Low-clearance bridge stay cable replacement construction method

Abstract

The invention discloses a low-clearance bridge stay cable replacement construction method which comprises the steps that firstly, a temporary supporting structure is arranged at the weak position of a main bridge deck of a cable-stayed bridge, and the temporary supporting structure and a main bridge of the bridge form a whole to increase the local rigidity of the bridge; secondly, tensioning force is applied to the temporary supporting structure, so that the bridge structure locally deforms upwards, and the downward deformation amount of the bridge after the stay cable is removed is offset; and finally, the stay cable is replaced, and the temporary supporting structure is dismantled after replacement is completed. The temporary supporting structure is additionally arranged on the bridge surface of the main bridge, the temporary supporting structure and the bridge are connected together to form a superposed beam, the rigidity of a local area of the bridge is improved, deformation of a weak area of the structure during cable replacement is reduced, and the safety of the bridge structure in the stay cable replacement process is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge maintenance and reinforcement construction (cable-stayed cable replacement). More specifically, the present invention relates to a construction method for replacing cable-stayed cables of a low-clearance bridge. Background Art

[0002] Cable-stayed cables are important load-bearing components in bridges. They can transfer the vertical and horizontal loads on the bridge deck to the cable towers to ensure the overall stability of the bridge. Through the connection with the cable towers, the cable-stayed cables convert the bridge deck loads into tensile forces and support the main structure of the bridge. Over time, cable-stayed cables may gradually experience a decrease in strength, deformation, or cracks due to various factors such as fatigue, corrosion, mechanical damage, and environmental impacts. In severe cases, it may lead to the fracture or failure of the cable-stayed cables. Therefore, to ensure the safe use of the bridge, cable-stayed cables need to be regularly inspected, evaluated, and replaced or repaired in a timely manner when problems are found. Regular maintenance and timely replacement are key measures to ensure the long-term safe operation of the bridge.

[0003] The replacement of cable-stayed cables is often a complex process that needs to consider factors such as the overall stability of the structure, the bearing capacity of the bridge, and the construction environment. During the design of some cable-stayed bridges, considering the replacement of cable-stayed cables during the operation period, the bridge structure can still ensure safety in the case of missing one cable-stayed cable. Some cable-stayed bridges use the bracket method for construction. After the cable-stayed cables are installed, the brackets are removed again. At the same time, due to the long cable-free area of some cable-stayed bridges, during the replacement of cable-stayed cables, if there is no support system, the concrete in the cable-free area has a risk of cracking, which will affect the safety of the bridge structure. Therefore, a support structure must be used to bear the loads originally borne by the cable-stayed cables. For low-clearance cross-river or cross-stream bridges, temporary supports can be set at the bottom of the beam. However, due to limited space, it is difficult to construct pile foundations, and the on-site geological conditions are complex. By constructing steel pipe piles at the bottom of the beam, the construction cost is high and uncontrollable. To ensure the safety and stability of the bridge structure during the replacement of cable-stayed cables, therefore, it is a difficult problem in the current cable-stayed cable replacement construction to propose a safe, economical, and highly efficient construction method for replacing cable-stayed cables of a low-clearance bridge. Summary of the Invention

[0004] An object of the present invention is to provide a construction method for replacing cable-stayed cables of a low-clearance bridge to ensure the safety of the bridge structure during the replacement of cable-stayed cables and solve problems such as difficult construction, high cost, and low construction efficiency of temporary supports at the bottom of the beam.

[0005] In order to solve the above technical problems, the present invention provides a construction method for replacing the cable-stayed cable of a low-clearance bridge, comprising: first, setting a temporary support structure at a weak position of the main bridge deck of the cable-stayed bridge, which is formed as a whole with the main bridge of the bridge to increase the local stiffness of the bridge; second, applying a tensioning force to the temporary support structure so that the bridge structure is partially deformed upward to offset the downward deformation of the bridge after the cable-stayed cable is removed; finally, replacing the cable-stayed cable, and removing the temporary support structure after the replacement is completed.

[0006] Preferably, the weak locations of the main bridge deck include the cable-free area of ​​the side span of the cable-stayed bridge, the tower base and other weak areas that need to be supported during the replacement of the cable-stayed cables.

[0007] Preferably, when the temporary support structure is arranged at the side span, the main structure of the temporary support structure extends toward the approach road or the approach bridge, so that part of the main structure of the temporary support structure is fixed on the approach road or the approach bridge.

[0008] Preferably, the method for determining the weak position of the main bridge deck includes: modeling analysis, establishing a structural model of the bridge according to the structural form of the bridge; then conducting an analysis of the construction phase of cable-stayed cable replacement, extracting the stress and deformation results of the bridge structure to determine the weak position of the bridge structure under various working conditions of cable-stayed cable replacement, and then determining the layout position of the temporary support structure; then establishing a model of the temporary support structure at the weak position, bringing it into the bridge structure model for design analysis, and performing trial calculations based on the design structural form of the temporary support structure until the stress and deformation at the weak position are within the allowable range, and the temporary support structure form at this time is obtained as the temporary support structure to be set up.

[0009] Preferably, the temporary support structure includes a plurality of support beams, a main structure fixedly mounted on the support beams and a plurality of distribution beams mounted on the main structure, the plurality of support beams are spaced apart and all or partly mounted on the main bridge deck, and partly mounted on the approach or bridge approach, the support beams are extended transversely along the main bridge; the main structure is a Bailey frame; a plurality of distribution beams are spaced apart on the main structure and extended transversely along the main bridge; a plurality of reaction beams are spaced apart on the bottom surface of the main bridge, corresponding one to one to the plurality of distribution beams; a plurality of vertically through pre-tensioning member holes are provided on the main bridge, and a plurality of distribution beams and a plurality of reaction beams are tensioned by pre-tensioning members passing through the pre-tensioning member holes; the pre-tensioning members include high-quality rolled threaded steel bars or steel strands.

[0010] Preferably, the temporary support structure is arranged in the following manner: first, according to the design structure and position of the temporary support structure, a plurality of vertical full-length pre-tightening member holes are drilled at corresponding positions on the bridge deck; Secondly, according to the designed positions, a plurality of cushion beams are laid at intervals along the longitudinal direction of the bridge and temporarily fixed. The top surfaces of the plurality of cushion beams are on the same horizontal plane. The main structure of the temporary support structure is fixedly installed on the cushion beams. A plurality of distribution beams are fixedly installed at intervals along the longitudinal direction of the bridge on the main structure. Finally, a plurality of reaction beams are installed at the designed positions on the bottom surface of the bridge. They correspond to the plurality of distribution beams one by one. The plurality of distribution beams and the plurality of reaction beams are connected into one body through pre-tightening members passing through pre-tightening member holes, thereby connecting the temporary support structure and the main bridge into one body.

[0011] Preferably, the temporary support structure includes a main beam arranged along the longitudinal direction of the bridge, columns vertically arranged on the main beam, and several stay beams symmetrically and parallelly arranged between the columns and the main beam. Part of the main beam is arranged on the main bridge and part is arranged on the approach road or approach bridge. A plurality of distribution beams are arranged at intervals on the top of the part of the main beam located on the main bridge. A plurality of reaction beams are arranged at intervals on the bottom surface of the main bridge, corresponding to the plurality of distribution beams one by one. There are several vertically penetrating pre-tightening member holes on the main bridge. The plurality of distribution beams and the plurality of reaction beams are tensioned through pre-tightening members passing through the pre-tightening member holes. The pre-tightening members include rolled threaded steel or steel strands. A plurality of rear anchor cross beams are arranged on the top of the part of the main beam located on the approach road or approach bridge. It is anchored to the main beam and the approach road or approach bridge through anchor bolts as one body.

[0012] Preferably, a tensile force is applied to the temporary support structure. A jack is used to tension the pre-tightening members synchronously and symmetrically in multiple points and in stages. At the same time, during the tensioning process, the deformations of the corresponding main structure and the bridge structure after each tensioning stage are recorded. The tensioning displacement is the deformation displacement value of the weak position when the to-be-set temporary support structure is obtained. At the same time, the deformation of the bridge structure is monitored within the design range.

[0013] Preferably, during the replacement of the stay cables, displacement sensors are arranged at the beam end anchor heads of the replaced stay cables. At the same time, displacement sensors are also arranged at the beam end anchor heads of the stay cables in front of and behind the replaced stay cables. The stay cables are loosened in stages during the removal and installation of the stay cables, and the deflection changes of the main longitudinal beams in each stage are collected in real time during the tensioning construction. The next stage of construction can be carried out only after there is no abnormality in each stage. Strain gauges are arranged vertically on both sides of the temporary support structure to monitor the stress of the temporary support structure. A displacement gauge is arranged at the mid-span position of the temporary support structure to monitor the displacement deformation of the temporary support structure.

[0014] The present invention has at least the following beneficial effects: 1. By adding a temporary support structure on the main bridge deck, the temporary support structure and the bridge are connected together to form a composite beam, which increases the stiffness of the local area of the bridge, reduces the deformation of the weak area of the structure during the cable replacement period, and ensures the safety of the bridge structure during the stay cable replacement process.

[0015] 2. According to the characteristics of the bridge structure, through modeling and analysis, the present invention effectively adjusts the stiffness of the temporary support structure by increasing the number of main structure components of the temporary support to meet the on-site use requirements.

[0016] 3. The present invention sets the temporary support structure on the upper part of the bridge structure, making the construction more convenient, efficient and safer.

[0017] 4. The present invention sets the temporary support structure on the upper part of the bridge structure, reducing the impact on the waterway. The structural form is simple and clear, and the construction cost is controllable and more economical.

[0018] 5. The present invention makes the local part of the bridge structure undergo upward deformation by tensioning the pre-tightening members to offset the downward deformation amount after the stay cables are removed, preventing excessive deformation and over-limit tensile stress of the bridge main girder and cracks from occurring, and ensuring the safety of the bridge structure during the stay cable replacement process.

[0019] Other advantages, objectives and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is an elevation view of the temporary support structure of the present invention all arranged on the main bridge; Figure 2 It is a plan view of the temporary support structure of the present invention all arranged on the main bridge; Figure 3 It is a side view of the temporary support structure of the present invention all arranged on the main bridge; Figure 4 It is an elevation view of the temporary support structure of the present invention partially arranged on the main bridge; Figure 5 It is an elevation view of another structural form of the temporary support structure of the present invention partially arranged on the main bridge; Figure 6 It is a schematic diagram of establishing a bridge structure model of the present invention; Figure 7 It is a schematic simulation diagram of establishing a bridge structure model of the present invention; Figure 8 It is a schematic diagram between the temporary support structure and the bridge structure in the bridge structure model established by the present invention.

[0021] Description of the reference numerals: 1. Main bridge, 2. Temporary support structure, 20. Lateral support, 21. Cushion beam, 22. Main structure, 23. Distribution beam, 24. Reaction beam, 25. Pre-tightening member, 26. Main beam, 27. Column, 28. Cable-stayed beam, 29. Rear anchor cross beam, 3. Approach road, 41. Beam element, 42. General support, 43. Simulated bearing, 44. Truss element, 45. Rigid connection, 46. Elastic connection. Detailed implementation manners

[0022] In order to better understand the purpose, structure and function of the present invention, the following further detailed description of the present invention is made in conjunction with the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0023] It should be noted that, in the following implementation manners, the experimental methods are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified; in the description of the present invention, the terms "transverse", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention.

[0024] As Figures 1 to 5 shown, the present invention provides a construction method for replacing the stay cables of a low-clearance bridge, including: First, a temporary support structure 2 is set at the weak position of the main bridge 1 deck of the cable-stayed bridge, which forms an integral body with the main bridge of the bridge to increase the local stiffness of the bridge; Secondly, a tensile force is applied to the temporary support structure so that the local bridge structure deforms upward to offset the downward deformation amount of the bridge after the stay cables are removed; Finally, the stay cables are replaced, and the temporary support structure is removed after the replacement is completed.

[0025] The present invention increases the local stiffness of the bridge by adding a temporary support structure on the main bridge deck, which forms a composite beam with the bridge to increase the local stiffness of the bridge and reduce the deformation of the weak area of the structure during the cable replacement. In addition, by tensioning the pre-tightening member, the local bridge structure deforms upward to offset the downward deformation amount after the stay cables are removed, preventing excessive deformation of the main beam of the bridge and exceeding the allowable tensile stress and resulting in cracks.

[0026] In another technical solution, the weak positions of the main bridge deck include the cable-free area of the side span of the cable-stayed bridge, the tower root, and other weak areas that need to be supported during the replacement of the stay cables, that is, the temporary support structure is set in the cable-free area of the side span of the cable-stayed bridge, the tower root, and other weak areas that need to be supported during the replacement of the stay cables.

[0027] In another technical solution, when the temporary support structure is arranged in the side span, the main structure of the temporary support structure 2 extends towards the approach 3 or the approach bridge, so that a part of the main structure of the temporary support structure is fixed on the approach or the approach bridge.

[0028] In some construction cases, when the temporary support structure is extended to the approach bridge or the approach, due to the expansion joint between the main bridge and the approach bridge or the approach, when the stay cables are replaced, the bridge deck within the range of the approach bridge or the approach will not be affected when the main bridge undergoes load deformation and other conditions. Additionally, if the temporary support structure is entirely arranged on the bridge deck, after the construction pre-tightening force, the load will also be entirely concentrated on the main bridge deck; if the temporary support structure is partially arranged on the bridge deck, part of the load can also be transmitted to the approach bridge or the approach through the temporary support structure, thereby improving the construction safety of the main bridge.

[0029] In another technical solution, the method for determining the weak positions of the main bridge deck includes: modeling analysis, establishing a structural model of the bridge according to the structural form of the bridge; then conducting an analysis of the stay cable replacement construction stage, extracting the stress and deformation results of the bridge structure to determine the weak positions of the bridge structure under various working conditions of the stay cable replacement, and further determining the layout positions of the temporary support structures; then establishing a model of the temporary support structure, such as a bar system model, at the weak positions, and carrying it into the bridge structural model for design analysis, and conducting trial calculations according to the designed structural form of the temporary support structure until the stress and deformation at the weak positions are within the allowable range, and the obtained form of the temporary support structure at this time is the temporary support structure to be set.

[0030] The structural model includes a grillage model, a solid model, or a finite element analysis model. A model of the bridge is established according to the structural form of the bridge for analysis to determine the weak positions of the bridge structure under various working conditions of the stay cable replacement, and further determine the layout positions of the temporary support structures and carry them into the bridge structural model for design analysis. The model of the temporary support structure can first set an initial designed structure, and then be carried into the bridge structural model for analysis and trial calculations. When the stay cables are replaced, whether the setting of the temporary support structure can ensure that the stress and strain at the weak positions of the bridge deck are within the allowable range of the design. If not, increase the number of members of the main body structure of the temporary support according to the actual situation, so as to effectively adjust the stiffness of the temporary support structure to meet the on-site use requirements. Additionally, during the process of obtaining the form of the temporary support structure, the increase in the load ensures that the concrete tensile force of the main bridge deck will not exceed the limit during the stay cable replacement. According to the load of the temporary support structure at this time, record the deformation displacement values of the main beam and the temporary support structure at this time, which are the deformation displacement values for the subsequent pre-tightening force tensioning.

[0031] In another technical solution, the temporary support structure includes multiple cushion beams 21, a main structure 22 fixedly arranged on the cushion beams, and multiple distribution beams 23 arranged on the main structure. The multiple cushion beams are arranged at intervals and are all arranged on the main bridge deck (as shown in Figure 1 ), or partially arranged on the main bridge deck and partially arranged on the approach road or approach bridge (as shown in Figure 4 ). The cushion beams extend along the transverse direction of the main bridge; the main structure is a Bailey truss; the multiple distribution beams are arranged at intervals on the main structure and extend along the transverse direction of the main bridge; multiple reaction beams 24 are arranged at intervals on the bottom surface of the main bridge, and they correspond to the multiple distribution beams one by one; several vertically penetrating pre-tightening member holes are arranged on the main bridge, and the multiple distribution beams and the multiple reaction beams are tensioned through pre-tightening members 25 inserted into the pre-tightening member holes; the pre-tightening members include high-strength rolled thread steel or steel strands. On one side of the main structure of the temporary support structure close to the bridge center, multiple lateral supports 20 are also arranged, and their two ends are respectively arranged on the bridge deck and the main structure to improve the support firmness of the temporary support structure.

[0032] In another technical solution, the setting method of the temporary support structure includes: First, according to the design structure and position of the temporary support structure, drill several vertically through pre-tightening member holes at the corresponding position on the bridge deck; drill holes on the bridge deck, carry out on-site layout and positioning according to the design scheme, and drill vertically through pre-tightening member holes on the bridge deck; before drilling, it is necessary to determine the layout of the original structure prestressed tendons to prevent cutting the original bridge prestressed tendons during drilling.

[0033] Second, according to the design position, lay multiple cushion beams at intervals along the longitudinal direction of the bridge and carry out temporary fixation. The top surfaces of the multiple cushion beams are on the same horizontal plane; determine the position of the cushion beams according to the layout line, and the bottom of the cushion beams should be temporarily fixed to the bridge deck to prevent the cushion beams from moving. Before laying the cushion beams, the bottom of the cushion beams needs to be leveled to ensure that the longitudinal and transverse elevations of the cushion beams are the same.

[0034] Fix and install the main structure of the temporary support structure on the cushion beams; assemble the profiled steel / standard Bailey sheets together by welding / pin shafts according to the design drawings to form the main body of the temporary support structure. The main structure is assembled in the same direction from one end to the other end. Before the other end of the support main structure is placed on the cushion beam, multiple temporary shims need to be set in the middle of the main structure.

[0035] Fix and install multiple distribution beams at intervals along the longitudinal direction of the bridge on the main structure; the distribution beam structure is multi-assembled profiled steel, and the single root length is the same as the width of the main structure, and it is fixed to the upper chord of the main structure with U-shaped hoops. The distribution beams reserve holes in the middle of their transverse directions according to the bridge deck drilling positions in the above steps for passing through the pre-tightening members.

[0036] Finally, install multiple reaction beams at the designed positions on the bottom surface of the bridge. They correspond one by one to multiple distribution beams. The multiple distribution beams and the multiple reaction beams are connected into an integral body through pre-tightening members passing through the pre-tightening member holes, thereby connecting the temporary support structure and the main bridge into an integral body. The reaction beam structure is multi-piece profiled steel, and the length of a single piece is determined according to the design drawing. The pre-tightening member can be precision rolled threaded steel or steel strand. Nuts or clamps are used to fix both ends of the pre-tightening member. At the same time, to prevent local compression of the distribution beam and the reaction beam, steel plate gaskets should be placed at both ends of the pre-tightening member.

[0037] In another technical solution, as Figure 5 shown, the temporary support structure includes a main beam 26 arranged longitudinally along the bridge, columns 27 vertically arranged on the main beam, and several symmetric and parallel stay beams 28 arranged between the columns and the main beam. Part of the main beam is arranged on the main bridge and part is arranged on the approach road or approach bridge. Multiple distribution beams are arranged at intervals on the top of the part of the main beam located on the main bridge. Multiple reaction beams are arranged at intervals on the bottom surface of the main bridge, corresponding one by one to the multiple distribution beams; several vertically penetrating pre-tightening member holes are arranged on the main bridge. The multiple distribution beams and the multiple reaction beams are tensioned through pre-tightening members inserted into the pre-tightening member holes; the pre-tightening members include precision rolled threaded steel or steel strand; multiple post-anchoring shoulder beams 29 are arranged on the top of the part of the main beam located on the approach road or approach bridge, and they are anchored into an integral body with the main beam and the approach road or approach bridge through anchor bolts.

[0038] In another technical solution, apply tensile force to the temporary support structure. Use a jack to perform multi-point synchronous and symmetric step-by-step tensioning on the pre-tightening members. At the same time, record the deformation of the corresponding main structure and bridge structure after each tensioning stage during the tensioning process. When the tensioning displacement is the deformation displacement value of the weak position when obtaining the temporary support structure to be set; at the same time, monitor that the deformation of the bridge structure is within the design range. To prevent the single-point tensioning reaction beam / main structure from tipping over, symmetric step-by-step tensioning should be carried out to determine a reasonable tensioning sequence. At the same time, the main structure should be monitored during the tensioning process, and the structural deflection change after each tensioning stage should be recorded.

[0039] In another technical solution, during the construction process of replacing the stay cables, it is necessary to monitor the displacement of the main longitudinal girder in real time. During the process of replacing the stay cables, displacement sensors are set at the beam-end anchor heads of the stay cables to be replaced. At the same time, displacement sensors are also set at the stay-cable end anchor heads in front of and behind the stay cables to be replaced. When the stay cables are removed and installed, tension release is carried out in stages, and during the tensioning construction process, the deflection changes of the main longitudinal girder at each stage are collected in real time. Only when there is no abnormality in each stage can the construction of the next stage be carried out. At the same time, it is also necessary to monitor the deformation and stress changes of the temporary support structure itself. Strain gauges are set vertically on both sides of the temporary support structure (for the Bailey truss structure, on the vertical rods at both ends). They are used to monitor the stress of the temporary support structure. A displacement meter is set at the mid-span position of the temporary support structure (for the Bailey truss structure, at the lower end in the middle) to monitor the displacement deformation of the temporary support structure.

[0040] Embodiment: A construction method for replacing stay cables of a low-clearance bridge is carried out according to the following steps: In this example, the bridge structure form is a single-tower straight-column double-cable-plane prestressed slab-girder structure cable-stayed bridge. The long area at its end is a cable-free area, and the temporary support structure is set in a partial area at the end to prevent the main girder concrete from being damaged due to excessive tensile stress in the cable-free area with a large span after the end stay cables are removed.

[0041] Step 1: Modeling and analysis. The bridge in this embodiment is a prestressed slab-girder structure. The beam grillage method is used to establish the bridge structure model. As shown in and, the cable tower, main longitudinal girder, secondary longitudinal girder, and cross beam are simulated using beam element 41. Among them, the secondary longitudinal girder and cross beam use concrete materials without unit weight to only simulate the longitudinal and transverse stiffness of the components, and the structural weight is equivalent by applying loads. General support 42 constraints are added at the bottom of the cable tower to simulate the interaction with the ground. The main bridge bearings are simulated by using a fulcrum elastic support + elastic connection to form a simulated bearing 43. The stay cables are simulated using truss element 44. The rigid connection 45 is used to simulate the connection between the beam ends and tower ends of the stay cables and the main tower and main longitudinal girder. There are a total of 48 stay cables in this embodiment. The replacement order of the stay cables is from long cables to short cables, and the two symmetrical stay cables upstream and downstream are replaced and constructed. There are a total of 48 working conditions (removal, installation). The stress / deformation results of the structure are analyzed and extracted for each working condition to determine the weak positions of the structure. Figure 6 and Figure 7 After the weak positions are determined, a temporary support structure model is established near the weak area on the basis of the original model. The pre-tightening components of the temporary support structure model are simulated using truss elements, and the rest of the components are simulated using beam elements. As shown in, the elastic connection 46 is used to simulate the interaction between the temporary support structure and the bridge structure. Through trial calculation and analysis until the stress / deformation of the bridge structure is within the allowable range, the form of the temporary support structure is determined.

[0042] Figure 8

[0043]

[0043] Step 2: Drill through-holes for pre-tightening components on the bridge deck according to the design plan. In this embodiment, a water drill is used to drill through-holes with a diameter of 5 cm on the bridge deck, and the drilling depth is about 50 cm. There are 30 holes in total, 6 holes at each of the 5 locations for a single support. The longitudinal spacing of the holes at a single location is 70 cm, and the transverse spacing is 90 cm.

[0044] Step 3: Lay the bearing beams. In this embodiment, double-spliced HN300*150 steel sections are used for the bearing beams, and there are two single steel sections with a length of 3.55 m. During the construction process, the heights of the bearing beams at both ends need to be kept consistent, and the top surfaces of the steel sections of the bearing beams are on the same horizontal plane. When the bottom of the bearing beam is relatively high from the bridge deck, a concrete cushion should be poured at the bottom of the bearing beam, and the bottom of the bearing beam is connected to the bridge deck using anchor bolts.

[0045] Step 4: Assemble the main structure. In this embodiment, two layers of standard Bailey sheets with a length of 3 m are used for the main structure. A total of 8 sheets are arranged longitudinally to form a Bailey beam, and a group with a transverse spacing of 22.5 cm forms a Bailey truss. Three Bailey trusses are arranged at a spacing of 45 cm to form the first layer of the temporary support. The second layer has the same form as the first layer, and the upper and lower layers of Bailey trusses are connected together using screws to form the main structure of the temporary support. To enhance the overall stiffness of the Bailey temporary support, the upper and lower chord members of the Bailey beam are strengthened using standard steel members of the same type. The end of a single Bailey beam is welded and reinforced using channel 10 steel, and the single Bailey beams are connected into a whole using lattice windows between the Bailey beams.

[0046] Step 5: Install the distribution beams. In this embodiment, double-spliced channel 28a steel sections are used for the distribution beams, and the length of a single steel section is 3.55 m. The two channel steels are welded together using gusset plates. The spacing of the distribution beams is the same as the width of the drilled holes on the bridge deck. To prevent the distribution beams from sliding, U-shaped clamps should be used to fix the distribution beams to the upper chord members of the Bailey beams during the installation process.

[0047] Step 6: Install the reaction beams and pre-tightening components. In this example, double-spliced channel 28a steel sections are used for the reaction beams, and the length of a single section is 1.2 m. The pre-tightening components use PSB930 precision rolled threaded steel with a diameter of 25 mm, and the length of a single piece is about 7 m. Double nuts are used to fix the upper and lower ends of the threaded steel, and thickened backing plates are used. When installing the threaded steel, it is necessary to ensure verticality to prevent it from contacting the bridge deck.

[0048] Step 7: Tension the pre-tightening components. During the tensioning process, synchronization and symmetry should be maintained. In this embodiment, 4 jacks are used to tension the precision rolled threaded steel components in a graded, synchronous, and symmetric manner. During the tensioning, the deformations of the main structure and the bridge structure after each stage of tensioning are recorded.

[0049] Step 8: Demolish the temporary support structure. Remove the support, release the pre-tightening force, and use a crane to demolish the temporary support structure. Before demolition, use a jack to relieve the pre-tightening force of the precision rolled threaded steel, and then use a truck crane to lift a single Bailey beam to the bridge deck, knock out the pin shafts, and cycle through the construction to demolish the temporary support structure.

[0050] It is understood that the present invention is described by way of some embodiments, and those skilled in the art will know that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated examples herein.

Claims

1. A construction method for replacing a low-clearance bridge cable, characterized in that: include: First, a temporary support structure is set up at the weak position of the main bridge deck of the cable-stayed bridge, which is integrated with the main bridge to increase the local stiffness of the bridge; Secondly, tensioning force is applied to the temporary support structure to cause the bridge structure to partially deform upward, in order to offset the downward deformation of the bridge after the cable-stayed cables are removed; finally, the cable-stayed cables are replaced, and after the replacement is completed, the temporary support structure is removed.

2. The low-clearance bridge cable replacement construction method according to claim 1 is characterized in that: The weak locations of the main bridge deck include the cable-free area of ​​the side span of the cable-stayed bridge, the tower base and other weak areas that need to be supported during the replacement of the cable-stayed cables.

3. The low-clearance bridge cable replacement construction method according to claim 1 is characterized in that: When the temporary support structure is arranged at the side span, the main structure of the temporary support structure extends toward the approach road or the approach bridge, so that part of the main structure of the temporary support structure is fixed on the approach road or the approach bridge.

4. The low-clearance bridge cable replacement construction method according to claim 1 is characterized in that: The method for determining the weak position of the main bridge deck includes: modeling analysis, establishing a structural model of the bridge according to the structural form of the bridge; then conducting an analysis of the construction phase of cable-stayed cable replacement, extracting the stress and deformation results of the bridge structure to determine the weak position of the bridge structure under various working conditions of cable-stayed cable replacement, and then determining the layout position of the temporary support structure; then establishing a model of the temporary support structure at the weak position, bringing it into the bridge structure model for design analysis, and performing trial calculations based on the design structural form of the temporary support structure until the stress and deformation at the weak position are within the allowable range, and the temporary support structure form at this time is obtained as the temporary support structure to be set.

5. The low-clearance bridge cable replacement construction method according to claim 3 is characterized in that: The temporary support structure includes a plurality of support beams, a main structure fixedly arranged on the support beams and a plurality of distribution beams arranged on the main structure. The plurality of support beams are arranged at intervals and are all arranged on the main bridge deck or partially arranged on the main bridge deck, and are partially arranged on the approach or the approach bridge. The support beams are extended transversely along the main bridge; the main structure is a Bailey frame; a plurality of distribution beams are arranged at intervals on the main structure and are extended transversely along the main bridge; a plurality of reaction beams are arranged at intervals on the bottom surface of the main bridge, which correspond to the plurality of distribution beams one by one; a plurality of vertically penetrating pre-tensioning component holes are arranged on the main bridge, and the plurality of distribution beams and the plurality of reaction beams are tensioned by pre-tensioning components passing through the pre-tensioning component holes; the pre-tensioning components include precision-rolled threaded steel bars or steel strands.

6. The low-clearance bridge cable replacement construction method according to claim 5, characterized in that: The temporary support structure setting method includes: first, according to the design structure and position of the temporary support structure, several vertical full-length pre-tightening member holes are drilled at the corresponding positions of the bridge surface; Secondly, according to the design position, multiple support beams are laid at intervals along the longitudinal direction of the bridge and temporarily fixed, and the top surfaces of the multiple support beams are on the same horizontal plane; the main structure of the temporary support structure is fixedly installed on the support beams; and multiple distribution beams are fixedly installed on the main structure along the longitudinal direction of the bridge; Finally, multiple reaction beams are installed at the designed positions on the bottom surface of the bridge, which correspond to the multiple distribution beams one by one. The multiple distribution beams and the multiple reaction beams are connected as a whole through pre-tightening components passing through the pre-tightening component holes, thereby connecting the temporary support structure with the main bridge as a whole.

7. The low-clearance bridge cable replacement construction method according to claim 3, characterized in that: The temporary support structure includes a main beam arranged along the longitudinal direction of the bridge, columns arranged vertically on the main beam and several cable-stayed beams symmetrically and parallelly arranged between the columns and the main beam, wherein the main beam is partially arranged on the main bridge and partially arranged on the approach road or the bridge approach, and a plurality of distribution beams are arranged at intervals on the top of the portion of the main beam located on the main bridge, and a plurality of reaction beams are arranged at intervals on the bottom surface of the main bridge, which correspond to the plurality of distribution beams one by one; a plurality of vertically penetrating prestressing member holes are arranged on the main bridge, and the plurality of distribution beams and the plurality of reaction beams are tensioned by prestressing members passing through the prestressing member holes; the prestressing member includes fine-rolled threaded steel or steel strand; a plurality of rear-anchor shoulder beams are arranged on the top of the portion of the main beam located on the approach road or the bridge approach, and the rear-anchor shoulder beams are anchored as a whole with the main beam and the approach road or the bridge approach through anchor rods.

8. The method for replacing the low-clearance bridge cable according to any one of claims 5 to 7, characterized in that: Apply tensioning force to the temporary support structure, and use jacks to tension the prestressed components synchronously and symmetrically at multiple points. At the same time, the deformation of the corresponding main structure and bridge structure after each tensioning stage is recorded during the tensioning process. The tensioning displacement is the deformation displacement value of the weak position when the temporary support structure to be set up is obtained; at the same time, the deformation of the bridge structure is monitored to be within the design range.

9. The low-clearance bridge cable replacement construction method according to claim 8, characterized in that: During the replacement of the cable-stayed cable, a displacement sensor is installed at the anchor head of the replaced cable beam. At the same time, displacement sensors are also installed at the anchor heads of the replaced cable beam ends. The cable-stayed cable is tensioned in stages during removal and installation, and the deflection changes of the main longitudinal beams in each stage are collected in real time during the tensioning construction. The next stage of construction can be carried out only after there are no abnormalities in each stage. Strain gauges are installed vertically on both sides of the temporary support structure to monitor the stress of the temporary support structure. A displacement meter is installed at the mid-span position of the temporary support structure to monitor the displacement and deformation of the temporary support structure.

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