CN115287992A - A composite box girder structure and construction method - Google Patents

Abstract

The invention relates to the technical field of bridge engineering, in particular to a combined box girder structure and a construction method thereof. The combined box girder has light hoisting weight, convenient construction, strong anti-cracking capability of the web plate and low maintenance cost; meanwhile, the construction method is simple and convenient.

Description

A composite box girder structure and its construction method

technical field

The invention relates to the technical field of bridge engineering, in particular to a composite box girder structure and a construction method.

Background technique

Steel box girder has the advantages of light weight and fast construction, and is the main girder form commonly used in bridges in my country. However, steel box girder is prone to coating deterioration, steel corrosion, fatigue damage, and bridge deck pavement is easily damaged. The cost of regular painting and maintenance is also higher. However, the application of concrete beams in bridges is limited due to its heavy weight, high section height, easy cracking of the web, and difficulty in hoisting. Compared with the steel box girder, although the corrugated steel web-concrete composite girder has relatively light weight, there are still problems such as the web steel is easily corroded and requires regular maintenance.

For this reason, a new type of composite box girder structure is proposed, the web of which is made of steel coated with ultra-high performance concrete (UHPC for short), and the top and bottom plates are still made of prestressed ordinary concrete structure. UHPC is a new type of building material with high strength, corrosion resistance and penetration resistance. The web of the new composite box girder structure is made of high-strength steel and UHPC, and its cross-sectional size is smaller than that of the traditional prestressed concrete box girder. There are many, which can significantly reduce the structural weight of the box girder, and have greater stiffness and bearing capacity; the section steel is embedded in the UHPC, which can avoid the corrosion of the web, improve the rigidity and fatigue resistance of the structure, and reduce maintenance costs.

In terms of construction methods, the web and bottom slab steel bars of the new composite box girder are all prefabricated in the factory. After being transported to the site as a whole, they are hoisted by trucks, and then the portal supports are erected by using the caps of the bridge piers to carry out the top and bottom slab concrete. Cast-in-place construction. Compared with the traditional prestressed concrete box girder, the hoisting weight of the prefabricated part of the new composite box girder is very light, and it can be easily hoisted by a car; the cast-in-place concrete only includes the top and bottom slabs, and relatively simple portal brackets can be used, and The bracket uses the cap as the foundation, which can greatly reduce the construction cost of the bracket compared with the traditional full hall bracket; the steel bars of the bottom plate and the web are prefabricated in the factory, which can greatly reduce the workload of tying the steel bars on site, and can achieve fast purpose of construction. Compared with the traditional steel box girder, the new composite box girder only uses section steel at the web position, which can greatly reduce the workload of on-site welding and anti-corrosion coating of steel materials, which is conducive to energy saving and environmental protection.

Contents of the invention

The object of the present invention is to provide a combined box girder structure and construction method, the combined box girder has light hoisting weight, convenient construction, strong web crack resistance, low maintenance cost and simple construction method.

The technical solution of the present invention is: a combined box girder structure, including a bottom plate, prefabricated webs are arranged on both sides of the bottom plate, a top plate is arranged above the two prefabricated webs, and a steel plate is arranged inside the prefabricated web The upper and lower ends of the steel frame pass through the prefabricated web respectively to connect with the bottom plate and the top plate, between the two prefabricated webs, a plurality of cast-in-place transverse diaphragms are arranged at intervals along the length direction of the composite box girder, and located at Prefabricated transverse diaphragms are arranged at the fulcrums at both ends of the composite box girder.

Further, the prefabricated web, the steel frame, the prefabricated diaphragm, the stirrups of the bottom plate, and the longitudinal reinforcement of the bottom plate form a prefabricated hoisting structure.

Further, the two ends of the combined box girder along the direction of the bridge are provided with pier top cast-in-place sections, and the combined box girders of two adjacent spans in one connection are connected through the pier top cast-in-place sections.

Further, the cast-in-place section of the top of the pier is provided with steel bars for the cast-in-place section of the top of the pier, wherein some of the steel bars of the cast-in-place section of the top of the pier are connected with some longitudinal reinforcement of the top plate, longitudinal reinforcement of the prefabricated web, and longitudinal reinforcement of the bottom plate.

Further, the prefabricated diaphragm and the cast-in-place diaphragm are both provided with reinforcing bars for the diaphragm, and part of the reinforcing bars of the diaphragm extend into the prefabricated web, top plate and bottom plate.

Further, the roof is a cast-in-place structure, including roof stirrups and roof longitudinal reinforcement; only when the bridging system of the bridge is a continuous system, the middle of the roof is provided with longitudinal bridge-direction roof prestressed steel tendons at intervals along the transverse bridge direction , the top plate tooth block is arranged on the bottom surface of the top plate.

Further, the prefabricated web is provided with web stirrups, web longitudinal reinforcement, stalk axillary reinforcement and section steel web strengthening reinforcement; the base plate is a cast-in-place structure, including the stirrups of the base plate and the longitudinal reinforcement of the base plate, A row of prestressed steel tendons of the bottom plate in the direction of the longitudinal bridge are arranged in the bottom plate along the horizontal bridge direction, and a bottom plate tooth block is arranged on the upper side of the bottom plate; some stirrups of the bottom plate extend into the prefabricated web.

Further, the steel frame includes a steel frame web arranged in the prefabricated web, the upper end of the steel frame web protrudes into the top plate and is provided with a steel frame upper flange, and the steel frame upper flange is along the length direction The upper flange studs are welded at intervals, the upper and lower parts of both sides of the steel frame web are welded with web studs at intervals along the length direction, and the lower end of the steel frame web extends into the bottom plate and is provided with a steel frame lower flange.

Further, the steel frame web is provided with a mid-span web hole and a beam end web hole, and the radius of the beam end web hole is smaller than the mid-span web hole; each mid-span web hole and beam end web hole A stiffener is provided between them, and a stiffener hole is arranged on the stiffener, and the longitudinal reinforcement of the prefabricated web passes through the hole of the stiffener and is connected as a whole with a PBL key.

A construction method for a combined box girder, comprising a combined box girder structure, the steps are as follows:

Step 1: Determine the bridge span and bridge system, and determine the specific dimensions of each component according to the span;

Step 2: Bind the stirrups of the bottom plate and the longitudinal reinforcement of the bottom plate in the prefabrication yard, and then install the prefabricated but not welded steel frame with flange studs, bind the web stirrups of the prefabricated web, the longitudinal reinforcement of the web, Stem axillary steel bars and section steel web reinforcement bars form an integral steel frame and steel bar skeleton, and bind the steel bars of prefabricated transverse diaphragms and cast-in-place transverse diaphragms;

Step 3: Concrete two prefabricated webs and prefabricated diaphragms each set at the fulcrum to form a prefabricated hoisting structure, and maintain it in the prefabrication yard according to relevant specifications; after the material strength reaches the specified value required in the specification, transport to the construction site;

Step 4: Set up portal brackets on the caps of the substructure at the site, and then hoist the prefabricated hoisting structure to the designed main beam position through the hoisting equipment. For the temporary support of the hoisting structure, pour the bottom plate of the composite box girder. After the material strength reaches the specified value in the specification, the prestressed steel strands of the bottom plate are stretched and anchored on the tooth block of the bottom plate; The upper flange of the steel frame is welded with studs on the upper flange, and the roof stirrups and longitudinal steel bars of the roof are bound, and the roof is poured; Casting section, which connects the combined box girders of two adjacent spans in one connection; when the bridge forming system of the bridge is a continuous system, it is also necessary to set and tension the prestressed steel tendons of the roof and anchor them on the roof tooth block.

Compared with the prior art, the present invention has the following advantages:

1. The composite box girder decomposes the structure into a prefabricated hoisting part and a cast-in-place part by making a prefabricated web and pre-binding some steel bars, combining the advantages of both prefabricated and cast-in-place construction methods, and reducing the cost of The construction difficulty of the cast-in-place construction method greatly improves the construction efficiency on site; because the weight of the web is greatly reduced, the hoisting weight is light, and small hoisting equipment can be used in the hoisting work, which saves hoisting costs and has a wide range of applications .

2. During the construction of the composite box girder, portal brackets can be erected on the caps of the substructure, whether it is a dry bridge or a bridge crossing a river, this structure can be used for construction; this structure can reduce the size of the structure, reduce the weight of the structure and the structure Internal force, improve the spanning capacity and bending resistance of the bridge, significantly reduce the cracking probability of the composite box girder and the structural deformation under the load; and compared with the steel structure, it has higher corrosion resistance, fire resistance and corrosion resistance, which can improve The structure is safe and durable, and the bridge deck is not easily damaged; both steel and UHPC are high-performance materials, and the SUHPC structure combining the two also has a high load-bearing capacity.

Description of drawings

Fig. 1 is the prefabricated hoisting structure schematic diagram of composite box girder of the present invention;

Fig. 2 is the facade structure schematic diagram of composite box girder of the present invention;

Fig. 3 is the schematic diagram of the prestressed steel beam facade arrangement of the composite box girder of the present invention;

Fig. 4 is the I-I sectional view among Fig. 2;

Fig. 5 is II-II sectional view among Fig. 2;

Fig. 6 is the sectional reinforcement diagram of the I-I section in Fig. 2;

Fig. 7 is the cross-sectional reinforcement diagram of the II-II section in Fig. 2;

Fig. 8 is a structural schematic diagram of a prefabricated diaphragm or a cast-in-place diaphragm of the present invention;

Fig. 9 is a cross-sectional schematic diagram of the cast-in-place section of the pier top of the present invention;

Fig. 10 is the schematic diagram of steel frame facade structure of the present invention;

Fig. 11 is a schematic diagram of a cross-sectional structure of a steel frame of the present invention;

Fig. 12 is a structural schematic diagram of steel web hole reinforced reinforcement of the present invention;

In the figure: 1, roof; 11, roof stirrup; 12, roof longitudinal reinforcement; 13, roof prestressed beam; 14, roof tooth block;

2. Steel frame; 21. Steel frame web; 211. Mid-span web hole; 212. Beam end web hole; 22. Steel frame lower flange; 23. Steel frame upper flange; 24. Upper flange studs ; 25, web pegs; 26, stiffeners; 261, stiffener holes;

3. Prefabricated web; 311. Web stirrup; 312. Web longitudinal reinforcement; 313. Stem axillary reinforcement;

4. Bottom plate; 41. The stirrup of the bottom plate; 42. The longitudinal reinforcement of the bottom plate; 43. The prestressed steel beam of the bottom plate; 44. The tooth block of the bottom plate;

5. Prefabricated transverse diaphragm; 5', cast-in-place transverse diaphragm; 51. Reinforcement of transverse diaphragm;

6. Reinforcing bars for section steel webs; 61. Reinforcement mesh; 62. Longitudinal short bars;

7. The cast-in-place section at the top of the pier; 71. The steel bars for the cast-in-place section at the top of the pier;

8. Thickened layer.

Detailed ways

In order to make the above-mentioned features and advantages of the present invention easier to understand, the following specific embodiments are described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.

Refer to Figure 1 to Figure 12

A composite box girder structure, comprising a bottom plate 4, prefabricated webs 3 are arranged on both sides of the bottom plate 4, a top plate 1 is arranged above the two prefabricated webs 3, steel frames are arranged inside the prefabricated webs 3 2. The upper and lower ends of the steel frame 2 pass through the prefabricated web 3 to connect with the bottom plate 4 and the top plate 1, and between the two prefabricated webs 3, a plurality of cast-in-place horizontal beams are arranged at intervals along the length direction of the composite box girder. The diaphragm 5', and the prefabricated transverse diaphragm 5 is arranged at the fulcrums at both ends of the composite box girder.

In this embodiment, the prefabricated web 3 , steel frame 2 , prefabricated diaphragm 5 , stirrups 41 of the bottom plate, and longitudinal steel bars 42 of the bottom plate form a prefabricated hoisting structure, and the rest of the structures are cast-in-place structures.

By combining the prefabricated web 3, the steel frame 2, the stirrup 41 of the bottom plate, the longitudinal reinforcement 42 of the bottom plate, and the prefabricated transverse partition 5 to form a prefabricated hoisting structure, not only the structural part can be prefabricated in the factory, the construction speed can be improved, and it can also be used as Stress structure during construction. By arranging the steel frame 2 in the prefabricated web 3, the weight of the web is greatly reduced, which facilitates hoisting of small equipment.

In this embodiment, the two ends of the composite box girder along the direction of the bridge are provided with pier top cast-in-place sections 7, and the composite box girders of two adjacent spans in one connection are connected through the pier top cast-in-place sections. The cast-in-place section of the pier top is provided with steel bars 71 for the cast-in-place section of the pier top, wherein part of the steel bars 71 of the cast-in-place section of the pier top are connected with some longitudinal reinforcement bars 12 of the roof, longitudinal reinforcement bars 312 of the prefabricated web, and longitudinal reinforcement bars 42 of the bottom plate .

In this embodiment, the thickness of the cast-in-place section 7 at the top of the pier is 1m-2m, and the material is ordinary concrete.

In this embodiment, both the prefabricated diaphragm and the cast-in-place diaphragm are provided with reinforcing bars 61 for the diaphragm, and part of the reinforcing bars 61 of the diaphragm extend into the prefabricated web 3 , top plate 1 and bottom plate 4 .

In this embodiment, the thicknesses of the prefabricated transverse diaphragm 5 and the cast-in-place transverse diaphragm 5' are both 0.2m-0.5m, and the prefabricated transverse diaphragm 5 must be installed Partition plates 5' are evenly arranged at intervals of 10m-30m along the length direction of the composite box girder. The top plate 1 and the bottom plate 4 are provided with a thickened layer 8 near the fulcrum, the thickness of the thickened layer 8 is 0.1m-0.3m, and the prefabricated transverse diaphragm 5 and the cast-in-place transverse diaphragm 5' are connected with the thickened The material of layer 8 is ordinary concrete.

By setting the prefabricated transverse diaphragm 5 at the fulcrums at both ends, it can not only be used as a temporary support after the prefabricated hoisting structure is hoisted, but also can be used as a construction template for the cast-in-place section 7 of the pier top; by setting a plurality of cast-in-place transverse diaphragms 5' , can also improve the integrity of the composite box girder.

In this embodiment, the roof 1 is a cast-in-place structure, including roof stirrups 11 and roof longitudinal steel bars 12; only when the bridging system of the bridge is a continuous system, the middle of the roof is provided with longitudinal bridges at intervals along the horizontal bridge direction. The top plate prestressed steel bundle 13, the top plate tooth block 14 is arranged on the bottom surface of the top plate, and the top plate prestressed steel beam 13 is anchored on the top plate tooth block 14.

In this embodiment, the thickness of the top plate 1 is 0.15m-0.4m, and the material of the top plate 1 is ordinary concrete.

In this embodiment, the prefabricated web 3 is a prefabricated structure, and the prefabricated web 3 is provided with web stirrups 311, web longitudinal reinforcement 312, stem armpit reinforcement 313 and section steel web reinforcement reinforcement 6, and the stem armpit The reinforcement is arranged at the corner where the prefabricated web and the roof are connected. Reinforcing steel bars through section steel web prevents web cracking, prevents concrete from falling, and reduces stress concentration.

In this embodiment, the thickness of the single prefabricated web is 0.15m-0.4m, and the material of the prefabricated web 3 is ultra-high performance concrete.

In this embodiment, the base plate 4 is a cast-in-place structure, including the stirrups 41 of the base plate bound in advance in the factory and the longitudinal steel bars 42 of the base plate bound in advance in the factory. The bottom plate prestressed steel bundle 43 in the longitudinal bridge direction is located on the upper side of the bottom plate with a bottom plate tooth block 44; part of the stirrups 41 of the bottom plate extend into the prefabricated web 3 and are connected with the prefabricated web.

In this embodiment, the thickness of the bottom plate 4 is 0.15m-0.4m, and the material of the bottom plate 4 is ordinary concrete.

In this embodiment, the thickness of the steel frame 2 is 0.01m-0.05m, and the material is ordinary carbon structural steel. The steel frame 2 includes a steel frame web 21 arranged in the prefabricated web 3 , the upper end of the steel frame web 21 extends into the top plate 1 and is provided with a steel frame upper flange 23 , and the steel frame upper wing 23 The edge is welded with upper flange studs 24 at intervals along the length direction, and the upper and lower parts of both sides of the steel frame web 21 are welded with web studs 25 at intervals along the length direction, and the lower end of the steel frame web extends into the bottom plate 4 and sets Steel rib lower flange 22 is arranged. The vertical distance between the upper flange studs 24 and the web studs 25 is 0.05m-0.5m, and the material is ML15 or ML15A1 steel.

In this embodiment, the steel frame web 21 is provided with a circular mid-span web hole 211 and a beam end web hole 212, the radius of the beam end web hole 212 is smaller than the radius of the mid-span web hole 211, The radius of the beam end web hole 211 is 0.1m-0.8m; the radius of the mid-span web hole 212 is 0.3m-1.2m. A stiffener 26 is provided between each mid-span web hole 211 and the beam end web hole 212, and a stiffener hole 261 is provided on the stiffener 26, and the longitudinal steel bars 312 of the prefabricated web pass through the stiffener hole 261 and adopt PBL keys are connected as a whole. The profiled steel web reinforcing bars include steel bar mesh 61 and transverse short bars 62 . In order to improve the crack resistance of the web, the reinforced steel bars of the shaped steel web are arranged along the entire section of the web along the direction of the bridge (ie, the driving direction). The short transverse steel bar 62 needs to be provided only when the reinforced steel bar of the shaped steel web is arranged in the mid-span web hole 211 or the beam end web hole 212 .

By arranging the steel frame lower flange 21 and the steel frame upper flange 22 on the steel frame 2, the steel frame 2 can be better placed and fixed in the steel frame, making it a whole, preventing the gap between the steel and concrete materials. The slippage makes the steel more fully participate in the bearing.

By setting the upper flange stud 24 extending into the roof 1 on the upper flange 22 of the steel frame, it connects the steel frame 2 and the roof 1 as a shear connector, which improves the shear resistance of the structure and further prevents the roof from being damaged. Slip between 1 and steel frame 2.

By setting the mid-span web hole 211 and the beam end web hole 212 on the steel frame web 21, the material is saved, the dead weight of the structure is reduced, and the manufacturing cost is reduced.

Through the stiffener 26 and the web longitudinal reinforcement 312 passing through the stiffener hole 261, not only the integrity of the section steel and the reinforcement is strengthened, but also the stress concentration phenomenon between the mid-span web hole 211 and the beam end web hole 212 is reduced.

By arranging the reinforced steel bar 6 of the shaped steel web, not only the bearing capacity of the mid-span web hole 211 and the beam end web hole 212 is strengthened, but also the concrete material at the hole can be prevented from falling when the structure is damaged and the anti-resistance of the prefabricated web 3 can be strengthened. cracking ability.

A construction method for a combined box girder, comprising a combined box girder structure, the steps are as follows:

Step 1: Determine the bridge span and bridge system, and determine the specific size of each component according to the span.

Step 2: Bind the stirrups 41 of the bottom plate and the longitudinal steel bars 42 of the bottom plate in the prefabrication yard, then install the prefabricated steel frame 2 that has not been welded with the flange studs 24, and bind the web stirrups 311 of the prefabricated web 3 , web longitudinal reinforcing bar 312, stalk axillary reinforcing bar 313 and shaped steel web reinforcing bar 6 to form an integral steel frame 2 and reinforcing bar skeleton, and bind the reinforcing bar 61 of the prefabricated transverse diaphragm and the cast-in-place transverse diaphragm.

Step 3: Pouring two prefabricated webs 3 and prefabricated transverse diaphragms 5 each set at the fulcrum to form a prefabricated hoisting structure, and maintain it in the prefabrication yard in accordance with relevant specifications; wait until the material strength reaches the specified value required in the specification After that, the web prestressed steel tendons are stretched and transported to the construction site.

Step 4: Set up portal supports on the caps of the substructure at the site, and then hoist the prefabricated hoisting structure to the designed main beam position through hoisting equipment. At this time, the prefabricated transverse diaphragm 5 set at the fulcrum is used as For the temporary support of the prefabricated hoisting structure, pour the bottom plate 4 of the composite box girder. After the material strength reaches the specified value required in the specification, the prestressed steel beam 43 of the bottom plate is stretched and anchored on the tooth block 44 of the bottom plate; Partition plate 5'; weld upper flange studs 24 on the upper flange 23 of the steel frame, bind the top plate stirrup 11 and the longitudinal steel bar 12 of the roof, and pour the roof 1; bind the steel bar 71 of the cast-in-place section on the top of the pier, and set it at the fulcrum The prefabricated diaphragm 5 is used as a template to pour the cast-in-place section 7 on the top of the pier to connect the combined box girders of two adjacent spans in one connection; The top plate is prestressed and anchored to the top plate tooth block.

Embodiment one:

Bridges often need to be built across rivers. In traditional construction methods, cofferdams are generally set in rivers to build full-height supports. The structure proposed by the present invention is used for bridges across rivers. Since the inventive structure is decomposed into the prefabricated hoisting part and the cast-in-place part, combining the advantages of both the prefabricated construction method and the cast-in-place construction method, a relatively simple portal support can be built on the cap of the substructure during construction, reducing the cost of the prefabricated construction method. Compared with the construction difficulty of cast-in-place construction method, the cost of cofferdam and support and the time of building cofferdam are saved, and the construction progress is accelerated.

Embodiment two:

When building a dry bridge in the middle, because it is inconvenient to use large-scale hoisting equipment in the middle, the light weight of the structure is particularly important in the construction of the bridge, and the structure proposed by the present invention is used for the dry bridge. Since the present invention decomposes the structure into a prefabricated hoisting part and a cast-in-place part, and at the same time, the web adopts high-strength UHPC and section steel, the weight of the hoisting structure is greatly reduced, and the car can be used for hoisting during construction, which saves hoisting costs; roof, The steel bars of the bottom plate and the web are prefabricated in the factory, which can greatly reduce the workload of binding steel bars on site. The construction speed is fast, the construction period is short, and the impact of construction on traffic is greatly reduced.

The above descriptions are only preferred embodiments of the present invention. For those of ordinary skill in the art, according to the teachings of the present invention, designing different forms of combined box girder structures and construction methods does not require creative work. All equivalent changes, modifications, replacements and modifications made according to the patent scope of the present invention without departing from the principle and spirit of the present invention shall fall within the scope of the present invention.

Claims (10)

1. The utility model provides a combination box girder structure, includes the bottom plate, its characterized in that, the both sides of bottom plate all are provided with prefabricated web, and the top that is located two prefabricated webs is provided with the roof, be provided with the reinforcing bar in the prefabricated web, the prefabricated web is worn out respectively to the upper and lower end of reinforcing bar and is connected with bottom plate, roof, is located and is provided with a plurality of cast-in-place cross slab along the length direction interval of combination box girder between two prefabricated webs, and the both ends fulcrum department that is located combination box girder is provided with prefabricated cross slab.

2. The assembled box girder structure of claim 1, wherein the prefabricated web plate, the steel ribs, the prefabricated diaphragm plate, the stirrups of the bottom plate and the longitudinal steel bars of the bottom plate form a prefabricated hoisting structure.

3. A combined box girder structure according to claim 1 or 2, wherein pier top cast-in-place sections are provided at both ends of the combined box girder in the bridge direction, and the combined box girders of two adjacent spans in a unit are connected through the pier top cast-in-place sections.

4. The combination box girder structure of claim 3, wherein the pier top cast-in-place section is internally provided with pier top cast-in-place section steel bars, and part of the pier top cast-in-place section steel bars are connected with part of longitudinal steel bars of the top plate, longitudinal steel bars of the prefabricated web plate and longitudinal steel bars of the bottom plate.

5. A composite box girder structure according to claim 1, 2 or 4 wherein the prefabricated diaphragm plates and the cast-in-place diaphragm plates are provided with diaphragm plate reinforcing bars, and part of the diaphragm plate reinforcing bars extend into the prefabricated web plate, the top plate and the bottom plate.

6. The composite box girder structure according to claim 1, wherein the top plate is a cast-in-place structure comprising a top plate stirrup and a top plate longitudinal reinforcement; and only when the bridge forming system of the bridge is a continuous system, the middle part of the top plate is provided with top plate prestressed steel bundles in the longitudinal bridge direction at intervals along the transverse bridge direction, and the bottom surface of the top plate is provided with top plate tooth blocks.

7. The combined box girder structure of claim 1, 2, 4 or 6, wherein a web stirrup, a web longitudinal steel bar, a peduncle steel bar and a section steel web reinforcing steel bar are arranged in the prefabricated web plate; the bottom plate is of a cast-in-place structure and comprises stirrups of the bottom plate and longitudinal steel bars of the bottom plate, a row of longitudinal bridge direction bottom plate prestressed steel bundles are arranged in the bottom plate along a transverse bridge direction, and bottom plate tooth blocks are arranged on the upper side of the bottom plate; the stirrups of part bottom plate stretch into prefabricated web.

8. The combined box girder structure of claim 7, wherein the steel skeleton comprises a steel skeleton web arranged in the prefabricated web, the upper end of the steel skeleton web extends into the top plate and is provided with a steel skeleton upper flange, the steel skeleton upper flange is welded with upper flange studs at intervals along the length direction, the web studs are welded at intervals along the length direction on the upper and lower parts of two side surfaces of the steel skeleton web, and the lower end of the steel skeleton web extends into the bottom plate and is provided with a steel skeleton lower flange.

9. The composite box girder structure of claim 8, wherein the steel skeleton web is provided with a mid-span web hole and a beam end web hole, and the radius of the beam end web hole is smaller than that of the mid-span web hole; be equipped with the stiffening rib between web hole and beam-ends web hole in each strides, be equipped with the stiffening rib hole on the stiffening rib, the longitudinal reinforcement of prefabricated web passes the stiffening rib hole and adopts the PBL key-type connection as whole.

10. A construction method of a composite box girder comprising a composite box girder structure according to claim 9, characterized by comprising the steps of:

the method comprises the following steps: determining the span of a bridge and a bridge system, and determining the specific size of each part according to the span;

step two: binding stirrups of the bottom plate and longitudinal steel bars of the bottom plate in a prefabricated yard, then installing steel ribs which are prefabricated in advance but not welded with upper flange studs, binding web stirrups of the prefabricated web, longitudinal steel bars of the web, peduncle steel bars and reinforcing steel bars of the profile steel web to form an integral steel rib and steel bar framework, and binding the steel bars of the prefabricated diaphragm plate and the cast-in-situ diaphragm plate;

step three: pouring two prefabricated webs and prefabricated diaphragm plates arranged at the branch points respectively to form a prefabricated hoisting structure, and maintaining the prefabricated hoisting structure in a prefabricated field according to relevant specifications; after the strength of the material reaches a specified value required in the specification, transporting the material to a construction site;

step four: a portal support is arranged on a bearing platform of a lower structure on site, then a prefabricated hoisting structure is hoisted to the designed main beam position through hoisting equipment, at the moment, a prefabricated diaphragm plate arranged at a fulcrum is used as a temporary support of the prefabricated hoisting structure, a bottom plate of the combined box girder is poured, and after the material strength reaches a specified value required in the specification, the Zhang Lade plate prestressed steel bundles are anchored on the bottom plate tooth blocks; pouring the residual cast-in-place diaphragm plate; welding an upper flange stud on the upper flange of the steel rib, binding a top plate stirrup and a top plate longitudinal steel bar, and pouring a top plate; binding reinforcing steel bars of the pier top cast-in-place section, pouring the pier top cast-in-place section by taking the prefabricated transverse partition plate arranged at the fulcrum as a template, and connecting the adjacent two-span combined box girders in one block; when the bridge forming system of the bridge is a continuous system, the prestressed steel bundles of the tensioning top plate are required to be arranged and anchored on the tooth blocks of the top plate.

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