Prestressed UHPC-steel plate-NC combined continuous box girder bridge and construction method

Abstract

The invention relates to the technical field of bridge engineering, in particular to a prestressed UHPC-steel plate-NC combined continuous box girder bridge and a construction method.The continuous box girder bridge comprises pile foundations, piers and a bridge deck, the bridge deck comprises a plurality of segments which are arranged side by side and connected end to end, and the segments comprise UHPC-steel plate-NC combined box girder segments and UHPC-NC combined box girder segments; each UHPC-steel plate-NC combined box girder segment comprises UHPC outer webs arranged in parallel, the bottoms of the UHPC outer webs are connected through UHPC outer bottom plates to form a U-shaped section, UHPC upper transverse ribs are arranged on the tops of the UHPC outer webs, the inner sides of the UHPC outer webs are connected with NC inner webs through steel plates with PBL, the inner sides of the UHPC outer bottom plates are connected with NC inner bottom plates, and the tops of the UHPC upper transverse ribs are connected with NC top plates. And the UHPC-NC combined box girder section is not provided with a steel plate. And the performance and cost of the bridge are balanced through the combination of the UHPC, the steel plate and the NC.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering technology, specifically to a prestressed UHPC-steel plate-NC composite continuous box girder bridge and its construction method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Prestressed concrete box girder bridges (continuous beam bridges and continuous rigid frame bridges) are simple in structure, convenient to construct, and low in cost, making them a widely used bridge type. However, existing large-span prestressed concrete box girder bridges commonly exhibit problems such as excessive deflection of the main span and cracking of the girder during operation. According to existing research, these problems are often caused by the inherent characteristics of ordinary concrete (NC) (extremely low tensile strength and high creep coefficient). Summary of the Invention

[0004] To address the technical problems mentioned above, this invention provides a prestressed UHPC-steel plate-NC composite continuous box girder bridge and its construction method. Through material innovation (UHPC + steel plate), structural optimization (composite section, PBL key), and economical design (local reinforcement), it systematically overcomes the industry challenges of deflection and cracking in long-span box girder bridges, combining technological advancement with engineering applicability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a prestressed UHPC-steel plate-NC composite continuous box girder bridge, including pile foundations, piers and bridge deck, the bridge deck including multiple parallel segments connected end to end, the segments including UHPC-steel plate-NC composite box girder segments and UHPC-NC composite box girder segments;

[0007] The UHPC-steel plate-NC composite box girder segment includes parallel UHPC outer webs. The bottom of the UHPC outer webs is connected by the UHPC outer bottom plate to form a U-shaped section. The top is provided with UHPC upper transverse ribs. The inner side of the UHPC outer webs is connected to the NC inner webs by steel plates with PBLs. The inner side of the UHPC outer bottom plate is connected to the NC inner bottom plate. The top of the UHPC upper transverse ribs is connected to the NC top plate.

[0008] The UHPC-NC composite box girder segment includes parallel UHPC outer webs. The bottom of the UHPC outer webs is connected by the UHPC outer bottom plate to form a U-shaped section. The top is provided with UHPC upper transverse ribs. The inner side of the UHPC outer webs is connected to the NC inner webs. The inner side of the UHPC outer bottom plate is connected to the NC inner bottom plate. The top of the UHPC upper transverse ribs is connected to the NC top plate.

[0009] Furthermore, in the UHPC-steel plate-NC composite box girder segment, the UHPC outer web, the steel plate with PBL, the UHPC outer bottom plate, and the UHPC upper transverse rib are prefabricated components, forming a U-shaped outer formwork for the UHPC-steel composite.

[0010] Furthermore, the connection between two adjacent UHPC-steel plate-NC composite box girder segments is achieved by welding steel plates with PBL.

[0011] Furthermore, in the UHPC-NC composite box girder segment, the UHPC outer web, UHPC outer bottom plate, and UHPC upper transverse rib are prefabricated components, forming the U-shaped outer formwork of the UHPC.

[0012] Furthermore, the NC inner web, NC inner bottom plate, and NC top plate in the segment are cast-in-place components.

[0013] Furthermore, the UHPC outer web has UHPC vertical ribs with set thickness, height and spacing, while the UHPC outer bottom plate does not have horizontal ribs; the UHPC vertical ribs, UHPC outer web, and UHPC outer bottom plate are prefabricated as a whole in the same process, with holes reserved during prefabrication.

[0014] Furthermore, longitudinal reinforcing bars are inserted into the holes, and the longitudinal reinforcing bars between adjacent segments are connected by welding.

[0015] Furthermore, shear keys are provided on the end faces of the UHPC outer web plate and UHPC outer bottom plate. The shear keys include matching tenons and mortises. The UHPC outer web plate and UHPC outer bottom plate of two adjacent segments are spliced ​​together by the tenon and mortise.

[0016] Furthermore, the NC inner bottom plate is connected to the reserved steel bars on the UHPC outer bottom plate to form an integral whole, and the NC top plate is connected to the reserved steel bars on the UHPC upper transverse rib and the UHPC outer web plate to form an integral whole.

[0017] A second aspect of the present invention provides a construction method for a prestressed UHPC-steel plate-NC composite continuous box girder bridge, comprising the following steps:

[0018] Construction of the bridge substructure, including the prefabrication of external formwork for each segment;

[0019] Install the outer formwork of the target segment, cast in place the NC inner box, tension the prestress, and complete the consolidation of the pier top;

[0020] Apply adhesive to the tenons and mortises in adjacent segments, install the outer formwork of the next segment, temporarily tension the prestressing, cast the NC inner box in place, and remove the temporary prestressing after formal tensioning.

[0021] Symmetrical construction of the remaining segments corresponding to the current segment continues until the side span is closed;

[0022] Cast-in-place side span segments, completing side span closure and prestressing tensioning;

[0023] For continuous beams, the mid-span closure and prestressing tensioning are carried out, and the temporary consolidation is removed.

[0024] Complete the ancillary works and bridge deck paving.

[0025] Compared with existing technologies, one or more of the above technical solutions have the following beneficial effects:

[0026] 1. Through material innovation (UHPC + steel plate) + structural optimization (composite section, PBL key) + economical design (local reinforcement), the industry problem of deflection and cracking in long-span box girder bridges has been systematically overcome, combining technological advancement and engineering applicability.

[0027] 2. The mid-span deflection of long-span prestressed concrete continuous box girder bridges is mainly caused by concrete creep. According to the linear creep theory of concrete, creep deformation is positively correlated with the material's creep coefficient and stress. During the bridge's service life, for a fully NC structure, due to the higher beam height near the pier top and the negative bending moment, the compressive stress at the lower edge of the box girder will be greater than that at the upper edge. Consequently, the creep compressive strain at the lower edge will be greater than that at the upper edge, leading to creep rotation in the negative bending moment region at the pier top, and the main girder will experience significant bending creep deflection. However, for a UHPC-NC composite structure where the bottom slab and web of the box girder utilize UHPC, the bottom uses UHPC material with a higher elastic modulus and a lower creep coefficient. This bottom UHPC material can bear more compressive stress, thus reducing the compressive stress in the upper NC section. Under long-term loads, because the creep coefficient of UHPC is only 15% of that of NC, the stress redistribution along the section height of the UHPC-NC composite structure in the negative bending moment region at the pier top will occur. That is, the stress in the NC part will be smaller and more uniform, thus reducing the creep deformation of NC. The stress in the bottom UHPC will increase accordingly. However, due to the small creep coefficient of UHPC, even with the increase in stress, there will be no significant creep deformation. By using precast UHPC structures in the bottom plate and web of the box girder, the shrinkage and creep of NC can be constrained. The shrinkage and creep coefficients of the resulting UHPC-NC composite structure are lower than those of the NC structure, effectively suppressing the bending and creep deflection of the beam in long-span continuous box girder bridges, thereby avoiding the risk of deflection of the bridge as a whole caused by long-term creep.

[0028] 3. Introducing ultra-high performance concrete (UHPC) into critical load-bearing areas (such as the web and base slab) significantly reduces long-term creep deflection and provides ultra-high tensile strength (including fiber reinforcement), effectively inhibiting crack propagation. Steel plates can be optionally used in the web, further enhancing shear stiffness and crack resistance through the UHPC-steel combination. Since UHPC is used only in stress concentration or vulnerable areas (such as the web and base slab), while non-concrete composites (NC) are retained in other areas, costs can be reduced. Furthermore, the precast UHPC portion serves as permanent formwork, reducing construction steps. The steel plate functions as both formwork and shear-resistant components, improving efficiency and achieving an economic balance.

[0029] 4. A precast UHPC-steel or a combination of UHPC and cast-in-place NC structure is adopted. Based on the high tensile strength of UHPC and the high strength of the steel plate, the tensile strength of the web is improved, effectively suppressing the diagonal cracks in the web caused by insufficient vertical prestressing in traditional box girder bridges. Secondly, the addition of high-strength materials further improves the normal and oblique section strength of the cross-section, effectively suppressing mid-span deflection of the main girder. Furthermore, the steel plate set in the box girder web can act as the outer formwork during UHPC casting, reducing formwork removal work. The PBL set on the steel plate not only strengthens the connection between the steel plate and NC but also further improves the out-of-plane stiffness of the web. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 A schematic diagram of the overall structure of a continuous box girder bridge with prestressed UHPC-steel plate-NC combination provided for one or more embodiments of the present invention;

[0032] Figure 2 A schematic diagram of the UHPC-steel plate-NC composite box girder segment structure in a box girder bridge provided in one or more embodiments of the present invention;

[0033] Figure 3 A schematic diagram of the tenon and groove structure on the end face of a UHPC-steel plate-NC composite box girder segment in a box girder bridge provided in one or more embodiments of the present invention;

[0034] Figure 4 This is a structural schematic diagram of a UHPC-NC composite box girder segment in a box girder bridge provided in one or more embodiments of the present invention;

[0035] Figure 5 A schematic diagram of the U-shaped external formwork structure for a UHPC-steel plate-NC composite box girder in a box girder bridge provided in one or more embodiments of the present invention;

[0036] Figure 6A schematic diagram of the U-shaped external formwork structure for a UHPC-NC composite box girder segment in a box girder bridge provided in one or more embodiments of the present invention;

[0037] Figure 7 A schematic diagram of a steel plate with PBL in a box girder bridge provided for one or more embodiments of the present invention;

[0038] Figure 8 A comparison chart showing the trend of the nominal creep coefficient of the UHPC-NC combined structure under compression calculated by finite element method for one or more embodiments of the present invention with the calculation results of the full NC structure over time.

[0039] In the diagram: 1. UHPC-steel plate-NC composite box girder segment; 2. UHPC-NC composite box girder segment; 3. UHPC outer web; 4. Steel plate with PBL; 5. NC inner web; 6. UHPC outer bottom plate; 7. NC inner bottom plate; 8. UHPC upper transverse rib; 9. NC top plate; 10. Tenon; 11. Mortise and tenon; 12. PBL; 13. Longitudinal reinforcement; 14. Reserved reinforcement in UHPC outer web; 15. Reserved reinforcement in UHPC upper transverse rib; 16. UHPC vertical rib; 17. Stud; 18. Reserved reinforcement in UHPC outer bottom plate; 19. Reserved hole. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0042] As described in the background section, long-span prestressed concrete box girder bridges (including continuous beam bridges and continuous rigid frame bridges) commonly experience excessive deflection of the main span and cracking of the girder during operation. To address this issue, the following embodiments present a prestressed UHPC-steel plate-NC composite continuous box girder bridge and its construction method. Through material innovation (UHPC + steel plate), structural optimization (composite section, PBL key), and economical design (local reinforcement), this method systematically overcomes the industry challenge of deflection and cracking in long-span box girder bridges, combining technological advancement with engineering applicability.

[0043] The technical terms involved in this solution are as follows.

[0044] Excessive deflection of the main span: Due to the large creep coefficient of ordinary concrete (NC), under long-term load, the accumulated creep deformation caused by stress gradient in the beam leads to continuous deflection at the mid-span, affecting the bridge alignment, driving comfort and structural safety.

[0045] Beam cracking (especially diagonal cracks in the web): Low NC tensile strength, coupled with insufficient or failed vertical prestressing, leads to diagonal cracks in the web at an angle of 20° to 50° with the beam axis, weakening the structural bearing capacity and durability.

[0046] Ultra-High Performance Concrete (UHPC) is a fiber-reinforced cementitious composite material with ultra-high mechanical properties and superior durability. UHPC components undergo high-temperature steam curing, exhibiting virtually no post-contraction shrinkage. Furthermore, its dense internal structure and low porosity prevent the gel from flowing under pressure, resulting in a creep coefficient that is only about 15% of that of ordinary concrete. Existing engineering practice shows that when applied to bridge engineering, UHPC can reduce structural dimensions, thereby reducing the bridge's self-weight load, decreasing stress on the main girder, and significantly improving the bridge's crack resistance.

[0047] PBL (Perfobond Leiste) is a perforated rib connector widely used in steel-concrete composite structures for shear resistance. It consists of a perforated steel plate (or steel rib) and through-bar reinforcement. Its core function is to enhance the shear force transfer between steel and concrete (or UHPC), prevent interface slippage, and ensure the overall coordinated operation of the composite structure.

[0048] Example 1:

[0049] This embodiment proposes a prestressed UHPC-steel plate-NC composite continuous box girder bridge.

[0050] A prestressed UHPC-steel plate-NC composite continuous box girder bridge includes pile foundations, piers and bridge deck. The bridge deck includes multiple parallel segments connected end to end, including UHPC-steel plate-NC composite box girder segments and UHPC-NC composite box girder segments.

[0051] The UHPC-steel plate-NC composite box girder segment includes parallel UHPC outer webs. The bottom of the UHPC outer webs is connected by the UHPC outer bottom plate to form a U-shaped section. The top is provided with UHPC upper transverse ribs. The inner side of the UHPC outer webs is connected to the NC inner webs by steel plates with PBLs. The inner side of the UHPC outer bottom plate is connected to the NC inner bottom plate. The top of the UHPC upper transverse ribs is connected to the NC top plate.

[0052] The UHPC-NC composite box girder segment includes parallel UHPC outer webs. The bottom of the UHPC outer webs is connected by the UHPC outer bottom plate to form a U-shaped section. The top is provided with UHPC upper transverse ribs. The inner side of the UHPC outer webs is connected to the NC inner webs. The inner side of the UHPC outer bottom plate is connected to the NC inner bottom plate. The top of the UHPC upper transverse ribs is connected to the NC top plate.

[0053] like Figures 1-7 As shown, the prestressed UHPC-(steel plate)-NC composite continuous box girder bridge in this embodiment is a continuous beam bridge with a span arrangement of 65m+120m+65m. This composite continuous box girder bridge is composed of either UHPC-steel plate-NC composite box girder segment 1 or UHPC-NC composite box girder segment 2. UHPC-steel plate-NC composite box girder segment 1 can be arranged in the high shear force region of the bridge (from the pier top to 1 / 3 of the span). The entire bridge adopts longitudinal whole-body prestressing. The stress system, UHPC-steel plate-NC composite box girder segment 1 includes UHPC part (3, 6, 8, 10), steel part (4) and NC part (5, 7, 9), UHPC-NC composite box girder segment 2 includes UHPC part (3, 6, 8, 10) and NC part (5, 7, 9), UHPC part (3, 6, 8, 10) and steel part (4) adopt an integrated prefabrication form, and NC part (5, 7, 9) adopt an integrated cast-in-place form.

[0054] like Figure 2 and Figure 3 As shown, in this embodiment, the UHPC-steel plate-NC composite box girder segment 1 includes a UHPC outer web 3, a steel plate 4 with PBL, a UHPC outer bottom plate 6, a UHPC upper transverse rib 8, an NC inner web 5, an NC inner bottom plate 7, and an NC top plate 9.

[0055] Two UHPC outer web plates 3 are arranged side by side, with the bottom connected to the UHPC outer bottom plate 6 to form a U-shaped cross section, and the top connected to the UHPC upper transverse rib 8. The inner side of the UHPC outer web plate 3 is connected to the NC inner web plate 5 through the steel plate 4 with PBL, the inner side of the UHPC outer bottom plate 6 is connected to the NC inner bottom plate 7, and the top of the upper transverse rib 8 is connected to the NC top plate 9.

[0056] The UHPC outer web 3, the steel plate 4 with PBL, the UHPC outer bottom plate 6, and the UHPC upper transverse rib 8 are prefabricated components that together form the UHPC-steel composite U-shaped outer formwork (see...). Figure 5 ); NC inner web 5, NC inner bottom plate 7, and NC top plate 9 are a cast-in-place component.

[0057] UHPC-steel composite U-shaped external formwork (see...) Figure 5 It can be used as part of the external formwork for cast-in-place NC inner web 5, NC inner bottom slab 7, and NC top slab 9. Among them, the thickness of UHPC outer web 3 and UHPC outer bottom slab 6 is 5~10cm, the thickness of steel plate 4 with PBL is 5~8mm, the thickness of UHPC upper transverse rib 8 is 10~15cm, and the minimum height is 20cm; the thickness of NC inner web 5 is 30~40cm, the thickness of NC inner bottom slab 7 is 15~25cm, and the minimum thickness of NC top slab 9 is 20cm.

[0058] like Figure 7As shown, in this embodiment, the steel plate 4 with PBL is connected to the outer web 3 of the UHPC via studs 17, and can serve as the outer formwork during the casting of the outer web 3 of the UHPC. Between two segments, the steel plate 4 with PBL is connected by welding. The PBL thickness is 6-10mm, the height of PBL12 is approximately 5cm, and the spacing is approximately 0.5m. Holes with a diameter of approximately 15mm are drilled in the PBL 12, spaced approximately 10cm apart, and longitudinal reinforcing bars 13 are inserted into the holes. The longitudinal reinforcing bars 13 are structural measures to strengthen the connection between the steel plate 4 with PBL and the inner web 5 of the NC, and have a diameter of 8-12mm. The longitudinal reinforcing bars between two adjacent segments are connected by welding.

[0059] like Figure 4 As shown, in this embodiment, the UHPC-NC composite box girder segment 2 includes a UHPC outer web 3, a UHPC outer bottom plate 6, a UHPC upper transverse rib 8, an NC inner web 5, an NC inner bottom plate 7, and an NC top plate 9.

[0060] Two UHPC outer web plates 3 are arranged side by side, with the bottom connected to the UHPC outer bottom plate 6 to form a U-shaped cross section, and the top connected to the UHPC upper transverse rib 8. The inner side of the UHPC outer web plate 3 is connected to the NC inner web plate 5, the inner side of the UHPC outer bottom plate 6 is connected to the NC inner bottom plate 7, and the top of the upper transverse rib 8 is connected to the NC top plate 9.

[0061] The UHPC outer web 3, UHPC outer bottom plate 6, and UHPC upper transverse rib 8 are prefabricated components that together form the UHPC U-shaped outer formwork (see...). Figure 6 The NC inner web 5, NC inner bottom plate 7, and NC top plate 9 are a single cast-in-place component. UHPC U-shaped outer formwork (see...) Figure 6 It can be used as part of the external formwork for cast-in-place NC inner web 5, NC inner bottom slab 7, and NC top slab 9. Among them, the thickness of UHPC outer web 3 and UHPC outer bottom slab 6 is 8~12cm, the thickness of UHPC upper transverse rib 8 is 10~15cm, and the minimum height is 20cm; the thickness of NC inner web 5 is 40~50cm, the thickness of NC inner bottom slab 7 is 15~25cm, and the minimum thickness of NC top slab 9 is 20cm.

[0062] like Figure 6As shown, in this embodiment, UHPC vertical ribs 16 are provided on the outer web 3 of the UHPC. The thickness of the UHPC vertical ribs 16 is about 3cm, the height is about 5cm, and the spacing is about 0.5m. No horizontal ribs are provided on the outer bottom plate 6 of the UHPC. The UHPC vertical ribs 16 are prefabricated integrally with the outer web 3 and the outer bottom plate 6 of the UHPC. During prefabrication, reserved holes 19 are provided on them. The reserved holes 19 are about 15mm in diameter and spaced about 10cm apart. If there are reinforcing bars around the reserved holes 19, the reinforcing bars need to be cut or bent to ensure that the reserved holes 19 can pass through the reinforcing mesh smoothly. Longitudinal reinforcing bars 13 pass through the reserved holes 19. The longitudinal reinforcing bars 13 are structural measures to strengthen the connection performance between the outer web 3 of the UHPC and the inner web 5 of the NC, and have a diameter of 8~12mm. The longitudinal reinforcing bars between two adjacent segments are connected by welding.

[0063] In this embodiment, the upper transverse rib 8 of the UHPC is a reinforcement of the UHPC-steel composite outer formwork (see...). Figure 5 ) or UHPC U-shaped external template (see Figure 6 The stability construction measures are set at intervals of 3 to 5 meters and connected to the UHPC vertical ribs 16 or PBL12.

[0064] like Figures 2-4 As shown, in this embodiment, the UHPC outer web 3 and the UHPC outer bottom plate 6 are provided with shear keys on the end faces of the segments. The shear keys are mortise and tenon structures including tenons 10 and mortises 11. The UHPC outer web 3 and UHPC outer bottom plate 6 of adjacent segments are connected by the mortise and tenon structure composed of tenons 10 and mortises 11. When splicing, epoxy resin adhesive with a thickness of no more than 3mm is evenly applied to the end faces of the UHPC outer web 3 and UHPC outer bottom plate 6 and the tenons 10 and mortises 11.

[0065] like Figure 5 and Figure 6 As shown, in this embodiment, the NC inner bottom plate 7 is connected to the UHPC outer bottom plate 6 as a whole through the UHPC outer bottom plate reserved steel bar 18, and the NC top plate 9 is connected to the UHPC outer web plate 3 and the UHPC upper transverse rib 8 as a whole through the UHPC outer web plate reserved steel bar 14 and the UHPC upper transverse rib reserved steel bar 15.

[0066] In this embodiment, the prestressing system includes an internal prestressing structure installed in UHPC-steel plate-NC composite box girder segment 1 or UHPC-NC composite box girder segment 2. When the internal prestressing structure conflicts with the position of PBL12 or UHPC vertical rib 16, PBL12 and UHPC vertical rib 16 can be cut off at the conflicting position.

[0067] In this design, the box girder web adopts a precast UHPC-steel or a combination of UHPC and cast-in-place NC structure. Traditionally, the vertical prestressing of the web of long-span prestressed concrete continuous box girder bridges typically uses a precision-rolled threaded steel anchorage system. However, during later operation, numerous diagonal cracks at 25° to 50° to the beam axis appear in the box girder web. Article 6.3.3 of the "Design Specification for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts JTG 3362-2018" states that insufficient vertical prestressing is one of the main causes of diagonal cracks in the box girder web, primarily due to the low tensile strength of the NC. Furthermore, mid-span deflection often occurs simultaneously with diagonal cracks in the web, mutually reinforcing each other. Therefore, ensuring sufficient normal and diagonal section strength of the main girder is paramount.

[0068] Based on this, the box girder web of this scheme adopts a precast UHPC-steel or a combination of UHPC and cast-in-place NC structure. Leveraging the high tensile strength of UHPC and the high strength of the steel plate, the tensile strength of the web can be improved, effectively suppressing the diagonal cracks in the web caused by insufficient vertical prestressing in traditional box girder bridges. Secondly, the addition of high-strength materials can further improve the normal and oblique section strength of the cross-section, effectively suppressing mid-span deflection of the main girder. Furthermore, the steel plate in the box girder web can act as the outer formwork during UHPC casting, reducing formwork removal work. The PBL (Polymerized Bar Bearing) on ​​the steel plate not only strengthens the connection between the steel plate and NC but also further improves the out-of-plane stiffness of the web; the longitudinal reinforcement inserted on the PBL is connected between adjacent segments by welding, greatly improving the overall integrity between different NC segments. Considering economic factors, the web of the box girder can also adopt a combination of precast UHPC and cast-in-place NC, which can also improve the shear resistance of the web. The UHPC is tightly connected to the NC through UHPC vertical ribs with interlaced longitudinal reinforcement, and the UHPC vertical ribs can play a role similar to PBL.

[0069] In this design, the bottom slab of the box girder adopts a combined structure of precast UHPC and cast-in-place NC. The mid-span deflection of the long-span prestressed concrete continuous box girder bridge is mainly caused by concrete creep. Figure 8 The trend of the nominal creep coefficient (the ratio of the long-term strain increment of NC or UHPC to the initial elastic strain of NC or UHPC) of a structure calculated by finite element method under compression as a function of time is presented.

[0070] The nominal creep coefficient is defined as the ratio of the long-term strain increment of the NC or UHPC to the initial elastic strain of the NC or UHPC.

[0071] Consider two scenarios: ① UHPC-NC composite structure, ② all-NC structure. As shown in the figure, after one year, the nominal creep coefficient of the UHPC-NC composite structure is approximately half that of the all-NC structure, indicating that this composite structure can reduce the shrinkage and creep deformation of the bridge under long-term loads.

[0072] According to the linear creep theory of concrete, creep deformation is positively correlated with the creep coefficient and stress of the material. During the service life of a bridge, for a fully NC structure, due to the high beam height near the pier top and the negative bending moment, the compressive stress at the lower edge of the box girder will be greater than that at the upper edge. Consequently, the creep compressive strain at the lower edge will be greater than that at the upper edge, resulting in a creep rotation angle in the negative bending moment region at the pier top. The main beam will then experience significant bending creep deflection.

[0073] For the box girder's bottom slab and web sections, a UHPC-NC composite structure using UHPC is employed. The bottom section utilizes UHPC material with a high elastic modulus and low creep coefficient, allowing it to withstand more compressive stress and thus reducing the compressive stress in the upper NC section. Under long-term loads, because the creep coefficient of UHPC is only 15% of that of NC, stress redistribution occurs along the section height in the negative bending moment region at the pier top. Specifically, the stress in the NC section is lower and more uniform, further reducing NC creep deformation. Conversely, the stress in the bottom UHPC section increases accordingly. However, due to the low creep coefficient of UHPC, even with increased stress, significant creep deformation will not occur.

[0074] The prestressed UHPC-(steel plate)-NC composite continuous box girder bridge provided by this scheme not only uses UHPC material in the bottom plate of the box girder, but also in the web of the box girder. Therefore, it can further reduce the compressive stress borne by the NC material and reduce the creep deformation of the NC material, effectively suppress the bending creep deflection of the beam of the long-span continuous box girder bridge, and thus avoid the risk of deflection of the bridge as a whole caused by long-term creep.

[0075] In this design, the box girder segments adopt a precast UHPC-steel composite U-shaped structure or a combination of a UHPC U-shaped structure and cast-in-place NC. Given the current high cost of UHPC and steel plates, for economic reasons, only the outer bottom slab of the box girder uses UHPC, while the outer web uses either UHPC or UHPC-steel. Due to the use of ultra-high mechanical properties of UHPC and high-strength steel plates, the dimensions of the box girder web and bottom slab can be reduced, which helps to reduce the bridge's self-weight and further reduce the stress on the main girder. The precast UHPC outer bottom slab can form a U-shaped outer formwork together with the UHPC-steel or UHPC outer web, serving as part of the outer formwork during bridge construction, greatly improving construction convenience and saving significant formwork costs. Furthermore, the use of low-permeability UHPC material on the exterior of the box girder web and bottom slab effectively resists corrosive environments and maintains its good performance and appearance integrity over the long term, thus ensuring the safety and durability of the bridge structure.

[0076] The transverse ribs on the UHPC in this design can improve the stability of the precast UHPC external formwork during the cast-in-place NC construction process, and can also improve the lateral bending stiffness of the box girder NC top slab, thereby further reducing the thickness of the NC top slab, reducing material usage, and lowering costs.

[0077] This solution systematically overcomes the industry challenge of deflection and cracking in long-span box girder bridges through material innovation (UHPC + steel plate), structural optimization (composite cross-section, PBL key), and economical design (local reinforcement), combining technological advancement with engineering applicability.

[0078] Breakthroughs in material properties, specifically:

[0079] UHPC (with a creep coefficient of only 15% of NC) is used in the maximum compressive stress zone (bottom plate) to reduce creep deformation at the source;

[0080] The use of UHPC-steel composite structure in the area of ​​maximum shear force (web plate) increases tensile strength by 5-10 times and directly inhibits crack formation.

[0081] Throughout the entire structural system, the UHPC-NC composite section allows the UHPC to bear the high stress, reducing the stress on the NC. The PBL key and tenon-and-mortise structure ensure the coordinated work of different materials, preventing interface failures from causing new defects and ensuring connection reliability.

[0082] The economic balance is achieved by using UHPC only in stress concentration or vulnerable areas (such as the web and base plate), while retaining NC in other areas, thus reducing costs (the cost of full UHPC is approximately 6 to 10 times that of NC). The precast UHPC portion serves as permanent formwork, reducing construction steps; the steel plate also functions as formwork and shear-resistant components, improving efficiency, thereby achieving an economic balance through the combined structure.

[0083] In terms of specific costs, only 20% to 30% of the volume uses UHPC, which saves costs compared to full UHPC; UHPC precast components also serve as permanent formwork, indirectly reducing the amount of formwork work; the construction period is reduced by combining precasting and cast-in-place operations; the steel plates in the structure serve as both shear-resistant components and formwork, saving on special formwork costs.

[0084] Structural optimization, specifically:

[0085] UHPC-NC composite section: The UHPC bears the load in the high stress area, reduces the stress of NC, and reduces NC creep deformation;

[0086] PBL key and vertical rib: enhance the interface connection between UHPC / steel plate and NC, and ensure the integrity of the combined structure;

[0087] Internal prestressing system: avoids the vulnerability of external prestressing and improves long-term reliability.

[0088] In terms of construction, a "sandwich" material layout is adopted: the top plate uses NC (non-conductive steel) for ample compressive strength; the web uses a UHPC / steel-NC composite layer as the shear core; and the bottom plate uses a UHPC-NC gradient transition to form a critical zone for creep resistance. Through precise material-oriented reinforcement and maximizing structural efficiency, the amount of UHPC used is controlled within an economically reasonable range while ensuring structural performance.

[0089] Example 2:

[0090] The construction method for the prestressed UHPC-(steel plate)-NC composite continuous box girder bridge in this embodiment includes the following steps:

[0091] Step 1: Construct the bridge substructure, including pile foundations and piers; simultaneously, prefabricate the UHPC-steel composite U-shaped external formwork for each segment (see...). Figure 5 ) or UHPC U-shaped external template (see Figure 6 Traditional long-span prestressed continuous box girder bridges generally employ cantilever cast-in-place construction methods, requiring the erection of external formwork around the box girder. This not only consumes a large amount of external formwork, increasing construction costs, but also delays the construction schedule. The precast UHPC-steel composite U-shaped structure or UHPC U-shaped structure used in this scheme can serve as part of the external formwork during cantilever cast-in-place construction, reducing formwork costs and lowering overall construction costs, while also improving construction speed and convenience.

[0092] Step 2: Install the 0# segment UHPC-steel composite U-shaped external formwork or UHPC U-shaped external formwork on the top of the main pier. Use it as part of the external formwork to cast the internal NC part in place. After the NC reaches the corresponding strength, prestress the 0# segment and temporarily consolidate the 0# segment.

[0093] Step 3: Apply epoxy resin evenly to the connecting end faces of the UHPC outer web 3 and UHPC outer bottom plate 6 of segment 0, the tenon groove 11, and the connecting end faces of the UHPC outer web 3 and UHPC outer bottom plate 6 of segment 1 and the tenon 10. Install the UHPC-steel composite U-shaped outer formwork or UHPC U-shaped outer formwork of segment 1 and apply temporary prestressing tension to ensure a firm bond between the UHPC outer web 3 and UHPC outer bottom plate 6 between segments. Then, use it as part of the outer formwork to cast the NC inner web 5, NC inner bottom plate 7, and NC top plate 9 of segment 1. During this process, the magnitude of the temporary prestress can be adjusted to avoid excessive local stress in the precast UHPC outer web 3 and UHPC outer bottom plate 6. Finally, after the NC reaches the corresponding strength, apply prestressing tension to segment 1 and remove the temporary prestress.

[0094] Step 4: Following the construction process of segment 1 above, construct the remaining UHPC-steel plate-NC composite box girder segment 1 or UHPC-NC composite box girder segment 2 symmetrically on both sides until the side span is closed.

[0095] Step 5: Erect a full-span scaffold, on which the UHPC-steel composite U-shaped outer formwork or UHPC U-shaped outer formwork of the side span is spliced. Using it as part of the outer formwork, the inner web 5, inner bottom slab 7, and top slab 9 of the NC of the side span are poured. After the NC reaches the corresponding strength, the side span is closed and the corresponding prestressed tendons are tensioned.

[0096] Step 6: After the side spans are closed, the middle span is closed and the corresponding prestressing tensioning is completed; before the middle span is closed, the temporary consolidation of segment #0 is removed.

[0097] Step 7: Complete the bridge ancillary works and bridge deck paving.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A continuous box girder bridge composed of prestressed UHPC-steel plate-NC composite, characterized in that, It includes pile foundations, piers and bridge deck, the bridge deck comprising multiple parallel segments connected end to end, the segments including UHPC-steel plate-NC composite box girder segments and UHPC-NC composite box girder segments; The UHPC-steel plate-NC composite box girder segment includes parallel UHPC outer webs. The bottom of the UHPC outer webs is connected by UHPC outer bottom plates to form a U-shaped section. The top is provided with UHPC upper transverse ribs. The inner side of the UHPC outer webs is connected to the NC inner webs by steel plates with PBLs. The inner side of the UHPC outer bottom plates is connected to the NC inner bottom plates. The top of the UHPC upper transverse ribs is connected to the NC top plates. The UHPC-NC composite box girder segment includes parallel UHPC outer webs. The bottom of the UHPC outer webs is connected by UHPC outer bottom plates to form a U-shaped section. The top is provided with UHPC upper transverse ribs. The inner side of the UHPC outer webs is connected to the NC inner webs. The inner side of the UHPC outer bottom plates is connected to the NC inner bottom plates. The top of the UHPC upper transverse ribs is connected to the NC top plates.

2. The prestressed UHPC-steel plate-NC composite continuous box girder bridge as described in claim 1, characterized in that, In the UHPC-steel plate-NC composite box girder segment, the UHPC outer web, the steel plate with PBL, the UHPC outer bottom plate, and the UHPC upper transverse rib are prefabricated components, forming a U-shaped outer formwork for the UHPC-steel composite.

3. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, The connection between two adjacent UHPC-steel plate-NC composite box girder segments is achieved by welding steel plates with PBL.

4. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, In the UHPC-NC composite box girder segment, the UHPC outer web, UHPC outer bottom plate, and UHPC upper transverse rib are prefabricated components, forming the U-shaped outer formwork of the UHPC.

5. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, The NC inner web, NC inner bottom plate, and NC top plate in the segment are cast-in-place components.

6. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, The UHPC outer web has UHPC vertical ribs with a set thickness, height and spacing, while the UHPC outer bottom plate does not have horizontal ribs; the UHPC vertical ribs, the UHPC outer web, and the UHPC outer bottom plate are prefabricated as a whole in the same process, and holes are reserved during prefabrication.

7. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, The hole is filled with longitudinal steel bars, and the longitudinal steel bars between adjacent segments are connected by welding.

8. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, The UHPC outer web and the UHPC outer bottom plate are provided with shear keys on the end face of the segments. The shear keys include matching tenons and mortises. The UHPC outer web and the UHPC outer bottom plate of two adjacent segments are spliced ​​together by the matching tenons and mortises.

9. A continuous box girder bridge with prestressed UHPC-steel plate-NC composite structure as described in claim 1, characterized in that, The NC inner bottom plate is connected to the reserved steel bars on the UHPC outer bottom plate to form an integral whole, and the NC top plate is connected to the reserved steel bars on the UHPC upper transverse rib and the UHPC outer web plate to form an integral whole.

10. A construction method for a prestressed UHPC-steel plate-NC composite continuous box girder bridge according to any one of claims 1-9, characterized in that, Includes the following steps: Construction of the bridge substructure, including the prefabrication of external formwork for each segment; Install the outer formwork of the target segment, cast in place the NC inner box, tension the prestress, and complete the consolidation of the pier top; Apply adhesive to the tenons and mortises in adjacent segments, install the outer formwork of the next segment, temporarily tension the prestressing, cast the NC inner box in place, and remove the temporary prestressing after formal tensioning. Symmetrical construction of the remaining segments corresponding to the current segment continues until the side span is closed; Cast-in-place side span segments, completing side span closure and prestressing tensioning; Perform mid-span closure and prestressing tensioning; if it is a continuous beam, remove the temporary consolidation. Complete the ancillary works and bridge deck paving.

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