Vertical shear stiffness quantitative identification and safety monitoring evaluation method for new and old widened bridge joint

Abstract

The invention discloses a vertical shear stiffness quantitative identification and safety monitoring evaluation method for a new and old widened bridge joint, and belongs to the field of bridge engineering safety detection and structural performance monitoring. The invention relates to a method for identifying the rigidity of an abutted seam of a widened bridge, which is characterized in that under the excitation of a low-speed vehicle load, the ratio of response time cumulants of quasi-static displacement generated in the midspan of a new bridge and an old bridge and the vertical rigidity of the abutted seam connecting the two have a clear and stable mathematical mapping relationship; and a stable and reliable dimensionless identification index which is directly associated with the abutted seam rigidity is constructed, so that quantitative evaluation of the health state of the abutted seam is realized. The invention discloses a new and old widened bridge joint safety assessment method. The method comprises the following steps: step 1, arranging a new and old widened bridge joint structure performance monitoring system; 2, deploying a signal processing module and a parameter calculation and state evaluation module in a background; and step 3, deploying a display and monitoring early warning module on a client, wherein a manager can see the content of the display and monitoring early warning module.

Description

Technical Field

[0001] This invention relates to a quantitative identification and monitoring technology for vertical shear stiffness of the joint between new and old bridges, belonging to the field of bridge engineering safety inspection and structural performance monitoring. Background Technology

[0002] Early-built highway bridges generally adopted a two-way four-lane standard, and their load-bearing capacity and cross-sectional width are no longer adequate for the current heavy-load, high-volume traffic demands. Therefore, widening existing highway bridges has become an important strategic measure to improve the overall efficiency of the road network and alleviate traffic pressure. In widening projects between old and new bridges, the joints, as key force-transmitting components connecting the old and new structures, directly affect the overall stress performance, load distribution efficiency, and long-term service safety of the widened bridge due to their mechanical properties—especially vertical shear stiffness. Insufficient joint stiffness or degradation will lead to inconsistent deformation between the old and new bridge decks, causing a series of problems such as cracking of the pavement layer and stress concentration in components, seriously affecting structural durability and operational safety.

[0003] Currently, the detection of joint conditions mostly employs on-site loading tests, which involve applying known loads to the bridge and inferring the joint stiffness by measuring the bridge's deformation and stress. While this method can realistically reflect the actual stress state of the bridge, it faces challenges such as complex sensor deployment, high costs, and highly specialized data analysis, making it particularly unsuitable for the rapid detection and long-term monitoring needs of the numerous small-to-medium span bridges. Another common approach is to establish a finite element model of the bridge and adjust the joint stiffness parameters to ensure the numerical simulation results match the measured data, thereby identifying the joint stiffness. This method can simulate various load conditions, but it requires high accuracy of the model and precise parameter selection, limiting its applicability. Summary of the Invention

[0004] This method aims to overcome the shortcomings of existing technologies. Based on the difference in quasi-static displacement at mid-span between new and old bridges under vehicle loads, it proposes a rapid identification method for the joint status of widened bridges. This is crucial for the accurate simulation of the dynamic behavior of the vehicle-dual-bridge coupled system in in-service widened bridges and the development of indirect measurement technology for joint status. From the strategic need to improve the level of intelligent bridge maintenance and the long-term structural performance, there is an urgent need to develop a theoretically rigorous, easy-to-operate, and reliable quantitative identification method for joint stiffness, providing key technical support for quality control, operational performance evaluation, and scientific maintenance decision-making in bridge widening projects.

[0005] Technical solution: A method for identifying the stiffness of joints in widened bridges, characterized by: the ratio of the cumulative quasi-static displacement response time generated at the mid-span of the new and old bridges under low-speed vehicle load excitation, and the vertical stiffness of the joint connecting the two. There exists a clear and stable mathematical mapping relationship; therefore, a stable and reliable dimensionless identification index directly related to the joint stiffness is constructed. This allows for a quantitative assessment of the health status of the seams.

[0006] The mathematical mapping relationship can be expressed as follows: or ,respectively Dimensionless identification indicators for new and old bridges, thereby determining joint stiffness. The calculation is transformed into a ratio of cumulative displacements that can be easily obtained through response monitoring. This method effectively avoids the interference of complex dynamic response analysis and provides a powerful theoretical tool and practical reference for quickly and accurately diagnosing the service status of joints in engineering practice.

[0007] Based on the aforementioned method for identifying the stiffness of joints in widened bridges, a further disclosed method for safety assessment of joints between old and new widened bridges includes: Step 1: Deploy a structural performance monitoring system for the joints of the new and old bridges that have been widened, including a data acquisition system and its testing vehicle at the bridge site. Step 2: Deploy the signal processing module, parameter calculation and status assessment module in the background, and run the background signal processing module, parameter calculation and status assessment module: Step 1. Data Acquisition: Control the inspection vehicle to pass over the new bridge at a low and constant speed. During this process, simultaneously collect the time history data of the vertical displacement between the old and new bridge spans through the on-site data acquisition system. Step 2. Signal Processing: Perform bandpass filtering on the acquired raw dynamic deflection signal, setting the upper limit of the filter frequency to be higher than the driving frequency. Separate and extract the quasi-static displacement; Step 3. Parameter Calculation: Based on the obtained quasi-static displacement time histories at the mid-span of the new and old bridges, during the entire bridge crossing period... Integrating the components separately, the cumulative displacement of the new bridge is calculated. Cumulative displacement of the old bridge Calculate the joint stiffness identification index; the formula for calculating the identification index. ; Step 4. Status Assessment: The obtained identification indicators Substituting the relationship between joint stiffness and identification index The actual stiffness of the splice joint can then be calculated. By comparing the identified stiffness with the design stiffness, the collaborative performance of the splice joint can be quantitatively assessed. Step 3: Deploy the display and monitoring early warning module on the client side. The quantitative assessment results output by the status evaluation module running in the background are provided to the connected client via the Internet. Administrators can view the content of the display and monitoring early warning module on their handheld client or through a PC.

[0008] The testing vehicle needs to run on both the new and old bridges, corresponding to the platform's subsequent stiffness identification indicators. and ,pass and The stiffness of the seam can be calculated from both.

[0009] The remote backend system needs to input the displacement data of the old and new bridges at mid-span (or other cross-sectional positions such as 1 / 4 span, 1 / 8 span, etc.) as the inspection vehicle crosses the bridge for subsequent processing. Selecting to collect the mid-span displacement data of the old and new bridges is optimal because the displacement difference between the two bridges is most significant at this location.

[0010] Highway operation and management units and bridge maintenance departments will be the core stakeholders of this monitoring system. Managers can view the content of the display and monitoring early warning modules via handheld clients or PCs. This system provides them with an efficient screening and assessment scheme for the service status of widened bridge joints, significantly saving time and economic costs. Based on the rapid assessment results from the display and monitoring early warning modules, management departments can promptly take targeted joint reinforcement measures—such as bonding steel plates or carbon fiber composite materials to damaged joints—effectively extending the service life of widened bridges and improving the initiative and economy of operation and maintenance work. Attached Figure Description

[0011] Figure 1 This is a schematic diagram illustrating the scenario for identifying seam stiffness according to the present invention. Figure 2 This is a schematic diagram of a double-beam model (simplified mechanical model) under the load of a moving vehicle in the principle of this invention; Figure 3 This is a flowchart of the splice seam stiffness identification process of the present invention; Figure 4 This is a schematic diagram of the splicing structure of the right lane widening project of the golf passage bridge in the example of this invention; Figure 5 A comparison of theoretical and finite element methods to simulate the system dynamic response of a test vehicle running on a new bridge. Figure 6 Comparison of mid-span displacement of the two beams when vehicles are running on the new bridge; Figure 7 For illustration With the change in joint stiffness; Figure 8 Table 1: Parameter Annotation Table; Figure 9 Table 2: Basic parameters of the twin-beam-vehicle coupling system; Figure 10 The data acquisition system, its testing vehicle, and the background stiffness identification system are deployed as an example. Detailed Implementation

[0012] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0013] A method for identifying the stiffness of joints in bridges with widened spans, the technical solution of which can be described as follows: A stable and reliable dimensionless identification index directly related to the joint stiffness is constructed. This is to achieve a quantitative assessment of the health status of the seams. Specifically, the indicators... The construction is based on the following findings ( Figure 1 As shown): Under vehicle (especially low-speed vehicle) load excitation, the ratio of the cumulative quasi-static displacement response time at the mid-span of the new and old bridges, and the vertical stiffness of the joint connecting the two, is... There exists a clear and stable mathematical mapping relationship. This relationship can be expressed as: or This allows for the measurement of joint stiffness, which is difficult to measure directly. This method transforms the displacement into a ratio that can be easily obtained through response monitoring for calculation. It effectively avoids the interference of complex dynamic response analysis, providing a powerful theoretical tool and practical reference for quickly and accurately diagnosing the service status of joints in engineering practice.

[0014] Based on the aforementioned method for identifying the stiffness of joints in widened bridges, a further disclosed method for safety assessment of joints between old and new widened bridges is presented, comprising the following steps: Figure 3 , Figure 10 The following is a scene diagram: (The example described uses a test vehicle crossing a new bridge as an example.) In practical engineering, for example, microwave radar is used as a displacement sensor to collect the vertical displacement at the mid-span of new and old bridges. The force and acceleration do not need to be collected in actual applications.

[0015] Step 1: Deploy a structural performance monitoring system for the joints of the new and old bridges, including a data acquisition system and its testing vehicle at the bridge site, a signal processing module, a parameter calculation and status assessment module running in the background, and a display and monitoring early warning module running on the client side. The signal processing module, parameter calculation and status assessment module are deployed in the background, and the display and monitoring early warning module is deployed on the client. The assessment results output by the status assessment module running in the background are provided to the client connected to it via the Internet. The administrator can see the content of the display and monitoring early warning module by holding the client or through the PC.

[0016] Figure 10 middle: 1. The two measuring points represent the locations where two displacement sensors are deployed on the old and new bridges, respectively. This belongs to the on-site data acquisition system.

[0017] 2. The inspection vehicle provides input force, which excites the bridge; controlling the inspection vehicle to pass over the bridge at a lower speed (recommended range: 1m / s-5m / s) will yield better results (weaker transient response). 3. In this embodiment, two microwave radars (one can also be used in practice) are placed on a stable area of ​​the ground below the widened bridge, and respectively aligned with corner reflectors (measuring point 1 and measuring point 2) installed at the bottom of the mid-span section of the new and old bridges. This is a field data acquisition system.

[0018] 4. To achieve synchronous data acquisition at both points, the two radars should be connected via a local area network and controlled by a unified control and acquisition system to ensure that the timestamps of all measurement points are synchronized. This belongs to the field data acquisition system.

[0019] 5. To ensure the capture of continuous deflection changes between new and old bridges during slow vehicle movement, the sampling frequency should be high enough. A minimum of 20Hz is recommended. This is for on-site data acquisition systems.

[0020] 6. Before the load test begins, and before the vehicle is on the bridge, the radar system should be activated and all measurement point data should be zeroed to eliminate initial environmental interference and establish a stable baseline. This is part of the on-site data acquisition system.

[0021] Step 1. Data Acquisition: Control the inspection vehicle to pass over the new bridge at a low and constant speed. During this process, collect the time history data of the vertical displacement between the old and new bridge spans simultaneously through the on-site data acquisition system.

[0022] Step 2. Signal Processing: Perform bandpass filtering on the raw dynamic deflection signal acquired in Step 1, setting the upper limit of the filter frequency to be slightly higher than the driving frequency. (For example, for a bridge with a span of 30m, if the inspection vehicle is set to pass at a speed of 5m / s, the driving frequency calculation formula is used.) The dominant first-order driving frequency can be calculated. If the frequency is 0.52Hz, then setting the upper limit of the filter to 1Hz is sufficient to accurately separate and extract the quasi-static displacement.

[0023] Step 3. Parameter Calculation: Based on the quasi-static displacement time histories of the new and old bridge mid-spans obtained in Step 2, during the entire vehicle crossing period... Integrating the components separately, the cumulative displacement of the new bridge is calculated. Cumulative displacement of the old bridge Calculate the joint stiffness identification index; the formula for calculating the identification index. .

[0024] Step 4. Status Assessment: The identification indicators obtained in Step 3 are used for... Substituting the relationship between joint stiffness and identification index The actual stiffness of the splice joint can then be calculated. By comparing the identified stiffness with the design stiffness, the collaborative performance of the splice joint can be quantitatively assessed.

[0025] As an example, the testing vehicle needs to run on both the new and old bridges, corresponding to the platform's subsequent stiffness identification indicators. and ,pass and The stiffness of the seam can be calculated from both.

[0026] The remote backend needs to input the displacement data of the old and new bridges at the mid-span (or: 1 / 4 span, 1 / 8 span, or other cross-sectional positions) during the crossing of the bridge by the inspection vehicle, and then subsequent processing can be performed.

[0027] The optimal choice is to collect mid-span displacement data of both the old and new bridges because the displacement difference between the two bridges is most significant at this location.

[0028] Highway operation and management units and bridge maintenance departments will be the core stakeholders of this monitoring system. Managers can view the content of the display and monitoring early warning modules via handheld clients or PCs. This system provides them with an efficient screening and assessment scheme for the service status of widened bridge joints, significantly saving time and economic costs. Based on the rapid assessment results from the display and monitoring early warning modules, management departments can promptly take targeted joint reinforcement measures—such as bonding steel plates or carbon fiber composite materials to damaged joints—effectively extending the service life of widened bridges and improving the initiative and economy of operation and maintenance work.

[0029] As an application example, a bridge joint condition screening report can also be generated based on the results obtained from the condition assessment module. The report can be visually identified using red, yellow, and green color codes. Green: The joints are in normal service condition, the new and old bridges work well together, and routine maintenance is sufficient.

[0030] Yellow: Mild abnormality. It is recommended to strengthen regular observation or arrange further special tests.

[0031] Red: Serious abnormality. The seam may have functional defects or damage, triggering an "assessment warning". It is recommended to start a detailed assessment immediately.

[0032] The effectiveness of the technical solutions of the above embodiments of the present invention will be demonstrated below through theoretical derivation and numerical examples.

[0033] I. Theoretical Basis: The following section will reveal the working mechanism of this joint stiffness assessment method by deriving the closed-loop solution and its simplified form of the mid-span quasi-static displacement of the double-beam system under the action of moving vehicle load, and further clarify the advantages of this method.

[0034] In this method, the following is adopted: Figure 2 The simplified mechanical model shown is used to derive the closed-loop solution of the car-dual-bridge coupled response and related theories: both the new and old bridges are simplified to Euler-Bernoulli beams. The vehicle is simplified to a single-degree-of-freedom moving spring-mass element.

[0035] Let subscripts 1 and 2 represent the new bridge and the old bridge, respectively. The dynamic equilibrium equations for the new and old bridges, as the car crosses them, are expressed as follows: (1) (2) (3) In the formula: Let these be the coordinates of the car's position on the bridge surface. This corresponds to the car's running time. Represents coordinates Find the fourth derivative. Indicates time Find the second derivative. Subscripts 1 and 2 represent the new bridge and the old bridge, respectively. , These are the elastic moduli of the new and old bridges, respectively. , These are the moments of inertia of the cross sections of the new and old bridges, respectively. , These are the mass per unit length of the new and old bridges, respectively. , These are the vertical displacements of the new and old bridges, respectively. This represents the displacement of the vehicle-bridge contact point. Vertical stiffness of the joints between new and old bridges; Forces acting on the new bridge (such as) Figure 2 (Partial view shown). For vehicle body mass; For vehicle body suspension stiffness; This represents the vertical displacement of the vehicle body; It is the Dirac function; This is the acceleration due to gravity.

[0036] The studied double-beam system has simply supported ends, and the boundary conditions are as follows: (4-a) (4-b) (4-c) (4-d) In the formula: For the span of the new and old bridges, Represents coordinates Find the second derivative.

[0037] Based on the above boundary conditions, the vertical displacements of the new and old bridges can be approximated by the following function using the superposition method: (5) (6) In the formula: For the simply supported beam Mode shape represents the variation of each displacement component between two boundary endpoints; , The first and second represent the vertical displacements of the new and old bridges, respectively. Modal coordinates of the first mode.

[0038] Substitute equations (5) and (6) into equations (1) and (2), and multiply both sides by . and to From 0 to Integral, according to the Dirac function Properties (here) By applying the orthogonality conditions of trigonometric functions, we can obtain the modal equations of the double-beam system: (7) (8) Before the new and old bridges are joined together, the natural frequencies of their free vibrations can be expressed as: (9-a) (9-b) For ease of expression, (10-a) (10-b) These represent the joint stiffness, respectively. Additional effects on the natural frequencies of new and old simply supported bridges.

[0039] Substituting equations (9) and (10) into equations (7) and (8) further simplifies the equations: (11) (12) Based on structural dynamics, we can assume that the equations of vertical free vibration for the new and old bridges are as follows: , .in, , They represent the first time. Under coupled vibration modes, the vibration amplitudes of the new and old bridges, i.e., the relative magnitudes of the modal coordinates; The first beam of the double-beam coupled system is represented by the second beam. The first modal frequency. Based on this, the homogeneous parts of equations (11) and (12) can be rewritten in matrix form: (13) Equation (13) has a non-zero solution if the eigenvalue of the determinant of its coefficient matrix is ​​0. The solution is: (14) For equation (14), by solving the quadratic equation, the coupled dual frequencies of the bridge's vertical vibration can be obtained as follows: Equation (15) shows that for any first-order mode of a bridge that has been widened Both types of bridges exhibit a pair of conjugate frequencies, corresponding to two different vibration modes. One type involves the vibration modes of both new and old bridges being identical and synchronized in direction, known as synchronous vibration, with corresponding frequencies... The frequency is defined as synchronous frequency (see equation (15-a)); another type is asynchronous vibration, where the vibration modes of the old and new bridges are the same but in opposite directions, and the corresponding frequency is... Defined as asynchronous frequency (see equation (15-b)). In practice, since the old and new bridges have the same structural form and the joints impose constraints on both, synchronous vibration typically has a lower frequency and is easier to excite. Asynchronous vibration, on the other hand, has a higher frequency and is more difficult to excite.

[0040] For the eigenvalues ​​obtained by the solution and Substituting it back into equation (13), we get and The proportional relationship between them, that is, the ratio of the vibration amplitudes of the new and old bridges under corresponding modes. Specifically, under synchronous vibration modes ( The ratio of the amplitudes of the two waves is adopted. express: (16-a) In asynchronous vibration modes ( The ratio of the amplitudes of the two waves is adopted. express: (16-b) It is worth noting that, A constant value of positive indicates that the new and old bridges have the same displacement direction, i.e., they vibrate synchronously. A constant value of negative indicates that the displacement directions of the new and old bridges are opposite, i.e., asynchronous vibration.

[0041] According to equations (11) and (12), the dynamic equations of the double beam system can be written as: (17) in: stiffness matrix Force vector , , indicating the frequency of driving.

[0042] Since the dynamic equations of a double-beam system are a coupled set of second-order differential equations, solving them directly in physical coordinates is not only computationally complex but also fails to clearly reveal the system's essential dynamic characteristics. Therefore, this method introduces modal transformation to decouple the equations.

[0043] make , Substituting into equation (17), we get: (18) in, , representing the transformation matrix, is used to describe the relative displacement relationship between the old and new bridges.

[0044] Multiply both sides of equation (18) by the left side. The decoupled modal equations are obtained. (19) in, , .

[0045] make Equation (19) can be rewritten as: (20-a) (20-b) in, (21-a) (21-b) Here, and Let represent the load distribution coefficients of the dual-axle system under vehicle load in the synchronous and asynchronous vibration modes, respectively. They always satisfy . That is, the sum of the load on the synchronous vibration mode and the load on the asynchronous vibration mode is equal to the externally applied load.

[0046] The Duhamel integral is used to solve the decoupled dynamic equations of the double beam. For zero initial conditions, , The Duhamel integral gives the convolutional form of the solution: (twenty two) in, This is the impulse response function. For a two-beam coupled system, the impulse response function is: (23-a) (23-b) Equations (23-a), (23-b), and Substituting the expression into equation (22), we get: (24-a) (24-b) By decomposing the integral using trigonometric transformation formulas such as product-to-sum and sum-to-decomposition, and then integrating each decomposition separately, substituting back, and simplifying, we obtain: (25-a) (25-b) Then through Substituting the result back and simplifying it, we get: (26) in, , , representing the static amplitudes excited by the vehicle load in the synchronous and asynchronous vibration modes, respectively. , , respectively representing driving frequency Synchronous vibration frequency of the double-beam coupled system ( ) and asynchronous vibration frequency ( The ratio of ) is a dimensionless velocity parameter.

[0047] From the analysis formula (26) of the vibration components, it can be seen that for any order mode... Its corresponding modal displacement coordinates It mainly consists of two parts: one part is related to driving frequency. The related forced vibration term reflects the steady-state (i.e., quasi-static) response caused by a vehicle passing over the bridge at a constant speed; another part is related to the modal frequencies (synchronous vibration frequencies) of the double beams. and asynchronous vibration frequency The related free vibration term represents the system's inherent transient response. Under common engineering parameters, it satisfies the driving frequency... Much smaller than the bridge coupling frequency and Furthermore, the two exhibit significant differences in their time-domain characteristics: the former displays a half-sine wave time history, while the latter exhibits a periodic oscillation with zero mean. Based on these differences in frequency and time domain characteristics, a bandpass filter can be used to separate them: by setting the filter upper limit slightly higher than the driving frequency. This allows for the effective extraction of the quasi-static response from the total response.

[0048] On the other hand, further analysis of the vibration coupling relationship reveals that the vibration of the new bridge is transmitted to the old bridge through the joints, resulting in the coupled vibration response of the two bridges. Specifically, for any mode... The transmissibility of synchronous vibration of the new bridge is The vibration transmissibility corresponding to asynchronous vibration modes is .

[0049] Substitute equation (26) into equations (5) and (6) respectively, and simultaneously let Considering that the bridge vibration is dominated by the first-order mode, the displacement responses of the new and old bridges at the mid-span position can be obtained as follows: (27) As the foregoing analysis shows, the dynamic displacement response of a bridge is a superposition of forced vibration and free vibration, and the two exhibit significant differences in their characterization properties, making them relatively easy to separate. In particular, when the vehicle speed is low, the speed parameter... and Approaching zero, the amplitude of free vibration in the mid-span displacement response of the old and new bridges will be much smaller than the amplitude of forced vibration. At this point, the system response approximates the response generated by a slow-moving static load across the bridge, i.e., the quasi-static displacement response. Compared with free vibration, quasi-static displacement exhibits a distinct half-sine waveform characteristic, is more stable in shape, and is easier to accurately separate. Therefore, this method will use quasi-static displacement as a basis to construct an identification index for the stiffness of the splice joint.

[0050] Bundle Substituting into equation (27), the quasi-static mid-span displacements of the old and new bridges are obtained as follows: (28-a) (28-b) Considering that the test vehicle crossing the bridge is a dynamic process, the displacement value at a single time point is random and cannot fully reflect the overall performance of the double-beam structure. Therefore, this method integrates the quasi-static displacement response of the old and new bridges throughout the entire bridge crossing process of the test vehicle, constructing a cumulative quantity that can represent the structural response throughout the entire process, serving as a more stable and reliable observation indicator.

[0051] Let the time interval during which the test vehicle traverses the new bridge be . The cumulative time of quasi-static displacement at mid-span of the new and old bridges and Defined respectively (29-a) (29-b) Based on this, a joint stiffness identification index is constructed. And by simplifying, we get: (30) In the formula, This represents the ratio of the cumulative mid-span quasi-static displacement transmitted to the old bridge 2 when vehicle loads are applied to the new bridge 1 to the cumulative mid-span quasi-static displacement of the new bridge 1.

[0052] Similarly, when vehicle loads are applied to old bridge 2, corresponding identification indicators can be defined. : (31) Observing equations (30) and (31), it can be seen that the identification index ( In addition to the bending stiffness of new and old bridges and bridge span In addition to the above, it is also related to the joint stiffness. A significant positive correlation was observed. Given... and The joint stiffness can be determined in advance through design data or preliminary testing. Become an influence The main variable. This index is a dimensionless parameter, and its value can intuitively reflect the mechanical state of the seam: The larger, the more it indicates The larger the bridge, the better the collaborative performance between the old and new bridges; The smaller the value, the more it indicates The smaller the value, the lower the degree of coordinated stress between the two. Based on the above relationship, this method proposes to achieve the inversion identification of the stiffness of the splice joint by measuring the cumulative quasi-static displacement at the mid-span of the old and new bridges during vehicle crossing.

[0053] Furthermore, to further clarify the physical meaning of the indicators, consider the following two extreme operating conditions: 1. When hour, This indicates that the new and old bridges have not yet formed an effective connection and are in an independent working state; 2. When hour, This indicates that the new and old bridges are nearly rigidly coupled and approximate as a whole, which can be regarded as a whole coordinating the forces.

[0054] In fact, This represents the ratio of the cumulative mid-span quasi-static displacement transferred through the joints to the co-bearing old bridge (Bridge 2) when a vehicle load is applied to the new bridge (Bridge 1), to the cumulative mid-span quasi-static displacement of the directly bearing new bridge (Bridge 1), i.e., the quasi-static displacement transfer rate from the new bridge to the old bridge. Similarly, when a vehicle load is applied to the old bridge (Bridge 2), it can be defined as... The quasi-static displacement transfer rate is the rate of transfer from the old bridge to the new bridge.

[0055] II. Verification of Implementation Examples Under the action of moving vehicle load, the following will use the finite element method to verify the mid-span displacement analytical solution of the double-beam coupled system. Through a specific case, the effectiveness of the joint stiffness identification method proposed by the core method of this invention will be verified.

[0056] This invention's method is based on the widening project of the right lane of the golf course passage bridge at the He'ao-Shuihe Interchange, setting the calculation parameters for the new and old bridges in the numerical simulation. In this project ( Figure 4 As shown), both the new and old bridges have a span of 30m. The new bridge is 5m wide, and the old bridge is 25m wide. The width of the joint is 1m. C50 concrete with a modulus of elasticity of [missing value] was used in the pouring of both the new and old bridges and the joint. .

[0057] The parameters of the double beam-vehicle system used in the numerical simulation are shown in Table 2.

[0058] Figure 5 The vehicle was demonstrated to be running on the new bridge and the joint stiffness was shown. The theoretical solution and numerical simulation results for the mid-span displacement of the old and new bridges were compared. The good agreement between the two results confirms the accuracy of the derived closed-form solution.

[0059] Figure 6 Partial joint stiffness is given A comparison of the mid-span deflection time history curves of new and old bridges and the quasi-static displacement time history curves obtained by bandpass filtering is presented. The results show that, considering bridge deck roughness, the bandpass filtering method can still effectively extract the quasi-static displacement components in the mid-span of both bridges; furthermore, with the increase in joint stiffness... As the load increases, the mid-span deflection of the new bridge gradually decreases, while the mid-span deflection of the old bridge increases accordingly. When the joint stiffness is very high, the mid-span deflections of the new and old bridges tend to be consistent, and the two bridges exhibit rigid coupling stress characteristics.

[0060] Based on the quasi-static displacement time history curves at mid-span of the new and old bridges obtained through filtering, identification indices corresponding to different joint stiffnesses were calculated. And a scatter plot of its variation with stiffness was drawn, such as Figure 7 As shown. Analysis shows that: when At 0~ When within range, An approximation of 0 indicates that the coupling effect between the new and old bridges is weak and can be ignored; when achieve At or above, Approaching 100% indicates that the new and old bridges have achieved overall coordinated stress distribution.

[0061] Further observation Figure 7 Findings: When the seam stiffness changes from Down to At that time, identify indicators The percentage dropped sharply from 97.65% to 3.26%, a decrease of 94.39%, indicating that within the low stiffness range... It is highly sensitive to changes in stiffness. Based on Figure 7 middle Based on the changing characteristics, the damage state of the seam can be divided into the following three stages: Phase 1 ( ): This condition is undamaged or slightly damaged. The seams can still meet normal usage requirements. Durability repair is recommended to prevent further damage.

[0062] Phase Two ( ): This is the damage development stage, where the collaborative performance of the old and new bridges is significantly reduced. It is necessary to perform resistance calculations on the joints and assess whether reinforcement measures should be taken based on the results.

[0063] Phase Three ( The difference in mid-span deflection between the old and new bridges is very significant, and the damage to the joints seriously affects the overall performance of the structure, so reinforcement is urgently needed.

Claims

1. A method for identifying the stiffness of joints in widened bridges, characterized in that, Under low-speed vehicle load excitation, the ratio of the cumulative quasi-static displacement response time at the mid-span of the new and old bridges is related to the vertical stiffness of the joint connecting the two. There exists a clear and stable mathematical mapping relationship; therefore, a stable and reliable dimensionless identification index directly related to the joint stiffness is constructed. This allows for a quantitative assessment of the health status of the seams.

2. The method for identifying the joint stiffness of a bridge spanning width as described in claim 1, characterized in that, The mathematical mapping relationship is expressed as follows: or ,respectively Dimensionless identification indicators for new and old bridges, thereby determining joint stiffness. It is converted into a ratio of cumulative displacement that is easily obtained through response monitoring for calculation.

3. A new and old method for safety assessment of joints in widened bridges, based on the method for identifying the stiffness of joints in widened bridges as described in claim 1 or 2, characterized in that... include: Step 1: Deploy a structural performance monitoring system for the joints of the new and old bridges that have been widened, including a data acquisition system and its testing vehicle at the bridge site. Step 2: Deploy the signal processing module, parameter calculation and status assessment module in the background, and run the background signal processing module, parameter calculation and status assessment module: Step 1. Data Acquisition: Control the inspection vehicle to pass over the new bridge at a low and constant speed. During this process, simultaneously collect the time history data of the vertical displacement between the old and new bridge spans through the on-site data acquisition system. Step 2. Signal Processing: Perform bandpass filtering on the acquired raw dynamic deflection signal, setting the upper limit of the filter frequency to be higher than the driving frequency. Separate and extract the quasi-static displacement; Step 3. Parameter Calculation: Based on the obtained quasi-static displacement time histories at the mid-span of the new and old bridges, during the entire bridge crossing period... Integrating the components separately, the cumulative displacement of the new bridge is calculated. Cumulative displacement of the old bridge ; Calculate the joint stiffness identification index; the formula for calculating the identification index. ; Step 4. Status Assessment: The obtained identification indicators Substituting the relationship between joint stiffness and identification index The actual stiffness of the splice joint can then be calculated. ; By comparing the identified stiffness with the design stiffness, the collaborative performance of the splice joint can be quantitatively assessed. Step 3: Deploy the display and monitoring early warning module on the client side. The quantitative assessment results output by the status evaluation module running in the background are provided to the connected client via the Internet. Administrators can view the content of the display and monitoring early warning module on their handheld client or through a PC.

4. The new and old methods for assessing the safety of joints in widened bridges, as described in claim 3, for identifying the stiffness of joints in widened bridges, are characterized in that... The testing vehicle needs to run on both the new and old bridges, corresponding to the platform's subsequent stiffness identification indicators. and ,pass and The stiffness of the seam can be calculated in reverse.

5. The new and old methods for assessing the safety of joints in widened bridges, as described in claim 3, for identifying the stiffness of joints in widened bridges, are characterized in that... Displacement data at mid-span, 1 / 4 span, or 1 / 8 span positions of both the old and new bridges.

6. The new and old methods for assessing the safety of joints in widened bridges, as described in claim 3, for identifying the stiffness of joints in widened bridges, are characterized in that... Managers of highway operation and management units and bridge maintenance and management departments can view and monitor the contents of the early warning module through handheld clients or PCs.

7. The new and old methods for assessing the safety of joints in widened bridges, as described in claim 3, for identifying the stiffness of joints in widened bridges, are characterized in that... The inspection vehicle provides input force, which excites the bridge; it controls the inspection vehicle to pass over the bridge at a low speed, ranging from 1m / s to 5m / s.

8. The new and old methods for assessing the safety of joints in widened bridges, as described in claim 3, for identifying the stiffness of joints in widened bridges, are characterized in that... Two microwave radars were placed on a stable area of ​​the ground below the widened bridge, respectively, and aimed at the corner reflectors installed at the bottom of the mid-span sections of the new and old bridges, designated as measuring points 1 and 2. To achieve synchronous data acquisition at the two points, the two radars should be connected through a local area network and controlled by a unified control and acquisition system to ensure that the timestamps of all measuring point data are synchronized.

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