Cable replacement construction method for extradosed cable-stayed bridge

Abstract

The invention discloses an extradosed cable-stayed bridge cable replacement construction method, and relates to the technical field of cable-stayed bridge cable replacement construction, and the method comprises the following steps: construction preparation: sequentially carrying out old cable force and cable length measurement, bridge floor elevation measurement, main beam damage maintenance and reinforcement, and construction machinery and materials; construction operation platforms are erected, specifically, the tower top construction operation platform and the beam end construction operation platform are erected correspondingly; installing a temporary cable; the cable force of the old cable is equivalently replaced by adopting a tower top temporary cable, and four-stage loading and unloading are carried out, so that system conversion between the old cable and the temporary cable is realized; installing a new cable; checking and replacing a next cable: measuring cable force, bridge deck elevation and stress according to the actual situation on site after a new cable is installed, checking whether the bridge deck has a crack or crack width change condition or not, and ensuring that the bridge deck meets the design requirement and meets the use function and safety requirements; the temporary inhaul cable is fixed to the tower top, equivalent replacement of tension of all old cables can be achieved at a time, and vertical movement is not needed.

Description

Technical Field

[0001] The invention relates to the technical field of cable-stayed bridge cable replacement construction, and in particular to a cable-stayed bridge cable replacement construction method for a short-tower cable-stayed bridge. Background Art

[0002] A cable-stayed bridge is a complex, statically indeterminate structure composed of three basic elements: cables, beam ends, and towers. It is one of the most complex structures in terms of load bearing capacity. Low-tower cable-stayed bridges are one of the main structural systems of cable-stayed bridges. They are characterized by shorter towers, smaller cable inclination angles, and longer cable-free zones at the beam ends. Because the cables of low-tower cable-stayed bridges bear a smaller proportion of the vertical live load and the beam ends have greater stiffness, they exhibit a load-bearing characteristic where the beam ends are the primary load-bearing element, with the cables providing a secondary load-bearing element.

[0003] Since the cables of early low-tower cable-stayed bridges mostly use parallel steel strands, under normal circumstances, there is no need to close the bridge deck to traffic. Only the steel strands can be replaced one by one to complete the replacement of new cables. However, some old bridge main beams have many structural defects, reduced bearing capacity and serious aging of cable components. In order to ensure the safe and smooth progress of cable replacement construction, the entire bridge needs to be closed to traffic and temporary cables need to be added to replace the old cables.

[0004] In the existing technology, the temporary cable tower ends are often anchored on the main tower or the temporary steel support on the side of the main tower. Every time a pair of cables is replaced, the position of the tower end anchor point needs to be moved, which not only causes certain damage to the main tower structure but also the construction process is complicated and tedious, which brings great safety hazards to the smooth progress of the construction work. Summary of the Invention

[0005] The purpose of the present invention is to provide a cable replacement construction method for a low-tower cable-stayed bridge to solve the following technical problems:

[0006] The temporary cable tower ends are often anchored on the main tower or the temporary steel support on the side of the main tower. Every time a pair of cables is replaced, the position of the tower end anchor point needs to be moved, which not only causes certain damage to the main tower structure but also the construction process is complicated and tedious, which brings great safety hazards to the smooth progress of the construction work.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A cable replacement construction method for a low-tower cable-stayed bridge comprises the following steps:

[0009] Construction preparation: measurement of old cable forces and lengths, bridge deck elevation, repair and reinforcement of main beam defects, and construction machinery and materials;

[0010] Set up construction operation platforms: set up the tower top construction operation platform and the beam end construction operation platform respectively;

[0011] Install temporary cables;

[0012] Removal of old cables: Use temporary hoists on the tower top and use temporary cables to replace the old cables with equivalent cable forces. This is divided into four levels of loading and unloading to achieve system conversion between old cables and temporary cables.

[0013] Install new cables: Release the temporary cable forces in stages according to the system conversion between new cables and temporary cables

[0014] Check and replace the next cable: According to the actual situation on site, after a new cable is installed, measure the cable force, bridge deck elevation, and stress, and check whether there are cracks or changes in crack width on the bridge deck to ensure that it meets the design requirements and meets the functional and safety requirements. If there is no abnormality, continue to replace the next old cable.

[0015] Preferably, the installation of the tower top construction operation platform includes the following steps:

[0016] Use a truck crane to transport the basket assembly materials, equipment and construction workers to the top of the tower;

[0017] The construction workers use chemical bolts or expansion bolts to install the tower embedded pipe steel plate on the tower top;

[0018] After the installation is completed, use a car crane to install the tower top crossbeam and cable saddle on the tower top, install the tower top crossbeam and cable saddle on the tower top, and weld the tower top crossbeam and the tower top embedded steel plate into one;

[0019] A construction operation platform is set up on each tower column, and diagonal braces are set up at the bottom of the construction operation platform to support the load of the platform.

[0020] Preferably, the beam end construction operation platform is a triangular truss movable construction platform, and its installation includes the following steps:

[0021] Spliced steel truss main beam;

[0022] Lay a layer of impact net on the steel truss main beam and fix it with steel wire;

[0023] Lay wood panels on the wire mesh.

[0024] Preferably, the installation of the temporary cable comprises the following steps:

[0025] A hole is opened on the bridge deck at an angle consistent with the inclination of the temporary cable during operation, and a seamless steel pipe is installed in the hole;

[0026] Use a truck crane to extend both ends of the temporary cable to the bridge deck on both sides of the bridge tower;

[0027] Insert the temporary cable into the seamless steel pipe and anchor it to the lower crossbeam set under the tie beam;

[0028] After the anchoring is completed, the temporary cable is pre-tightened by the front card jack;

[0029] After pre-tensioning is completed, the two ends of the temporary cable are tensioned by through-type jacks and the lower beam is slowly lifted until the temporary cable is tensioned to the required cable force, and then the tensioning is stopped and the pressure is maintained.

[0030] Preferably, the old cables are replaced equivalently with temporary cables, and the old cables are tensioned symmetrically and graded on both sides. After each grade of tensioning of the old cables is completed, the temporary cables are tensioned immediately. The cable force applied by the temporary cables must be equivalent to the cable force of the old cables. When the temporary cables completely replace the cable force of the old cables, the steel strands of the old cables are cut and removed one by one.

[0031] Preferably, the old cable and temporary cable system are converted as follows:

[0032] Working condition 1: Tension the temporary cable to 30% of the cable force; release the old cable to 70% of the cable force;

[0033] Working condition 2: Tension the temporary cable to 60% of its force; release the old cable to 40% of its force;

[0034] Working condition 3: Tension the temporary cable to 80% of its force; release the old cable to 20% of its force;

[0035] Working condition 4: Tension the temporary cable to 100% cable force; release the old cable to 0% cable force.

[0036] Preferably, installing the new cable comprises the following steps:

[0037] Insert the steel strands into the HDPE pipe in sequence, insert the front end of the HDPE pipe into the extension pipe and anchor tube at once, install the cable clamps in front of the anchor tube and behind the extension pipe respectively, and use the holes on the cable clamp ear plate to fix the anchor tube and extension pipe with a sling;

[0038] Set the diverting pulley on the tower column and weld and fix the outer casing lifting point;

[0039] Use the lifting machinery to lift the outer sheath into place, connect the clamp to the embedded pipe on the tower column, and use the wire rope to fix it, ensuring that the distance between the HDPE outer sheath and the embedded pipe is 1m, and loosen the shackle on the truck crane;

[0040] By using the traction rope, the steel strand passes through the embedded steering tubes on the two tower columns and then comes out and passes through the embedded tube under the beam at the other end;

[0041] Initially tension the steel strands to 10% of the cable force, anchor them to the anchor pads at the bottom of the beam ends, cut the steel strands and mark them with codes at both ends;

[0042] After all the steel strands are installed, the temporary cable forces are released in stages according to the conversion between the new cable and the temporary cable system. The tension of the temporary cables is equal to the tension of the new cables.

[0043] Preferably, the temporary cable and the new cable system are converted as follows:

[0044] Working condition 1: tension the new cable to 30% of the cable force; release the temporary cable to 70% of the cable force;

[0045] Working condition 2: tension the new cable to 60% of the cable force; release the temporary cable to 40% of the cable force;

[0046] Working condition 3: tension the new cable to 90% of its tension; release the temporary cable to 10% of its tension;

[0047] Working condition 4: Tension the new cable to 105% of the cable force; release the temporary cable to 0% of the cable force.

[0048] Preferably, the tension of a single steel strand is calculated as follows:

[0049] The first tensioning of the cable is achieved by accumulating the force of a single cable to reach the designed first tensioning force of the entire cable bundle. The actual construction operation should follow the following principles:

[0050] First and second strands: To reduce the nonlinear effect of the HDPE outer tube on the tension of a single strand, the first and second strands are used to bear the weight of the HDPE outer tube, so the tension is determined by the sag of the tube.

[0051] The third one: After the average tension of the entire cable bundle is calculated, the deformation of the main beam and the cable tower is corrected to ensure that the cumulative value of the single cable tension after installation is equal to the design value, avoiding large adjustments to the cable tension after a single cable is hung. The cable tension is determined by the following formula:

[0052]

[0053]

[0054] Where: N, cable control force; N 12 , the control force of the first and second steel strands; n, the number of cable holes; δ, the theoretical value of the relative deformation of the anchor point during cable installation, provided by the monitoring unit; l, the cable length; E C \A, elastic modulus of steel strand\cross-sectional area; α, cable design elevation angle;

[0055] The i-th root: T i =T i-1 -Δ i , Δ i , the sensor change value when the i-th root is installed;

[0056] Press T when pulling the first and second strands i =T i-1 -Δ i The control method is determined.

[0057] Beneficial effects of the present invention:

[0058] (1) The present invention places temporary cables at the top of the tower, which can achieve equivalent replacement of the tension of each old cable at one time, avoiding the repeated work of placing temporary cables on the pier body and adjusting the position of the temporary cables on the tower body every time a pair is replaced, thereby simplifying the construction steps and saving operation time; the temporary cables located at the top of the tower are more conducive to the temporary cables providing traction to the main beam; at the same time, the tower top working platform is also convenient for installing the tower external hanging basket, which is convenient for construction personnel to work outside the tower;

[0059] (2) The present invention is based on the equivalent replacement of old cables with temporary cables, and the old cables are tensioned symmetrically and graded on both sides. After each stage of tensioning of the old cables is completed, the temporary cables are tensioned immediately. The cable force applied by the temporary cables must be equivalent to the cable force of the old cables. After the temporary cables completely replace the cable force of the old cables, the old cable strands are cut and removed one by one. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will be further described below with reference to the accompanying drawings.

[0061] Figure 1 This is a structural schematic diagram of step 1 in a cable replacement construction method for a low-tower cable-stayed bridge according to the present invention;

[0062] Figure 2 This is a structural schematic diagram of step three in a cable replacement construction method for a low-tower cable-stayed bridge according to the present invention;

[0063] Figure 3 This is a structural schematic diagram of step 4 in a cable replacement construction method for a low-tower cable-stayed bridge according to the present invention;

[0064] Figure 4 This is a structural schematic diagram of step five in a cable replacement construction method for a low-tower cable-stayed bridge according to the present invention;

[0065] Figure 5 This is a structural schematic diagram of step six in a cable replacement construction method for a low-tower cable-stayed bridge according to the present invention;

[0066] Figure 6 The present invention is a schematic structural diagram of a temporary cable tensioning method for a cable replacement construction method for a low-tower cable-stayed bridge.

[0067] In the figure: 1. Beam end; 2. Tower top construction operation platform; 3. Truck crane; 4. Temporary cable; 101. Bridge deck; 102. Bridge tower; 103. Tower column; 201. Tower top beam; 202. Cable saddle; 203. Hanging basket; 204. Channel steel; 301. Beam end construction operation platform; 302. Lower beam; 303. Winch; 401. Old cable; 402. New cable; 403. Traction cable. DETAILED DESCRIPTION

[0068] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0069] See also Figure 1 As shown, the present invention is a cable replacement construction method for a low-tower cable-stayed bridge, comprising the following steps:

[0070] S100, Construction Preparation: Conduct cable force measurement and cable length measurement of old cable 401, bridge deck 101 elevation measurement, main beam defect repair and reinforcement, and construction machinery and materials;

[0071] S200, setting up construction operation platforms: setting up the tower top construction operation platform 2 and the beam end construction operation platform 301 respectively;

[0072] Specifically, in this embodiment, the installation of the tower top construction operation platform 2 includes the following steps:

[0073] S201, using the mobile crane 3 to transport the hanging basket assembly materials, equipment and construction workers to the top of the tower;

[0074] S202. Construction workers use chemical bolts or expansion bolts to install the tower embedded pipe steel plate on the tower top;

[0075] S203: After the installation is completed, use a mobile crane 3 to install the tower top crossbeam 201 and the cable saddle 202 on the tower top, install the tower top crossbeam 201 and the cable saddle 202 on the tower top, and weld the tower top crossbeam 201 and the tower top embedded steel plate into one;

[0076] S204. A construction platform is set up on each of the tower columns 103 of the two bridge towers 102 at a position 400 mm from the top. A diagonal brace is set up at the bottom of the construction platform to support the load of the platform.

[0077] It should also be noted that the length and width of the construction operation platform are based on the sides of the tower column 103 and extend 1 meter outward on all four sides. The construction operation platform is constructed based on 10# channel steel 204. The spacing between the constructed channel steel 204 is 700mm and arranged in a crisscross shape. The entire construction operation platform is mainly constructed by welding. After the construction is completed, the template and welded guardrail are laid on the construction operation platform. The material of the guardrail is D28*2 seamless pipe, and the height of the guardrail is 1.2m.

[0078] The beam end construction operation platform 301 is a triangular truss movable construction platform, and its installation includes the following steps:

[0079] S205. Splicing the steel truss main beam. In this embodiment, the main beam is made of three Φ48*4 steel pipes. The length of a single segment is 6m. Since the width of the bridge deck 101 is 19.5m, four segments need to be spliced to meet the construction requirements. The total length after assembly is 24m. It should be noted that the single steel truss splicing method adopts internal pipe pinning or welding.

[0080] S206. Lay a layer of impact net on the steel truss main beam and secure it with steel wire;

[0081] S207. Lay another layer of 15mm thick wood board on the wire mesh.

[0082] See also Figure 2 , S300, install temporary cable 4;

[0083] Specifically, in this embodiment, please refer to Figure 6 , installing the temporary cable 4 includes the following steps:

[0084] S301. Drill a hole in the bridge deck 101 at an angle consistent with the inclination of the temporary cable 4 during operation. Install a D95*3 seamless steel pipe in the hole. A water drill is used for drilling the hole. In this embodiment, the temporary cable 4 is a Φ15.2-15 steel strand temporary cable 4.

[0085] S302, using the mobile crane 3 to extend both ends of the temporary cable 4 to the bridge deck 101 on both sides of the bridge tower 102;

[0086] S303, inserting the temporary cable 4 into the seamless steel pipe and anchoring it to the lower crossbeam 302 provided under the tie beam; in addition, the anchoring method is to use clip anchoring;

[0087] S304. After anchoring is completed, the temporary cable 4 is pre-tightened using a 25 or 26 ton front cassette jack;

[0088] S305. After pre-tightening is completed, the two ends of the temporary cable 4 are tensioned by 350-ton through-type jacks and the lower crossbeam 302 is slowly lifted so that the wedge block abuts against the bottom of the tie beam. After the temporary cable 4 is tensioned to the required cable force, the tensioning is stopped and the pressure is maintained.

[0089] See also Figure 3 , S400, remove the old cable 401;

[0090] Specifically, in this embodiment, removing the old cable 401 includes the following steps:

[0091] A temporary hoist is used on the tower top, and the temporary cable 4 is used to equivalently replace the cable force of the old cable 401. The system is divided into four levels of loading and unloading to realize the system conversion between the old cable 401 and the temporary cable 4. The protective cover, shield, waterproof cover and HDPE pipe and other ancillary facilities on the old cable 401 are removed. According to the equivalent replacement of the old cable 401 and the temporary cable 4, the cable force of the old cable 401 is symmetrically released in stages on both sides. After each level of the old cable 401 is released, the temporary cable 4 is immediately tensioned. The cable force applied by the temporary cable 4 must be equivalent to the cable force released by the old cable 401. After the temporary cable 4 completely replaces the cable force of the old cable 401, the steel strands of the old cable 401 are cut and removed one by one.

[0092] Specifically, in this embodiment, the old cable 401 and the temporary cable 4 are converted as follows:

[0093] Working condition 1: Tension the temporary cable by 4 to 30% of its force; release the old cable by 401 to 70% of its force;

[0094] Working condition 2: Tension the temporary cable to 4 to 60% of its force; release the old cable to 401 to 40% of its force;

[0095] Working condition 3: Tension the temporary cable 4 to 80% of its force; release the old cable 401 to 20% of its force;

[0096] Working condition 4: tensioning the temporary cable 4 to 100% of the cable force; releasing the old cable 401 to 0% of the cable force;

[0097] It should be noted that each level of tensioning and each level of release requires monitoring of the cable forces of 3 to 5 adjacent cables and the bridge deck elevation 101. After each working condition is completed, measurement and verification are carried out. Only after confirming that the measurement results are correct can the construction of the next working condition be carried out. While tensioning each level according to the cable force, the elongation of the cable needs to be recorded, and the cable is tensioned to the designed cable force value and anchored.

[0098] See also Figure 4 , S500, install new cable 402;

[0099] Specifically, in this embodiment, installing the new cable 402 includes the following steps:

[0100] S501. Insert the steel strands into the HDPE pipe in sequence. Insert the front end of the HDPE pipe into the extension pipe and anchor tube at once. Install cable hoops in front of the anchor tube and behind the extension pipe respectively. Secure the anchor tube and extension pipe with slings using the holes on the cable hoop lugs.

[0101] S502, set the steering pulley on the tower column 103, and weld and fix the outer casing hanging point;

[0102] S503. Use mechanical equipment such as a truck crane, a tower top hanging basket, and a bridge deck winch 303 to lift the outer sheath into place. Connect the clamp to the embedded pipe on the tower column 103 at the embedded pipe position. Secure it with a wire rope, ensuring that the distance between the HDPE outer sheath and the embedded pipe is 1 meter. Loosen the shackle on the truck crane.

[0103] S504: Using the traction rope 403, the steel strand passes through the pre-buried steering tubes on the two tower columns 103 and then passes through the pre-buried tube under the beam at the other end;

[0104] Specifically, during traction, the steel strands are pulled from the lower hole of the anchor to the upper hole one by one using mechanical equipment such as the truck crane 3, the tower top hanging basket 203 and the winch 303, so that the steel strands pass through the pre-buried steering tubes of the two tower columns 103 and then pass through the pre-buried tube under the beam at the other end.

[0105] S505, initially tensioning the steel strand to 10% of the cable force, anchoring it to the anchor pad at the bottom of beam end 1, cutting the steel strand and marking both ends with a code;

[0106] S506: After all the strands are installed, the new cables 402 and the temporary cables 4 are switched, and the tension of the temporary cables 4 is released in stages, wherein the tension of the temporary cables 4 is equal to the tension of the new cables 402.

[0107] It should be noted that the conversion between the temporary cable 4 and the new cable 402 system is as follows:

[0108] Working condition 1: tension the new cable to 30% of the cable force; release the temporary cable to 70% of the cable force;

[0109] Working condition 2: tension the new cable to 60% of the cable force; release the temporary cable to 40% of the cable force;

[0110] Working condition 3: tension the new cable to 90% of its tension; release the temporary cable to 10% of its tension;

[0111] Working condition 4: tension the new cable to 105% of the cable force; release the temporary cable to 0% of the cable force;

[0112] In addition, in order to ensure that the stress of each steel strand in a single cable meets the design requirements and the cable force uniformity is controlled within 2%, the tensioning process is strictly controlled. The single tensioning force is calculated as follows:

[0113] The first tensioning of the cable is achieved by accumulating the force of a single cable to reach the designed first tensioning force of the entire cable bundle. The actual construction operation should follow the following principles:

[0114] A. First and second strands: To reduce the nonlinear effect of the HDPE outer tube on the tension of a single strand, the first and second strands are used to bear the weight of the HDPE outer tube, so the tension is determined by the sag of the tube.

[0115] B. The third cable: The average cable force of the entire cable bundle is corrected by the deformation of the main beam and the cable tower, so that the cumulative value of the single cable force after installation is equal to the design value, avoiding large adjustments to the cable force after a single cable is installed; the cable force is determined by the following formula:

[0116]

[0117]

[0118] Where: N, cable control force; N 12 , the control force of the first and second steel strands; n, the number of cable holes; δ, the theoretical value of the relative deformation of the anchor point during cable installation, provided by the monitoring unit; l, the cable length; E C \A, elastic modulus of steel strand\cross-sectional area; α, design elevation angle of cable.

[0119] C. Root i: T i =T i-1 -Δ i , Δ i , the sensor change value when the i-th root is installed;

[0120] D. Press T when pulling the first and second strands. i =T i-1 -Δ i The control method is determined.

[0121] It is important to note that the bridge deck elevation 101 must be monitored for each stage of tensioning and release. Measurements must be taken after each working condition is completed, and only after the measurement results are confirmed can the next working condition be constructed. As the cable tension is applied at each stage, the cable elongation must be recorded. The cable is then tensioned to the designed tension value and anchored.

[0122] See also Figure 6 S600, Inspection and Replacement of Next Cable: After installing the new cable 402, based on the actual site conditions, measure the cable tension, bridge deck 101 elevation, and stress. Check the bridge deck 101 for cracks or changes in crack width to ensure it meets design requirements, functional functionality, and safety requirements. If any anomalies are detected, tensioning will be discontinued until the cause is identified and resolved. If no anomalies are detected, replace the old cable with the next one.

[0123] In the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, and a specific direction structure and operation, and therefore, cannot be understood as limiting the present invention. In addition, "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0124] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0125] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A cable replacement construction method for a low-tower cable-stayed bridge, characterized in that: The steps include: Construction preparation: measurement of old cable forces and lengths, bridge deck elevation, repair and reinforcement of main beam defects, and construction machinery and materials; Set up construction operation platforms: set up the tower top construction operation platform and the beam end construction operation platform respectively; Install temporary cables; Removal of old cables: Use temporary hoists on the tower top and use temporary cables to replace the old cables with equivalent cable forces. This is divided into four levels of loading and unloading to achieve system conversion between old cables and temporary cables. Install new cables: Release the temporary cable forces in stages according to the system conversion between new cables and temporary cables Check and replace the next cable: According to the actual situation on site, after a new cable is installed, measure the cable force, bridge deck elevation, and stress, and check whether there are cracks or changes in crack width on the bridge deck to ensure that it meets the design requirements and meets the functional and safety requirements. If there is no abnormality, continue to replace the next old cable.

2. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 1 is characterized in that: The installation of the tower top construction operation platform includes the following steps: Use a truck crane to transport the basket assembly materials, equipment and construction workers to the top of the tower; The construction workers use chemical bolts or expansion bolts to install the tower embedded pipe steel plate on the tower top; After the installation is completed, use a car crane to install the tower top crossbeam and cable saddle on the tower top, install the tower top crossbeam and cable saddle on the tower top, and weld the tower top crossbeam and the tower top embedded steel plate into one; A construction operation platform is set up on each tower column, and diagonal braces are set up at the bottom of the construction operation platform to support the load of the platform.

3. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 2 is characterized in that: The beam end construction operation platform is a triangular truss mobile construction platform, and its installation includes the following steps: Spliced steel truss main beam; Lay a layer of impact net on the steel truss main beam and fix it with steel wire; Lay wood panels on the wire mesh.

4. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 1 is characterized in that: The installation of the temporary cable comprises the following steps: A hole is opened on the bridge deck at an angle consistent with the inclination of the temporary cable during operation, and a seamless steel pipe is installed in the hole; Use a truck crane to extend both ends of the temporary cable to the bridge deck on both sides of the bridge tower; Insert the temporary cable into the seamless steel pipe and anchor it to the lower crossbeam set under the tie beam; After the anchoring is completed, the temporary cable is pre-tightened by the front card jack; After pre-tensioning is completed, the two ends of the temporary cable are tensioned by through-type jacks and the lower beam is slowly lifted until the temporary cable is tensioned to the required cable force, and then the tensioning is stopped and the pressure is maintained.

5. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 4 is characterized in that: The old cables are replaced equivalently with temporary cables, and the old cables are tensioned symmetrically and graded on both sides. After each grade of tensioning of the old cables is completed, the temporary cables are tensioned immediately. The cable force applied by the temporary cables must be equivalent to the cable force of the old cables. When the temporary cables completely replace the cable force of the old cables, the steel strands of the old cables are cut and removed one by one.

6. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 5 is characterized in that: The conversion of the old cable and temporary cable system is as follows: Working condition 1: Tension the temporary cable to 30% of the cable force; release the old cable to 70% of the cable force; Working condition 2: Tension the temporary cable to 60% of the cable force; release the old cable to 40% of the cable force; Working condition 3: Tension the temporary cable to 80% of its force; release the old cable to 20% of its force; Working condition 4: Tensioning the temporary cable to 100% cable force; Release the old cable to 0% tension.

7. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 1 is characterized in that: Installing the new cable includes the following steps: Insert the steel strands into the HDPE pipe in sequence, insert the front end of the HDPE pipe into the extension pipe and anchor tube at once, install the cable clamps in front of the anchor tube and behind the extension pipe respectively, and use the holes on the cable clamp ear plate to fix the anchor tube and extension pipe with a sling; Set the diverting pulley on the tower column and weld and fix the outer casing lifting point; Use the lifting machinery to lift the outer sheath into place, connect the clamp to the embedded pipe on the tower column, and use the wire rope to fix it, ensuring that the distance between the HDPE outer sheath and the embedded pipe is 1m, and loosen the shackle on the truck crane; By using the traction rope, the steel strand passes through the embedded steering tubes on the two tower columns and then comes out and passes through the embedded tube under the beam at the other end; Initially tension the steel strands to 10% of the cable force, anchor them to the anchor pads at the bottom of the beam ends, cut the steel strands and mark them with codes at both ends; After all the steel strands are installed, the temporary cable forces are released in stages according to the conversion between the new cable and the temporary cable system. The tension of the temporary cables is equal to the tension of the new cables.

8. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 7 is characterized in that: The temporary cable and new cable system are converted as follows: Working condition 1: tension the new cable to 30% of the cable force; release the temporary cable to 70% of the cable force; Working condition 2: tension the new cable to 60% of the cable force; Release the temporary cable to 40% of its force; Working condition 3: tension the new cable to 90% of the cable force; Release the temporary cable to 10% of the cable force; Working condition 4: tension the new cable to 105% of the cable force; Release the temporary cable to 0% tension.

9. The cable replacement construction method for a low-tower cable-stayed bridge according to claim 1 is characterized in that: The tensile force of a single steel strand is calculated as follows: The first tensioning of the cable is achieved by accumulating the force of a single cable to reach the designed first tensioning force of the entire cable bundle. The actual construction operation should follow the following principles: First and second strands: To reduce the nonlinear effect of the HDPE outer tube on the tension of a single strand, the first and second strands are used to bear the weight of the HDPE outer tube, so the tension is determined by the sag of the tube. The third one: After the average tension of the entire cable bundle is calculated, the deformation of the main beam and the cable tower is corrected to ensure that the cumulative value of the single cable tension after installation is equal to the design value, avoiding large adjustments to the cable tension after a single cable is hung. The cable tension is determined by the following formula: Where: N, cable control force; N 12 , the control force of the first and second steel strands; n, the number of cable holes; δ, the theoretical value of the relative deformation of the anchor point during cable installation, provided by the monitoring unit; l, the cable length; E C \A, elastic modulus of steel strand\cross-sectional area; α, cable design elevation angle; The i-th root: T i =T i-1 -Δ i , Δ i , the sensor change value when the i-th root is installed; Press T when pulling the first and second strands i =T i-1 -Δ i The control method is determined.

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