A construction method suitable for a steel box-concrete partial cable-stayed bridge girder

Abstract

The application provides a construction method suitable for a steel box-concrete partial cable-stayed bridge girder, which comprises the following steps: S1, main pier 0# block construction; S2, no cable area 1#-5# and 1''#-5''# beam segment construction; S3, cable area 6#-14# and 6''#-14''# beam segment construction; S4, cable area 15# beam segment concrete girder construction; S5, cable area 16''# side span beam segment and steel-concrete joint segment 16-1# midspan girder construction; S6, cast-in-situ straight line segment 18''# side span and steel-concrete joint segment 16-2# midspan girder construction; S7, side span closure segment 17''# and steel box transition segment midspan girder construction; and S8, steel box midspan girder construction. The application can solve the problem that the large hanging basket bottom blue system cannot pass through the auxiliary pier during the cantilever pouring, the maximum construction segment length of the large hanging basket is 8 m, the construction speed is fast, the large hanging basket is transformed into a bridge deck crane, and investment is saved.

Description

Technical Field

[0001] This invention mainly relates to the technical field of bridge construction, specifically a construction method applicable to the main beam of a steel box girder-concrete cable-stayed bridge. Background Technology

[0002] For the construction of the main girder of a steel box girder-concrete cable-stayed bridge, the existing methods are generally as follows: the concrete main girder is cantilevered using conventional diamond-shaped or triangular hanging baskets, with each segment being 4m long. For the steel box girder, one conventional method is to erect an assembly platform in the water, use a large floating crane to lift the steel box girder segments onto the assembly platform, and then perform welding; another conventional method is to use a specialized bridge deck crane for lifting and construction.

[0003] The existing methods described above have the following problems in actual construction: When using conventional diamond-shaped or triangular hanging baskets for cantilever casting, the length of the beam segment is limited, the main concrete beam is poured multiple times, and there is a conflict between the movement of the hanging basket and the support of the auxiliary pier when construction reaches the auxiliary pier, requiring modification of the hanging basket. When using conventional methods to construct steel box girders, there are problems such as the difficulty in setting up the underwater assembly support, high safety risks, and impact on normal navigation, requiring the configuration of large floating cranes, the assembly accuracy of steel box girders being affected by water flow, large initial investment in bridge deck cranes, and long assembly cycle. Summary of the Invention

[0004] To address the shortcomings of current technologies, this invention, combining existing technologies and based on practical applications, provides a construction method suitable for the main girder of a steel box girder-concrete cable-stayed bridge. This method has the advantages of using a cantilever bridge-building machine for the concrete main girder, which allows for faster construction speed and avoids conflicts with the construction of auxiliary piers; and using a bridge deck crane instead of a cantilever bridge-building machine for the steel box girder, which avoids the need to erect assembly supports and configure large floating cranes in the water, reduces the impact of water flow on assembly accuracy, shortens assembly time, and reduces the initial investment in the bridge deck crane.

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

[0006] A construction method applicable to the main girder of a steel box girder-concrete composite cable-stayed bridge includes the following steps:

[0007] S1, Construction of Main Pier Block 0;

[0008] S2, construction of beam segments 1# to 5# and 1ˊ# to 5ˊ# in the cable-free zone, including symmetrical installation of large hanging baskets on both sides and symmetrical pouring of the corresponding beam segments on the large hanging baskets in sequence;

[0009] S3, construction of beam segments 6# to 14# and 6ˊ# to 14ˊ# in the cable-stayed area, including symmetrically pouring the corresponding beam segments and symmetrically installing the corresponding cables on the large hanging basket;

[0010] S4. Construction of the concrete main beam of beam segment 15 in the cable-stayed area, including removing the bottom railing of the large hanging basket on the side span, erecting the cast-in-place scaffold, casting the side span 15'# block on the scaffold, symmetrically cantilevering the middle span 15# block, and symmetrically installing the corresponding cables;

[0011] S5. Construction of the 16ˊ# side span beam segment in the cable-stayed zone and the 16-1# main beam in the steel-concrete composite section, including converting the side hanging basket in the middle span into a bridge deck crane, cantilever hoisting of the steel box girder in the steel-concrete composite zone of the 16-1# block in the middle span, cantilever casting of concrete for the 16-1#, 16-1ˊ#, and 16-2ˊ# blocks in the side span, and tensioning and anchoring the prestressed steel strands;

[0012] S6. Construction of the main beam of the cast-in-place straight section 18'# side span and the steel-concrete composite section 16-2# mid-span;

[0013] Construction of S7, the side span closure section 17ˊ# and the main beam of the middle span of the steel box transition section, including casting the side span closure section using scaffolding, dismantling the scaffolding of the side span cast-in-place section, dismantling the side hanging basket of the side span, moving the bridge deck crane of the middle span steel-concrete composite section forward, hoisting the steel box transition section into place, moving the bridge deck crane forward, and symmetrically installing the corresponding cables;

[0014] S8. Construction of the mid-span of the steel box girder, including hoisting and positioning each steel box girder segment and the mid-span closure segment of the steel box girder;

[0015] S9. Secondary cable adjustment construction, including pouring concrete bridge deck on the top surface of the steel box girder, secondary tensioning and adjustment of cables, and static and dynamic load tests.

[0016] Furthermore, step S1 specifically includes:

[0017] S11. Construction of temporary consolidation piers;

[0018] S22. Erect and preload the steel pipe support for block #0.

[0019] S23. Construct block #0 on the support and tension the prestressed steel strands;

[0020] S24. Remove the steel pipe support for block #0.

[0021] Furthermore, step S2 specifically includes:

[0022] S21. Install the large hanging baskets on both sides symmetrically and pre-press them;

[0023] S22. Symmetrically cast beam segments #1 and #1' on the large hanging basket, tension and anchor the prestressed steel strands, and move the large hanging basket forward;

[0024] S23. Repeat step S22 to complete the construction of beam segments 2#~5# and 2ˊ#~5ˊ#.

[0025] S24. While the construction of beam segments 5# and 5ˊ# is completed, the construction of the remaining tower columns and middle crossbeams shall be completed.

[0026] Furthermore, step S3 specifically includes:

[0027] S31. Symmetrically pour beam segments 6# and 6ˊ#, tension and anchor prestressed steel strands, and move the large hanging basket forward;

[0028] S32. Install and tension the corresponding cables symmetrically;

[0029] S33. Repeat the above steps to complete the construction of beam segments 7#~14# and 7ˊ~14ˊ# and the corresponding cables.

[0030] Furthermore, step S4 specifically includes:

[0031] S41. Remove the bottom basket of the large hanging basket in the side span and erect the cast-in-place support for the 15ˊ#, 16-1ˊ#, and 16-2ˊ# beam segments of the side span;

[0032] S42. Install permanent supports for auxiliary piers #16 and #19. Cast-in-place side span #15' and symmetrically cantilevered middle span #15. Before casting the middle span #15, counterweights need to be placed on side span #14'. Tension and anchor the prestressed steel strands. Move the large hanging basket forward. After moving the side hanging basket, it will serve as a temporary load counterweight.

[0033] S43. Install and tension the corresponding cables symmetrically;

[0034] S44. Pour counterweight iron sand concrete for the 15ˊ# beam segment of the side span.

[0035] Furthermore, step S5 specifically includes:

[0036] S51. The side hanging basket of the mid-span is converted into a bridge deck crane. During the conversion, the bottom basket system, formwork system, suspension system and front upper crossbeam of the hanging basket are removed, and the crossbeam load-bearing system of the bridge deck crane, as well as the crane suspension system and lifting gear system are installed.

[0037] S52, cantilever hoisting of the steel box girder in the steel-concrete composite zone of the middle span 16-1# block, cantilever casting of concrete for the 16-1# beam segment, casting of concrete for the side spans 16-1ˊ# and 16-2ˊ# blocks on the support, tensioning and anchoring of prestressed steel strands;

[0038] S53, pour counterweight iron sand concrete for beam segments 16-1ˊ# and 16-2ˊ# in the side span.

[0039] Furthermore, step S6 specifically includes:

[0040] S61, cantilevered concrete for the 16-2# block beam segment in the middle span, tensioned and anchored prestressed steel strands;

[0041] S62. Install permanent supports at the beam ends and lock the longitudinal displacement of the beam end supports;

[0042] S63. Pour concrete for the side span in place.

[0043] Furthermore, step S7 specifically includes:

[0044] S71. After the concrete strength of the side span cast-in-place section reaches the required level, install temporary locking measures for the side span closure section.

[0045] S72. Use the support frame to pour the side span closure section, release the longitudinal locking of the side pier support, and tension and anchor the side span steel strands.

[0046] S73, counterweighted iron sand concrete for beam segments 13ˊ#, 14ˊ#, 17ˊ#, and 18ˊ# on opposite sides;

[0047] S74. Remove the support frame of the cast-in-place section of the side span, remove the side hanging basket of the side span, and move the bridge deck crane of the steel-concrete composite section of the middle span forward;

[0048] S75. Hoist the steel box transition section into place and pour the filling concrete.

[0049] S76. Tension and anchor the prestressed steel strands of the steel-concrete transition section, move the mid-span bridge deck crane forward, and symmetrically install the tensioning cables.

[0050] Furthermore, step S8 specifically includes:

[0051] S81. Hoist steel box section I into place, move the bridge deck crane forward, and install the tension cables;

[0052] S82. Hoist steel box section II into place, move the bridge deck crane forward, and install the tension cables;

[0053] S83. Hoist the steel box section III into place;

[0054] S84. Hoist the steel box girder of the mid-span closure section into place;

[0055] S85. Remove the temporary anchor piers of the main tower and convert the temporary supports into permanent supports to complete the system conversion.

[0056] Furthermore, step S9 specifically includes:

[0057] S91. Cast concrete bridge deck on top of steel box girder;

[0058] S92. Secondary tensioning and cable adjustment to adjust the alignment;

[0059] S93. Cast the remaining approach bridge caps of the side piers and construct the bridge deck system.

[0060] S94. Static and dynamic load test.

[0061] The beneficial effects of this invention are:

[0062] The concrete main beams are constructed using a large segment method, which can speed up the construction progress and shorten the construction period. The cantilever length of beam segments 6#~14# and 6#ˊ~14#ˊ is 8m, which reduces the number of cantilever pouring operations.

[0063] The 15ˊ#, 16-1ˊ# and 16-2ˊ# beam segments were constructed using the scaffolding cast-in-place method, which resolved the conflict between the traveling formwork and the auxiliary pier supports, and accelerated the construction progress.

[0064] The cantilever bridge-building machine, which is used for cantilever construction of the main beam, can be modified into a bridge deck crane, which can reduce the fabrication of some components and shorten the on-site assembly time.

[0065] Using bridge cranes to assist in assembly operations avoids the need to build assembly platforms in the water, reducing construction difficulty and minimizing waterway occupancy time.

[0066] Using bridge-mounted cranes to assist in hoisting operations avoids the need for large floating cranes, reduces the investment in large equipment, and lowers safety risks.

[0067] The bridge deck crane is fixed to the completed beam segment, reducing the impact of water on the construction when using floating cranes and improving the assembly accuracy. Attached Figure Description

[0068] Appendix Figure 1 This is a flowchart of the construction method of the present invention.

[0069] Appendix Figure 2 This is a structural diagram corresponding to construction step S1 of the present invention.

[0070] Appendix Figure 3 This is a structural diagram corresponding to construction step S2 of the present invention.

[0071] Appendix Figure 4 This is a structural diagram corresponding to construction step S3 of the present invention.

[0072] Appendix Figure 5 This is a structural diagram corresponding to construction step S4 of the present invention.

[0073] Appendix Figure 6 This is a structural diagram corresponding to construction step S5 of the present invention.

[0074] Appendix Figure 7 This is a structural diagram corresponding to construction step S6 of the present invention.

[0075] Appendix Figure 8 This is a structural diagram corresponding to construction step S7 of the present invention.

[0076] Appendix Figure 9 This is a structural diagram corresponding to construction step S8 of the present invention.

[0077] Appendix Figure 10 This is a structural diagram corresponding to construction step S9 of the present invention.

[0078] Appendix Figure 11 The original structure of the hanging basket of this invention. Figure 1 .

[0079] Appendix Figure 12 The original structure of the hanging basket of this invention. Figure 2 .

[0080] Appendix Figure 13 The modified bridge deck crane structure of this invention Figure 1 .

[0081] Appendix Figure 14 The modified bridge deck crane structure of this invention Figure 2 . Detailed Implementation

[0082] The present invention will be further described in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0083] This invention provides a construction method for the main beam of a steel box girder-concrete cable-stayed bridge, which can solve the problem that the large hanging basket bottom basket system cannot pass through the auxiliary pier during cantilever casting. The large hanging basket has a maximum construction segment length of 8m, the construction speed is fast, and the large hanging basket can be modified into a bridge deck crane, saving investment.

[0084] like Figure 1 The diagram shows the main construction process of this invention, which specifically includes the following steps.

[0085] (1) Construction of main pier block #0, such as Figure 2 As shown.

[0086] ① Construction of temporary consolidation piers.

[0087] ② Erect the No. 0 block steel pipe support and pre-stress it.

[0088] ③ Construct block #0 on the support and tension the prestressed steel strands.

[0089] ④ Remove the steel pipe support for block #0.

[0090] (2) Construction of beam segments 1# to 5# in the cable-free zone, such as Figure 3 As shown.

[0091] ① Install the cantilever bridge-building machines (large hanging baskets) symmetrically on both sides and preload them.

[0092] ② Pour beam segment 1 (1ˊ#) symmetrically on the large hanging basket, tension and anchor the prestressed steel strands, and move the large hanging basket forward.

[0093] ③ Repeat step ② to complete the construction of beam segments 2# (2ˊ#) to 5# (5ˊ#).

[0094] ④ While the construction of beam segment 5 (5ˊ#) is completed, the construction of the remaining tower columns and middle cross beams shall be completed.

[0095] (3) Construction of concrete main beams in sections 6# to 14# of the cable-stayed zone, such as Figure 4 As shown.

[0096] ①Symmetrically cast beam segment 6 (6ˊ#), tension and anchor prestressed steel strands, and move the large hanging basket forward.

[0097] ② Install and tension cables B1, Z1, B1ˊ, and Z1ˊ symmetrically.

[0098] ③ Repeat the above steps to complete the construction of beam segments 7# (7ˊ#) - 14# (14ˊ#) and cables B2~B9, Z2~Z9, B2ˊ~B9ˊ, and Z2ˊ~Z9ˊ.

[0099] The concrete main beams are constructed using a large segment method, which can speed up the construction progress and shorten the construction period. The cantilever length of beam segments 6#~14# and 6ˊ~14ˊ# is 8m, which reduces the number of cantilever pouring operations.

[0100] (4) Construction of the concrete main beam of beam segment 15 in the cable-stayed zone, such as Figure 5 As shown.

[0101] ① Remove the bottom basket of the large hanging basket in the side span and erect the cast-in-place support for the 15ˊ#, 16-1ˊ#, and 16-2ˊ# beam segments of the side span.

[0102] ② Install permanent supports for auxiliary piers #16 and #19, and cast-in-place side span 15'# block / symmetrical cantilevered middle span 15'# block. Before casting the middle span 15'# block, counterweights need to be placed on side span 14'# block. Tension and anchor the prestressed steel strands, and move the large hanging basket forward (the large hanging basket on the side of the side span is moved to serve as a temporary load counterweight).

[0103] ③ Install and tension the B10, Z10, B10ˊ, and Z10ˊ cables symmetrically.

[0104] ④ Pour the counterweight iron sand concrete for the 15ˊ# beam segment of the side span.

[0105] (5) Construction of the main beams of the 16ˊ# beam segment (side span) in the cable-stayed zone and the 16-1# (middle span) in the steel-concrete composite section, such as Figure 6 As shown.

[0106] ① The side hanging basket of the mid-span will be converted into a bridge deck crane.

[0107] ② The 3.25m steel box girder in the steel-concrete composite zone of the 16-1# block in the middle span was cantilevered and the concrete of the 16-1# beam segment (4m) was poured / supported and the concrete of the side spans 16-1ˊ# and 16-2ˊ# blocks was poured, and the prestressed steel strands were tensioned and anchored.

[0108] ③ Pour counterweight iron sand concrete for beam segments 16-1ˊ# and 16-2ˊ# in the side spans.

[0109] The 15ˊ#, 16-1ˊ# and 16-2ˊ# beam segments were constructed using the scaffolding cast-in-place method, which resolved the conflict between the traveling formwork and the auxiliary pier supports, and accelerated the construction progress.

[0110] In step ① of this embodiment, the original hanging basket structure is as follows: Figure 11 , Figure 12 As shown, it mainly includes the front upper crossbeam 1, suspension system 2, outer formwork system 3, bottom basket system 4, and inner formwork system 5. Its structural diagram after being modified into a bridge deck crane is as follows. Figure 13 , Figure 14 As shown.

[0111] The main modifications involved dismantling the cantilever bridge-building machine's base basket system 4, formwork system (outer formwork system 3, inner formwork system 5), suspension system 2, and front upper crossbeam 1. The bridge deck crane's crossbeam load-bearing system 7, crane suspension system 6, and lifting equipment system 8 were then installed. The modified cantilever bridge-building machine retained its main truss system, traveling system, and rear anchoring system. The anchoring methods of the traveling system and rear anchoring system within the steel box girder area were improved. The modified bridge deck crane can meet the needs of steel box girder hoisting construction, while reducing the overall processing costs and assembly time of the bridge deck crane.

[0112] Meanwhile, the cantilever bridge-building machine used for main beam cantilever construction is modified into a bridge deck crane, which can reduce the fabrication of some components and shorten the on-site assembly time; using a bridge deck crane to assist in assembly operations avoids the need to set up an assembly platform in the water, reducing construction difficulty and the time spent occupying the waterway; using a bridge deck crane to assist in hoisting operations avoids the need to invest in large floating crane equipment, reducing the investment in large equipment and lowering safety risks; the bridge deck crane is fixed on the completed beam segment, reducing the impact of water on the construction when using floating cranes and improving assembly accuracy.

[0113] (6) Construction of the main beams of the cast-in-place straight section 18'# (side span) and the steel-concrete composite section 16-2# (middle span), such as Figure 7 As shown.

[0114] ① Cast concrete for the 16-2# block (3m) beam segment in the middle span; tension and anchor the prestressed steel strands.

[0115] ② Install permanent supports at the beam ends and lock the longitudinal displacement of the beam end supports.

[0116] ③ Pour concrete for the side span in place.

[0117] (7) Construction of the main beam of the side span closure section 17'# and the steel box transition section (mid span), such as Figure 8 As shown.

[0118] ①After the concrete strength of the cast-in-place section of the side span reaches the required level, install temporary locking measures (rigid frame) for the closure section of the side span.

[0119] ②Use the support frame to pour the side span closure section, release the longitudinal locking of the side pier support, and tension and anchor the side span steel strands.

[0120] ③ Counterweighted iron sand concrete for beam segments 13ˊ#, 14ˊ#, 17ˊ#, and 18ˊ# on the side spans.

[0121] ④ Remove the supports for the cast-in-place section of the side span, remove the side hanging baskets for the side span, and move the bridge deck crane of the steel-concrete composite section of the middle span forward.

[0122] ⑤ Hoist the steel box transition section (steel box section) into place and pour the filling concrete.

[0123] ⑥ Tension and anchor the prestressed steel strands in the steel-concrete transition section, move the mid-span bridge deck crane forward, and symmetrically install and tension cables B11, Z11, B11ˊ, and Z11ˊ.

[0124] (8) Construction of the steel box girder (mid span), such as Figure 9 As shown.

[0125] ① Hoist the steel box section 1 (8.5m) into place, move the bridge deck crane forward, and install and tension cables B12, Z12, B12ˊ, and Z12ˊ.

[0126] ② Hoist the steel box section 2 (10m) into place, move the bridge deck crane forward, and install and tension cables B13, Z13, B13, and Z13.

[0127] ③ Hoist the steel box section 3 (10m) into place.

[0128] ④ The steel box girder (10) of the mid-span closure section was hoisted into place.

[0129] ⑤ Remove the temporary anchor piers of the main tower and convert the temporary supports into permanent supports to complete the system conversion.

[0130] (9) Secondary cable adjustment construction, such as Figure 10 As shown.

[0131] ① Pour concrete bridge deck on the top surface of the steel box girder.

[0132] ② Secondary tensioning and adjustment of the cable to adjust the alignment.

[0133] ③ Cast the remaining approach bridge caps for the side piers and construct the bridge deck system.

[0134] ④ Static and dynamic load tests.

Claims

1. A construction method applicable to the main girder of a steel-concrete composite cable-stayed bridge, characterized in that, Includes the following steps: S1, Construction of Main Pier Block 0; S2, construction of beam segments 1# to 5# and 1ˊ# to 5ˊ# in the cable-free zone, including symmetrical installation of large hanging baskets on both sides and symmetrical pouring of the corresponding beam segments on the large hanging baskets in sequence; S3, construction of beam segments 6# to 14# and 6ˊ# to 14ˊ# in the cable-stayed area, including symmetrically pouring the corresponding beam segments and symmetrically installing the corresponding cables on the large hanging basket; S4. Construction of the concrete main beam of beam segment 15 in the cable-stayed area, including removing the bottom railing of the large hanging basket on the side span, erecting the cast-in-place scaffold, casting the side span 15'# block on the scaffold, symmetrically cantilevering the middle span 15# block, and symmetrically installing the corresponding cables; S5. Construction of the 16ˊ# side span beam segment in the cable-stayed zone and the 16-1# main beam in the steel-concrete composite section, including converting the side hanging basket in the middle span into a bridge deck crane, cantilever hoisting of the steel box girder in the steel-concrete composite zone of the 16-1# block in the middle span, cantilever casting of concrete for the 16-1#, 16-1ˊ#, and 16-2ˊ# blocks in the side span, and tensioning and anchoring the prestressed steel strands; S6. Construction of the main beam of the cast-in-place straight section 18'# side span and the steel-concrete composite section 16-2# mid-span; Construction of S7, the side span closure section 17ˊ# and the main beam of the middle span of the steel box transition section, including casting the side span closure section using scaffolding, dismantling the scaffolding of the side span cast-in-place section, dismantling the side hanging basket of the side span, moving the bridge deck crane of the middle span steel-concrete composite section forward, hoisting the steel box transition section into place, moving the bridge deck crane forward, and symmetrically installing the corresponding cables; S8. Construction of the mid-span of the steel box girder, including hoisting and positioning each steel box girder segment and the mid-span closure segment of the steel box girder; S9. Secondary cable adjustment construction, including pouring concrete bridge deck on the top surface of the steel box girder, secondary tensioning and adjustment of cables, and static and dynamic load tests.

2. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S1 specifically includes: S11. Construction of temporary consolidation piers; S22. Erect and preload the steel pipe support for block #0. S23. Construct block #0 on the support and tension the prestressed steel strands; S24. Remove the steel pipe support for block #0.

3. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S2 specifically includes: S21. Install the large hanging baskets on both sides symmetrically and pre-press them; S22. Symmetrically cast beam segments #1 and #1' on the large hanging basket, tension and anchor the prestressed steel strands, and move the large hanging basket forward; S23. Repeat step S22 to complete the construction of beam segments 2#~5# and 2ˊ#~5ˊ#. S24. While the construction of beam segments 5# and 5ˊ# is completed, the construction of the remaining tower columns and middle crossbeams shall be completed.

4. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S3 specifically includes: S31. Symmetrically pour beam segments 6# and 6ˊ#, tension and anchor prestressed steel strands, and move the large hanging basket forward; S32. Install and tension the corresponding cables symmetrically; S33. Repeat the above steps to complete the construction of beam segments 7#~14# and 7ˊ~14ˊ# and the corresponding cables.

5. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S4 specifically includes: S41. Remove the bottom basket of the large hanging basket in the side span and erect the cast-in-place support for the 15ˊ#, 16-1ˊ#, and 16-2ˊ# beam segments of the side span; S42. Install permanent supports for auxiliary piers #16 and #19. Cast-in-place side span #15' and symmetrically cantilevered middle span #15. Before casting the middle span #15, counterweights need to be placed on side span #14'. Tension and anchor the prestressed steel strands. Move the large hanging basket forward. After moving the side hanging basket, it will serve as a temporary load counterweight. S43. Install and tension the corresponding cables symmetrically; S44, pour counterweight iron sand concrete for the 15ˊ# beam segment of the side span.

6. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S5 specifically includes: S51. The side hanging basket of the mid-span is converted into a bridge deck crane. During the conversion, the bottom basket system, formwork system, suspension system and front upper crossbeam of the hanging basket are removed, and the crossbeam load-bearing system of the bridge deck crane, as well as the crane suspension system and lifting gear system are installed. S52, cantilever hoisting of the steel box girder in the steel-concrete composite zone of the middle span 16-1# block, cantilever casting of concrete for the 16-1# beam segment, casting of concrete for the side spans 16-1ˊ# and 16-2ˊ# blocks on the support, tensioning and anchoring of prestressed steel strands; S53, pour counterweight iron sand concrete for beam segments 16-1ˊ# and 16-2ˊ# in the side span.

7. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S6 specifically includes: S61, cantilevered concrete for the 16-2# block beam segment in the middle span, tensioned and anchored prestressed steel strands; S62. Install permanent supports at the beam ends and lock the longitudinal displacement of the beam end supports; S63. Pour concrete for the side span in place.

8. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S7 specifically includes: S71. After the concrete strength of the side span cast-in-place section reaches the required level, install temporary locking measures for the side span closure section. S72. Use the support frame to pour the side span closure section, release the longitudinal locking of the side pier support, and tension and anchor the side span steel strands. S73, counterweighted iron sand concrete for beam segments 13ˊ#, 14ˊ#, 17ˊ#, and 18ˊ# on opposite sides; S74. Remove the support frame of the cast-in-place section of the side span, remove the side hanging basket of the side span, and move the bridge deck crane of the steel-concrete composite section of the middle span forward; S75. Hoist the steel box transition section into place and pour the filling concrete. S76. Tensioning and anchoring the prestressed steel strands of the steel-concrete composite section, moving the mid-span bridge deck crane forward, and symmetrically installing the tensioning cables.

9. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S8 specifically includes: S81. Hoist steel box section I into place, move the bridge deck crane forward, and install the tension cables; S82. Hoist steel box section II into place, move the bridge deck crane forward, and install the tension cables; S83. Hoist the steel box section III into place; S84. Hoist the steel box girder of the mid-span closure section into place; S85. Remove the temporary anchor piers of the main tower and convert the temporary supports into permanent supports to complete the system conversion.

10. The construction method for the main girder of a steel-concrete composite cable-stayed bridge according to claim 1, characterized in that, Step S9 specifically includes: S91. Cast concrete bridge deck on top of steel box girder; S92. Secondary tensioning and cable adjustment to adjust the alignment; S93. Cast the remaining approach bridge caps of the side piers and construct the bridge deck system. S94. Static and dynamic load test.

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