Construction method for adjusting cable force of bridge sling through reverse jacking of beam bottom

Abstract

The invention discloses a construction method for bridge sling force adjustment through beam bottom reverse jacking, and particularly relates to the technical field of cable bridges, the construction method comprises the following steps of S1, construction preparation, S2, counter-force support installation, and material hoisting, first-layer bridge direction H-shaped steel fixing, second-layer bridge transverse direction H-shaped steel welding and vertical column vertical installation are completed in sequence, and the error is 1t; s3, mounting, debugging and jacking a reverse jacking jack; and S4, mounting and debugging a cable adjusting tool, namely mounting the cable adjusting tool, releasing the cable force in a grading manner, feeding back the cable force to a master control in real time, and carrying out the next cycle after design rechecking. A plurality of sets of jacks are arranged at the safe position of the maximum deflection section structure of the bridge bottom to jack the bridge upwards, midspan downwarping caused by the dead weight of the bridge is reduced, then the stress level of a bridge body, an arch rib and a sling is reduced, and the structural safety in the cable force adjusting process is guaranteed.

Description

Technical Field

[0001] This application relates to the technical field of cable - stayed bridges. More specifically, this application relates to a construction method for adjusting the cable force of bridge suspension cables by jacking from the bottom of the beam. Background Art

[0002] With the development of urban construction towards a livable and green direction, as one of the important urban infrastructure, the construction of urban bridges inevitably undertakes more important landscape requirements. The landscaping of urban bridges faces challenges such as larger spans, more complex shapes, and higher technological standards, which also pose higher requirements for the construction of urban bridges. The force - bearing system of bridges is no longer limited to a single system. In long - span steel - structure bridges, beam - arch composite force - bearing system bridges are increasingly used. During the construction process of beam - arch composite system bridges, multiple stress system conversion processes are often involved. As the force - transfer structure between the beam and the arch, the suspension cables often need to undergo multi - stage cable force adjustment operations to enable the bridge to reach the designed stress state. How to safely and efficiently adjust the cable force of the suspension cables when the cable force is too large is a research topic worthy of study; After retrieval, the existing publication number: CN104947592A discloses a tensioning and cable - force adjustment construction method for the suspension cables of a cable - stayed bridge, including the steps of: installing an intelligent tensioning jack at the tensioning end of each suspension cable of the cable - stayed bridge, and all intelligent tensioning jacks are wired to a computer control platform; through the control of the computer control platform, pre - tighten and overall synchronously and hierarchically tension all the suspension cables at the same time; when the cable force level feedback by the intelligent tensioning jack on the computer control platform reaches 90% - 96% of the stage calculation target value, sequentially perform asynchronous tensioning adjustment on all the suspension cables so that the cable forces of all the suspension cables reach the calculation target value of this stage; after the second - stage construction is completed, perform overall cable - force adjustment on all the suspension cables so that the final cable force reaches the designed target value. It can perform "synchronous" or "asynchronous" tensioning on all the suspension cables of the bridge, simplifies the construction procedures and techniques of the suspension cables, improves the construction quality and reliability, shortens the construction period by more than 70%, and saves the construction cost by more than 30%. The inventor found the following problems in the process of implementing this application: In the construction of cable - stayed bridges, the precise adjustment of the cable force of the suspension cables is the key to ensuring the structural force. Traditional cable - force adjustment methods often perform single - cable adjustment, which is likely to cause sudden changes in adjacent cable forces, resulting in local stress exceeding the standard. At the same time, during the process of jacking from the bottom of the bridge beam, support and fixation can often only be carried out under the conditions of deep foundation treatment or pile foundation construction; Therefore, in view of the above problems, a construction method for adjusting the cable force of bridge suspension cables by jacking from the bottom of the beam is proposed. Summary of the Invention

[0003] To overcome the above defects of the prior art, the present application provides a construction method for adjusting the cable force of bridge suspension cables by using beam bottom reverse jacking to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present application provides the following technical solutions: A construction method for adjusting the cable force of bridge suspension cables by using beam bottom reverse jacking, including the following steps: S1. Construction preparation, conduct cable force measurement and calculation analysis, design and position the reaction support, generate a three-dimensional point cloud model of the bridge bottom through the unmanned aerial vehicle real-scene modeling technology, and cooperate with the BIM model to pre-evaluate the spatial interference between the support and the suspension cable, and optimize the positioning of the reaction support; S2. Installation of the reaction support, completed in sequence: hoist materials → fix the first-layer H-shaped steel along the bridge direction → weld the second-layer H-shaped steel across the bridge direction → vertically install the columns, with an error < 5 cm → connect the channel steel tie beam → shim the jacking plate; S3. Installation, debugging and jacking up of the reverse jack, use 6 sets of 300t jacks to load symmetrically and synchronously, increase 2000kN per stage to the target reverse jacking force, monitor the deformation of the beam body and the change of cable force in real time, verify the accuracy of the calculation model, and insert steel plates to shim and lock the displacement after jacking up; S4. Installation and debugging of the cable adjustment tooling, completed in sequence: install the cable adjustment tooling → release the cable force in stages → feedback the cable force to the total control in real time → enter the next cycle after design review; S5. Tensioning of the suspension cable tooling and cable force adjustment, multi-cable collaborative dynamic force adjustment, implant a PID controller, and automatically calculate the output pressure of the hydraulic station according to the cable force deviation; S6. Unloading of the reverse jack, the unloading is carried out in 5 levels: 100% → 80% → 60% → 40% → 20% → 0, and 2 pieces of 20mm steel shims are synchronously removed at each interval. Use a photogrammetry system to monitor the linear rebound of the beam body, and control the rebound rate ≤ 3 mm / min; S7. Secondary review of the cable force and removal of the support, jointly verify through the vibration frequency method + hydraulic sensor method + total station measurement of the mid-span deflection of the bridge to achieve secondary review of the cable force, and the modular support unit is removed by a magnetic lifting device.

[0005] Preferably, in the step S1, the cable force of the suspension cable is measured by the pressure sensor method and the vibration frequency method, the data is reviewed by combining the cable elongation calculation method, the cable force influence matrix is calculated by the finite element software Midas, the influence of the adjustment of a single suspension cable on the adjacent cable force is analyzed, and it is confirmed that there is a fluctuation of 10% - 40%. According to the ratio of the measured cable force to the designed maximum cable force, determine the number of the suspension cable to be adjusted first and the required reverse jacking force, and arrange the reaction support at the maximum deflection section of the bridge mid-span and the position with the minimum offset.

[0006] Preferably, in step S2, the support is arranged at the intersection of the web and diaphragm of the steel structure bridge, and the bearing capacity of the concentrated load is calculated. A double-layer H-shaped steel foundation is adopted, arranged alternately in the longitudinal direction and transverse direction of the bridge, and cooperated with a Φ800×20mm steel pipe. The column reaction support is the foundation of the existing steel box girder assembly support, with a 20cm C30 concrete + 50cm crushed stone cushion at the bottom. The reaction support is in the form of a double-pinned H-shaped steel foundation + steel pipe columns. The size of the double-pinned H-shaped steel is 650*740mm, and the single root length is 6m. The first layer of double-pinned H-shaped steel is placed in the longitudinal direction of the bridge, and the second layer of double-pinned H-shaped steel is placed in the transverse direction of the bridge. Two double-pinned H-shaped steels are placed under each column. The column is a φ800*20mm steel pipe column with a height of 1.5m. The 10# channel steel is used to connect between the steel pipe columns. Three steel backing plates with a thickness of 20mm and a size of 800*800mm are set at the top of each column. Jacks are placed on the top of the steel backing plates, and a 400*400*20mm steel plate shim is placed above the jacks. The thickness of the shim is determined according to the distance between the jack and the bottom plate of the box girder, the expected jacking stroke, and the expected beam lowering stroke.

[0007] Preferably, in step S1, the cable force influence matrix generated by the finite element software includes a temperature compensation term, and the matrix elements are dynamically corrected according to the following rules: ; is the cable force influence matrix element after temperature correction, is the temperature influence factor, taking 0.002 - 0.005 / ℃, is the temperature of the steel box girder monitored in real time, and the corrected matrix is updated every 2 hours.

[0008] Preferably, in step S2, a prestressed anchoring system is provided at the connection node between the double-pinned H-shaped steel and the steel pipe column, including 4 Φ15.2mm steel strands, symmetrically arranged around the column, a 200t-class tensioning jack, applying a pre-tightening force of 50 - 80kN, and a node stiffness enhancement module, which is cut from a 50mm-thick Q345 steel plate and connected to the H-shaped steel flange through high-strength bolts.

[0009] Preferably, in step S3, the synchronous loading of the reaction jacks adopts a distributed hydraulic control system, including an electro-hydraulic proportional valve, a PLC controller, and a laser displacement sensor. The multi-jack synchronous control is realized through the following formula: ; is the displacement compensation amount of the i-th jack, is the proportional control coefficient, taking 0.8 - 1.2, is the integral control coefficient, taking 0.05 - 0.1, is the target jacking height, is the real-time jacking height of the jack, and the difference in the jacking height of each jack is controlled within ±0.5 mm. When the synchronous error exceeds 1 mm, the deviation correction program is automatically started.

[0010] Preferably, in the step S7, the modular support is removed by a magnetic lifting tool, the working magnetic flux density of its electromagnetic chuck is 1.5 - 2.0 T, and it is equipped with a fall protection device. When it is detected that the sudden change in the weight of the component exceeds 10%, the hydraulic brake system is automatically started.

[0011] Preferably, in the step S4, the cable adjustment operation steps are as follows: measuring the cable force → equipment positioning → starting the beam bottom jacking → super-padding and unloading the jack reaction force → releasing the sling → rechecking the sling force → applying part of the jack reaction force and super-padding → final round of cable adjustment. According to the reaction force position and the reaction force against the top, through model calculation, for every 10,000 kN of reaction force against the top, the linear relationship of the cable force reduction amount can be obtained.

[0012] Preferably, in the step S4, the debugging of the cable adjustment tooling includes the cable clip slip test, and the friction coefficient is verified according to the following formula: ; where 、 are the cable forces on both sides of the cable clip, is the wrap angle radian value, and it is required that the measured ≥0.15, otherwise the anti-slip early warning is automatically triggered.

[0013] The technical effects and advantages of this application: 1. Compared with the prior art, this construction method for adjusting the cable force of bridge suspension cables by jacking against the bottom of the beam arranges multiple sets of jacks at the safe position of the maximum deflection section at the bottom of the beam to jack the bridge upward, reducing the mid-span deflection caused by the self-weight of the bridge, and thus reducing the stress levels of the bridge beam body, arch rib, and suspension cables, ensuring the structural safety during the cable force adjustment process.

[0014] 2. Compared with the prior art, this construction method for adjusting the cable force of bridge suspension cables by jacking against the bottom of the beam jacks against the bottom of the bridge beam, and the reaction jack transfers the force to the foundation through the steel structure reaction support. Without deep foundation treatment or pile foundation construction, stress diffusion is carried out through steel pipe columns + multi-layer I-beam foundations to meet the foundation bearing capacity requirements.

[0015] 3. Compared with the prior art, this construction method for adjusting the cable force of bridge suspension cables by jacking against the bottom of the beam adjusts the cable force simultaneously through multiple sets of cable adjustment tooling, reducing the possibility of structural damage caused by the sudden increase in the cable force of adjacent suspension cables that may be caused by reducing the cable force of a single suspension cable, and at the same time improving the construction efficiency of cable force adjustment of suspension cables. Brief Description of the Drawings

[0016] Figure 1This is a flow chart of the overall construction method of this application; Figure 2 This is a cross-sectional layout diagram of the anti-top support of this application; Figure 3 This is the linear relationship table between reaction force and cable force for this application. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] Example As attached Figures 1 to 3 A construction method for adjusting the cable tension of a bridge by means of a beam bottom anti-top is shown, comprising the following steps: S1, construction preparation, cable tension measurement and calculation analysis, design and positioning of the reaction force bracket, generation of a three-dimensional point cloud model of the bridge bottom by using drone real-scene modeling technology, preview of the spatial interference between the bracket and the cable in conjunction with the BIM model, optimization of the positioning of the reaction force bracket, measurement of the cable tension by using the pressure sensor method and the vibration frequency method, verification of the data by combining the cable elongation calculation method, calculation of the cable tension influence matrix by using the finite element software Midas, analysis of the influence of the adjustment of a single cable on the adjacent cable tension, confirmation of a fluctuation of 10% to 40%, determination of the cable number and the anti-top force requirement to be adjusted first according to the ratio of the measured cable tension to the designed maximum cable tension, arrangement of the reaction force bracket at the maximum deflection section and the minimum offset position in the mid-span of the bridge, the cable tension influence matrix generated by the finite element software contains temperature compensation items, and the matrix elements are dynamically corrected according to the following rules: ; is the cable force influence matrix element after temperature correction, The temperature influence factor is 0.002-0.005 / ℃, The temperature of the steel box girder is monitored in real time. The corrected matrix is updated every 2 hours. The vibration frequency method, error ±3%, hydraulic sensor method, error ±1.5%, and total station deflection monitoring, accuracy 0.1mm triple calibration system are used to achieve a comprehensive error of cable force measurement of ≤2%, which is 60% higher than the traditional single method measurement accuracy. The temperature correction factor is introduced into the cable force influence matrix. , real-time data is collected through temperature sensors embedded in the steel box beams, and matrix parameters are updated every 2 hours to eliminate cable tension deviations caused by temperature changes, reducing the cable tension rebound rate after cable adjustment from the industry average of 12% to less than 3%; S2. Installation of the reaction support is completed in the following order: hoisting materials → fixing the H-shaped steel longitudinally along the bridge on the first floor → welding the H-shaped steel transversely across the bridge on the second floor → vertically installing the columns with an error < 5 cm → connecting the channel steel girders → shimming with jack pads. The support is arranged at the intersection of the web and diaphragm of the steel structure bridge. Calculate the bearing capacity of the concentrated load. A double-layer H-shaped steel foundation is adopted, arranged alternately longitudinally and transversely along the bridge. In cooperation with the Φ800×20mm steel pipe, the column reaction support is the foundation of the existing steel box girder assembly support. The bottom is a 20 cm C30 concrete + 50 cm crushed stone cushion. The reaction support is in the form of a double-pinned H-shaped steel foundation + steel pipe columns. The size of the double-pinned H-shaped steel is 650*740mm, and the single root length is 6m. The double-pinned H-shaped steel on the first floor is placed longitudinally along the bridge, and the double-pinned H-shaped steel on the second floor is placed transversely across the bridge. Two double-pinned H-shaped steels are placed under each column. The column is a φ800*20mm steel pipe column with a height of 1.5m. The steel pipes of each column are connected by 10# channel steel. Three 20mm thick 800*800mm steel pads are set at the top of each column. Jacks are placed on the top of the steel pads, and 400*400*20mm steel plates are placed on top of the jacks for shimming. The shimming thickness is determined according to the distance between the jack and the bottom plate of the box girder, the expected jacking stroke, and the expected beam lowering stroke. A prestressed anchoring system is set at the connection node between the double-pinned H-shaped steel and the steel pipe column, including 4 Φ15.2mm steel strands, symmetrically arranged around the column, a 200t class tensioning jack, applying a pre-tightening force of 50 - 80kN, and a node stiffness improvement module, which is cut from a 50mm thick Q345 steel plate and connected to the flange of the H-shaped steel by high-strength bolts. Among them, through the orthogonal arrangement of the double-layer H-shaped steel, the combined design of 650×740mm double-pinned + Φ800×20mm steel pipe columns increases the foundation bearing capacity from 180kPa of the traditional single-layer structure to 320kPa, expands the stress diffusion angle from 45° to 63°, the foundation settlement ≤ 3mm, and the anti-overturning coefficient of the support is increased from 1.5 to 2.8, meeting the construction requirements in strong wind areas. Through the gradient arrangement of 3 levels of steel pads 20mm thick 800×800mm → jacks → 400×400×20mm shimming steel plates, the contact surface compressive stress is gradually reduced from 85MPa to 32MPa → 18MPa → 9MPa, avoiding local buckling of the bottom plate of the box girder and avoiding phenomena such as excessive foundation settlement, node stress concentration, and asynchronous jacking in the cable adjustment construction of long-span bridges; S3. Installation, commissioning and jacking up of the reaction jacks. 6 sets of 300t jacks are used for symmetric and synchronous loading. Each level is increased by 2000kN to the target reaction jacking force. The deformation of the beam body and the change of cable force are monitored in real time to verify the accuracy of the calculation model. After jacking up, insert the steel plate for shimming and lock the displacement. The synchronous loading of the reaction jacks adopts a distributed hydraulic control system, including an electro-hydraulic proportional valve, a PLC controller and a laser displacement sensor. The multi-jack synchronous control is realized through the following formula: ; is the displacement compensation of the i-th jack, is the proportional control coefficient, taking values from 0.8 to 1.2, is the integral control coefficient, taking values from 0.05 to 0.1, is the target jacking height, is the real-time jacking height of the jacks. The height difference of each jack is controlled within ±0.5mm. When the synchronous error exceeds 1mm, the deviation correction program is automatically started. Among them, by adopting the PID algorithm of the distributed hydraulic system, the synchronous error of 6 jacks is ≤0.5mm, and the accuracy is increased by 5 times compared with the traditional mechanical linkage method, effectively avoiding the torque deformation of the beam body; S4. Install and debug the cable adjustment tooling, and complete it in sequence: install the cable adjustment tooling → release the cable force in stages → feedback the cable force to the total control in real time → enter the next cycle after design review. The cable adjustment operation steps: measure the cable force → position the equipment → start the jacking under the beam → over-pad and unload the jack reaction force → release the sling → review the sling force → apply part of the jack reaction force and over-pad → final round of cable adjustment. According to the reaction force position and the reaction top force, through model calculation, for every 10,000kN of reaction top force, the linear relationship of the cable force reduction can be obtained. The debugging of the cable adjustment tooling includes the slip test of the cable clamp, and verify the friction coefficient according to the following formula: ; where 、 are the cable forces on both sides of the cable clamp, is the value of the included angle in radians, and the actual measurement is required ≥0.15, otherwise the anti-slip warning is automatically triggered. Among them, precise control is achieved through the reaction top force - cable force linear model. The deviation of the cable force reduction corresponding to every 10,000kN of reaction top force is ≤3%. During the cable adjustment process, due to the reduction of the cable force, the reaction top force under the beam increases. Monitor the change of the jacking force of the jack under the beam to keep it at a fixed value to avoid damage to the reaction top jack. Multiple sets of cable adjustment tooling are used to adjust the cable force simultaneously, reducing the possibility of structural damage caused by the sharp increase of the adjacent sling force due to the reduction of the single sling force, and improving the construction efficiency of the sling force adjustment at the same time; S5. Tension the sling tooling and adjust the cable force, and perform multi-cable coordinated dynamic force adjustment. Install the PID controller and automatically calculate the output pressure of the hydraulic station according to the cable force deviation; S6. Unload the reaction top jack. The unloading is carried out in 5 levels: 100% → 80% → 60% → 40% → 20% → 0. At each level interval, 2 pieces of 20mm steel backing plates are synchronously removed. Use the photogrammetry system to monitor the linear rebound of the beam body and control the rebound rate ≤3mm / min; S7. Secondary cable force verification and support removal. Through the combined verification of the vibration frequency method + hydraulic sensor method + total station measurement of mid-span deflection, the secondary cable force verification is realized. The modular support unit is removed by a magnetic sling. The electromagnetic chuck of the magnetic sling has an operating magnetic flux density of 1.5 - 2.0 T and is equipped with a fall protection device. When the sudden change in the weight of the component is monitored to exceed 10%, the hydraulic brake system is automatically activated. Among them, through the cooperation of the magnetic sling and the modular support unit, the support removal efficiency is increased by 300%. At the same time, the fall protection system activates the hydraulic brake within 0.2 seconds when the weight suddenly changes, ensuring construction safety.

[0019] Among them, the design positioning of the reaction force support is determined according to the reaction force required for calculation. It is arranged symmetrically at multiple points to reduce the demand for the bearing capacity of the foundation by the support and the concentrated load on the bridge floor slab. The reaction force support is arranged at the mid-span of the bridge. If the mid-span does not have the conditions for arrangement, it can be appropriately offset towards the large and small mileage directions. The offset distance should ensure that the deflection deformation of the bridge mid-span can reach the best effect during the reverse jacking. The reaction force support should be arranged at the intersection of important stressed components such as the web and diaphragm of the steel structure bridge, and calculate the maximum concentrated load-bearing capacity at this location to ensure that the bridge floor slab is not damaged due to excessive concentrated load of the jack during the reverse jacking and lifting process. The specific installation steps of the reaction force support are as follows: According to the design of the support, after the materials arrive at the site, use a truck crane to lift the materials to under the bridge, and use a forklift for transfer under the bridge. Place two rows of double-row H-shaped steel along the bridge direction according to the support drawing, with a spacing of 60 cm between the H-shaped steel to achieve the best stress diffusion effect. Each piece of H-shaped steel is fixed to the hardened foundation through expansion bolts. The arrangement of the first layer of H-shaped steel should meet the requirement of converting the concentrated load of the jack into a uniform load and transmitting it to the foundation, and the arrangement area should meet the requirement of the bearing capacity of the foundation. After the first layer of H-shaped steel is placed, place the second layer of H-shaped steel. The second layer of H-shaped steel is placed transversely across the bridge, with three groups set, and each group consists of 2 pieces of double-pinned H-shaped steel, which are fixed to the first layer of H-shaped steel by welding. The center line position of each group of H-shaped steel should be consistent with the center position of the column, and the deviation should be <5 cm. Arrange columns on the second layer of H-shaped steel. The specific position of the column is shown in the plan layout drawing. The height of the column is assembled according to actual needs. Column head plates should be provided at both the top and bottom of the column. The bottom column head plate is spot-welded to the second layer of H-shaped steel. The center point of the column should be located at the intersection of the bridge diaphragm and web to ensure that the reverse jacking force is effectively transmitted to the whole bridge without causing damage to the floor slab. The tie beam uses a general channel steel support. According to the clear distance between the columns, the tie beam is cut and welded. The tie beam is arranged in a Z shape. The tie beam can improve the integrity of the reaction force support and prevent the column from becoming unstable. Around the reverse jacking support, an operation platform is built using a disc buckle support, and then a jack is placed on the top of the column. Determine the specific number of shim plates according to the distance between the jack and the beam top. The single stroke of the jack should meet the requirements of the jacking height, and multi-stroke jacking is not recommended. The prestressed anchorage node + double-layer staggered H-shaped steel foundation can increase the bearing capacity of the foundation by 40%. By reconstructing the bridge force system through the mid-span reverse jacking force system, it breaks through the limitations of the traditional single-cable adjustment one by one, realizes the efficient coordinated cable adjustment of the cable group of the long-span beam-arch composite bridge, and at the same time improves the cable adjustment efficiency. Arrange multiple sets of jacks at the safe position of the maximum deflection section at the bottom of the beam to jack the bridge upward, reduce the mid-span deflection caused by the self-weight of the bridge, and then reduce the stress levels of the bridge beam body, arch rib, and cable, ensuring the structural safety during the cable force adjustment process. Jack at the bottom of the bridge beam. The reverse jacking jack conducts the force to the foundation through the steel structure reaction force support. Under the condition of not carrying out deep foundation treatment or pile foundation construction, stress diffusion is carried out through the steel pipe column + multi-layer I-shaped steel foundation to meet the requirement of the bearing capacity of the foundation.

[0020] The working process of this application is as follows: First, vibration accelerometers and fiber Bragg grating sensors are arranged at the mid-span position of the bridge to synchronously collect sling frequency signals and data. The unmanned aerial vehicle flies along the set route of the bridge to generate a three-dimensional point cloud model of the bridge bottom, conducts spatial interference analysis with the BIM model to determine the optimal positioning points of the reaction brackets, installs the reaction brackets, lays the first-layer double-joined H-shaped steel longitudinally along the bridge with a spacing of 800 mm, and connects it to the embedded parts with M24 high-strength bolts. The second-layer H-shaped steel is cross-welded transversely to the bridge, and prestressed steel strands with a diameter of Φ15.2 mm are installed at the joints to increase the joint stiffness by 30%. The verticality of the steel pipe columns is calibrated by a laser theodolite, and the vertical deviation is ≤3 cm. The columns are obliquely connected with 10# channel steel to form a stable triangular truss. The jacks are synchronously lifted. Six 300t jacks are connected to the central controller through hydraulic pipelines. During loading, each stage is loaded with 2000 kN and lasts for 10 minutes, and the settlement data of the displacement gauges are monitored. When the height difference between adjacent jacks > 0.5 mm, the PLC automatically adjusts the opening of the electro-hydraulic proportional valve to compensate for the cumulative error. After lifting in place, a wedge-shaped steel pad is inserted between the jack piston and the beam bottom to achieve displacement self-locking. When adjusting the cables, a multi-cable collaborative algorithm is used. During the unloading process, the photogrammetry system captures the rebound trajectory of the beam body at a frequency of 10 Hz, and the pause mechanism is triggered when the rebound rate exceeds the limit. The cable force is rechecked by combining the vibration frequency method + hydraulic sensor method + total station measurement of the mid-span deflection. During disassembly, the modular support unit is removed by a magnetic lifting device.

Claims

1. A construction method for adjusting the cable force of bridge suspension cables by using inverted beams at the bottom of beams, characterized in that: It includes the following steps: S1. Construction preparation: Conduct cable force measurement and calculation analysis, design and position the reaction support. Generate a 3D point cloud model of the bridge bottom through the UAV real-scene modeling technology, and cooperate with the BIM model to preview the spatial interference between the support and the sling, and optimize the positioning of the reaction support. S2. Installation of the reaction support: Complete in sequence: hoist materials → fix the first-layer H-shaped steel along the bridge direction → weld the second-layer H-shaped steel across the bridge direction → vertically install the columns with an error < 5 cm → connect the channel steel tie beams → shim the jack pads. S3. Installation, debugging and jacking up of the reaction jacks: Use 6 sets of 300t jacks to load symmetrically and synchronously, increase 2000kN per stage to the target reaction jacking force, monitor the beam deformation and cable force change in real time, verify the accuracy of the calculation model, and insert steel plates for shimming and locking the displacement after jacking up. S4. Installation and debugging of the cable adjustment tooling: Complete in sequence: install the cable adjustment tooling → release the cable force in stages → feedback the cable force to the master control in real time → enter the next cycle after design review. S5. Tensioning of the sling tooling and cable force adjustment: Multicable collaborative dynamic force adjustment, implant a PID controller, and automatically calculate the output pressure of the hydraulic station according to the cable force deviation. S6. Unloading of the reaction jacks: The unloading is carried out in 5 levels: 100% → 80% → 60% → 40% → 20% → 0. Remove 2 pieces of 20mm steel pads synchronously at intervals of each level. Use the photogrammetry system to monitor the linear rebound of the beam body, and control the rebound rate ≤ 3mm / min. S7. Secondary cable force review and support removal: Jointly verify through the vibration frequency method + hydraulic sensor method + total station measurement of the mid-span deflection of the bridge to achieve the secondary cable force review. The modular support unit is removed by a magnetic lifting tool.

2. The construction method for adjusting the cable force of bridge suspension cables by using the inverted top at the bottom of the beam according to claim 1, characterized in that: In the step S1, the cable force of the sling is measured by the pressure sensor method and the vibration frequency method, the data is reviewed by combining the cable elongation calculation method, the cable force influence matrix is calculated by the finite element software Midas, the influence of the adjustment of a single cable on the adjacent cable forces is analyzed, and it is confirmed that the fluctuation is within 10% - 40%. According to the ratio of the measured cable force to the design maximum cable force, determine the sling number to be adjusted first and the reaction jacking force requirement, and arrange the reaction support at the maximum deflection section of the bridge mid-span and the position with the minimum offset.

3. The construction method for adjusting the cable force of the bridge sling by using the inverted roof at the bottom of the beam according to claim 1, wherein: In step S2, the bracket is arranged at the intersection of the web and diaphragm of the steel structure bridge, and the bearing capacity of the concentrated load is calculated. A double-layer H-shaped steel foundation is adopted, arranged staggeredly in the longitudinal direction and transverse direction of the bridge, and is matched with a Φ800×20mm steel pipe. The reaction support of the column is the foundation of the existing steel box girder assembly support. The bottom is a 20cm C30 concrete + 50cm crushed stone cushion. The reaction support is in the form of a double-pin H-shaped steel foundation + steel pipe column. The size of the double-pin H-shaped steel is 650*740mm, and the single root length is 6m. The first layer of double-pin H-shaped steel is placed in the longitudinal direction of the bridge, and the second layer of double-pin H-shaped steel is placed in the transverse direction of the bridge. Two double-pin H-shaped steels are placed under each column. The column is a φ800*20mm steel pipe column with a height of 1.5m. The 10# channel steel is used to connect between the steel pipes of each column. Three steel backing plates with a thickness of 20mm and a size of 800*800mm are set at the top of each column. A jack is placed on the top of the steel backing plate, and a 400*400*20mm steel plate is placed on the top of the jack for padding. The padding thickness is determined according to the distance between the jack and the bottom plate of the box girder, the expected jacking stroke, and the expected beam lowering stroke.

4. The construction method for adjusting the cable force of bridge suspension cables by using the inverted top at the bottom of the beam according to claim 2, characterized in that: In the step S1, the cable force influence matrix generated by the finite element software includes a temperature compensation term, and the matrix elements are dynamically corrected according to the following rules: ; is the element of the cable force influence matrix after temperature correction, is the temperature influence factor taking 0.002 - 0.005 / °C, is the temperature of the steel box girder monitored in real time, and the corrected matrix is updated every 2 hours.

5. The construction method for adjusting the cable force of the bridge sling by using the inverted top at the bottom of the beam according to claim 3, characterized in that: In step S2, a prestressed anchorage system is set at the connection node between the double-pin H-shaped steel and the steel pipe column, including 4 Φ15.2mm steel strands, symmetrically arranged around the column, a 200t-level tensioning jack, applying a pre-tightening force of 50-80kN, and a node stiffness enhancement module, which is cut from a 50mm-thick Q345 steel plate and connected to the flange of the H-shaped steel through high-strength bolts.

6. The construction method for adjusting the cable force of bridge suspension cables by using the inverted top under the beam bottom according to claim 1, characterized in that: In the step S3, the synchronous loading of the reverse jack adopts a distributed hydraulic control system, which includes an electro-hydraulic proportional valve, a PLC controller, and a laser displacement sensor. The multi-jack synchronous control is achieved through the following formula: ; is the displacement compensation amount of the i-th jack, is the proportional control coefficient, taking values from 0.8 to 1.2, is the integral control coefficient, taking values from 0.05 to 0.1, is the target jacking height, is the real-time jacking height of the jack. The difference in the jacking height of each jack is controlled within ±0.5 mm. When the synchronous error exceeds 1 mm, the deviation correction program is automatically started.

7. The construction method for adjusting the cable force of the bridge sling by using the inverted top at the bottom of the beam according to claim 1, characterized in that: In step S7, a magnetic lifting tool is used to remove the modular support. The working magnetic flux density of its electromagnetic chuck is 1.5-2.0T, and it is equipped with a fall protection device. When it is monitored that the sudden change in the weight of the component exceeds 10%, the hydraulic brake system is automatically started.

8. The construction method for adjusting the cable force of the bridge sling by using the inverted top at the bottom of the beam according to claim 1, characterized in that: In step S4, the cable adjustment operation steps: measure the cable force → equipment positioning → start of beam bottom jacking → padding and unloading the reaction force of the jack → relaxation of the suspension cable → cable force recheck of the suspension cable → partial reaction force of the jack and padding → final round of cable adjustment. According to the reaction force position and the reaction force against the top, through model calculation, for every 10000kN reaction force against the top, a linear relationship of the cable force reduction amount can be obtained.

9. The construction method for adjusting the cable force of bridge suspension cables by using the inverted top at the bottom of the beam according to claim 8, characterized in that: In the step S4, the debugging of the cable adjustment tooling includes the cable clip slip test, and the friction coefficient is verified according to the following formula: ; Among them and are the cable forces on both sides of the cable clamp, is the wrap angle radian value, and it is required to measure actually ≥ 0.15, otherwise the anti-slip warning will be triggered automatically.

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