Concrete pier based on UHPC prefabricated formwork and construction method

Abstract

The invention discloses a concrete pier based on a UHPC prefabricated formwork and a construction method. The pier comprises the UHPC prefabricated assembly formwork, and an FRP stirrup belt is arranged in the middle of the UHPC prefabricated assembly formwork; longitudinal reserved hole channels of the UHPC prefabricated assembly formwork are located on the inner side of the FRP stirrup belt, and the hole channels are evenly distributed in the circumferential direction of the UHPC prefabricated assembly formwork. The steel longitudinal bars are uniformly arranged on the bearing platform; the steel stirrups are uniformly arranged on the outer sides of the steel longitudinal bars to form a reinforcement cage with the steel longitudinal bars; an anchorage device is arranged at one end of the prestressed FRP longitudinal bar and sequentially penetrates through the bearing platform, the UHPC prefabricated assembly formwork and the cover beam; and the prestressed FRP longitudinal bars are tensioned, grouting is conducted in the hole channels, all the UHPC prefabricated assembly formwork bodies are tightly assembled, and then the whole pier pouring formwork body is formed and filled with concrete in a pouring mode. According to the method, on-site wet operation and formwork work amount are greatly reduced, the construction efficiency is remarkably improved, residual deformation after earthquake unloading is effectively reduced, rapid repairing of the pier after an earthquake is greatly promoted, and the anti-seismic toughness and post-disaster recovery capacity of the pier are remarkably improved.

Description

Technical Field

[0001] This invention relates to a bridge structure, and more particularly to a concrete bridge pier based on a UHPC precast mold and its construction method. Background Technology

[0002] Bridge piers are crucial load-bearing components in bridge structures, and their durability directly and profoundly affects the service life, safety, reliability, and operational efficiency of the entire bridge structure. In marine environments, traditional reinforced concrete bridge piers face severe durability challenges, being susceptible to chloride corrosion, freeze-thaw cycles, and erosion. In addition to environmental erosion, as vital urban lifeline infrastructure, bridges must also possess excellent seismic resilience. This means that after an earthquake, bridges must not only avoid complete collapse but also quickly restore their transportation functions, ensuring the timely delivery of relief supplies and the rapid recovery of urban economic activities. Therefore, the design and construction of bridge piers operating in marine environments must comprehensively consider the combined effects of multiple environmental erosion factors and seismic loads to ensure they maintain good structural performance and functional status throughout their entire life cycle, effectively resisting various challenges.

[0003] However, traditional reinforced concrete bridge piers, when used in marine environments for extended periods, often suffer from severe damage such as concrete protective layer spalling and exposed reinforcement due to environmental corrosion. This not only significantly shortens the service life of the piers and even the entire bridge but also increases maintenance costs considerably. Furthermore, after experiencing strong earthquakes, traditional reinforced concrete bridge piers often exhibit excessive residual deformation, making them difficult or even impossible to repair. This severely hinders the rapid restoration of traffic flow and negatively impacts rescue and post-disaster reconstruction efforts. Summary of the Invention

[0004] Purpose of the Invention: To address the aforementioned problems, the purpose of this invention is to provide a concrete bridge pier based on a UHPC precast mold, which improves the durability and post-earthquake recoverability of the pier, facilitates construction, and thus enhances the service life and seismic toughness of bridges in marine environments. A construction method for this invention is also provided.

[0005] Technical Solution: A concrete bridge pier based on UHPC precast formwork includes a pier cap, a cap beam, and multiple UHPC precast assembly formworks coaxially stacked between the pier cap and the cap beam. The UHPC precast assembly formworks are cylindrical, with FRP stirrups serving as an intermediate layer inside the formwork. Multiple longitudinal steel bars and stirrups are alternately connected to form a reinforcing cage, which is placed within the internal cavity of each UHPC precast assembly formwork. Prestressed FRP longitudinal bars run along the UHPC... Multiple precast assembly formworks are spaced circumferentially. Prestressed FRP longitudinal bars are sequentially inserted from top to bottom into the cap beam, multiple UHPC precast assembly formworks, and the pier cap. Grouting material is injected into the gaps between the prestressed FRP longitudinal bars and the three components to seal them. The two ends of the prestressed FRP longitudinal bars are fastened and tensioned to the pier cap and the cap beam respectively, so that multiple UHPC precast assembly formworks are tightly assembled between the pier cap and the cap beam to form an integral pier casting formwork. The reinforcing cage is connected to the pier cap. Concrete is poured and filled into the internal cavity of the UHPC precast assembly formwork.

[0006] Furthermore, the cross-sectional shape of the UHPC prefabricated assembly shell is circular, square, or elliptical, with a wall thickness of 60–120 mm.

[0007] Furthermore, the UHPC prefabricated assembly formwork is bonded to the internally filled concrete after surface treatment by roughening, setting concave and convex textures, or applying an interface agent. The concrete grade is C40 to C60.

[0008] Furthermore, the FRP stirrup strip is formed by continuous fiber winding, resin impregnation and curing, forming a strip-shaped stirrup with completely closed internal fibers, and its enclosing shape is consistent with the shape of the UHPC prefabricated assembly shell.

[0009] Ideally, the tensile strength of the FRP stirrup strip at the bend should be greater than or equal to 90% of the tensile strength at the straight section; the thickness of the FRP stirrup strip should be 4–12 mm and the width should be 40–100 mm.

[0010] Ideally, the resins used to prepare FRP stirrups include epoxy resin, vinyl ester, polyester resin, etc., and the fibers include aramid fiber, carbon fiber, glass fiber, basalt fiber.

[0011] Furthermore, the UHPC precast assembly formwork has multiple axially spaced pre-reserved ducts for installing prestressed FRP longitudinal reinforcement bars within its circumferential direction. These ducts are located inside the FRP stirrup bands and have a circular cross-sectional shape with a diameter of 20–40 mm. Grouting material is filled into these ducts. The number of pre-reserved ducts depends on the number of prestressed FRP longitudinal reinforcement bars. Each pre-reserved duct accommodates one prestressed FRP longitudinal reinforcement bar, the diameter of which is determined based on the internal force analysis calculations of the pier.

[0012] Furthermore, multiple longitudinal steel bars are arranged at equal intervals on the pier cap, and multiple steel stirrups are arranged at equal intervals around the periphery of the longitudinal steel bars. The diameter, spacing, and quantity of the longitudinal steel bars and stirrups are determined based on the internal force analysis calculations of the pier.

[0013] Ideally, the two ends of the prestressed FRP longitudinal reinforcement are anchored to the pier cap and the cap beam respectively, and then prestressed. The tension control stress level of the FRP longitudinal reinforcement depends on the size of the pier.

[0014] A construction method for the above-mentioned concrete bridge pier based on UHPC precast mold shell includes the following steps:

[0015] Step 1: Prepare the casting template for the UHPC prefabricated assembly formwork, place the FRP stirrups in it, and put PVC pipes in it to reserve the ducts. Complete the fabrication of the UHPC prefabricated assembly formwork at the prefabrication plant.

[0016] Step 2: Complete the fabrication of the cap beam in the prefabrication plant. The top of the cap beam is equipped with ducts for inserting prestressed FRP longitudinal reinforcement and pouring concrete.

[0017] Step 3: Transport the UHPC prefabricated assembly formwork and cap beam to the construction site;

[0018] Step 4: First, complete the construction of the foundation at the construction site, and then insert the prestressed FRP longitudinal reinforcement with anchors installed at one end through the foundation.

[0019] Step 5: Tie longitudinal steel bars and steel hoops on the foundation to form a steel cage;

[0020] Step 6: Install all the UHPC precast assembly formwork and cap beams through the reserved ducts, and insert the prestressed FRP longitudinal reinforcement. The UHPC precast assembly formwork surrounds the steel cage.

[0021] Step 7: Install anchorages at the top of the prestressed FRP longitudinal reinforcement, tension the prestressed FRP longitudinal reinforcement, fill the ducts with grout, and after curing, complete the fabrication of the overall pier casting formwork.

[0022] Step 8: Fill the cavity of the UHPC prefabricated assembly mold with ordinary concrete and after standard curing, a high-durability concrete bridge pier based on FRP stirrup strip-UHPC prefabricated assembly mold is obtained.

[0023] Beneficial effects: Compared with the prior art, the advantages of the present invention are:

[0024] 1. Improve the durability of bridge piers and construction efficiency;

[0025] This invention utilizes ultra-high performance concrete (UHPC), known for its exceptional durability, as the casting formwork for bridge piers. The dense internal structure of UHPC effectively prevents chloride ion intrusion, significantly enhancing the corrosion resistance of the piers. Simultaneously, UHPC exhibits an extremely low mass loss rate under freeze-thaw cycles and an extremely low abrasion coefficient under scouring, greatly strengthening the structure's freeze-thaw resistance and abrasion resistance. Factory prefabrication of the UHPC formwork not only ensures casting quality but also significantly reduces on-site wet work and formwork requirements when used as a formwork for ordinary concrete, thereby significantly improving construction efficiency.

[0026] 2. Enhance the seismic toughness and post-earthquake recoverability of bridge piers;

[0027] This invention introduces closed fiber-reinforced polymer (FRP) stirrups made of continuous fibers. Due to their linear elasticity and high strength, FRP stirrups provide continuous and effective restraint to the concrete, effectively preventing buckling of the longitudinal steel reinforcement and significantly reducing the risk of pier collapse under strong earthquakes. Furthermore, the linear elastic prestressed FRP longitudinal reinforcement continues to provide load-bearing capacity even after the steel reinforcement yields, imparting a "secondary stiffness" to the pier after yielding. This unique advantage effectively reduces residual deformation after earthquake unloading, greatly promoting rapid pier repair after earthquakes and significantly improving its seismic toughness and post-disaster recovery capabilities. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the cross-sectional structure of the present invention;

[0029] Figure 2 A three-dimensional structural diagram of the prefabricated assembly shell for UHPC;

[0030] Figure 3 This is a schematic diagram of the overall structure of the bridge pier. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] A type of concrete bridge pier based on UHPC precast mold shell, such as Figures 1-3 As shown, it includes UHPC precast assembly formwork 1, FRP stirrup strip 2, prestressed FRP longitudinal reinforcement 3, foundation 4, steel longitudinal reinforcement 5, steel stirrup 6, cap beam 7, grouting material 8, and concrete 9.

[0033] The precast assembly formwork is cast from ultra-high performance concrete (UHPC). Closed FRP stirrups 2, made of continuous fibers, are positioned in the middle of the UHPC precast assembly formwork 1. Longitudinal pre-reserved ducts in the UHPC precast assembly formwork 1 are located inside the FRP stirrups 2, and the ducts are evenly distributed circumferentially around the UHPC precast assembly formwork 1. Steel longitudinal reinforcement 5 is evenly distributed on the pier cap 4, and steel stirrups 6 are evenly distributed outside the steel longitudinal reinforcement 5, forming a reinforcing cage. Anchors are installed at one end of the prestressed FRP longitudinal reinforcement 3, which sequentially pass through the ducts of the pier cap 4, all the UHPC precast assembly formwork 1s, and the cap beam 7. The prestressed FRP longitudinal reinforcement 3 is tensioned, and grout is injected into the ducts to tightly assemble all the UHPC precast assembly formwork 1s, forming an integral pier casting formwork. Concrete 9 is poured and filled into the integral pier casting formwork.

[0034] The cross-sectional shape of the UHPC prefabricated assembly formwork 1 can be circular, square, elliptical, etc., with a preferred wall thickness of 60–120 mm. The longitudinal pre-reserved holes in the UHPC prefabricated assembly formwork 1 are located inside the FRP stirrup strips 2. The cross-sectional shape of the holes is circular, with a preferred diameter of 20–40 mm. The pre-reserved holes are evenly arranged circumferentially along the UHPC prefabricated assembly formwork 1, and the number of holes depends on the number of prestressed FRP longitudinal reinforcement bars 3.

[0035] The FRP stirrup strip 2 is formed by continuous fiber winding, resin impregnation, and curing, creating a strip-shaped stirrup with completely closed internal fibers. The enclosing shape of this stirrup strip can be circular, square, or elliptical, etc., and the tensile strength of its bent portion is not less than 90% of the tensile strength of its straight portion. The preferred thickness of the FRP stirrup strip 2 is 4–12 mm.

[0036] Multiple longitudinal steel bars 5 are arranged at equal intervals on the pier cap 4, and multiple steel stirrups 6 are arranged at equal intervals on the outer side of the longitudinal steel bars 5. The diameter, spacing, and quantity of the longitudinal steel bars 5 and steel stirrups 6 are determined based on the internal force analysis calculation of the pier, and their preferred diameters are 16-32 mm and 12-20 mm, respectively.

[0037] Prestressed FRP longitudinal bars 3 pass sequentially through the longitudinal ducts of the pier cap 4, the UHPC precast assembly formwork 1, and the beam cap. One prestressed FRP longitudinal bar 3 is placed in each duct, and its diameter is determined based on the internal force analysis calculation of the pier. The two ends of the prestressed FRP longitudinal bars 3 are anchored to anchorages for prestressing tension. The prestress level of the FRP longitudinal bars depends on the pier dimensions.

[0038] After the prestressed FRP longitudinal reinforcement 3 is constructed, the longitudinal reserved holes of the UHPC prefabricated assembly form 1 are filled with grout 8.

[0039] The UHPC precast assembly formwork 1 is preferably bonded to the filled concrete 9 by roughening, setting concave and convex textures, and applying an interface agent. The preferred grade of the concrete 9 is C40 to C60.

[0040] Preferred resins for preparing FRP stirrups 2 and prestressed FRP longitudinal bars 3 include epoxy resin, vinyl ester, polyester resin, etc., and preferred fibers include aramid fiber, carbon fiber, glass fiber, basalt fiber.

[0041] In one embodiment, the pier has a circular cross-section with a diameter of 1000 mm and a height of 3200 mm. The UHPC prefabricated assembly formwork 1 has a thickness of 70 mm, a height of 800 mm, an inner and outer protective layer thickness of 20 mm, and a duct diameter of 24 mm. The UHPC has a compressive strength of 123 MPa and a flexural strength of 32 MPa. The FRP stirrups 2 have a thickness of 6 mm, a width of 40 mm, a tensile strength of 900 MPa, an elastic modulus of 50 GPa, and are arranged longitudinally at a spacing of 160 mm. The longitudinal steel reinforcement 5 has a diameter of 14 mm, is grade HRB400, has a yield strength of 430 MPa, a tensile strength of 510 MPa, and an elastic modulus of 200 GPa, and is arranged at equal intervals along the circumference. The steel stirrups 6 have a diameter of 10 mm, are grade HRB400, have a yield strength of 495 MPa, a tensile strength of 550 MPa, and an elastic modulus of 200 GPa, and are arranged at 120 mm intervals along the longitudinal direction. The prestressed FRP longitudinal reinforcement 3 has a diameter of 16 mm, a tensile strength of 1300 MPa, an elastic modulus of 55 GPa, and a tension control stress of 15% of the tensile strength of the FRP longitudinal reinforcement, and is arranged at equal intervals along the longitudinal direction. The concrete 9 is grade C60, and its cubic block compressive strength is 65 MPa.

[0042] The above-mentioned construction method for concrete bridge piers based on FRP stirrup strips and UHPC precast mold shells includes the following steps:

[0043] 1) Prepare the casting template for the UHPC prefabricated assembly form 1, arrange the FRP stirrup strip 2 in it, and place the PVC pipe to reserve the channel, pour the UHPC grout, and cure it in water bath to complete the production of the UHPC prefabricated assembly form 1.

[0044] 2) The cap beam 7 is fabricated in the prefabrication plant. The top of the cap beam 7 is provided with interpenetrating prestressed FRP longitudinal reinforcement 3 and ducts for pouring concrete.

[0045] 3) Transport the UHPC prefabricated assembly formwork 1 and the cap beam 7 to the construction site;

[0046] 4) First, complete the construction of the foundation 4 at the construction site, and insert the prestressed FRP longitudinal reinforcement 3 with the anchor at one end through the foundation 4.

[0047] 5) Tie steel longitudinal bars 5 and steel stirrups 6 on the foundation 4 to form a steel cage;

[0048] 6) Install all UHPC prefabricated assembly formwork 1 and cap beam 7 through the reserved ducts, and pass through the prestressed FRP longitudinal reinforcement 3;

[0049] 7) Install anchorages at the top of the prestressed FRP longitudinal reinforcement 3, tension the prestressed FRP longitudinal reinforcement 3, fill the duct with grout 8, and after curing, complete the fabrication of the overall pier casting formwork.

[0050] 8) Fill with ordinary concrete and after standard curing, the high-durability concrete bridge pier based on FRP stirrup strip 2-UHPC prefabricated assembly mold 1 is obtained.

[0051] The performance of the present invention is as follows:

[0052] The chloride ion diffusion coefficient of the UHPC prefabricated assembly shell 1 prepared in step 1) was determined to be 0.02 10 using the rapid chloride ion migration coefficient method. -12 m 2 The spalling rate of UHPC prefabricated assembly formwork 1 prepared in step 1) is only 7 g / cm³, which is only 1 / 50 of that of ordinary concrete, indicating its excellent resistance to chloride ion erosion. Meanwhile, the spalling rate of UHPC prefabricated assembly formwork 1 prepared in step 1) under freeze-thaw conditions, as determined by the de-icing salt spalling test, is only 7 g / cm³. 2 The wear coefficient is only 5‰ that of ordinary concrete, demonstrating excellent resistance to freeze-thaw spalling. Furthermore, the wear coefficient of the UHPC prefabricated assembly mold shell 1 produced in step 1), determined by the ball bearing method, is only 1.3, which is 1 / 4 that of ordinary concrete, confirming its superior wear resistance.

[0053] A quasi-static cyclic loading test was conducted to compare the seismic performance of the bridge piers fabricated in step 8) with that of traditional ordinary reinforced concrete bridge piers. The results showed that the seismic energy dissipation performance of the new bridge piers was basically the same as that of traditional ordinary reinforced concrete bridge piers, but the residual deformation was reduced by more than 50%, and no collapse occurred during the large deformation stage. These results fully demonstrate the excellent seismic toughness and collapse resistance of the new bridge piers.

Claims

1. A concrete bridge pier based on UHPC prefabricated formwork, comprising a pile cap (4), a bent cap (7), characterized in that: Also included is a UHPC prefabricated assembly formwork (1), which is coaxially stacked with multiple UHPC prefabricated assembly formworks (1) between the pile cap (4) and the bent cap (7), the UHPC prefabricated assembly formwork (1) is cylindrical, and the FRP stirrup belt (2) is arranged as an intermediate layer inside the shell body of the UHPC prefabricated assembly formwork (1); multiple steel longitudinal reinforcement bars (5) and steel stirrups (6) are connected in an alternating manner to form a steel reinforcement cage, which is arranged in the internal cavity of each UHPC prefabricated assembly formwork (1); multiple prestressed FRP longitudinal reinforcement bars (3) are arranged in a circumferential direction, and the prestressed FRP longitudinal reinforcement bars (3) are sequentially arranged in the bent cap (7), the multiple UHPC prefabricated assembly formworks (1), and the pile cap (4) from top to bottom, and the gaps between the prestressed FRP longitudinal reinforcement bars (3) and the three are respectively sealed by grouting material (8), and the two ends of the prestressed FRP longitudinal reinforcement bars (3) are respectively fastened and tensioned with the pile cap (4) and the bent cap (7), so that the multiple UHPC prefabricated assembly formworks (1) are tightly assembled between the pile cap (4) and the bent cap (7) to form an integrated pier pouring formwork, and the steel reinforcement cage is connected with the pile cap (4); and the concrete (9) is poured and filled in the internal cavity of the UHPC prefabricated assembly formwork (1).

2. A UHPC precast formwork based concrete bridge pier according to claim 1, characterized in that: The cross-sectional shape of the UHPC prefabricated assembly formwork (1) is circular, square, or oval, and the wall thickness is 60-120 mm.

3. A UHPC precast formwork based concrete bridge pier according to claim 1, characterized in that: The UHPC prefabricated assembly formwork (1) is bonded with the internal concrete (9) after surface treatment by roughening, setting concave-convex textures, or brushing interface agents, and the grade of the concrete (9) is C40-C60.

4. A UHPC precast formwork based concrete bridge pier according to claim 1, characterized in that: The FRP stirrup belt (2) is formed by continuous fiber winding, resin impregnation, and curing, and constitutes a belt-shaped stirrup with completely closed internal fibers, and the enclosed shape is consistent with the shape of the UHPC prefabricated assembly formwork (1).

5. A UHPC precast formwork based concrete bridge pier according to claim 4, characterized in that: The tensile strength of the bending part of the FRP stirrup belt (2) is greater than or equal to 90% of the tensile strength of the straight part; the thickness of the FRP stirrup belt (2) is 4-12 mm, and the width is 40-100 mm.

6. A UHPC precast formwork based concrete bridge pier according to claim 4, characterized in that: The resin used to prepare the FRP stirrup belt includes epoxy resin, vinyl ester, and polyester resin, and the fibers include aramid fiber, carbon fiber, glass fiber, and basalt fiber.

7. A UHPC precast formwork based concrete bridge pier according to claim 1, characterized in that: The UHPC prefabricated assembly formwork (1) is provided with multiple reserved hole channels for arranging the prestressed FRP longitudinal reinforcement bars (3) in the circumferential direction, and the reserved hole channels are located on the inner side of the FRP stirrup belt (2), the cross-sectional shape of the reserved hole channels is circular, the diameter is 20-40 mm, and the grouting material (8) is filled in the reserved hole channels.

8. A UHPC precast formwork based concrete bridge pier according to claim 1, characterized in that: Multiple steel longitudinal reinforcement bars (5) are arranged at equal intervals on the pile cap (4), and multiple steel stirrups (6) are arranged at equal intervals on the outer periphery of the multiple steel longitudinal reinforcement bars (5).

9. A UHPC precast formwork based concrete bridge pier according to claim 1, characterized in that: The two ends of the prestressed FRP longitudinal reinforcement bar (3) are respectively anchored and prestressed tensioned with the pile cap (4) and the bent cap (7) through anchorage devices.

10. A method of construction of a concrete bridge pier based on UHPC precast formwork according to any one of claims 1 to 9, characterized in that The steps include: Step one: prepare the pouring formwork of the UHPC prefabricated assembly formwork (1), arrange the FRP stirrup belt (2) therein, and place the PVC pipe to reserve the hole channels, and complete the production of the UHPC prefabricated assembly formwork (1) in the prefabrication factory; Step two: The fabrication of the cap beam (7) is completed in the precast plant, and the holes for inserting the prestressed FRP longitudinal reinforcement (3) and pouring concrete are set on the top of the cap beam (7); Step three: The UHPC prefabricated assembly formwork (1) and the cap beam (7) are transported to the construction site; Step four: The construction of the pile cap (4) is first completed at the construction site, and the prestressed FRP longitudinal reinforcement (3) with an anchor installed at one end is inserted through the pile cap (4); Step five: The steel longitudinal reinforcement (5) and the steel stirrup (6) are tied on the pile cap (4) to form a steel reinforcement cage; Step six: All the UHPC prefabricated assembly formwork (1) and the cap beam (7) are installed through the reserved holes, and the prestressed FRP longitudinal reinforcement (3) is inserted, and the UHPC prefabricated assembly formwork (1) surrounds the steel reinforcement cage; Step seven: The anchor is installed at the top end of the prestressed FRP longitudinal reinforcement (3), and the prestressed FRP longitudinal reinforcement (3) is tensioned, and the grouting material (6) is filled in the hole, and after curing, the fabrication of the overall bridge pier pouring formwork is completed; Step eight: The ordinary concrete (9) is filled and poured in the cavity of the UHPC prefabricated assembly formwork (1), and after standard curing, the high-durability concrete bridge pier based on the FRP stirrup belt-UHPC prefabricated assembly formwork is prepared.

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