection point C L / 4-L / 2 Location; (b) Intersection C L / 4-3L / 4 Location. Detailed Implementation

[0058] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0059] Example 1

[0060] A test method for damage identification of precast assembled beam bridges based on strain curves includes the following steps:

[0061] (1) Arrange strain measurement points: Multiple strain measurement points are arranged on the precast assembled beam bridge to be tested, respectively set at the spans L / 4, L / 2 and 3L / 4 of the middle beam C, the side beam A and the secondary side beam E; the strain gauges are arranged on the bottom surface of the T beam and connected to the acquisition and analysis system.

[0062] (2) Applying moving load: Apply moving load to the beam bridge by uniformly moving the load at low speed along the bridge deck from one end of the bridge to the other using a loading vehicle. Collect strain data of the strain sections at spans L / 4, L / 2, and L3 / 4 of the side beams and middle beams using a data acquisition and analysis system. The data acquisition and analysis system includes a dynamic signal acquisition instrument, a switch, and a computer. The dynamic signal acquisition instrument is connected to the switch via a network cable, and the switch is connected to the computer via a network cable. The dynamic acquisition instrument is connected to strain gauges. Before collecting data, the strain values ​​at the acquisition points need to be zeroed through the system's self-check, and the strain acquisition frequency needs to be set.

[0063] (3) Data extraction and processing: Strain data for each strain section is extracted. Due to the influence of equipment sensitivity and environmental factors, the extracted strain influence line data will inevitably contain some noise, especially the influence of residual strain and strain hysteresis. The error caused by the influence of residual strain is corrected by the following algorithm:

[0064]

[0065] Where A pTo influence the strain value at point p in the online time history, m is the time history coordinate corresponding to the peak point, T is the effective time history, and ε is the strain value at point T;

[0066] The collected strain influence lines are denoised to obtain the strain influence lines for each strain section; preliminary fitting is performed using a "balance shift" method, with a balance distance of 30 numerical points. The steps are as follows:

[0067]

[0068]

[0069]

[0070] Where K is the number of equilibrium numerical points, m is the total number of data points collected by the data acquisition and analysis system, and A n B represents the measured strain value on the strain influence line when the time history is n. n The measured strain value is given by the strain influence line after initial fitting when the time history is n; p represents a time point in the time period, which is a number from 1 to 15; Q represents a time point in the time period, which is a number from m to 15.

[0071] The influence lines obtained from the initial noise reduction are then subjected to secondary noise reduction: a polynomial piecewise fitting method is used for secondary fitting, dividing the initially fitted ε-t influence lines into 8 equal parts, and fitting them using the least squares method. The fitting principle is as follows:

[0072] Preset n-term polynomial y n (x), and the number of fitting iterations is N = n + 1.

[0073] y n =A0+A1x+A2x 2 +...+A n (5)

[0074] Wherein, error a n for:

[0075] a n =Y i -y i =Y i -A0-A1x-A2x 2 -...-A n (6)

[0076] Where Y n y represents the measured strain value. n Let be the fitted strain value. The total average error of the polynomial is δ.

[0077]

[0078] The coefficients A0, A1, A2...A can be obtained by combining equation (6) with the measured strain influence line. n These coefficients satisfy the following analytical expression:

[0079]

[0080] Rearrange equation (6).

[0081]

[0082] Equation (7) is finally transformed into the following form:

[0083]

[0084] Since equation (10) is an ill-conditioned system of equations, rounding errors during the solution process will cause the calculated A to be affected. n There is a large error, and the error increases with the degree n of the polynomial, so n should be less than 7.

[0085] The negative correlation coefficient E is used as an indicator of the correlation between the fitted influence line and the measured influence line, and its expression is as follows:

[0086]

[0087] In the formula, y i Let be the measured strain at the i-th sampling point. Let be the fitted strain at the i-th acquisition point. This represents the average measured strain. The closer E is to 1, the higher the fitting accuracy.

[0088] Output the fitting results for each influence line segment. The fitting accuracy must meet the following requirement: the difference between the envelope area of ​​the second-fit influence line and the first-fit influence line is less than 5%. The specific data processing flow is as follows: Figure 1 As shown.

[0089] (4) Determination of longitudinal damage location: The strain influence line at the L / n section on the longitudinal beam N and the strain influence line at the L / m section are intersected at point N. L / n-L / m The form numbering, when the strain influence line intersection point C L / 4-L / 2 and C L / 4-3L / 4 Compared to the intersection of the strain influence lines in the undamaged state, the ordinate value decreases, indicating damage to the middle beam; when the intersection of the strain influence lines is C... L / 4-L / 2 and C L / 4-3L / 4Compared to the intersection of the strain influence lines in the undamaged state, the ordinate value increases, indicating damage to the edge or side beams. When the middle and edge beams are damaged, the intersection of the strain influence lines at the damaged longitudinal beam section moves towards the damage location compared to the intersection in the undamaged state. The magnitude of this movement increases with the extent of damage. The location and extent of damage are determined based on the direction and magnitude of the movement of the strain influence line intersection. For example, when the middle beam is damaged, C... L / 4-L / 2 Move to the lower right, C L / 4-3L / 4 Moving to the lower left will cause the damaged area to be closer to the mid-span.

[0090] Experimental Example 2

[0091] 1. Engineering test objects and test equipment

[0092] The prototype bridge used in this experiment was a 40-meter T-beam bridge template issued by the Ministry of Transport in 2009, and a scaled-down test model was fabricated at a 20:1 scale. Considering the good workability of PMMA (polymethyl methacrylate) material and its ability to effectively simulate the material properties of the bridge, a third party was commissioned to fabricate the scaled-down test model using PMMA. The model contains 5 longitudinal beams, with a span of 2000 mm, a bridge width of 600 mm, a height of 120 mm, a T-beam flange thickness of 18 mm, a diaphragm thickness of 10 mm, a web thickness of 18 mm, and diaphragm spacing of 340 mm × 2 + 330 mm × 4. The elevation and cross-sectional views of the model are shown below. Figure 2 and Figure 3 The scaled-down test model of the T-beam bridge can be seen in the physical object. Figure 4 .

[0093] A distributed dynamic signal acquisition and analysis system was adopted, which includes dynamic signal acquisition units, network cables, connecting instruments, a computer and a switch, and signal input lines. Two dynamic signal acquisition units were used, each with eight signal test channels. The acquisition units were connected to the switch via network cables, and the switch was connected to the computer via network cables. The dynamic strain range was 0–50000 με, and the resolution frequency was 0.1 με, fully meeting the experimental accuracy requirements. Before data acquisition, the strain values ​​at the acquisition points needed to be zeroed through system self-check, and the strain acquisition frequency needed to be set. This experiment used a range of 0–1000 με and employed a half-bridge method to connect the specimen and temperature compensation plate. The connection relationships between the various components are shown in [reference needed]. Figure 5 .

[0094] The vehicle model is a dual-axle, four-wheel counterweight model car, with iron blocks used to balance the weight to 20.38 kg. These iron blocks are symmetrically arranged on the vehicle chassis to ensure equal weight on all four wheels. The vehicle has a wheelbase of 200 mm and a track width of 80 mm. The vehicle is traction-based using a variable frequency motor, and the speed can be controlled by adjusting the motor speed via a frequency regulator.

[0095] 2. Experimental Procedure

[0096] This model test consisted of four parts, arranged in the following order: non-destructive testing, diaphragm damage testing, central beam damage testing, and side beam damage testing. All damage tests were conducted based on the model from the previous test. Because the elastic modulus of acrylic glass is highly sensitive to temperature changes, the indoor temperature was adjusted to 20°C using air conditioning before each test, and maintained for 3 hours before the test began.

[0097] The specific damage conditions of the T-beam are as follows:

[0098] To fully represent the influence of cracks in bridge components on the strain line, this experiment simulated transverse and longitudinal damage to the bridge by cutting cracks at the bottom of the longitudinal beams and transverse diaphragms. Due to the small scale of the model and the high sensitivity of the testing instruments, the quasi-static load test was susceptible to errors caused by environmental factors. To minimize the impact of these errors and to highlight the mechanical performance characteristics of the damaged bridge structure, larger cracks were incorporated into the predetermined damage area.

[0099] The experiment included a no-destructive test and three damage conditions: damage to the mid-span diaphragm, damage to the middle beam, and damage to the side beams. Details of each condition are shown in Table 1. Cracks in the diaphragm and longitudinal beams are shown in [Table 1]. Figure 6 See the schematic diagram of the damage location under each working condition. Figure 7 Assuming the area with cracks completely loses its bending resistance, the bending stiffness loss in the cracked area of ​​the model is set to 50%. Finite element simulation verifies that after damage occurs, the area envelope of the strain influence line recorded at measuring points near the damaged area changes by approximately 10%, highlighting the effect of damage on the influence line characteristics. The simulation of transverse damage is achieved by creating cracks in the middle beam and the left and right secondary side beams of the mid-span diaphragm of the specimen. The crack height is selected as 14 mm, and the stiffness of the diaphragm is reduced by half after the cracks appear.

[0100] Table 1 Damage Conditions

[0101]

[0102]

[0103] (1) Strain measurement point arrangement: The sensor placement and specific numbering are shown in the figure. Figure 8 Strain gauges are uniformly attached to the bottom edge of the T-beam. Temperature compensation blocks, made of the same material and thickness as the bottom edge of the T-beam, are attached next to the strain section. The locations of the strain gauges are shown in the attached diagram. Figure 8 .

[0104] (2) Applying the moving load: At the start of the test, the test vehicle should be placed at the front end of the acceleration ramp and its travel track should be strictly corrected. Then, the frequency regulator should be set to 20 r / min. After completion, the traction motor should be started to make the vehicle model travel at a constant speed. After the rear axle of the test model vehicle enters the deceleration ramp, the motor should be turned off and the recording of dynamic strain values ​​should be stopped. After waiting for 10 minutes, the vehicle should be reset to start the next test. The test under the same working condition should be repeated 15 times to ensure that relatively ideal data can be obtained.

[0105] To ensure the representativeness of the collected data, this experiment used two loading methods: normal load and off-center load. The specific paths are as follows: Figure 9 As shown in the pictures of the test site... Figure 10 As shown.

[0106] (3) Data extraction and processing:

[0107] The strain influence lines collected under various working conditions were denoised. Initial fitting was performed using a "balance shift" method. However, the influence lines still exhibited significant fluctuations after initial denoising. Therefore, secondary denoising was required for the data collected in this experiment, with a balance distance of 30 numerical points. The fitting was performed using a polynomial piecewise fitting method, dividing the initially fitted ε-t influence line into eight equal parts and fitting it using the least squares method. Figure 11 In the normal load test of the undamaged model, C L / 2 The strain influence lines at the mid-span section (of the beam) after unreduced noise, preliminary noise reduction, and secondary noise reduction are shown in the figure. It can be seen that the unreduced strain influence line exhibits significant fluctuations, especially when the vehicle enters and exits the test model and travels to the mid-span L / 2. After the initial noise reduction, the noise in the influence line is largely eliminated, but noticeable fluctuations still exist in some areas. After the secondary noise reduction, the influence line is essentially composed of smooth lines, effectively reflecting the static characteristics of the model.

[0108] (4) Analysis of the intersection point of strain influence lines:

[0109] The intersection points of the strain influence lines at beam C in the normal load test and at beam A in the eccentric load test were statistically analyzed, and the results are shown in Table 2. Table 2 shows that the intersection point of the strain influence lines at beam C in load condition 2 is... L / 4-L / 2 and C L / 4-3L / 4 The decrease in the ordinate value of the corresponding intersection point compared to condition 1 indicates damage to the middle beam, which is consistent with the facts. The intersection point C of the middle beam strain influence lines in condition 3... L / 4-L / 2 and C L / 4-3L / 4 The increase in the ordinate value of the corresponding intersection point compared to condition 2 indicates damage to the side beam, which is consistent with the facts.

[0110] Table 2 Information on the location of the intersection of the influence lines

[0111]

[0112] The simulation data in Table 2 were obtained using a finite element model of acrylic glass built with MidasCivil. The model elevation is shown below. Figure 12 As shown. Based on the data provided by the manufacturer, the elastic modulus, Poisson's ratio, and unit weight of the model material at room temperature of 20℃ are specified. Dynamic load on the model vehicle was simulated by establishing multiple static load cases along the dynamic load path. Data was collected every 0.01 units the vehicle advanced along the path, resulting in a total of 225 static load cases. The model consists of 3803 elements and 1408 nodes.

[0113] Compare the test data from the normal load test in Table 2, where the intersection point C... L / 4-L / 2 and C L / 4-3L / 4 The positions in operating conditions 1 and 2 are as follows: Figure 13 As shown in the figure, when the load path is under positive load, the intersection point C L / 4-L / 2 Due to damage to the central beam, it moved to the lower right, intersection point C L / 4-3L / 4 Moving to the lower left, the coordinate changes of the two intersection points are basically consistent in both the simulation and experimental results. Measured intersection point C L / 4-L / 2 The point shifted 0.014 to the right due to the damage, close to the simulated value of 0.02; the measured intersection point C... L / 4-3L / 4 The beam shifted 0.055 to the left due to the damage, which is close to the simulated value of 0.06. All intersections moved in the direction of the damage location, indicating that the damage location was the middle beam near the mid-span.

[0114] In summary, the direction of movement of the intersection point of the strain influence lines indicates the location of damage. This direction of movement through the intersection point C of the strain influence lines... L / 4-L / 2 and C L / 4-3L / 4 Compared to the intersection of the strain influence lines in the undamaged state, the ordinate value decreases, indicating damage to the middle beam; when the intersection of the strain influence lines C... L / 4-L / 2 and C L / 4-3L / 4 Compared to the intersection of the strain influence lines in the undamaged state, the ordinate value increases, indicating damage to the side beam. When the middle and side beams are damaged, the intersection of the strain influence lines of the damaged longitudinal beam section moves towards the damage location compared to the intersection in the undamaged state. The magnitude of the movement increases with the increase of damage. The location and magnitude of damage can be determined based on the direction and magnitude of the movement of the intersection of the strain influence lines, which has been verified in the examples.

[0115] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A test method for damage identification of precast assembled beam bridges based on strain curves, characterized in that, Includes the following steps: (1) Arrange strain test points: Arrange multiple strain test points on the precast assembled beam bridge to be tested. The multiple strain test points are respectively set at the spans L / 4, L / 2 and L3 / 4 of the middle beam C, the side beam A and the side beam E; (2) Applying moving load: Apply moving load to the beam bridge by moving the loading vehicle at a constant low speed along the bridge deck from the end of the bridge to the end of the bridge, and collect strain data of the strain section at the spans L / 4, L / 2 and L3 / 4 of the side beams and the middle beams through the data acquisition and analysis system. (3) Data extraction and processing: Extract strain data for each strain section, and perform noise reduction on the strain data to obtain the strain influence lines for each strain section; the noise reduction of the strain data is performed by using the "balance shift" method for preliminary fitting and preliminary noise reduction, with a balance distance of 30 numerical points, specifically: in, K To balance the number of numerical points, m This represents the total number of data collected by the data acquisition and analysis system. A n The measured strain value is given by the strain influence line when the time history is n. B n The measured strain values ​​on the strain influence line with time history n after preliminary fitting; The influence lines obtained from the initial noise reduction are subjected to secondary noise reduction: a polynomial piecewise fitting method is used for secondary fitting, and the results of the initial fitting are then processed. ε-t The influence line was divided into 8 equal parts and fitted using the least squares method. (4) Determination of longitudinal damage location: The longitudinal damage location is determined by the change in the position of the intersection of the strain influence lines at span L / 4 and L / 2 and the intersection of the strain influence lines at span L / 4 and L3 / 4 with the corresponding intersection of the strain influence lines in the undamaged state.

2. The test method for damage identification of precast assembled beam bridges based on strain curves according to claim 1, characterized in that, In step (2), the moving load is applied using positive load and / or off-center load.

3. The test method for damage identification of precast assembled beam bridges based on strain curves according to claim 1, characterized in that, The fitting accuracy must meet the following requirement: the difference between the area of ​​the influence line envelope of the second-fit strain and the influence line of the first-fit strain must be less than 5%.

4. The test method for damage identification of precast assembled beam bridges based on strain curves according to claim 1, characterized in that, A temperature compensation block is attached next to the strain section.

5. The test method for damage identification of precast assembled beam bridges based on strain curves according to claim 1, characterized in that, On the longitudinal beam N L / n Strain influence lines at the cross section and L / m The strain influence lines at the cross section intersect at the point N L / n - L / m The form numbering, when the strain influence line intersection point C L / 4-L / 2 and C L / 4-3L / 4 Compared to the intersection of the strain influence lines in the undamaged state, the ordinate value decreases, indicating damage to the middle beam; when the intersection of the strain influence lines is C... L / 4-L / 2 and C L / 43-L / 4 The vertical coordinate value increases compared to the intersection of the strain influence lines in the undamaged state, indicating damage to the side beam.

6. The test method for damage identification of precast assembled beam bridges based on strain curves according to claim 5, characterized in that, When the middle beam and the side beam are damaged, the location of the damage is determined by the direction of movement of the intersection of the strain influence lines of the damaged longitudinal beam section compared to the intersection in the undamaged state.

7. The test method for damage identification of precast assembled beam bridges based on strain curves according to claim 1, characterized in that, The corresponding strain influence line under the undamaged state is determined by finite element calculation.

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