Construction method for mid-span closure section of long-span cable-stayed bridge

Abstract

The application discloses a construction method for a closure segment of a large-span cable-stayed bridge, which comprises the following steps: in process one, before pouring concrete of the last cantilever section of the large and small mileage, pre-buried parts are buried at the end of the last cantilever pouring section of the large and small mileage; in process two, a closure segment formwork is installed; in process three, a jacking device is installed, the jacking device comprises the same number of jacking jacks as the pre-buried parts of the jacking support, and a jacking rod is installed on each jacking jack; in process four, a jacking force is applied; in process five, a stiff skeleton is locked; in process six, the following steps are sequentially performed: a bottom mould is installed, prestressed pipe positioning in a bottom plate is performed, an inner mould is installed, top plate steel bars of the closure segment are bound, and prestressed pipe positioning in the top plate is performed; and in process seven, a temporary closure segment prestressed steel bar is first tensioned, and water in a counterweight water bag is simultaneously discharged in the process of pouring concrete of the closure segment. The application has the characteristics of simple operation and small influence from the outside world.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of bridge building, in particular to a construction method for a mid-span closure section of a long-span cable-stayed bridge. BACKGROUND

[0002] Pylon-tower-beam fixed low-tower cable-stayed bridges have the advantages of strong spanning capacity, good structural stability, mature construction technology, and good driving comfort, and in particular have strong competitive advantages in cable-stayed bridges with a main span of 200-350 m. However, long-span bridges, due to the use of cantilever construction, will cause prestress loss, main beam deflection, and main beam and bridge pier horizontal displacement under the long-term load action in the later construction and use process. In addition, temperature changes will also cause main beam deformation, so the bridge structure design specification has clear provisions for uniform temperature action. Calculation shows that excessive temperature difference will significantly increase the additional internal force of the main beam and the bridge pier, especially at the bottom of the bridge pier, where the additional internal force is even greater. For this reason, relevant personnel in the industry have developed a solution, which is to apply a horizontal thrust to the two cantilever ends when the mid-span is closed, causing the main pier to produce a horizontal displacement in the opposite direction, which can effectively offset the displacement caused by temperature difference and later concrete shrinkage and creep, improve the stress state of the bridge after completion, and ensure the structural safety of the bridge. However, how to implement this solution is a problem that needs to be solved by bridge construction enterprises. SUMMARY

[0003] The present application aims to overcome the defects of the prior art and provide a construction method for a mid-span closure section of a long-span cable-stayed bridge, which has the characteristics of simple operation, small external influence, strong economy, and low construction safety risk.

[0004] The purpose of the present application is achieved by a construction method for a mid-span closure section of a long-span cable-stayed bridge, comprising the following processes:

[0005] Process one, burying the embedded part, that is, before pouring the concrete of the last section of the box girder of the cantilever in the large and small mileage, the embedded part is buried in the end of the last section of the box girder of the cantilever in the large and small mileage; The embedded part includes a pushing support embedded part and a stiff skeleton embedded part; The pushing support embedded part is respectively buried at the intersection of the top plate and all the webs at the end of the last section of the box girder of the cantilever in the large and small mileage, and each pushing support embedded part is electrically welded with the transverse reinforcement in the beam body; Each pushing support embedded part is composed of three channel steels, which are arranged in the form of an inverted isosceles triangle with a center line; The stiff skeleton embedded part is buried on both sides of the top plate at the end of the last section of the box girder of the cantilever in the large and small mileage, one on each side of the top plate near all the webs, one on each side of the bottom plate, one on each side of the bottom plate near all the webs, and two staggered on each of all the webs; Each stiff skeleton embedded part includes two rows of skeleton support steel plates; The lower part of each skeleton support steel plate is a buried section, and two threaded steels are respectively and symmetrically welded on the opposite surfaces of the buried sections of the two rows of skeleton support steel plates, one above the other; The two threaded steels on the two rows of skeleton support steel plates are welded with the transverse reinforcement in the beam body; The stiff skeleton is assembled by two channel steels through a plurality of top and bottom connecting steel plates arranged at intervals, one end of the stiff skeleton is welded with the upper part of the two rows of skeleton support steel plates in the last section of the box girder of the cantilever in the large mileage or the last section of the box girder of the cantilever in the small mileage, and the other end of the support pipe is not welded with the upper part of the two rows of skeleton support steel plates in the corresponding last section of the box girder of the cantilever in the small mileage or the last section of the box girder of the cantilever in the large mileage;

[0006] After all the embedded parts are buried, the concrete of the last section of the box girder of the cantilever in the large and small mileage is poured and cured;

[0007] Process two, installing the middle span closure section formwork, including the following steps:

[0008] S1, first remove the platform at the front end of the hanging basket of the last section of the box girder of the cantilever in the large and small mileage, then pull out the inner mold of the hanging basket of the last section of the box girder of the cantilever in the large and small mileage, and then pull out the inner sliding beam of the hanging basket of the last section of the box girder of the cantilever in the large mileage;

[0009] S2, convert the lifting belts on the front support beam of the hanging basket of the last section of the box girder of the cantilever in the large and small mileage into finished threaded steels one by one, and the conversion sequence is symmetrically converted from inside to outside;

[0010] S3, the outer slide beam of the last section of box girder of the small mileage mid-span cantilever is moved forward and anchored on the hanging basket of the last section of box girder of the large mileage mid-span cantilever, and the outer side form of the last section of box girder of the small mileage mid-span cantilever is dragged on the outer slide beam after moving forward until it is connected with the outer side form of the last section of box girder of the large mileage mid-span cantilever to form the outer side form of the mid-span closure section; the longitudinal distribution beam of the front support beam of the bottom basket of the hanging basket of the last section of box girder of the large and small mileage mid-span cantilever is longitudinally arranged as the bottom form distribution beam of the mid-span closure section, the square wood is transversely laid on the I-shaped steel, and the bamboo plywood is laid on the square wood to form the bottom form system of the mid-span closure section; the inner formwork of the mid-span closure section adopts scattered wood formwork;

[0011] Process three, installing the jacking device, the jacking device includes a plurality of jacking jacks and matched jacking rod members which are horizontally installed on the bottom form system of the mid-span closure section and correspondingly located at the junction of the bottom plate and all the web plates, and the jacking device further includes a plurality of jacking jacks and matched jacking rod members which are horizontally and correspondingly fixed between the jacking bracket embedded members embedded at the ends of the last sections of box girder of the large and small mileage mid-span cantilevers;

[0012] Process four, first, placing counterweight water bags on the bridge deck of the last sections of box girder of the large and small mileage mid-span cantilevers respectively and uniformly, then, increasing the weight of the counterweight water bags by water injection, so that the weight of the counterweight water bags on the last sections of box girder of the large and small mileage mid-span cantilevers is half of the total weight of the mid-span closure section concrete respectively, and then, simultaneously starting a plurality of oil pumps driving all the jacking jacks to load the jacking force of all the jacking jacks at the time period when the air temperature is the lowest in a day;

[0013] Process five, after the jacking jacks are loaded, the plurality of oil pumps driving the jacking jacks are controlled to maintain stable pressure, the other end of the two sides of the stiff skeleton on each stiff skeleton embedded member is welded with the two rows of skeleton support steel plates in the corresponding small mileage mid-span cantilever or the upper part of the two rows of skeleton support steel plates in the large mileage mid-span cantilever, and the top connecting plate fixed to the head of the stiff skeleton is filled with weld at the intersection with the top of the corresponding skeleton support steel plate, so as to lock the ends of the last sections of box girder of the large and small mileage mid-span cantilevers, then, the jacking force of all the jacking jacks is released, and then, the jacking device is removed, that is, all the jacking jacks and all the jacking rod members are removed;

[0014] Process six, the following steps are sequentially performed: installing the bottom form of the mid-span closure section, binding the bottom plate reinforcement of the mid-span closure section, positioning the prestressed pipe in the bottom plate of the mid-span closure section, installing the inner form of the mid-span closure section, binding the top plate reinforcement of the mid-span closure section, positioning the prestressed pipe in the top plate of the mid-span closure section, and threading the temporary closure prestressed steel strand;

[0015] Process seven, first tensioning temporary closure prestressed steel strand, then pouring the middle span closure section concrete, at the same time discharging water in the counterweight water bag on the last section of the middle span cantilever box girder, the drainage weight is consistent with the pouring weight of the middle span closure section concrete.

[0016] The construction method for the middle span closure section of the long-span cable-stayed bridge, wherein, when the process one is performed, the two ends of the threaded steel in the stiff skeleton pre-embedded part are provided with hooks.

[0017] The construction method for the middle span closure section of the long-span cable-stayed bridge, wherein, when the process three is performed, the pushing rod part is a spiral pipe, the spiral pipe is filled with C50 concrete, and the two ends of the spiral pipe are sealed by steel plates.

[0018] The construction method for the middle span closure section of the long-span cable-stayed bridge, wherein, when the process four is performed, the pushing force is loaded to all pushing jacks according to the principles of symmetry, synchronization and grading, and the pushing force is loaded according to the following principles:

[0019] The pushing force is loaded to 30% of the total pushing force for the first time, the displacement of the pier top is measured after 15 minutes of observation;

[0020] The pushing force is loaded to 50% of the total pushing force for the second time, the length of the middle span closure section and the displacement of the pier top are observed after 15 minutes of observation;

[0021] The pushing force is loaded to 80% of the total pushing force for the third time, the length of the middle span closure section and the displacement of the pier top are continuously observed;

[0022] The pushing force is loaded to 100% of the total pushing force for the fourth time, and the pushing is stopped when the displacement of the pier top reaches 90% of the design requirement.

[0023] The construction method for the middle span closure section of the long-span cable-stayed bridge has the following characteristics: simple operation, small influence from the outside world, strong economy, low construction safety risk, effective release of the internal stress of the main girder, and better improvement of the deformation of the bridge and the pier. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the embedding position diagram of the pushing support pre-embedded part when the process one of the present application is performed;

[0025] Figure 2 is the A-A view in Figure 1 ;

[0026] Figure 3 is the embedding position diagram of the stiff skeleton pre-embedded part when the process one of the present application is performed;

[0027] Figure 4This is a schematic diagram of the cross-sectional structure of the rigid frame embedded part used in this invention;

[0028] Figure 5 yes Figure 4 Side view;

[0029] Figure 6 This is an elevation view of the rigid frame after connection during step two of process four of the present invention.

[0030] Figure 7 This is a plan view of the rigid skeleton after connection during step two of process four of the present invention. Detailed Implementation

[0031] The invention will be further explained below with reference to a large-span cable-stayed bridge with a single-box three-cell steel box girder structure. The length of the mid-span closure section of the large-span cable-stayed bridge is 3m.

[0032] Please see Figures 1 to 7 The construction method of the present invention for the mid-span closure section of a long-span cable-stayed bridge includes the following steps:

[0033] Step 1: Installing embedded parts. Before the concrete pouring of the last cantilever box girder segment 10A (large mileage) and 10B (small mileage), embedded parts are installed at the ends of both segments. These embedded parts include jacking support embedded parts and stiffening frame embedded parts.

[0034] The jacking support embedded parts 10 are installed at the junction of the top plate 2 and the four web plates 3 at the end of the last cantilever box girder segment 10A in the high-mileage mid-span section and at the junction of the top plate 2 and the four web plates 3 at the end of the last cantilever box girder segment 10B in the low-mileage mid-span section, with a total of 4 at each end (see...). Figure 1 Each jacking support embedded part 10 is composed of three No. 20 channel steels, which are arranged in an inverted isosceles triangle with their center lines connected. Each jacking support embedded part 10 is welded to the transverse steel bars 4 in the beam body, and ensures that the center line between the jacking support embedded part 10 on the last box girder segment 10A of the large mileage mid-span cantilever and the jacking support embedded part 10 on the corresponding last box girder segment 10B of the small mileage mid-span cantilever is parallel to the axis of the bridge.

[0035] The stiffening frame embedded parts 20 are installed on both sides of the top plate 2 at the ends of the last box girder segment 10A of the mid-span cantilever at the high mileage and the last box girder segment 10B of the mid-span cantilever at the low mileage. One is also installed on each side of the top plate 2 near the four web plates 3, and one is installed on each side of the bottom plate 1. One is also installed on each side of the bottom plate 1 near the four web plates 3, and two are staggered on each of the four web plates 3, for a total of 20 at one end (see...).Figure 3 Each stiffening frame embedded part 20 includes two rows of frame support steel plates; each row of frame support steel plates consists of three frame support steel plates 24, with a spacing of 7.5mm between the three frame support steel plates 24. Each frame support steel plate 24 is 200mm long, 680mm high, and 240mm deep. The lower part of each frame support steel plate 24 is the embedded section. On the opposite sides of the embedded sections of the two rows of frame support steel plates 24, two threaded steel bars 25 with a length of 1m and a diameter of Φ20mm are symmetrically welded, one above the other, with a net spacing of 13mm between the two threaded steel bars 25. The two threaded steel bars 25 on the two rows of frame support steel plates 24 are welded to the transverse reinforcing bars in the beam body; the stiffening frame 21 consists of two steel bars with a length of 4m and a diameter of Φ20mm. A 0.5m 40C channel steel is assembled from four spaced-apart top connecting steel plates 22 and bottom connecting steel plates 23; the length of the top connecting steel plate 22 and the bottom connecting steel plate 23 is 40mm and the width is 20mm; one end of the stiffening frame 21 is welded to the upper part of the two rows of frame support steel plates 24 in the last box girder segment 10A of the large mileage mid-span cantilever or the two rows of frame support steel plates 24 in the last box girder segment 10B of the small mileage mid-span cantilever, while the other end of the stiffening frame 21 is not welded to the upper part of the two rows of frame support steel plates 24 in the corresponding last box girder segment 10B of the small mileage mid-span cantilever or the two rows of frame support steel plates 24 in the last box girder segment 10A of the large mileage mid-span cantilever (see...). Figure 4 and Figure 5 );

[0036] After all the embedded parts are installed, pour the concrete for the last box girder segment 10A of the cantilever in the middle span of the large mileage and the last box girder segment 10B of the cantilever in the middle span of the small mileage, and then carry out curing.

[0037] Step 2, installing the template for the mid-span closure section, includes the following steps:

[0038] S1. First, remove the platform at the front end of the hanging basket of the last box girder segment of the cantilever in the middle span of the large mileage and the platform at the front end of the hanging basket of the last box girder segment of the cantilever in the middle span of the small mileage. Then, remove the inner formwork of the last box girder segment 10A of the cantilever in the middle span of the large mileage and the inner formwork of the last box girder segment 10B of the cantilever in the middle span of the small mileage. Finally, remove the inner sliding beam of the hanging basket of the last box girder segment of the cantilever in the middle span of the large mileage.

[0039] S2. The slings on the front support beam of the last section of the cantilever box girder in the middle span of the large mileage and the front support beam of the last section of the cantilever box girder in the middle span of the small mileage are converted into precision rolled threaded steel bars one by one, with the conversion sequence being symmetrical from the inside to the outside.

[0040] S3, the outer sliding beam of the hanging basket of the last section of the small-midspan cantilever box girder is moved forward and anchored on the hanging basket of the last section of the large-midspan cantilever box girder, the outer side form of the last section of the small-midspan cantilever box girder is dragged on the outer sliding beam after moving forward until the outer side form of the last section of the large-midspan cantilever box girder is connected, forming the outer side form of the midspan closure section; the gap between the longitudinal distribution beams of the front supporting beams of the bottom baskets of the last sections of the large-midspan cantilever box girders and the gap between the longitudinal distribution beams of the front supporting beams of the bottom baskets of the last sections of the small-midspan cantilever box girders are longitudinally arranged with I-beams as the bottom form distribution beams of the midspan closure section, 10cm*10cm square wood is transversely laid on the I-beams with a gap of 15cm, bamboo plywood is laid on the square wood, forming the bottom form system of the midspan closure section, and steel plates or small steel plates are used for local gaps; the inner formwork of the midspan closure section adopts scattered wood formwork;

[0041] Process three, installing the pushing device, the pushing device including eight pushing jacks 30 and eight pushing rods 31; the maximum pushing force of each pushing jack 30 is 6000kN, and the maximum value during pushing is 3000kN; the pushing rod 31 adopts a spiral pipe with a length of 2410mm and a diameter of φ630*8mm, the spiral pipe is filled with C50 concrete, and the both ends of the spiral pipe are sealed with 10mm thick steel plates; four pushing rods 31 and four pushing jacks 30 are fixed on the bottom form system of the midspan closure section and correspondingly located at the junctions of the bottom plate 1 and the four webs 3, and the other four pushing rods 31 and four pushing jacks 30 are horizontally and correspondingly fixed between the end embedded pushing support embedded parts 10 of the four large-midspan cantilever last section box girders 10A and the end embedded pushing support embedded parts 10 of the corresponding small-midspan cantilever last section box girders 10B (see Figure 2 ), and the axes of the eight pushing rods 31 and the axes of the eight pushing jacks 30 are parallel to the axis of the girder body;

[0042] Process four, a plurality of counterweight water bags are placed on the bridge deck of the large-midspan cantilever last section box girder 10A and the bridge deck of the small-midspan cantilever last section box girder 10B respectively, then the counterweight water bags are filled with water to increase the weight, the weight of the counterweight water bags on the large-midspan cantilever last section box girder 10A and the weight of the counterweight water bags on the small-midspan cantilever last section box girder 10B are each half of the total weight of the midspan closure section concrete, then a plurality of oil pumps driving the eight pushing jacks are started at the time period with the lowest temperature in a day, the eight pushing jacks are loaded with pushing force according to the principles of symmetry, synchronization and grading, so that the steel box girder and the main pier completed by cantilever pouring are displaced, thereby adjusting the length of the midspan closure section 100 to be constructed, and the pushing force is loaded in stages according to the following principles:

[0043] The first loading is to 30% of the total jacking force, and the displacement of the pier top is observed for 15 minutes;

[0044] The second loading is to 50% of the total jacking force, and the length of the midspan closure segment and the displacement of the pier top are observed for 15 minutes;

[0045] The third loading is to 80% of the total jacking force, and the length of the midspan closure segment and the displacement of the pier top are continuously observed;

[0046] The fourth loading is to 100% of the total jacking force, that is, a total of 24000KN, and when the displacement of the pier top reaches 90% of the design requirement, the jacking is stopped;

[0047] After the jacking of the jacking jack is completed, the multiple oil pumps for driving the jacking jack are controlled to maintain stable pressure, the other end of the two sides of the stiff skeleton 21 on each stiff skeleton pre-embedded piece 20 is welded with the two rows of skeleton support steel plates 24 in the last section of the box girder segment 10B of the small-midspan cantilever or the upper part of the two rows of skeleton support steel plates 24 in the last section of the box girder segment 10A of the large-midspan cantilever, meanwhile, the top connecting plate 22 fixed at the head of the stiff skeleton 21 is filled with a welding seam at the intersection with the top of the corresponding skeleton support steel plate 24, so that the end of the large-midspan cantilever last section of the box girder segment 10A and the end of the small-midspan cantilever last section of the box girder segment 10B are locked (see Figure 6 and Figure 7 ), and the 20 stiff skeletons 21 are ensured to be parallel to the axis of the bridge; then the jacking force of the eight jacking jacks 30 is released, and the jacking device is removed, that is, the eight jacking jacks 30 and the eight jacking rod pieces 31 are removed;

[0048] The following steps are sequentially performed: installing the bottom die of the midspan closure segment, binding the bottom plate steel bars of the midspan closure segment, positioning the prestressed ducts in the bottom plate of the midspan closure segment, installing the inner die of the midspan closure segment 100, binding the top plate steel bars of the midspan closure segment, positioning the prestressed ducts in the top plate of the midspan closure segment, and threading the temporary closure prestressed steel strands;

[0049] The temporary closure prestressed steel strands are first tensioned, and then the midspan closure segment concrete is poured, and meanwhile, the water in the counterweight water bags on the large-midspan cantilever last section of the box girder segment 10A and the water in the counterweight water bags on the small-midspan cantilever last section of the box girder segment 10B are discharged, and the drainage speed (weight) is consistent with the pouring speed (weight) of the midspan closure segment concrete.

[0050] The construction method for the midspan closure segment of the long-span cable-stayed bridge has the characteristics of simple operation, small influence from the outside world, strong economy, low construction safety risk, effective release of the internal stress of the main girder, and more favorable to improve the deformation of the bridge and the pier.

[0051] The above examples are only for illustrating the present application, and are not intended to limit the present application. Those skilled in the art can make various changes or modifications without departing from the spirit and scope of the present application, and all equivalent technical solutions should belong to the scope of the present application, which should be defined by the claims.

Claims

1. A construction method for a closure segment of a long-span cable-stayed bridge, characterized in that, The construction method comprises the following procedures: Procedure one, embedding the embedded parts, i.e. embedding the embedded parts at the ends of the last box girder segments of the middle-span cantilever of the large and small mileage before pouring the concrete of the last box girder segments of the middle-span cantilever of the large and small mileage; the embedded parts comprise pushing support embedded parts and stiff skeleton embedded parts; the pushing support embedded parts are respectively embedded at the junctions of the top plates and all the webs at the ends of the last box girder segments of the middle-span cantilever of the large and small mileage, and each pushing support embedded part is fixed with the transverse steel bars in the beam body by electric welding; each pushing support embedded part is composed of three channel steels which are arranged in the form of an inverted isosceles triangle with a central connecting line; one stiff skeleton embedded part is embedded at each side of the top plate at the ends of the last box girder segments of the middle-span cantilever of the large and small mileage, one is embedded at each side of the top plate close to all the webs, one is embedded at each side of the bottom plate, one is embedded at each side of the bottom plate close to all the webs, and two are staggered embedded on all the webs; each stiff skeleton embedded part comprises two rows of skeleton support steel plates; the lower part of each skeleton support steel plate is a buried segment, two threaded steels are symmetrically and one above the other welded on the opposite surfaces of the buried segments of the two rows of skeleton support steel plates, and the two threaded steels on the two rows of skeleton support steel plates are welded with the transverse steel bars in the beam body; the stiff skeleton is assembled by two channel steels through a plurality of top connecting steel plates and bottom connecting steel plates arranged at intervals, one end of the stiff skeleton is welded with the upper parts of the two rows of skeleton support steel plates in the last box girder segment of the middle-span cantilever of the large mileage or the two rows of skeleton support steel plates in the last box girder segment of the middle-span cantilever of the small mileage, and the other end of the stiff skeleton is not welded with the upper parts of the two rows of skeleton support steel plates in the corresponding last box girder segment of the middle-span cantilever of the small mileage or the two rows of skeleton support steel plates in the last box girder segment of the middle-span cantilever of the large mileage; After all the embedded parts are embedded, the concrete of the last box girder segments of the middle-span cantilever of the large and small mileage is poured and cured; Procedure two, installing the middle-span closure segment formwork, comprising the following steps: S1, first, remove the platform at the front end of the hanging basket of the last box girder segment of the middle-span cantilever of the large and small mileage, then pull out the inner mold of the hanging basket of the last box girder segment of the middle-span cantilever of the large and small mileage, and then pull out the inner sliding beam of the hanging basket of the last box girder segment of the middle-span cantilever of the large mileage; S2, convert the lifting belts on the front support beams of the hanging baskets of the last box girder segments of the middle-span cantilever of the large and small mileage into finished rolled threaded steels one by one, and the conversion sequence is symmetrically converted from inside to outside; S3, the outer sliding beam of the last section of the small mileage mid-span cantilever box girder is moved forward and anchored on the last section of the large mileage mid-span cantilever box girder, the outer side form of the last section of the small mileage mid-span cantilever box girder is dragged on the outer sliding beam after moving forward until it is connected with the outer side form of the last section of the large mileage mid-span cantilever box girder to form the outer side form of the mid-span closure section; the longitudinal distribution beam of the front supporting beam of the bottom basket of the hanging basket of the last section of the large and small mileage mid-span cantilever box girder is longitudinally arranged as the bottom form distribution beam of the mid-span closure section, the square wood is transversely laid on the I-beam, and the bamboo plywood is laid on the square wood to form the bottom form system of the mid-span closure section; the inner form of the mid-span closure section is scattered and assembled; Process three, install the pushing device, the pushing device includes a plurality of horizontal pushing jacks and matched pushing rod members which are horizontally installed on the bottom form system of the mid-span closure section and correspondingly located at the junction of the bottom plate and all the web plates, and the pushing device further includes a plurality of horizontal pushing jacks and matched pushing rod members which are fixed between the top pushing bracket embedded members embedded at the ends of the last sections of the large and small mileage mid-span cantilever box girders; Process four, first, place the counterweight water bags on the bridge deck of the last sections of the large and small mileage mid-span cantilever box girders respectively and uniformly, then increase the weight of the counterweight water bags by adding water, so that the weight of the counterweight water bags on the last sections of the large and small mileage mid-span cantilever box girders is half of the total weight of the mid-span closure section concrete respectively, and then simultaneously start a plurality of oil pumps driving all the pushing jacks at the time period when the air temperature is the lowest in a day to load the pushing force for all the pushing jacks; Process five, after the pushing jacks are loaded, control the plurality of oil pumps driving the pushing jacks to maintain stable pressure, first, weld the other end of the two sides of the stiff skeleton on each stiff skeleton embedded member to the two rows of skeleton support steel plates in the last section of the small mileage mid-span cantilever box girder or the upper part of the two rows of skeleton support steel plates in the last section of the large mileage mid-span cantilever box girder, and simultaneously fill the intersection of the top connecting plate fixed to the head of the stiff skeleton and the top of the corresponding skeleton support steel plate with a weld to lock the ends of the last sections of the large and small mileage mid-span cantilever box girders, then release the pushing force of all the pushing jacks, and then remove the pushing device, that is, remove all the pushing jacks and all the pushing rod members; Process six, the following steps are sequentially performed: installing the bottom form of the mid-span closure section, binding the bottom plate reinforcement of the mid-span closure section, positioning the prestressed pipe in the bottom plate of the mid-span closure section, installing the inner form of the mid-span closure section, binding the top plate reinforcement of the mid-span closure section, positioning the prestressed pipe in the top plate of the mid-span closure section, and threading the temporary closure prestressed steel strand; Process seven, first, tension the temporary closure prestressed steel strand, then pour the mid-span closure section concrete, and simultaneously drain the water in the counterweight water bags on the last sections of the large and small mileage mid-span cantilever box girders, and the drainage weight is consistent with the pouring weight of the mid-span closure section concrete.

2. The construction method for the closure segment of a long-span cable-stayed bridge according to claim 1, characterized in that, When process one is performed, the two ends of the threaded steel in the stiff skeleton embedded member are provided with hooks.

3. The construction method for the closure segment of a long-span cable-stayed bridge according to claim 1, characterized in that, When process three is performed, the pushing rod member adopts a spiral pipe, the spiral pipe is filled with concrete, and the two ends of the spiral pipe are sealed with steel plates.

4. The construction method for the closure segment of a long-span cable-stayed bridge according to claim 1, characterized in that, When performing step four, the jacking force should be applied to all jacks according to the principles of symmetry, synchronization, and gradation, and the jacking force should be applied in stages according to the following principles: The load was initially applied up to 30% of the total thrust, and the load was held for 15 minutes to observe the displacement of the pier top. The second loading was applied to 50% of the total thrust, and the load was held for 15 minutes to observe the length of the mid-span closure section and the displacement of the pier top. When the load is applied for the third time to 80% of the total thrust, continue to observe the length of the mid-span closure section and the displacement of the pier top. The fourth loading is applied to 100% of the total jacking force. When the displacement at the top of the pier reaches 90% of the design requirement, the jacking is stopped.

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