A construction method for replacing stay cables of a low-clearance bridge

Abstract

The present invention discloses a construction method for replacing stay cables of a low-clearance bridge, which includes: First, a temporary support structure is set at a weak position on the main bridge deck of the cable-stayed bridge, and it forms an integral body with the main bridge of the bridge to increase the local stiffness of the bridge; Second, a tensile force is applied to the temporary support structure so that the local part of the bridge structure undergoes an upward deformation to offset the downward deformation amount of the bridge after the stay cable is removed; Finally, the stay cable is replaced, and after the replacement is completed, the temporary support structure is removed. By adding a temporary support structure on the main bridge deck, the temporary support structure is connected to the bridge to form a composite beam to increase the local stiffness of the bridge, reduce the deformation of the weak area of the structure during the cable replacement, and ensure the safety of the bridge structure during the stay cable replacement process.

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 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 decline 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, which 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 be ensured to be safe in the case of missing one cable-stayed cable. Some cable-stayed bridges are constructed using the bracket method, and the brackets are removed again after the cable-stayed cables are installed. At the same time, due to the long cable-free zone in some cable-stayed bridges, during the replacement of cable-stayed cables, if there is no support system, the concrete in the cable-free zone 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, proposing a safe, economical, and highly efficient construction method for replacing cable-stayed cables of a low-clearance bridge is currently a difficult problem in cable-stayed cable replacement construction. 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 the high construction difficulty, high cost, and low construction efficiency of the temporary support at the bottom of the beam.

[0005] To solve the above technical problems, the present invention provides a construction method for replacing stay cables of a low-clearance bridge, including: First, a temporary support structure is set at a weak position on the main bridge 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; Second, 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 cable is removed; Finally, the stay cable is replaced, and the temporary support structure is removed after the replacement is completed.

[0006] Preferably, the weak positions on 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 other stay cables.

[0007] Preferably, when the temporary support structure is set in the side span, the main structure of the temporary support structure extends towards 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 positions on the main bridge deck includes: Modeling analysis, establishing a structural model of the bridge according to the structural form of the bridge; Then, perform an analysis of the construction stage of replacing the stay cable, extract the stress and deformation results of the bridge structure to determine the weak positions of the bridge structure under various working conditions of replacing the stay cable, and then determine the layout positions of the temporary support structures; Next, establish a model of the temporary support structure at the weak position, and bring it into the bridge structural model for design analysis, and perform a trial calculation according to the designed 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 the temporary support structure to be set.

[0009] Preferably, the temporary support structure includes multiple cushion beams, a main structure fixedly arranged on the cushion beams, and multiple distribution beams arranged on the main structure. The multiple cushion beams are arranged at intervals and all are arranged on the main bridge deck or part of them are arranged on the main bridge deck while part of them are arranged on the approach road or the approach bridge. The cushion beams extend along the transverse direction of the main bridge; The main structure is a Bailey truss; Multiple distribution beams are arranged at intervals on the main structure and extend along the transverse direction of the main bridge; Multiple reaction beams are arranged at intervals on the bottom surface of the main bridge, which correspond to the multiple distribution beams one by one; 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 passing through the pre-tightening member holes; The pre-tightening members include high-strength deformed steel bars or steel strands.

[0010] Preferably, the setting method of the temporary support structure includes: First, according to the designed structure and position of the temporary support structure, drill several vertically through pre-tightening member holes at the corresponding positions on the bridge deck;

[0011] Secondly, according to the designed positions, lay multiple cushion beams at intervals along the longitudinal direction of the bridge and conduct temporary fixation. The top surfaces of the multiple cushion beams are on the same horizontal plane; fixedly install the main structure of the temporary support structure on the cushion beams; fixedly install multiple distribution beams at intervals along the longitudinal direction of the bridge on the main structure;

[0012] Finally, install multiple reaction beams 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 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.

[0013] 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 inclined 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. 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, which correspond to the multiple distribution beams one by one; several vertically penetrating pre-tightening member holes are arranged on the main bridge. Tension is carried out between the multiple distribution beams and the multiple reaction beams through pre-tightening members passing through the pre-tightening member holes; the pre-tightening members include high-strength rolled thread steel or steel strands; multiple rear anchor cross beams are arranged on the top of the part of the main beam located on the approach road or approach bridge, and it is anchored to the main beam and the approach road or approach bridge through anchor bolts.

[0014] Preferably, apply tensile force to the temporary support structure, use a jack to perform synchronous and symmetric multi-point staged tension on the pre-tightening members. At the same time, record the deformation of the corresponding main structure and bridge structure after each tension stage during the tension process. The tension displacement is the deformation displacement value of the weak position when obtaining the to-be-set temporary support structure; at the same time, monitor that the deformation of the bridge structure is within the design range.

[0015] Preferably, during the process of replacing 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 released 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 tension construction process. The next stage of construction can only be carried out 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.

[0016] The present invention has at least the following beneficial effects:

[0017] 1. The present invention increases the local stiffness of the bridge by adding a temporary support structure on the main bridge deck. The temporary support structure is connected to the bridge to form a composite beam, reducing the deformation of the structurally weak area during the cable replacement period and ensuring the safety of the bridge structure during the stay cable replacement process.

[0018] 2. The present invention adjusts the stiffness of the temporary support structure effectively by increasing the number of components of the temporary support main structure according to the characteristics of the bridge structure and through modeling analysis to meet the on-site usage requirements.

[0019] 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.

[0020] 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.

[0021] 5. The present invention causes local upward deformation of the bridge structure by tensioning the pre-tightening components to offset the downward deformation amount after the stay cables are removed, preventing excessive deformation of the bridge main girder and over-limit tensile stress and cracks, and ensuring the safety of the bridge structure during the stay cable replacement process.

[0022] Other advantages, objectives and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the elevation view of the temporary support structure of the present invention entirely arranged on the main bridge;

[0024] Figure 2 is the plan view of the temporary support structure of the present invention entirely arranged on the main bridge;

[0025] Figure 3 is the side view of the temporary support structure of the present invention entirely arranged on the main bridge;

[0026] Figure 4 is the elevation view of the temporary support structure of the present invention partially arranged on the main bridge;

[0027] Figure 5 is the elevation view of another structural form of the temporary support structure of the present invention partially arranged on the main bridge;

[0028] Figure 6 is the schematic diagram of establishing the bridge structure model of the present invention;

[0029] Figure 7 is the simulation schematic diagram of establishing the bridge structure model of the present invention;

[0030] Figure 8Schematic diagram of the temporary support structure and the bridge structure in the bridge structure model established for the present invention.

[0031] Explanation of reference numerals:

[0032] 1. Main bridge, 2. Temporary support structure, 20. Lateral support, 21. Pad beam, 22. Main body structure, 23. Distribution beam, 24. Reaction beam, 25. Pre-tightening member, 26. Main beam, 27. Column, 28. Cable-stayed beam, 29. Rear anchor 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

[0033] In order to better understand the purpose, structure and function of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0034] It should be noted that the experimental methods described in the following implementation schemes are all 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 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 should not be construed as a limitation to the present invention.

[0035] 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 arranged 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; Second, a tensile force is applied to the temporary support structure so that the local part of the 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.

[0036] The present invention increases the local stiffness of the bridge by adding a temporary support structure to the main bridge deck, which forms a composite beam with the bridge to reduce the deformation of the weak area of the structure during the cable replacement. In addition, by tensioning the pre-tightening member, the local part of the 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, resulting in cracks.

[0037] 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 other stay cables, that is, the temporary support structure is arranged 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 other stay cables.

[0038] 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 road 3 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.

[0039] In some construction cases, when the temporary support structure is extended to the approach bridge or the approach road, since there is an expansion joint between the main bridge and the approach bridge or the approach road, when the stay cables are replaced and constructed, and when the main bridge undergoes load deformation and other conditions, the bridge deck within the range of the approach road or the approach bridge will not be affected. In addition, 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 part of the temporary support structure is arranged on the bridge deck, part of the load can also be transferred to the approach bridge or the approach road through the temporary support structure, thereby improving the construction safety of the main bridge.

[0040] In another technical solution, the method for determining the weak positions of the main bridge deck includes: modeling and analysis, establishing a structural model of the bridge according to the structural form of the bridge; then conducting an analysis of the construction stage of stay cable replacement, extracting the stress and deformation results of the bridge structure to determine the weak positions of the bridge structure under various working conditions of stay cable replacement, and further determining the layout positions of the temporary support structure; 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 arranged.

[0041] 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 bridge structure form to analyze and determine the weak positions of the bridge structure under various conditions of stay cable replacement. Furthermore, the layout positions of the temporary support structures are determined and then brought into the bridge structural model for design analysis. The model of the temporary support structure can first set an initial design structure and then be brought into the bridge structural model for analysis and trial calculation. When the stay cables are replaced, it is checked whether the stresses and strains at the weak positions of the bridge deck can be kept within the allowable range of the design by the temporary support structure. If not, the number of main structural members of the temporary support is increased according to the actual situation, so as to effectively adjust the stiffness of the temporary support structure to meet the on-site use requirements. In addition, during the process of obtaining the form of the temporary support structure, the increase in the load ensures that the concrete tension 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, the deformation and displacement values of the main girder and the temporary support structure are recorded, which are the deformation and displacement values for the subsequent pre-tensioning.

[0042] 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 all are arranged on the main bridge deck (as shown in Figure 1 ), or part of them are arranged on the main bridge deck and part of them are 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, which correspond to the multiple distribution beams one by one; several vertically penetrating pre-tensioning member holes are arranged on the main bridge. The multiple distribution beams and the multiple reaction beams are tensioned by pre-tensioning members 25 passing through the pre-tensioning member holes; the pre-tensioning members include high-strength rolled ribbed steel bars or steel strands. Multiple lateral supports 20 are also arranged on one side of the main structure of the temporary support structure close to the bridge center, 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.

[0043] In another technical solution, the setting method of the temporary support structure includes:

[0044] First, according to the design structure and position of the temporary support structure, several vertically through pre-tensioning member holes are drilled at the corresponding positions on the bridge deck; for the bridge deck drilling, on-site layout and positioning are carried out according to the design scheme, and vertically through pre-tensioning member holes are drilled on the bridge deck; before drilling, it is necessary to determine the layout of the original structural prestressing tendons to prevent cutting the original bridge prestressing tendons during drilling.

[0045] Secondly, according to the designed positions, lay multiple bearing beams at intervals along the longitudinal direction of the bridge and make temporary fixation. The top surfaces of the multiple bearing beams are on the same horizontal plane. Determine the positions of the bearing beams according to the lofting line. The bottom of the bearing beam and the bridge deck should be temporarily fixed to prevent the bearing beam from moving. Before laying the bearing beam, the bottom of the bearing beam needs to be leveled to ensure that the longitudinal and transverse elevations of the bearing beam are the same.

[0046] Fix and install the main structure of the temporary support structure on the bearing beam. Assemble the steel sections / standard Bailey trusses together by welding / pin shafts according to the design drawings to form the main structure 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 bearing beam, multiple temporary shims need to be set in the middle of the main structure.

[0047] 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 steel sections, and the single root length is the same as the width of the main structure. Use U-shaped hoops to fix it to the upper chord of the main structure. The distribution beam reserves holes in the middle of its transverse direction according to the bridge deck drilling positions in the above steps for passing through the pre-tightening members.

[0048] Finally, install multiple reaction beams at the designed positions on the bottom surface of the bridge. They correspond to the multiple distribution beams one by one. The multiple distribution beams and the multiple reaction beams are connected into one body by passing the pre-tightening members through the pre-tightening member holes, thereby connecting the temporary support structure and the main bridge into one body. The reaction beam structure is multi-assembled steel sections, and the single root length is determined according to the design drawing. The pre-tightening members can be precision rolled threaded steel or steel strands. Nuts or clamps are used to fix both ends of the pre-tightening members. 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 members.

[0049] In another technical solution, as Figure 5 shown, the temporary support structure includes a main beam 26 arranged along the longitudinal direction of the bridge, columns 27 vertically arranged on the main beam, and several inclined stay beams 28 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. 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 to the multiple distribution beams one by one. There are several vertically penetrating pre-tightening member holes on the main bridge. The multiple distribution beams and the multiple reaction beams are tensioned by passing the pre-tightening members through the pre-tightening member holes. The pre-tightening members include precision rolled threaded steel or steel strands. Multiple rear anchor cross 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 to the main beam and the approach road or approach bridge by anchor bolts as one body.

[0050] In another technical solution, a tensile force is applied to the temporary support structure, and a jack is used to tension the pre-tightening member synchronously and symmetrically in multiple points and in a graded manner. Meanwhile, 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 obtaining the temporary support structure to be set. At the same time, the deformation of the bridge structure is monitored within the design range. To prevent the single-point tensioning reaction beam / main structure from overturning, symmetric graded tensioning should be carried out to determine a reasonable tensioning sequence. Meanwhile, during the tensioning process, the main structure should be monitored and the structural deflection changes after each tensioning stage should be recorded.

[0051] In another technical solution, during the construction of replacing the stay cables, the displacement of the main girder needs to be monitored 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. Meanwhile, displacement sensors are also set at the beam-end anchor heads of the stay cables in front of and behind the stay cables to be replaced. When removing and installing the stay cables, relaxation is carried out in stages, and the deflection changes of the main girder at each stage are collected in real time during the tensioning construction. The next stage of construction can only be carried out after there is no abnormality in each stage. 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 bars at both ends). They are used to monitor the stress of the temporary support structure. A displacement gauge is set at the mid-span position of the temporary support structure (for the Bailey truss structure, at the lower end in the middle). It is used to monitor the displacement deformation of the temporary support structure.

[0052] Embodiment:

[0053] A construction method for replacing the stay cables of a low-clearance bridge is carried out according to the following steps:

[0054] 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. 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 when the end stay cables are removed because the span of the cable-free area is relatively large.

[0055] 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, such as Figure 6 and Figure 7As shown in the figure, the pylon, main longitudinal beams, secondary longitudinal beams, and cross beams are simulated using beam element 41. Among them, the secondary longitudinal beams and cross beams use concrete materials without specific gravity parameters to only simulate the longitudinal and transverse stiffness of the components, and the structural weight is equivalent through the application of loads. A general support 42 is added at the bottom of the pylon to simulate the interaction with the ground. The main bridge bearings are simulated using a fulcrum elastic support + elastic connection to form a simulated bearing 43. The stay cables are simulated using truss element 44. The beam ends and tower ends of the stay cables are rigidly connected 45 to the main tower and main longitudinal beams for simulation. There are a total of 48 stay cables in this embodiment. The replacement sequence of the stay cables is from the long cables to the short cables, and the two symmetrical stay cables on the upstream and downstream are replaced and constructed. There are a total of 48 working conditions (demolition and installation). The stress / deformation results are extracted by analyzing the structure under each working condition to determine the weak positions of the structure.

[0056] After the weak positions are determined, a temporary support structure model is established near the weak areas 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 Figure 8 shown, the interaction between the temporary support structure and the bridge structure is simulated using an elastic connection 46. Through trial calculation and analysis, the form of the temporary support structure is determined until the stress / deformation of the bridge structure is within the allowable range.

[0057] Step 2: Drill holes through the pre-tightening components on the bridge deck according to the design scheme. In this embodiment, a water drill is used to drill through holes with a diameter of 5 cm on the bridge deck. The drilling depth is about 50 cm. There are 5 holes for each support, 6 holes for each place, a total of 30 holes. The longitudinal spacing of the holes at a single place is 70 cm, and the transverse spacing is 90 cm.

[0058] Step 3: Lay the bearing beams. In this embodiment, double-spliced HN300*150 steel sections are used for the bearing beams, with a total of two places and the length of a single steel section being 3.55 m. During the construction process, the heights of the bearing beams at both ends need to be kept the same, 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.

[0059] Step 4: Assemble the main structure. In this embodiment, standard Bailey trusses with a length of 3 m are used for the main structure, with a total of two layers. Along the longitudinal direction, a total of 8 trusses are set up to form a Bailey beam. Transversely, they are spaced 22.5 cm apart as a group to form a Bailey truss frame. Three Bailey truss frames 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 truss frames are connected together using screws to form the main body 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 sections of the same type. The ends of a single Bailey beam are welded and reinforced using channel 10 steel sections. The Bailey beams are connected into a whole using lattice windows between the Bailey beams.

[0060] Step 5: Installation of the distribution beam. In this embodiment, the distribution beam is made of double-channel 28a steel, with a single steel section being 3.55 m long. Two channel steels are welded together with gusset plates. The spacing of the distribution beam is the same as the width of the drilled holes on the bridge deck. To prevent the distribution beam from sliding, U-shaped hoops should be used to fix the distribution beam to the upper chord of the Bailey beam during installation.

[0061] Step 6: Installation of the reaction beam and pre-tightening components. In this example, the reaction beam uses double-channel 28a steel, with a single length of 1.2 m. The pre-tightening components use PSB930 rolled thread steel with a diameter of 25 mm, and the single length 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.

[0062] Step 7: Tensioning of the pre-tightening components. During the tensioning process, synchronization and symmetry should be maintained. In this embodiment, 4 jacks are used to tension the rolled thread steel components in a graded, synchronous, and symmetric manner. During tensioning, the deformations of the main structure and the bridge structure after each stage of tensioning are recorded.

[0063] Step 8: Removal of the temporary support structure. Remove the support, release the pre-tightening force, and use a crane to remove the temporary support structure. Before removal, use a jack to release the pre-tightening force of the rolled thread steel, and then use a truck crane to lift a single Bailey beam to the bridge deck, knock out the pin shafts, and cycle the construction to remove the temporary support structure.

[0064] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Although the embodiments of the present invention have been disclosed above, they are not limited to only 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 field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated examples described herein.

Claims

1. A construction method for replacing stay cables of a low-clearance bridge, characterized in that, include: First, a temporary support structure is set up at the weak position above 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, a tensile 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 stay cables are removed; finally, the stay cables are replaced, and the temporary support structure is removed after the replacement is completed; 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, an analysis of the construction phase of cable-stayed cable replacement is carried out, and the stress and deformation results of the bridge structure are extracted to determine the weak positions of the bridge structure under various working conditions of cable-stayed cable replacement, and then determine the layout position of the temporary support structure; then, a model of the temporary support structure is established at the weak position, and it is brought into the bridge structure model for design analysis, and trial calculations are carried out according to the design structural form of the temporary support structure until the stress and deformation at the weak position are within the allowable range. The temporary support structure form at this time is the temporary support structure to be set up.

2. The cable replacement construction method for low-clearance cable-stayed bridges according to claim 1, 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 cable replacement construction method for low headroom cable-stayed bridges as described in claim 1, 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 method for replacing the stay cables of a low-clearance bridge according to claim 3, 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.

5. The method for replacing the stay cables of a low-clearance bridge according to claim 4, wherein, 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.

6. The method for replacing stay cables of a low-clearance bridge according to claim 3, characterized in that, The temporary support structure includes a main beam arranged longitudinally along 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. Multiple distribution beams are arranged at intervals on the top of the part of the main beam located on the main bridge, and multiple reaction beams are arranged at intervals on the bottom surface of the main bridge, which correspond to the multiple distribution beams one by one. Several vertically penetrating pre-tensioning member holes are arranged on the main bridge. The multiple distribution beams and the multiple reaction beams are tensioned by pre-tensioning members passing through the pre-tensioning member holes. The pre-tensioning members include high-strength deformed bars or steel strands. Multiple post-anchorage shoulder beams are arranged on the top of the part of the main beam located on the approach road or approach bridge, and it is anchored to the main beam and the approach road or approach bridge as a whole through anchor bolts.

7. The method for replacing the stay cables of a low-clearance bridge according to any one of claims 4 to 6, characterized in that, Apply tensile force to the temporary support structure, use a jack to tension the pre-tensioning members synchronously and symmetrically in multiple points and in stages. 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.

8. The construction method for replacing stay cables of a low-clearance bridge as described in claim 7, characterized in that, During the replacement process of the stay cables, displacement sensors are arranged at the beam-end anchor heads of the stay cables to be replaced. At the same time, displacement sensors are also arranged at the stay cable end anchor heads in front of and behind the stay cables to be replaced. 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 process. 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.

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