A method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating

Abstract

The present invention discloses a method for evaluating the elastic modulus and strength of a concrete bridge main beam based on fiber grating, and relates to the technical field of nondestructive testing of bridges. The method comprises: constructing a multi-scale finite element model, simulating the wheel weight of a vehicle with concentrated force in the multi-scale finite element model to obtain loading vehicle parameters, and determining a vehicle loading test scheme; performing dynamic and static force loading tests on the main beam respectively, and collecting strain response data in the dynamic and static force loading tests using a distributed fiber grating strain sensor; updating the elastic modulus of the multi-scale finite element model according to the dynamic characteristics of the bridge structure, and using the elastic modulus after parameter update as a reference value for evaluating the elastic modulus of the actual bridge; evaluating the elastic modulus using the reference value; and inferring the concrete compressive strength according to the calculated concrete elastic modulus. The present invention can achieve effective evaluation of the elastic modulus and compressive strength of the concrete bridge main beam in a non-destructive manner.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing of bridges, and in particular to a method for evaluating the elastic modulus and strength of a concrete bridge main beam based on optical fiber gratings. Background Art

[0002] The main beam is the main load-bearing structure of the bridge to bear traffic loads. The reliability of its service performance directly determines the safety of the bridge structure under the operation load. For concrete / prestressed concrete main beams, their service performance is mainly determined by the strength of concrete materials, structural stiffness, stability, dynamic characteristics, etc. Among them, the material strength directly determines the bearing performance of the main beam in terms of compression, tension, torsion, etc.

[0003] During the pouring and curing of the main beam concrete, due to the large temperature difference between day and night and the tight construction schedule, there will be insufficient concrete vibration, premature demoulding, and inadequate curing measures, resulting in the concrete failing to reach the specified strength. Insufficient concrete strength will cause tiny and imperceptible cracks in the main beam during the bridge construction stage. Under the long-term effects of environmental and operational loads such as temperature and traffic loads, the tiny cracks will expand into significantly visible structural cracks, exposing the bridge to the risk of damage or even collapse during service. In this case, in order to trace the causes of the cracks, it is necessary to accurately and reliably evaluate the concrete strength of the main beam and its spatial distribution.

[0004] Among the existing bridge inspection and assessment technologies, the rebound method and the core drilling method are two commonly used concrete strength test methods. The rebound method is to estimate the strength of concrete by testing the surface hardness of concrete with a rebound hammer. It is one of the most widely used methods in bridge inspection. However, the rebound test process will be affected by many factors, making the measured concrete strength inaccurate. For example, the presence of sand lines and water marks on the concrete surface will cause the identification result to be low; the rebound method needs to correct the rebound result according to the carbonization depth of the concrete and the thickness of the component. When the carbonization is serious or the thickness of the component is insufficient, the rebound result cannot be corrected as required, and the identified concrete strength is no longer reliable; in addition, the rebound method can only estimate the concrete strength on the surface of the main beam, and cannot be used to identify the internal concrete strength. The core drilling method measures the strength by drilling a core sample at a specific part of the main beam and performing a compressive test on the core sample to determine the concrete strength at the coring part. Since the test method is similar to the standard test for compressive strength, the concrete strength measured by the core drilling method is more accurate and reliable than the rebound method. The problems with the core drilling method are: it is a destructive test that causes great damage to the main beam, has high testing costs, and is difficult to use in large quantities; in order to avoid damaging the beam, the core drilling needs to avoid important structural stress-bearing parts, so it is impossible to identify the spatial distribution of concrete strength along the main beam; there are also high technical requirements for the standardization of coring, and it is necessary to strictly ensure that the upper and lower surfaces of the core sample to be tested are polished smooth and parallel, so the test quality is difficult to control. In summary, there is currently no reliable method that can effectively identify and evaluate concrete strength and its spatial distribution along the main beam of the bridge.

[0005] Currently, no effective solution has been proposed for the problems in the related technologies. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In view of the deficiencies in the prior art, the present invention provides a method for evaluating the elastic modulus and strength of a concrete bridge main beam based on fiber Bragg gratings. The method has the advantages of being able to effectively evaluate the elastic modulus and compressive strength of a concrete bridge main beam in a non-destructive manner, and is not affected by problems such as severe carbonization of concrete, limited thickness of the main beam, and uneven concrete surface. This solves the problem in the prior art of lacking a reliable method for effectively identifying and evaluating concrete strength and its spatial distribution along the main beam of a bridge.

[0008] (II) Technical solution

[0009] In order to achieve the above advantages of being able to effectively evaluate the elastic modulus and compressive strength of the main beam concrete in a non-destructive manner, and not being affected by problems such as severe concrete carbonization, limited main beam thickness, and uneven concrete surface, the specific technical solution adopted by the present invention is as follows:

[0010] A method for evaluating elastic modulus and strength of a concrete bridge main beam based on fiber grating, the method comprising:

[0011] S1. Determine the number and location of fiber Bragg grating sensors based on the cross-sectional form of the main beam, and arrange distributed fiber Bragg grating strain sensors on the main beam in combination with the number and location of the sensors;

[0012] S2. construct a multi-scale finite element model based on the main beam characteristics, simulate the wheel weight of the vehicle with concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and determine the vehicle loading test plan according to the loaded vehicle parameters;

[0013] S3. Counterweight the vehicle according to the vehicle loading test plan, and after the counterweight is completed, perform dynamic and static force loading tests on the main beam respectively, and use distributed fiber grating strain sensors to collect strain response data in the dynamic and static force loading tests;

[0014] S4. Calculate the dynamic characteristics of the bridge structure based on the strain response data, update the elastic modulus of the multi-scale finite element model according to the dynamic characteristics of the bridge structure, and use the elastic modulus after parameter update as a benchmark reference value for evaluating the elastic modulus of the actual bridge;

[0015] S5. According to the vehicle counterweight of the actual loading test, the same value of concentrated force load is applied in the multi-scale finite element model after parameter update, the stress value of each part of the main beam is calculated, and the elastic modulus of concrete is calculated by taking the quotient with the strain response measured by the distributed fiber grating at the corresponding position, and the elastic modulus is evaluated using the benchmark reference value;

[0016] S6. The concrete compressive strength is inferred based on the calculated concrete elastic modulus, and the concrete compressive strength is combined with the internal and external environmental factors of the main beam to comprehensively evaluate the strength of the bridge main beam to obtain the main beam strength assessment result.

[0017] Preferably, a multi-scale finite element model is constructed based on the main beam characteristics, the wheel weight of the vehicle is simulated by concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and the vehicle loading test scheme is determined according to the loaded vehicle parameters, including:

[0018] S21. Construct a multi-scale finite element model based on the main beam characteristics, and divide the measuring point area on the main beam. In the multi-scale finite element model, solid units are used to simulate the measuring points for evaluating the elastic modulus and strength, and beam units are used to simulate the remaining measuring points.

[0019] S22. Use a multi-scale finite element model to simulate the wheel weight of the vehicle to ensure that the stress generated at the measuring point is greater than or equal to the preset range as a constraint condition to determine the loading vehicle parameters, and formulate a vehicle loading test plan based on the loading vehicle parameters. The loading vehicle parameters include the weight, model, number of vehicles and the loading position of the vehicles along the transverse and longitudinal directions of the bridge.

[0020] Preferably, the vehicle is counterweighted according to the vehicle loading test plan, and after the counterweight is completed, the main beam is subjected to dynamic and static force loading tests respectively, and the strain response data in the dynamic and static force loading tests are collected using a distributed fiber grating strain sensor, including:

[0021] S31. Counterweight the vehicle according to the vehicle loading test plan, and after the vehicle counterweight is completed, arrange the vehicle in the transverse and longitudinal directions according to the loading positions, combine the loading positions between the vehicles into a loading condition, and record the actual position of the vehicle in the transverse and longitudinal directions under the loading condition;

[0022] S32, analyzing the change of strain data collected by the fiber grating sensor under the loading condition, and when the strain data is in a stable state, obtaining the static load response data at the measuring point to complete the static loading test of the main beam;

[0023] S33. After the static loading test is completed, a dynamic loading test is performed on the bridge, and dynamic load response data at the measuring point when a vehicle passes through the main beam during the dynamic loading test is obtained.

[0024] Preferably, the dynamic characteristics of the bridge structure are calculated based on the strain response data, the elastic modulus of the multi-scale finite element model is updated according to the dynamic characteristics of the bridge structure, and the elastic modulus after the parameter update is used as the benchmark reference value for evaluating the elastic modulus of the actual bridge, including:

[0025] S41. Calculate the measured vibration natural frequency and vibration mode of the main beam structure based on the dynamic load response data, and analyze the calculated vibration natural frequency and vibration mode of the main beam structure through a multi-scale finite element model;

[0026] S42, dividing the main beam into sections along the length direction, and taking the elastic modulus of the concrete member in the section as the target update parameter;

[0027] S43, respectively calculating the sensitivity between the calculated value of the vibration natural frequency and the calculated value of the vibration mode and the elastic modulus of the section, obtaining the sensitivity analysis results of the vibration natural frequency and the vibration mode of the main beam structure, and selecting the parameters corresponding to the sensitivity within a preset range as the update parameters corresponding to the target based on the sensitivity analysis results;

[0028] S44, using the elastic modulus of the segment as an update parameter and the upper and lower limits of the elastic modulus of the segment as constraint conditions to construct an objective function for updating the parameters of the multi-scale finite element model;

[0029] S45. Perform iterative analysis on the objective function of updating the parameters of the multi-scale finite element model, input the optimal solution obtained by the iterative analysis into the original multi-scale finite element model to complete the parameter update of the multi-scale finite element model, obtain the updated value of the elastic modulus in the segment, and use the updated value as the benchmark reference value for the elastic modulus evaluation.

[0030] Preferably, the calculation formula of sensitivity is:

[0031]

[0032] In the formula, S ij represents the sensitivity of the i-th vibration mode to the elastic modulus of the j-th segment; f(E′ j ) represents the calculated value of vibration natural frequency or vibration mode; E′ j represents the elastic modulus within the jth segment; E′ represents the elastic modulus within the segment.

[0033] Preferably, according to the vehicle counterweight of the actual loading test, the same value of concentrated force load is applied in the multi-scale finite element model after parameter update, the stress value of each part of the main beam is calculated, and the elastic modulus of concrete is calculated by taking the quotient with the strain response measured by the distributed fiber grating at the corresponding position, and the elastic modulus is evaluated by using the benchmark reference value, including:

[0034] S51, performing concentrated force loading on the multi-scale finite element model after parameter update according to the vehicle counterweight of the vehicle loading scheme, and calculating the stress value of each part of the main beam;

[0035] S52. By taking the quotient of the stress value of each part of the main beam calculated by the multi-scale finite element model and the strain value measured in the static load test, the elastic modulus at each measuring point is calculated, and the elastic modulus at each measuring point of the actual bridge is evaluated using the benchmark reference value of the elastic modulus.

[0036] Preferably, the elastic modulus at each measuring point is calculated by taking the quotient of the stress value of each part of the main beam calculated by the multi-scale finite element model and the strain value measured in the static load test, and the elastic modulus at each measuring point of the actual bridge is evaluated using the reference value of the elastic modulus, including:

[0037] S521, based on the number of grids divided by the multi-scale finite element model in the beam section corresponding to the measuring point, calculating the average value of the stress at each grid in the beam section corresponding to the measuring point;

[0038] S522, calculating the measured elastic modulus of concrete at each measuring point based on the average value of stress at each grid of the multi-scale finite element model and the measured strain value obtained from the static loading test;

[0039] S523. Compare the elastic modulus benchmark reference value obtained by updating the multi-scale finite element model parameters with the measured elastic modulus at the measuring point calculated by the actual static loading test, and evaluate the elastic modulus of the concrete of the main beam based on the comparison result.

[0040] Preferably, the concrete compressive strength is inferred from the calculated concrete elastic modulus, and the concrete compressive strength is combined with the internal and external environmental factors of the main beam to comprehensively evaluate the strength of the bridge main beam, and the main beam strength evaluation results include:

[0041] S61, calculating the measured estimated value of the strength grade of the concrete at the measuring point based on the measured elastic modulus at the measuring point calculated by the actual static loading test;

[0042] S62, calculating a strength grade reference value of concrete in the section based on the elastic modulus in the section calculated by the multi-scale finite element model after parameter update;

[0043] S63, comparing the measured estimated value of the strength grade of concrete at the measuring point with the reference value of the strength grade of concrete in the section, and selecting a reference value of the strength grade of concrete based on the comparison result;

[0044] S64, comparing the concrete strength grade reference value with the actual measured estimated value of the concrete strength grade at the measuring point, and obtaining an evaluation result of the concrete strength of the main beam based on the comparison result;

[0045] S65. Simulate the damage evolution law of cracks inside the main beam and the environmental change law outside the main beam based on the predefined internal and external environmental factors of the main beam;

[0046] S66. Combine the simulation results with the evaluation results of the concrete strength of the main beam, comprehensively evaluate the strength of the main beam, and obtain the strength evaluation results of the main beam.

[0047] Preferably, simulating the damage evolution law of cracks inside the main beam and the environmental change law outside the main beam based on predefined internal and external environmental factors of the main beam includes:

[0048] S651, collecting internal environment data and external environment data, wherein the internal environment data includes crack parameters and main beam structure parameters, and the external environment data includes thermal expansion parameters and moisture migration parameters;

[0049] S652. A thermal-hydraulic-mechanical coupling model is established based on thermal expansion parameters, water migration parameters and strain response data, and the thermal-hydraulic-mechanical coupling model is used to analyze the change law of the external environment of the main beam;

[0050] S653. A continuous damage mechanics model is established based on crack parameters and main beam structure parameters, and the continuous damage mechanics model is used to simulate the damage evolution law of cracks inside the main beam.

[0051] Preferably, a thermal-hydraulic-mechanical coupling model is established based on thermal expansion parameters, moisture migration parameters and strain response data, and the thermal-hydraulic-mechanical coupling model is used to analyze the change law of the external environment of the main beam, including:

[0052] S6521. Establish a thermal-hydraulic-mechanical coupling model based on thermal expansion parameters, moisture migration parameters and strain response data, and use the thermal-hydraulic-mechanical coupling model to analyze the coupling relationship between thermal expansion parameters, moisture migration parameters and strain response data;

[0053] S6522. Based on the coupling relationship between thermal expansion parameters, moisture migration parameters and strain response data, a group of partial differential equations is established to describe the changing law of the external environment of the main beam;

[0054] S6523. Divide the first boundary condition, the second boundary condition and the third boundary condition in the multi-scale finite element model, wherein the first boundary condition is a thermal expansion parameter, the second boundary condition is a moisture migration parameter, and the third boundary condition is strain response data;

[0055] S6524. Based on the boundary conditions after the multi-scale finite element model is divided, the partial differential equations are solved using iterative solution technology, and the coupling relationship between thermal expansion parameters, moisture migration parameters and strain response data is updated based on the solution results until the solution converges.

[0056] Preferably, the expression of the parameter update target of the multi-scale finite element model is:

[0057]

[0058] Where OBJ(E′) represents the parameter update target of the multi-scale finite element model; s represents the selection of the first s-order modes for the parameter update of the multi-scale finite element model; ω i Represents the measured value of the vibration natural frequency of the main beam structure; ω′ i Indicates the calculated value of the vibration natural frequency of the main beam structure; Φ i Represents the measured value of the vibration mode of the main beam structure; Φ′ i It represents the calculated value of the vibration mode of the main beam structure; E′ represents the elastic modulus within the section.

[0059] (III) Beneficial effects

[0060] Compared with the prior art, the present invention provides a method for evaluating the elastic modulus and strength of a concrete bridge main beam based on fiber Bragg grating, which has the following beneficial effects:

[0061] The present invention collects structural strain response data of different parts along the main beam through distributed fiber Bragg grating strain sensors, and infers the concrete elastic modulus at each measuring point in combination with the calculation results of the multi-scale finite element model, and infers the concrete strength at each measuring point according to the corresponding relationship between the elastic modulus and the concrete strength. At the same time, the model parameters are used to update the reference values ​​of the elastic modulus and the strength grade, and the reference values ​​are used as references to compare and analyze the actual measured conditions, so that the elastic modulus and compressive strength of the concrete bridge main beam can be effectively evaluated in a non-destructive manner, and will not be affected by problems such as severe concrete carbonization, limited main beam thickness, and uneven concrete surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0063] Figure 1 is a flow chart of a method for evaluating elastic modulus and strength of a concrete bridge main beam based on fiber Bragg grating according to an embodiment of the present invention;

[0064] Figure 2 is a specific implementation diagram of a method for evaluating elastic modulus and strength of a concrete bridge main beam based on fiber Bragg grating according to an embodiment of the present invention;

[0065] Figure 3 Schematic diagram of the arrangement of a distributed fiber Bragg grating array of a small box girder bridge in a method for evaluating elastic modulus and strength of a concrete bridge main beam based on fiber Bragg grating according to an embodiment of the present invention;

[0066] Figure 4 is a schematic diagram of the arrangement of a distributed fiber Bragg grating array of a hollow slab bridge in a method for evaluating elastic modulus and strength of a concrete bridge main beam based on fiber Bragg grating according to an embodiment of the present invention;

[0067] Figure 5 It is a layout diagram of a distributed fiber Bragg grating array of a single small box beam segment in a fiber Bragg grating-based concrete bridge main beam elastic modulus and strength evaluation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0068] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention and are mainly used to illustrate the embodiments. They can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, ordinary technicians in this field should be able to understand other possible implementation methods and advantages of the present invention.

[0069] According to an embodiment of the present invention, a method for evaluating the elastic modulus and strength of a concrete bridge main beam based on fiber Bragg grating is provided.

[0070] The present invention is further described with reference to the accompanying drawings and specific embodiments. Figure 1-Figure 2 As shown, according to an embodiment of the present invention, a method for evaluating elastic modulus and strength of a concrete bridge main beam based on fiber Bragg gratings comprises:

[0071] S1. Determine the number and location of fiber Bragg grating sensors based on the cross-sectional form of the main beam, and arrange distributed fiber Bragg grating strain sensors on the main beam in combination with the number and location of sensors.

[0072] It should be noted that, in order to facilitate understanding of the above technical solution of the present invention, the following is a detailed description of the present invention in the actual process of determining the number and location of fiber Bragg grating sensors based on the cross-sectional form of the main beam, and arranging distributed fiber Bragg grating strain sensors on the main beam in combination with the number and location of the sensors:

[0073] (1) Determination of the layout position: The number and layout position of distributed fiber grating sensors along the height direction of the main beam are determined according to the cross-sectional form of the main beam. For small box girder bridges, the sensors can be laid out at different heights of the bottom plate and the webs on both sides, such as Figure 3 As shown in the figure, the hollow slab beam should have the sensor arranged on the bottom surface of the beam, as shown in the figure. Figure 4 As shown in the figure (where A represents a distributed fiber grating array and B represents a loading vehicle), the T-beam bridge can arrange sensors at different heights of the flange plate, the lower edge of the web and one side of the web.

[0074] (2) Determination of layout parameters: Determine the total layout length of the distributed fiber Bragg grating along the driving direction to ensure that it can cover the key stress-bearing sections of the main beam and the locations prone to diseases; determine the spacing between fiber optic bases at different locations (i.e., the sensor range of each strain measurement point) based on the observation accuracy requirements. The spacing between fiber optic bases near the key stress-bearing sections should not be greater than 2 m.

[0075] (3) Fiber optic base installation: Mark the position of the distributed fiber grating fixed base on the actual bridge according to the layout plan, polish the concrete surface near the corresponding position, and install the sensor fixed base at the marked position using strong glue. Figure 5 As shown, C represents a fixed base and D represents a fiber grating array.

[0076] (4) Installation of fiber grating sensor: Fix the distributed fiber grating cable on the pasted base and pre-tighten the cable during the fixing process.

[0077] S2. Construct a multi-scale finite element model based on the main beam characteristics, simulate the wheel weight of the vehicle with concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and determine the vehicle loading test plan based on the loaded vehicle parameters.

[0078] Among them, a multi-scale finite element model is constructed based on the main beam characteristics, and the wheel weight of the vehicle is simulated by concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and the vehicle loading test plan is determined according to the loaded vehicle parameters, including:

[0079] S21. Construct a multi-scale finite element model based on the main beam characteristics, and divide the measuring point area on the main beam. In the multi-scale finite element model, solid units are used to simulate the measuring points for evaluating the elastic modulus and strength, and beam units are used to simulate the remaining measuring points.

[0080] S22. Use a multi-scale finite element model to simulate the wheel weight of the vehicle to ensure that the stress generated at the measuring point is greater than or equal to a preset range as a constraint condition to determine the loading vehicle parameters, and formulate a vehicle loading test plan based on the loading vehicle parameters.

[0081] It should be noted that, in order to facilitate understanding of the above technical solution of the present invention, the following is a detailed description of the construction of a multi-scale finite element model based on the main beam characteristics in the actual process of the present invention, the wheel weight of the vehicle is simulated by concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and the determination of the vehicle loading test scheme according to the loaded vehicle parameters:

[0082] (1) Construction of multi-scale finite element model: A multi-scale finite element model of the bridge is constructed according to the span, beam cross-section, and material properties of the actual bridge. The main beams whose elastic modulus and compressive strength need to be evaluated are simulated with solid units, and the remaining main beams are simulated with beam units. The number of units in the area where the fiber Bragg grating is planned to be installed is increased to ensure that at least four units are divided within every two fiber optic base sections.

[0083] (2) Determination of vehicle loading scheme: Using the constructed multi-scale finite element model, the weight of the loaded vehicle wheels is simulated with concentrated force. The stress at each measuring point is guaranteed to be no less than 1 MPa. The weight, model, number of loaded vehicles and the loading positions of each vehicle along the transverse and longitudinal directions of the bridge are determined.

[0084] S3. Counterweight the vehicle according to the vehicle loading test plan. After the counterweight is completed, dynamic and static force loading tests are performed on the main beam respectively, and the strain response data in the dynamic and static force loading tests are collected using distributed fiber grating strain sensors.

[0085] Among them, the vehicle is counterweighted according to the vehicle loading test plan, and after the counterweight is completed, the main beam is subjected to dynamic and static force loading tests respectively, and the distributed fiber grating strain sensor is used to collect the strain response data in the dynamic and static force loading tests, including:

[0086] S31. Counterweight the vehicle according to the vehicle loading test plan, and after the vehicle counterweight is completed, arrange the vehicle in the transverse and longitudinal directions according to the loading positions, combine the loading positions between the vehicles into a loading condition, and record the actual position of the vehicle in the transverse and longitudinal directions under the loading condition;

[0087] S32, analyzing the change of strain data collected by the fiber grating sensor under the loading condition, and when the strain data is in a stable state, obtaining the static load response data at the measuring point to complete the static loading test of the main beam;

[0088] S33. After the static loading test is completed, a dynamic loading test is performed on the bridge, and dynamic load response data at the measuring point when a vehicle passes through the main beam during the dynamic loading test is obtained.

[0089] It should be noted that, in order to facilitate understanding of the above technical solution of the present invention, the following is a detailed description of the present invention in the actual process of counterweighting the vehicle according to the vehicle loading test scheme, performing dynamic and static force loading tests on the main beam after the counterweight is completed, and using a distributed fiber grating strain sensor to collect strain response data in the dynamic and static force loading tests:

[0090] (1) Prepare to load vehicles and weigh them: Prepare to load vehicles according to the number and type of vehicles determined by the loading plan, balance the weights according to the specified weights of each vehicle, and weigh them to determine the actual weight of each vehicle, the axle weight of each axle, the wheel weight, etc.

[0091] (2) Carry out vehicle loading test according to the test plan: close the traffic on the bridge, arrange the loading vehicles at different positions along the transverse and longitudinal directions of the bridge according to the loading positions of each vehicle in the loading plan, and the combination of each loading position of different vehicles is a loading condition. Record the actual position of each vehicle along the transverse and longitudinal directions of the bridge under each loading condition.

[0092] (3) Strain data acquisition under static load test: Observe the changes in strain data of each fiber Bragg grating sensor under each loading condition. When the strain data no longer changes, maintain the vehicle loading state for 2 minutes and record the response ε at each strain measurement point. i (i represents the i-th strain measurement point). After the recording is completed, the loaded vehicle leaves the bridge.

[0093] (4) Bridge structure dynamic characteristics test: After the static load test (equivalent to the static loading test) is completed, a dynamic test (equivalent to the dynamic loading test) is carried out on the bridge. A loading vehicle drives across the bridge at a constant speed to collect strain response data at each measuring point during the entire vehicle passage process.

[0094] S4. Calculate the dynamic characteristics of the bridge structure based on the strain response data, update the elastic modulus of the multi-scale finite element model according to the dynamic characteristics of the bridge structure, and use the elastic modulus after parameter update as the benchmark reference value for evaluating the elastic modulus of the actual bridge.

[0095] Among them, the dynamic characteristics of the bridge structure are calculated based on the strain response data, the elastic modulus of the multi-scale finite element model is updated according to the dynamic characteristics of the bridge structure, and the elastic modulus after parameter update is used as the benchmark reference value for the actual bridge elastic modulus evaluation, including:

[0096] S41. Calculate the measured vibration natural frequency and vibration mode of the main beam structure based on the dynamic load response data, and analyze the calculated vibration natural frequency and vibration mode of the main beam structure through a multi-scale finite element model;

[0097] S42, dividing the main beam into sections along the length direction, and taking the elastic modulus of the concrete member in the section as the target update parameter;

[0098] S43, respectively calculating the sensitivity between the calculated value of the vibration natural frequency and the calculated value of the vibration mode and the elastic modulus of the section, obtaining the sensitivity analysis results of the vibration natural frequency and the vibration mode of the main beam structure, and selecting the parameters corresponding to the sensitivity within a preset range as the update parameters corresponding to the target based on the sensitivity analysis results;

[0099] S44, using the elastic modulus of the segment as an update parameter and the upper and lower limits of the elastic modulus of the segment as constraint conditions to construct an objective function for updating the parameters of the multi-scale finite element model;

[0100] S45. Perform iterative analysis on the objective function of updating the parameters of the multi-scale finite element model, input the optimal solution obtained by the iterative analysis into the original multi-scale finite element model to complete the parameter update of the multi-scale finite element model, obtain the updated value of the elastic modulus in the segment, and use the updated value as the benchmark reference value for the elastic modulus evaluation.

[0101] S5. According to the vehicle weight of the actual loading test, the same value of concentrated force load is applied in the multi-scale finite element model after parameter update, the stress value of each part of the main beam is calculated, and the concrete elastic modulus is calculated by dividing it with the strain response measured by the distributed fiber grating at the corresponding position, and the elastic modulus is evaluated using the benchmark reference value.

[0102] Among them, according to the vehicle weight of the actual loading test, the same value of concentrated force load is applied in the multi-scale finite element model after parameter update, the stress value of each part of the main beam is calculated, and the concrete elastic modulus is calculated by taking the quotient with the strain response measured by the distributed fiber grating at the corresponding position. The elastic modulus is evaluated using the benchmark reference value, including:

[0103] S51, performing concentrated force loading on the multi-scale finite element model after parameter update according to the vehicle counterweight of the vehicle loading scheme, and calculating the stress value of each part of the main beam;

[0104] S52. By taking the quotient of the stress value of each part of the main beam calculated by the multi-scale finite element model and the strain value measured in the static load test, the elastic modulus at each measuring point is calculated, and the elastic modulus at each measuring point of the actual bridge is evaluated using the benchmark reference value of the elastic modulus.

[0105] Among them, the elastic modulus at each measuring point is calculated by taking the quotient of the stress value of each part of the main beam calculated by the multi-scale finite element model and the strain value measured in the static load test. The elastic modulus at each measuring point of the actual bridge is evaluated using the benchmark reference value of the elastic modulus, including:

[0106] S521, based on the number of grids divided by the multi-scale finite element model in the beam section corresponding to the measuring point, calculating the average value of the stress at each grid in the beam section corresponding to the measuring point;

[0107] S522, calculating the measured elastic modulus of concrete at each measuring point based on the average value of stress at each grid of the multi-scale finite element model and the measured strain value obtained from the static loading test;

[0108] S523. Compare the elastic modulus benchmark reference value obtained by updating the multi-scale finite element model parameters with the measured elastic modulus at the measuring point calculated by the actual static loading test, and evaluate the elastic modulus of the concrete of the main beam based on the comparison result.

[0109] It should be noted that (1) the measured values ​​of the dynamic characteristics of the bridge structure are obtained: the dynamic strain data collected by the bridge dynamic test are used to calculate the measured values ​​of the natural frequencies of each order of vibration of the structure ω i And the measured value of vibration mode Φ i .

[0110] (2) Obtaining the calculated values ​​of the dynamic characteristics of the bridge structure: Using the multi-scale finite element model to analyze the calculated values ​​of the natural frequencies of each order of vibration of the structure ω′ i And the vibration mode calculation value Φ′ i .

[0111] (3) Determination of update parameters of multi-scale finite element model: The main beam is divided into parameter update sections along the length direction. Each section is a concrete beam section between two adjacent fixed bases of the optical fiber. The elastic modulus of the concrete components (bottom plate, web, etc.) in each section is used as the target update parameter. Here, the elastic modulus of each section of the bottom plate of the beam is E′=[E′1, E′2, ..., E′ n ] as an example to illustrate the parameter updating process.

[0112] (4) Update parameter sensitivity analysis: Perform parameter sensitivity analysis on the structural frequency and vibration mode, and calculate the frequency, vibration mode and elastic modulus of each section E′=[E′1, E′2, ..., E′ n ]Corresponding sensitivity:

[0113]

[0114] In the formula, S ij represents the sensitivity of the i-th frequency or vibration mode to the elastic modulus of the j-th section; f(E′ j ) represents the calculated value of vibration natural frequency or vibration mode, where f(E′ j ) corresponds to ω′ i (E′ j ) or Φ′ i (E′ j ); E′ j represents the elastic modulus in the jth segment; E′ represents the elastic modulus in the segment; ΔE′ can be taken as E′ j / 100.

[0115] According to the results of sensitivity analysis, the parameters with relative sensitivity greater than 0.1 are selected as the update parameters of the corresponding targets, namely:

[0116] ω′ i =ω′ i (E′ i1 , E′ i2 , ..., E′ im )=ω′ i (E′);

[0117] Φ′ i =Φ′ i (E′ i1 , E′ i2 , ..., E′ im )=Φ′ i (E′);

[0118] In the formula, E′ im It represents the elastic modulus of the mth section which is more sensitive to the i-th frequency or vibration mode.

[0119] (5) Construct the objective function of updating the parameters of the multi-scale finite element model: First, the elastic modulus is used as the update parameter, and the parameter update target is determined by the proximity between the measured values ​​of each frequency and vibration mode of the bridge and the theoretical value. The expression is:

[0120]

[0121] Where OBJ(E′) represents the parameter update target of the multi-scale finite element model; ω iRepresents the measured value of the vibration natural frequency of the main beam structure; ω′ i Indicates the calculated value of the vibration natural frequency of the main beam structure; Φ i Represents the measured value of the vibration mode of the main beam structure; Φ′ i represents the calculated value of the vibration mode of the main beam structure; E′ represents the elastic modulus in the section; s represents the selection of the first s order modes for the parameter update of the multi-scale finite element model; MAC represents the modal confidence criterion, which is used to compare the similarity between the measured vibration mode value and the calculated vibration mode value, which can be taken as:

[0122]

[0123] In the formula, represents the measured value of the transposed main beam structure vibration mode, and the constraint conditions for model parameter update (i.e., the upper and lower limits of the elastic modulus of the parameter section E′) are determined according to the bridge inspection results. max , E′ min ), construct the objective function for updating the parameters of the multi-scale finite element model:

[0124]

[0125] (6) Multi-scale finite element model parameter update: Perform iterative optimization analysis on the above formula, bring the optimal solution back to the initial multi-scale finite element model, complete the multi-scale finite element model parameter update based on the structural dynamic characteristics, and obtain the updated value of the elastic modulus of each section E′=[E′1, E′2, ..., E′ n ].

[0126] According to the actual wheel position and wheel weight of the loaded vehicle, a concentrated force load of the same magnitude is applied to the corresponding position of the multi-scale finite element model after parameter update, and a static loading test analysis is performed, including the following steps:

[0127] (1) Apply concentrated force load according to wheel weight: According to the actual recorded transverse and longitudinal loading positions of each vehicle under each loading condition, the corresponding positions of each wheel in the multi-scale finite element model are meshed, and a concentrated force equal to the actual weight of each wheel is applied to the corresponding finite element nodes.

[0128] (2) Calculation of static response data (equivalent to static load response data): Static analysis is performed on the multi-scale finite element model to obtain the calculated stress response values ​​at each sensor position under different loading conditions. Where i represents the beam segment corresponding to the i-th fiber Bragg grating measurement point, and j represents the finite element node at the i-th grid in the i-th beam segment.

[0129] Among them, the elastic modulus in the beam section corresponding to each measuring point is calculated by the stress value calculated by the multi-scale finite element model and the measured strain value, and the distribution of the measured elastic modulus is evaluated, which includes the following steps:

[0130] (1) Average stress calculation: For each fiber Bragg grating measurement point, calculate the average stress of each grid in the beam section corresponding to each measurement point, that is:

[0131]

[0132] Where n represents the number of grids divided in the beam segment corresponding to a measuring point in the multi-scale finite element model.

[0133] (2) Calculation of elastic modulus: For each beam segment corresponding to a measuring point, obtain the strain value ε measured by the loading test. i and stress values ​​calculated by finite element analysis By formula Calculate the concrete elastic modulus E=[E1, E2, ..., E n ].

[0134] (3) Spatial distribution evaluation of elastic modulus: Compare the elastic modulus of concrete in each section calculated by updating the model parameters one by one. n ] and the elastic modulus of concrete at each measuring point deduced from the measured strain E = [E1, E2, ..., E n ], if the elastic modulus of concrete at a certain measuring point is E i Lower than E' i , indicating that the elastic modulus of concrete at this measuring point is relatively low, thereby realizing the evaluation of the elastic modulus of concrete at various locations of the main beam.

[0135] S6. The concrete compressive strength is inferred based on the calculated concrete elastic modulus, and the concrete compressive strength is combined with the internal and external environmental factors of the main beam to comprehensively evaluate the strength of the bridge main beam to obtain the main beam strength assessment result.

[0136] Among them, the concrete compressive strength is inferred based on the calculated concrete elastic modulus, and the concrete compressive strength is combined with the internal and external environmental factors of the main beam to comprehensively evaluate the strength of the bridge main beam. The main beam strength evaluation results include:

[0137] S61, calculating the measured estimated value of the strength grade of the concrete at the measuring point based on the measured elastic modulus at the measuring point calculated by the actual static loading test;

[0138] S62, calculating a strength grade reference value of concrete in the section based on the elastic modulus in the section calculated by the multi-scale finite element model after parameter update;

[0139] S63, comparing the measured estimated value of the strength grade of concrete at the measuring point with the reference value of the strength grade of concrete in the section, and selecting a reference value of the strength grade of concrete based on the comparison result;

[0140] S64. Compare the concrete strength grade reference value with the actual estimated value of the concrete strength grade at the measuring point, and obtain an evaluation result of the concrete strength of the main beam based on the comparison result.

[0141] It should be noted that (1) the actual measured value of concrete strength grade is estimated by inferring the elastic modulus of concrete at each measuring point from the actual measured strain E = [E1, E2, ..., E n ] into the formula in the relevant literature The actual estimated value of the concrete strength grade near each measuring point is calculated one by one:

[0142] F cu,k =[f cu,k_1, f cu,k_2, …f cu,k_n ];

[0143] (2) Calculation of concrete strength grade benchmark value: Update the model parameters to calculate the concrete elastic modulus of each section E′=[E′1, E′2, ..., E′ n ]Substitute into the formula Calculate the reference value of concrete strength grade in each section:

[0144] F′ cu,k =[f′ cu,k_1, f′ cu,k_2, f′ cu,k_n, ];

[0145] One by one with the concrete strength grade design value Compare and take the smaller value of the two As the benchmark value of concrete strength grade.

[0146] (3) Main beam concrete strength assessment: The actual estimated value of concrete strength grade at the i-th measuring point fcu,k_i is compared with the benchmark reference value For comparison, if This indicates that the concrete strength at this measuring point is insufficient, thereby enabling an assessment of the concrete strength at various locations on the main beam.

[0147] S65. Based on the predefined internal and external environmental factors of the main beam, the damage evolution law of the cracks inside the main beam and the environmental change law outside the main beam are simulated.

[0148] Among them, the damage evolution law of the cracks inside the main beam and the environmental change law outside the main beam are simulated based on the predefined internal and external environmental factors of the main beam, including:

[0149] S651. Collect internal environment data and external environment data, wherein the internal environment data includes crack parameters and main beam structure parameters, and the external environment data includes thermal expansion parameters and moisture migration parameters.

[0150] It should be noted that, in order to facilitate understanding of the above technical solution of the present invention, the following is a detailed description of the collection of internal environmental data and external environmental data in the actual process of the present invention, and the internal environmental data includes crack parameters and main beam structure parameters, and the external environmental data includes thermal expansion parameters and moisture migration parameters:

[0151] Internal environmental data refers to the parameters that directly reflect the internal structural characteristics and damage status of concrete bridges. They are used to describe the structural performance and the evolution of internal damage, and include the following:

[0152] Crack parameters:

[0153] Crack density: The number of cracks per unit area or volume, which represents the degree of damage distribution.

[0154] Crack width: The opening width of the crack, reflecting the scale of damage development.

[0155] Crack length: The length of the crack extension, used to analyze the crack expansion trend.

[0156] Crack distribution: spatial distribution characteristics of cracks in concrete structures.

[0157] Main beam structural parameters:

[0158] Geometric parameters: structural characteristics such as main beam cross-sectional dimensions and length.

[0159] Material parameters: elastic modulus and Poisson's ratio of the main beam material, etc.

[0160] Stress distribution: the stress concentration area of ​​the main beam under load.

[0161] Deformation state: the deformation amplitude of the main beam under static or dynamic load.

[0162] External environmental data refers to the physical field parameters that affect the external state of concrete bridges, mainly including the factors affecting the structural performance due to temperature and humidity conditions, including:

[0163] Thermal expansion parameters:

[0164] Coefficient of linear expansion: The rate of change of length of a material per unit temperature change, describing the thermal expansion stress caused by temperature.

[0165] Temperature distribution: Temperature gradients on the surface and inside the bridge structure.

[0166] Thermal conductivity: describes the thermal conductivity of a material and affects the rate of temperature diffusion.

[0167] Thermal stress distribution: the area where thermal stress is concentrated due to temperature difference.

[0168] Moisture migration parameters:

[0169] Pore ​​saturation: The proportion of water in concrete pores, reflecting the moisture distribution.

[0170] Moisture Gradient: The rate of change of moisture in and on the surface of concrete.

[0171] Diffusion coefficient: The rate at which water migrates in the pores of concrete, which affects the law of humidity diffusion.

[0172] Pore ​​pressure: The pressure generated by water in the pores, which has a significant effect on crack growth and volume change.

[0173] S652. A thermal-hydraulic-mechanical coupling model is established based on thermal expansion parameters, moisture migration parameters and strain response data, and the thermal-hydraulic-mechanical coupling model is used to analyze the changing pattern of the external environment of the main beam.

[0174] Among them, a thermal-hydraulic-mechanical coupling model is established based on thermal expansion parameters, moisture migration parameters and strain response data, and the thermal-hydraulic-mechanical coupling model is used to analyze the changes in the external environment of the main beam, including:

[0175] S6521. Establish a thermal-hydraulic-mechanical coupling model based on thermal expansion parameters, moisture migration parameters and strain response data, and use the thermal-hydraulic-mechanical coupling model to analyze the coupling relationship between thermal expansion parameters, moisture migration parameters and strain response data;

[0176] S6522. Based on the coupling relationship between thermal expansion parameters, moisture migration parameters and strain response data, a group of partial differential equations is established to describe the changing law of the external environment of the main beam;

[0177] S6523. Divide the first boundary condition, the second boundary condition and the third boundary condition in the multi-scale finite element model, wherein the first boundary condition is a thermal expansion parameter, the second boundary condition is a moisture migration parameter, and the third boundary condition is strain response data;

[0178] S6524. Based on the boundary conditions after the multi-scale finite element model is divided, the partial differential equations are solved using iterative solution technology, and the coupling relationship between thermal expansion parameters, moisture migration parameters and strain response data is updated based on the solution results until the solution converges.

[0179] It should be noted that, in order to facilitate understanding of the above technical solution of the present invention, the following is a detailed description of the establishment of a thermal-hydraulic-mechanical coupling model based on thermal expansion parameters, moisture migration parameters and strain response data in the actual process of the present invention, and the use of the thermal-hydraulic-mechanical coupling model to analyze the external environment change law of the main beam:

[0180] Step 1: Establish a coupling model

[0181] The heat conduction equation is used to describe the thermal field and establish the relationship between temperature and thermal expansion stress.

[0182] Combined with Fick's diffusion law, the distribution of moisture gradient and pore pressure is described.

[0183] Using the mechanical equilibrium equation, the dynamic and static load responses are combined with the thermal expansion and moisture migration fields to construct a complete thermal-hydraulic-mechanical coupling model.

[0184] Step 2: Analyze the coupling relationship

[0185] The model simulations investigated how temperature changes affect moisture migration and how moisture gradients change stress distribution. For example, temperature increases cause thermal expansion, which changes the pore structure and thus affects the moisture migration rate and pore pressure distribution.

[0186] Step 3: Establish a set of partial differential equations to describe the coupling relationship and the law of change of the external environment. The set of partial differential equations includes:

[0187] Hot Field:

[0188]

[0189] In the formula, T represents temperature distribution; k represents thermal conductivity; Q represents internal heat source term; p represents material density; c represents specific heat capacity;

[0190] Moisture Migration Field:

[0191]

[0192] Where h is the humidity distribution (dimensionless); D is the humidity diffusion coefficient (m2 / sm2 / s); and t is the time.

[0193] Mechanics Field:

[0194]

[0195] Where σ=σ T +σ h +σ ext represents the total stress, including thermal stress σ T , humidity stress σ h and external stress σ ext ; f represents volume force (such as self-weight and inertia force).

[0196] Step 4: Coupling Analysis

[0197] The temperature gradient, humidity gradient, and stress distribution of the thermal field are coupled to form a complete set of partial differential equations. For example, under high temperature conditions in summer, the increase in temperature will intensify humidity migration and crack expansion, thereby changing the overall stress state of the main beam.

[0198] Step 5: Divide boundary conditions

[0199] The first boundary condition (thermal expansion parameter): Set the temperature distribution on the bridge surface affected by the temperature difference as the boundary condition for heat conduction.

[0200] Second boundary condition (moisture migration parameter): defines the distribution range of moisture gradient and pore pressure, such as moisture variation on the exposed surface of the bridge.

[0201] The third boundary condition (strain response data): specifies the location and magnitude of dynamic and static loads acting on the bridge.

[0202] Define the interactions between thermal, moisture migration, and mechanical fields to ensure that the multi-scale finite element model reflects the real physical process.

[0203] Step 6: Use iterative solution techniques to update the coupling relationship and solve the partial differential equations

[0204] Thermal field solution: Calculate temperature distribution and determine thermal expansion stress based on temperature gradient.

[0205] Moisture migration field solution: Update the moisture gradient and pore pressure distribution based on the temperature field results.

[0206] Mechanical field solution: Calculate stress distribution and deformation state based on thermal field and moisture migration field.

[0207] Iterative update: Repeat the above process and update the parameters of each physical field until convergence (such as changes in temperature, humidity and stress meet the convergence criteria).

[0208] For example, based on the damage evolution of prestressed concrete bridge girders under high temperature and humidity changes in summer:

[0209] Thermal expansion parameters: measured linear expansion coefficient 1.2×10 -5 K -1 and thermal conductivity 1.8W / m.

[0210] Moisture migration parameters: pore pressure range 0-1.5MPa, humidity gradient 0-0.3kg / m 3 .

[0211] Dynamic and static load response: The main beam bears a static load of 200kN and a dynamic load of 50kN.

[0212] Simulation steps:

[0213] A thermal-hydraulic-mechanical coupling model was established and the above parameters were input.

[0214] Use finite element method to divide the main beam and define boundary conditions: temperature difference 15℃, humidity gradient 0.2kg / m 3, the dynamic and static load loading points are located in the middle of the main beam.

[0215] The partial differential equations are solved iteratively to obtain the temperature distribution, moisture migration field and mechanical field stress distribution.

[0216] Result analysis:

[0217] Temperature gradients cause thermal expansion stresses to concentrate at the ends of the bridge.

[0218] The humidity gradient and pore pressure intensify the stress concentration at the crack tip and accelerate the crack propagation rate.

[0219] The simulation results show that the elastic modulus of the main beam decreases by 12% and the compressive strength decreases by 8%.

[0220] It should be noted that the thermal-hydraulic-mechanical coupling model can accurately analyze the complex coupling relationship between thermal expansion, moisture migration and strain response data, and establish a group of partial differential equations to dynamically describe the change law of the main beam under the influence of different environmental factors; the thermal expansion parameters, moisture migration parameters and strain response data boundary conditions divided in the multi-scale finite element model make the simulation more in line with the actual working conditions, and combined with the iterative solution technology, it can effectively capture the coupling effect under the action of multiple fields and improve the convergence and accuracy of the solution results; in terms of crack damage evolution, the continuous damage mechanics model based on crack parameters and main beam structural parameters can dynamically simulate the crack propagation process and its impact on structural performance, providing a scientific basis for the evolution law of cracks inside the main beam, thereby realizing a comprehensive evaluation of the internal crack propagation of the main beam and changes in the external environment, and providing strong technical support for the structural health monitoring, strength assessment and maintenance optimization of concrete bridges.

[0221] S653. A continuous damage mechanics model is established based on crack parameters and main beam structure parameters, and the continuous damage mechanics model is used to simulate the damage evolution law of cracks inside the main beam.

[0222] It should be noted that the continuous damage mechanics model is established based on the crack parameters and the main beam structure parameters, and the damage evolution law of the cracks inside the main beam is simulated by using the continuous damage mechanics model, including:

[0223] Step 1: Continuum Damage Mechanics Model

[0224] (1) The damage variable is defined as the degree to which cracks or defects weaken material properties, ranging from 0 ≤ D ≤ 1:

[0225] D=0: completely lossless state;

[0226] D=1: Complete failure state.

[0227] (2) Damage affects the actual bearing capacity of the material. The corrected stress expression is:

[0228] σ=(1-D)·σ0;

[0229] Where σ represents the actual stress and σ0 represents the stress in the undamaged state.

[0230] (3) The evolution of the damage variable D follows the following equation:

[0231]

[0232] In the formula, the damage evolution function f is related to stress σ, strain θ, and strain rate Regarding this, the energy density drive model is usually adopted.

[0233] Step 2: Establishment of damage mechanics model

[0234] (1) Input of crack parameters and main beam structure parameters:

[0235] Crack parameters:

[0236] Crack density: the number of cracks per unit area or volume.

[0237] Crack Width: The opening width of the crack.

[0238] Crack length: The length of crack extension.

[0239] Main beam structural parameters:

[0240] Modulus of elasticity.

[0241] Poisson's ratio.

[0242] Main beam geometry and material properties.

[0243] (2) Coupling of stress-strain relationship and crack influence:

[0244] In the main beam structure, the effect of the crack is modified by the damage variable D to modify the elastic modulus:

[0245] B d =(1-D)·B;

[0246] In the formula, B d A represents the equivalent elastic modulus after damage; B represents the elastic modulus in the undamaged state.

[0247] Step 3: Simulate the evolution of crack damage

[0248] (1) The evolution equation of the damage variable D is introduced into the multi-scale finite element model of the main beam; the initial crack density, crack width and crack length are initialized and set; static load, dynamic load or combined load is applied to calculate the stress distribution; the crack length l = l + Δl is updated when the crack is calculated, and the damage variable D is adjusted.

[0249] (2) After each loading step, the crack parameters (density, width, length) and damage variable D are updated and iterated until the structure fails or reaches the limit state.

[0250] It should be noted that by introducing the damage variable D, the model establishes a weakening relationship between microscopic parameters such as crack width, length and density and the macroscopic properties of the main beam (such as elastic modulus and bearing capacity), which can accurately reflect the dynamic impact of crack expansion on the strength and stiffness of the main beam; the model combines the main beam structural parameters to simulate the initiation, expansion path and final failure process of crack expansion in real time, especially under the combined action of dynamic and static loads and environmental factors, it can reveal the nonlinear law and key driving factors of crack expansion; by quantitatively analyzing the cumulative damage of crack expansion to the main beam structural performance, the model can predict the remaining life and failure mode of the main beam, thereby providing a scientific basis for bridge evaluation.

[0251] S66. Combine the simulation results with the evaluation results of the concrete strength of the main beam, comprehensively evaluate the strength of the main beam, and obtain the strength evaluation results of the main beam.

[0252] In summary, with the aid of the above technical scheme of the present invention, the present invention collects structural strain response data at different parts along the main beam through distributed fiber Bragg grating strain sensors, and infers the concrete elastic modulus at each measuring point in combination with the calculation results of the multi-scale finite element model, and infers the concrete strength at each measuring point according to the corresponding relationship between the elastic modulus and the concrete strength, and at the same time, uses the model parameters to update the reference values ​​of the elastic modulus and the strength grade, and uses them as a reference to compare and analyze the actual measured conditions, thereby being able to achieve an effective evaluation of the elastic modulus and compressive strength of the concrete bridge main beam in a non-destructive manner, and is not affected by problems such as severe concrete carbonization, limited main beam thickness, and uneven concrete surface.

[0253] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating, characterized in that: include: S1. Determine the number and location of fiber Bragg grating sensors based on the cross-sectional form of the main beam, and arrange distributed fiber Bragg grating strain sensors on the main beam in combination with the number and location of the sensors; S2. construct a multi-scale finite element model based on the main beam characteristics, simulate the wheel weight of the vehicle with concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and determine the vehicle loading test plan according to the loaded vehicle parameters; S3. Counterweight the vehicle according to the vehicle loading test plan, and after the counterweight is completed, perform dynamic and static force loading tests on the main beam respectively, and use distributed fiber grating strain sensors to collect strain response data in the dynamic and static force loading tests; S4. Calculate the dynamic characteristics of the bridge structure based on the strain response data, update the elastic modulus of the multi-scale finite element model according to the dynamic characteristics of the bridge structure, and use the elastic modulus after parameter update as a benchmark reference value for evaluating the elastic modulus of the actual bridge; S5. According to the vehicle counterweight of the actual loading test, the same value of concentrated force load is applied in the multi-scale finite element model after parameter update, the stress value of each part of the main beam is calculated, and the elastic modulus of concrete is calculated by taking the quotient with the strain response measured by the distributed fiber grating at the corresponding position, and the elastic modulus is evaluated using the benchmark reference value; S6. Inversely infer the concrete compressive strength based on the calculated concrete elastic modulus, and comprehensively evaluate the strength of the bridge main beam by combining the concrete compressive strength with the internal and external environmental factors of the main beam to obtain the main beam strength evaluation result; The S4 includes: Calculate the measured vibration natural frequency and vibration mode of the main beam structure based on the dynamic load response data, and analyze the calculated vibration natural frequency and vibration mode of the main beam structure through a multi-scale finite element model; The main beam is divided into sections along the length direction, and the elastic modulus of the concrete components in the section is used as the target update parameter; The sensitivity between the calculated value of the vibration natural frequency and the calculated value of the vibration mode and the elastic modulus of the section is calculated respectively, and the sensitivity analysis results of the vibration natural frequency and vibration mode of the main beam structure are obtained. Based on the sensitivity analysis results, the parameters corresponding to the sensitivity within the preset range are selected as the update parameters of the corresponding targets; The elastic modulus of the segment is used as the update parameter, and the upper and lower limits of the elastic modulus of the segment are used as constraints to construct the objective function of updating the parameters of the multi-scale finite element model. Iteratively analyze the objective function of the multi-scale finite element model parameter update, input the optimal solution obtained by the iterative analysis into the original multi-scale finite element model to complete the parameter update of the multi-scale finite element model, obtain the updated value of the elastic modulus in the section, and use the updated value as the benchmark reference value for the elastic modulus evaluation; The use of a reference value to evaluate the elastic modulus includes: The elastic modulus obtained by updating the parameters of the multi-scale finite element model is used as a benchmark reference value and compared with the calculated concrete elastic modulus; if the calculated concrete elastic modulus is less than the benchmark reference value, it means that the concrete elastic modulus at the current measuring point is low, otherwise, it means that the concrete elastic modulus at the current measuring point is high, so as to complete the evaluation of the spatial distribution of the elastic modulus; The S6 includes: Based on the measured elastic modulus at the measuring point calculated by the actual static loading test, the measured estimated value of the strength grade of the concrete at the measuring point is calculated; Calculate the reference value of the strength grade of concrete in the section based on the elastic modulus in the section calculated by the multi-scale finite element model after parameter update; Compare the measured estimated value of the strength grade of concrete at the measuring point with the reference value of the strength grade of concrete in the section, and select the reference value of the concrete strength grade based on the comparison result; The concrete strength grade reference value is compared with the actual measured estimated value of the concrete strength grade at the measuring point, and the evaluation result of the concrete strength of the main beam is obtained based on the comparison result.

2. The method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating according to claim 1, characterized in that: The multi-scale finite element model is constructed based on the main beam characteristics, the wheel weight of the vehicle is simulated by concentrated force in the multi-scale finite element model to obtain the loaded vehicle parameters, and the vehicle loading test scheme is determined according to the loaded vehicle parameters, including: S21. Construct a multi-scale finite element model based on the main beam characteristics, and divide the measuring point area on the main beam. In the multi-scale finite element model, solid units are used to simulate the measuring points for evaluating the elastic modulus and strength, and beam units are used to simulate the remaining measuring points. S22. Use a multi-scale finite element model to simulate the wheel weight of the vehicle to ensure that the stress generated at the measuring point is greater than or equal to a preset range as a constraint condition to determine the loading vehicle parameters, and formulate a vehicle loading test plan based on the loading vehicle parameters.

3. The method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating according to claim 2, characterized in that: The method of counterweighting the vehicle according to the vehicle loading test plan, performing dynamic and static force loading tests on the main beam after the counterweighting is completed, and collecting strain response data in the dynamic and static force loading tests using a distributed fiber grating strain sensor includes: S31. Counterweight the vehicle according to the vehicle loading test plan, and after the vehicle counterweight is completed, arrange the vehicle in the transverse and longitudinal directions according to the loading positions, combine the loading positions between the vehicles into a loading condition, and record the actual position of the vehicle in the transverse and longitudinal directions under the loading condition; S32, analyzing the change of strain data collected by the fiber grating sensor under the loading condition, and when the strain data is in a stable state, obtaining the static load response data at the measuring point to complete the static loading test of the main beam; S33. After the static loading test is completed, a dynamic loading test is performed on the bridge, and dynamic load response data at the measuring point when a vehicle passes through the main beam during the dynamic loading test is obtained.

4. The method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating according to claim 3 is characterized in that: According to the vehicle counterweight of the actual loading test, the same value of concentrated force load is applied in the multi-scale finite element model after parameter update, the stress value of each part of the main beam is calculated, and the elastic modulus of concrete is calculated by taking the quotient with the strain response measured by the distributed fiber grating at the corresponding position, and the elastic modulus is evaluated by using the benchmark reference value, including: S51, performing concentrated force loading on the multi-scale finite element model after parameter update according to the vehicle counterweight of the vehicle loading scheme, and calculating the stress value of each part of the main beam; S52. By taking the quotient of the stress value of each part of the main beam calculated by the multi-scale finite element model and the strain value measured in the static load test, the elastic modulus at each measuring point is calculated, and the elastic modulus at each measuring point of the actual bridge is evaluated using the benchmark reference value of the elastic modulus.

5. The method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating according to claim 4, characterized in that: The elastic modulus at each measuring point is calculated by taking the quotient of the stress value of each part of the main beam calculated by the multi-scale finite element model and the strain value measured in the static load test, and the elastic modulus at each measuring point of the actual bridge is evaluated by using the reference value of the elastic modulus, including: S521, based on the number of grids divided by the multi-scale finite element model in the beam section corresponding to the measuring point, calculating the average value of the stress at each grid in the beam section corresponding to the measuring point; S522, calculating the measured elastic modulus of concrete at each measuring point based on the average value of stress at each grid of the multi-scale finite element model and the measured strain value obtained from the static loading test; S523. Compare the elastic modulus benchmark reference value obtained by updating the multi-scale finite element model parameters with the measured elastic modulus at the measuring point calculated by the actual static loading test, and evaluate the elastic modulus of the concrete of the main beam based on the comparison result.

6. The method for evaluating elastic modulus and strength of concrete bridge main beam based on fiber Bragg grating according to claim 5, characterized in that: The expression of the parameter update target of the multi-scale finite element model is: Where OBJ(E′) represents the parameter update target of the multi-scale finite element model; s represents the selection of the first s-order modes for the parameter update of the multi-scale finite element model; ω i Represents the measured value of the vibration natural frequency of the main beam structure; ω i ′ represents the calculated value of the vibration natural frequency of the main beam structure; Φ i Represents the measured value of the vibration mode of the main beam structure; Φ i ′ represents the calculated value of the vibration mode of the main beam structure; E′ represents the elastic modulus in the section; MAC represents the modal confidence criterion, which is used to compare the similarity between the measured vibration mode value and the calculated vibration mode value.

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