UHPC-nc hybrid girder low tower cable-stayed bridge and construction method thereof

Abstract

This invention discloses a UHPC-NC hybrid beam-tower cable-stayed bridge and its construction method, comprising at least one pier, at least one tower, a first abutment, and a second abutment, all cast in NC (non-concrete composite) formwork. Multiple stay cables are mounted on the tower. UHPC-NC pier-top box girder segments are installed on the pier. Multiple prefabricated UHPC box girder segments are arranged sequentially and closely in the main span area, and multiple prefabricated NC box girder segments are arranged sequentially and closely in the side span areas. Prefabricated UHPC-NC transition sections are provided between the UHPC-NC pier-top box girder segments and adjacent NC box girder segments. Each UHPC box girder segment, each NC box girder segment, and the UHPC-NC transition section are connected to the tower via stay cables. This UHPC-NC hybrid beam-tower cable-stayed bridge has advantages such as high crack resistance, convenient construction, and good economic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of bridges, and in particular relates to a UHPC-NC hybrid beam-low tower cable-stayed bridge and its construction method. Background Technology

[0002] Low-tower cable-stayed bridges are a transitional bridge type between beam bridges and cable-stayed bridges, consisting of a composite system of beams, towers, and cables sharing the load. Due to their advantages such as large span capacity (100m–300m), good economic efficiency, convenient construction, and aesthetically pleasing appearance, low-tower cable-stayed bridges have been widely used in cross-river and cross-mountain bridges facing harsh geological conditions and high construction difficulty. However, due to limitations in the actual tower locations, some low-tower cable-stayed bridges with single-tower structures have asymmetrical spans. This leads to challenges in construction simulation, the need for large counterweights in symmetrical cantilever construction, and difficulties in controlling construction quality. Furthermore, cracking is prone to occur in the top slab of the main girder intersecting with the tower and in the bottom slab of the main girder in some cable-free areas, seriously affecting the normal service life of the bridge.

[0003] Ultra-High Performance Concrete (UHPC) is a novel cement-based composite material with superior mechanical properties, ultra-high elastic modulus, and excellent durability. Practical application has proven that UHPC can effectively overcome the problems of easy cracking and poor toughness in main beams when applied to bridge engineering. Furthermore, under the same load-bearing capacity, UHPC structures have thinner and lighter plates than traditional concrete structures, weighing approximately 50% of traditional concrete components. Therefore, UHPC structures have broad application prospects in long-span bridges.

[0004] Currently, to address the shortcomings of asymmetrical low-tower cable-stayed bridges, existing technologies have proposed using steel box girders to improve the crack resistance of the main girder. However, this technology, due to the use of steel structures, not only increases the total life-cycle cost (such as construction and installation costs and steel structure corrosion protection and maintenance costs), but also adds a significant amount of welding work, making construction quality control difficult and increasing construction complexity. Furthermore, because of the substantial difference in stiffness and density between steel and concrete structures, a complex steel-concrete composite section is required to ensure a smooth transition of stress, further increasing construction difficulty. Therefore, it is necessary to provide a new bridge structure and construction method to solve the aforementioned technical problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a UHPC-NC hybrid beam low tower cable-stayed bridge with high crack resistance, convenient construction and good economy, and its construction method.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A UHPC-NC hybrid beam-tower cable-stayed bridge includes at least one pier, a bridge tower connected to the pier and corresponding to it, a first abutment, and a second abutment. The pier, bridge tower, first abutment, and second abutment are all cast in NC (non-concrete composite) form. UHPC-NC pier-top box girder segments are installed on the pier. In the main span area of ​​the UHPC-NC hybrid beam-tower cable-stayed bridge, multiple prefabricated UHPC box girder segments are arranged in close succession. In the side span area of ​​the UHPC-NC hybrid beam-tower cable-stayed bridge, multiple prefabricated NC box girder segments are arranged in close succession. The UHPC-NC pier-top box girder segments are connected to adjacent NC box girder segments through a prefabricated UHPC-NC transition section. Each UHPC box girder segment, each NC box girder segment, and the UHPC-NC transition section are connected to the bridge tower by stay cables. The beam segments are connected by prestressed tendons.

[0008] As a further improvement to the above technical solution:

[0009] The UHPC-NC pier top box girder segment includes a UHPC box girder ring section prefabricated from UHPC. The UHPC box girder ring section includes a first top plate, a first bottom plate, two first outer webs, and two first inner webs. The first top plate, the first bottom plate, and the two first outer webs form a first closed ring structure. The two first inner webs are spaced apart and connected between the first top plate and the first bottom plate. The UHPC-NC pier top box girder segment also includes two first partitions cast in NC on site. The two first partitions are located at both ends of the UHPC box girder ring section and are connected to the UHPC box girder ring section to form a box-shaped structure.

[0010] The UHPC-NC transition section includes a second top plate, a second bottom plate, two second outer webs, two second inner webs, and a second partition plate prefabricated from UHPC. The second top plate and the second bottom plate are arranged at intervals. The second top plate, the second bottom plate, and the two second outer webs form a second closed annular structure. The second partition plate is connected between the second top plate and the second bottom plate, and the extension direction of the second partition plate is parallel to the extension direction of the second top plate. The two second inner webs are arranged at intervals and connected between the second top plate and the second bottom plate. The extension direction of the second inner webs is perpendicular to the extension direction of the second top plate.

[0011] The NC box girder segment includes a third top plate, a third bottom plate, two third outer webs, two third inner webs, and a third diaphragm, all prefabricated by NC. The third top plate and the third bottom plate are arranged alternately, forming a third closed ring structure. The third diaphragm connects the third top plate and the third bottom plate, with its extension direction parallel to that of the third top plate. The two third inner webs are arranged alternately and connected between the third top plate and the third bottom plate, with their extension direction perpendicular to that of the third top plate. The thickness of the second top plate at both ends is the same as the thickness of the first top plate in the adjacent UHPC-NC pier top box girder segment and the thickness of the third top plate in the adjacent NC box girder segment, respectively. The thickness of the second top plate extends from the first top plate towards the third top plate. The thickness of the second bottom plate gradually increases. The thickness of the second bottom plate at both ends is the same as the thickness of the first bottom plate in the adjacent UHPC-NC pier top box girder segment and the thickness of the third bottom plate in the adjacent NC box girder segment, respectively. The thickness of the second bottom plate gradually increases from the first bottom plate to the third bottom plate. The thickness of the second outer web plate at both ends is the same as the thickness of the first outer web plate in the adjacent UHPC-NC pier top box girder segment and the thickness of the third outer web plate in the adjacent NC box girder segment, respectively. The thickness of the second outer web plate gradually increases from the first outer web plate to the third outer web plate. The thickness of the second inner web plate at both ends is the same as the thickness of the first inner web plate in the adjacent UHPC-NC pier top box girder segment and the thickness of the third inner web plate in the adjacent NC box girder segment, respectively. The thickness of the second inner web plate gradually increases from the first inner web plate to the third inner web plate.

[0012] The UHPC box girder segment includes a fourth top plate, a fourth bottom plate, two fourth outer webs, two fourth inner webs, two small diaphragms, and a large diaphragm, all prefabricated from UHPC. The fourth top plate and the fourth bottom plate are arranged alternately, forming a fourth closed ring structure. The large diaphragm connects the fourth top plate and the fourth bottom plate and is located in the middle of the fourth closed ring structure. The two small diaphragms connect the fourth top plate and the fourth bottom plate and are located on opposite sides of the large diaphragm. The extending directions of the small diaphragms and the large diaphragm are parallel to the extending direction of the fourth top plate. The two fourth inner webs are arranged alternately and connected between the fourth top plate and the fourth bottom plate. The extending direction of the fourth inner webs is perpendicular to the extending direction of the fourth top plate.

[0013] The fourth top plate is a short rib plate component composed of a flat plate and multiple rib plates. The multiple rib plates are arranged at intervals and connected to the side of the flat plate near the fourth bottom plate. The extension direction of the rib plates is perpendicular to the extension direction of the flat plate.

[0014] The length of the UHPC box girder segment is 1.5 to 2 times that of the NC box girder segment.

[0015] The UHPC-NC hybrid beam-low tower cable-stayed bridge is designed as a fully prestressed component, the UHPC box girder segment adopts a longitudinal prestressed component design, and the NC box girder segment adopts a triaxial prestressed component design.

[0016] The first abutment is connected to the adjacent UHPC box girder segment via a main span closure segment, which is formed by UHPC casting. The second abutment is connected to the adjacent NC box girder segment via a side span closure segment, which is formed by NC casting.

[0017] As a general inventive concept, another aspect of the present invention provides a construction method for the aforementioned UHPC-NC hybrid beam-low tower cable-stayed bridge, comprising the following steps:

[0018] S1. Cast NC on site to form bridge piers, bridge towers, first abutment and second abutment;

[0019] S2. Precast main beam, including UHPC box girder segments, NC box girder segments, UHPC-NC transition segments, and the UHPC box girder ring section of the UHPC-NC pier top box girder segment. Among them, after natural curing for at least 2 days, the UHPC components also need to be steam cured at 90-100℃ for at least 48 hours.

[0020] S3. Install the UHPC box girder ring section of the UHPC-NC pier top box girder segment to the designated position, and erect the formwork to cast the first NC diaphragm of the UHPC-NC pier top box girder segment on site.

[0021] S4. Install the UHPC-NC transition section. While installing the UHPC-NC transition section, assemble the UHPC box girder segment on the other side. Then, in sequence, first install the NC box girder segment on the cantilever, then assemble the UHPC box girder segment, and then tension the prestressed steel strands and stay cables in sequence until the side span closure segment and the main span closure segment.

[0022] S5. First, pour NC to form the side span closure section, then pour UHPC on site to form the main span closure section, and tension the prestressed tendons of the entire bridge.

[0023] S6. Once the ancillary works and bridge deck paving are completed, the construction is finished.

[0024] Compared with existing technologies, the advantages of this invention are as follows: The UHPC box girder segments, NC box girder segments, and UHPC-NC transition sections of the UHPC-NC hybrid beam-low tower cable-stayed bridge of this invention are all prefabricated, and the UHPC-NC pier-top box girder segments are also partially prefabricated. The prefabrication and assembly construction method reduces on-site construction difficulty, shortens the construction cycle, facilitates construction, and easily ensures construction quality. The use of UHPC box girder segments in the main span area, instead of steel box girder structures, not only significantly reduces welding workload and improves the bridge's assembly level, effectively ensuring construction quality, but also avoids the maintenance costs associated with steel structures, demonstrating good economic efficiency. Furthermore, the use of UHPC box girder segments in the main span fully utilizes the superior toughness of UHPC, significantly improving the crack resistance of the pier-top main girder segments and the main girder segments in the cable-free zone, resulting in high crack resistance. UHPC also possesses good volumetric stability, avoiding the long-term deflection problem of traditional cable-stayed bridges. The use of inexpensive NC box girder segments in the well-stressed and largely defect-free side spans offers excellent economic benefits and enhances the overall competitiveness of this bridge type. Furthermore, unlike steel and concrete structures, which require complex steel-concrete composite sections to ensure a smooth stress transition due to significant differences in stiffness and density, the UHPC-NC structure eliminates the need for such complex sections. Instead, prefabricated UHPC-NC transition sections facilitate the transition, further reducing construction difficulty. More importantly, because the main side spans of this UHPC-NC hybrid beam-low tower cable-stayed bridge utilize both UHPC and NC box girder segments, the material properties of UHPC and NC allow for consistent weight distribution across the main side span segments while meeting length and mechanical performance requirements. This avoids the counterweight issues caused by asymmetrical spans, reduces construction steps, and lowers construction difficulty. Moreover, compared to using steel box girders for the main span, the use of UHPC box girder segments addresses deflection and cracking issues while allowing for an increase in the bridge's suitable span diameter. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the UHPC-NC hybrid beam-low tower cable-stayed bridge in Example 1.

[0026] Figure 2 This is a partial three-dimensional structural diagram of the UHPC-NC pier top box girder segment, the UHPC-NC transition segment, and the NC box girder segment.

[0027] Figure 3 This is a partial three-dimensional structural diagram of a UHPC box girder segment.

[0028] Figure 4 This is a schematic diagram of the cross-sectional structure at the large diaphragm in a UHPC box girder segment.

[0029] Figure 5This is a schematic diagram of the cross-sectional structure of the box girder including the diaphragm in the NC box girder segment.

[0030] Figure 6 This is a schematic diagram of the cross-sectional structure at the second partition in the UHPC-NC transition section.

[0031] Figure 7 This is a schematic diagram of the cross-sectional structure at the first diaphragm in the UHPC-NC pier top box girder segment.

[0032] Figure 8 This is a structural schematic diagram of S1 in the construction method of the UHPC-NC hybrid beam-low tower cable-stayed bridge.

[0033] Figure 9 This is a structural schematic diagram of S3 in the construction method of the UHPC-NC hybrid beam low tower cable-stayed bridge.

[0034] Figure 10 This is a structural schematic diagram of S4 in the construction method of the UHPC-NC hybrid beam low tower cable-stayed bridge.

[0035] Figure 11 This is a structural schematic diagram of S5 in the construction method of the UHPC-NC hybrid beam low tower cable-stayed bridge.

[0036] Figure 12 This is a schematic diagram of the overall structure of the UHPC-NC hybrid beam-low tower cable-stayed bridge in Example 2.

[0037] Legend:

[0038] 1. Pier; 10. Main span closure section; 2. Bridge tower; 20. Side span closure section; 3. First abutment; 4. Second abutment; 5. UHPC-NC pier top box girder segment; 51. First top slab; 52. First bottom slab; 53. First outer web; 54. First inner web; 55. First diaphragm; 6. UHPC box girder segment; 61. Fourth top slab; 62. Fourth bottom slab; 63. Fourth outer web; 64. Fourth inner web; 65. Small diaphragm; 66. Large diaphragm; 7. NC box girder segment; 71. Third top slab; 72. Third bottom slab; 73. Third outer web; 74. Third inner web; 75. Third diaphragm; 8. UHPC-NC transition section; 81. Second top slab; 82. Second bottom slab; 83. Second outer web; 84. Second inner web; 85. Second diaphragm; 9. Stay cables. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Example 1:

[0041] like Figures 1 to 11As shown, the UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment is a double-span asymmetric UHPC-NC hybrid beam-low tower cable-stayed bridge, including a pier 1, a bridge tower 2 connected to the pier 1 and correspondingly arranged on the pier 1, a first abutment 3 and a second abutment 4. In the double-span asymmetric cable-stayed bridge system, the main span area is the long span area, that is, the area between the pier 1 and the first abutment 3. In the double-span asymmetric cable-stayed bridge system, the side span area is the short span area, that is, the area between the pier 1 and the second abutment 4. Its span arrangement is 90m+169m, the tower height of the bridge tower 2 is 35m, the side span consists of a side span closure segment 20, nineteen NC box girder segments 7 and a UHPC-NC transition segment 8, and the main span consists of twenty UHPC box girder segments 6 and a main span closure segment 10. The bridge pier 1, bridge tower 2, first abutment 3 and second abutment 4 are all cast in NC. UHPC-NC pier top box girder segments 5 are installed on the bridge pier 1. Multiple precast UHPC box girder segments 6 are arranged closely in sequence in the main span area. Multiple precast NC box girder segments 7 are arranged closely in sequence in the side span area. The UHPC-NC pier top box girder segments 5 are connected to the adjacent NC box girder segments 7 by a precast UHPC-NC transition section 8. Each UHPC box girder segment 6, each NC box girder segment 7 and the UHPC-NC transition section 8 are connected to the bridge tower 2 by cable stays 9. The beam segments are connected by prestressed tendons.The UHPC-NC hybrid beam-tower cable-stayed bridge features prefabricated UHPC box girder segments 6, NC box girder segments 7, and UHPC-NC transition segments 8. This prefabrication method reduces on-site construction difficulty, shortens the construction period, facilitates construction, and ensures construction quality. The main span utilizes UHPC box girder segments 6 instead of steel box girders, significantly reducing welding work, improving bridge assembly, and effectively guaranteeing construction quality. It also avoids the maintenance costs associated with steel structures, demonstrating good economic efficiency. Furthermore, the use of UHPC box girder segments 6 in the main span fully utilizes the superior toughness of UHPC, significantly enhancing the crack resistance of the main girder segments at the pier top and in the cable-free zone. UHPC also exhibits good volumetric stability, preventing the long-term deflection problem common in traditional cable-stayed bridges. Meanwhile, the side spans, which are well-stressed and largely free of defects, utilize inexpensive NC box girder segments 7, demonstrating good economic efficiency. The UHPC-NC structure offers several advantages. Firstly, it enhances the overall competitiveness of the bridge type. Secondly, unlike steel and concrete structures, which require complex steel-concrete composite sections to ensure a smooth stress transition due to significant differences in stiffness and density, the UHPC-NC structure eliminates the need for such sections. Instead, it utilizes prefabricated UHPC-NC transition sections 8 for connection, further reducing construction difficulty. More importantly, the main spans of this UHPC-NC hybrid beam-low tower cable-stayed bridge utilize UHPC box girder segments 6 and NC box girder segments 7, respectively. Due to the material properties of UHPC and NC, the design allows for consistent weight distribution across the main span segments while meeting length and mechanical performance requirements. This avoids the counterweight issues caused by asymmetrical spans, reduces construction steps, and lowers construction difficulty. Furthermore, compared to using steel box girder structures for the main span, the use of UHPC box girder segments 6 addresses deflection and cracking issues while increasing the bridge's suitable span.

[0042] In this embodiment, as Figure 6As shown, the UHPC-NC pier top box girder segment 5 includes a UHPC box girder ring section prefabricated from UHPC. The UHPC box girder ring section includes a first top plate 51, a first bottom plate 52, two first outer web plates 53, and two first inner web plates 54. The first top plate 51, the first bottom plate 52, and the two first outer web plates 53 form a first closed ring structure. The two first inner web plates 54 are spaced apart and connected between the first top plate 51 and the first bottom plate 52. The UHPC-NC pier top box girder segment 5 also includes two first partition plates 55 cast in place by NC. The two first partition plates 55 are located at both ends of the UHPC box girder ring section and are connected to the UHPC box girder ring section to form a box-shaped structure. The UHPC box girder ring section is prefabricated first, and then the first diaphragm 55 is cast on site. This design method can make full use of the lightweight and high-strength mechanical properties of UHPC. The outermost layer uses a thin-walled UHPC structure to avoid cracking, and the first diaphragm 55 uses inexpensive NC material to resist the shear force at the pier top. This combined structure is convenient to construct and economical and efficient. 。 UHPC-NC pier top box girder segment 5 includes the UHPC box girder section. UHPC has high mechanical strength and good volume stability, which can fundamentally solve the problem of cracking in the top plate of the pier top girder segment. Optionally, the thickness of the first top plate 51 is 0.15-0.40m, the thickness of the first bottom plate 52 is 0.20-0.60m, the thickness of the first outer web 53 is 0.15-0.50m, the thickness of the first inner web 54 is 0.15-0.40m, the thickness of the first diaphragm 55 is 1.00-1.50m, and the height of the first diaphragm 55 is 2.00-4.00m.

[0043] In this embodiment, as Figure 2 As shown, the UHPC-NC transition section 8 includes a second top plate 81, a second bottom plate 82, two second outer webs 83, two second inner webs 84, and a second partition 85, all prefabricated from UHPC. The second top plate 81 and the second bottom plate 82 are arranged alternately, forming a second closed annular structure. The second partition 85 connects the second top plate 81 and the second bottom plate 82, with its extension direction parallel to that of the second top plate 81. The two second inner webs 84 are arranged alternately and connect the second top plate 81 and the second bottom plate 82, with their extension directions perpendicular to that of the second top plate 81. The UHPC-NC transition section 8 is entirely made of UHPC material, has a simple structure, and is prefabricated in the factory. The UHPC-NC transition section 8 connects the UHPC structure and the NC structure, ensuring a smooth transition in stiffness between the two structures without causing abrupt changes in stiffness, making the structure reliable under stress and simplifying analysis.

[0044] In this embodiment, as Figures 2 to 6As shown, the NC box girder segment 7 includes a third top plate 71, a third bottom plate 72, two third outer webs 73, two third inner webs 74, and a third diaphragm 75, all prefabricated from NC materials. The third top plate 71 and the third bottom plate 72 are arranged alternately, forming a third closed ring structure. The third diaphragm 75 connects the third top plate 71 and the third bottom plate 72, with its extension direction parallel to that of the third top plate 71. The two third inner webs 74 are arranged alternately and connected between the third top plate 71 and the third bottom plate 72, with their extension direction perpendicular to that of the third top plate 71. The NC box girder segment 7 uses NC material, resulting in a simple structure, easy fabrication, and low cost. Optionally, the thickness of the third top plate 71 is 0.25–0.40 m, the thickness of the third bottom plate 72 is 0.25–0.60 m, the thickness of the third outer web plate 73 is 0.25–0.50 m, the thickness of the third inner web plate 74 is 0.20–0.40 m, and the thickness of the third partition plate 75 is 0.30–0.50 m.

[0045] In this embodiment, the thicknesses at both ends of the second top plate 81 are the same as the thicknesses of the first top plate 51 in the adjacent UHPC-NC pier top box girder segment 5 and the third top plate 71 in the adjacent NC box girder segment 7, respectively. The thickness of the second top plate 81 gradually increases from the first top plate 51 to the third top plate 71. The thicknesses at both ends of the second bottom plate 82 are the same as the thicknesses of the first bottom plate 52 in the adjacent UHPC-NC pier top box girder segment 5 and the third bottom plate 72 in the adjacent NC box girder segment 7, respectively. The thickness of the second bottom plate 82 gradually increases from the first bottom plate 52 to the third bottom plate 72. The thickness of the web plate 83 at both ends is the same as the thickness of the first outer web plate 53 in the adjacent UHPC-NC pier top box girder segment 5 and the thickness of the third outer web plate 73 in the adjacent NC box girder segment 7, respectively. The thickness of the second outer web plate 83 gradually increases from the first outer web plate 53 to the third outer web plate 73. The thickness of the second inner web plate 84 at both ends is the same as the thickness of the first inner web plate 54 in the adjacent UHPC-NC pier top box girder segment 5 and the thickness of the third inner web plate 74 in the adjacent NC box girder segment 7, respectively. The thickness of the second inner web plate 84 gradually increases from the first inner web plate 54 to the third inner web plate 74. The thicknesses of the second top plate 81, second bottom plate 82, second outer web plate 83, and second inner web plate 84 in the UHPC-NC transition section 8 are gradually varied, ensuring a smooth force transmission as the thickness of the UHPC-NC pier top box girder segment 5 gradually increases from the NC box girder segment 7 to the NC box girder segment 7.

[0046] In this embodiment, the UHPC box girder segment 6 includes a fourth top plate 61, a fourth bottom plate 62, two fourth outer webs 63, two fourth inner webs 64, two small partitions 65, and a large partition 66, all prefabricated from UHPC. The fourth top plate 61 and the fourth bottom plate 62 are arranged at intervals, and the fourth top plate 61, the fourth bottom plate 62, and the two fourth outer webs 63 form a fourth closed ring structure. The large partition 66 is connected between the fourth top plate 61 and the fourth bottom plate 62 and is located in the middle of the fourth closed ring structure. The two small partitions 65 are connected between the fourth top plate 61 and the fourth bottom plate 62 and are located on opposite sides of the large partition 66. The extending directions of the small partitions 65 and the large partition 66 are parallel to the extending direction of the fourth top plate 61. The two fourth inner webs 64 are arranged at intervals and connected between the fourth top plate 61 and the fourth bottom plate 62. The extending direction of the fourth inner webs 64 is perpendicular to the extending direction of the fourth top plate 61. UHPC box girder segment 6 is made of UHPC material, has a simple structure, and is prefabricated in the factory, making it easy to manufacture. Optionally, the thickness of the fourth bottom plate 62 is 0.15–0.50 m, the thickness of the fourth outer web plate 63 is 0.15–0.40 m, the thickness of the fourth inner web plate 64 is 0.15–0.50 m, the thickness of the small diaphragm 65 is 0.15–0.30 m, the height of the small diaphragm 65 is 0.50–1.50 m, the thickness of the large diaphragm 66 is 0.15–0.40 m, the height of the large diaphragm 66 is 0.80–2.0 m, the total width of UHPC box girder segment 6 is 12 m–35 m, and the total length of UHPC box girder segment 6 is 6 m–10 m. Optionally, the large partition 66 includes at least one of the top plate stiffening rib, the web plate stiffening rib, and the bottom plate stiffening rib, and the small partition 65 includes at least one of the top plate stiffening rib, the web plate stiffening rib, and the bottom plate stiffening rib. The top plate stiffening rib is perpendicular to the bottom of the fourth top plate 61, the web plate stiffening rib is perpendicular to the side wall of the fourth outer web plate 63, and the bottom plate stiffening rib is perpendicular to the upper part of the fourth bottom plate 62.

[0047] In this embodiment, the fourth top plate 61 is a low-ribbed member composed of a flat plate and multiple ribs. The multiple ribs are spaced apart and connected to the side of the flat plate near the fourth bottom plate 62, with the extension directions of the ribs perpendicular to the extension direction of the flat plate. Designing the fourth top plate 61 as a low-ribbed member structure provides sufficient space for arranging the internal prestressed tendons. Furthermore, for the same area, the local stiffness of the low-ribbed member is much greater than that of the flat plate. Optionally, the flat plate thickness is 0.12m to 0.30m, the rib height is 0.10m to 0.25m, the upper edge width of the ribs is 0.12m to 0.32m, the lower edge width of the ribs is 0.10m to 0.30m, and the center-to-center distance between adjacent ribs is 0.30m to 1.50m.

[0048] In this embodiment, the length of UHPC box girder segment 6 is 1.5 to 2 times that of NC box girder segment 7. Under the premise of the same load-bearing capacity, since UHPC box girder segment 6 is more than 50% lighter than NC box girder segment 7, the length of UHPC box girder segment 6 is 1.5 to 2 times that of NC box girder segment 7, ensuring that the weight of the main and side span segments is the same during the cantilever construction stage. This effectively avoids the construction counterweight problem caused by the asymmetry of the two spans, reduces the heavy side span counterweight stage, reduces construction steps, and improves construction efficiency.

[0049] In this embodiment, the UHPC-NC hybrid beam-low tower cable-stayed bridge is designed as a fully prestressed component. The UHPC box girder segment 6 adopts a longitudinal prestressed component design, and the NC box girder segment 7 adopts a three-dimensional prestressed component design. Since this bridge type only adopts the internal prestressed tendon design, there is no need to consider the formwork cost of external prestressed turning blocks and toothed blocks, which simplifies the structure and reduces the amount of prefabrication work.

[0050] In this embodiment, the first abutment 3 is connected to the adjacent UHPC box girder segment 6 via a main span closure segment 10, which is cast using UHPC. The second abutment 4 is connected to the adjacent NC box girder segment 7 via a side span closure segment 20, which is cast using NC. The main span closure segment 10 is made of UHPC material, which has high mechanical properties and good volume stability, and can fundamentally solve the problem of beam cracking in the cable-free zone. The side span closure segment 20 is made of NC material, which can reduce material costs while ensuring load-bearing capacity, thus exhibiting good economic efficiency.

[0051] The construction method of the UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment includes the following steps:

[0052] S1. Cast NC on site to form pier 1, bridge tower 2, first abutment 3 and second abutment 4;

[0053] S2. Precast main beam, including UHPC box girder segment 6, NC box girder segment 7, UHPC-NC transition section 8 and UHPC-NC pier top box girder segment 5 UHPC box girder ring part, wherein the UHPC components need to be naturally cured for at least 2 days and then steam cured at 90-100℃ for at least 48 hours.

[0054] S3. Install the UHPC box girder ring part of UHPC-NC pier top box girder segment 5 to the designated position, and erect the formwork to cast the first partition 55 of UHPC-NC pier top box girder segment 5 on site.

[0055] S4. Install UHPC-NC transition section 8. While installing UHPC-NC transition section 8, cantilever UHPC box girder segment 6 is assembled on the other side. Then, in sequence, cantilever NC box girder segment 7 is installed first, followed by UHPC box girder segment 6, and prestressed steel strands and stay cables 9 are tensioned in sequence until the side span closure segment 20 and the main span closure segment 10 are assembled.

[0056] S5. First, pour NC to form the side span closure segment 20, then pour UHPC on site to form the main span closure segment 10, and tension the prestressed tendons of the entire bridge.

[0057] S6. Once the ancillary works and bridge deck paving are completed, the construction is finished.

[0058] This construction method is simple in steps and has a reasonable design. It does not require heavy counterweights during the cantilever construction stage, which reduces the number of construction steps and facilitates construction.

[0059] Example 2:

[0060] The UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment is basically the same as that in Embodiment 1, with the main difference being that, Figure 12 As shown, the UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment is a three-span UHPC-NC hybrid beam-low tower cable-stayed bridge, including two piers 1, bridge towers 2 connected to the piers 1 and corresponding to the piers 1, a first abutment 3 and a second abutment 4. UHPC-NC pier-top box girder segments 5 are installed on the two piers 1. In the multi-span cable-stayed bridge system, the main span area is the beam segment between the piers 1, that is, the area between the two piers 1 is the main span area, and the remaining part is the side span area in the multi-span cable-stayed bridge system, that is, the UHPC-NC pier-top box girder segments. The area between segment 5 and the adjacent first abutment 3 or second abutment 4 is the side span area. The main span area has multiple prefabricated UHPC box girder segments 6 arranged in close succession, and the side span area has multiple prefabricated NC box girder segments 7 arranged in close succession. The UHPC-NC pier top box girder segment 5 is connected to the adjacent NC box girder segment 7 by a prefabricated UHPC-NC transition section 8. Each UHPC box girder segment 6, each NC box girder segment 7 and the UHPC-NC transition section 8 are connected to the bridge tower 2 by cable stays 9. The beam segments are connected by prestressed tendons.

[0061] In this embodiment, the first abutment 3 and the second abutment 4 are connected to the adjacent NC box girder segment 7 via a side span closure segment 20, which is formed by NC casting. There is no need to set up a main span closure segment 10. Therefore, the construction method of the UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment is basically the same as in Embodiment 1, except that the main span closure segment 10 is not required in S5.

[0062] Example 3:

[0063] The UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment is basically the same as that in Embodiment 2. The main difference is that the UHPC-NC hybrid beam-low tower cable-stayed bridge in this embodiment is a four-span UHPC-NC hybrid beam-low tower cable-stayed bridge, including three piers 1, bridge towers 2 connected to the piers 1 and corresponding to the piers 1, a first abutment 3 and a second abutment 4. Each pier 1 is equipped with a UHPC-NC pier top box girder segment 5. The area between each pier 1 is the main span area, and the remaining part is a multi-span cable-stayed bridge. In the bridge system, the side span area and the main span area are arranged with multiple prefabricated UHPC box girder segments 6 in sequence and multiple prefabricated NC box girder segments 7 in sequence and closely arranged. The UHPC-NC pier top box girder segment 5 is connected to the adjacent NC box girder segment 7 by a prefabricated UHPC-NC transition section 8. Each UHPC box girder segment 6, each NC box girder segment 7 and the UHPC-NC transition section 8 are connected to the bridge tower 2 by cable stays 9. The beam segments are connected by prestressed tendons.

[0064] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

Claims

1. A UHPC-NC hybrid beam-tower cable-stayed bridge, comprising at least one pier (1), a bridge tower (2) connected to the pier (1) and corresponding to the pier (1), a first abutment (3), and a second abutment (4), wherein the pier (1), bridge tower (2), first abutment (3), and second abutment (4) are all formed by NC casting, characterized in that: UHPC-NC pier top box girder segments (5) are installed on the piers (1) near the side span area. Multiple prefabricated UHPC box girder segments (6) are arranged closely in sequence in the main span area of ​​the UHPC-NC hybrid beam low tower cable-stayed bridge. Multiple prefabricated NC box girder segments (7) are arranged closely in sequence in the side span area of ​​the UHPC-NC hybrid beam low tower cable-stayed bridge. The UHPC-NC pier top box girder segment (5) is connected to the adjacent NC box girder segment (7) through a prefabricated UHPC-NC transition section (8). Each UHPC box girder segment (6), each NC box girder segment (7) and the UHPC-NC transition section (8) are connected to the bridge tower (2) through cable stays (9). The beam segments are connected by prestressed tendons. The UHPC-NC pier top box girder segment (5) includes a UHPC box girder ring section prefabricated by UHPC. The UHPC box girder ring section includes a first top plate (51), a first bottom plate (52), two first outer web plates (53) and two first inner web plates (54). The first top plate (51), the first bottom plate (52) and the two first outer web plates (53) form a first closed ring structure. The two first inner web plates (54) are spaced apart and connected between the first top plate (51) and the first bottom plate (52). The UHPC-NC pier top box girder segment (5) also includes two first partition plates (55) cast in place by NC. The two first partition plates (55) are located at both ends of the UHPC box girder ring section and connected to the UHPC box girder ring section to form a box structure. The UHPC box girder segment (6) includes a fourth top plate (61), a fourth bottom plate (62), two fourth outer webs (63), two fourth inner webs (64), two small partitions (65), and a large partition (66) prefabricated from UHPC. The fourth top plate (61) and the fourth bottom plate (62) are arranged at intervals. The fourth top plate (61), the fourth bottom plate (62), and the two fourth outer webs (63) form a fourth closed ring structure. The large partition (66) connects the fourth top plate (61) and the fourth bottom plate (62). The four inner webs are located between the fourth top plate (61) and the fourth bottom plate (62) and are located in the middle of the fourth closed ring structure. Two small partitions (65) are connected between the fourth top plate (61) and the fourth bottom plate (62) and are located on opposite sides of the large partition (66). The extension directions of the small partitions (65) and the large partitions (66) are parallel to the extension direction of the fourth top plate (61). Two fourth inner webs (64) are arranged at intervals and connected between the fourth top plate (61) and the fourth bottom plate (62). The extension direction of the fourth inner webs (64) is perpendicular to the extension direction of the fourth top plate (61).

2. The UHPC-NC hybrid beam-low tower cable-stayed bridge according to claim 1, characterized in that: The UHPC-NC transition section (8) includes a second top plate (81), a second bottom plate (82), two second outer webs (83), two second inner webs (84), and a second partition (85) prefabricated from UHPC. The second top plate (81) and the second bottom plate (82) are arranged at intervals. The second top plate (81), the second bottom plate (82), and the two second outer webs (83) form a second closed ring structure. The second partition (85) is connected between the second top plate (81) and the second bottom plate (82), and the extension direction of the second partition (85) is parallel to the extension direction of the second top plate (81). The two second inner webs (84) are arranged at intervals and connected between the second top plate (81) and the second bottom plate (82). The extension direction of the second inner webs (84) is perpendicular to the extension direction of the second top plate (81).

3. The UHPC-NC hybrid beam-low tower cable-stayed bridge according to claim 2, characterized in that: The NC box girder segment (7) includes a third top plate (71), a third bottom plate (72), two third outer webs (73), two third inner webs (74), and a third partition plate (75) prefabricated by NC. The third top plate (71) and the third bottom plate (72) are arranged at intervals. The third top plate (71), the third bottom plate (72), and the two third outer webs (73) form a third closed ring structure. The third partition plate (75) connects the third top plate (71) and the third bottom plate (72), and the extension direction of the third partition plate (75) is perpendicular to the direction of the third bottom plate (74). The extension direction of the third top plate (71) is parallel, and two third inner web plates (74) are arranged at intervals and connected between the third top plate (71) and the third bottom plate (72). The extension direction of the third inner web plates (74) is perpendicular to the extension direction of the third top plate (71). The thickness of both ends of the second top plate (81) is the same as the thickness of the first top plate (51) in the adjacent UHPC-NC pier top box girder segment (5) and the thickness of the third top plate (71) in the adjacent NC box girder segment (7). The thickness of the second top plate (81) is along the first top plate (51). The thickness of the second bottom plate (82) gradually increases towards the third top plate (71). The thickness of the second bottom plate (82) at both ends is the same as the thickness of the first bottom plate (52) in the adjacent UHPC-NC pier top box girder segment (5) and the thickness of the third bottom plate (72) in the adjacent NC box girder segment (7). The thickness of the second bottom plate (82) gradually increases from the first bottom plate (52) towards the third bottom plate (72). The thickness of the second outer web plate (83) at both ends is the same as the thickness of the first outer web plate (53) in the adjacent UHPC-NC pier top box girder segment (5) and the thickness of the third bottom plate (72) in the adjacent N-type box girder segment (7). The thickness of the third outer web (73) in the C box girder segment (7) is the same. The thickness of the second outer web (83) gradually increases from the first outer web (53) to the third outer web (73). The thickness of the two ends of the second inner web (84) is the same as the thickness of the first inner web (54) in the adjacent UHPC-NC pier top box girder segment (5) and the thickness of the third inner web (74) in the adjacent NC box girder segment (7). The thickness of the second inner web (84) gradually increases from the first inner web (54) to the third inner web (74).

4. The UHPC-NC hybrid beam-low tower cable-stayed bridge according to claim 3, characterized in that: The fourth top plate (61) is a short rib plate component composed of a flat plate and multiple rib plates. The multiple rib plates are arranged at intervals and connected to the side of the flat plate near the fourth bottom plate (62). The extension direction of the rib plates is perpendicular to the extension direction of the flat plate.

5. The UHPC-NC hybrid beam-low tower cable-stayed bridge according to claim 1, characterized in that: The length of the UHPC box girder segment (6) is 1.5 to 2 times that of the NC box girder segment (7).

6. The UHPC-NC hybrid beam-low tower cable-stayed bridge according to claim 1, characterized in that: The UHPC-NC hybrid beam-low tower cable-stayed bridge is designed as a fully prestressed component, the UHPC box girder segment (6) is designed as a longitudinal prestressed component, and the NC box girder segment (7) is designed as a triaxial prestressed component.

7. The UHPC-NC hybrid beam-low tower cable-stayed bridge according to any one of claims 1 to 6, characterized in that: The first abutment (3) is connected to the adjacent UHPC box girder segment (6) through a main span closure segment (10), which is formed by UHPC casting. The second abutment (4) is connected to the adjacent NC box girder segment (7) through a side span closure segment (20), which is formed by NC casting.

8. A construction method for a UHPC-NC hybrid beam-low tower cable-stayed bridge, applied to a UHPC-NC hybrid beam-low tower cable-stayed bridge as described in any one of claims 1 to 7, characterized in that: Includes the following steps: S1. Cast NC on site to form bridge pier (1), bridge tower (2), first abutment (3) and second abutment (4); S2. Precast main beam, including UHPC box girder segment (6), NC box girder segment (7), UHPC-NC transition segment (8) and UHPC-NC pier top box girder segment (5) UHPC box girder ring part, wherein the UHPC component needs to be naturally cured for at least 2 days and then steam cured at 90~100℃ for at least 48 hours. S3. Install the UHPC box girder ring part of the UHPC-NC pier top box girder segment (5) to the designated position, and erect the formwork to cast the first NC partition of the UHPC-NC pier top box girder segment (5) on site. S4. Install the UHPC-NC transition section (8). While installing the UHPC-NC transition section (8), assemble the UHPC box girder segment (6) on the other side. Then, in sequence, first install the NC box girder segment (7) on the cantilever, then assemble the UHPC box girder segment (6), and tension the prestressed steel strands and stay cables (9) in sequence until the side span closure section (20) and the main span closure section (10). S5. First, pour NC to form the side span closure section (20), then pour UHPC on site to form the main span closure section (10), and tension the prestressed tendons of the whole bridge. S6. Once the ancillary works and bridge deck paving are completed, the construction is finished.

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