A steel pot-bellied web uHPC-RC combined box girder and a construction method thereof

Abstract

This invention relates to the field of bridge engineering technology and discloses a prefabricated construction method for a steel-clad UHPC-RC composite box girder. The method includes a steel-UHPC composite U-beam, a UHPC shell formwork-RC composite bridge deck, internal prestressing tendons, a wet-joint UHPC, and seismic strengthening components. The seismic strengthening components include shear pins and viscous dampers, with the viscous dampers symmetrically arranged inside the UHPC steel web to work in conjunction with the shear pins to enhance seismic performance. The construction method includes prefabrication, on-site assembly, wet-joint pouring and curing, corrosion protection, and installation of monitoring components. The method features a high degree of prefabrication, improving construction efficiency and structural durability; ensuring the load-bearing capacity and service life of the bridge structure; preventing connection failure and displacement under seismic loads; improving the structure's corrosion resistance; and providing excellent stiffness, torsional and bending resistance. It can effectively cope with various loads during bridge use, enhancing structural stability and disaster resistance, extending the bridge's service life, and has a wider range of applications.

Description

Technical Field

[0001] This invention relates to the technical field of bridge engineering, and in particular to a UHPC-RC composite box girder with steel-clad web and its construction method. Background Technology

[0002] As bridge engineering develops towards longer spans, lighter weight, and higher durability, traditional box girder structures and construction methods have gradually revealed many shortcomings. Currently, the box girder structures commonly used in bridge engineering mainly include pure steel box girders, pure concrete box girders, and ordinary steel-concrete composite box girders.

[0003] While pure steel box girders are relatively lightweight and have strong spanning capacity, they are prone to fatigue cracking, especially at the junction of the orthotropic steel bridge deck and the U-ribs, and at the weld holes of the U-ribs and the transverse diaphragms. These areas are susceptible to fatigue damage and cracks can easily develop and propagate rapidly. To solve this problem, a large number of stiffening ribs need to be arranged, which leads to a significant increase in steel consumption, resulting in high construction costs and high maintenance costs in the later stages.

[0004] Pure concrete box girders have a large self-weight, which places high demands on the load of the substructure, has a long construction period, and has poor crack resistance. After long-term service, cracks are prone to appear, affecting the durability of the structure.

[0005] While ordinary steel-concrete composite box girders can combine the advantages of steel and concrete, the bridge decks are mostly constructed using traditional formwork, which involves cumbersome formwork erection and dismantling procedures and low construction efficiency. In addition, the bridge decks are relatively thick, which increases the structural self-weight and makes it difficult to achieve large cantilever designs.

[0006] In existing box girder structures, prestressing is mostly applied using the post-tensioning method. The post-tensioning method requires pre-reserving ducts after the concrete has hardened, inserting prestressing tendons and tensioning them, and then grouting the ducts. The grouting quality is difficult to control precisely. If the grouting is not dense, it can easily lead to corrosion, loosening or even breakage of the prestressing tendons, which in turn can cause insufficient bearing capacity of the bridge structure and affect the safety and lifespan of the bridge.

[0007] The existing composite box girder U-shaped beams and bridge decks are mostly constructed by on-site casting, which involves complex construction procedures, is greatly affected by the site environment, makes it difficult to guarantee construction quality, and has low construction efficiency, thus failing to meet the needs of rapid construction of modern bridges.

[0008] Ultra-high performance concrete (UHPC), as a new type of cement-based composite material, has ultra-high strength, high toughness, high durability and good crack resistance. Its extremely low porosity and good density can effectively resist the erosion of harmful media. Combining it with steel and ordinary reinforced concrete (RC) can effectively improve the defects of traditional box girder structures. Summary of the Invention

[0009] This invention aims to provide a UHPC-RC composite box girder with steel-clad web and its construction method, realizing lightweight, prefabricated, and efficient construction of box girder structures, solving the problems of poor fatigue performance, large steel consumption, low construction efficiency, and heavy structural weight of traditional box girders, reducing construction and maintenance costs, and improving the durability and load-bearing capacity of bridge structures.

[0010] Therefore, the technical solution adopted by the present invention is: a steel-clad web UHPC-RC composite box girder, comprising a composite box girder structure formed by assembling a steel-UHPC composite U-shaped beam and a UHPC shell formwork-RC composite bridge deck;

[0011] The steel-UHPC composite U-shaped beam is composed of a UHPC base plate and a UHPC steel web. The bottom of the UHPC steel web is fixedly connected to the left and right ends of the UHPC base plate to form a U-shaped groove structure. Prestressed tendons are arranged within the UHPC base plate along its length. The UHPC shell-RC composite bridge deck is composed of a UHPC shell mold and an RC layer. The UHPC shell mold is located below the RC layer. Prestressed tendons are arranged transversely within the RC layer. The assembly gap between the steel-UHPC composite U-shaped beam and the UHPC shell-RC composite bridge deck forms a wet joint, within which UHPC is poured.

[0012] The composite box girder structure is equipped with seismic reinforcement components and protective components. The seismic reinforcement components include shear pins for connecting the RC layer and the UHPC base plate and multiple viscous dampers symmetrically arranged on the inner side of the UHPC steel web. The protective components include an anti-corrosion coating applied to the surface of the UHPC steel web and a penetrating anti-corrosion coating applied to the UHPC base plate. The anti-corrosion coating includes epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and fluorocarbon topcoat applied sequentially.

[0013] As a preferred embodiment of the above scheme, the UHPC steel web is formed by bending steel plate, and its top is provided with an outward flange. The bottom of the UHPC shell mold is provided with a groove that matches the outward flange. The outward flange is embedded in the groove. Through holes are evenly opened on the outward flange. The groove is provided with a pre-embedded bolt corresponding to the through hole. The pre-embedded bolt passes through the through hole and is locked and fixed by a nut. A sleeve for connecting with the anti-shear pin is provided in the groove.

[0014] More preferably, the UHPC shell mold and the RC layer are provided with an interlocking structure and filled with an interface agent. The RC layer is provided with transverse steel bars and longitudinal steel bars, which interweave to form an RC layer steel mesh. The UHPC base plate is provided with a UHPC base plate steel mesh. The prestressed tendons in the UHPC base plate and the prestressed tendons in the RC layer are respectively arranged below the UHPC base plate steel mesh and the RC layer steel mesh. The surface of the steel mesh is coated with a rust inhibitor.

[0015] More preferably, the prestressing tendons in the UHPC base plate and the prestressing tendons in the RC layer are both made of high-strength, low-relaxation steel strands with a diameter of 15.2-18.0 mm and a tension control stress of 1395-1860 MPa. The spacing between two adjacent prestressing tendons is 150-250 mm. The end reinforcement bars of two adjacent UHPC shell formwork-RC composite bridge decks overlap each other, and the UHPC is poured at the splice joint to form an integral bridge deck.

[0016] Preferably, the shear pin is made of high-strength alloy steel with a diameter of 20-30mm and threads at both ends. The lower end of the shear pin passes through the outward-flaring flange and is firmly connected to the UHPC base plate through a pre-embedded socket connector. The upper end is embedded in the RC layer and screwed into the sleeve. The lower end of the pre-embedded socket connector passes through the steel mesh of the UHPC base plate and is embedded in the area where the prestressing tendons are located within the UHPC base plate for proper pre-embedding. The viscous damper has a damping coefficient of 500-1500kN·s / m, with one end connected to the UHPC steel web and the other end connected to the UHPC base plate.

[0017] A construction method for a steel-clad web-based UHPC-RC composite box girder includes the following steps:

[0018] S1: Prefabrication of steel-UHPC composite U-beam: Fabricate UHPC steel web and fix it on the prefabrication platform, set outward flanges and open through holes, pre-embed socket connectors, install shear pins on the outward flanges and connect them with the socket connectors, connect the UHPC base plate, pre-embed prestressing tendons in the UHPC base plate and tie the UHPC base plate steel mesh, apply rust inhibitor to the surface of the steel bars, use the pre-tensioning method to tension and fix the prestressing tendons in the UHPC base plate, pour the UHPC, release the tension after curing to the standard, release the fixation of the UHPC base plate prestressing tendons, and complete the prefabrication;

[0019] S2. Prefabrication of UHPC shell formwork-RC composite bridge deck: Fabricate UHPC shell formwork, pre-embed prestressing tendons in the RC layer, open grooves and pre-embed bolts, tie RC layer steel mesh, apply rust inhibitor to the surface of steel bars, pour RC layer and cure, and complete the prefabrication of UHPC shell formwork-RC composite bridge deck after curing.

[0020] S3. On-site assembly: Transport the prefabricated steel-UHPC composite U-beam and UHPC shell formwork-RC composite bridge deck to the construction site. Hoist and fix the steel-UHPC composite U-beam, then hoist the UHPC shell formwork-RC composite bridge deck to the top of the steel-UHPC composite U-beam. Adjust the assembly accuracy, grind the connection surface, and then assemble the bridge deck. After that, embed the outward flange of the steel-UHPC composite U-beam into the groove of the UHPC shell formwork-RC composite bridge deck and fix it. Fill with structural adhesive and install anti-shear pins so that they can be screwed into the sleeves in the RC layer. Connect the bolts in the groove to the nuts on the outward flange to complete the assembly.

[0021] S4. Wet joint pouring and curing: Wet joint UHPC is poured at the assembly gap, and geotextile is used for covering and watering curing. The curing time is not less than 14 days, and the wet joint UHPC is cured until it reaches the design strength, forming an integral continuous box girder structure, and the main bridge construction is completed.

[0022] S5. Corrosion protection: All components shall be treated with anti-corrosion coatings and paints, and cured for no less than 24 hours after application.

[0023] More preferably, in step S1, the tensioning sequence of the internal prestressing tendons is symmetrical tensioning from both ends to the middle, and the tensioning speed is controlled at 0.5-1.0 mm / min.

[0024] Further preferably, in steps S1 and S2, steam curing is used, the curing temperature is controlled at 35-45℃, and the curing time is not less than 7 days.

[0025] A further preferred embodiment is that the RC layer in step S2 is naturally cured for a period of not less than 14 days.

[0026] The beneficial effects of this invention are: high degree of prefabrication, eliminating the need for on-site installation and dismantling of formwork, significantly simplifying construction procedures and reducing formwork investment costs; reducing on-site wet work, shortening the construction cycle, improving construction efficiency, and reducing on-site construction interference to the surrounding environment and traffic; reducing steel consumption, saving manufacturing costs, effectively alleviating the pain point of fatigue cracking in steel box girders, and improving the durability of the structure; effectively ensuring the load-bearing capacity and service life of the bridge structure, avoiding increased maintenance and reinforcement costs and traffic interference caused by grouting defects; reducing the thickness of the bridge deck to achieve structural lightweighting, combined with internal prestressed tendons, improving the lateral span capacity of the bridge deck, realizing a large cantilever design, reducing the overall self-weight of the bridge while expanding the usable space of the bridge deck, and adapting to the design requirements of bridges with different spans;

[0027] Compared to on-site casting, the dimensional accuracy and construction quality of precast components are easier to guarantee, avoiding quality defects caused by factors such as weather and personnel operation that may result in on-site casting, thereby reducing later maintenance costs; precast components are convenient to transport and efficient to assemble on-site, further shortening the construction cycle and reducing interference with the surrounding traffic and ecological environment;

[0028] By setting shear pins to enhance the shear resistance of connection nodes, dampers effectively dissipate seismic energy, preventing connection failure and displacement of the structure under seismic action, making it suitable for use in earthquake-prone areas and improving the safety of bridge structures; coating protective components solve the problems of steel component corrosion, UHPC component erosion, and rebar corrosion, extending the service life of the structure and reducing later maintenance costs.

[0029] The overall structure exhibits excellent stiffness, torsional and bending resistance, effectively coping with various loads during bridge use, enhancing structural stability and disaster resistance, and ensuring long-term safe and stable operation. It reduces subsequent maintenance workload and costs, extends bridge service life, and improves the economy and practicality of engineering applications. It has a wider range of applications and broad engineering application prospects and promotional value. Attached Figure Description

[0030] Fig. 1 This is a schematic diagram of the assembled state of the combined box girder structure of the present invention.

[0031] Fig. 2 This is a cross-sectional view of the combined box girder structure of the present invention. Detailed Implementation

[0032] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0033] like Figs. 1-2 As shown, a steel-clad web UHPC-RC composite box girder includes a composite box girder structure assembled from a steel-UHPC composite U-shaped beam and a UHPC shell formwork-RC composite bridge deck.

[0034] The steel-UHPC composite U-shaped beam consists of a UHPC base plate 1 and a UHPC steel web plate 2. Pins are sequentially nailed to the outer side of the UHPC steel web plate 2 for fixing the outer steel plates. The bottom of the UHPC steel web plate 2 is fixedly connected to the left and right ends of the UHPC base plate 1, forming a U-shaped groove structure. Prestressing tendons 3 are arranged within the UHPC base plate 1, along the length of the steel-UHPC composite U-shaped beam. The UHPC shell-RC composite bridge deck consists of a UHPC shell mold 4 and an RC layer 5. The UHPC shell mold 4 is located below the RC layer 5. Prestressing tendons 6 are arranged transversely within the RC layer 5. The assembly gap between the steel-UHPC composite U-shaped beam and the UHPC shell-RC composite bridge deck forms a wet joint, within which UHPC is poured.

[0035] The composite box girder structure is equipped with seismic strengthening components and protective components. The seismic strengthening components include shear pins 7 for connecting the RC layer 5 and the UHPC base plate 1 and multiple viscous dampers 8 symmetrically arranged on the inner side of the UHPC steel web 2, which are used to dissipate the energy generated by the seismic action and prevent destructive displacement of the structure. The protective components include an anti-corrosion coating applied to the surface of the UHPC steel web 2 and a penetrating anti-corrosion coating applied to the UHPC base plate 1. The anti-corrosion coating includes epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and fluorocarbon topcoat applied in sequence.

[0036] Multiple sets of shear pins 7 and viscous dampers 8 are installed along the length of a UHPC shell formwork-RC composite bridge deck and a steel-UHPC composite U-beam according to the actual needs of the bridge to improve the bridge's seismic resistance.

[0037] The UHPC steel web 2 is formed by bending steel plate, and its top is provided with an outward flange 9. The bottom of the UHPC shell mold 4 is provided with a groove 10 that matches the outward flange 9. The outward flange 9 is embedded in the groove 10. Through holes are evenly opened on the outward flange 9. The groove 10 is provided with a pre-embedded bolt 11 corresponding to the through hole. The pre-embedded bolt 11 passes through the through hole and is locked and fixed by a nut 12. A sleeve 13 for connecting with the anti-shear pin 7 is provided in the groove 10.

[0038] The UHPC shell mold 4 and the RC layer 5 are provided with a concave-convex interlocking structure and filled with an interface agent. The concave-convex interlocking structure can be provided with mechanical interlocking force by using keyways, roughening, or rebar installation. The interface agent can be a cement-based two-component binder or a polymer-modified slurry to improve the chemical bonding strength of the micro-interface. The RC layer 5 is provided with transverse and longitudinal steel bars, which interweave to form the RC layer steel mesh 14. The UHPC base plate 1 is provided with a UHPC base plate steel mesh 15. The prestressed tendons 3 in the UHPC base plate and the prestressed tendons 6 in the RC layer are respectively arranged below the UHPC base plate steel mesh 15 and the RC layer steel mesh 14.

[0039] Both the prestressing tendons 3 in the UHPC base slab and the prestressing tendons 6 in the RC layer are made of high-strength, low-relaxation steel strands with a diameter of 15.2-18.0 mm and a tension control stress of 1395-1860 MPa. The spacing between two adjacent prestressing tendons is 150-250 mm. The end reinforcements of two adjacent UHPC shell formwork-RC composite bridge decks are lapped together, and UHPC is poured at the splice joint to form an integral bridge deck.

[0040] The shear pin 7 is made of high-strength alloy steel with a diameter of 20-30mm. Both ends are threaded. The lower end of the shear pin 7 passes through the outward flange 9 and is firmly connected to the UHPC base plate 1 through the pre-embedded socket connector 16. The upper end is embedded in the RC layer 5 and screwed into the sleeve 13. The lower end of the pre-embedded socket connector 16 passes through the UHPC base plate steel mesh 15 and is embedded in the area where the prestressed tendons 3 are located in the UHPC base plate for matching pre-embedding. The viscous damper 8 has a damping coefficient of 500-1500kN·s / m. One end is connected to the UHPC steel web plate 2 and the other end is connected to the UHPC base plate 1.

[0041] The shear pin 7 is integrally formed from high-strength alloy steel, with a threaded section at the upper end. The lower end of the shear pin 7 is screwed and fixed to the pre-embedded connector, while the upper end can rotate slightly (1-2 turns, ≤90°). The rotation range is small and the force is light, so it will not cause the lower fixed structure to loosen, nor will it damage the UHPC base plate steel mesh 15 and prestressing tendons. The sleeve 13 is provided with threads that match the threaded section of the shear pin 7, and all of them are fine threads. The threads are interference fit, and after screwing, the threads fit tightly together, which not only ensures the fixing effect, but also prevents loosening after rotation. At the same time, the length of the threaded section is adapted to the depth of the installation groove, requiring no extra space and not affecting the overall stress.

[0042] The shear pin 7 can be made of SNC631 alloy steel, which has high shear strength (≥800MPa) and fatigue resistance, making it suitable for heavy machinery or bridge connection scenarios. The lower end screws into the pre-embedded connector (such as the base sleeve) with an M20×60 thread to ensure pull-out resistance. The upper movable section is equipped with an internal or external thread interface (such as M16) for connecting external components, supporting ≤90° micro-rotation (1-2 turns) and a rotation torque ≤5N·m to avoid transmitting torque to the fixed end. A locking washer and anti-loosening adhesive are added at the end of the threaded section to prevent thread backing due to vibration, while allowing elastic deformation to adapt to micro-displacement.

[0043] A construction method for a steel-clad web-based UHPC-RC composite box girder includes the following steps:

[0044] S1: Prefabrication of steel-UHPC composite U-shaped beam: Fabricate UHPC steel web 2 and fix it on the prefabrication platform, set outward flange 9 and open through holes, pre-embed socket connector 16, install shear pin 7 on outward flange 9 and connect it with socket connector 16, connect UHPC base plate 1, pre-embed prestressing tendons 3 in UHPC base plate and tie UHPC base plate steel mesh 15, apply rust inhibitor to the surface of steel bars, use pre-tensioning method to tension and fix the prestressing tendons 3 in UHPC base plate, pour UHPC, after curing to standard, release tension, release the fixation of prestressing tendons in UHPC base plate 1, and complete the prefabrication;

[0045] S2. Prefabrication of UHPC shell formwork-RC composite bridge deck: Fabricate UHPC shell formwork 4, pre-embed prestressing tendons 6 in the RC layer, open grooves 10 and pre-embed bolts 11, tie RC layer steel mesh 14, apply rust inhibitor to the surface of the steel bars, pour RC layer 5 and cure, and complete the prefabrication of UHPC shell formwork-RC composite bridge deck after curing.

[0046] S3. On-site assembly: Transport the prefabricated steel-UHPC combined U-beam and UHPC shell formwork-RC combined bridge deck to the construction site. Hoist and fix the steel-UHPC combined U-beam, then hoist the UHPC shell formwork-RC combined bridge deck to the top of the steel-UHPC combined U-beam. Adjust the assembly accuracy, grind the connection surface, and then assemble the bridge deck. After that, embed the outward flange 9 of the steel-UHPC combined U-beam into the groove 10 of the UHPC shell formwork-RC combined bridge deck and fix it. Fill with structural adhesive and install the shear pin 7 so that it engages with the sleeve 13 in the RC layer 5. Connect the bolt 11 in the groove 10 to the nut 12 on the outward flange 9 to complete the assembly.

[0047] S4. Wet joint pouring and curing: Wet joint UHPC is poured at the assembly gap, and geotextile is used for covering and watering curing. The curing time is not less than 14 days, and the wet joint UHPC is cured until it reaches the design strength, forming an integral continuous box girder structure, and the main bridge construction is completed.

[0048] S5. Corrosion protection: All components shall be treated with anti-corrosion coatings and paints, and cured for no less than 24 hours after application.

[0049] In step S1, the tensioning sequence of the prestressed tendons in the body is symmetrical tensioning from both ends to the middle, and the tensioning speed is controlled at 0.5-1.0 mm / min.

[0050] In steps S1 and S2, steam curing is used, with the curing temperature controlled at 35-45℃ and the curing time not less than 7 days.

[0051] In step S2, RC layer 5 is naturally cured for no less than 14 days.

[0052] With a high degree of prefabrication, there is no need for on-site installation and dismantling of formwork, which greatly simplifies the construction process and reduces the cost of formwork investment; it reduces the amount of on-site wet work, shortens the construction cycle, improves construction efficiency, and reduces the interference of on-site construction on the surrounding environment and traffic; it reduces the amount of steel used, saves manufacturing costs, effectively alleviates the pain point of fatigue cracking of steel box girders, and improves the durability of the structure; it effectively ensures the load-bearing capacity and service life of the bridge structure, and avoids the increase in maintenance and reinforcement costs and traffic interference caused by grouting defects; it reduces the thickness of the bridge deck to achieve structural lightweighting, and with the addition of internal prestressed tendons, it improves the lateral span capacity of the bridge deck, realizes the large cantilever design, and expands the usable space of the bridge deck while reducing the overall self-weight of the bridge, adapting to the design requirements of bridges with different spans;

[0053] Compared to on-site casting, the dimensional accuracy and construction quality of precast components are easier to guarantee, avoiding quality defects caused by factors such as weather and personnel operation that may result in on-site casting, thereby reducing later maintenance costs; precast components are convenient to transport and efficient to assemble on-site, further shortening the construction cycle and reducing interference with the surrounding traffic and ecological environment;

[0054] By setting shear pins 7 to enhance the shear resistance of the connection nodes, the damper effectively dissipates seismic energy, preventing connection failure and displacement of the structure under seismic action, making it suitable for use in earthquake-prone areas and improving the safety of the bridge structure; the coating of protective components solves the problems of steel component corrosion, UHPC component erosion, and rebar corrosion, extending the service life of the structure and reducing later maintenance costs.

[0055] The overall structure exhibits excellent stiffness, torsional and bending resistance, effectively coping with various loads during bridge use, enhancing structural stability and disaster resistance, and ensuring long-term safe and stable operation. It reduces subsequent maintenance workload and costs, extends bridge service life, and improves the economy and practicality of engineering applications. It has a wider range of applications and broad engineering application prospects and promotional value.

[0056] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A UHPC-RC composite box girder with steel-clad web, characterized in that, This includes a composite box girder structure formed by assembling steel-UHPC composite U-shaped beams and UHPC shell formwork-RC composite bridge decks; The steel-UHPC composite U-shaped beam is composed of a UHPC base plate (1) and a UHPC steel web plate (2). The bottom of the UHPC steel web plate (2) is fixedly connected to the left and right ends of the UHPC base plate (1) to form a U-shaped groove structure. The UHPC base plate (1) is provided with UHPC prestressing tendons (3), which are arranged along the length of the steel-UHPC composite U-shaped beam. The UHPC shell mold-RC composite bridge deck is composed of a UHPC shell mold (4) and an RC layer (5). The UHPC shell mold (4) is located below the RC layer (5). The RC layer (5) is provided with RC prestressing tendons (6), which are arranged laterally in the RC layer (5). The assembly gap between the steel-UHPC composite U-shaped beam and the UHPC shell mold-RC composite bridge deck forms a wet joint, and UHPC is poured into the wet joint. The composite box girder structure is equipped with seismic reinforcement components and protective components. The seismic reinforcement components include shear pins (7) for connecting the RC layer (5) and the UHPC base plate (1) and multiple viscous dampers (8) symmetrically arranged on the inner side of the UHPC steel web (2). The protective components include an anti-corrosion coating applied to the surface of the UHPC steel web (2) and a penetrating anti-corrosion coating applied to the UHPC base plate (1). The anti-corrosion coating includes epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and fluorocarbon topcoat applied in sequence.

2. The steel-UHPC-RC composite box girder structure according to claim 1, characterized in that, The UHPC steel web (2) is formed by bending steel plate, and its top is provided with an outward flange (9). The bottom of the UHPC shell mold (4) is provided with a groove (10) that matches the outward flange (9). The outward flange (9) is embedded in the groove (10). Through holes are evenly opened on the outward flange (9). The groove (10) is provided with a pre-embedded bolt (11) corresponding to the through hole. The pre-embedded bolt (11) passes through the through hole and is locked and fixed by a nut (12). The groove (10) is provided with a sleeve (13) for connecting with the anti-shear pin (7).

3. The steel-UHPC-RC composite box girder structure according to claim 2, characterized in that, The UHPC shell mold (4) and the RC layer (5) are provided with an interlocking structure and filled with an interface agent. The RC layer (5) is provided with transverse steel bars and longitudinal steel bars, which interweave to form an RC layer steel mesh (14). The UHPC base plate (1) is provided with a UHPC base plate steel mesh (15). The prestressed tendons (3) in the UHPC base plate and the prestressed tendons (6) in the RC layer are respectively arranged below the UHPC base plate steel mesh (15) and the RC layer steel mesh (14). The surface of the steel mesh is coated with a rust inhibitor.

4. The steel-UHPC-RC composite box girder structure according to claim 3, characterized in that, The prestressed tendons (3) in the UHPC base plate and the prestressed tendons (6) in the RC layer are both made of high-strength, low-relaxation steel strands with a diameter of 15.2-18.0 mm and a tension control stress of 1395-1860 MPa. The spacing between two adjacent prestressed tendons is 150-250 mm. The end reinforcement bars of two adjacent UHPC shell formwork-RC composite bridge decks are lapped together, and UHPC is poured at the splice joint to form an integral bridge deck.

5. A steel-UHPC-RC composite box girder structure according to claim 4, characterized in that, The shear pin (7) is made of high-strength alloy steel with a diameter of 20-30mm. Both ends are threaded. The lower end of the shear pin (7) passes through the outward flange (9) and is firmly connected to the UHPC base plate (1) through the pre-embedded socket connector (16). The upper end is embedded in the RC layer (5) and screwed in through the sleeve (13). The lower end of the pre-embedded socket connector (16) passes through the UHPC base plate steel mesh (15) and is embedded in the area where the prestressed tendons (3) are located in the UHPC base plate for matching and pre-embedding. The viscous damper (8) has a damping coefficient of 500-1500kN·s / m. One end is connected to the UHPC steel web plate (2) and the other end is connected to the UHPC base plate (1).

6. A construction method for a steel-clad web UHPC-RC composite box girder, using the steel-UHPC-RC composite box girder structure as described in claim 5, characterized in that, Includes the following steps: S1: Prefabrication of steel-UHPC composite U-shaped beam: fabricate UHPC steel web (2) and fix it on the prefabrication platform, set outward flange (9) and open through holes, pre-embed socket connector (16), install shear pin (7) on outward flange (9) and connect it with socket connector (16), connect UHPC base plate (1), pre-embed prestressing tendons (3) in UHPC base plate and tie UHPC base plate steel mesh (15), apply rust inhibitor to the surface of steel bars, use pre-tensioning method to tension and fix the prestressing tendons (3) in UHPC base plate, pour UHPC, release tension after curing to standard, release the fixation of prestressing tendons in UHPC base plate (1) to complete the prefabrication; S2. Prefabrication of UHPC shell formwork-RC composite bridge deck: Make UHPC shell formwork (4), pre-embed prestressing tendons (6) in the RC layer, open grooves (10) and pre-embed bolts (11), tie RC layer steel mesh (14), apply rust inhibitor to the surface of the steel bars, pour RC layer (5) and cure, and complete the prefabrication of UHPC shell formwork-RC composite bridge deck after the curing meets the standards. S3. On-site assembly: Transport the prefabricated steel-UHPC combined U-beam and UHPC shell mold-RC combined bridge deck to the construction site, hoist and fix the steel-UHPC combined U-beam, then hoist the UHPC shell mold-RC combined bridge deck to the top of the steel-UHPC combined U-beam, adjust the assembly accuracy, grind the connection surface and then assemble the bridge deck. After that, embed the outward flange (9) of the steel-UHPC combined U-beam into the groove (10) of the UHPC shell mold-RC combined bridge deck and fix it, fill with structural adhesive, and at the same time install the anti-shear pin (7) so that it can be screwed into the sleeve (13) in the RC layer (5). Connect the bolt (11) in the groove (10) to the nut (12) on the outward flange (9) to complete the assembly. S4. Wet joint pouring and curing: Wet joint UHPC is poured at the assembly gap, and geotextile is used for covering and watering curing. The curing time is not less than 14 days, and the wet joint UHPC is cured until it reaches the design strength, forming an integral continuous box girder structure, and the main bridge construction is completed. S5. Corrosion protection: All components shall be treated with anti-corrosion coatings and paints, and cured for no less than 24 hours after application.

7. The construction method of a steel-clad web-based UHPC-RC composite box girder according to claim 6, characterized in that, In step S1, the tensioning sequence of the prestressed tendons in the body is symmetrical tensioning from both ends to the middle, and the tensioning speed is controlled at 0.5-1.0 mm / min.

8. The construction method of a UHPC-RC composite box girder with steel-clad web according to claim 6, characterized in that, In steps S1 and S2, steam curing is used, with the curing temperature controlled at 35-45℃ and the curing time not less than 7 days.

9. The construction method of a UHPC-RC composite box girder with steel-clad web according to claim 6, characterized in that, In step S2, the RC layer (5) is naturally cured for a period of no less than 14 days.

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