Construction method of steel-concrete mixed section of cable-stayed bridge

Abstract

The present invention provides a method for constructing a steel-concrete composite section of a cable-stayed bridge, characterized by comprising the following steps: pre-embedding thick steel plates during the construction of beam section 15 of the middle span for later welding of a rigid frame; simultaneously converting a cantilever bridge-building machine into a bridge crane, moving the bridge crane forward and anchoring it, and entering a state for hoisting a steel box girder in the steel-concrete composite section; moving steel-concrete composite section I into a predetermined position; utilizing the bridge crane's vertical lifting system to lift the steel girder to the designed position; securing beam section 15 and steel-concrete composite section I; pouring concrete for beam section 16-1 of the middle span; and constructing beam sections 16-1ˊ and 16-2ˊ of the side spans; disconnecting the bridge crane from composite composite section I, pouring concrete for beam section 16-2 of the middle span; erecting supports for beam section 18ˊ of the side span cast-in-place section; installing permanent beam end supports; and pouring concrete for the cast-in-place side span sections. The present invention can address the problems of long construction periods and high investment costs in the prior art.

Description

Technical Field

[0001] The present invention mainly relates to the technical field related to building construction, and in particular to a construction method for a steel-concrete mixed section of a cable-stayed bridge. Background Art

[0002] When constructing the steel-concrete composite section of a traditional cable-stayed bridge, conventional method 1 is to set up an assembly platform in the water, use a large floating crane to lift the steel box block segments to the assembly platform, and then carry out welding construction; conventional method 2 uses a special bridge crane for lifting and construction coordination.

[0003] The disadvantages of the conventional method 1 are that the construction period of setting up a platform in the water is long, the construction is difficult, part of the waterway is occupied, the safety risk is high, and a large floating crane is required to cooperate with the operation; the disadvantage of the conventional method 2 is that a special large bridge crane needs to be processed, the processing and assembly period is long, and the cost investment is high. Therefore, this application proposes a new method of using a cantilever bridge-building machine to transform it into a bridge crane to cooperate with the construction to solve the problems existing in the existing technology. Summary of the Invention

[0004] In order to solve the deficiencies of current technology, the present invention combines existing technology and, based on practical application, provides a construction method for the steel-concrete mixed section of a cable-stayed bridge. The advantages of this construction method are: first, the cantilever bridge-building machine used for main beam cantilever casting construction is transformed into a bridge crane, which reduces the processing and on-site assembly time of the bridge crane and reduces the one-time investment cost of the equipment; second, the platform erection process is reduced, saving construction time and reducing the impact on the waterway; third, the investment in large-scale floating crane equipment is avoided, reducing the impact on the waterway and saving construction costs.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for constructing a steel-concrete mixed section of a cable-stayed bridge comprises the following steps:

[0007] S1. During the construction of the No. 15 beam section in the middle span, thick steel plates were embedded to be used for welding the rigid frame later. At the same time, the cantilever bridge-building machine was converted into a bridge crane, which was moved forward and anchored to start the hoisting of the steel box girder in the steel-concrete joint area.

[0008] S2. Move the steel-concrete composite section I into the predetermined position, use the vertical lifting system of the bridge crane to lift the steel beam to the designed position, fix beam section No. 15 and steel-concrete composite section I, pour concrete for the middle span beam section No. 16-1, and construct the side span beam sections No. 16-1ˊ and No. 16-2ˊ;

[0009] S3. Disconnect the bridge crane from the steel-concrete composite section I, pour concrete for the middle span beam section 16-2, erect supports for the side span cast-in-place beam section 18ˊ, install permanent beam end supports, and pour concrete for the side span cast-in-place sections.

[0010] S4. Install temporary locking measures for the closure section, the closure basket, and the side span. Remove the side span baskets and move the bridge crane forward to position the steel-concrete composite section II into the predetermined position. Use the bridge crane's vertical lifting system to lift the steel beam to the installation location.

[0011] S5. Temporarily lock and weld the steel-concrete joint section I and the steel-concrete joint section II, and pour concrete inside the steel grid chamber;

[0012] S6. Move the bridge crane forward to start the cantilever assembly of the steel box girder;

[0013] S7. The bridge crane lifts steel box girders I, II, and III to the designed positions in sequence, temporarily fixes them, and then welds them into a whole, completing the construction of steel boxes I, II, and III.

[0014] S8. Move the bridge crane forward to start construction of the steel box girder closure section;

[0015] S9. The bridge crane lifts the steel box girder IV to the designed position. The steel box girder IV and steel box III are temporarily fixed and welded into a whole. The temporary anchor pier of the main tower and the temporary support on the pier top are removed, and the formal support is converted into a permanent support.

[0016] Furthermore, in step S9, the middle span is closed by the temperature difference closing method, which specifically includes: after the assembly of steel box III is completed, the bridge cranes on both sides move forward, and a water tank counterweight is added to the completed beam section of the closing section, and the displacement of the beam end is measured for 48 hours. According to the measurement results, the closing section is converted into the length when the closing temperature is 20°C, and a second cutting is performed. The closing section is hoisted, and the water in the counterweight water tank is drained at the same time. After hoisting to the designed position, it is matched and connected by tie rods and bolts, and the weld width is adjusted and locked before welding.

[0017] Furthermore, step S1 specifically includes:

[0018] During the construction of S11 and the No. 15 beam section in the middle span, 2cm thick steel plates were embedded in the top surface of the bottom slab concrete and the bottom surface of the top slab concrete respectively, which were used for welding and fixing the rigid skeleton of the steel box girder in the steel-concrete composite section later;

[0019] S12. Convert the cantilever bridge crane into a bridge crane and complete the acceptance work;

[0020] S13. Move the bridge crane forward and anchor it, with the front support at an appropriate distance from the beam end. Do not move the original hanging basket bottom frame, outer formwork, and inner formwork for the time being. Only move the inner and outer sliding beams forward along with the bridge crane.

[0021] S14, completing the hanging and tensioning construction of the corresponding inclined cables;

[0022] S15, complete the iron sand concrete counterweight of the side span 15ˊ beam section;

[0023] S16. Enter the steel-concrete joint area steel box girder hoisting state.

[0024] Further, step S2 specifically includes:

[0025] S21. Transport the steel-concrete joint section I of the steel-concrete joint area to the predetermined position under the bridge by barge;

[0026] S22. Use the bridge crane vertical lifting system to lift the steel beam to the designed position;

[0027] S23, install the rigid frame and fix beam segment 15 and steel-concrete joint segment I;

[0028] S24, the bottom basket system of the bridge-building machine moves forward, connecting the front sling and the rear anchor;

[0029] S25, the outer mold and the inner mold slide into place along the guide beam;

[0030] S26: Tie the steel bars, install the prestressed pipes, install the plug formwork, and then pour the concrete for the middle span beam section 16-1. Simultaneously, construct the side span beam sections 16-1ˊ and 16-2ˊ and maintain the concrete. The side span side beam sections will be cast in place using supports, while the middle span side beam sections will be constructed using a bridge deck crane.

[0031] S27, tensioning and anchoring the corresponding prestressed steel tendons;

[0032] S28. Complete the iron sand concrete counterweight of the side span 16-1ˊ and 16-2ˊ beam sections.

[0033] Further, step S3 specifically includes:

[0034] S31. Release the connection between the bridge crane and the steel-concrete joint section I;

[0035] S32: Tie the steel bars, install the prestressed pipes, install the plug formwork, pour the concrete of the middle span beam section No. 16-2 and maintain it;

[0036] S33, tension and anchor the corresponding longitudinal and vertical prestressed steel tendons;

[0037] S34. Erect the support for the No. 18 beam section of the cast-in-place side span. You may also simultaneously erect the support for the No. 15 beam section, No. 16-1 beam section, No. 16-2 beam section, and No. 18 beam section of the side span.

[0038] S35. Install permanent supports at the beam ends and lock the longitudinal displacement of the beam end supports;

[0039] S36. Pour the cast-in-place concrete of the side span.

[0040] Further, step S4 specifically includes:

[0041] S41. After the cast-in-place concrete of the side span reaches the appropriate strength, install temporary locking measures for the closure section and the closure hanging basket;

[0042] S42, close the side span and release the longitudinal lock of the side support;

[0043] S43. Tension and anchor the longitudinal, transverse and vertical prestressed steel tendons of the side span closure section;

[0044] S44, iron sand concrete counterweights are applied to the side span closure section No. 17ˊ, the side span straight section No. 18ˊ, and the side span No. 13ˊ to No. 14ˊ beam sections;

[0045] S45, remove the side span straight section supports;

[0046] S46, remove the side span hanging basket and move the bridge crane forward a certain distance;

[0047] S47, transport the steel-concrete composite section II to the predetermined position under the bridge by barge;

[0048] S48, dismantle the bottom formwork system of the bridge-building machine;

[0049] S49. Use the bridge crane vertical lifting system to lift the steel beam to the designed position.

[0050] Further, step S5 specifically includes:

[0051] S51. Temporarily lock and weld the steel-concrete joint section II and the steel-concrete joint section I, and release the connection between the sling and the steel beam;

[0052] S52, pouring concrete inside the steel grid chamber and curing;

[0053] S53. Tension and anchor the longitudinal, transverse and vertical prestressed steel strands.

[0054] Further, step S7 specifically includes:

[0055] S71. The beam transport barge is in place, anchored, and adjusted;

[0056] S72. The bridge crane lowers the lifting device to the top of the steel box girder to be lifted;

[0057] S73. The bridge crane lifts the steel box girder I to the designed position;

[0058] S74, steel box girder I and steel box transition section are temporarily fixed and welded into a whole;

[0059] S75, bridge crane moves forward;

[0060] S76. Install and symmetrically tension the corresponding stay cables;

[0061] S76. Repeat the above steps to complete the construction of steel box I, steel box II, and steel box III in sequence.

[0062] Further, step S9 specifically includes:

[0063] S91, beam transport barge is in place, anchored, and adjusted;

[0064] S92. The bridge crane lowers the lifting device to the top of the steel box girder to be lifted;

[0065] S93, the bridge crane lifts the steel box girder IV to the designed position;

[0066] S94, steel box beam IV and steel box beam III on both sides are temporarily fixed and then welded into a whole;

[0067] S95. Except for the temporary anchoring piers of the main tower and the temporary supports on the pier top, the formal supports shall be converted into permanent supports.

[0068] Furthermore, in step S9, during the construction of the closure section, a bridge crane on one side may be used for construction, or two bridge cranes may be used to cooperate to complete the construction of the closure section.

[0069] Beneficial effects of the present invention:

[0070] Transforming the cantilever bridge-building machine used for main beam cantilever casting construction into a bridge crane can reduce the production of some components and shorten the on-site assembly time; using a bridge crane to assist in assembly operations can avoid setting up an assembly platform in the water, reduce construction difficulty, and shorten the time the waterway is occupied; using a bridge crane to assist in lifting operations can avoid the investment in large floating crane equipment, reduce the investment in large equipment, and reduce safety risks; the bridge crane is fixed on the completed beam section to reduce the impact of water during floating crane construction and improve assembly accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a construction flow chart of the present invention;

[0072] Figure 2 This is a schematic diagram of the steel-concrete combined section of the present invention;

[0073] Figure 3 This is a structural schematic diagram corresponding to step S1 of the steel-concrete combined section construction process of the present invention;

[0074] Figure 4 This is a structural schematic diagram corresponding to step S2 of the steel-concrete combined section construction of the present invention;

[0075] Figure 5 This is a structural schematic diagram corresponding to step S3 of the steel-concrete combined section construction process of the present invention;

[0076] Figure 6 This is a structural schematic diagram corresponding to step S4 of the steel-concrete combined section construction process of the present invention;

[0077] Figure 7 This is a structural schematic diagram corresponding to step S5 of the steel-concrete combined section construction process of the present invention;

[0078] Figure 8 This is a structural schematic diagram corresponding to step S6 of the steel-concrete combined section construction process of the present invention;

[0079] Figure 9 This is the structural diagram corresponding to the construction step S7 of the steel-concrete joint section of the present invention. Figure 1 ;

[0080] Figure 10 This is the structural diagram corresponding to the construction step S7 of the steel-concrete joint section of the present invention. Figure 2 ;

[0081] Figure 11 This is the structural diagram corresponding to the construction step S7 of the steel-concrete joint section of the present invention. Figure 3 ;

[0082] Figure 12 This is a structural diagram corresponding to step S8 of the steel-concrete combined section construction process of the present invention;

[0083] Figure 13 This is a structural schematic diagram corresponding to step S9 of the steel-concrete combined section construction process of the present invention;

[0084] Figure 14 This is a front elevation view of the iron sand concrete counterweight arrangement of the present invention;

[0085] Figure 15 It is a side elevation view of the iron sand concrete counterweight arrangement of the present invention. DETAILED DESCRIPTION

[0086] The present invention will be further described with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present application.

[0087] This embodiment provides a construction method for a steel-concrete mixed section of a cable-stayed bridge.

[0088] For the steel-concrete interface, C60 self-compacting, slightly expansive concrete is used. Measures must be taken to ensure dense concrete pouring, and an attached vibrator can be used to assist with vibration. Necessary grouting holes and vents should be reserved at the top and bottom slabs. Grouting pipes should be embedded in the grouting holes and sealed with grouting after construction is complete. After concrete pouring, the feed holes should be sealed with steel plates of equal thickness, using single-sided bevel fillet welds with a 12mm weld diameter.

[0089] The steel-concrete joint section is composed of Figure 2As shown, it mainly includes beam section No. 15, steel-concrete joint area, steel box filling area and steel box transition section from left to right.

[0090] The main construction process of this embodiment is as follows Figure 1 As shown, the construction steps are mainly as follows.

[0091] (1) Construction step 1 of the steel-concrete joint section (e.g. Figure 3 shown).

[0092] ① During the construction of the No. 15 beam section in the middle span, 2 cm thick steel plates were embedded in the top surface of the bottom slab concrete and the bottom surface of the top slab concrete, respectively, for later welding and fixing the rigid skeleton of the steel box girder of the steel-concrete composite section.

[0093] ② Convert the hanging basket (cantilever bridge-building machine) into a bridge crane and complete the acceptance work.

[0094] ③ Move the bridge crane forward and anchor it, with the front support 1.6m away from the beam end. The original hanging basket bottom blue, outer formwork and inner formwork will not be moved for the time being. Only the inner and outer sliding beams will be moved forward with the bridge crane.

[0095] ④ Complete the hanging and tensioning construction of the inclined cables B10, Z10, B10ˊ, and Z10ˊ.

[0096] ⑤ Complete the iron sand concrete counterweight of the side span No. 15 beam section.

[0097] ⑥ Enter the steel-concrete joint area steel box girder hoisting state.

[0098] (2) Construction step 2 of the steel-concrete joint section ( Figure 4 )

[0099] ① Transport the 4.875m steel box section of the steel-concrete joint area (referred to as steel-concrete joint section I, weighing 150t) by barge to the predetermined position under the bridge.

[0100] ② Use the bridge crane vertical lifting system to lift the steel beam to the designed position.

[0101] ③Install the rigid frame to fix beam section No. 15 and steel-concrete combined section I.

[0102] ④The bottom basket system of the bridge-building machine moves forward, connecting the front sling and the rear anchor.

[0103] ⑤ The outer mold and inner mold slide into place along the guide beam.

[0104] ⑥ Tie up the steel bars, install the prestressed pipes, install the plug formwork, and then pour the concrete of the middle span No. 16-1 beam section. At the same time, construct the side span No. 16-1ˊ and No. 16-2ˊ beam sections and maintain them. The side span side beam sections are constructed using cast-in-place supports, and the middle span side beam sections are constructed using a bridge crane.

[0105] ⑦ Tension and anchor the corresponding prestressed steel strands.

[0106] ⑧ Complete the iron sand concrete counterweight of the side span 16-1ˊ and 16-2ˊ beam sections.

[0107] (3) Construction step 3 of the steel-concrete joint section ( Figure 5 )

[0108] ①Remove the connection between the bridge crane and the steel-concrete joint section I.

[0109] ② Tie the steel bars, install the prestressed pipes, install the plug formwork, pour the concrete of the middle span beam section No. 16-2 and maintain it.

[0110] ③Tension and anchor the corresponding longitudinal and vertical prestressed steel strands.

[0111] ④ Erect the support for beam section No. 18ˊ of the cast-in-place section of the side span (the supports for beam sections No. 15ˊ, 16-1ˊ, 16-2ˊ, and 18ˊ of the side span can be erected at the same time).

[0112] ⑤Install permanent supports at the beam ends and lock the longitudinal displacement of the beam end supports.

[0113] ⑥ Pour the cast-in-place concrete of the side span.

[0114] (4) Construction step 4 of the steel-concrete joint section ( Figure 6 )

[0115] ① After the cast-in-place concrete of the side span reaches a certain strength, install temporary locking measures for the closure section and the closure hanging basket.

[0116] ② Close the side spans and release the longitudinal lock of the side supports.

[0117] ③Tension and anchor the longitudinal, transverse and vertical prestressed steel strands of the side span closure section.

[0118] ④ Use iron sand concrete as counterweight for the side span joint section No. 17ˊ, the side span straight section No. 18ˊ, and the side span No. 13ˊ~No. 14ˊ beam sections.

[0119] ⑤Remove the supports of the straight section of the side span.

[0120] ⑥ Remove the side span hanging basket, move the bridge crane forward 0.85m, and the front support is 3.75m away from the end of beam 16-2.

[0121] ⑦ The remaining 7.425m steel box section of the steel-concrete composite section (referred to as steel-concrete composite section II, weighing 280t) is transported to the predetermined position under the bridge by barge.

[0122] ⑧Dismantle the bottom formwork system of the bridge-building machine.

[0123] ⑨ Use the bridge crane vertical lifting system to lift the steel beam to the designed position.

[0124] (5) Construction step 5 of the steel-concrete joint section ( Figure 7 )

[0125] ① Temporarily lock the steel-concrete joint section II and the steel-concrete joint section I and then weld them to release the connection between the sling and the steel beam.

[0126] ② Pour concrete inside the steel grid room and maintain it.

[0127] ③Tension and anchor longitudinal, transverse and vertical prestressed steel strands.

[0128] (6) Construction step 6 of the steel-concrete joint section ( Figure 8 )

[0129] ①The bridge crane moves forward 9.5m, and the front support is 2.25m away from the front end of the steel box transition section.

[0130] ② Complete the hanging and tensioning construction of the inclined cables B11, Z11, B11ˊ, and Z11ˊ.

[0131] ③ Enter the steel box girder cantilever assembly construction.

[0132] After the construction of the steel-concrete joint section is completed, the steel box girder hoisting construction can be carried out.

[0133] (1) Construction step 1 of the standard section of steel box ( Figure 9 )

[0134] ①The beam transport barge is in place, anchored, and adjusted.

[0135] ② The bridge crane lowers the lifting device to the top of the steel box girder to be lifted.

[0136] ③The bridge crane lifts the steel box girder I to the designed position.

[0137] ④ Steel box girder I and the steel box transition section are temporarily fixed and then welded into a whole.

[0138] ⑤The bridge crane moves forward 8.8m.

[0139] ⑥Install and symmetrically tension B12, Z12, B12ˊ, and Z12ˊ cables.

[0140] (2) Construction step 2 of the standard section of steel box ( Figure 10 )

[0141] ①The beam transport barge is in place, anchored, and adjusted.

[0142] ② The bridge crane lowers the lifting device to the top of the steel box girder to be lifted.

[0143] ③The bridge crane lifts the steel box girder II to the designed position.

[0144] ④ Steel box girder II and steel box I are temporarily fixed and welded into a whole.

[0145] ⑤The bridge crane moves forward 10m.

[0146] ⑥Install and symmetrically tension B13, Z13, B13ˊ, and Z13ˊ cables.

[0147] (3) Construction step 3 of the standard section of steel box ( Figure 11 )

[0148] ①The beam transport barge is in place, anchored, and adjusted.

[0149] ② The bridge crane lowers the lifting device to the top of the steel box girder to be lifted.

[0150] ③The bridge crane lifts the steel box girder III to the designed position.

[0151] ④ Steel box girder III and steel box II are temporarily fixed and welded into a whole.

[0152] (3) Construction step 4 of the standard section of steel box ( Figure 12 )

[0153] ①The bridge crane moves forward 10m.

[0154] ② Enter the construction of the steel box girder joint section.

[0155] After the hoisting and welding of the steel box girder III at both ends of the mid-span is completed, construction can begin on the closure section. This section can be completed using either a single deck crane or two cranes working together.

[0156] (1) Construction technology of closure section ( Figure 13 )

[0157] ①The beam transport barge is in place, anchored, and adjusted.

[0158] ② The bridge crane lowers the lifting device to the top of the steel box girder to be lifted.

[0159] ③The bridge crane lifts the steel box girder IV to the designed position.

[0160] ④ Steel box girder IV is temporarily fixed to the steel box III on both sides and then welded into a whole.

[0161] ⑤ Remove the temporary anchoring piers of the main tower and the temporary supports on the pier top, and convert the formal supports into permanent supports.

[0162] (2) Guarantee measures for the construction of the closure section

[0163] ①Temperature control of jointing

[0164] The mid-span closure was achieved using the temperature differential closure method. The main method involved: After the steel box III was assembled, the bridge cranes on both sides were moved forward 10 meters. Water tank counterweights were added to the completed beam section of the closure, and the beam end displacement was measured over a 48-hour period. Based on the measurement results, the closure section was converted to its length at a closure temperature of 20°C. A second cut was then made, and the closure section was hoisted while the counterweight water tank was drained. After hoisting to the designed position, it was connected using tie rods and bolts. The weld width was adjusted, locked, and then welded.

[0165] ②Iron sand concrete counterweight

[0166] In order to offset the unbalanced bending moment when the middle span steel box is connected, iron sand concrete counterweights are poured inside the side span box chamber.

[0167] After the construction of beam section 15 is completed, cast iron sand concrete in the A1 and A2 areas of its box chamber. After the prestressed tendons of beam sections 16-1 and 16-2 are tensioned, cast iron sand concrete in area B of its box chamber. Partially reserve space for tensioning the bottom plate tendons of the side span. After the bottom plate tendons of the side span are tensioned, cast the reserved space. After the tensioning of the side span joint tendons is completed, cast iron sand concrete in area C of the box chamber of beam sections 13 and 14, the side span joint section 17, and the side span cast-in-place section 18. The layout of the iron sand concrete pouring area is as follows: Figure 14 、 Figure 15 shown.

Claims

1. A method for constructing a steel-concrete mixed section of a cable-stayed bridge, characterized in that: The steps include: S1. During the construction of the No. 15 beam section in the middle span, thick steel plates were embedded to be used for welding the rigid frame later. At the same time, the cantilever bridge-building machine was converted into a bridge crane, which was moved forward and anchored to start the hoisting of the steel box girder in the steel-concrete joint area. S2. Move the steel-concrete composite section I into the predetermined position, use the vertical lifting system of the bridge crane to lift the steel beam to the designed position, fix beam section No. 15 and steel-concrete composite section I, pour concrete for the middle span beam section No. 16-1, and construct the side span beam sections No. 16-1ˊ and No. 16-2ˊ; S3. Disconnect the bridge crane from the steel-concrete composite section I, pour concrete for the middle span beam section 16-2, erect supports for the side span cast-in-place beam section 18ˊ, install permanent beam end supports, and pour concrete for the side span cast-in-place sections. S4. Install temporary locking measures for the closure section, the closure basket, and the side span. Remove the side span baskets and move the bridge crane forward to position the steel-concrete composite section II into the predetermined position. Use the bridge crane's vertical lifting system to lift the steel beam to the installation location. S5. Temporarily lock and weld the steel-concrete joint section I and the steel-concrete joint section II, and pour concrete inside the steel grid chamber; S6. Move the bridge crane forward to start the cantilever assembly of the steel box girder; S7. The bridge crane lifts steel box girders I, II, and III to the designed positions in sequence, temporarily fixes them, and then welds them into a whole, completing the construction of steel boxes I, II, and III. S8. Move the bridge deck crane forward to start construction at the steel box girder closure section; S9. The bridge crane lifts the steel box girder IV to the designed position. The steel box girder IV and steel box III are temporarily fixed and welded into a whole. The temporary anchor pier of the main tower and the temporary support on the pier top are removed, and the formal support is converted into a permanent support.

2. The method for constructing a cable-stayed bridge steel-concrete mixed section according to claim 1, wherein: In step S9, the middle span is closed by the temperature difference closing method, which specifically includes: after the assembly of steel box III is completed, the bridge cranes on both sides are moved forward, and a water tank counterweight is added to the completed beam section of the closing section, and the displacement of the beam end is measured for 48 hours. According to the measurement results, the closing section is converted into the length when the closing temperature is 20℃, and a second cutting is performed. The closing section is hoisted and the counterweight water tank is drained at the same time. After hoisting to the designed position, it is matched and connected by tie rods and bolts, and the weld width is adjusted and locked before welding.

3. The method for constructing a cable-stayed bridge steel-concrete mixed section according to claim 1, wherein: Step S1 specifically includes: During the construction of S11 and the No. 15 beam section in the middle span, 2cm thick steel plates were embedded in the top surface of the bottom slab concrete and the bottom surface of the top slab concrete respectively, which were used for welding and fixing the rigid skeleton of the steel box girder in the steel-concrete composite section later; S12. Convert the cantilever bridge crane into a bridge crane and complete the acceptance work; S13. Move the bridge crane forward and anchor it, with the front support at an appropriate distance from the beam end. Do not move the original hanging basket bottom frame, outer formwork, and inner formwork for the time being. Only move the inner and outer sliding beams forward along with the bridge crane. S14, completing the hanging and tensioning construction of the corresponding inclined cables; S15, complete the iron sand concrete counterweight of the side span 15ˊ beam section; S16. Enter the steel-concrete joint area steel box girder hoisting state.

4. The method for constructing a cable-stayed bridge steel-concrete mixed section according to claim 1, wherein: Step S2 specifically includes: S21. Transport the steel-concrete joint section I of the steel-concrete joint area to the predetermined position under the bridge by barge; S22. Use the bridge crane vertical lifting system to lift the steel beam to the designed position; S23, install the rigid frame and fix beam segment 15 and steel-concrete joint segment I; S24, the bottom basket system of the bridge-building machine moves forward, connecting the front sling and the rear anchor; S25, the outer mold and the inner mold slide into place along the guide beam; S26: Tie the steel bars, install the prestressed pipes, install the plug formwork, and then pour the concrete for the middle span beam section 16-1. Simultaneously, construct the side span beam sections 16-1ˊ and 16-2ˊ and maintain the concrete. The side span side beam sections will be cast in place using supports, while the middle span side beam sections will be constructed using a bridge deck crane. S27, tensioning and anchoring the corresponding prestressed steel tendons; S28. Complete the iron sand concrete counterweight of the side span 16-1ˊ and 16-2ˊ beam sections.

5. The method for constructing a steel-concrete mixed section of a cable-stayed bridge according to claim 1, wherein: Step S3 specifically includes: S31. Release the connection between the bridge crane and the steel-concrete joint section I; S32: Tie the steel bars, install the prestressed pipes, install the plug formwork, pour the concrete of the middle span beam section No. 16-2 and maintain it; S33, tension and anchor the corresponding longitudinal and vertical prestressed steel tendons; S34. Erect the support for the No. 18 beam section of the cast-in-place side span. You may also simultaneously erect the support for the No. 15 beam section, No. 16-1 beam section, No. 16-2 beam section, and No. 18 beam section of the side span. S35. Install permanent supports at the beam ends and lock the longitudinal displacement of the beam end supports; S36. Pour the cast-in-place concrete of the side span.

6. The method for constructing a cable-stayed bridge steel-concrete mixed section according to claim 1, wherein: Step S4 specifically includes: S41. After the cast-in-place concrete of the side span reaches the appropriate strength, install temporary locking measures for the closure section and the closure hanging basket; S42, close the side span and release the longitudinal lock of the side support; S43, tensioning and anchoring the longitudinal, transverse and vertical prestressed steel strands of the side span closure S44, iron sand concrete counterweight for the side span joint section No. 17, side span straight section No. 18, side span No. 13 ~ No. 14 beam sections S45, remove the side span straight section supports; S46, remove the side span hanging basket and move the bridge crane forward a certain distance; S47, transport the steel-concrete composite section II to the predetermined position under the bridge by barge; S48, dismantle the bottom formwork system of the bridge-building machine; S49. Use the bridge crane vertical lifting system to lift the steel beam to the designed position.

7. The method for constructing a steel-concrete mixed section of a cable-stayed bridge according to claim 1, wherein: Step S5 specifically includes: S51. Temporarily lock and weld the steel-concrete joint section II and the steel-concrete joint section I, and release the connection between the sling and the steel beam; S52, pouring concrete inside the steel grid and curing; S53. Tension and anchor the longitudinal, transverse and vertical prestressed steel strands.

8. The method for constructing a steel-concrete mixed section of a cable-stayed bridge according to claim 1, wherein: Step S7 specifically includes: S71. The beam transport barge is in place, anchored, and adjusted; S72. The bridge crane lowers the lifting device to the top of the steel box girder to be lifted; S73. The bridge crane lifts the steel box girder I to the designed position; S74, steel box girder I and steel box transition section are temporarily fixed and welded into a whole; S75, bridge crane moves forward; S76. Install and symmetrically tension the corresponding stay cables; S77. Repeat the above steps to complete the construction of steel box I, steel box II, and steel box III in sequence.

9. The method for constructing a steel-concrete mixed section of a cable-stayed bridge according to claim 1, wherein: Step S9 specifically includes: S91, beam transport barge is in place, anchored, and adjusted; S92. The bridge crane lowers the lifting device to the top of the steel box girder to be lifted; S93, the bridge crane lifts the steel box girder IV to the designed position; S94, steel box beam IV and steel box beam III on both sides are temporarily fixed and then welded into a whole; S95. Except for the temporary anchoring piers of the main tower and the temporary supports on the pier top, the formal supports shall be converted into permanent supports.

10. The method for constructing a steel-concrete mixed section of a cable-stayed bridge according to claim 1, wherein: In step S9, the closure section may be constructed using a bridge crane on one side, or two bridge cranes may be used to cooperate to complete the closure section construction.

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