Fabricated prestressed variable cross-section concrete filled steel tube pier

Abstract

The utility model discloses an assembly type prestress variable cross-section concrete filled steel tube pier which comprises an upper steel cylinder, a middle steel cylinder, a lower steel cylinder and four groups of steel strands, and the upper steel cylinder, the middle steel cylinder and the lower steel cylinder are coaxially, sequentially and fixedly connected from top to bottom. A concrete column body is arranged in each steel cylinder, four threading holes are formed in each concrete column body, the threading holes in any two adjacent concrete column bodies are in one-to-one correspondence, each group of steel strands are arranged in the corresponding threading holes in the vertical direction in a penetrating mode, an upper anchorage device is arranged at the upper end of each group of steel strands, and a lower anchorage device is arranged at the lower end of each group of steel strands. And after the prestressed tension of each group of steel strands is completed, mortar is poured into each threading hole, and after the mortar is solidified, the mortar and each concrete column body form an integrated structure. The bridge pier is manufactured in a factory in a segmented mode, quality control is facilitated, transportation is convenient, the construction period can be greatly shortened, the construction difficulty and the engineering cost are reduced, steel strand prestress tensioning assembly construction is adopted, and the overall stability and the anti-seismic performance of the bridge pier are effectively improved.

Description

Technical Field

[0001] This utility model relates to the field of prefabricated building technology, specifically to a prefabricated prestressed variable cross-section steel tube concrete bridge pier. Background Technology

[0002] Concrete-filled steel tube (CFST) piers have been widely used in bridges and other major engineering projects, becoming one of the most favored structural designs in structural engineering. This structure consists of two parts: a steel tube and concrete, with the concrete filling the interior of the steel tube. This structural form combines the high ductility of ordinary steel tubes with the high compressive strength of concrete piers. Furthermore, when bearing loads as a load-bearing component, the presence of the steel tube restricts the deformation of the internal concrete due to the confinement effect, significantly improving the overall load-bearing capacity of the concrete-filled steel tube.

[0003] Prefabricated steel-concrete composite bridge piers, as an application of prefabricated building technology in bridge engineering, offer significant advantages in construction efficiency and quality control. Prefabricated technology allows for the prefabrication of various pier components in a factory, ensuring consistency and precision of the components and reducing uncertainties during on-site construction. In bridge construction, prefabricated steel-concrete composite bridge piers can accelerate construction progress through rapid on-site assembly, reduce traffic disruption, and improve construction safety. Furthermore, prefabricated structures facilitate standardized and modular design, reducing construction difficulty and project costs.

[0004] Existing concrete bridge piers require extensive on-site casting and assembly, making the construction process often cumbersome and time-consuming. The construction period is lengthy, especially under adverse conditions such as inclement weather or complex terrain, which can significantly impact on-site progress and extend the project duration. Furthermore, the complexity of the on-site working environment makes it difficult to strictly control the quality of concrete pouring.

[0005] While prefabricated steel-concrete composite structures offer significant advantages in construction efficiency and durability, they still face limitations in impact resistance when subjected to loads, especially in the middle sections of bridge piers which are located at the waterline and are susceptible to impacts from ships or ice floes in winter. As critical load-bearing components, the pier columns bear the brunt of external impact loads; these instantaneous high-intensity loads can easily cause localized damage, thus affecting the overall structural stability. Therefore, existing technologies require further improvement and enhancement. Utility Model Content

[0006] In view of the shortcomings of the existing technology, the purpose of this utility model is to provide a prefabricated prestressed variable cross-section steel tube concrete bridge pier, which solves the problems that existing concrete bridge piers need to be poured on the construction site, the construction process is often cumbersome and time-consuming, the construction period is long, the progress of on-site operations is more easily affected by the external environment, resulting in the extension of the project cycle, and existing bridge piers have insufficient impact resistance.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0008] A prefabricated prestressed variable cross-section steel tube concrete bridge pier includes an upper steel cylinder, a middle steel cylinder, a lower steel cylinder, and four sets of steel strands. The upper steel cylinder, the middle steel cylinder, and the lower steel cylinder are arranged coaxially from top to bottom. The corresponding end flanges of any two adjacent steel cylinders are fixedly connected. The upper steel cylinder and the lower steel cylinder are straight cylindrical bodies with equal cross-sections, while the middle steel cylinder is a variable cross-section cylindrical body that is thicker in the middle and thinner at both ends.

[0009] The upper steel cylinder contains a first concrete column, the middle steel cylinder contains a second concrete column, and the lower steel cylinder contains a third concrete column. The lower end of the first concrete column and the upper end of the second concrete column form a first post-cast cavity, and the lower end of the second concrete column and the upper end of the third concrete column form a second post-cast cavity.

[0010] The first concrete column has a first steel reinforcement cage fixedly embedded inside, the second concrete column has a second steel reinforcement cage fixedly embedded inside, and the third concrete column has a third steel reinforcement cage fixedly embedded inside.

[0011] Each concrete column has a number of through holes equal to the number of groups of steel strands inside. All the through holes in each concrete column are arranged in a ring on the circumference of the concrete column with the axis of the concrete column as the center. The two ends of each through hole extend to the end face of the concrete column.

[0012] Each group of steel strands is threaded through the inside of each threading hole. The upper end of each group of steel strands passes through the upper surface of the first concrete column and is equipped with an upper anchor, while the lower end passes through the lower surface of the third concrete column and is equipped with a lower anchor.

[0013] After each group of steel strands is prestressed and fixed, mortar is injected into each threading hole through the upper anchor. The mortar fills the first post-cast cavity, the second post-cast cavity and each threading hole. After solidification, it forms an integral structure with the concrete column. Then, mortar is poured into the inner side of the upper end of the upper steel cylinder. After solidification, it forms a sealing anchor body with an integral structure with the first concrete column.

[0014] Furthermore, a first flange is fixed to the lower outer side of the upper steel cylinder, a second flange is fixed to the upper and lower outer sides of the middle steel cylinder, and a third flange is fixed to the upper outer side of the lower steel cylinder.

[0015] A first annular sealing plate is provided between the first flange and the second flange at the upper end of the intermediate steel cylinder, and they are fixedly connected by bolts. A second annular sealing plate is provided between the second flange at the upper end of the intermediate steel cylinder and the third flange, and they are also fixedly connected by bolts.

[0016] Furthermore, the outer surfaces of the upper steel cylinder, the middle steel cylinder, the lower steel cylinder, the first flange, the second flange, and the third flange all have a corrosion-resistant FRP protective layer.

[0017] The inner sides of the upper steel cylinder, the middle steel cylinder, and the lower steel cylinder are provided with multiple sets of shear studs. Each set of shear studs is arranged in a ring on the inner circumference of the steel cylinder in which it is located. Each set of shear studs includes multiple shear studs arranged vertically at equal intervals. Each shear stud is set perpendicular to the axis of the steel cylinder in which it is located, and its end is fixedly welded to the inner wall of the steel cylinder.

[0018] Each shear stud is fixedly embedded inside the concrete column on the inner side of the steel cylinder.

[0019] Furthermore, the first, second, and third reinforcing cages are all cylindrical reinforcing cages, each comprising a plurality of longitudinal bars arranged in a ring and uniformly, and each longitudinal bar having a plurality of ring bars arranged at equal intervals along its length.

[0020] The lower end faces of the first, second, and third concrete columns are all provided with grouting holes that are equal in number and correspond one-to-one with the longitudinal bars of the same cylindrical steel cage.

[0021] During assembly, the upper ends of the longitudinal bars of the third steel cage are inserted into the corresponding grouting holes at the bottom of the second concrete column, and the upper ends of the longitudinal bars of the second steel cage are inserted into the corresponding grouting holes at the bottom of the first concrete column.

[0022] Furthermore, both the upper and lower anchors include an anchor plate, an anchor plate, and multiple clamping pieces. The anchor plate of each upper anchor is fixed to the upper end of the corresponding through hole of the first concrete column in an embedded manner, and the anchor plate of each lower anchor is fixed to the lower end of the corresponding through hole of the third concrete column in an embedded manner.

[0023] Furthermore, each concrete column is equipped with four corrugated pipes inside, all of which are located inside the corresponding reinforcing cage, and the inner side of each corrugated pipe forms the through hole of the concrete column in which it is located.

[0024] Each corrugated pipe inside the first and third concrete columns is arranged parallel to the axis of the steel cylinder outside the concrete column, while the four corrugated pipes inside the second concrete column are arranged in a radially outward convex arc shape.

[0025] The upper ends of all the corrugated pipes in the second concrete column correspond one-to-one with all the corrugated pipes in the first concrete column, and are connected to the corrugated pipes in the first concrete column through the first post-cast cavity. The lower ends of all the corrugated pipes in the third concrete column correspond one-to-one with all the corrugated pipes in the third concrete column, and are connected to the corrugated pipes in the third concrete column through the second post-cast cavity.

[0026] Furthermore, the anchor plate of each of the upper anchors is connected to the upper end of the corresponding corrugated pipe in the first concrete column, and the anchor plate of each of the lower anchors is connected to the lower end of the corresponding corrugated pipe in the third concrete column.

[0027] The upper anchor plate is an anchor plate with a grouting channel, and the lower anchor plate is an anchor plate with a venting channel.

[0028] Furthermore, a fourth flange is fixed to the lower end of the lower steel cylinder, and the outer wall of the fourth flange has the same FRP protective layer as the outer wall of the lower steel cylinder.

[0029] By adopting the above technical solution, the beneficial technical effects of this utility model are as follows: The steel-concrete composite bridge piers of this utility model are manufactured in sections in the factory, which is conducive to the quality control of the steel-concrete composite bridge piers, facilitates transportation, greatly shortens the construction cycle, reduces construction difficulty and project cost, and adopts steel strand prestressed tensioning assembly construction, which has good integrity and high strength, effectively enhances the overall stability and seismic performance of the bridge pier, enhances the overall impact resistance of the structure, and also effectively improves the corrosion resistance of the bridge pier shell. Attached Figure Description

[0030] Figure 1 This is a structural schematic diagram of a prefabricated prestressed variable cross-section steel tube concrete bridge pier according to this utility model.

[0031] Figure 2 This is a schematic diagram of the upper steel cylinder and its internal structure of this utility model.

[0032] Figure 3 This is a top view of the steel cylinder and its internal structure of this utility model.

[0033] Figure 4 This is a schematic diagram of the intermediate steel cylinder and its internal structure of this utility model.

[0034] Figure 5 This is a top view of the intermediate steel cylinder and its internal structure of this utility model.

[0035] Figure 6 This is a schematic diagram of the lower steel cylinder and its internal structure of this utility model.

[0036] Figure 7 This is a top view of the lower steel cylinder and its internal structure of this utility model. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings:

[0038] Combination Figures 1 to 7 A prefabricated prestressed variable cross-section steel tube concrete bridge pier includes an upper steel cylinder 1, a middle steel cylinder 2, a lower steel cylinder 3, and four sets of steel strands 4. The upper steel cylinder 1, the middle steel cylinder 2, and the lower steel cylinder 3 are arranged coaxially from top to bottom. The corresponding end flanges of any two adjacent steel cylinders are fixedly connected. The upper steel cylinder 1 and the lower steel cylinder 3 are straight cylindrical bodies with equal cross-sections, while the middle steel cylinder 2 is a variable cross-section cylindrical body that is thicker in the middle and thinner at both ends.

[0039] A first flange 11 is fixedly welded to the lower outer side of the upper steel cylinder 1. A second flange 21 is fixedly welded to the upper and lower outer sides of the middle steel cylinder 2. A third flange 31 is fixedly welded to the upper outer side of the lower steel cylinder 3. A fourth flange 32 is fixedly welded to the lower outer side of the lower steel cylinder 3. All the above flanges are of the same specification and model. Each flange has multiple bolt holes arranged at equal intervals along its circumference.

[0040] The outer surfaces of the upper steel cylinder 1, the middle steel cylinder 2, the lower steel cylinder 3, and each flange are all covered with a corrosion-resistant FRP protective layer. Furthermore, the bottom of the first flange 11, the bottom of the fourth flange 32, and the bottom of the second flange 21 at the lower end of the middle steel cylinder 2 are all provided with annular grooves. The upper surface of the third flange 31 and the upper surface of the second flange 21 at the upper end of the middle steel cylinder 2 are also provided with the same annular grooves, and each bolt hole is located inside the corresponding annular groove.

[0041] A first annular sealing plate 51 is provided between the first flange 11 and the second flange 21 at the upper end of the intermediate steel cylinder 2, and they are fixedly connected by bolts. A second annular sealing plate 52 is provided between the second flange 21 at the upper end of the intermediate steel cylinder 2 and the third flange 31, and they are also fixedly connected by bolts.

[0042] The inner sides of the upper steel cylinder 1, the middle steel cylinder 2, and the lower steel cylinder 3 are each provided with multiple sets of shear studs 61. Each set of shear studs 61 is arranged in a ring on the inner circumference of the steel cylinder in which it is located. Each set of shear studs 61 includes multiple shear studs 61 arranged vertically at equal intervals. Each shear stud 61 is set perpendicular to the axis of the steel cylinder in which it is located, and its end is fixedly welded to the inner wall of the steel cylinder.

[0043] The upper steel cylinder 1, the middle steel cylinder 2, and the lower steel cylinder 3 are all welded from steel plates, and a shear nail 61 is welded on the inner wall. Then, shot blasting is performed on both the inner and outer sides of each steel cylinder. Anti-rust paint is sprayed and putty is applied to the outer wall of the steel cylinder. Then, glass fiber is wrapped around the outer wall of the steel cylinder and the flange and resin is applied. After solidification, an FRP protective layer is formed on the outer wall of the steel cylinder and is integrated with the outer wall of the steel cylinder and the flange.

[0044] The upper steel cylinder 1 has a first concrete column 12 inside, the middle steel cylinder 2 has a second concrete column 22 inside, and the lower steel cylinder 3 has a third concrete column 33 inside. Each shear nail 61 is fixedly embedded inside the concrete column on the inner side of its respective steel cylinder.

[0045] The first post-cast cavity is located between the lower end of the first concrete column 12 and the upper end of the second concrete column 22, and the second post-cast cavity is located between the lower end of the second concrete column 22 and the upper end of the third concrete column 33.

[0046] A first reinforcing cage 13 is fixedly embedded inside the first concrete column 12, a second reinforcing cage 23 is fixedly embedded inside the second concrete column 22, and a third reinforcing cage 34 is fixedly embedded inside the third concrete column 33. The first reinforcing cage 13, the second reinforcing cage 23, and the third reinforcing cage 34 are all cylindrical reinforcing cages. Each cylindrical reinforcing cage includes a plurality of longitudinal bars arranged in a ring evenly, and each longitudinal bar has a plurality of annular bars arranged at equal intervals along its length.

[0047] The lower end faces of the first concrete column 12, the second concrete column 22, and the third concrete column 33 are all provided with grouting holes 7, the number of which are equal to and the positions of the longitudinal bars of the same cylindrical steel cage. During assembly, the upper ends of each longitudinal bar of the third steel cage 34 pass through the corresponding grouting holes 7 at the bottom of the second concrete column 22, and the upper ends of each longitudinal bar of the second steel cage 23 pass through the corresponding grouting holes 7 at the bottom of the first concrete column 12.

[0048] During the prefabrication process, cylindrical steel cages are placed and fixed inside the upper steel cylinder 1, the middle steel cylinder 2, and the lower steel cylinder 3. Then, four corrugated pipes 62 are installed and fixed inside the steel cages. After that, sealing plates are installed at both ends of each steel cylinder and concrete is poured. The concrete pouring inside the upper steel cylinder 1, the middle steel cylinder 2, and the lower steel cylinder 3 is carried out separately. The grouting holes 7 at the bottom of each concrete column are formed by the rod structure of the sealing plate. After the sealing plate is removed, the grouting holes 7 at the bottom of the concrete column are formed.

[0049] Each concrete column has the same number of threading holes as the steel strand 4 inside. All the threading holes in each concrete column are arranged in a ring on the circumference with the axis of the concrete column as the center. The two ends of each threading hole extend to the end face of the concrete column.

[0050] Specifically, each concrete column has four corrugated pipes 62 evenly distributed inside, and the four corrugated pipes 62 are all located inside the corresponding steel cage, with the wire hole of the concrete column forming the inner side of each corrugated pipe 62.

[0051] Each corrugated pipe 62 inside the first concrete column 12 and the third concrete column 33 is arranged parallel to the axis of the steel cylinder outside the concrete column, and the four corrugated pipes 62 inside the second concrete column 22 are arranged in a radially outward arc shape.

[0052] The upper ends of all the corrugated pipes 62 inside the second concrete column 22 correspond one-to-one with all the corrugated pipes 62 inside the first concrete column 12, and are connected to the corrugated pipes 62 inside the first concrete column 12 through the first post-cast cavity. The lower ends of all the corrugated pipes 62 inside the third concrete column 33 correspond one-to-one with all the corrugated pipes 62 inside the third concrete column 33, and are connected to the corrugated pipes 62 inside the third concrete column 33 through the second post-cast cavity.

[0053] After the internal structures of the upper steel cylinder 1, the middle steel cylinder 2, and the lower steel cylinder 3 are fabricated, they are transported to the construction site. First, four sets of steel strands 4 are installed inside the lower steel cylinder 3, and lower anchors 42 are installed at the bottom of the third concrete column 33. Then, the lower steel cylinder 3 is installed on the prefabricated concrete base. The reinforcing bars of the concrete base are inserted into the corresponding grouting holes 7 at the bottom of the third concrete column 33. The fourth flange 32 of the lower steel cylinder 3 is bolted to the steel components on the surface of the concrete base, and the cavity between the bottom of the third concrete column 33 and the concrete base is grouted until it is full.

[0054] Subsequently, the intermediate steel cylinder 2 and the lower steel cylinder 3 are installed and fixedly connected in sequence. Each set of steel strands 4 passes through the top of the first concrete column 12, and four upper anchors 41 are installed on the top of the first concrete column 12. The four sets of steel strands 4 are prestressed and tensioned respectively. After tensioning is completed, the excess part of the steel strands 4 is cut off, and grouting is carried out through the grouting channel located in the upper anchor 41. The mortar fills the first post-cast cavity, the second post-cast cavity, and each wire hole. After the mortar in the first post-cast cavity solidifies, it forms the first concrete connector 81. After the mortar in the second post-cast cavity solidifies, it forms the second concrete connector 82. The first concrete connector 81 and the second concrete connector 82 are combined with the three concrete columns to form an integrated structure, giving the steel-concrete composite pier good integrity and high strength.

[0055] Each group of steel strands 4 is threaded through the inside of each threading hole. The upper end of each group of steel strands 4 passes through the upper end face of the first concrete column 12 and is equipped with an upper anchor 41, and the lower end passes through the lower end face of the third concrete column 33 and is equipped with a lower anchor 42.

[0056] Both the upper anchor 41 and the lower anchor 42 include an anchor plate, an anchor plate, and multiple clamping pieces. The anchor plate of each upper anchor 41 is fixed to the upper end of the corresponding through hole of the first concrete column 12 in an embedded manner, and the anchor plate of each lower anchor 42 is fixed to the lower end of the corresponding through hole of the third concrete column 33 in an embedded manner.

[0057] The anchor plates of each upper anchor 41 are connected to the upper ends of the corresponding corrugated pipes 62 within the first concrete column 12, and the anchor plates of each lower anchor 42 are connected to the lower ends of the corresponding corrugated pipes 62 within the third concrete column 33. The anchor plates of the upper anchors 41 are anchor plates with grouting channels, and the anchor plates of the lower anchors 42 are anchor plates with venting channels.

[0058] After the prestressing tensioning and fixing of each group of steel strands 4 is completed, mortar is injected into the inside of each wire hole through the upper anchor 41. The mortar fills the first post-cast cavity, the second post-cast cavity and each wire hole. After solidification, it forms an integral structure with the concrete column. Then, mortar is poured into the inner side of the upper end of the upper steel cylinder 1. After solidification, it forms a sealing anchor body 14 with an integral structure with the first concrete column 12, which supports the crossbeam and bridge deck above the steel pipe concrete pier.

[0059] The middle section of the steel-concrete composite pier utilizes ellipsoidal pier segments. Their unique curved shape effectively disperses and absorbs impact forces, reduces localized stress concentration, and significantly improves the pier's impact resistance. This feature allows the ellipsoidal pier segments to greatly enhance their impact resistance when facing ships, ice floes, or other external impacts, protecting the pier structure from sudden failure or localized damage. Other sections use cylindrical pier segments, maintaining the traditional cylindrical structure. This not only facilitates standardized production and construction but also reduces material consumption and costs.

[0060] The parts not mentioned in this utility model can be achieved by adopting or referencing existing technologies.

[0061] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0063] Of course, the above description is not intended to limit the present utility model, and the present utility model is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present utility model should also fall within the protection scope of the present utility model.

Claims

1. A fabricated prestressed variable cross-section steel tube concrete bridge pier, characterized in that, The steel cylinder includes an upper steel cylinder, a middle steel cylinder, a lower steel cylinder and four groups of steel strands, the upper steel cylinder, the middle steel cylinder and the lower steel cylinder are coaxially arranged from top to bottom, the flanges at the corresponding ends of any two adjacent steel cylinders are fixedly connected, the upper steel cylinder and the lower steel cylinder are straight cylindrical bodies with equal cross sections, and the middle steel cylinder is a variable cross section cylindrical body with a thick middle and thin ends. The inside of the upper steel cylinder has a first concrete column, the inside of the middle steel cylinder has a second concrete column, the inside of the lower steel cylinder has a third concrete column, the first concrete column and the second concrete column are connected through a first post-cast cavity, and the second concrete column and the third concrete column are connected through a second post-cast cavity. The inside of the first concrete column is fixedly embedded with a first steel reinforcement cage, the inside of the second concrete column is fixedly embedded with a second steel reinforcement cage, and the inside of the third concrete column is fixedly embedded with a third steel reinforcement cage. The inside of each concrete column has a number of threading holes equal to the number of groups of steel strands, all the threading holes in each concrete column are arranged in a ring shape on the circumference of the axis of the concrete column, and the two ends of each threading hole penetrate the end face of the concrete column. Each group of steel strands is arranged in each threading hole, the upper ends of the steel strands penetrate the upper end face of the first concrete column and are provided with an upper anchor, and the lower ends of the steel strands penetrate the lower end face of the third concrete column and are provided with a lower anchor. After the prestress tensioning of each group of steel strands is completed, the inside of each threading hole is grouted with mortar through the upper anchor, the mortar fills the first post-cast cavity, the second post-cast cavity and each threading hole, and forms an integral structure with the concrete column after solidification, then mortar is grouted in the inside of the upper end of the upper steel cylinder, and an anchor sealing body is formed in an integral structure with the first concrete column after solidification.

2. The fabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 1, characterized in that, The lower end of the upper steel cylinder is fixedly provided with a first flange, the upper and lower ends of the middle steel cylinder are each fixedly provided with a second flange, and the upper end of the lower steel cylinder is fixedly provided with a third flange. A first annular sealing piece is arranged between the first flange and the second flange at the upper end of the middle steel cylinder and is fixedly connected through bolts, and a second annular sealing piece is arranged between the second flange at the upper end of the middle steel cylinder and the third flange and is fixedly connected through bolts.

3. The fabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 2, characterized in that, The outer surfaces of the upper steel cylinder, the middle steel cylinder, the lower steel cylinder, the first flange, the second flange and the third flange are each provided with a FRP protective layer for corrosion prevention. The inside of each of the upper steel cylinder, the middle steel cylinder and the lower steel cylinder is provided with a plurality of groups of shear nails, each group of shear nails is arranged in a ring shape on the inner side wall of the circumference of the steel cylinder, each group of shear nails includes a plurality of shear nails vertically and equally spaced, each shear nail is arranged perpendicularly to the axis of the steel cylinder, and the end is fixedly welded to the inner wall of the steel cylinder. Each shear nail is fixedly embedded in the inside of the concrete column of the steel cylinder.

4. The fabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 1, characterized in that, The first, second and third steel reinforcement cages are cylindrical steel reinforcement cages, each cylindrical steel reinforcement cage includes a plurality of longitudinal reinforcements arranged in a ring shape, and the outside of each longitudinal reinforcement is provided with a plurality of ring reinforcements equally spaced along the length direction of the longitudinal reinforcement. The lower end face of each of the first, second and third concrete columns is provided with a plurality of grouting holes corresponding to the number of longitudinal reinforcements of the same cylindrical steel reinforcement cage. In the assembling process, the upper ends of the longitudinal reinforcements of the third reinforcement cage are arranged in the corresponding grouting holes in the bottom of the second concrete column, and the upper ends of the longitudinal reinforcements of the second reinforcement cage are arranged in the corresponding grouting holes in the bottom of the first concrete column.

5. The prefabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 1, characterized in that, The upper anchor and the lower anchor each include an anchor base plate, an anchor plate and a plurality of clamping pieces, the anchor base plate of each upper anchor is fixed in an embedded manner to the upper end of the corresponding threading hole of the first concrete column, and the anchor base plate of each lower anchor is fixed in an embedded manner to the lower end of the corresponding threading hole of the third concrete column.

6. The fabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 5, characterized in that, Four corrugated pipes are arranged in the interior of each concrete column, and the four corrugated pipes are located on the inner side of the corresponding reinforcement cage, and the inner side of each corrugated pipe forms the threading hole of the concrete column in which the corrugated pipe is located. Each corrugated pipe in the interior of the first concrete column and the third concrete column is arranged in parallel with the axis of the steel cylinder outside the concrete column, and the four corrugated pipes in the interior of the second concrete column are arranged in an arc shape protruding radially outward. The upper ends of all the corrugated pipes in the second concrete column correspond one by one to all the corrugated pipes in the interior of the first concrete column and are connected to the corrugated pipes in the first concrete column through the first post-cast cavity, and the lower ends of all the corrugated pipes in the second concrete column correspond one by one to all the corrugated pipes in the interior of the third concrete column and are connected to the corrugated pipes in the third concrete column through the second post-cast cavity.

7. The fabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 6, characterized in that, The anchor base plate of each upper anchor is connected to and communicates with the upper end of the corresponding corrugated pipe in the first concrete column, and the anchor base plate of each lower anchor is connected to and communicates with the lower end of the corresponding corrugated pipe in the third concrete column. The anchor base plate of the upper anchor is an anchor base plate with a grouting channel, and the anchor base plate of the lower anchor is an anchor base plate with an exhaust channel.

8. The fabricated prestressed variable cross-section steel tube concrete bridge pier according to claim 3, characterized in that, The lower end of the lower steel cylinder is fixed with a fourth flange outside, and the outer wall of the fourth flange has the same FRP protective layer as the outer wall of the lower steel cylinder.

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