Service performance monitoring and evaluation method of key-tooth adhesive joints in segmental assembled box girders

Abstract

The present invention discloses a method for monitoring and evaluating the service performance of key-tooth adhesive joints in segmented box girders. The method comprises: distributing multiple first stress measuring points, multiple second stress measuring points, multiple third stress measuring points, and adjacent segment vertical displacement measuring points in the region of 1 / 4 to 1 / 8 of the beam span, as well as at joint locations where cracks, defects, or suspected defects are detected through nondestructive testing, with each stress measuring point distributed in the tensile and compressive zones of the joint section; distributing multiple first measuring points along the beam-height span joint, distributing multiple second measuring points on the key teeth along the beam height, and distributing multiple third measuring points simultaneously on the key teeth on both sides of the joint along the beam height, staggered from the placement of the multiple second measuring points; and evaluating the service status of the joint based on the monitoring results of each of the aforementioned measuring points and shear-friction theory. The present invention can address the problems of poor feasibility of current destructive testing methods for joint service status, the accuracy and lack of verification of nondestructive testing results, and the limitations of the application of load test results.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge key health monitoring, and more particularly to a method for monitoring and evaluating the service performance of key-tooth adhesive joints of segmental assembled box girders. Background Art

[0002] Segmental prefabricated bridges divide the beam into several segments along the longitudinal direction. After casting and curing at the beam yard, they are transported to the bridge site. The segments are hoisted and transported by mechanical equipment. After installation and positioning, prestressing is applied and joints are glued, integrating the multiple segments into a single unit. This type of bridge is widely used in current prestressed concrete beam bridge construction due to its advantages such as fast construction, minimal impact on surrounding traffic, flexible construction, and wide span adaptability. However, segmental prefabricated beam bridges often have numerous segmental joints, where steel bars are interrupted and the joint adhesives are susceptible to hygrothermal aging. Furthermore, during service, the mechanical properties of the joints degrade and crack under the complex bending and shear forces. These factors seriously affect the overall performance of the segmental bridge and even the serviceability of both the local and overall bridge structures. Therefore, monitoring the service performance indicators of segmental beam joints and understanding the characteristics and evolution of the service state of segmental beam joints can provide basic data for further evaluation of the service performance of segmental beam bridges.

[0003] Currently, the service condition of segmental assembled beam bridges is primarily assessed through core sampling and nondestructive ultrasonic testing (NDT). Core sampling, due to the potential for damage to actual structures, is difficult to implement, and the number of tests conducted is limited. The test results lack generalizability, making it difficult to assess mechanical properties. For NDT, the precision and accuracy of segmental joint service condition measurements are significantly affected by factors such as internal reinforcement, reinforcement measures on existing bridges, and the distribution of measurement lines and test areas. Furthermore, test results cannot be fully validated, and performance indicators are often lacking to identify suspected defects. The service condition and performance characterization of segmental joints are key components of structural performance assessment for segmental assembled bridges. For this purpose, actual bridge load tests are also currently used to evaluate the connection performance by measuring the vertical displacement difference and segment strain change between adjacent segments under vehicle loads. However, due to the relatively small vehicle loads applied, which differ from the load conditions experienced during operation, segment displacement changes are minimal, making it difficult to assess defects and performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for monitoring and evaluating the service performance of key-tooth adhesive joints of segmented assembled box girders, so as to overcome the application limitations of current joint damage coring and non-destructive testing methods, such as poor feasibility in actual engineering sites, small number of test samples, large uncertainty in results, and strong subjectivity of test results, as well as defects such as short duration of load tests on real bridges, large difference between applied loads and actual operating loads, and poor local effects of measured results of segment stress and macro-deformation, and to solve the problem that current joint service performance evaluation results are inaccurate and lack quantitative evaluation indicators.

[0005] To achieve these objectives and other advantages of the present invention, a method for monitoring and evaluating the service performance of key-tooth adhesive joints of segmental assembled box girders is provided, comprising:

[0006] S1. Arrange multiple first stress measuring points, multiple second stress measuring points, multiple third stress measuring points, and adjacent segment vertical displacement measuring points in the 1 / 4 to 1 / 8 beam span area and at joint locations where cracks or defects are present or suspected defects are detected by nondestructive testing.

[0007] Wherein, for any of the joints, a plurality of first measuring points are arranged along the beam height-span joint and distributed in the tension zone and compression zone of the joint section; a plurality of second measuring points are arranged on the key teeth along the beam height direction and distributed in the tension zone and compression zone of the joint section; a plurality of third measuring points are arranged simultaneously on the key teeth on both sides of the joint along the beam height direction and distributed in the tension zone and compression zone of the joint section, and are staggered with the layout positions of the plurality of second measuring points;

[0008] S2. Evaluate the service condition of the joint based on the monitoring results of each of the above measuring points and the shear-friction theory;

[0009] Based on the shear-friction theory, assuming that the width of the multi-joint joint area is ω, the width of the shear surface of a single joint is b, and the height of the shear surface of a single key tooth gap is d, the theoretical calculation formula for the average shear stress is:

[0010] ν=V / bd (1)

[0011] σ x =pf y +σ Nx (2)

[0012] Where, ν is the shear stress of the joint section; V is the shear force at the joint; σ x is the normal stress at the joint; p is the reinforcement ratio of the steel bars running through the joint; f y is the yield strength of the joint restraining reinforcement; σ Nx is the tensile / compressive stress acting on the joint surface, with tension being positive and compression being negative;

[0013] According to the shear-friction theory, without considering the initial cracking of the joint, the formula for calculating the ultimate shear stress of the joint is as follows:

[0014] ν u =(φpf y +σ Nx )μ (3)

[0015] Where, ν u is the ultimate shear stress of the joint; φ is the bearing capacity reduction coefficient; μ is the friction coefficient of the joint interface;

[0016] For the tensile force N u Acting on the shear plane A cr , and the joint has initial cracking, the calculation formulas for the ultimate shear stress and ultimate shear bearing capacity of the joint are as follows:

[0017] ν u =(φA s f y / A cr -N u / A cr )μ (4)

[0018] or V u / μ=(φA s f y -N u ) (5)

[0019] Where V u A is the ultimate shear bearing capacity of the joint; s is the total reinforcement area passing through the shear surface; A cr is the cross-sectional area of ​​the joint; N u is the axial compressive load acting on the joint section;

[0020] ① Interface shear-slip state determination

[0021] Formula (1) is used to calculate the joint cross-section shear stress ν. Based on whether the joint has initial cracking, the joint limit shear stress ν calculated by formula (3) or formula (4) is calculated. u For comparison, a binary discrimination method is used to formulate the interface shear-slip discrimination criteria as follows:

[0022] When ν≤ν u , indicating that no shear-friction slip occurs at the interface;

[0023] When ν>ν u , indicating that shear-friction slip occurs at the interface;

[0024] In addition, the ultimate shear bearing capacity V of the joint can be calculated based on the shear force V at the joint and formula (5): u For comparison, a binary discrimination method is used to formulate the interface shear-slip discrimination criteria as follows:

[0025] When V≤V u , indicating that no shear-friction slip occurs at the interface;

[0026] When V > V u , indicating that shear-friction slip occurs at the interface;

[0027] ② Determination of the opening state of the joint interface based on cross-joint stress test results

[0028] The cross-seam stress test results σ1 measured at multiple first stress measurement points are compared with the normal stress at the joint calculated by formula (2). A binary discrimination method is used to formulate the preliminary discrimination criteria for the open or closed state of the joint as follows:

[0029] σ1≤σ x , indicating that the seam does not open;

[0030] σ1>σ x , indicating that the seam has opened;

[0031] ③ Determination of ultimate shear strength of joints under open joint interface

[0032] For the specimen with initial cracking, when the reinforcement ratio is high and the shear stress exceeds 5.9 MPa, tanφ=1.0, pf y Less than 0.3f c ' or 10.5 MPa, where f c ′ is the design value of the compressive strength of cylindrical concrete;

[0033] Based on this, when the joint is open, depending on whether the joint has initial cracking, the joint limit shear stress ν calculated with formula (3) or formula (4) is u For comparison, a binary discrimination method is adopted to formulate the following criteria for the discrimination of joint shear strength:

[0034] When ν≤ν u , indicating that the shear strength of the joint interface meets the requirements, and the open or closed state of the interface does not affect its shear strength;

[0035] When ν>ν u , indicating that the reduction of interface shear strength causes friction slip at the joint;

[0036] ④ Determination of joint shear force transmission capacity

[0037] Formula (1) is used to calculate the joint cross-section shear stress ν. Based on whether the joint has initial cracking, the joint limit shear stress ν calculated by formula (3) or formula (4) is calculated. u Compare the joint shear force V with the joint ultimate shear bearing capacity V calculated by formula (5) uFor comparison, a binary discrimination method is adopted to formulate the following criteria for the shear force transfer capacity of joints:

[0038] When ν≤ν u or V≤V u At the same time, if the deviation of the vertical stress σ3 on both sides of the key tooth gap of adjacent segments measured at each third stress measuring point is less than 5%, it indicates that the shear force transmission capacity of the key tooth joint is strong;

[0039] ⑤ Determination of joint shear force transfer capacity based on segment vertical displacement test results

[0040] When the deviation of the vertical stress σ3 on both sides of the key-tooth gap between adjacent segments is greater than 5%, and it is preliminarily determined that there is a local or overall joint opening phenomenon, the vertical displacement of the adjacent segments on both sides of the joint or the vertical displacement of each segment along the bridge span direction is further monitored to obtain and compare the variation patterns of the vertical displacement of the bridge span and the vertical displacement deviation amplitude Δ1-Δ2 of the adjacent segments under different temperatures and operating vehicle loads. If there is a sudden change in the local vertical displacement or the segment vertical displacement test results show an increasing trend, it indicates that the shear force transmission capacity of the joint is reduced and the shear strength of the joint is declining.

[0041] ⑥ Determination of joint shear stiffness based on segment vertical displacement test results

[0042] Shear stiffness K of segmental assembled beam joints Fν The calculation formula is as follows:

[0043]

[0044] Where Δ1 and Δ2 are the measured results of vertical displacements of adjacent segments on both sides of the joint;

[0045] According to the shear stiffness K of the bridge joint during operation Fν Time-varying law (the relationship curve between shear stiffness and operation time) or the bearing capacity variation trend (the relationship curve between shear stiffness and vehicle load), when the shear stiffness K of the segmental assembled beam joint is Fν When there is a decay trend, it means that the macro shear stiffness at the joint is degraded, affecting the integrity of the structure.

[0046] ⑦ Identification of key tooth cracking status based on key tooth stress test results

[0047] The key tooth stress test results σ2 measured at multiple second stress measurement points are respectively compared with the concrete cracking stress σ cr For comparison, a binary discrimination method is adopted to formulate the following criteria for judging the cracking state of key teeth:

[0048] When σ2≤σ cr , indicating that the key teeth are not cracked;

[0049] When σ2>σ cr, indicating that the key teeth are cracked.

[0050] Preferably, in the service performance monitoring and assessment method of the key-tooth adhesive joints of the segmented assembled box beam, the segment vertical displacement test method is: target lights are arranged in the 1 / 4 to 1 / 8 beam span length area, and in adjacent segments of the joints where cracks or defects occur or suspected defects are obtained by non-destructive testing, the camera is fixed, and the target light image is clearly displayed, and the vertical displacement test results of different segments are obtained based on the correlation between the video image pixels and the displacement.

[0051] Preferably, in the method for monitoring and evaluating the service performance of the key-tooth adhesive joints of the segmented assembled box beam, the camera is arranged on the ground or at the pier top.

[0052] Preferably, in the method for monitoring and evaluating the service performance of the key-tooth adhesive joints of the segmented assembled box beam, the camera is arranged at the pier top diaphragm.

[0053] The present invention has at least the following beneficial effects:

[0054] The present invention can realize long-term observation of monitoring indicators and characterization of joint performance, and can verify with non-destructive defect monitoring and load test results, so as to more comprehensively grasp the segment connection status and performance evolution process.

[0055] The present invention can solve the problems of poor feasibility of destructive testing methods for the service status of joints, the accuracy and lack of verification of non-destructive testing results, and the application limitations of load test results.

[0056] The present invention can overcome the application limitations of current joint damage coring and non-destructive testing methods, such as poor feasibility in actual engineering sites, small number of test samples, large uncertainty in results, and strong subjectivity of test results, as well as defects such as short duration of load tests on real bridges, large differences between applied loads and actual operating loads, and poor local effects of measured results of segmental stress and macro-deformation. It also solves the problem of inaccurate results of current joint service performance evaluation and the lack of quantitative evaluation indicators.

[0057] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is the geometric configuration characteristics of the key tooth gap of the segmental assembled beam and the stress state diagram of the splicing joint;

[0059] Figure 2 It is the location diagram of the joint test section;

[0060] Figure 3 It is the arrangement diagram of measuring points of joint stress state;

[0061] Figure 4 It is the on-site layout diagram of the joint stress state measurement points;

[0062] Figure 5 This is a schematic diagram of the test results of the joint stress state measurement points;

[0063] Figure 6 This is the on-site layout diagram of the non-contact photoelectric measuring points for the vertical displacement of the segmental box girder;

[0064] Figure 7 This is the test result diagram of the vertical displacement of the segmental box girder;

[0065] Figure 8 This is the test result diagram when the local vertical displacement undergoes a sudden change. DETAILED DESCRIPTION

[0066] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0067] For precast concrete segmented assembled beam structures, each segmental beam is independently arranged with steel mesh, and the steel bars between segments are not connected. Usually, through prestressed tendons are arranged on the top and bottom surfaces of the segmental beam to enhance its integrity. Joints are the weak points of the segmented assembled beam structure. In order to ensure the connection strength and durability of the joints, they are gradually transformed from flat joints, dry joints, and wet joints to key-tooth adhesive joints. In view of the fact that during the service of the segmented assembled beam structure, under the combined effects of operating vehicle loads, dead loads, temperature, etc., the joint sections along the length of the beam are in a complex bending and shear stress state, and the joint sections along the height of the beam are in a tensile or compressive, shear stress state (such as Figure 1 As shown), and as the service time of the bridge continues to increase, the wet and hot aging performance of the joint glue becomes prominent, causing the local or overall technical condition of the bridge to deteriorate, which in turn causes the overall performance of the structure to decay, deformation to increase, and increase the potential safety risk of the segmented assembled beam structure. In order to timely grasp the service status of the joint and take reasonable safety precautions in time, this application provides a monitoring method for the service performance of the key tooth glue joint of the segmented assembled box beam based on the joint shear-friction theory. In order to provide basic data for the service status evaluation of the serving segmented assembled beam, it is necessary to Figure 1 The stress state of the joint (tension, compression, and shear stress state) and the deformation characteristics of the segmental beam are determined. The types of service performance monitoring indicators of joints of different scales are clarified, and a monitoring method with long-term, strong stability, and remote data collection and transmission functions is implemented. The specific implementation steps are as follows:

[0068] (1) Develop a monitoring plan for the service status of key tooth adhesive joints

[0069] According to the characteristics of the joint stress and vertical deflection deformation along the length of the segment beam, based on the key points of the joint shear-friction theory, that is, under the action of shear force, friction slip can occur at the joint interface, therefore, the joint status in the area of ​​1 / 4L to 1 / 8L (L is the span length of the beam) is mainly monitored or detected. When cracks and defects appear in the joints of the segment assembled beams in service, that is, cracks and damage appear along the segment key teeth or adjacent segments of the joint height, the joint test section position should be arranged at this location. In summary, the joint test sections are mainly located in the 1 / 4L to 1 / 8L area, as well as the joint positions where cracks and defects appear or suspected defects are obtained by non-destructive testing (such as Figure 2 shown).

[0070] At each section of the joint test, according to the joint stress state (such as Figure 1 As shown) and the vertical deflection deformation characteristics of the segmental beam, mainly testing the stress state of the joints, key teeth, segments, etc. (test results as shown Figure 5 ) and the vertical deformation of the segment or the relative vertical deformation parameters of adjacent segments (test results as shown in Figure 7 The test objectives and rationale are briefly described below:

[0071] ① The epoxy resin glue used in the joint has quantitative indicators of tensile, compressive and shear mechanical properties of the bonded joint. In order to determine the open or closed state of the joint, the tensile or compressive stress of the segmental beam joint is tested under the coupling of normal stress and shear stress. The measuring points are arranged along the high span joint of the beam (such as Figure 3 The measuring points should be distributed in the tension and compression areas of the joint section; the number of measuring points can be adjusted according to the number of key teeth.

[0072] ② Under the bending and shear coupling effect, vertical cracks may occur at the key teeth of the joint area. In order to determine the cracking state of the joint key teeth, the unidirectional normal stress state is tested. Measuring points are arranged on the key teeth along the beam height direction (such as Figure 3 b), the measuring points are distributed in the tension and compression areas of the joint section; the number of measuring points can be adjusted according to the number of key teeth.

[0073] ③ As the service time of segmental beams increases, the aging performance of joint adhesive develops, its durability deteriorates and its service performance deteriorates, resulting in the decline of the shear force transfer effect of the joint. In order to understand the changing law of the shear force transfer effect of the glue joints of segmental assembled beams, the vertical stress on both sides of the joint is tested or monitored. Measuring points are arranged on the key teeth on both sides of the joint along the height of the beam (such as Figure 3 c), the measuring points are distributed in the tension and compression zones of the joint section. Their locations should be staggered with the key tooth stress measuring points. The number of measuring points can be adjusted based on the number of key teeth.

[0074] ④ When the joint state deteriorates, the local and overall performance of the segmental assembled beam may change, which can be reflected in the amplitude and rate of vertical displacement change of the segmental beam along the beam length during operation, as well as the local segment displacement change. Therefore, segment vertical displacement measurement points are arranged for the segmental assembled beam glue joint area (1 / 4L~1 / 8L area) of the key stress-bearing parts of focus, as well as the joint positions with cracks or suspected defects obtained by non-destructive testing (on-site installation such as Figure 4 shown).

[0075] ⑤ When the amplitude and rate of change of the segment vertical displacement increase, further test the dynamic characteristics (such as frequency) that reflect the overall performance of the structure. At least three dynamic measurement points should be arranged along the beam span of the segmental assembled beam bridge of interest, and the beam dynamic characteristics testing plan should comply with the current relevant standards.

[0076] (2) Develop a method for monitoring or testing the service status of key-tooth adhesive joints

[0077] In order to grasp the integrity of the superstructure during the operation of segmental assembled beam bridges, as well as the evolution of the service status of segmental joints, the monitoring or detection methods adopted should meet the functional requirements of long-term maintenance, strong stability, and remote wireless data collection and transmission. To this end, the cross-joint stress, key tooth stress, and shear transfer stress detection instruments adopt contact testing methods with strong stability, such as vibrating wire strain gauges and bow strain gauges. In order to reflect the dynamic impact of operating vehicle loads, the acquisition system should meet the adjustable frequency function. For the vertical displacement index of the segmental beam, since the contact test method involves the difficulty of laying out the reference points, non-contact video image testing technology is used. The key points of test implementation are:

[0078] ① Along the span of the beam, target lights are placed in each test section or in the sections adjacent to the joints (on-site installation is as follows: Figure 6 b);

[0079] ② Place the camera in a basically fixed position, such as on the ground, on the top of a pier, etc., and clearly display the target light image (on-site installation such as Figure 6 a);

[0080] ③According to the correlation between video image pixels and displacement, obtain the vertical displacement test results of different segments ( Figure 7 shown);

[0081] ④ Use the segment vertical displacement measurement results to calculate the segment beam fundamental frequency.

[0082] (3) Layout of the segment key tooth adhesive joint service status monitoring system

[0083] According to the service status monitoring or detection indicators and methods of the key tooth glue joint, contact stress measurement points and non-contact video displacement measurement points are set on the box beam body, and relevant instruments and meters, as well as optoelectronic video equipment, are installed. In order to meet the needs of long-term and short-term data collection and transmission under special circumstances, a monitoring system with both wired and wireless network collection and transmission is formed. Its specific components are as follows:

[0084] (4) Calculation of shear strength of key tooth joints based on shear-friction theory

[0085] According to the existing shear-friction theory, combined with the stress characteristics of the joint under the combined action of shear force or shear force and bending moment, the main indicators that can characterize the joint performance are shear strength, ultimate shear stress, joint slip, etc.

[0086] Assume that the width of the multi-key joint area is ω, the width of the single joint shear surface is b, and the height of the single key tooth gap shear surface is d. The average shear stress theoretical calculation formula is:

[0087] ν=V / bd (1)

[0088] σ x =pf y +σ Nx (2)

[0089] Where ν is the shear stress; V is the shear force at the joint; σ x is the normal stress at the joint; p is the reinforcement ratio of the steel bars running through the joint; f y is the yield strength of the joint restraining reinforcement; σ Nx It is the tensile (compressive) stress acting on the joint surface, tension is positive and compression is negative.

[0090] Without considering the initial cracking of the joint, according to the shear-friction theory, the formula for calculating the ultimate shear stress is as follows:

[0091] ν u =(φpf y +σ Nx )μ (3)

[0092] Where, ν u is the ultimate shear stress of the joint; φ is the bearing capacity reduction factor, μ is the friction coefficient of the joint interface; according to ACI318-71 section11.15, μ=1.4,φ=1.0.

[0093] For the shear transfer strength of the initially cracked specimen with tensile stress on the shear surface, the shear friction theory in Section 11.5 of ACI318-71 and the shear strength design formula in Section 6.1.9 of PCI Design Handbook use the bearing capacity reduction factor φ=1.0. Both formulas are conservative estimates of the shear transfer strength.u Acting on the shear plane A cr , and there is an initial crack, the shear stress calculation formula of the shear-friction theory is as follows:

[0094] ν u =(φA s f y / A cr -N u / A cr )μ (4)

[0095] or V u / μ=(φA s f y -N u ) (5)

[0096] Where V u A is the ultimate shear bearing capacity of the joint; s is the total reinforcement area passing through the shear surface; A cr is the cross-sectional area of ​​the joint; N u is the axial compressive load acting on the joint section; φ is the bearing capacity reduction coefficient, which is taken as 0.85.

[0097] (5) Assessment of joint service status based on monitoring results

[0098] During the long-term service of segmental assembled box girders, in order to grasp the service status and overall performance of segmental assembled box girders, it is necessary to further understand the mechanical properties of the joints in combination with a small amount of damage and non-destructive testing results, and comprehensively evaluate the service status of the joints from the aspects of defect status and performance. At present, through core damage sampling and ultrasonic non-destructive testing technology, a preliminary analysis of internal defects in the joints, such as cracking of the joint interface and overall looseness, can be made. However, the accuracy of the test results and the analysis of their impact on local and overall service performance need to be further verified. Therefore, a calculation and analysis method for relevant characterization indicators for the identification of joint service status and the analysis of the overall performance of segmental assembled box girders was developed, mainly including the judgment of the slip state of the joint interface, the judgment of the opening state of the joint interface, the judgment of the cracking state of the key tooth gap, as well as the evaluation of the shear force transmission performance of the joint, the evaluation of the shear resistance performance of the joint interface, and the analysis of the integrity of the box girder.

[0099] ① Interface shear-slip state determination

[0100] Apply formula (1) to calculate the joint section shear stress ν, and compare it with the ultimate shear stress ν calculated by formula (3) or formula (4) u For comparison, based on the binary discrimination method, the interface shear-slip discrimination criteria are as follows:

[0101] When ν≤ν u , no shear-friction slip occurs at the interface;

[0102] When ν>ν u , shear-friction slip occurs on the interface;

[0103] In addition, the interface shear-slip judgment standard can be obtained by comparing the joint section shear force (the section shear force action value is determined according to the applied load) with the ultimate shear bearing capacity of formula (5) using the binary judgment method as follows:

[0104] When V≤V u , no shear-friction slip occurs at the interface;

[0105] When V > V u , shear-friction slip occurs on the interface;

[0106] ② Determination of the opening state of the seam interface:

[0107] When the cross-joint tensile force or tensile stress exceeds the tensile strength of the adhesive joint, the adhesive joint interface is considered to be cracking or opening. Simultaneously, the ultimate shear strength of the adhesive joint decreases, and continued service may degrade the overall performance of the structure. A preliminary assessment of the open or closed state of the joint interface can be made based on the cross-joint tensile or compressive stress of each key joint distributed along the cross-section height. Based on this assessment, a comprehensive assessment of the joint opening state is made, taking into account variations in the ultimate shear strength of the interface.

[0108] Using the binary discrimination method and formula (2), the preliminary discrimination criteria for the open or closed state of the seam are formulated as follows:

[0109] σ1≤σ x , indicating that the seam does not open;

[0110] σ1>σ x , indicating that the seam has opened;

[0111] Where σ1 is the cross-gap stress test result. The σ1 test result only represents the joint condition of the key tooth at the measurement point. Combined with the cross-gap stress test results of multiple key teeth along the beam height, the joint opening height or range can be determined. The test results of σ3 and σ2 are the same below.

[0112] ③ Determination of ultimate shear strength of joints when the joints are open

[0113] When the joint is in an open state, the shear strength of the joint is further determined. Considering the changes in the axial compressive stress of the joint section during service (such as prestress loss, etc.) and the cracking state of the joint interface, the ultimate shear stress ν of the joint is calculated according to formula (3) and formula (4). u .

[0114] The results of J.A.Hofbeck's research show that for specimens with initial cracking, when the reinforcement ratio is high and the shear stress exceeds 5.9 MPa, it is necessary to take a smaller value of tanφ and pf during design. y Upper limit. That is, tanφ=1.0, pf y Less than 0.3f c ′ or 10.5MPa.

[0115] Based on this, when the joint is in the open state, the shear strength level of the joint is determined as follows:

[0116] When ν≤ν u , the shear strength of the joint interface meets the requirements, and the open or closed state of the interface does not affect its shear strength;

[0117] When ν>ν u , the reduction of interface shear strength causes friction slip at the joint.

[0118] Therefore, the long-term variation trend of joint shear strength during the bridge operation period should be further combined with the results of joint shear force transfer capacity determination for a more accurate judgment.

[0119] ④ Determination of joint shear force transmission capacity:

[0120] For segmental assembled beams with multi-key joints, the open or closed state of the interface can affect the shear force transmission capacity of the joint, as well as the stress and deformation coordination capacity of the local structure or the overall structure. During the long-term operation of the bridge, under the influence of the hygrothermal aging of the interface glue and the axial stress of the joint section (such as prestress loss), the shear strength of the joint interface degrades, directly affecting its shear force transmission capacity. Therefore, combined with the calculation results of the ultimate shear stress of the joint, ν u (Considering the seam σ Nx The shear force transfer capacity of the joint is determined by the following:

[0121] When ν≤ν u or V≤V u At the same time, the vertical stress σ3 on both sides of the key tooth gap of adjacent segments is basically consistent (the vertical stress deviation on both sides of the key tooth gap of adjacent segments is less than 5%), indicating that the shear force transmission capacity of the key tooth joint is strong;

[0122] When the deviation of the vertical stress σ3 on both sides of the key tooth gap between adjacent segments is greater than 5%, it does not necessarily mean that the shear force transmission capacity of the key tooth joint is weakened. The shear force transmission capacity of the joint should be comprehensively judged by combining ② the joint opening state and the macro-segment vertical deformation test results (vertical deformation of adjacent segments on both sides of the non-contact joint).

[0123] ⑤ Determination of joint shear force transfer capacity based on segment vertical deformation test results

[0124] When the vertical stress σ3 deviation on both sides of the key tooth gap of adjacent segments is large (greater than 5%), and it is preliminarily judged that there is a local or overall opening phenomenon in the joint, the vertical displacement of the adjacent segments on both sides of the joint (Δ1, Δ2) or the vertical displacement of the segments along the span direction (Δ1, Δ2...Δ N ) to monitor the vertical displacement of the bridge span and the vertical displacement deviation amplitude (Δ1-Δ2) of the adjacent segments under different temperatures and operating vehicle loads. Figure 8 As shown) or the segment vertical displacement test results have an increasing trend, it means that the shear force transmission capacity of the joint is reduced and the shear strength of the joint is declining. In the long-term operation process, because the load and environmental conditions of the operating vehicles are basically the same, under the same value standards (such as the same temperature, the same load conditions, the maximum value or the average value of a certain period of time, etc.), the change in the vertical displacement of a certain position remains basically constant. When the vertical displacement of the monitoring position has an increasing trend in the long-term monitoring process, real-time monitoring or staged monitoring is usually used, and it can be identified by looking at the time-varying law curve.

[0125] ⑥ Analysis of joint shear stiffness based on segment vertical deformation test results

[0126] When the joint service condition assessment results show joint opening, decreased ultimate shear force, attenuated shear force transfer capacity, or cracked key teeth, the macroscopic shear stiffness of the joint section is a key indicator to accurately assess the impact of these joint defects on the local and overall performance of the segmental beam, including the stiffness, deformation, and strength of the assembled beam. This macroscopic shear stiffness can also characterize the shear force transfer capacity of the joint.

[0127] The vertical displacement test results of the segmental assembled beams were obtained based on the non-contact photoelectric video testing technology. The shear stiffness K of the segmental assembled beam joints was Fν The calculation formula is as follows:

[0128]

[0129] Where K Fν is the shear stiffness of the joint of the segmental assembled beam; Δ1 and Δ2 are the measured results of the vertical displacement of the adjacent segments on both sides of the joint, and the measuring points should be located on both sides of the joint as much as possible.

[0130] By comparing the calculation results of macroscopic shear stiffness under different operating vehicle load conditions and joint service conditions, if the results decay, it means that the shear stiffness at the joint has degraded and the integrity of the structure has decreased. Combined with the above judgment results such as joint opening, shear force transfer effect, and interface friction slip, a comprehensive judgment is made on the shear capacity and shear force transfer capacity of the joint.

[0131] ⑦ Identification of key tooth cracking status based on key tooth stress test results

[0132] For segmental beams in service, key teeth can improve the shear resistance of joints. Under the combined effects of bending moment and shear force, joint key teeth have the potential risk of cracking, especially in the shear control area (1 / 8L-1 / 4L). Key tooth cracking can reduce the shear resistance of local joints, thereby affecting the overall performance of the segmental beam structure. Therefore, in order to timely grasp the shear performance level of key teeth or the overall service status of joints during bridge operation, the joint key tooth stress σ2 is tested or monitored. Based on its changing trend, the key tooth cracking status and causes are analyzed, and the key tooth cracking status judgment criteria are formulated as follows:

[0133] When σ2≤σ cr , indicating that the key teeth are not cracked; where σ2 is the key tooth stress test result; σ cr is the concrete cracking stress.

[0134] When σ2>σ cr , indicating that the key teeth are cracked.

[0135] When the key tooth stress reaches the cracking strength, the service status of the joint is comprehensively judged in combination with the results of joint status judgments ① to ⑤.

[0136] ⑧ Mechanical performance analysis of segmental assembled beams based on joint stress state test results

[0137] To better understand the impact of joint conditions on the mechanical properties of segmented beams and the evolution of these properties, finite element simulation is typically used. Within a refined three-dimensional solid finite element numerical model of a segmented beam, elements reflecting the mechanical properties and service state of the joints are established and assigned a corresponding theoretical constitutive model. Friction element properties, based on joint shear-friction theory, are applied to these joint elements. Therefore, correctly inputting parameters such as the ultimate shear stress and friction coefficient for the joint friction element is crucial for obtaining accurate analysis results.

[0138] First, considering the joint anchoring steel bars and prestressing penetration conditions as well as the prestressing loss during operation, the cross-section normal stress value is calculated according to formula (1); for different service states (initial uncracked state and cracked state), the joint ultimate shear stress and joint interface friction coefficient are obtained according to formulas (3) and (4), respectively. Then, the key parameters of the friction unit properties are input into the model, and the evolution process and change law of the local and overall mechanical properties of the segmented assembled beams under different stress states are analyzed. The finite element numerical simulation results are compared with the field test results to verify the rationality and accuracy of the refined finite element numerical model of the segmented assembled beams. At the same time, the accuracy of the joint service state identification results based on the joint stress test results is verified.

[0139] ⑨Analysis of mechanical properties of segmental assembled beams based on vertical deformation test results

[0140] In addition to using a refined three-dimensional solid finite element numerical model of segmental assembled beams to analyze, evaluate, and predict the performance of such assembled beams, beam unit simulation can also be used. The segmental beam joint mechanical model can introduce spring connection units and assign them corresponding theoretical constitutive models. Among them, accurately assigning tangential stiffness to the connection unit is the key. Therefore, based on the joint shear stiffness analysis results of the segment vertical deformation test results and the calculation results of the segment ultimate shear bearing capacity, the corresponding unit model parameters can be obtained. Then, the key parameters of the determined connection unit properties are input into the model. Among them, the normal stiffness can be determined based on the calculation formula of the ultimate tensile strength of the adhesive joint (Formula 2) and the elastic modulus of the epoxy adhesive; the tangential stiffness can be determined based on the ultimate shear strength formula (5) and the joint shear stiffness formula (6) under a certain state, corresponding to the macroscopic shear stiffness in the initial uncracked and cracked states, respectively. Then, the evolution process and change law of the local and overall mechanical properties of segmental assembled beams under different stress states are analyzed, and the finite element numerical simulation results are compared with the field test results to verify the rationality and accuracy of the finite element numerical model of the segmental assembled beams. At the same time, the accuracy of the joint service status identification results based on the joint deformation test results is verified.

[0141] This invention proposes a joint service performance monitoring and evaluation method based on shear-friction theory for multi-key tooth-glued joints in segmented box girders. It also employs contact and non-contact stress and deformation testing methods, as well as wireless network transmission and cloud platform technologies, to meet both short-term and long-term, static and dynamic data collection requirements. This method overcomes the limitations of current joint damage coring and non-destructive testing methods, such as their limited practical application in actual engineering sites, small number of test samples, high uncertainty in results, and high subjectivity in test results. Furthermore, the test results are not suitable for application in the service status assessment of multi-key tooth-glued joints, due to the short duration of actual bridge load tests, the large difference between the applied load and the actual operating load, and the poor local effect of measured segmental stress and macro-deformation.

[0142] For multi-key tooth-bonded joints in segmental box girders, a joint service performance monitoring and evaluation method based on shear-friction theory is proposed. To meet the needs of joint service status testing and service performance evaluation, a joint service performance monitoring scheme is proposed under the guidance of shear-friction theory, including monitoring indicators, monitoring methods, and monitoring systems. Based on the scale and accuracy requirements of joint service performance monitoring indicators, a combination of contact and non-contact stress and deformation testing methods, as well as wireless network transmission and cloud platform technologies, is adopted to achieve short-term and long-term, static and dynamic data collection capabilities. Based on the test results of joint performance at different scales and combined with typical limit state calculation results, the service status and performance of each joint are judged.

[0143] Different from existing technologies:

[0144] 1) Adopt contact stress testing technology: Surface strain gauges are arranged in the key joint area inside the box. Vibrating wire or resistance type large deformation strain gauges are arranged according to the needs of long-term and short-term joint stress state testing. Different strain measurement points can be staggered according to the site conditions.

[0145] 2) Utilizing non-contact segment vertical deformation testing technology: Focusing on the key joints within the chamber, the vertical displacement of adjacent segments is measured, with testing locations located mid-segment and adjacent to the joints. Depending on the power supply within the chamber, active or passive target lights are configured, and a video image acquisition device is installed at a fixed location on the pier top. The acquisition system features adjustable frequency to accommodate acquisition requirements at varying time periods and durations.

[0146] 3) Wireless network transmission and wired data transmission: In view of the weak network signal inside the box, limited and wireless acquisition systems can be configured to meet short-term and long-term monitoring needs; the remote signal receiving and processing system includes a wireless data transmission module and a computer device;

[0147] 4) Cloud platform technology: Through the remote signal receiving and processing system, the collected data is displayed in real time on the cloud platform data management module, and the time history curves of time-displacement and time-stress can be extracted.

[0148] 5) Adjustable static and dynamic acquisition function: By installing a portable wireless intelligent static and dynamic acquisition system, the measuring points can be connected to the corresponding acquisition system according to the acquisition needs, and the data acquisition frequency can be changed to realize dynamic and static acquisition functions.

[0149] This application provides a joint service performance monitoring and evaluation method based on shear-friction theory. It overcomes the application limitations of current joint damage coring and non-destructive testing methods, such as poor practical application in actual engineering sites, small number of test samples, large uncertainty in results, and strong subjectivity of test results. It also overcomes the shortcomings of short duration of load tests on real bridges, large differences between applied loads and actual operating loads, and poor local effects of measured segmental stress and macro-deformation results. It also solves the problem of inaccurate joint service performance evaluation results and the lack of quantitative evaluation indicators. The method includes the following steps:

[0150] Step 1:

[0151] Develop a monitoring plan for the service condition of key-tooth adhesive joints. Focus on the segmental box girder 1 / 4 span and 1 / 8 span areas, as well as the segmental joints in cracked and defective areas, and determine the joint test indicators, measurement point locations, and test methods.

[0152] Step 2:

[0153] Test instruments, data acquisition and transmission equipment, and data acquisition and observation equipment are selected based on the actual project power supply and environmental conditions. These include strain gauges, wired or wireless dynamic and static acquisition systems, wireless network signal receivers, voltage regulators, active or passive targets, active or passive video image acquisition devices, power supplies, and on-site data acquisition test systems and real-time observation equipment to meet both short-term and long-term monitoring needs.

[0154] Step 3: Arrangement of measurement points for key tooth rubber joint service status.

[0155] According to the test plan, measuring points are defined in the segmental beam joint area, polished, cleaned, and anchored. Appropriate instruments and meters are installed at the measuring points. Instruments and meters should be kept at a certain distance from each other to avoid mutual interference, and wiring at the measuring points should not affect inspections under normal operating conditions. If an external power supply is used, safety protection devices should be installed. The video image acquisition device should be fixed in a location that is not prone to vertical deformation, such as the pier top diaphragm. The stress and deformation of the segmental joints are measured simultaneously at multiple points and reproduced in real time, greatly improving monitoring efficiency.

[0156] Step 4: Debugging the key tooth adhesive joint service status test system

[0157] Conduct on-site testing of instruments, meters, and equipment at each measurement point to ensure their normal and stable operation. The on-site data acquisition test system or software can extract the time-course curve of monitoring indicators and clearly display the location of each measurement point and the operating status of the monitoring device.

[0158] Step 5: Extraction of service condition monitoring data of key-tooth adhesive joints

[0159] Through on-site data collection and storage devices or system platforms, the time history curves of monitoring indicators are extracted, including strain and vertical deformation time history curves, and the data of characteristic time periods and time points can be displayed and output.

[0160] Step 6: Analysis of service status monitoring data of key tooth adhesive joints

[0161] By extracting the results from on-site data collection, the relative and absolute values ​​of stress and deformation at different locations were obtained. Based on the shear-friction theory and the geometric configuration characteristics and loading conditions of the actual segmented box girder, the corresponding theoretical calculation results of adhesive joint shear stress, ultimate shear stress, tensile (compressive) stress, and ultimate shear force were calculated and compared with the measured results.

[0162] Step 7: Determine the service status of the key tooth glue joint

[0163] By comparing the stress and deformation test results with the theoretical calculation results, the shear and tension states of the key tooth gap, the bonding or opening state of the joint, the interface slip state, etc. can be determined.

[0164] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for monitoring and evaluating the service performance of key-tooth adhesive joints of segmental assembled box girders, characterized in that: include: S1. Arrange multiple first stress measuring points, multiple second stress measuring points, multiple third stress measuring points, and adjacent segment vertical displacement measuring points in the 1 / 4 to 1 / 8 beam span area and at joint locations where cracks or defects are present or suspected defects are detected by nondestructive testing. Wherein, for any of the joints, a plurality of first measuring points are arranged along the beam height-span joint and distributed in the tension zone and compression zone of the joint section; a plurality of second measuring points are arranged on the key teeth along the beam height direction and distributed in the tension zone and compression zone of the joint section; a plurality of third measuring points are arranged simultaneously on the key teeth on both sides of the joint along the beam height direction and distributed in the tension zone and compression zone of the joint section, and are staggered with the layout positions of the plurality of second measuring points; S2. Evaluate the service condition of the joint based on the monitoring results of each of the above measuring points and the shear-friction theory; Based on the shear-friction theory, assuming that the width of the multi-joint joint area is ω, the width of the shear surface of a single joint is b, and the height of the shear surface of a single key tooth gap is d, the theoretical calculation formula for the average shear stress is: ν=V / bd (1) s x =pf y +s Nx (2) Where, ν is the shear stress of the joint section; V is the shear force at the joint; σ x is the normal stress at the joint; p is the reinforcement ratio of the steel bars running through the joint; f y is the yield strength of the joint restraining reinforcement; σ Nx is the tensile / compressive stress acting on the joint surface, with tension being positive and compression being negative; According to the shear-friction theory, without considering the initial cracking of the joint, the formula for calculating the ultimate shear stress of the joint is as follows: n u =(φpf y +s Nx )m (3) Where, ν u is the ultimate shear stress of the joint; φ is the bearing capacity reduction coefficient; μ is the friction coefficient of the joint interface; For the tensile force N u Acting on the shear plane A cr , and the joint has initial cracking, the calculation formulas for the ultimate shear stress and ultimate shear bearing capacity of the joint are as follows: n u =(φA s f y / A cr -N u / A cr )m (4) or V u / μ=(φA s f y -N u ) (5) Where V u A is the ultimate shear bearing capacity of the joint; s is the total reinforcement area passing through the shear surface; A cr is the cross-sectional area of ​​the joint; N u is the axial compressive load acting on the joint section; ① Interface shear-slip state determination Formula (1) is used to calculate the joint cross-section shear stress ν. Based on whether the joint has initial cracking, the joint limit shear stress ν calculated by formula (3) or formula (4) is calculated. u For comparison, a binary discrimination method is used to formulate the interface shear-slip discrimination criteria as follows: When ν≤ν u , indicating that no shear-friction slip occurs at the interface; When ν>ν u , indicating that shear-friction slip occurs at the interface; In addition, the ultimate shear bearing capacity V of the joint can be calculated based on the shear force V at the joint and formula (5): u For comparison, a binary discrimination method is used to formulate the interface shear-slip discrimination criteria as follows: When V≤V u , indicating that no shear-friction slip occurs at the interface; When V > V u , indicating that shear-friction slip occurs at the interface; ② Determination of the opening state of the joint interface based on cross-joint stress test results The cross-seam stress test results σ1 measured at multiple first stress measurement points are compared with the normal stress at the joint calculated by formula (2). A binary discrimination method is used to formulate the preliminary discrimination criteria for the open or closed state of the joint as follows: σ1≤σ x , indicating that the seam does not open; σ1>σ x , indicating that the seam has opened; ③ Determination of ultimate shear strength of joints under open joint interface For the specimen with initial cracking, when the reinforcement ratio is high and the shear stress exceeds 5.9 MPa, tanφ=1.0, pf y Less than 0.3f′ c or 10.5 MPa, where f′ c is the design value of the compressive strength of cylindrical concrete; Based on this, when the joint is open, depending on whether the joint has initial cracking, the joint limit shear stress ν calculated by formula (3) or formula (4) is u For comparison, a binary discrimination method is adopted to formulate the following criteria for the discrimination of joint shear strength: When ν≤ν u , indicating that the shear strength of the joint interface meets the requirements, and the open or closed state of the interface does not affect its shear strength; When ν>ν u , indicating that the reduction of interface shear strength causes friction slip at the joint; ④ Determination of joint shear force transmission capacity Formula (1) is used to calculate the joint cross-section shear stress ν. Based on whether the joint has initial cracking, the joint limit shear stress ν calculated by formula (3) or formula (4) is calculated. u Compare the joint shear force V and the joint ultimate shear bearing capacity V calculated by formula (5) u For comparison, a binary discrimination method is adopted to formulate the following criteria for the shear force transfer capacity of joints: When ν≤ν u or V≤V u At the same time, if the deviation of the vertical stress σ3 on both sides of the key tooth gap of adjacent segments measured at each third stress measuring point is less than 5%, it indicates that the shear force transmission capacity of the key tooth joint is strong; ⑤ Determination of joint shear force transfer capacity based on segment vertical displacement test results When the deviation of the vertical stress σ3 on both sides of the key-tooth gap between adjacent segments is greater than 5%, and it is preliminarily determined that there is a local or overall joint opening phenomenon, the vertical displacement of the adjacent segments on both sides of the joint or the vertical displacement of each segment along the bridge span direction is further monitored to obtain and compare the variation patterns of the vertical displacement of the bridge span and the vertical displacement deviation amplitude Δ1-Δ2 of the adjacent segments under different temperatures and operating vehicle loads. If there is a sudden change in the local vertical displacement or the segment vertical displacement test results show an increasing trend, it indicates that the shear force transmission capacity of the joint is reduced and the shear strength of the joint is declining. ⑥ Determination of joint shear stiffness based on segment vertical displacement test results Shear stiffness K of segmental assembled beam joints Fν The calculation formula is as follows: Where Δ1 and Δ2 are the measured results of vertical displacements of adjacent segments on both sides of the joint; According to the shear stiffness K of the bridge joint during operation Fν Time-varying law or bearing capacity variation trend, when the shear stiffness K of the segmental assembled beam joint Fν When there is a decay trend, it indicates that the macro shear stiffness at the joint is degraded, affecting the integrity of the structure; ⑦ Identification of key tooth cracking status based on key tooth stress test results The key tooth stress test results σ2 measured at multiple second stress measurement points are respectively compared with the concrete cracking stress σ cr For comparison, a binary discrimination method is adopted to formulate the following criteria for judging the cracking state of key teeth: When σ2≤σ cr , indicating that the key teeth are not cracked; When σ2>σ cr , indicating that the key teeth are cracked.

2. The method for monitoring and evaluating the service performance of the key-tooth adhesive joints of the segmented assembled box beam according to claim 1, characterized in that: The segment vertical displacement test method is as follows: target lights are placed in the area of ​​1 / 4 to 1 / 8 of the beam span length, as well as in adjacent segments of joints where cracks or defects or suspected defects are found in non-destructive testing. The camera is fixed and the target light image is clearly displayed. Based on the correlation between the pixels of the video image and the displacement, the vertical displacement test results of different segments are obtained.

3. The method for monitoring and evaluating the service performance of the key-tooth adhesive joints of the segmented assembled box beam according to claim 2, characterized in that: The camera is installed on the ground or on the top of the pier.

4. The method for monitoring and evaluating the service performance of the key-tooth adhesive joints of the segmented assembled box beam according to claim 3, characterized in that: The camera is installed on the diaphragm at the top of the pier.

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