A composite box beam structure and construction method

Abstract

The present invention relates to the technical field of bridge engineering, and in particular to a composite box girder structure and construction method, comprising a bottom plate, both sides of the bottom plate are provided with prefabricated webs, a top plate is provided above the two prefabricated webs, a steel frame is provided inside the prefabricated webs, the upper and lower ends of the steel frame respectively pass through the prefabricated webs and are connected to the bottom plate and the top plate, a plurality of cast-in-place diaphragms are provided at intervals along the length direction of the composite box girder between the two prefabricated webs, and prefabricated diaphragms are provided at the two end fulcrums of the composite box girder. The composite box girder has light hoisting weight, convenient construction, strong web crack resistance, and low maintenance cost; and the construction method is simple.

Description

Technical Field

[0001] The invention relates to the technical field of bridge engineering, and in particular to a combined box girder structure and a construction method. Background Art

[0002] Steel box girders have the advantages of light weight and fast construction, and are a common main beam form for bridges in my country. However, steel box girders are prone to paint degradation, steel corrosion, fatigue damage, and easy damage to the bridge deck pavement. The cost of regular painting and maintenance after construction is also high. The application of concrete beams in bridges is limited due to their large weight, high cross-sectional height, easy cracking of the web, and difficulty in lifting. Compared with steel box girders, although the corrugated steel web-concrete composite beam has a relatively light weight, it still has problems such as the web steel is easily corroded and requires regular maintenance.

[0003] To this end, a new type of composite box girder structure is proposed, whose web is made of steel wrapped with ultra-high performance concrete (UHPC), 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 anti-permeability. The web of the new composite box girder structure is made of high-strength steel and UHPC. Its cross-sectional size is much smaller than that of the web of the traditional prestressed concrete box girder, which can significantly reduce the structural deadweight of the box girder and has greater rigidity and bearing capacity; the steel is buried inside the UHPC, which can avoid corrosion of the web, improve the rigidity and fatigue resistance of the structure, and reduce maintenance costs.

[0004] In terms of construction methods, the steel bars of the web and bottom plates of the new composite box girder are prefabricated in the factory. After being transported to the site as a whole, they are hoisted by trucks, and then the piers of the bridge abutments are used to set up portal brackets for cast-in-place construction of the top and bottom plates. Compared with traditional prestressed concrete box girders, the prefabricated parts of the new composite box girder are very light in weight and can be easily hoisted by trucks; the cast-in-place concrete only includes the top and bottom plates, and relatively simple portal brackets can be used. The brackets use the piers as the foundation, which can greatly reduce the construction cost of the brackets compared with traditional full-height brackets; the steel bars of the bottom plate are prefabricated in the factory together with the webs, which can greatly reduce the workload of on-site steel bar binding and achieve the purpose of rapid construction. Compared with traditional steel box girders, the new composite box girder only uses steel sections at the web position, which can greatly reduce the workload of on-site welding and anti-corrosion coating of steel materials, which is beneficial to energy conservation and environmental protection. Summary of the invention

[0005] The purpose of the present invention is to provide a composite box girder structure and a construction method, wherein the composite box girder has light hoisting weight, convenient construction, strong web crack resistance, and low maintenance cost; and the construction method is simple.

[0006] The technical solution of the present invention is: a composite box girder structure, including a bottom plate, both sides of the bottom plate are provided with precast webs, a top plate is provided above the two precast webs, steel frames are provided inside the precast webs, the upper and lower ends of the steel frames respectively pass through the precast webs and are connected to the bottom plate and the top plate, a plurality of cast-in-place diaphragms are provided between the two precast webs at intervals along the length direction of the composite box girder, and precast diaphragms are provided at the two end supports of the composite box girder.

[0007] Furthermore, the prefabricated web, steel frame, prefabricated transverse diaphragm, stirrups of the bottom plate, and longitudinal steel bars of the bottom plate constitute a prefabricated hoisting structure.

[0008] Furthermore, cast-in-place sections on pier tops are provided at both ends of the composite box girder in the direction along the bridge, and composite box girders of two adjacent spans in one unit are connected via the cast-in-place sections on the pier tops.

[0009] Furthermore, the pier top cast-in-place section is provided with pier top cast-in-place section steel bars, wherein part of the pier top cast-in-place section steel bars are connected to part of the longitudinal steel bars of the top plate, the longitudinal steel bars of the prefabricated web plate, and the longitudinal steel bars of the bottom plate.

[0010] Furthermore, both the prefabricated diaphragms and the cast-in-place diaphragms are provided with diaphragm steel bars, and part of the diaphragm steel bars extend into the prefabricated webs, top plates and bottom plates.

[0011] Furthermore, the top plate is a cast-in-place structure, including top plate stirrups and top plate longitudinal steel bars; only when the bridge system of the bridge is a continuous system, top plate prestressed steel strands in the longitudinal direction of the bridge are arranged at intervals in the middle part of the top plate along the transverse direction of the bridge, and top plate tooth blocks are arranged on the bottom surface of the top plate.

[0012] Furthermore, the prefabricated web is provided with web stirrups, web longitudinal steel bars, axil steel bars and steel web reinforcing steel bars; the bottom plate is a cast-in-place structure, including stirrups of the bottom plate and longitudinal steel bars of the bottom plate, a row of bottom plate prestressed steel strands in the longitudinal direction of the bottom plate are arranged along the transverse direction of the bridge, and bottom plate teeth are arranged on the upper side of the bottom plate; part of the stirrups of the bottom plate extend into the prefabricated web.

[0013] Furthermore, the steel frame includes a steel frame web arranged in a prefabricated web, the upper end of the steel frame web extends into the top plate and is provided with a steel frame upper flange, the steel frame upper flange is welded with upper flange bolts at intervals along the length direction, the upper and lower parts of both side surfaces of the steel frame web are welded with web bolts 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.

[0014] Furthermore, the steel frame web is provided with mid-span web holes and beam end web holes, and the radius of the beam end web holes is smaller than the mid-span web holes; stiffening ribs are provided between each mid-span web hole and beam end web hole, and stiffening rib holes are provided on the stiffening ribs, and the longitudinal steel bars of the prefabricated web pass through the stiffening rib holes and are connected as a whole by PBL keys.

[0015] A composite box beam construction method includes a composite box beam structure, and the steps are as follows:

[0016] Step 1: Determine the bridge span and bridge system, and determine the specific dimensions of each component based on the span;

[0017] Step 2: Tie the stirrups and longitudinal reinforcement of the bottom plate in the prefabrication yard, then install the steel frame that has been prefabricated but not welded with flange bolts, tie the web stirrups, longitudinal reinforcement of the web, axil reinforcement and web reinforcement of the prefabricated web to form an integral steel and reinforcement skeleton, and tie the reinforcement of the prefabricated diaphragm and cast-in-place diaphragm;

[0018] Step 3: Cast two prefabricated webs and prefabricated transverse diaphragms set at the fulcrums to form a prefabricated hoisting structure, and maintain it in the prefabrication yard in accordance with relevant specifications; after the material strength reaches the specified value required by the specifications, transport it to the construction site;

[0019] Step 4: Set up a portal support on the pedestal of the lower structure on site, and then use the lifting equipment to lift the prefabricated lifting structure to the designed main beam position. At this time, the prefabricated diaphragm set at the fulcrum will be used as a temporary support for the prefabricated lifting structure, and the bottom plate of the composite box girder will be cast. After the material strength reaches the specified value required by the specification, the prestressed steel strands of the bottom plate will be tensioned and anchored on the tooth blocks of the bottom plate; cast the remaining cast-in-place diaphragms; weld flange bolts on the upper flange of the steel frame, tie the top plate stirrups and the longitudinal steel bars of the top plate, and cast the top plate; tie the steel bars of the cast-in-place section of the pier top, and use the prefabricated diaphragm set at the fulcrum as a template to cast the cast-in-place section of the pier top, and connect the composite box girders of two adjacent spans in a unit; when the bridge system is a continuous system, it is also necessary to set and tension the prestressed steel strands of the top plate and anchor them on the tooth blocks of the top plate.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The composite box girder is made by prefabricated webs and pre-binding some steel bars, decomposing the structure into prefabricated hoisting parts and cast-in-place parts, combining the advantages of both prefabrication and cast-in-place methods, reducing the construction difficulty of prefabrication and cast-in-place methods, and greatly improving the on-site construction efficiency; since the weight of the webs is greatly reduced and the hoisting weight is light, small hoisting equipment can be used for hoisting work, saving hoisting costs and having a wide range of applications.

[0022] 2. During the construction of the composite box girder, a portal support can be set up on the pedestal of the lower structure. This structure can be used for both dry bridges and river crossing bridges. This structure can reduce the size of the structure, reduce the deadweight and internal forces of the structure, improve the spanning capacity and bending resistance of the bridge, and significantly reduce the cracking probability of the composite box girder and the structural deformation under the load. Compared with steel structures, it has higher corrosion resistance, fire resistance and erosion resistance, which can improve the safety and durability of the structure, and the bridge deck is not easily damaged. Both steel and UHPC are high-performance materials, and the SUHPC structure that combines the two also has a higher bearing capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the prefabricated hoisting structure of the composite box girder of the present invention;

[0024] Figure 2 It is a schematic diagram of the elevation structure of the composite box girder of the present invention;

[0025] Figure 3 It is a schematic diagram of the elevation arrangement of the prestressed steel strands of the composite box girder of the present invention;

[0026] Figure 4 for Figure 2 II section view in;

[0027] Figure 5 for Figure 2 Section II-II in ;

[0028] Figure 6 for Figure 2 The cross-sectional reinforcement diagram of Section II in the figure;

[0029] Figure 7 for Figure 2 The cross-sectional reinforcement diagram of section II-II in the figure;

[0030] Figure 8 It is a schematic diagram of the structure of the prefabricated diaphragm or cast-in-place diaphragm of the present invention;

[0031] Fig. 9 It is a schematic diagram of the cross-section reinforcement of the cast-in-place section of the pier top of the present invention;

[0032] Fig.10 It is a schematic diagram of the steel frame facade structure of the present invention;

[0033] Fig.11 It is a schematic diagram of the cross-sectional structure of the steel frame of the present invention;

[0034] Fig.12 This is a schematic diagram of the steel web hole reinforcement steel bar structure of the present invention;

[0035] In the figure: 1, top plate; 11, top plate stirrups; 12, top plate longitudinal reinforcement; 13, top plate prestressed steel strands; 14, top plate tooth blocks;

[0036] 2. Steel frame; 21. Steel frame web; 211. Hole in the mid-span web; 212. Hole in the beam end web; 22. Steel frame lower flange; 23. Steel frame upper flange; 24. Upper flange bolts; 25. Web bolts; 26. Stiffener; 261. Hole in the stiffener;

[0037] 3. Prefabricated web; 311. Web stirrups; 312. Web longitudinal reinforcement; 313. Axillary reinforcement;

[0038] 4. Bottom plate; 41. Stirrups of bottom plate; 42. Longitudinal reinforcement of bottom plate; 43. Prestressed steel strands of bottom plate; 44. Tooth blocks of bottom plate;

[0039] 5. Prefabricated diaphragm; 5', cast-in-place diaphragm; 51, diaphragm reinforcement;

[0040] 6. Steel web reinforcement; 61. Steel mesh; 62. Longitudinal short steel bars;

[0041] 7. Cast-in-place section of pier top; 71. Steel bars of cast-in-place section of pier top;

[0042] 8. Thickening layer. DETAILED DESCRIPTION

[0043] In order to make the above features and advantages of the present invention more easily understood, embodiments are given below with reference to the accompanying drawings for detailed description, but the present invention is not limited thereto.

[0044] refer to Figures 1 to 12

[0045] A composite box girder structure comprises a bottom plate 4, both sides of which are provided with precast webs 3, a top plate 1 is provided above the two precast webs 3, a steel frame 2 is provided inside the precast webs 3, the upper and lower ends of the steel frame 2 respectively pass through the precast webs 3 and are connected to the bottom plate 4 and the top plate 1, a plurality of cast-in-place transverse diaphragms 5' are provided between the two precast webs 3 at intervals along the length direction of the composite box girder, and precast transverse diaphragms 5 are provided at the two end supports of the composite box girder.

[0046] In this embodiment, the prefabricated web 3, steel frame 2, prefabricated transverse diaphragm 5, stirrups 41 of the bottom plate, and longitudinal steel bars 42 of the bottom plate constitute a prefabricated hoisting structure, and the remaining structures are all cast-in-place structures.

[0047] By arranging the prefabricated web 3, steel frame 2, stirrups 41 of the bottom plate, longitudinal steel bars 42 of the bottom plate and prefabricated transverse diaphragm 5 to form a prefabricated hoisting structure, not only can the structural part be prefabricated in the factory to improve the construction speed, but it can also serve as a load-bearing structure during construction. By arranging the steel frame 2 in the prefabricated web 3, the weight of the web is greatly reduced, making it convenient to hoist small equipment.

[0048] In this embodiment, the two ends of the composite box girder along the bridge direction are provided with pier top cast-in-place sections 7, and the composite box girders of two adjacent spans in one unit are connected via the pier top cast-in-place sections. The pier top cast-in-place sections are provided with pier top cast-in-place section steel bars 71, wherein part of the pier top cast-in-place section steel bars 71 is connected with part of the longitudinal steel bars 12 of the top plate, the longitudinal steel bars 312 of the prefabricated web plate, and the longitudinal steel bars 42 of the bottom plate.

[0049] In this embodiment, the pier top cast-in-place section 7 has a thickness of 1m-2m and is made of ordinary concrete.

[0050] In this embodiment, both the prefabricated diaphragm and the cast-in-place diaphragm are provided with diaphragm reinforcements 61 , and part of the diaphragm reinforcements 61 extend into the prefabricated web 3 , the top plate 1 and the bottom plate 4 .

[0051] In this embodiment, the thickness of the precast diaphragm 5 and the cast-in-place diaphragm 5' are both 0.2m-0.5m. The precast diaphragm 5 must be set at the support points at both ends of the composite box beam, and the remaining cast-in-place diaphragms 5' are evenly set at intervals of 10m-30m along the length direction of the composite box beam. The top plate 1 and the bottom plate 4 are provided with a thickening layer 8 near the support point, and the thickness of the thickening layer 8 is 0.1m-0.3m. The materials of the precast diaphragm 5 and the cast-in-place diaphragm 5' and the thickening layer 8 are ordinary concrete.

[0052] By setting prefabricated transverse diaphragms 5 at the two end supports, it can not only serve as a temporary support after the prefabricated hoisting structure is hoisted, but also serve as a construction template for pouring the cast-in-place section 7 on the pier top; by setting multiple cast-in-place transverse diaphragms 5', the integrity of the composite box girder can also be improved.

[0053] In this embodiment, the top plate 1 is a cast-in-place structure, including top plate stirrups 11 and top plate longitudinal steel bars 12; only when the bridge system of the bridge is a continuous system, top plate prestressed steel bundles 13 in the longitudinal direction of the bridge are arranged at intervals in the middle part of the top plate along the transverse direction of the bridge, and top plate tooth blocks 14 are arranged on the bottom surface of the top plate, and the top plate prestressed steel bundles 13 are anchored on the top plate tooth blocks 14.

[0054] 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.

[0055] In this embodiment, the prefabricated web 3 is a prefabricated structure, and the prefabricated web 3 is provided with web stirrups 311, web longitudinal steel bars 312, spur steel bars 313 and profiled steel web reinforcing steel bars 6. The spur steel bars are arranged at the corner where the prefabricated web is connected to the top plate. The profiled steel web reinforcing steel bars are used to prevent the web from cracking, prevent concrete from falling, and reduce stress concentration.

[0056] In this embodiment, the thickness of the single prefabricated web is 0.15m-0.4m, and the material of the prefabricated webs 3 is ultra-high performance concrete.

[0057] In this embodiment, the base plate 4 is a cast-in-place structure, including base plate stirrups 41 pre-tied in the factory and longitudinal steel bars 42 pre-tied in the factory. A row of base plate prestressed steel strands 43 in the longitudinal direction are arranged in the transverse direction of the base plate, and base plate tooth blocks 44 are arranged on the upper side of the base plate; part of the base plate stirrups 41 extend into the prefabricated web 3 and are connected to the prefabricated web.

[0058] 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.

[0059] 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, the upper flange studs 24 are welded at intervals along the length direction of the steel frame upper flange 23, the upper and lower parts of the two sides of the steel frame web 21 are welded at intervals along the length direction with web studs 25, and the lower end of the steel frame web extends into the bottom plate 4 and is provided with a steel frame lower flange 22. The longitudinal arrangement spacing of the upper flange studs 24 and the web studs 25 is 0.05m-0.5m, and the material is ML15 or ML15A1 steel.

[0060] In this embodiment, the steel 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 stiffening rib 26 is provided between each mid-span web hole 211 and the beam end web hole 212. The stiffening rib 26 is provided with a stiffening rib hole 261. The longitudinal steel bars 312 of the prefabricated web pass through the stiffening rib hole 261 and are connected as a whole by a PBL key. The steel web reinforcement steel bars include a steel mesh 61 and a transverse short steel bar 62. In order to improve the crack resistance of the web, the steel web reinforcement steel bars are arranged in the web along the entire cross section along the direction of the bridge (i.e., the driving direction). The transverse short steel bars 62 need to be provided only when the steel web reinforcement steel bars are provided in the mid-span web holes 211 or the beam end web holes 212.

[0061] 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 skeleton to form a whole, thereby preventing slippage between the steel and concrete materials and allowing the steel to participate more fully in the load-bearing.

[0062] By arranging an upper flange bolt 24 extending into the top plate 1 on the upper flange 22 of the steel frame, the upper flange bolt 24 is used as a shear connector to connect the steel frame 2 and the top plate 1, thereby improving the shear resistance of the structure and further preventing slippage between the top plate 1 and the steel frame 2.

[0063] By arranging the mid-span web holes 211 and the beam end web holes 212 on the steel web 21, materials are saved, the deadweight of the structure is reduced, and the construction cost is lowered.

[0064] By providing the stiffening rib 26 and allowing the web longitudinal reinforcement 312 to pass through the stiffening rib hole 261, not only the integrity of the steel section and the reinforcement is strengthened, but also the stress concentration phenomenon of the web hole 211 in the mid-span and the web hole 212 at the beam end is reduced.

[0065] By providing the steel web reinforcement steel bars 6, not only the bearing capacity of the mid-span web holes 211 and the beam end web holes 212 is enhanced, but also the concrete material at the holes can be prevented from falling when the structure is damaged and the crack resistance of the precast web 3 can be enhanced.

[0066] A composite box beam construction method includes a composite box beam structure, and the steps are as follows:

[0067] Step 1: Determine the bridge span and bridge system, and determine the specific dimensions of each component based on the span.

[0068] Step 2: Tie the stirrups 41 and longitudinal reinforcement 42 of the bottom plate in the prefabrication yard, then install the steel frame 2 that has been prefabricated but not welded with the flange bolts 24, tie the web stirrups 311, web longitudinal reinforcement 312, axil reinforcement 313 and web reinforcement 6 of the prefabricated web 3 to form an integral steel frame 2 and reinforcement skeleton, and tie the reinforcement 61 of the prefabricated diaphragm and the cast-in-place diaphragm.

[0069] Step 3: Cast two prefabricated webs 3 and prefabricated transverse diaphragms 5 arranged at the fulcrums to form a prefabricated hoisting structure, and maintain it in the prefabrication yard in accordance with relevant specifications; after the material strength reaches the specified value required by the specifications, tension the web prestressed steel strands and transport them to the construction site.

[0070] Step 4: Set up a portal support on the base of the lower structure on site, and then hoist the prefabricated hoisting structure to the designed main beam position through the hoisting equipment. At this time, the prefabricated diaphragm 5 set at the fulcrum is used as a temporary support for the prefabricated hoisting structure, and the bottom plate 4 of the composite box beam is cast. After the material strength reaches the specified value required by the specification, the bottom plate prestressed steel bundle 43 is tensioned and anchored on the bottom plate tooth block 44; cast the remaining cast-in-place diaphragms 5'; weld the flange bolts 24 on the flange 23 of the steel frame, tie the top plate stirrups 11 and the top plate longitudinal steel bars 12, and cast the top plate 1; tie the steel bars 71 of the cast-in-place section of the pier top, and use the prefabricated diaphragm 5 set at the fulcrum as a template to cast the cast-in-place section 7 of the pier top to connect the composite box beams of two adjacent spans in a unit; when the bridge system is a continuous system, it is also necessary to set and tension the top plate prestressed steel bundle and anchor it on the top plate tooth block.

[0071] Embodiment 1:

[0072] Bridges often need to be built across rivers. In traditional construction methods, a cofferdam is generally set up in the river to build a full-bridge support. The structure proposed in the present invention is used for a bridge across a river. Since the structure of the invention is decomposed into a prefabricated hoisting part and a cast-in-place part, the advantages of both the prefabrication method and the cast-in-place method are combined. During construction, a relatively simple portal support can be built on the pedestal of the lower structure, which reduces the construction difficulty of the prefabrication method and the cast-in-place method, saves the cost of the cofferdam and the support and the time of building the cofferdam, and speeds up the construction progress.

[0073] Embodiment 2:

[0074] When building a dry bridge in China, it is inconvenient to use large-scale lifting equipment. Therefore, the lightweight structure is particularly important in the construction of the bridge. The structure proposed in the present invention is used for the dry bridge. Since the present invention decomposes the structure into a prefabricated lifting part and a cast-in-place part, and the web plate uses high-strength UHPC and steel, the weight of the lifting structure is greatly reduced. During construction, it can be lifted by a car, saving the lifting cost; the steel bars of the top plate and the bottom plate are prefabricated in the factory together with the web plate, which can greatly reduce the workload of tying steel bars on site, and the construction speed is fast, the construction period is short, and the impact of construction on traffic is greatly reduced.

[0075] The above description is only a preferred embodiment of the present invention. For ordinary technicians in this field, according to the teachings of the present invention, designing different forms of composite box girder structures and construction methods does not require creative labor. Without departing from the principles and spirit of the present invention, all equal changes, modifications, substitutions and variations made within the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A composite box girder structure, comprising a bottom plate, characterized in that: Precast webs are arranged on both sides of the bottom plate, a top plate is arranged above the two precast webs, steel frames are arranged inside the precast webs, the upper and lower ends of the steel frames respectively pass through the precast webs to be connected with the bottom plate and the top plate, a plurality of cast-in-place transverse diaphragms are arranged at intervals along the length direction of the composite box girder between the two precast webs, and precast transverse diaphragms are arranged at the two end fulcrums of the composite box girder; the precast webs, steel frames, precast transverse diaphragms, stirrups of the bottom plate, and longitudinal steel bars of the bottom plate constitute a precast hoisting structure; web stirrups, longitudinal steel bars of the web, axil steel bars and steel web reinforcing steel bars are arranged inside the precast webs; the steel web reinforcing steel bars include steel mesh and transverse short steel bars; the bottom plate is a cast-in-place structure, including stirrups of the bottom plate and longitudinal steel bars of the bottom plate, and a row of longitudinal steel bars are arranged in the transverse direction of the bottom plate The bottom plate prestressed steel bundle is provided with a bottom plate tooth block on the upper side of the bottom plate; the stirrups of part of the bottom plate extend into the prefabricated web; the steel frame includes a steel frame web arranged in the prefabricated web, the upper end of the steel frame web extends into the top plate and is provided with a steel frame upper flange, the steel frame upper flange is welded with upper flange bolts at intervals along the length direction, the upper and lower parts of the two side surfaces of the steel frame web are welded with web bolts at intervals along the length direction, the lower end of the steel frame web extends into the bottom plate and is provided with a steel frame lower flange; the steel frame web is provided with a mid-span web hole and a beam end web hole, the radius of the beam end web hole is smaller than the mid-span web hole; stiffening ribs are provided between each mid-span web hole and the beam end web hole, and stiffening rib holes are provided on the stiffening ribs, and the longitudinal reinforcement of the prefabricated web passes through the stiffening rib holes and is connected as a whole by PBL keys.

2. A composite box beam structure according to claim 1, characterized in that: Cast-in-place sections are provided at both ends of the composite box girder along the bridge direction, and the composite box girders of two adjacent spans in one unit are connected via the cast-in-place sections at the pier tops.

3. A composite box beam structure according to claim 2, characterized in that: The pier top cast-in-place section is provided with pier top cast-in-place section steel bars, wherein part of the pier top cast-in-place section steel bars are connected with part of the longitudinal steel bars of the top plate, the longitudinal steel bars of the prefabricated web plate, and the longitudinal steel bars of the bottom plate.

4. A composite box beam structure according to claim 1 or 3, characterized in that: The prefabricated transverse diaphragm and the cast-in-place transverse diaphragm are both provided with transverse diaphragm steel bars, and part of the transverse diaphragm steel bars extend into the prefabricated web, top plate and bottom plate.

5. The composite box beam structure according to claim 1, characterized in that: The top plate is a cast-in-place structure, including top plate stirrups and top plate longitudinal steel bars; only when the bridge system of the bridge is a continuous system, top plate prestressed steel strands in the longitudinal direction of the bridge are arranged at intervals in the middle of the top plate along the transverse direction of the bridge, and top plate tooth blocks are arranged on the bottom surface of the top plate.

6. A method for constructing a composite box beam, comprising a composite box beam structure according to claim 1, characterized in that: Here are the steps: Step 1: Determine the bridge span and bridge system, and determine the specific dimensions of each component based on the span; Step 2: Tie the stirrups and longitudinal reinforcement of the bottom plate in the prefabrication yard, then install the steel frame that has been prefabricated but not welded with flange bolts, tie the web stirrups, longitudinal reinforcement of the web, axil reinforcement and web reinforcement of the prefabricated web to form an integral steel and reinforcement skeleton, and tie the reinforcement of the prefabricated diaphragm and cast-in-place diaphragm; Step 3: Cast two prefabricated webs and prefabricated transverse diaphragms set at the fulcrums to form a prefabricated hoisting structure, and maintain it in the prefabrication yard in accordance with relevant specifications; after the material strength reaches the specified value required by the specifications, transport it to the construction site; Step 4: Set up a portal support on the cap of the lower structure on site, and then hoist the prefabricated hoisting structure to the designed main beam position through the hoisting equipment. At this time, the prefabricated transverse diaphragm set at the fulcrum is used as a temporary support for the prefabricated hoisting structure, and the bottom plate of the composite box beam is cast. After the material strength reaches the specified value required by the specification, the prestressed steel strands of the bottom plate are tensioned and anchored on the bottom plate tooth blocks; Cast the remaining cast-in-place diaphragms; weld flange bolts on the upper flange of the steel frame, tie the top plate stirrups and the top plate longitudinal steel bars, and cast the top plate; tie the steel bars of the cast-in-place section on the pier top, and use the prefabricated diaphragms set at the fulcrum as a template to cast the cast-in-place section on the pier top, and connect the composite box girders of two adjacent spans in a unit; when the bridge system is a continuous system, it is also necessary to set and tension the prestressed steel strands on the top plate and anchor them on the top plate teeth.

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