Prefabricated double-layer steel tube concrete composite bridge pier structure and construction method thereof

Abstract

The present invention discloses a prefabricated and assembled double-layer steel tube concrete composite pier structure and a construction method thereof. The pier structure includes a foundation pedestal, a double-layer steel tube concrete column, a cap beam, and prestressed tendons; the double-layer steel tube concrete column is located between the foundation pedestal and the cap beam, and is assembled by a number of prefabricated double-layer steel tube concrete segments; the prefabricated double-layer steel tube concrete segments include an outer steel pipe, an inner steel pipe, a stiffening plate, and an interlayer concrete; a pedestal embedded steel pipe connector is provided in the foundation pedestal, and a cap beam embedded steel pipe connector is provided in the cap beam, and the pedestal / cap beam embedded steel pipe connectors all include embedded steel pipes, perforated stiffening plates, and end plates. The pier structure of the present invention has the advantages of high axial bearing capacity and strong lateral resistance, and can realize fully prefabricated and assembled construction, shorten the construction period, and reduce environmental impact. The pier structure of the present invention also has a self-reset function, which can significantly reduce or eliminate the residual deformation of the bridge structure after an earthquake, and ensure the normal use of the bridge after an earthquake.

Description

Technical Field

[0001] The present invention belongs to the field of bridge engineering, and in particular relates to a prefabricated segmented double-layer steel tube concrete composite pier structure that can be prefabricated in a factory in a standardized manner and assembled on site, and a construction method thereof. Background Art

[0002] Prefabricated and assembled bridges conform to the concepts of green, environmental protection, and sustainable development. They are particularly suitable for urban bridge construction in sections with complex traffic conditions where long-term traffic interruptions are not suitable, as well as highway bridge construction in difficult environments such as deep canyon areas where long-term on-site construction is not suitable. They are an important development direction for future bridge engineering construction.

[0003] As a superior and rapid construction method, precast segmental assembly technology is gaining increasing attention and recognition from owners, construction companies, and research institutes. In current precast segmental concrete pier construction, to ensure the integrity of the piers, segmental component connection methods such as grouting sleeves, grouting bellows, socket-and-socket joints, and cast-in-place wet joints are commonly used, placing high demands on on-site positioning and operation. With dry connections using post-tensioned prestressed tendons, only prestressed tendons pass through the joints between the segmental piers, resulting in poor lateral and torsional bearing capacity and energy efficiency. Furthermore, precast segmental concrete piers require high positioning accuracy for formwork and pre-reserved holes during the fabrication of the precast segmental components, making the construction processes, such as rebar binding and formwork erection, more complex than those for cast-in-place concrete piers.

[0004] In recent years, steel-concrete composite structures have been widely used in bridge structures due to their superior mechanical properties. However, their engineering applications are mainly concentrated in bridge superstructures, with limited application in bridge substructures. Compared to reinforced concrete columns, steel tube concrete columns offer advantages such as high bearing capacity, good plasticity and toughness, strong energy dissipation capacity, and superior fire resistance. Furthermore, they can eliminate a large amount of work and costs associated with formwork and scaffolding during construction, speeding up the construction cycle and achieving good economic benefits. Double-layer steel tube concrete columns are a derivative of steel tube concrete columns. Compared to steel tube concrete columns, they also offer advantages such as lighter weight, greater flexural stiffness, and a high stiffness-to-weight ratio, and have broad prospects for engineering application. Steel tube concrete columns have been widely used as load-bearing columns in high-rise buildings and industrial plants, but their application in bridge piers is currently rare. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the existing technology and give full play to the performance advantages of double-layer steel tube concrete columns and the advantages of prefabricated assembly construction technology, the present invention provides a prefabricated and assembled double-layer steel tube concrete composite bridge pier structure, which can overcome the shortcomings of the existing prefabricated and assembled bridge piers with post-tensioned prestressed connections, such as poor lateral and torsional resistance, and can easily realize factory standardized production of prefabricated segments and on-site mechanized construction, reduce the amount of on-site assembly and positioning work, speed up the construction progress, and reduce construction carbon emissions and the impact of the construction process on the surrounding environment.

[0006] Technical solution: The technical solution of the present invention is as follows:

[0007] A prefabricated assembled double-layer steel tube concrete composite bridge pier, comprising a foundation cap, a double-layer steel tube concrete column and a cap beam, wherein: the number of double-layer steel tube concrete columns is M, M≧1; the double-layer steel tube concrete column is located between the foundation cap and the cap beam, and is assembled from N prefabricated double-layer steel tube concrete segments and pre-embedded with prestressed tendons, wherein N>1; the prefabricated double-layer steel tube concrete segment comprises an outer steel tube, an inner steel tube and an interlayer concrete; the inner steel tube comprises an inner steel tube- and the inner steel pipe 2, the outer edge size of the cross section of the inner steel pipe 1 matches the inner edge size of the cross section of the inner steel pipe 2, one end of the inner steel pipe 1 is nested in one end of the inner steel pipe 2 and welded together; the other end of the inner steel pipe 2 is aligned with one end of the outer steel pipe, and the other end of the inner steel pipe 1 is higher than the other end of the outer steel pipe; a sandwich concrete is poured between the outer steel pipe and the inner steel pipe to form the prefabricated double-layer steel pipe concrete segment, and the two end surfaces of the poured sandwich concrete are flush with the two end surfaces of the outer steel pipe;

[0008] The lengths L1, L2, L3 and L4 of the outer steel pipe, the inner steel pipe, the inner steel pipe 1 and the inner steel pipe 2, and the nested overlap length L5 of the inner steel pipe 1 and the inner steel pipe 2 are in the following relationship: L3+L4≧L2>L1, L4-L5≧L2-L1, L3≧L4;

[0009] The prestressed tendons pass through the embedded steel pipes of the pedestal, the inner steel pipes of the double-layer steel tube concrete segment and the embedded steel pipes of the cap beam in sequence, applying a tensile force equivalent to 10%~40% of the ultimate axial compressive bearing capacity of the prefabricated double-layer steel tube concrete segment, and are then anchored to the foundation pedestal and cap beam respectively through anchors.

[0010] Preferably, the foundation pedestal includes a pedestal embedded steel pipe connector, which includes a pedestal embedded steel pipe, a perforated stiffening plate and an end steel plate. The cross-sectional size of the pedestal embedded steel pipe is consistent with the cross-sectional size of the inner steel pipe. The length embedded in the foundation pedestal is not less than 2 times the diameter, and the length L6=L2-L1 higher than the top surface of the foundation pedestal; a number of perforated stiffening plates are welded along the circumferential distribution of the pedestal embedded steel pipe; and the end steel plate is welded at one end of the perforated stiffening plate close to the top surface of the foundation pedestal.

[0011] Preferably, the cap beam includes a cap beam embedded steel pipe connector; the cap beam embedded steel pipe connector includes a cap beam embedded steel pipe, a perforated stiffening plate and an end steel plate. The cross-sectional size of the cap beam embedded steel pipe is consistent with the cross-sectional size of the inner layer steel pipe 2. The length of the cap beam embedded steel pipe L7≧L2-L1 and is not less than 2 times the diameter. It is embedded in the cap beam and one end is flush with the bottom surface of the cap beam. Several perforated stiffening plates are welded along the circumferential distribution of the cap beam embedded steel pipe; and the end steel plate is welded at one end of the perforated stiffening plate close to the bottom surface of the cap beam.

[0012] Preferably, the cross-sectional shape of the outer steel pipe is circular or polygonal.

[0013] Preferably, the cross-sectional shape of the inner steel pipe 1 and the inner steel pipe 2 can be circular or polygonal.

[0014] Preferably, a certain length of the upper portion of the inner layer steel pipe 1 and a certain length of the lower portion of the inner layer steel pipe 2 are both circumferentially provided with a plurality of mutually meshing tooth keys.

[0015] Preferably, a plurality of stiffening plates are welded circumferentially on the inner sides of both ends of the outer steel pipe, the outer side of one end of the inner steel pipe, and the outer side of the inner steel pipe at a distance L2-L1 from the end.

[0016] Preferably, the interlayer concrete cast in the prefabricated double-layer steel tube concrete segment is made of ultra-high performance concrete within the local height range at both ends, or is entirely made of ultra-high performance concrete.

[0017] Preferably, epoxy resin glue joints are used on the connection interfaces between adjacent prefabricated double-layer steel tube concrete segments and between the double-layer steel tube concrete columns and the foundation pedestal and cap beam.

[0018] Another technical object of the present invention is to provide a construction method for the above-mentioned prefabricated and assembled double-layer steel tube concrete composite bridge pier, comprising the following steps:

[0019] Step 1: Factory prefabrication

[0020] Factory-made prefabricated double-layer steel tube concrete segments, pre-buried steel pipe connectors for pedestals and pre-buried steel pipe connectors for cap beams:

[0021] Step 2: On-site assembly

[0022] Step 2.1: Hoist the prefabricated double-layer steel tube concrete segment No. N1 and nest the two ends of the inner steel tube of the segment No. N1 on the pre-buried steel tube of the foundation cap, keeping the axis of the pre-buried steel tube of the foundation cap aligned with the axis of the double-layer steel tube concrete segment;

[0023] Step 2.2: Hoist the prefabricated double-layer steel tube concrete segment No. N2, keeping the axis direction of the segment No. N2 aligned with the axis direction of the segment No. N1;

[0024] Step 2.3, nest the inner steel pipe 2 of the N2 segment onto the protruding portion of the inner steel pipe 1 of the N1 segment;

[0025] Step 2.4: Use the same method to sequentially hoist, position, and assemble other prefabricated double-layer steel tube concrete segments;

[0026] Step 2.5: Hoist the cap beam, align the axis of the embedded steel pipe of the cap beam with the axis of the double-layer steel tube concrete column, and install it in the extended part of the inner steel pipe of the top segment of the double-layer steel tube concrete column;

[0027] Step 2.6, tension the prestressed tendons and anchor them.

[0028] Beneficial effects: Compared with conventional prefabricated assembled concrete bridge piers, the present invention not only has the advantages of double-layer steel tube concrete columns such as high axial bearing capacity, good plastic toughness, and excellent fire resistance, but also has the following advantages: the inner / outer steel tubes of the prefabricated double-layer steel tube concrete segment components can serve as templates, without the need to tie steel bars and set up additional concrete pouring molds, easy to standardize prefabrication in the factory, improve prefabrication production efficiency, save construction costs, and improve economic benefits; during on-site assembly construction, the inner steel tube of the double-layer steel tube concrete segment component can play a positioning role, and there is no need for other Its connection structure that requires on-site operation and convenient on-site assembly and construction can shorten the construction period of bridge piers and reduce the adverse effects of bridge construction on surrounding traffic and ecological environment. It can well adapt to the construction of bridges in areas with poor on-site construction conditions such as deep canyons and mountainous areas, and urban main roads and other sections where traffic should not be interrupted for a long time; the nested steel pipe connection structure at the connection part can improve the initial bending stiffness and shear resistance of the segmented assembled bridge piers, and the toothed connection structure at the connection part can improve the torsional performance of the segmented assembled bridge piers. The connection has good reliability, good integrity, and strong lateral and torsional resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of the prefabricated assembled double-layer steel tube concrete composite bridge pier of the present invention;

[0030] Figure 2a is an elevation view of a prefabricated double-layer steel tube concrete segment component according to an embodiment of the present invention. Figure 2b yes Figure 2a AA cross-section in;

[0031] Figure 3a Schematic diagram of the welding connection between the inner steel pipe 1 and the inner steel pipe 2 in an embodiment of the present invention. Figure 3b yes Figure 3aSchematic diagram of the enlarged structure of part I;

[0032] Figure 4a Schematic diagram of the arrangement of stiffening ribs and toothed keys of a prefabricated double-layer steel tube concrete segmental component in an embodiment of the present invention; Figure 4b yes Figure 4a BB cross-section diagram in; Figure 4c yes Figure 4a CC cross-section in;

[0033] FIG5 is a schematic diagram of the structure of the foundation bearing platform in an embodiment of the present invention; Figure 5b yes Figure 5a DD cross-section diagram in;

[0034] FIG6 is a schematic diagram of the structure of the cap beam according to an embodiment of the present invention; Figure 6b yes Figure 6a EE cross-section diagram in;

[0035] Figure 7 It is a flowchart of on-site assembly construction of prefabricated assembled double-layer steel tube concrete composite bridge piers in an embodiment of the present invention.

[0036] In the figure: 1. Prefabricated double-layer steel tube concrete segment, 2. Foundation pedestal, 3. Cap beam, 11. Inner steel pipe, 12. Outer steel pipe, 13. Stiffener, 14. Sandwich concrete, 15. Inner steel pipe one, 16. Inner steel pipe two, 17. Welding structure, 18. Toothed key, 21. Pre-embedded steel pipe connector for pedestal, 22. Pre-embedded steel pipe for pedestal, 31. Pre-embedded steel pipe connector for cap beam, 32. Pre-embedded steel pipe for cap beam, 40. Perforated stiffener, 50. End steel plate, 60. Anchor, 70. Prestressed tendons. DETAILED DESCRIPTION

[0037] Below, combined with the attached Figures 1 to 7 The specific embodiments of the present invention are further described in detail, but are not limited to the following examples.

[0038] like Figure 1 As shown, the prefabricated assembled double-layer steel tube concrete composite pier of the present invention includes a foundation cap 2, a double-layer steel tube concrete column and a cap beam 3, wherein: the number of double-layer steel tube concrete columns is M, M≧1; the double-layer steel tube concrete column is located between the foundation cap and the cap beam, and is assembled from N prefabricated double-layer steel tube concrete segments 1 and pre-embedded with prestressed tendons 70, wherein N>1; the prefabricated double-layer steel tube concrete segments 1 are as shown Figure 2a 、 Figure 2bAs shown, it includes an outer steel pipe 12, an inner steel pipe 11 and a sandwich concrete 14; the inner steel pipe 11 includes an inner steel pipe 15 and an inner steel pipe 2 16, the outer edge size of the inner steel pipe 15 section matches the inner edge size of the inner steel pipe 2 section 16, one end of the inner steel pipe 15 is nested in one end of the inner steel pipe 2 16 and welded together, the specific structure is shown in the attached Figure 3a 、 3b ; The other end of the inner steel pipe 16 is aligned with one end of the outer steel pipe 12, and the other end of the inner steel pipe 15 is higher than the other end of the outer steel pipe 12; an interlayer concrete 14 is poured between the outer steel pipe 12 and the inner steel pipe 11 to form the prefabricated double-layer steel pipe concrete segment 1, and the two end surfaces of the poured interlayer concrete 14 are flush with the two end surfaces of the outer steel pipe 12; in the present invention, the cross-sectional shape of the outer steel pipe 12 is circular or polygonal.

[0039] The lengths L1, L2, L3 and L4 of the outer steel pipe 12, the inner steel pipe 11, the inner steel pipe 15 and the inner steel pipe 2 16, and the nested overlap length L5 of the inner steel pipe 11 and the inner steel pipe 2 16 are in the following relationship: L3+L4≧L2>L1, L4-L5≧L2-L1, L3≧L4;

[0040] The prestressed tendons 70 pass through the pre-embedded steel pipe 22 of the foundation, the inner steel pipe 11 of the double-layer steel tube concrete segment 1 and the pre-embedded steel pipe 32 of the cap beam in sequence, applying a tensile force equivalent to 10% to 40% of the ultimate axial compressive bearing capacity of the prefabricated double-layer steel tube concrete segment, and are anchored to the foundation foundation 2 and the cap beam 3 through the anchor 60.

[0041] Specifically, the foundation support 2, refer to the attached Figure 5a 、 5b , including a pre-buried steel pipe connector 21 for the pedestal, the pre-buried steel pipe connector 21 includes a pre-buried steel pipe 22 for the pedestal, a perforated stiffening plate 40 and an end steel plate 50. The cross-sectional size of the pre-buried steel pipe 22 for the pedestal is consistent with the cross-sectional size of the inner steel pipe 15. The length embedded in the foundation pedestal 2 is not less than 2 times the diameter, and the length L6=L2-L1 above the top surface of the foundation pedestal 2 is higher. Several perforated stiffening plates 40 are welded along the circumferential distribution of the pre-buried steel pipe 22 for the pedestal; and the end steel plate 50 is welded at one end of the perforated stiffening plate 40 close to the top surface of the foundation pedestal 2. As for the cap beam 3, refer to the attached Figure 6a 、 6b, including a cap beam embedded steel pipe connector 31; the cap beam embedded steel pipe connector 31 includes a cap beam embedded steel pipe 32, a perforated stiffening plate 40 and an end steel plate 50. The cross-sectional size of the cap beam embedded steel pipe 32 is consistent with the cross-sectional size of the inner steel pipe 16. The length L7 of the cap beam embedded steel pipe 32 is ≧ L2-L1 and is not less than 2 times the diameter. It is embedded in the cap beam 3 and one end is flush with the bottom surface of the cap beam 3; a number of perforated stiffening plates 40 are welded along the circumferential distribution of the cap beam embedded steel pipe 32; and an end steel plate 50 is welded at one end of the perforated stiffening plate 40 close to the bottom surface of the cap beam 3. In the present invention, the purpose of welding a number of perforated stiffening plates distributed circumferentially on the cap beam embedded steel pipe is to strengthen the connection performance between the cap beam embedded steel pipe and the cap beam. The purpose of welding an end steel plate at one end of the perforated stiffening plate close to the bottom surface of the cap beam is to prevent local crushing of the concrete on the bottom surface of the cap beam.

[0042] In the present invention, several stiffening ribs are welded circumferentially on the inner sides of both ends of the outer steel pipe, on the outer sides of both bottom ends of the inner steel pipe, and on the outer sides of the inner steel pipe at a distance L2-L1 from the top end. This prevents local buckling of the steel pipe at the ends and joints, thereby improving the interfacial bond between the concrete and the steel pipe in these areas. Furthermore, to enhance the shear slip resistance of the interface between the steel pipe, stiffening ribs, and the sandwich concrete, holes are drilled in the stiffening ribs and concrete is poured to form concrete pins.

[0043] In order to improve the torsional performance of prefabricated double-layer steel tube concrete composite piers, several toothed keys are arranged circumferentially between the double-layer steel tube concrete segments and at the connection parts between the double-layer steel tube concrete segments and the foundation pedestal and cap beam to form an anti-torsion structure. Figure 4a -c.

[0044] In order to suppress the premature local damage of concrete at the joints between the double-layer steel tube concrete segments and between the foundation pedestal and the cap beam due to rotational deformation, and to achieve better stress-bearing performance, ultra-high performance concrete is used to cast the sandwich concrete at both ends within a certain height range, or ultra-high performance concrete can be used to cast the entire segment.

[0045] In order to better connect the components of the prefabricated double-layer steel tube concrete composite piers, reduce the residual deformation of the pier structure after an earthquake disaster, and ensure the normal use of the bridge after the earthquake, post-tensioned prestressed tendons are set, which pass through the embedded steel pipes of the pedestal, the inner steel pipes of the double-layer steel tube concrete segment, and the embedded steel pipes of the cap beam in sequence, and apply a tensioning force equivalent to 10%~40% of the axial compressive bearing capacity of the double-layer steel tube concrete column, and then anchored to the foundation pedestal and cap beam through anchors.

[0046] In order to reduce the joint gap between the double-layer steel tube concrete segments and between the foundation pedestal and cap beam to achieve better connection effect and stress performance, epoxy resin glue is coated on the connection interface. Example

[0047] The above-mentioned prefabricated double-layer steel tube concrete composite pier, such as Figure 7 As shown, it is manufactured and assembled through the following steps.

[0048] 1. Factory-made prefabricated double-layer steel tube concrete segment 1, pedestal embedded steel pipe connector 21 and cap beam embedded steel pipe connector 31:

[0049] 1. Prefabricated double-layer steel tube concrete segment 1: Prepare an outer steel tube 12, an inner steel tube 1 15, and an inner steel tube 2 16, weld the inner steel tube 15 and the inner steel tube 2 16 together to form an inner steel tube 11, and weld the stiffening plates 13 to both ends of the outer steel tube 12 and the inner steel tube 11; fix the outer steel tube 12 and the inner steel tube 11 on a horizontal working surface, and directly pour the sandwich concrete inside them without setting up other molds to form a prefabricated double-layer steel tube concrete segment 1;

[0050] 2. Cap embedded steel pipe connector 21: Make the cap embedded steel pipe 22, weld the perforated stiffening plates 40 evenly around the periphery of the cap embedded steel pipe 22, and weld the end steel plate 50 to the upper end of the perforated stiffening plates 40;

[0051] 3. Cap beam embedded steel pipe connector 31: Make cap beam embedded steel pipe 32, weld perforated stiffening plates 40 evenly around the periphery of the cap beam embedded steel pipe 32, and weld end steel plates 50 to the lower ends of the perforated stiffening plates 40;

[0052] 2. On-site construction and assembly of bridge piers. The construction process is as follows Figure 7 As shown, the following steps are included:

[0053] 1. Construction of foundation cap 2: embed the cap embedded steel pipe connector 21 into the foundation cap 2 and position it. Pass the prestressed tendons 70 that have previously passed through the embedded anchor 60 in the foundation cap 2 through the cap embedded steel pipe 22, and pour the foundation cap 2 concrete.

[0054] 2. Construction of cap beam 3: embed the cap beam pre-embedded steel pipe connector 31 into the cap beam 3 for positioning, and pour the cap beam 3 concrete on site;

[0055] 3. Hoist the first prefabricated double-layer steel tube concrete segment 1, and nest the second end 16 of the inner steel tube of the double-layer steel tube concrete segment 1 on the pre-buried steel tube 22 of the foundation cap, keeping the axis direction of the pre-buried steel tube 22 of the foundation cap aligned with the axis direction of the double-layer steel tube concrete segment 1;

[0056] 4. Hoist the second prefabricated double-layer steel tube concrete segment 1, keep the axis direction of the second segment aligned with the axis direction of the first segment, and nest the inner steel pipe 2 16 of the second segment into the protruding part of the inner steel pipe 1 15 of the first segment;

[0057] 5. Use the same method as step 4 to sequentially hoist, position, and assemble the remaining prefabricated double-layer steel tube concrete segments 1;

[0058] 6. Hoisting the cap beam 3: Install the cast-in-place cap beam 3 on the upper end of the inner steel pipe 15 of the top double-layer steel tube concrete segment 1 through the cap beam embedded steel pipe 32, keeping the axial direction of the cap beam embedded steel pipe 32 aligned with the axial direction of the prefabricated double-layer steel tube concrete segment 1;

[0059] 7. During the above construction process, while hoisting the prefabricated double-layer steel tube concrete segment 1 and the cap beam 3, the prestressed tendons 70 are sequentially passed through the inner steel pipe 11 of the hoisted segment component and the embedded steel pipe 32 of the cap beam. After all components are assembled, the prestressed tendons 70 are tensioned on the top of the cap beam and anchored with anchors 60.

[0060] The above description is only a preferred embodiment of the present invention. It should be pointed out that several deductions or substitutions can be made without departing from the concept of the present invention, and these deductions or substitutions should be regarded as within the scope of protection of the present invention.

Claims

1. A prefabricated double-layer steel tube concrete composite bridge pier, comprising a foundation cap (2), a double-layer steel tube concrete column and a cap beam (3), wherein: The number of double-layer steel tube concrete columns is M, M≧1; the characteristics are: the double-layer steel tube concrete columns are located between the foundation pedestal and the cap beam, are assembled from N prefabricated double-layer steel tube concrete segments (1), and are pre-buried with prestressed tendons (70), wherein N>1; the prefabricated double-layer steel tube concrete segments (1) include an outer steel tube (12), an inner steel tube (11) and an interlayer concrete (14); the inner steel tube (11) includes an inner steel tube (15) and the inner steel pipe (16), the outer edge size of the cross section of the inner steel pipe (15) matches the inner edge size of the cross section of the inner steel pipe (16), one end of the inner steel pipe (15) is nested in one end of the inner steel pipe (16) and welded; the other end of the inner steel pipe (16) is aligned with one end of the outer steel pipe (12), and the other end of the inner steel pipe (15) is higher than the other end of the outer steel pipe (12); an interlayer concrete (14) is poured between the outer steel pipe (12) and the inner steel pipe (11) to form the prefabricated double-layer steel pipe concrete segment (1), and the two end faces of the poured interlayer concrete (14) are flush with the two end faces of the outer steel pipe (12); the lengths L1, L2, L3 of the outer steel pipe (12), the inner steel pipe (11), the inner steel pipe (15) and the inner steel pipe (16) are L1, L4, L5, L6, L7, L8, L9, L10, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20, L21, L22, L23, L24, L25, L26, L27, L28, L29, L29, L29, L30, L31, L32, L43, L44, L45, L46, L47, L48, L49, L50, L51, L52, L53, L54, L55, L56, L57, L58, L59, L60, L61, L62, L70, L71, L72, L73, L74, L75, L76, L77, L78, L79, L79, L80, L81, L82, L83 The following relationship exists between L2, L3 and L4 and the nested overlap length L5 of the inner steel pipe 1 (15) and the inner steel pipe 2 (16): L3+L4≧L2>L1, L4- L5≧L2-L1, L3≧L4; the prestressed tendons (70) sequentially pass through the pre-buried steel pipe (22) of the pedestal, the inner steel pipe (11) of the double-layer steel tube concrete segment (1), and the pre-buried steel pipe (32) of the cap beam, apply a tensile force equivalent to 10%-40% of the ultimate axial compressive bearing capacity of the precast double-layer steel tube concrete segment, and are then anchored to the foundation pedestal (2) and the cap beam (3) respectively through the anchor (60); the cross-sectional shape of the inner steel pipe 1 and the inner steel pipe 2 can be circular or polygonal; at the connection parts between the precast double-layer steel tube concrete segments (1), the connection parts between the precast double-layer steel tube concrete segment (1) and the foundation pedestal (2), and the connection parts between the precast double-layer steel tube concrete segment (1) and the cap beam (3), a plurality of toothed keys (18) are arranged along the circumference of the inner steel pipe (11) to form an anti-torsion structure.

2. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1 is characterized in that: The foundation pedestal (2) includes a pedestal embedded steel pipe connector (21), and the pedestal embedded steel pipe connector (21) includes a pedestal embedded steel pipe (22), a perforated stiffening plate (40) and an end steel plate (50). The cross-sectional size of the pedestal embedded steel pipe (22) is consistent with the cross-sectional size of the inner steel pipe (15), the length embedded in the foundation pedestal (2) is not less than 2 times the diameter, and the length L6=L2-L1 above the top surface of the foundation pedestal (2); a plurality of perforated stiffening plates (40) are welded along the circumferential distribution of the pedestal embedded steel pipe (22); and the end steel plate (50) is welded at one end of the perforated stiffening plate (40) close to the top surface of the foundation pedestal (2).

3. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1 is characterized in that: The cap beam (3) includes a cap beam embedded steel pipe connector (31); the cap beam embedded steel pipe connector (31) includes a cap beam embedded steel pipe (32), a perforated stiffening plate (40) and an end steel plate (50); the cross-sectional size of the cap beam embedded steel pipe (32) is consistent with the cross-sectional size of the inner layer steel pipe (16); the length L7 of the cap beam embedded steel pipe (32) is ≧ L2-L1 and is not less than 2 times the diameter; the cap beam embedded steel pipe (32) is embedded in the cap beam (3) and one end is flush with the bottom surface of the cap beam (3); a plurality of perforated stiffening plates (40) are welded along the circumferential distribution of the cap beam embedded steel pipe (32); and the end steel plate (50) is welded to one end of the perforated stiffening plate (40) close to the bottom surface of the cap beam (3).

4. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1, characterized in that: The cross-sectional shape of the outer steel pipe (12) is circular or polygonal.

5. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1 is characterized in that: A certain length of the upper portion of the inner layer steel pipe 1 (15) and a certain length of the lower portion of the inner layer steel pipe 2 (16) are both provided with a plurality of mutually meshing tooth keys (18) distributed along the circumferential direction.

6. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1, characterized in that: Several stiffening plates (13) are welded circumferentially to the inner sides of both ends of the outer steel pipe (12), the outer side of one end of the second inner steel pipe (16), and the outer side of the first inner steel pipe (15) at a distance L2-L1 from the end, and holes are opened on the stiffening plates (13).

7. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1, characterized in that: The interlayer concrete (14) cast in the prefabricated double-layer steel tube concrete segment (1) is made of ultra-high performance concrete in the local height range at both ends, or is entirely made of ultra-high performance concrete.

8. The prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1, characterized in that: Epoxy resin adhesive joints are used at the connection interfaces between adjacent prefabricated double-layer steel tube concrete segments (1) and between the double-layer steel tube concrete columns and the foundation pedestal (2) and cap beam (3).

9. A construction method for prefabricated and assembled double-layer steel tube concrete composite bridge pier according to claim 1, characterized in that: The specific steps include: Step 1: Factory prefabrication Prefabricated double-layer steel tube concrete segments (1), pre-buried steel tube connectors (21) for the pedestal, and pre-buried steel tube connectors (31) for the cap beam are manufactured in a factory; Step 2: On-site assembly Step 2.1, construction of foundation cap (2): embed the cap embedded steel pipe connector (21) into the foundation cap (2) and position it, pass the prestressed tendons (70) that have previously passed through the embedded anchor (60) in the foundation cap (2) through the cap embedded steel pipe (22), and pour the foundation cap concrete; Step 2.2, construction of the cap beam (3): embedding the cap beam pre-embedded steel pipe connector (31) into the cap beam (3) for positioning, and pouring the cap beam concrete on site; Step 2.3: Hoist the prefabricated double-layer steel tube concrete segment No. N1 and nest the two ends of the inner steel tube of segment No. N1 on the pre-buried steel tube of the foundation cap, keeping the axis of the pre-buried steel tube of the foundation cap aligned with the axis of the double-layer steel tube concrete segment; Step 2.4: Hoist the prefabricated double-layer steel tube concrete segment No. N2, keeping the axis direction of segment No. N2 aligned with the axis direction of segment No. N1; Step 2.5: nest the inner steel pipe 2 of the N2 segment onto the protruding portion of the inner steel pipe 1 of the N1 segment; Step 2.6: Use the same method to sequentially hoist, position, and assemble other prefabricated double-layer steel tube concrete segments; Step 2.7, hoist the cap beam, align the axial direction of the embedded steel pipe of the cap beam with the axial direction of the double-layer steel tube concrete column, and nest it in the protruding part of the inner layer steel pipe of the top segment of the double-layer steel tube concrete column; Step 2.8, tension the prestressed tendons and anchor them.

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