A socket-and-spigot steel pipe reinforced UHPC prefabricated pipe concrete composite pier structure and its construction method

Abstract

The present invention relates to a socket-and-spigot steel tube reinforced UHPC prefabricated tube concrete composite bridge pier structure and a construction method thereof, characterized in that: the steel tube reinforced UHPC prefabricated tube concrete composite bridge pier structure comprises a cap beam, a steel tube reinforced UHPC prefabricated tube and a pedestal; a socket-and-spigot connection is adopted between the cap beam and the upper end portion of the steel tube reinforced UHPC prefabricated tube, and between the lower end portion of the steel tube reinforced UHPC prefabricated tube and the pedestal; a gap filler is provided at the socket-and-spigot position; the steel tube reinforced UHPC prefabricated tube comprises an outer layer of UHPC, a steel tube and an inner layer of UHPC; the inner and outer walls of the steel tube are welded with spiral stirrups; a shear ring is vertically fixed on the lower end surface of the steel tube; a stiffening rib is provided on the outer surface of the steel tube where the steel tube reinforced UHPC prefabricated tube is inserted into the pedestal area; the stiffening rib is connected to the steel tube and the shear ring; the steel tube reinforced UHPC prefabricated tube concrete composite bridge pier structure formed by the present invention has high bearing capacity, good seismic performance, convenient and quick construction, and good pull-out resistance of the socket-and-spigot connection node.

Description

Technical Field

[0001] The present invention relates to various engineering technical fields using precast tubular concrete composite bridge piers, and in particular to a steel tube reinforced UHPC precast tubular concrete composite bridge pier structure and a construction method thereof. Background Art

[0002] The core idea of ​​prefabricated bridge technology is to pre-manufacture the main components of a bridge in a factory and then transport them to the construction site for assembly. This approach can greatly shorten the construction period of the bridge, reduce the impact on the environment, and improve the quality of the project. For this reason, prefabricated bridge technology is an important development trend in the field of construction engineering. It represents a more efficient, environmentally friendly and sustainable future direction. With the continuous advancement of science and technology and the changing needs of society, prefabricated bridges will play an increasingly important role in future bridge construction.

[0003] As key structural components bearing the upper loads of bridges, bridge piers are crucial for their mechanical properties. With the continuous advancement of material preparation technology, precast concrete-filled tube composite bridge piers have begun to utilize ultra-high-performance concrete (UHPC). UHPC is the latest generation of cement-based building materials. It eliminates coarse aggregate and is primarily composed of cement, silica fume, quartz sand, and a high-efficiency water reducer. Its dense internal structure, ultra-high compressive strength, and excellent durability significantly enhance the load-bearing capacity and service life of precast concrete-filled tube composite bridge piers. However, due to the inherent brittleness of concrete, which increases with strength, even with reinforcement cages, the improvement in the shear resistance and ductility of precast UHPC composite bridge piers is very limited. The mismatch between ductility and load-bearing capacity remains prominent, which to some extent limits their application and promotion in areas with moderate to high seismic intensities.

[0004] The mechanical performance of precast bridge piers is closely related to their connection structure. Socket-and-socket connection, a commonly used connection technology for precast components, achieves a strong bond between components by inserting precast components into the reserved holes of adjacent components and then pouring higher-strength concrete or grouting materials to fill the gaps in the reserved holes. Due to its simple structure and low construction tolerance, it has been widely used in the engineering community. However, due to the lack of reliable longitudinal connection keys, traditional socket-and-socket connections often suffer from poor pull-out resistance, resulting in poor performance when dealing with vertical loads and seismic forces.

[0005] For example, the Chinese patent "A UHPC pipe-concrete prefabricated assembled composite bridge pier with a socket-and-spigot joint and its construction method" (application number 2018108270878) was retrieved, which includes the steps of setting base holes, prefabricating the pier body, placing the pier body, and pouring the base. Although this assembled composite bridge pier and construction method effectively ensures the uniformity of structural quality, improves construction speed and the standardization of components, and enhances the bearing capacity and durability of the structure, and the structure has good bending resistance; however, the connection structure between the pier body and the pedestal has high requirements on the pedestal thickness and poor pull-out resistance, and performs poorly when dealing with vertical loads and seismic forces.

[0006] For example, a Chinese patent "A prefabricated and assembled steel tube concrete bridge pier with off-site prestressing and its construction method" (application number 202110935028.4) was retrieved, in which the steel tube concrete bridge pier includes at least two segmental steel pipes and inner filling concrete respectively filled in the segmental steel pipes. The two adjacent segmental steel pipes are fixedly connected by pier column energy-absorbing parts. Prestressed tendons are tensioned between the inner filling concrete at both ends of the pier. A through hole is opened in the center of the inner filling concrete, and the prestressed tendons are located in the through hole. Although the pier and construction method of this invention solve the problem of cumbersome tensioning of prestressed tendons at the construction site of prefabricated piers with prestressed connections, and achieves the advantages of less on-site workload and fast construction, the socket-type connection between the pier body and the abutment has poor pull-out resistance and performs poorly in response to vertical loads and seismic forces. Summary of the Invention

[0007] In view of the above-mentioned problems existing in the prior art, the present invention provides a socket-and-spigot steel pipe reinforced UHPC prefabricated pipe concrete composite bridge pier structure and a construction method thereof. The socket-and-spigot steel pipe reinforced UHPC prefabricated pipe concrete composite bridge pier structure and the construction method thereof can overcome the problems of poor shear resistance and ductility of UHPC prefabricated pipes and poor pull-out resistance of the socket-and-spigot connection.

[0008] In order to solve the above technical problems, the technical solution of the present invention is:

[0009] The steel tube reinforced UHPC prefabricated pipe concrete composite pier structure of the present invention is characterized by comprising a cap beam, a steel tube reinforced UHPC prefabricated pipe and a pedestal, wherein a socket-type connection is adopted between the cap beam and the upper end portion of the steel tube reinforced UHPC prefabricated pipe, and between the lower end portion of the steel tube reinforced UHPC prefabricated pipe and the pedestal, with gap filler provided at the socket position, the steel tube reinforced UHPC prefabricated pipe comprising an outer layer of UHPC, a steel pipe and an inner layer of UHPC, the inner and outer walls of the steel pipe being welded with spiral stirrups, a shear ring being vertically fixed to the lower end face of the steel pipe, and stiffening ribs being provided on the outer surface of the steel pipe where the steel tube reinforced UHPC prefabricated pipe is inserted into the pedestal, and the stiffening ribs are connected to the steel pipe and the shear ring.

[0010] Preferably, among the above-mentioned gap fillers, the gap filler between the steel tube reinforced UHPC prefabricated pipe and the pedestal is made of UHPC, and the gap filler between the steel tube reinforced UHPC prefabricated pipe and the cap beam is made of high-strength grouting material.

[0011] Preferably, a PBL shear key combination structure is provided at the center of the bottom of the socket hole of the above-mentioned pedestal, and the PBL shear key combination structure includes a plurality of PBL shear keys in a circumferential array and stirrups arranged around the PBL shear keys. The PBL shear keys are bent at both ends, and the lower part of the PBL shear key combination structure is pre-buried in the pedestal.

[0012] Preferably, the upper part of the above-mentioned PBL shear key combination structure extends into the lower part of the inner hole of the steel tube reinforced UHPC prefabricated pipe, and the plastic hinge area core concrete is poured in the lower part of the inner hole of the steel tube reinforced UHPC prefabricated pipe. The PBL shear key is made of a long steel plate, and the long steel plate is densely covered with openings. The two ends of the long steel plate are bent inward and outward respectively, the end embedded in the base is bent outward, and the end connected to the plastic hinge area core concrete is bent inward.

[0013] Preferably, the inner periphery of the socket hole of the above-mentioned support platform is formed by a bellows and serves as a permanent template.

[0014] Preferably, the outer layer of UHPC of the steel pipe reinforced UHPC prefabricated pipe socket inserted into the capping area is provided with a shear groove within the insertion depth range of the capping.

[0015] Preferably, the cap beam is provided with a socket hole for inserting and socketing the steel pipe reinforced UHPC prefabricated pipe, holes are reserved on both sides of the cap beam as grouting holes and slurry outlet holes for gap fillers respectively, and a number of holes are reserved on the top of the cap beam as exhaust holes. The steel pipe and the inner layer UHPC in the steel pipe reinforced UHPC prefabricated pipe are inserted into the cap beam, and the upper end of the outer layer UHPC is lower than the upper ends of the steel pipe and the inner layer UHPC to form a stepped upper end portion of the steel pipe reinforced UHPC prefabricated pipe, and the upper end of the outer layer UHPC overlaps with the bottom of the cap beam.

[0016] The construction method of the steel tube reinforced UHPC prefabricated concrete-filled composite bridge pier of the present invention is characterized by:

[0017] Step 1: Fabrication of steel-tube reinforced UHPC prefabricated pipes: First, prepare the steel pipes, spiral stirrups, stiffening ribs, and shear rings. Then, weld spiral stirrups to the inner and outer walls of the steel pipes, and weld stiffening ribs and shear rings to the bottom of the steel pipes. Finally, cast the outer and inner UHPC layers.

[0018] Step 2: Casting the cap: Install the metal bellows in the cap, accurately embed the PBL shear key assembly structure in place through the positioning ring, and cast the cap;

[0019] Step 3: Splicing the steel-tube reinforced UHPC prefabricated pipe with the cap: Position and install the steel-tube reinforced UHPC prefabricated pipe into the socket hole reserved in the cap, and pour filler into the gap between the cap and the steel-tube reinforced UHPC prefabricated pipe;

[0020] Step 4: Pouring the core concrete of the plastic hinge area: Pour the concrete from the top of the inner hole of the prefabricated tube to the bottom of the prefabricated tube, pour it to the designed height and vibrate it to compact it. Then, use steel plates of appropriate size to connect them to the steel tubes in the steel tube reinforced UHPC prefabricated tube by welding to close the opening above the prefabricated tube.

[0021] Step 5: Splice the steel-tube reinforced UHPC prefabricated pipe and the cap beam: Hoist the prefabricated cap beam, align the reserved socket with the prefabricated pipe, and place the cap beam in place after accurate positioning. The bottom of the cap beam overlaps the upper end of the UHPC outer layer of the prefabricated pipe, and pour the gap filler between the cap beam and the steel-tube reinforced UHPC prefabricated pipe from bottom to top through the UHPC grouting holes at the bottom of the cap beam until the gap filler is filled and overflows. The cap beam and the steel-tube reinforced UHPC form a whole, completing the assembly of the steel-tube reinforced UHPC prefabricated pipe concrete composite bridge pier.

[0022] Compared with the existing technology, the steel tube reinforced UHPC precast concrete-filled composite bridge pier of the present invention is a high-performance socket-and-spigot type composite bridge pier with advantages such as high bearing capacity, reliable socket-and-spigot connection, good seismic performance, and convenient and fast construction. The specific features include:

[0023] (1) Steel pipes are built into UHPC as a rigid skeleton, replacing the traditional steel cage skeleton. This not only simplifies the construction process and avoids the tedious steel bar binding process, but also enhances the stiffness and shear resistance of the UHPC prefabricated pipe composite bridge pier. Under the same conditions, the steel pipe reinforced UHPC prefabricated pipe composite bridge pier is less likely to suffer brittle shear failure;

[0024] (2) Under the action of an earthquake, the UHPC prefabricated tube composite bridge pier can consume energy through the deformation of the plastic hinge formed near the bottom of the pier, thereby reducing the impact of the earthquake on the structure. The addition of steel pipes will further effectively improve the seismic performance of the UHPC prefabricated tube composite bridge pier. When the core concrete is poured in the plastic hinge area, the brittle behavior of the inner layer of UHPC is significantly improved through the hoop effect provided by the steel pipe. The ductility of the steel pipe is also brought into play under the support of the UHPC. Therefore, the steel pipe reinforced UHPC prefabricated tube concrete composite bridge pier is expected to have better seismic performance.

[0025] (3) The spiral stirrups set on the inner and outer surfaces of the steel pipe can not only enhance the hoop effect on the UHPC inside the pipe, but also enhance the interface effect between the UHPC and the steel pipe, so that the UHPC and the steel pipe are closely combined, ensuring the coordinated work of the UHPC and the steel pipe, and making the steel pipe reinforced UHPC precast concrete pipe composite pier have good integrity;

[0026] (4) The socket-and-spigot connection structure is easy to construct. On site, it is only necessary to fill the gaps with filler to achieve the overall connection. In addition, a shear ring is set at the bottom of the steel tube reinforced UHPC prefabricated pipe, and a shear groove (horse tooth shape) is set in the area where it is inserted into the pedestal. The socket hole reserved in the pedestal is equipped with a metal bellows. The reserved PBL shear key connects the pedestal to the cast-in-place core concrete. The above measures can achieve a good longitudinal connection between the steel tube reinforced UHPC prefabricated pipe concrete composite pier and the pedestal, ensuring the reliability of the socket-and-spigot connection.

[0027] The present invention utilizes the lateral constraint of the steel pipe to improve the plastic deformation capacity of the concrete in the pipe, and relies on the support of the core concrete to avoid local buckling of the steel pipe, fully utilizing the ductility of the steel pipe and significantly improving the brittle behavior of the concrete; in addition, the socket-type connection with a simple structure and low construction tolerance is improved to enhance its pull-out resistance.

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the cross-sectional structure of an example of the present invention;

[0030] Figure 2 A three-dimensional schematic diagram of an example of the present invention;

[0031] Figure 3 for Figure 1 Sectional view of section AA;

[0032] Figure 4 A top view of an example of the present invention;

[0033] Figure 5 This is a front view of the cap beam in an example of the present invention;

[0034] Figure 6 A three-dimensional schematic diagram of the cap beam in the embodiment of the present invention

[0035] Figure 7 Schematic diagram of the steel pipe structure in the embodiment of the present invention;

[0036] Figure 8 Schematic diagram of the three-dimensional structure of the PBL shear key in an example of the present invention;

[0037] Figure 9 Schematic diagram of the three-dimensional structure of the PBL shear key combination structure in an example of the present invention;

[0038] Figure 10 Schematic diagram of the structure of the prefabricated tubular steel structure in an example of the present invention;

[0039] Figure 11 for Figure 10 Cross-sectional view of the middle BB section;

[0040] Figure 12 This is a schematic diagram of the state in step 1 of the present invention;

[0041] Figure 13 This is a schematic diagram of the state in step 2 of the present invention;

[0042] Figure 14 This is a three-dimensional schematic diagram of step 2 of the present invention;

[0043] Figure 15 This is a schematic diagram of the state in step 3 of the present invention;

[0044] Figure 16 A three-dimensional schematic diagram of the installation of prefabricated pipes in step 3 of the present invention

[0045] Figure 17 This is a schematic diagram of the state in step 4 of the present invention;

[0046] Figure 18 This is a schematic diagram of the state of installing the cap beam in step 5 of the embodiment of the present invention;

[0047] Figure 19 This is a schematic diagram of the state of pouring UHPC gap filling material in step 5 of the embodiment of the present invention;

[0048] In the figure: 1—cap beam; 2—steel tube reinforced UHPC precast tube; 3—core concrete in the plastic hinge area; 4—cap; 5—gap filler; 6—steel tube; 7—outer UHPC layer; 8—inner UHPC layer; 9—shear groove; 10—spiral stirrups; 11—stiffening ribs; 12—shear ring; 13—grouting hole; 14—vent; 15—corrugated pipe; 16—PBL shear key; 17—grouting hole; 18—stirrups; 19—opening. DETAILED DESCRIPTION

[0049] like Figures 1 to 19 As shown, a steel tube reinforced UHPC prefabricated tubular concrete composite bridge pier includes a steel tube reinforced UHPC prefabricated tube 2, a pedestal 4, a cap beam 1, gap filler 5, and plastic hinge zone core concrete 3.

[0050] Socket-type connections are adopted between the cap beam 1 and the upper end of the steel tube reinforced UHPC prefabricated pipe 2, and between the lower end of the steel tube reinforced UHPC prefabricated pipe 2 and the pedestal 4, with gap filler 5 provided at the socket position; among the gap fillers, UHPC is used as the gap filler between the steel tube reinforced UHPC prefabricated pipe and the pedestal, and high-strength grouting material is used as the gap filler between the steel tube reinforced UHPC prefabricated pipe and the cap beam.

[0051] In the example of the present invention, the steel tube reinforced UHPC prefabricated pipe 2 is prefabricated in the factory, including a steel tube 6, spiral stirrups 10, an outer layer of UHPC 7, an inner layer of UHPC 8, stiffening ribs 11, and a shear ring 12, wherein the inner and outer walls of the steel tube 6 are welded with spiral stirrups 10, and the shear ring 12 is vertically fixed to the lower end face of the steel tube 6. The outer surface of the steel tube of the steel tube reinforced UHPC prefabricated pipe 2 inserted into the base area is provided with the stiffening ribs 11, and the stiffening ribs 11 are connected to the steel tube 6 and the shear ring 12.

[0052] In the example of the present invention, the steel pipe 6 is built into the UHPC as a rigid skeleton, providing a hoop effect for the inner layer UHPC 8, and is used to improve the seismic performance of the steel pipe reinforced UHPC precast tube concrete composite bridge pier. The spiral stirrups 10 are fixed to the inner and outer walls of the steel pipe by welding. The spiral stirrups 10 can improve the interfacial bonding performance between the steel pipe 6 and the outer layer UHPC 7 and the inner layer UHPC 8, while enhancing the hoop effect on the UHPC in the plastic hinge area; stiffening ribs 11 and shear rings 12 are provided at the bottom of the steel pipe 6 to improve the pull-out resistance of the socket-and-spigot joint and avoid crushing of the base concrete.

[0053] A PBL shear key assembly structure is provided at the center of the bottom of the socket of the above-mentioned pedestal. The PBL shear key assembly structure includes a plurality of PBL shear keys 16 in a circumferential array and stirrups 18 arranged around the PBL shear keys. The PBL shear keys are bent at both ends, and the lower part of the PBL shear key assembly structure is pre-buried in the pedestal.

[0054] Specifically, the upper part of the PBL shear key assembly structure extends into the lower part of the inner hole of the steel tube reinforced UHPC prefabricated tube, and the plastic hinge area core concrete 3 is poured in the lower part of the inner hole of the steel tube reinforced UHPC prefabricated tube. The PBL shear key 16 is made of a long steel plate, and the long steel plate is densely covered with openings 19. The two ends of the long steel plate are bent inward and outward respectively. The end embedded in the base is bent outward, and the end connected to the plastic hinge area core concrete is bent inward.

[0055] The core concrete 3 of the plastic hinge area is poured after the steel tube reinforced UHPC prefabricated pipe is installed on the base. The core concrete 3 of the plastic hinge area ensures that the steel tube can play a role in the hoop provided by the UHPC inside the pipe.

[0056] In the present embodiment, the cap 4 is cast on site, and the socket is enclosed by a corrugated pipe 15 of corresponding diameter as a permanent formwork, forming a corrugated inner wall reserved hole (i.e., the socket). The corrugated inner wall and the shear groove 9 (horse tooth shape) help to form a whole with the cap and the steel pipe reinforced UHPC prefabricated pipe 2 through the gap filler 5. The lower part of the PBL shear key combination structure is embedded in the cap 4 and connected to the core concrete 3 of the plastic hinge area, further improving the pull-out resistance of the socket joint.

[0057] In the example of the present invention, the cap beam 1 is reserved for a socket hole for socketing the steel pipe reinforced UHPC prefabricated pipe, and holes are reserved on both sides of the cap beam as grouting holes 13 and grouting holes 17 for the gap filler respectively. A number of holes are reserved on the top of the cap beam as exhaust holes 14. The steel pipe 6 and the inner layer UHPC 8 of the steel pipe reinforced UHPC prefabricated pipe are inserted into the cap beam 1, and the upper end of the outer layer UHPC 7 is lower than the upper ends of the steel pipe and the inner layer UHPC to form a stepped upper end portion of the steel pipe reinforced UHPC prefabricated pipe, and the upper end of the outer layer UHPC overlaps with the bottom of the cap beam; a horse tooth-shaped shear groove 9 is provided in the socket hole of the cap beam, and the shear groove 9 can improve the interface effect between the cap beam 1 and the gap filler, and can improve the integrity of the cap beam 1 and the steel pipe reinforced UHPC prefabricated pipe 2.

[0058] A construction method for a steel tube reinforced UHPC precast tubular concrete composite bridge pier is carried out in the following steps:

[0059] Step 1, fabrication of steel tube reinforced UHPC prefabricated tube 2: First, fabricate steel tube 6, spiral stirrups 10, stiffening ribs 11, and shear rings 12. Then, weld spiral stirrups 10 to the inner and outer walls of the steel tube 6, and weld stiffening ribs 11 and shear rings 12 to the bottom of the steel tube. Finally, cast the outer UHPC layer 7 and inner UHPC layer 8.

[0060] Step 2, pouring the cap 4: installing the metal bellows 15 in the cap, accurately pre-embedding the PBL shear key assembly structure in place through the positioning ring, and pouring the cap 4;

[0061] Step 3, splicing the steel tube reinforced UHPC prefabricated pipe 2 and the cap 4: positioning and installing the steel tube reinforced UHPC prefabricated pipe 2 into the socket hole reserved in the cap 4, and pouring the gap filler 5 between the cap 4 and the steel tube reinforced UHPC prefabricated pipe 2;

[0062] Step 4, pouring of core concrete 3 in the plastic hinge area: pouring concrete from the top of the inner hole of the prefabricated tube to the bottom of the prefabricated tube to the designed height and vibrating it to compactness. Then, a steel plate of appropriate size is welded to the steel tube in the steel tube reinforced UHPC prefabricated tube 2 to close the top opening of the prefabricated tube;

[0063] Step 5, splicing the steel tube reinforced UHPC prefabricated pipe 2 and the cap beam 1: hoist the prefabricated cap beam, align the reserved socket with the prefabricated pipe, and put the cap beam into place after accurate positioning. The bottom of the cap beam 1 is overlapped on the upper end of the UHPC outer layer 7 of the prefabricated pipe, and the gap filler 5 between the cap beam and the steel tube reinforced UHPC prefabricated pipe is poured from bottom to top through the UHPC grouting hole 13 at the bottom of the cap beam until the grouting hole 17 is filled with gap filler and overflows. The cap beam and the steel tube reinforced UHPC form a whole, and the assembly of the steel tube reinforced UHPC prefabricated pipe concrete composite bridge pier is completed.

[0064] The above are preferred embodiments, which further explain the objectives, technical solutions and advantages of the present invention in detail. It should be understood that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A steel tube reinforced UHPC precast concrete tube composite pier structure, characterized by: The invention comprises a cap beam (1), a steel tube reinforced UHPC prefabricated pipe (2) and a pedestal (4), wherein the cap beam (1) and the upper end of the steel tube reinforced UHPC prefabricated pipe (2), and the lower end of the steel tube reinforced UHPC prefabricated pipe (2) and the pedestal (4) are connected by a socket-type connection, and a gap filler (5) is provided at the socket-type position. The steel tube reinforced UHPC prefabricated pipe (2) comprises an outer layer of UHPC (7), a steel pipe (6) and an inner layer of UHPC (8), the inner wall and the outer wall of the steel pipe are welded with spiral stirrups (10), and the lower end surface of the steel pipe is vertically fixed. A shear ring (12) is provided, and a stiffening rib (11) is provided on the outer surface of the steel pipe of the steel pipe reinforced UHPC prefabricated pipe inserted into the base area, and the stiffening rib (11) is connected to the steel pipe (6) and the shear ring (12); a PBL shear key combination structure is provided at the center of the bottom of the base socket hole, and the PBL shear key combination structure includes a plurality of PBL shear keys (16) in a circumferential array and stirrups (18) arranged around the PBL shear keys, the PBL shear keys are bent at both ends, and the lower part of the PBL shear key combination structure is pre-buried in the base; the PBL The upper part of the BL shear key composite structure extends into the lower part of the inner hole of the steel tube reinforced UHPC prefabricated pipe, and the plastic hinge zone core concrete (3) is poured in the lower part of the inner hole of the steel tube reinforced UHPC prefabricated pipe. The PBL shear key (16) is made of a long steel plate, and the long steel plate is densely covered with openings (19). The two ends of the long steel plate are bent inward and outward respectively, and the end embedded in the pedestal is bent outward, and the end connected to the plastic hinge zone core concrete is bent inward; the inner periphery of the socket hole of the pedestal is formed by a corrugated pipe (15) and serves as a permanent template; the cap beam ( 1) A socket hole is reserved for inserting and inserting a steel pipe reinforced UHPC prefabricated pipe, holes are reserved on both sides of the cap beam to serve as grouting holes (13) and grouting holes (17) for gap fillers, and a plurality of holes are reserved on the top of the cap beam to serve as exhaust holes (14). The steel pipe (6) and the inner layer UHPC (8) in the steel pipe reinforced UHPC prefabricated pipe are inserted into the cap beam (1), and the upper end of the outer layer UHPC (7) is lower than the upper ends of the steel pipe and the inner layer UHPC to form a stepped upper end of the steel pipe reinforced UHPC prefabricated pipe, and the upper end of the outer layer UHPC overlaps with the bottom of the cap beam.

2. The steel tube reinforced UHPC precast concrete-filled composite pier structure according to claim 1, characterized in that: Among the gap fillers, the gap filler between the steel tube reinforced UHPC prefabricated pipe and the pedestal is made of UHPC, and the gap filler between the steel tube reinforced UHPC prefabricated pipe and the cap beam is made of high-strength grouting material.

3. The steel tube reinforced UHPC precast concrete-filled composite pier structure according to claim 2, characterized in that: The outer UHPC layer of the steel pipe reinforced UHPC prefabricated pipe (2) inserted into the capping area is provided with a shear groove (9) within the insertion depth range of the capping area.

4. A construction method for a steel tube reinforced UHPC precast concrete-filled composite bridge pier structure according to any one of claims 1 to 3, characterized in that: Step 1, fabrication of a steel pipe reinforced UHPC prefabricated pipe (2): first fabricating a steel pipe (6), spiral stirrups (10), stiffening ribs (11) and a shear ring (12); then, welding the spiral stirrups (10) to the inner and outer walls of the steel pipe (6), respectively; welding the stiffening ribs (11) and the shear ring (12) to the bottom of the steel pipe; and finally, casting an outer layer of UHPC (7) and an inner layer of UHPC (8); Step 2, pouring the cap (4): installing the metal bellows (15) in the cap, accurately pre-embedding the PBL shear key assembly structure in place through the positioning ring, and pouring the cap (4); Step 3, splicing the steel tube reinforced UHPC prefabricated pipe (2) and the pedestal (4): positioning and installing the steel tube reinforced UHPC prefabricated pipe (2) into the socket hole reserved in the pedestal (4), and pouring the gap filler (5) between the pedestal (4) and the steel tube reinforced UHPC prefabricated pipe (2); Step 4, pouring of the core concrete (3) in the plastic hinge area: pouring the concrete from the upper part of the inner hole of the prefabricated tube to the bottom of the prefabricated tube, pouring it to the designed height and vibrating it to make it dense, and then connecting the steel tube in the steel tube reinforced UHPC prefabricated tube (2) with a steel plate of appropriate size by welding to close the upper opening of the prefabricated tube; Step 5, splicing the steel tube reinforced UHPC prefabricated pipe (2) and the cap beam (1): hoist the prefabricated cap beam, align the reserved socket with the prefabricated pipe, and place the cap beam in place after accurate positioning. The bottom of the cap beam (1) is overlapped on the upper end of the UHPC outer layer (7) of the prefabricated pipe, and the gap filler (5) between the cap beam and the steel tube reinforced UHPC prefabricated pipe is poured from bottom to top through the UHPC grouting hole (13) at the bottom of the cap beam until the grouting hole (17) is filled with the gap filler and overflows. The cap beam and the steel tube reinforced UHPC form a whole, and the assembly of the steel tube reinforced UHPC prefabricated pipe concrete composite bridge pier is completed.

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