Load test method for beam bridge based on time history curve

Abstract

The application belongs to the technical field of bridge construction, and is a beam bridge load test method based on time history curve. The method firstly carries out static load test, and then arranges test vehicles at key parts of the test bridge surface by using a step loading mode, and measures deflection points and strain points. Then, the static load test efficiency is calculated through the bridge static load test. According to the step loading mode and the static load test efficiency, a multi-working-condition bridge model is established by using a finite element method to collect time history curves. Finally, dynamic load test is carried out, control sections of each span of the bridge are selected as test sections, and strain fluctuation amplitude, impact coefficient and the like are measured through the dynamic load test. According to the test data, the stress state of the structure under dynamic load is analyzed. The application combines static load test and dynamic load test, can reflect the working performance of the bridge structure under design load, and has high reliability.

Description

Technical Field

[0001] This invention belongs to the field of bridge construction technology, specifically relating to a load test method for beam bridges based on time history curves. Background Technology

[0002] Currently, in the field of beam bridge testing, the main methods for assessing the load-bearing capacity of beam bridges are static load testing and dynamic load testing. Static load testing is a relatively intuitive method for assessing the load-bearing capacity of beam bridges; however, it relies heavily on on-site testing results and is subject to subjective judgment, making it difficult to determine and guarantee the accuracy and reliability of the measured data. Most importantly, it has a significant negative impact on traffic. Dynamic load testing involves less work, is less expensive, has a shorter testing time, and is convenient and quick to operate. However, it is currently not possible to establish a direct link between the results of dynamic load testing and the load-bearing capacity of beam bridges, and the data from dynamic load testing cannot be fully utilized.

[0003] Therefore, it is necessary to study a fast, convenient, accurate and reliable method for evaluating the load-bearing capacity of beam bridges. Combining accurate and reliable static load testing methods with fast and convenient dynamic load testing methods, and establishing a reliable link between dynamic load test data and the load-bearing capacity of beam bridge structures, is an important technical problem that urgently needs to be solved. Summary of the Invention

[0004] This invention overcomes the shortcomings of the aforementioned technical problems and provides a load testing method for beam bridges based on time-history curves. Through static load tests, the stress and deflection of the control sections of the bridge structure under test loads are measured and compared with theoretical calculations to evaluate the actual structural performance and working condition. Through dynamic load tests, the structural response is measured to assess the dynamic performance of the actual structure. By comprehensively analyzing the results of static and dynamic load tests, the existing bearing capacity of the bridge is evaluated, providing a technical basis for the safety of bridge operation and providing original data for future bridge maintenance and management.

[0005] The technical problem solved by this invention is achieved through the following technical solution:

[0006] A load test method for beam bridges based on time history curves, comprising the following steps:

[0007] (1) Static load test:

[0008] (1.1) Several vehicles with known axle load, wheelbase and number of axles were used as test vehicles. The test vehicles were arranged in a graded loading method at the key parts of the test bridge deck. The measuring points were deflection measuring points and strain measuring points, which were arranged at the positions of maximum stress or deformation.

[0009] (1.2) According to the measurement point layout plan, the sensors are deployed on site; according to the data accuracy requirements of the test bridge type, the appropriate sensors and data acquisition equipment are selected, and according to the site conditions, the appropriate auxiliary facilities are used to deploy the sensors at the measurement points.

[0010] (1.3) Conduct static load tests on the bridge and calculate the static load test efficiency. The static load test efficiency should be controlled between 0.85 and 1.05.

[0011] (1.4) Based on the graded loading method and the efficiency of static load test, a multi-condition bridge model was established using the finite element method, and time history curves were collected.

[0012] (2) Dynamic load test

[0013] (2.1) Select the control section of each span of the bridge as the test section and conduct dynamic load tests. The dynamic load tests include pulsation test, braking test and runaway test.

[0014] (2.2) Based on the pulsation test and the actual bridge test of the inherent modal parameters of the bridge span structure, test the natural frequency and damping ratio of the bridge span structure;

[0015] (2.3) Based on the braking test and the running car test, the strain fluctuation amplitude and impact coefficient of each test section of the bridge span structure under dynamic load were obtained;

[0016] (2.4) Analyze the stress state of the bridge span structure under dynamic load based on the data obtained from the tests in steps (2.2) and (2.3).

[0017] Furthermore, in the graded loading method, the strain and deflection of the test section caused by each level of vehicle under each working condition are first calculated. After the test vehicle of the previous level is in place, the relevant strain and deflection are measured and compared with the calculated values. According to the principle of elasticity, after confirming that the stress and deflection generated by the vehicle are within the range of the calculated values, the next level of vehicle load is added.

[0018] Furthermore, the formula for calculating the efficiency of static load tests is as follows:

[0019]

[0020] In the formula: S s —The maximum calculated effect value of internal force, stress or displacement of a loading control section corresponding to a certain loading test item under static test load;

[0021] S'—Calculated value of the most unfavorable effect of internal forces, stresses or displacements at the same loading control section caused by the check load;

[0022] μ—Impact coefficient used according to specifications;

[0023] η q —Static test load efficiency.

[0024] Furthermore, establishing a multi-condition bridge model using the finite element method refers to using the finite element calculation software MidasCivil to establish a solid finite element model of the entire bridge.

[0025] Furthermore, in the pulsation test, including test span A and test span C, a vertical velocity sensor is placed 1m away from the crash barrier on the right side of the roadway of the bridge at the test section of test span A and test span C respectively. The small and irregular vibrations of the bridge caused by various external factors are measured, and then the spectrum analysis is performed to finally obtain the natural frequency and damping ratio of the bridge structure.

[0026] Furthermore, in the braking test, a test vehicle was driven at a constant speed of 20 km / h to the control section of the test span and braked to determine the strain fluctuation amplitude of the bridge span structure under impact load.

[0027] Furthermore, in the sports car test, three dynamic strain measurement points were arranged at relatively symmetrical positions on the test sections of test span A and test span C. A test vehicle was used to travel back and forth at a constant speed along the bridge roadway at different speeds to collect the dynamic strain of each test section and calculate the impact coefficient.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention provides a load testing method for beam bridges based on time-history curves. Through static load tests, the stress and deflection of the bridge structure's control sections under test loads are determined and compared with theoretical calculations to evaluate the actual structural performance and operational status. Dynamic load tests are conducted to determine the structure's response and assess its dynamic performance. By comprehensively analyzing the results of static and dynamic load tests, the existing bearing capacity of the bridge is assessed, providing a technical basis for the safety of bridge operation and original data for future bridge maintenance and management.

[0030] This invention presents a time-history curve-based load testing method for beam bridges. Compared with traditional static load testing, this method saves 65-70% in testing costs, resulting in significant economic benefits; it also saves 60%-75% in testing time, greatly reducing the impact on traffic, thus offering better economic and social benefits; compared with traditional dynamic load testing methods, this method combines static and dynamic load testing, which can reflect the working performance of the bridge structure under design loads, has high reliability, and broad application prospects. Attached Figure Description

[0031] Figure 1This is a schematic diagram of the cross-sectional arrangement of strain measuring points at sections A, B, and C of the bridge according to an embodiment of the present invention;

[0032] Figure 2 This is a cross-sectional layout diagram of the bridge deflection measuring points in this embodiment;

[0033] Figure 3 This is a schematic diagram of the main test section structure of the bridge under static load according to an embodiment of the present invention;

[0034] Figure 4 These are the acceleration time history response curves of bridge sections A and C measured during the pulsation test in this embodiment of the invention.

[0035] Figure 5 These are the spectrum curves of bridge sections A and C measured during the pulsation test in an embodiment of the present invention. Figure (a) is the first-order spectrum curve, and Figure (b) is the second-order spectrum curve.

[0036] Figure 6 This is the time history curve of dynamic strain at measuring point A of the bridge during the braking test in an embodiment of the present invention;

[0037] Figure 7 This is the time history curve of dynamic strain at measuring point C of the bridge during the braking test according to an embodiment of the present invention;

[0038] Figure 8 These are the time history curves of dynamic strain at measuring points A and C of the bridge during the sports car test. Figure (c) is the time history curve when the test vehicle is traveling at 10 km / h, Figure (d) is the time history curve when the test vehicle is traveling at 20 km / h, and Figure (e) is the time history curve when the test vehicle is traveling at 30 km / h.

[0039] In the attached diagram, 1 represents the strain measurement point and 2 represents the deflection measurement point. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that the specific embodiments of the present invention are only for the purpose of more clearly describing the technical solution and should not be construed as limiting the scope of protection of the present invention.

[0041] A load test method for beam bridges based on time history curves, comprising the following steps:

[0042] (1) Static load test:

[0043] (1.1) Several vehicles with known axle loads, wheelbases, and number of axles were used as test vehicles. These vehicles were arranged at key locations on the test bridge deck using a graded loading method. Measurement points included deflection and strain, positioned at the locations of maximum stress or deformation. In this embodiment, the bridge type for the test beam bridge was a (20+32+20)m prestressed concrete continuous box girder. The bridge started at chainage K8+049.00 and ended at chainage K8+137.00, with a total length of 88.00m. The superstructure box girder was a single-box, single-cell structure with a top plate width of 10.00m, a bottom plate width of 5.50m, and a beam height of 1.70m. The beam height to span ratio was 1 / 18.82. The design loads (using the "General Specifications for Highway Bridge and Culvert Design" JTG D60-2004) were: Vehicle load: Highway-I; Pedestrian load: 3.0kN / m². 2 Bridge deck width: 10.0m = 1.25m (left-side pedestrian walkway and railing) + 7.5m (driving road) + 1.25m (right-side pedestrian walkway and railing).

[0044] (1.2) Sensors were deployed on-site according to the measurement point layout plan; appropriate sensors and data acquisition equipment were selected based on the data accuracy requirements of the test bridge type, and appropriate auxiliary facilities were used to deploy the sensors at the measurement points according to the site conditions; for the selection of the test bridge span, since the superstructure of the bridge is a 20+32+20m prestressed concrete continuous box girder, spans 1# and 2# were selected for load testing; strain and deflection measurement point layout: ① Strain test sections were arranged at sections A, B, and C, and concrete strain gauges were arranged on the bottom surface of the box girder and the side surface of the web, for a total of 3×9=27 concrete strain gauges. For details on the strain measurement point numbering and location layout, please refer to Figure 1 Strain measurement points are arranged on the concrete of the base plate and web plate.

[0045] ② Deflection testing was conducted using a digital level. A total of 12 deflection measuring points were set up in spans 1 and 2, all located on the box girder bridge deck. Details of the measuring point locations can be found in [link to relevant documentation]. Figure 2 .

[0046] (1.3) Conduct static load tests on the bridge and calculate the static load test efficiency. The static load test efficiency should be controlled between 0.85 and 1.05.

[0047] Under the most unfavorable load conditions, the strength and stiffness of the bridge are tested to determine whether they meet the specifications and design requirements by measuring the strain and deflection of the test section.

[0048] The main test sections and test contents are as follows:

[0049] ① Test the strain and deflection of the box girder at section A of the side span where the maximum positive bending moment effect occurs;

[0050] ② Test the strain of the box girder at section B of the bridge at the maximum negative bending moment effect at the pier top;

[0051] ③ Test the strain and deflection of the box girder at section C, where the maximum positive bending moment effect occurs in the mid-span of the bridge;

[0052] ④ Test the deflection of the box girder at the quarter points of the side span and the middle span of the bridge;

[0053] ⑤ Test the compression of the bearings at bridge abutment #0 and pier #1.

[0054] The main test sections and test contents are detailed in Table 1 and Figure 3 .

[0055] Table 1. Overview of Test Sections and Test Contents for Bridge Static Load Tests

[0056]

[0057] (1.4) Based on the graded loading method and the efficiency of static load testing, a multi-condition bridge model was established using the finite element method, and time history curves were collected. To determine the internal forces, deflections, and test vehicle configurations of the test bridge under the design load, it is necessary to understand the influence line distribution of the bridge, which can be calculated using the finite element method. MidasCivil was used for calculation and analysis to establish an overall structural analysis model of the bridge. The following assumptions were made during modeling:

[0058] ① Concrete and steel are ideal elastic materials, and their elastic modulus is constant;

[0059] ② The cross-sectional deformation conforms to the plane section assumption;

[0060] ③ The impact of the crash barrier on the bending stiffness of the superstructure is not considered.

[0061] ④ The impact of the pavement layer on the bending stiffness of the superstructure is not considered, but its quality is taken into account.

[0062] (2) Dynamic load test

[0063] (2.1) Select the control section of each span of the bridge as the test section and conduct dynamic load tests. The dynamic load tests include pulsation test, braking test and runaway test.

[0064] (2.2) Based on the pulsation test and the actual bridge test of the inherent modal parameters of the bridge span structure, test the natural frequency and damping ratio of the bridge span structure;

[0065] (2.3) Based on the braking test and the running car test, the strain fluctuation amplitude and impact coefficient of each test section of the bridge span structure under dynamic load were obtained;

[0066] (2.4) Analyze the stress state of the bridge span structure under dynamic load based on the data obtained from the tests in steps (2.2) and (2.3).

[0067] In this embodiment, to ensure test safety and avoid bridge damage caused by overload, the test vehicle will be loaded in stages using a graded loading method. The strain and deflection of the test section caused by each stage of the vehicle under each working condition are calculated in advance. After the previous stage test vehicle arrives, the relevant strain and deflection are measured and compared with the calculated values. Based on the principles of elasticity, after confirming that the stress and deflection generated by the vehicle are within the calculated range, the next stage of vehicle load is added.

[0068] The formula for calculating the efficiency of static load tests is as follows:

[0069]

[0070] In the formula: S s —The maximum calculated effect value of internal force, stress or displacement of a loading control section corresponding to a certain loading test item under static test load;

[0071] S'—Calculated value of the most unfavorable effect of internal forces, stresses or displacements at the same loading control section caused by the check load;

[0072] μ—Impact coefficient used according to specifications;

[0073] η q —Static test load efficiency.

[0074] Among them, establishing a multi-condition bridge model using the finite element method refers to using the finite element calculation software MidasCivil to establish a solid finite element model of the entire bridge.

[0075] In this embodiment of the pulsation test, there are two test spans: A and C. One vertical velocity sensor is placed 1 meter from the right-hand side of the crash barrier on the bridge deck at each test section of the bridge's driving lane at test spans A and C. The sensors measure the minute and irregular vibrations of the bridge caused by various external factors, and then perform spectral analysis to obtain the natural frequency and damping ratio of the bridge structure. The time history response curves of the bridge sections A and C measured during the pulsation test are shown below. Figure 4 The spectrum curve is as follows Figure 5 As shown.

[0076] By analyzing the various spectrum diagrams, the first two natural frequencies of the bridge can be obtained, as shown in Table 2. The data in the table shows that the measured natural frequencies of the test span are greater than the theoretically calculated frequencies.

[0077] Table 2 Summary of Bridge Natural Frequency and Damping Ratio Test Results

[0078]

[0079] In the braking test, a test vehicle was driven at a constant speed of 20 km / h to the control section of the test span and then braked to determine the strain fluctuation amplitude of the bridge span structure under impact load. The dynamic strain time history curve of the measuring point A of the bridge during the braking test is shown below. Figure 6 The dynamic strain time history curves at the measuring point C section of the bridge are shown below. Figure 7 .

[0080] By analyzing the dynamic strain time history curves of the test sections, the peak and trough values ​​of the dynamic strain oscillation can be obtained. The dynamic performance parameters of sections A and C of the Xiaodonggou Bridge under braking conditions are shown in Table 3.

[0081] Table 3. Overview of dynamic performance parameters of bridge sections A and C under braking conditions.

[0082]

[0083] Furthermore, in the sports car test, three dynamic strain measurement points were arranged at relatively symmetrical positions on the test sections of test spans A and C. A test vehicle traveled back and forth at a constant speed along the bridge deck at different speeds to collect the dynamic strain at each test section and calculate the impact coefficient. The test was arranged under the following three conditions:

[0084] Condition 1: The test vehicle travels across the test bridge at a constant speed of 10 km / h (one vehicle travels across the test bridge at a constant speed);

[0085] Condition 2: The test vehicle travels across the test bridge at a constant speed of 20 km / h (one vehicle travels across the test bridge at a constant speed);

[0086] Condition 3: The test vehicle travels across the test bridge at a constant speed of 30 km / h (one vehicle travels across the test bridge at a constant speed).

[0087] The dynamic strain test sections of the bridge were arranged at control sections A and C of the test span. Three dynamic strain measuring points were placed at relatively symmetrical positions on each test section. During the vehicle test, the dynamic strain time history curves of the measuring points at sections A and C of the bridge are shown below. Figure 8 As shown.

[0088] The impact coefficient can be calculated by analyzing the peak and trough values ​​of the dynamic strain time history curves at different vehicle speeds. The impact coefficients of the bridge dynamic strain test section are shown in Table 4.

[0089] Table 4. Summary of Measured Impact Coefficients of Bridge Sections A and C

[0090]

[0091]

[0092] The theoretical loads in this experiment were considered based on the design load level (Highway-I and pedestrian loads). Analysis of the dynamic load test data for each bridge span yielded the following conclusions:

[0093] (1) The structural natural frequencies of the bridge test section were tested. The measured first-order natural frequency was 5.391 Hz, which is greater than the theoretically calculated frequency. The test damping ratio corresponding to the first-order frequency of the test section was 0.70%. The measured second-order natural frequency was 11.250 Hz, which is greater than the theoretically calculated frequency. The test damping ratio corresponding to the second-order frequency of the test section was 0.27%.

[0094] (2) The impact coefficients of each test section are between 0.04 and 0.191, all of which are less than the theoretically calculated value of 0.270.

[0095] (3) Analysis of the dynamic strain observation results shows that the maximum strain of each control section under the running car and braking conditions is 24.29με and 17.59με, respectively. During the test, no phenomenon of rapid increase in dynamic strain and maintaining a large value for a considerable period of time was found.

[0096] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A load test method for beam bridges based on time history curves, characterized in that, The method includes the following steps: (1) Static load test: (1.1) Several vehicles with known axle load, wheelbase and number of axles are used as test vehicles. The test vehicles are arranged in a graded loading method at the key parts of the test bridge deck. The measuring points are deflection measuring points and strain measuring points, which are arranged at the position of maximum stress or deformation. (1.2) According to the measurement point layout plan, the sensors are deployed on site; according to the data accuracy requirements of the test bridge type, the appropriate sensors and data acquisition equipment are selected, and according to the site conditions, the appropriate auxiliary facilities are used to deploy the sensors at the measurement points. (1.3) Conduct static load tests on the bridge and calculate the static load test efficiency. The static load test efficiency should be controlled between 0.85 and 1.

05. (1.4) Based on the graded loading method and the efficiency of static load test, a multi-condition bridge model was established using the finite element method, and time history curves were collected. (2) Dynamic load test (2.1) Select the control section of each span of the bridge as the test section and conduct dynamic load tests. The dynamic load tests include pulsation test, braking test and runaway test. (2.2) Based on the pulsation test and the actual bridge test of the inherent modal parameters of the bridge span structure, the natural frequency and damping ratio of the bridge span structure are tested; the time history response curve and spectrum curve of the test section are measured during the pulsation test, and then spectrum analysis is performed to finally obtain the natural frequency and damping ratio of the bridge structure. (2.3) The strain fluctuation amplitude and impact coefficient of each test section of the bridge span structure under dynamic load are obtained based on the braking test and the running car test. During the braking test, the dynamic strain time history curve of the test section measuring point is obtained. By analyzing the dynamic strain time history curve of the test section, the oscillation peak value and valley value of the dynamic strain are obtained. During the running car test, the dynamic strain time history curve of the test section measuring point is obtained. By the oscillation peak value and valley value of the dynamic strain time history curve at different vehicle speeds, the impact coefficient can be calculated. (2.4) Analyze the stress state of the bridge span structure under dynamic load based on the data obtained from the tests in steps (2.2) and (2.3).

2. The load test method for beam bridges based on time history curves according to claim 1, characterized in that, In the graded loading method, the strain and deflection of the test section caused by each level of vehicle under each working condition are first calculated. After the test vehicle of the previous level is in place, the relevant strain and deflection are measured and compared with the calculated values. According to the principle of elasticity, after confirming that the stress and deflection generated by the vehicle are within the range of the calculated values, the next level of vehicle load is added.

3. The load test method for beam bridges based on time history curves according to claim 1, characterized in that, The formula for calculating the efficiency of static load tests is: ； In the formula: — The maximum calculated effect value of internal force, stress or displacement of a loading control section corresponding to a certain loading test item under static test load; — Calculate the most unfavorable effects of internal forces, stresses, or displacements at the same loading control section caused by the load; — Impact coefficient adopted according to specifications; — Static test load efficiency.

4. The load test method for beam bridges based on time history curves according to claim 1, characterized in that, Establishing a multi-condition bridge model using the finite element method refers to using the finite element calculation software Midas Civil to create a solid finite element model of the entire bridge.

5. The load test method for beam bridges based on time history curves according to claim 1, characterized in that, In the pulsation test, which includes test span A and test span C, a vertical velocity sensor is placed 1m away from the crash barrier on the right side of the roadway of the bridge at the test section of test span A and test span C respectively. The sensor measures the small and irregular vibrations of the bridge caused by various external factors, and then performs spectrum analysis to obtain the natural frequency and damping ratio of the bridge structure.

6. The load test method for beam bridges based on time history curves according to claim 1, characterized in that, In the braking test, a test vehicle was driven at a constant speed of 20 km / h to the control section of the test span and braked to determine the strain fluctuation amplitude of the bridge span structure under impact load.

7. The load test method for beam bridges based on time history curves according to claim 1, characterized in that, In the sports car test, three dynamic strain measurement points were arranged at relatively symmetrical positions of the test sections of test span A and test span C. A test vehicle was used to travel back and forth at a constant speed along the bridge roadway at different speeds to collect the dynamic strain of each test section and calculate the impact coefficient.

Images