NC-UHPC combined assembled prestressed concrete box girder, construction method and bridge thereof

Abstract

The invention discloses an NC-UHPC combined assembled prestressed concrete box girder, comprising a prefabricated NC top plate (11), a prefabricated NC bottom plate (21) and a prefabricated UHPC variable cross-section straight web plate (31), wherein the prefabricated UHPC variable cross-section straight web plate (31) is configured such that the plate surface areas at both ends of the web plate are larger than the plate surface area in the middle. By combining NC-UHPC, the advantages of high compressive strength and low price of NC are fully utilized, and the outstanding advantages of high strength, high elastic modulus, high durability, high toughness, high density, low creep, etc. of UHPC are fully utilized. The box girder has the advantages of excellent structural stress performance, light weight, high cost performance, light construction hoisting weight, reduced support construction, short construction period, etc.

Description

Technical Field

[0001] The present invention relates to the field of bridges, and in particular to an NC-UHPC combined assembled prestressed concrete box girder, a construction method and a bridge thereof. Background Art

[0002] At present, my country is vigorously promoting prefabricated and assembled bridges and composite structure bridges. Compared with cast-in-place concrete box girders, prefabricated and assembled box girders and composite structure box girders have the advantages of significantly improving construction quality and green construction benefits, effectively reducing construction risks and adverse effects of construction on traffic and the environment, and improving production efficiency. Traditional assembled prefabricated segmental prestressed concrete box girders require high construction accuracy, a relatively long prefabrication period, and high requirements for beam storage and transportation. Whether the whole hole segment assembly of the bridge erection machine or the cantilever segment assembly is used, the requirements for on-site construction equipment are very high. Traditional concrete box girders have the disadvantages of easy cracking of the web and heavy weight due to the low tensile and shear strength of ordinary concrete itself. In response to this problem, the disadvantages of traditional concrete box girders can be solved by using corrugated steel web concrete box girders and steel truss web concrete composite beams, but there are also problems such as large workload for later maintenance, stress concentration at the steel-concrete connection node, and complex force. Ultra-High Performance Concrete (UHPC) is a high-density cement-based composite engineering material prepared based on the principle of maximum packing density (reducing porosity and macropores) and low water-cement ratio. It has outstanding advantages such as high strength, high elastic modulus, high durability, high toughness, high density, and low creep. Many engineering practices have shown that UHPC can significantly reduce component size, reduce structural deadweight, and increase spanning capacity while ensuring the same strength and durability.

[0003] In bridge engineering, although UHPC has been widely used in many aspects such as combined bridge deck pavement structures and reinforcement of old bridges, from the current usage situation, one of the main factors restricting the development of UHPC bridge structures is its high cost and high self-shrinkage characteristics. In the field of bridge structure engineering technology, it would be very uneconomical to use UHPC as the main structural material, and because the bridge structure needs to meet multiple performance targets such as strength, stiffness, and stability, its ultra-high mechanical properties cannot be fully utilized, so that the advantages of UHPC materials will be idle and wasted. Summary of the invention

[0004] In view of this, the NC-UHPC combined assembled prestressed concrete box girder and the construction method thereof of the present invention, by combining NC-UHPC, fully utilizes the advantages of high compressive strength and low price of NC, and gives full play to the outstanding advantages of UHPC such as high strength, high elastic modulus, high durability, high toughness, high density, low creep, etc., and has the advantages of excellent structural stress performance, light weight, high cost performance, light construction hoisting weight, reduced support construction, short construction period, etc.

[0005] The NC-UHPC combined assembled prestressed concrete box girder of the present invention comprises a prefabricated NC top plate (11), a prefabricated NC bottom plate (21) and a prefabricated UHPC variable cross-section straight web plate (31), wherein the prefabricated UHPC variable cross-section straight web plate (31) is configured such that the plate surface areas at both ends of the web plate are larger than the plate surface area in the middle;

[0006] Furthermore, the prefabricated UHPC variable-section straight web (31) has vertical end plate surfaces that gradually decrease toward the middle to form an hourglass-shaped structure;

[0007] Furthermore, the prefabricated UHPC variable-section straight web (31) is pre-embedded with web vertical prestressed steel bars (35) and oblique prestressed steel bars (36) are arranged along the main tensile stress direction, the prefabricated NC top plate (11) is pre-embedded with top plate joint steel bars (18), the prefabricated NC bottom plate (21) is pre-embedded with bottom plate joint steel bars (27), both ends of the web vertical prestressed steel bars (35) are provided with web connection joints (7), the top plate joint steel bars (18) and the bottom plate joint steel bars (27) are respectively vertically overlapped with the web vertical prestressed steel bars (35) and laterally fixedly connected through the web connection joints (7);

[0008] Furthermore, a web pre-embedded perforated steel plate (33) is provided at the center of the top edge and the bottom edge of the prefabricated UHPC variable-section straight web (31), the openings on the web pre-embedded perforated steel plate (33) are traversed by a web shear key pre-embedded steel pipe (34) and welded firmly, and shear key steel bars (8, 9) are provided through the openings of the web pre-embedded perforated steel plate (33) and the steel pipes of the web pre-embedded steel pipe (34);

[0009] Furthermore, web reinforcement vertical ribs (32) are provided in the center of the longitudinal bridge direction on opposite sides of the prefabricated UHPC variable-section straight web plate (31);

[0010] Furthermore, a top plate reinforcing transverse rib (12) is provided at the center of the bottom edge of the prefabricated NC top plate (11) along the longitudinal bridge direction, and a bottom plate reinforcing transverse rib (22) is provided at the center of the top edge of the prefabricated NC bottom plate (21) along the longitudinal bridge direction, and the top plate reinforcing transverse rib (12), the bottom plate reinforcing transverse rib (22), and the web plate reinforcing vertical rib (32) are provided correspondingly.

[0011] Furthermore, after the prefabricated NC top plates (11) and the prefabricated NC bottom plates (21) are assembled, cast-in-situ UHPC forms a top plate connection belt (6) and a bottom plate connection belt (5), respectively, and both ends of the web pre-embedded perforated steel plate (33) along the longitudinal bridge direction are provided with splicing plates (37), and the splicing plates (37) are connected into a whole by high-strength bolts (38) and embedded between the bottom plate connection belt (5) and the top plate connection belt (6);

[0012] Furthermore, longitudinal prestressed steel bundle corrugated pipes are arranged in the NC prefabricated top plate (11) and the prefabricated NC bottom plate (21), and the prestressed steel bundles penetrate the longitudinal prestressed steel bundle corrugated pipes and are tensioned and anchored by steel bundle anchors (14);

[0013] Furthermore, a cantilever top plate reinforcement longitudinal beam (102) is arranged at the cantilever of the NC prefabricated top plate (11), and a UHPC prefabricated diagonal brace (10) is arranged at the intersection of the cantilever top plate reinforcement longitudinal beam (102) and the top plate reinforcement transverse rib (12), and the UHPC prefabricated diagonal brace (10) is connected to the top plate reinforcement transverse rib (12) and the prefabricated NC bottom plate (21) through a prefabricated diagonal brace UHPC cast-in-place connection joint (101).

[0014] The present invention also discloses a construction method of a NC-UHPC combined assembled prestressed concrete box girder, comprising the following steps:

[0015] Step a, setting up temporary brackets on both sides of the bridge pier, and installing the NC prefabricated bottom plate unit (2) composed of the prefabricated NC bottom plate (21) at the top section of the pier;

[0016] Step b, installing the prefabricated UHPC solid web plate unit (4) composed of the prefabricated UHPC variable-section straight web (31) of the pier top section, installing the prefabricated NC bottom plate (21) and the prefabricated UHPC solid web shear key through the steel bar (8) of the pier top section, and pouring the UHPC cast-in-place web connection joint (7);

[0017] Step c, installing the prefabricated NC top plate unit (1) composed of the prefabricated NC top plate (11) of the pier top section, installing the shear key through-steel bars of the NC prefabricated top plate and the UHPC prefabricated solid web plate of the pier top section, and pouring the UHPC cast-in-place connection joint;

[0018] Step d, using a temporary hanger to install the prefabricated NC bottom plate unit (2) composed of the conventional beam section and the prefabricated NC bottom plate (21) and temporarily fix it;

[0019] Step e, installing the prefabricated UHPC web plate unit (3) composed of the prefabricated UHPC variable-section straight web (31) of the conventional beam section, installing the high-strength bolt connection joint splicing plate (37) connected to the completed segment, tightening the high-strength bolts (38), installing the conventional beam section NC prefabricated bottom plate and the UHPC hourglass-shaped prefabricated web shear key through-steel (9), pouring the UHPC cast-in-place connection joint, and casting the UHPC cast-in-place prefabricated web reinforcement vertical rib connection joint (7);

[0020] Step f, using a temporary hanger to install the conventional beam section NC prefabricated top plate unit (1) and temporarily fix it; installing the conventional beam section prefabricated NC top plate (11) and the UHPC prefabricated web shear key through-steel bars (8), pouring the UHPC cast-in-place connection joint, and pouring the UHPC web reinforcement vertical rib connection joint (7);

[0021] Step g, casting the UHPC cast-in-place bottom plate connecting strip (5) and the UHPC cast-in-place top plate connecting strip (6) between the completed installation segments; after the UHPC cast-in-place strip has been cured to reach the design strength, installing the longitudinal prestressed steel strand anchor (14) and tensioning the top plate longitudinal prestressed steel strand (13), and then performing prestressed grouting and anchor sealing;

[0022] Step h: Repeat steps d to g by using the symmetrical cantilever assembly method to install conventional prefabricated beam segments segment by segment until the entire bridge is closed, and tension the prestressed closing steel strands of the top and bottom plates.

[0023] The invention also discloses a bridge, which comprises a NC-UHPC combined assembled prestressed concrete box girder.

[0024] The beneficial effects of the present invention are as follows: the NC-UHPC combined assembled prestressed concrete box girder and the construction method thereof disclosed in the present invention, by combining NC-UHPC, fully utilizes the advantages of NC's high compressive strength and low price, and gives full play to the outstanding advantages of UHPC such as high strength, high elastic modulus, high durability, high toughness, high density, low creep, etc., and has the advantages of excellent structural stress performance, light weight, high cost performance, light construction hoisting weight, reduced support construction, short construction period, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0026] Figure 1 It is a vertical layout diagram of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention;

[0027] Figure 2 The cross-sectional layout diagram of the NC-UHPC combined assembled prestressed concrete box girder of Example I of the present invention;

[0028] Figure 3 It is a cross-sectional layout diagram of the NC-UHPC combined assembled prestressed concrete box girder of Example II of the present invention;

[0029] Figure 4 A three-dimensional axial perspective view of the NC-UHPC combined assembled prestressed concrete box girder of Example I of the present invention;

[0030] Figure 5 A three-dimensional axial perspective view of the NC-UHPC combined assembled prestressed concrete box girder of Example II of the present invention;

[0031] Figure 6 Schematic diagram of the force mechanism of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention;

[0032] Figure 7 A typical cross-sectional view of the NC-UHPC combined assembled prestressed concrete box girder of Example Ⅰ of the present invention;

[0033] Figure 8 A typical cross-sectional view of the NC-UHPC combined assembled prestressed concrete box girder of Example II of the present invention;

[0034] Fig. 9 for Figure 7 and Figure 8 A partial enlarged view of the middle A;

[0035] Fig.10 for Figure 7 and Figure 8 A partial enlarged view of point B in the middle;

[0036] Fig.11 It is a schematic diagram of a typical segment three-dimensional decomposition structure of the NC-UHPC combined assembled prestressed concrete box girder according to Example I of the present invention;

[0037] Fig.12 It is a schematic diagram of a typical segment three-dimensional decomposition structure of the NC-UHPC combined assembled prestressed concrete box girder according to Example II of the present invention;

[0038] Fig.13 It is a schematic diagram of the three-dimensional structure of a typical segment prefabricated top plate of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention;

[0039] Fig.14 It is a schematic diagram of the three-dimensional structure of a typical segment prefabricated bottom plate of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention;

[0040] Fig.15The elevation and cross-sectional layout diagrams of typical segmental prefabricated webs of the NC-UHPC combined assembled prestressed concrete box girders of Examples I and II of the present invention;

[0041] Fig.16 It is a schematic diagram of a three-dimensional decomposed structure of a typical segmental prefabricated web of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention;

[0042] Fig.17 It is a schematic diagram of the construction method steps of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention;

[0043] Fig.18 It is a schematic diagram of the steps of the construction method of the pier top beam section and typical segments of the NC-UHPC combined assembled prestressed concrete box girder of Example I and Example II of the present invention.

[0044] The above drawings include the following reference numerals: 1—NC prefabricated top plate unit, 2—NC prefabricated bottom plate unit, 3—prefabricated UHPC web plate unit, 4—UHPC prefabricated solid web plate unit of pier top section, 5—bottom plate connecting strip, 6—top plate connecting strip, 7—web plate reinforced vertical rib connection joint, 8—shear key penetrating steel bar of prefabricated NC top plate and UHPC prefabricated variable-section straight web, 9—shear key penetrating steel bar of prefabricated NC bottom plate and UHPC prefabricated variable-section straight web, 10—UHPC prefabricated diagonal brace, 11—prefabricated NC top plate, 12—top plate reinforced transverse rib, 13—top plate longitudinal prestressed steel bundle, 14—longitudinal prestressed steel bundle anchor, 15—top plate shear key embedded perforated steel plate, 16—top plate shear key embedded steel pipe, 17—top plate shear key embedded through steel bar, 18—top plate Joint steel bars, 19—precast NC top plate longitudinal steel bars, 21—precast NC bottom plate, 22—bottom plate reinforced transverse ribs, 23—bottom plate longitudinal prestressed steel strands, 24—precast NC bottom plate shear key embedded perforated steel plate, 25—NC precast bottom plate shear key embedded steel pipe, 26—NC precast bottom plate shear key embedded through steel bars, 27—NC precast bottom plate and reinforced vertical rib connection joint embedded steel bar joint, 28—NC precast bottom plate longitudinal steel bars, 31—precast UHPC variable section straight web, 32—web plate reinforced vertical ribs, 33—web plate embedded perforated steel plate, 34—web plate shear key embedded steel pipe, 35—web plate reinforced vertical rib vertical prestressed steel bars, 36—diagonal prestressed steel bars, 37—splicing plate, 38—high-strength bolts, 101—precast diagonal brace UHPC cast-in-place connection joint, 102—cantilever top plate reinforced longitudinal beam. DETAILED DESCRIPTION

[0045] The NC-UHPC combined assembled prestressed concrete box girder of this embodiment includes a prefabricated NC top plate 11, a prefabricated NC bottom plate 21 and a prefabricated UHPC variable-section straight web 31, wherein the prefabricated UHPC variable-section straight web 31 is configured such that the plate surface area at both ends of the web is larger than the plate surface area in the middle; the assembled prestressed concrete box girder is composed of a pier top segment and a conventional segment, wherein the pier top segment is composed of a prefabricated NC top plate plate unit 1, a prefabricated NC bottom plate plate unit 2 and a pier top segment prefabricated UHPC solid variable-section straight web plate unit 4; the conventional segment is composed of a prefabricated NC top plate plate unit 1, a prefabricated NC bottom plate plate unit 2 and a prefabricated UHPC variable-section straight web plate unit 3. The prefabricated NC top plate unit 1 is composed of a prefabricated NC top plate 11, the prefabricated NC bottom plate unit 2 is composed of a prefabricated NC bottom plate 21, and the UHPC solid variable cross-section straight web plate unit 4 is composed of a prefabricated UHPC variable cross-section straight web 31, except that the prefabricated UHPC variable cross-section straight web 31 of the pier top section is thicker than that of the conventional section. The prefabricated UHPC variable cross-section straight web plate unit 3 is composed of a prefabricated UHPC variable cross-section straight web 31. The box girder adopts a straight web single-box single-chamber or single-box multi-chamber structure, with equal beam height and constant web height. A transverse diaphragm is arranged in the pier top section, and the bottom of the pier top section beam is connected to the pier by consolidation or a support is arranged. The prefabricated NC top plate unit 1, the prefabricated NC bottom plate unit 2, the UHPC prefabricated variable cross-section straight web plate unit 3, and the prefabricated UHPC solid variable cross-section straight web plate unit (4) of the pier top section are all prefabricated in a standardized factory. The top and bottom edges of the prefabricated UHPC variable-section straight web 31 are the same length along the bridge as the prefabricated NC top plate 11 and the prefabricated NC bottom plate 21. They are narrowest at the center of the web and can be regarded as a variable-section component that gradually changes along the height direction of the web. The force mechanism of the box girder is similar to that of a double Warren truss structure. Since the web is made of UHPC, its high-strength mechanical properties are fully utilized to reduce the plate thickness. At the same time, by opening holes and hollowing out the web, the deadweight of the structure is significantly reduced, and the cross-sectional area of ​​the lower structure piers and the number of foundation projects are effectively reduced. The traditional prefabricated box girder segments are large in size and heavy in weight. The present invention breaks down the prefabricated box girder segments into small pieces, disassembles them into NC top plates, NC bottom plates and UHPC web plates, and prefabricates them separately, eliminating the inner mold and support system of the prefabricated segment box girder, achieving lightweight and miniaturization of prefabricated components, avoiding over-limit transportation, and effectively reducing the weight of on-site hoisting. The main beam uses UHPC prefabricated perforated webs, which are high-quality components made in the factory. High-strength steel fibers are used in UHPC, which makes it have high tensile strength and ductility. No steel bars are required, so there will be no corrosion of steel bars caused by salt damage and concrete carbonization. It has high durability and further improves the maintenance-free performance of the structure. Due to the special structure of the prefabricated UHPC variable-section straight web 31, the hollow openings formed between the webs can provide good lighting, making the internal space of the main beam bright and convenient for inspection and maintenance.The hollow openings formed between the webs can ensure good ventilation inside and outside the box girder, effectively reducing the adverse effects of the temperature gradient secondary stress caused by the temperature difference inside and outside the box girder on the box girder structure.

[0046] In this embodiment, the prefabricated UHPC variable cross-section straight web 31 is a vertical structure with two end plate surfaces gradually decreasing toward the middle to form an hourglass shape (see Fig.15 , Fig.16 ); The hollow openings formed between the webs can provide good lighting, making the internal space of the main beam bright and convenient for inspection and maintenance. The hollow openings formed between the webs can ensure good ventilation inside and outside the box beam, and effectively reduce the adverse effects of the temperature gradient secondary stress caused by the temperature difference between the inside and outside of the box beam on the box beam structure. The precast UHPC variable-section straight web 31 of the conventional beam section uses high-strength fiber-reinforced concrete with a compressive strength of not less than 80MPa, and there is no need to configure ordinary steel bars in the web. The box beam top plate composed of the precast NC top plate 11 and the top plate connecting strip 6 serves as the bearing structure of the bridge deck load, and together with the precast NC bottom plate 21 and the bottom plate connecting strip 5, it bears the tensile and compressive loads generated by the main beam. The precast UHPC variable-section straight web 31 can be regarded as a variable-section component that gradually changes along the height direction of the web. The force mechanism of the box beam is similar to that of a double Warren truss structure (see Figure 6 ).

[0047] In this embodiment, the prefabricated UHPC variable-section straight web 31 is pre-embedded with web vertical prestressed steel bars 35 and oblique prestressed steel bars 36 are arranged along the direction of the main tensile stress, the prefabricated NC top plate 11 is pre-embedded with top plate joint steel bars 18, the prefabricated NC bottom plate 21 is pre-embedded with bottom plate joint steel bars 27, both ends of the web vertical prestressed steel bars 35 are provided with web connection joints 7, the top plate joint steel bars 18 and the bottom plate joint steel bars 27 are respectively vertically overlapped with the web vertical prestressed steel bars 35 and are laterally fixedly connected through the web connection joints 7; they are connected to form a whole through the web reinforcement vertical rib connection joints 7 to ensure the lateral stiffness of the prefabricated NC top plate 11, the prefabricated NC bottom plate 21 and the prefabricated UHPC variable-section straight web 31 and the torsional stiffness of the box girder.

[0048] The prefabricated UHPC variable-section straight web 31 has vertical prestressed steel bars 35 symmetrically arranged along the prefabricated web reinforcement vertical ribs on both sides and oblique prestressed steel bars 36 arranged along the main tensile stress direction; first, the tensioned prestressed steel bars are temporarily anchored on the pedestal, and then the UHPC is poured. When the UHPC is cured to a strength value not less than 90% of the design strength value and the prestressed steel bars are sufficiently bonded to the UHPC, the prestressed steel bars are relaxed, and prestress is applied to the hourglass-shaped UHPC prefabricated web by means of the bonding and anchoring of the UHPC and the prestressed steel bars. The number of the above-mentioned prestressed steel bars is based on the principle that no tensile stress is generated under the action of the constant load and no cracks are generated under the most unfavorable design load combination.

[0049] In this embodiment, the top edge and the bottom edge center of the prefabricated UHPC variable cross-section straight web 31 are provided with a web pre-embedded perforated steel plate 33, the openings on the web pre-embedded perforated steel plate 33 are traversed by a web shear key pre-embedded steel pipe 34 and are welded firmly, and the openings of the web pre-embedded perforated steel plate 33 and the steel pipes of the web pre-embedded steel pipe 34 are penetrated with shear key steel bars 8, 9; the top edge and the bottom edge center of the prefabricated UHPC variable cross-section straight web 31 of the conventional beam section are provided with a pre-embedded steel plate 33. The web plate pre-embedded perforated steel plate 33 is embedded in the hourglass-shaped UHPC prefabricated web plate 31, and the opening is penetrated by the web plate shear key embedded steel pipe 34 and welded firmly. The center of each circular hole of the prefabricated web plate pre-embedded perforated steel plate 33 and the center of each steel pipe of the web plate shear key embedded steel pipe 34 are provided with the NC prefabricated top plate and the UHPC hourglass-shaped prefabricated web shear key penetration steel bar 8 or the NC prefabricated bottom plate and the UHPC hourglass-shaped prefabricated web shear key penetration steel bar 9 (see Fig. 9 , Fig.10 , Figure 13 to Figure 16 ).

[0050] In this embodiment, web reinforcement vertical ribs 32 are arranged at the center of the longitudinal bridge direction on both sides of the prefabricated UHPC variable-section straight web plate 31; top plate reinforcement transverse ribs 12 are arranged at the center of the longitudinal bridge direction at the bottom edge of the prefabricated NC top plate 11, and bottom plate reinforcement transverse ribs 22 are arranged at the center of the longitudinal bridge direction at the top edge of the prefabricated NC bottom plate 21. The top plate reinforcement transverse ribs 12, the bottom plate reinforcement transverse ribs 22, and the web reinforcement vertical ribs 32 are arranged correspondingly; (See Figure 4 , Fig.11 ), the top plate reinforcing transverse ribs 12, the bottom plate reinforcing transverse ribs 22 and the web plate reinforcing vertical ribs 32 are aligned with each other and have the same thickness.

[0051] In this embodiment, after the prefabricated NC top plates 11 and the prefabricated NC bottom plates 21 are assembled, cast-in-place UHPC forms top plate connection belts 6 and bottom plate connection belts 5, respectively. Both ends of the web pre-embedded perforated steel plate 33 along the longitudinal bridge direction are provided with splicing plates 37, which are connected into a whole by high-strength bolts 38 and embedded between the bottom plate connection belt 5 and the top plate connection belt 6; the prefabricated NC top plate plate unit 1 between each segment is connected by UHPC cast-in-place top plate connection belt 6; the NC prefabricated bottom plate plate unit 2 is connected by UHPC cast-in-place bottom plate connection belt 5. The top plate connection belt 6 and the bottom plate connection belt 5 are both formed by cast-in-place UHPC at the joints after the prefabricated NC bottom plate 21 and the prefabricated NC top plate 11 are assembled.

[0052] In this embodiment, longitudinal prestressed steel bundle corrugated pipes are arranged in the NC prefabricated top plate 11 and the prefabricated NC bottom plate 21. The prestressed steel bundles penetrate the longitudinal prestressed steel bundle corrugated pipes and are tensioned and anchored by the steel bundle anchors 14; see Figure 8 , Fig. 9 and Fig.10The prefabricated NC top plate unit 1 and the prefabricated NC bottom plate unit 2 in the above-mentioned NC-UHPC combined assembled prestressed concrete box girder are both provided with longitudinal prestressed steel beam corrugated pipes, which are connected by longitudinal prestressed steel beams, and longitudinal prestressed steel beam anchors 14 are provided at the ends of the segments for tensioning and anchoring and providing precompression stress to offset the tensile stress on the beam cross section caused by self-weight and vehicle loads.

[0053] In this embodiment, a cantilever top plate reinforcement longitudinal beam 102 is arranged at the cantilever of the NC prefabricated top plate 11, and a UHPC prefabricated diagonal brace 10 is arranged at the intersection of the cantilever top plate reinforcement longitudinal beam 102 and the top plate reinforcement transverse rib 12, and the UHPC prefabricated diagonal brace 10 is connected to the top plate reinforcement transverse rib 12 and the prefabricated NC bottom plate 21 through a prefabricated diagonal brace UHPC cast-in-place connection joint 101; if it is necessary to increase the bridge deck width, without increasing the number of boxes or changing the box room width, the transverse bridge cantilever length of the prefabricated NC top plate 11 is appropriately increased, and a UHPC prefabricated diagonal brace 10 is arranged between the NC prefabricated top plate 11 and the prefabricated NC bottom plate 21 to assist the force bearing of the cantilever part of the NC prefabricated top plate.

[0054] The present invention also discloses a construction method of a NC-UHPC combined assembled prestressed concrete box girder, comprising the following steps:

[0055] Step a, setting up temporary brackets on both sides of the bridge pier, and installing the NC prefabricated bottom plate unit (2) composed of the prefabricated NC bottom plate (21) at the top section of the pier;

[0056] Step b, installing the prefabricated UHPC solid web plate unit (4) composed of the prefabricated UHPC variable-section straight web (31) of the pier top section, installing the prefabricated NC bottom plate (21) and the prefabricated UHPC solid web shear key through the steel bar (8) of the pier top section, and pouring the UHPC cast-in-place web connection joint (7);

[0057] Step c, installing the prefabricated NC top plate unit (1) composed of the prefabricated NC top plate (11) of the pier top section, installing the shear key through-steel bars of the NC prefabricated top plate and the UHPC prefabricated solid web plate of the pier top section, and pouring the UHPC cast-in-place connection joint;

[0058] Step d, using a temporary hanger to install the prefabricated NC bottom plate unit (2) composed of the conventional beam section and the prefabricated NC bottom plate (21) and temporarily fix it;

[0059] Step e, installing the prefabricated UHPC web plate unit (3) composed of the prefabricated UHPC variable-section straight web (31) of the conventional beam section, installing the high-strength bolt connection joint splicing plate (37) connected to the completed segment, tightening the high-strength bolts (38), installing the conventional beam section NC prefabricated bottom plate and the UHPC hourglass-shaped prefabricated web shear key through-steel (9), pouring the UHPC cast-in-place connection joint, and casting the UHPC cast-in-place prefabricated web reinforcement vertical rib connection joint (7);

[0060] Step f, using a temporary hanger to install the conventional beam section NC prefabricated top plate unit (1) and temporarily fix it; installing the conventional beam section prefabricated NC top plate (11) and the UHPC prefabricated web shear key through-steel bars (8), pouring the UHPC cast-in-place connection joint, and pouring the UHPC web reinforcement vertical rib connection joint (7);

[0061] Step g, casting the UHPC cast-in-place bottom plate connecting strip (5) and the UHPC cast-in-place top plate connecting strip (6) between the completed installation segments; after the UHPC cast-in-place strip has been cured to reach the design strength, installing the longitudinal prestressed steel strand anchor (14) and tensioning the top plate longitudinal prestressed steel strand (13), and then performing prestressed grouting and anchor sealing;

[0062] Step h, using the symmetrical cantilever assembly method to repeat steps d to g to install conventional prefabricated beam segments segment by segment until the entire bridge is closed, and tension the top plate and bottom plate prestressed closing steel strands;

[0063] Step i: Remove the temporary supports of the side spans and the temporary brackets on both sides of the piers to complete the main beam construction.

[0064] See also Figure 6-7 and Figures 9 to 12 The above-mentioned embedded steel pipes 16, 25 and 34 in the NC prefabricated top plate shear key, are also used as the shear pins of the shear key and the inner template of the circular opening of the shear key.

[0065] The cast-in-place UHPC for filling and pouring the gaps between the NC prefabricated top plate unit 1, the NC prefabricated top plate unit 2 and the UHPC hourglass-shaped prefabricated web plate unit 3 or the pier top section UHPC prefabricated solid web plate unit 4 adopts short steel fibers with a length of no more than 15 mm to ensure its fluidity, and is pressurized into these gaps by pre-embedded steel pipes 16 and 25 in the NC prefabricated top plate shear key pre-embedded steel pipes, to ensure that the gaps are fully filled with UHPC.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) The NC prefabricated top plate, NC prefabricated bottom plate, and UHPC prefabricated web plate are all prefabricated in the factory and installed on site. The UHPC cast-in-place wet joint has a short solidification time, which greatly shortens the erection period of the box girder.

[0068] (2) NC precast top slab, NC precast bottom slab and UHPC precast web slab can all be precast in a standardized manner using standard formwork. The horizontal curve, vertical curve, pre-arch and super-elevation slope gradient of the bridge deck can all be adjusted and adapted using the UHPC cast-in-place wet joints between the segments.

[0069] (3) Reducing the amount of engineering work for the substructure and foundation. Since the web plate is made of UHPC, its high-strength mechanical properties are fully utilized to reduce the plate thickness. At the same time, by opening holes and hollowing out the web plate, the deadweight of the structure is significantly reduced, effectively reducing the cross-sectional area of ​​the substructure piers and the amount of foundation engineering.

[0070] (4) Traditional prefabricated box girder segments are large in size and heavy in weight. The present invention breaks down the prefabricated box girder segments into parts, disassembling them into NC top plates, NC bottom plates and UHPC web plates, which are prefabricated separately. This eliminates the need for the inner mold and support system of the prefabricated segment box girder, achieves lightweight and miniaturized prefabricated components, avoids over-limit transportation, and effectively reduces the weight of on-site hoisting.

[0071] (5) UHPC materials are used for cast-in-place joints that connect node components. This reduces material usage, simplifies construction, shortens construction time, and increases the strength of the connection section, overcoming the weakness of prefabricated components in the connection nodes. This ensures that wet joint connections are no longer the weak link in prefabricated assembly structures.

[0072] (6) Energy saving, emission reduction, low carbon and environmental protection. Due to the significant reduction in the amount of materials used in the upper and lower structures, CO2 emissions during construction are reduced compared to NC box girder bridges of the same size.

[0073] (7) Improve maintenance-free performance. The main beam uses UHPC prefabricated perforated webs, which are high-quality components made in the factory. High-strength steel fibers are used in UHPC, which gives it high tensile strength and ductility. No steel bars are required, so there is no salt damage and concrete carbonization that causes steel bar corrosion. It has high durability, further improving the maintenance-free performance of the structure.

[0074] (8) The hollow openings on the web can provide good lighting, making the internal space of the main beam bright and convenient for inspection and maintenance.

[0075] (9) The hollow openings on the web can ensure good ventilation inside and outside the box girder, effectively reducing the adverse effects of the temperature gradient secondary stress caused by the temperature difference between the inside and outside of the box girder on the box girder structure.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A NC-UHPC combined assembled prestressed concrete box girder, characterized in that: The invention comprises a prefabricated NC top plate (11), a prefabricated NC bottom plate (21) and a prefabricated UHPC variable cross-section straight web plate (31), wherein the prefabricated UHPC variable cross-section straight web plate (31) is configured such that the plate surface area at both ends of the web plate in the vertical direction is larger than the plate surface area at the middle portion; a web plate pre-embedded perforated steel plate (33) is provided at the center of the top edge and the bottom edge of the prefabricated UHPC variable cross-section straight web plate (31); the openings on the web plate pre-embedded perforated steel plate (33) are traversed by a web plate shear key pre-embedded steel pipe (34) and are welded firmly; and shear key steel bars are provided through the openings of the web plate pre-embedded perforated steel plate (33) and the steel pipes of the web plate pre-embedded steel pipe (34).

2. The NC-UHPC combined assembled prestressed concrete box girder according to claim 1 is characterized in that: The prefabricated UHPC variable-section straight web (31) has a structure in the shape of an hourglass, with the vertical plate surfaces at both ends gradually decreasing toward the middle.

3. The NC-UHPC combined assembled prestressed concrete box girder according to claim 2 is characterized in that: The prefabricated UHPC variable-section straight web (31) is pre-embedded with web vertical prestressed steel bars (35) and is provided with oblique prestressed steel bars (36) along the main tensile stress direction; the prefabricated NC top plate (11) is pre-embedded with top plate joint steel bars (18); the prefabricated NC bottom plate (21) is pre-embedded with bottom plate joint steel bars (27); both ends of the web vertical prestressed steel bars (35) are provided with web connection joints (7); the top plate joint steel bars (18) and the bottom plate joint steel bars (27) are respectively vertically overlapped with the web vertical prestressed steel bars (35) and are laterally fixedly connected via the web connection joints (7).

4. The NC-UHPC combined assembled prestressed concrete box girder according to claim 3 is characterized in that: Web reinforcement vertical ribs (32) are arranged in the center of the longitudinal bridge direction on opposite sides of the prefabricated UHPC variable-section straight web plate (31).

5. The NC-UHPC combined assembled prestressed concrete box girder according to claim 4 is characterized in that: A top plate reinforcing transverse rib (12) is arranged at the center of the bottom edge of the prefabricated NC top plate (11) along the longitudinal bridge direction, and a bottom plate reinforcing transverse rib (22) is arranged at the center of the top edge of the prefabricated NC bottom plate (21) along the longitudinal bridge direction. The top plate reinforcing transverse rib (12), the bottom plate reinforcing transverse rib (22), and the web plate reinforcing vertical rib (32) are arranged correspondingly.

6. The NC-UHPC combined assembled prestressed concrete box girder according to claim 5 is characterized in that: After being assembled between the prefabricated NC top plates (11) and the prefabricated NC bottom plates (21), cast-in-place UHPC respectively forms a top plate connection belt (6) and a bottom plate connection belt (5); both ends of the web pre-embedded perforated steel plate (33) along the longitudinal bridge direction are provided with splicing plates (37); the splicing plates (37) are connected into a whole by high-strength bolts (38) and are embedded between the bottom plate connection belt (5) and the top plate connection belt (6).

7. The NC-UHPC combined assembled prestressed concrete box girder according to claim 6 is characterized in that: Longitudinal prestressed steel bundle corrugated pipes are arranged inside the prefabricated NC top plate (11) and the prefabricated NC bottom plate (21), and the prestressed steel bundles penetrate the longitudinal prestressed steel bundle corrugated pipes and are tensioned and anchored by steel bundle anchors (14).

8. The NC-UHPC combined assembled prestressed concrete box girder according to any one of claims 1 to 7, characterized in that: A cantilever top plate reinforcing longitudinal beam (102) is arranged at the cantilever of the prefabricated NC top plate (11), and a UHPC prefabricated diagonal brace (10) is arranged at the intersection of the cantilever top plate reinforcing longitudinal beam (102) and the top plate reinforcing transverse rib (12), wherein the UHPC prefabricated diagonal brace (10) is connected to the top plate reinforcing transverse rib (12) and the prefabricated NC bottom plate (21) via a prefabricated diagonal brace UHPC cast-in-place connection joint (101).

9. The construction method of the NC-UHPC combined assembled prestressed concrete box girder according to claim 1 is characterized in that: The following steps are involved: Step a, setting up temporary brackets on both sides of the bridge pier, and installing the prefabricated NC bottom plate unit (2) composed of the prefabricated NC bottom plate (21) at the top section of the pier; Step b, installing the prefabricated UHPC solid web plate unit (4) composed of the prefabricated UHPC variable-section straight web (31) of the pier top section, installing the prefabricated NC bottom plate (21) and the prefabricated UHPC solid web shear key through the steel bar (8) of the pier top section, and pouring the UHPC cast-in-place web connection joint (7); Step c, installing the prefabricated NC top plate unit (1) composed of the prefabricated NC top plate (11) of the pier top section, installing the shear key through-steel bars of the NC prefabricated top plate and the UHPC prefabricated solid web plate of the pier top section, and pouring the UHPC cast-in-place connection joint; Step d, using a temporary hanger to install the prefabricated NC bottom plate unit (2) composed of the conventional beam section and the prefabricated NC bottom plate (21) and temporarily fix it; Step e, installing the prefabricated UHPC web plate unit (3) composed of the prefabricated UHPC variable-section straight web (31) of the conventional beam section, installing the high-strength bolt connection joint splicing plate (37) connected to the completed segment, tightening the high-strength bolts (38), installing the conventional beam section NC prefabricated bottom plate and the UHPC hourglass-shaped prefabricated web shear key through-steel (9), pouring the UHPC cast-in-place connection joint, and casting the UHPC cast-in-place prefabricated web reinforcement vertical rib connection joint (7); Step f, using a temporary hanger to install the conventional beam section NC prefabricated top plate unit (1) and temporarily fix it; installing the conventional beam section prefabricated NC top plate (11) and the UHPC prefabricated web shear key through-steel bars (8), pouring the UHPC cast-in-place connection joint, and pouring the UHPC web reinforcement vertical rib connection joint (7); Step g, casting the UHPC cast-in-place bottom plate connecting strip (5) and the UHPC cast-in-place top plate connecting strip (6) between the completed installation segments; after the UHPC cast-in-place strip has been cured to reach the design strength, installing the longitudinal prestressed steel strand anchor (14) and tensioning the top plate longitudinal prestressed steel strand (13), and then performing prestressed grouting and anchor sealing; Step h: Repeat steps d to g by using the symmetrical cantilever assembly method to install conventional prefabricated beam segments segment by segment until the entire bridge is closed, and tension the prestressed closing steel strands of the top and bottom plates.

10. A bridge, characterized in that: The bridge has the NC-UHPC combined assembled prestressed concrete box girder as described in any one of claims 1-9.

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