A prestressing application device and preparation method for pre-tensioned FRP reinforced concrete pipe piles

Abstract

This invention discloses a prestressing application device and its preparation method for pre-tensioned FRP-reinforced concrete pipe piles, relating to the field of underground or groundwater structure construction technology. The prestressing application device applies prestress by bonding and anchoring the two ends of the FRP main reinforcement, changing the stress distribution of the FRP reinforcement. The ends pass through tensioning holes, screw into anchoring holes via reinforcement holes, and are positioned using a countersinking groove, improving positioning accuracy. The head and tail plates are fixed to the end plates using constraint screws and fastening nuts, providing sufficient space for the FRP anchoring ends and preventing shear stress concentration caused by the anchoring device from damaging the reinforcement. Its structural design is scientifically sound and reasonable, with a simple and clear construction, low processing difficulty, and extremely convenient assembly and disassembly of each component, exhibiting good assembly coordination. The prepared pipe pile has a stable and reliable overall structure, and the device can be reused repeatedly. It has significant application value for studying the durability of prestressed concrete structures and is suitable for widespread application.

Description

Technical Field

[0001] This invention relates to the field of underground or groundwater structure construction technology, and in particular to a prestressing application device and preparation method for pre-tensioned FRP reinforced concrete pipe piles. Background Technology

[0002] Prestressed concrete pipe piles are constructed by applying prestress to the reinforcing bars using either pre-tensioning or post-tensioning methods. Pre-tensioning involves tensioning and temporarily anchoring the reinforcing bars before pouring the concrete. Once the concrete reaches a certain strength, the prestressing bars are released, subjecting the concrete to pre-compressive stress. Post-tensioning involves pouring the concrete pipe pile first, and then, after the concrete reaches its design strength, inserting prestressing bars into pre-drilled ducts for tensioning and anchoring. The prestress is then transferred to the concrete through anchorages.

[0003] Reinforced concrete pipe piles in marine environments are susceptible to chloride ion corrosion. Once the chloride ion concentration at the depth of the reinforcing steel reaches a threshold concentration, corrosion damage begins to occur in the steel bars, leading to a decrease in pile stiffness and a reduction in load-bearing capacity. Simultaneously, in marine environments, pipe piles experience significant lateral displacement and bending moments under wind loads, tides, and waves. When the lateral displacement or bending moment exceeds the maximum load-bearing capacity of the pipe pile, it will lead to pile failure.

[0004] Fiber-reinforced polymer (FRP) rebar exhibits excellent corrosion resistance in harsh environments such as acids and alkalis, and combining FRP rebar with concrete structures can effectively solve the problem of steel reinforcement corrosion. However, the elastic modulus of FRP rebar is lower than that of steel reinforcement, which can lead to the structure becoming unusable due to excessive deflection before it can fully utilize the high strength of the FRP rebar during its service life. Combining prestressed FRP rebar with concrete structures can fully utilize the high strength of FRP rebar, improving the durability and safety of the structure.

[0005] However, during repeated clamping and friction of FRP bars by anchors, the fiber-resin interface is damaged due to shear stress concentration, making it difficult for the FRP bars to hold the load. At the same time, the dynamic load during the friction process will exacerbate interface slippage and destroy the chemical bonding force of the reinforcement.

[0006] Therefore, how to fully utilize the high strength properties of FRP materials while improving structural durability is of great engineering significance and application value. Summary of the Invention

[0007] This invention addresses the technical problems of current FRP (fiber-reinforced polymer) prestressed anchorages causing damage to fiber-reinforced resin materials and difficulty in bearing load. It proposes a prestressing application device and preparation method for pre-tensioned FRP-reinforced concrete pipe piles. The invention employs sleeve-type adhesive-filled anchoring technology to change the stress distribution of the FRP reinforcement, and features a completely new design for the end plates, head plates, and tail plates. Constraint screws are used to effectively apply prestress to the FRP reinforcement. While ensuring that the FRP reinforcement fully utilizes its material advantages, this invention effectively controls the stress distribution during tensioning, avoiding material damage caused by stress concentration and other problems. It facilitates assembly and construction operations, maintains prestress stability, and has significant application value for studying the durability of prestressed concrete structures, making it suitable for widespread application.

[0008] One objective of this invention is to provide a prestressing application device for pre-tensioned FRP-reinforced concrete pipe piles. The device applies prestress to the FRP main reinforcement bars extending from both ends of the FRP reinforcement cage. It includes end plates, head plates, tail plates, restraining bolts, and sleeves. The end plates, head plates, restraining bolts, and sleeves are located at one end of the FRP reinforcement cage, and the other end of the FRP reinforcement cage also has an end plate, tail plate, restraining bolts, and sleeves. Straight cylindrical anchoring sleeves are fitted at both ends of the FRP main reinforcement bars, and adhesive is injected into the anchoring sleeves to bond them to the FRP reinforcement bars, forming anchoring ends. The end plates, head plates, and tail plates are all made from circular substrates.

[0009] The end plate has a first side and a second side. The first side is located away from the FRP reinforcement cage, and the second side is located closer to the FRP reinforcement cage. The end plate has a through central hole in its center. Multiple tension holes are arranged around the central hole. The sides of the tension holes have connecting through holes and anchor holes. The anchor holes are used for anchoring the FRP main reinforcement. A pre-drilled groove is machined on the periphery of the second side of the end plate for connecting the sleeve.

[0010] The head plate has a first side and a second side, and a through central tensioning hole is provided in the middle of the head plate. A tensioning internal thread is provided inside the central tensioning hole, and a plurality of head plate screw holes are provided on the head plate evenly distributed around the central tensioning hole.

[0011] The tail plate has a through-hole in the middle and multiple tail plate screw holes evenly distributed around the circumference of the tail plate center hole.

[0012] The constraint screws located at both ends of the FRP reinforcing cage skeleton pass through the head plate screw holes and tail plate screw holes respectively and are detachably connected to the end plate tensioning holes located at both ends of the FRP reinforcing cage skeleton.

[0013] Furthermore, a groove is provided on the side of the anchor hole away from the FRP reinforcement cage, and the groove has a flat opening design.

[0014] Furthermore, the inner diameter of the sinking groove is larger than the inner diameter of the anchoring hole and larger than the outer diameter of the anchoring sleeve, and the sinking groove and the anchoring hole are connected by a planar connection.

[0015] Furthermore, the end plate has multiple anchoring holes, through holes, and tensioning holes evenly distributed around its central hole. The through holes, tensioning holes, and anchoring holes are machined by stamping or cutting.

[0016] Furthermore, the through hole is connected between the corresponding anchor hole and the tension hole, the anchor hole and the tension hole are on concentric circles, and the line connecting the center lines of the tension hole, the through hole and the anchor hole is an arc with the center hole of the end plate as the center.

[0017] Furthermore, the constraint screw is a hexagonal bolt, and the constraint screw is equipped with fastening nuts that respectively abut against the screw holes of the head plate and the screw holes of the tail plate for relative fixation.

[0018] Furthermore, the hexagonal head of the constraint screw is larger than the inner diameter of the screw hole in the head and tail plate, the diameter of the constraint screw body is larger than the thread type of the constraint screw, and the length of the constraint screw body is larger than the height of the anchor sleeve.

[0019] Furthermore, the lower thread of the constraint screw starts from the tail end and the thread height is consistent with the thickness of the end plate. The upper thread of the constraint screw starts from the height of the head and tail plates below the washer, and the upper thread height is consistent with the thickness of the fastening nut. A fastening nut is installed on the upper part of the constraint screw for fixing the screw to the head plate or tail plate.

[0020] Furthermore, the anchoring end of the FRP main reinforcement passes through the tensioning hole from the second side of the end plate and then through the corresponding reinforcement hole before being inserted into the anchoring hole, and the anchoring sleeve is inserted into the groove of the anchoring hole.

[0021] Furthermore, the outer diameter of the anchor sleeve is larger than the diameter of the through hole of the end plate and smaller than the inner diameter of the sinker, and the inner diameter of the anchor sleeve is more than 6 mm larger than the nominal diameter of the FRP reinforcement.

[0022] Furthermore, a welding groove is provided on the periphery of the first side of the end plate. The welding groove has an arc-shaped groove wall and an inclined groove wall. The arc-shaped groove wall is connected to the first side of the end plate, and the inclined groove wall is located between the arc-shaped groove wall and the outer peripheral wall of the end plate.

[0023] Furthermore, the head plate screw hole and the tail plate screw hole are both larger than the inner diameter of the tensioning hole and the outer diameter of the constraint screw.

[0024] Furthermore, the outer diameter of the tail plate is larger than that of the pipe pile, and the outer diameter of the head plate is the same as that of the end plate.

[0025] Furthermore, the thickness of the head plate is increased around the central tension hole on the first side of the head plate, the thread depth of the central tension hole is lengthened, and an arc-shaped groove wall is provided on the thickened head plate to connect with the outer peripheral wall of the head plate and the right-angle groove wall provided on the first side of the head plate.

[0026] Furthermore, a sealing baffle is welded to the center of the second side of the head plate, and the outer diameter of the sealing baffle is larger than the diameter of the central tension hole of the head plate.

[0027] The second objective of this invention is to provide a method for preparing pre-tensioned FRP reinforced concrete pipe piles, employing the aforementioned prestressing application device and the following steps:

[0028] S1. Forming of FRP Reinforcing Cage: Cut FRP reinforcing material, insert one end of FRP reinforcing material 52 into the anchor sleeve after injecting adhesive, ensure that the FRP reinforcing material and the anchor sleeve are coaxial, and make the adhesive 53 fully fill the gap to form the anchor end of the FRP main reinforcing bar; use non-metallic tensioning bands to tie the FRP main reinforcing bar and FRP stirrups to form the FRP reinforcing cage.

[0029] S2. Hoop plate fabrication and installation: Press and roll 2 to 4 pieces of sheet material into a circular hoop, and hammer the two ends together to align and weld them. Put the pressed hoop on the end plate and press the hoop and the reserved groove 18 into the full circumference.

[0030] S3. Install FRP reinforcement cage: Pass the anchor sleeves at the ends of the FRP main reinforcements in the prepared FRP reinforcement cage through the tensioning hole, rotate the end plate to make the FRP main reinforcements screw into the anchor hole through the reinforcement hole, pull the end plates at both ends to make the anchor sleeves fit and lock into the groove on the first side of the anchor hole for positioning.

[0031] S4. FRP reinforcement cage installation: Place the fabricated FRP reinforcement cage, end plate, head plate and tail plate into the lower half of the centrifugal pipe pile mold. The constraint screws are installed and locked through the screw holes of the head plate, the screw holes of the tail plate and the tensioning holes of the end plate respectively. The fastening nuts are installed and locked with the upper threads to make them fit tightly against the head plate and tail plate. The tail plate is in close contact with the tail of the steel mold.

[0032] S5. Concrete placement: Use a forced concrete mixer to produce concrete with a strength grade of not less than C80. According to the usage requirements of each centrifugal pipe pile, fill the lower half of the mold with freshly mixed concrete evenly.

[0033] S6. Mold closing: Clean both sides of the mold edge, place the grout-stopping rope, close the upper half of the centrifugal pipe pile mold and tighten the mold closing bolts;

[0034] S7. Prestressing tensioning: Tensioning the FRP rib cage skeleton after mold closing, locking the tensioning nut, maintaining stable pressure after reaching the specified parameters, and then releasing the pressure by returning oil.

[0035] S8. Centrifugal molding: The tensioned and anchored pipe pile mold is hoisted to the centrifuge for centrifugal compaction. After centrifugation, the rubber plug in the center hole of the tail plate is removed and the excess slurry is poured out.

[0036] S9. Normal pressure curing: After centrifugation, the pipe piles with molds are hoisted into the steam curing tank to make the concrete strength reach the specified level.

[0037] S10. Demolding: First remove the tail plate, then remove the template bolts, loosen the tension nuts and remove the tension baffle, lift the cover mold; remove the tension rods, loosen the constraint bolts and fastening nuts between the end plate and the head plate and tail plate, cut off the excess FRP reinforcement ends of the end plate, and lift the pile out of the mold.

[0038] S11. Autoclaving: The pipe piles are hoisted onto the autoclave car and pulled into the autoclave for secondary curing. After curing, the piles are pulled out of the autoclave and transported and stacked according to regulations.

[0039] Compared with the prior art, the technical effects of the present invention are as follows:

[0040] 1. The prestressing application device for pre-tensioned FRP-reinforced concrete pipe piles provided by this invention applies prestress by bonding and anchoring the two ends of the FRP main reinforcement, changing the stress mode of the FRP reinforcement. The ends pass through the tensioning hole, screw into the anchoring hole through the reinforcement hole, and are positioned using a countersinking groove, improving positioning accuracy. The head and tail plates are connected to the end plates by constraint screws and fastening nuts for limiting and fixing, providing sufficient space for the FRP anchoring end, and avoiding shear stress concentration caused by the anchoring device, which could lead to damage to the reinforcement. Its structural design is scientific and reasonable, its construction is simple and clear, and its processing and manufacturing difficulty is low. The specifications and dimensions of the device can be flexibly planned and designed according to actual needs. The assembly and disassembly of each component of the device are extremely convenient, with good assembly coordination. The overall structure is stable and reliable, can be reused, and has important application value for studying the durability of prestressed concrete structures, making it suitable for widespread application.

[0041] 2. This invention creatively uses FRP (fiberglass reinforced plastic) reinforcement to replace steel bars. FRP, as a novel composite material, possesses many excellent properties such as lightweight, high strength, and corrosion resistance. However, it differs significantly from traditional steel bars in terms of mechanical properties and elastic modulus. Therefore, this invention features a completely new design for the end plates, head plates, and tail plates, employing constraint screws to effectively apply prestress to the FRP reinforcement. This ensures that the FRP reinforcement fully utilizes its material advantages while effectively controlling the stress distribution during tensioning, avoiding material damage caused by stress concentration and other issues.

[0042] 3. This invention employs sleeve-grooved anchoring technology to fabricate pre-tensioned FRP-reinforced concrete pipe piles. By innovatively replacing traditional steel bars with FRP reinforcement, it achieves a dual breakthrough in corrosion protection mechanisms and structural load-bearing capacity. Compared to traditional prestressed concrete pipe piles, this product exhibits significant advantages under complex corrosive conditions such as chloride environments, acid and alkali media, and stray currents. The high strength of FRP ensures the stability of the pile structure while greatly enhancing the pile's load-bearing capacity, combining the advantages of high strength and high load-bearing capacity. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0044] Figure 1 This is a schematic diagram of the end plate structure according to some embodiments of the present invention;

[0045] Figure 2 This is a cross-sectional view of the end plate according to some embodiments of the present invention;

[0046] Figure 3 for Figure 2 Enlarged view of the structure at point A in the middle;

[0047] Figure 4 for Figure 1 Enlarged view of the structure at point B;

[0048] Figure 5 This is a schematic diagram of the headplate structure according to some embodiments of the present invention;

[0049] Figure 6 This is a cross-sectional view of the headplate according to some embodiments of the present invention;

[0050] Figure 7 This is a schematic diagram of the tail plate structure according to some embodiments of the present invention;

[0051] Figure 8 This is a cross-sectional view of the tail plate according to some embodiments of the present invention;

[0052] Figure 9 This is a schematic diagram of the structure of the constraint screw in some embodiments of the present invention;

[0053] Figure 10 This is a top view of a constraint screw according to some embodiments of the present invention;

[0054] Figure 11 This is a schematic diagram of the FRP main reinforcement structure in some embodiments of the present invention;

[0055] Figure 12 This is a schematic diagram of the tensioning end connection and installation structure according to some embodiments of the present invention;

[0056] Figure 13 This is a schematic diagram of the tail end connection and installation structure according to some embodiments of the present invention.

[0057] Explanation of reference numerals in the attached figures:

[0058] 10-End plate, 11-Welding groove, 111-Arc-shaped groove wall, 112-Sloping groove wall, 12-First side of end plate, 13-Second side of end plate, 14-Center hole of end plate, 15-Tensioning hole, 16-Through hole, 17-Anchoring hole, 171-Sinking groove, 18-Reserved groove.

[0059] 20-Head plate, 21-First side of head plate, 22-Second side of head plate, 23-Central tension hole, 231-Internal thread, 232-Sealing baffle, 233-Weld, 24-Head plate screw hole, 25-Arc-shaped connecting groove;

[0060] 30 - Tail plate, 31 - Tail plate center hole, 32 - Tail plate screw hole;

[0061] 40 - Constraint screw, 41 - Lower thread, 42 - Shaft, 43 - Washer, 44 - Hexagonal head, 45 - Upper thread;

[0062] 50-FRP main reinforcement, 51-anchor sleeve, 52-FRP reinforcement material, 53-adhesive colloid;

[0063] 60-FRP reinforced cage skeleton;

[0064] 70- Hoop;

[0065] 80 - Connection of the head plate of the constraint screw; 81 - Connection of the end plate of the constraint screw; 82 - Connection of the end plate of the FRP main reinforcement; 83 - Connection of the tail plate of the constraint screw.

[0066] 90 - Fastening nut. Detailed Implementation

[0067] To accurately demonstrate the purpose, technical solution, and advantages of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below in conjunction with the accompanying drawings. The accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. To more effectively present the features and details of each embodiment, some components in the drawings may be appropriately omitted, enlarged, or reduced, and are not equivalent to the actual dimensions of the product; certain structures known to those skilled in the art and their related descriptions may be omitted from the drawings.

[0068] In the description of this invention, expressions such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating the relative importance of the described objects, or implying the number of technical features involved. Therefore, when a feature is prefixed with qualifiers such as "first" or "second," it means that the feature explicitly or implicitly includes at least one of them.

[0069] In the description of this invention, it should be specifically noted that, unless there are explicit and specific provisions and limitations, the terms "installation," "tightening," "locking," and "connection" should be interpreted broadly, and can refer to fixed connections, detachable connections, integral connections, mechanical connections, etc., that achieve the combination between components. Those skilled in the art can accurately grasp the specific meaning of the above terms in this invention based on the specific technical background, design requirements, and other practical circumstances.

[0070] Meanwhile, terms such as "upper," "lower," "front," "rear," "inner," and "outer" indicate the orientation or positional relationship based on the state presented in the accompanying drawings. These terms are used merely to facilitate the explanation of the invention and to simplify its description; they are not intended to indicate that the devices or elements involved must have a specific orientation or be constructed and operated in a specific orientation. Therefore, these expressions should not be construed as limitations on the invention.

[0071] Example 1

[0072] like Figures 1-13 As shown, a prestressing application device for pre-tensioned FRP reinforced concrete pipe piles is applied to the FRP main reinforcement 50 extending from both ends of the FRP reinforcement cage 60. The device includes an end plate 10, a head plate 20, a tail plate 30, a restraining screw 40, and a sleeve 70. The end plate 10, head plate 20, restraining screw 40, and sleeve 70 are provided at one end of the FRP reinforcement cage 60, and the other end of the FRP reinforcement cage 60 is provided with the end plate 10, tail plate 30, restraining screw 40, and sleeve 70.

[0073] Both ends of the FRP main reinforcement 50 are respectively fitted with cylindrical anchor sleeves 51, and the anchor sleeves 51 are filled with adhesive 53 to bond with the FRP reinforcement 52 to form anchor ends.

[0074] The end plate 10, head plate 20 and tail plate 30 are all made from circular substrates.

[0075] The end plate 10 has a first side 12 and a second side 13. The first side 12 is located on the side away from the FRP reinforcement cage 60, and the second side 13 is located on the other side closer to the FRP reinforcement cage 60. A through-hole 14 is provided in the center of the end plate 10. Multiple tension holes 15 are provided circumferentially around the central hole 14. The sides of each tension hole 15 are provided with connecting through holes 16 and anchoring holes 17. The anchoring holes 17 are used for anchoring the FRP main reinforcement 50. Specifically, the anchoring holes 17, through holes 16, and tension holes 15 are evenly distributed circumferentially along the central hole 14. The through holes 16, tension holes 15, and anchoring holes 17 are machined by stamping or cutting, and the hole diameter can be adjusted according to the reinforcement requirements. The through hole 16 connects to the corresponding anchor hole 17 and tension hole 15. The anchor hole 17 and tension hole 15 are on concentric circles. The line connecting the center lines of tension hole 15, through hole 16 and anchor hole 17 is an arc with the center of the end plate center hole 14 as the center.

[0076] The anchoring hole 17 has a recess 171 on the side away from the FRP reinforcement cage 60 (first side 12 of the end plate) for assembling the anchoring sleeve 51. The recess 171 has a flat opening. Specifically, the inner diameter of the recess 171 is larger than the inner diameter of the anchoring hole 17 and larger than the outer diameter of the anchoring sleeve 51. The recess 171 and the anchoring hole 17 are connected by a planar connection. Further, the anchoring end of the FRP main reinforcement 50 passes through the tensioning hole 15 from the second side 13 of the end plate, passes through the corresponding through hole 16, and then is inserted into the anchoring hole 17. The anchoring sleeve 51 is inserted into the recess 171 of the anchoring hole 17 for positioning. Further, the outer diameter of the anchoring sleeve 51 is larger than the diameter of the through hole 16 and smaller than the inner diameter of the recess 171. The inner diameter of the anchoring sleeve 51 is more than 6 mm larger than the nominal diameter of the FRP reinforcement 52.

[0077] The periphery of the first side surface 12 of the end plate is provided with a welding groove 11. Specifically, the welding groove 11 has an arc-shaped groove wall 111 and a sloping groove wall 112. The arc-shaped groove wall 111 connects to the first side surface 12 of the end plate, and the sloping groove wall 112 is located between the arc-shaped groove wall 111 and the outer peripheral wall of the end plate 10. The periphery of the second side surface 13 of the end plate is provided with a reserved groove 18 for connecting the sleeve 70, which restrains and protects the pile head concrete, and enhances the pile head strength and impact resistance. The reserved groove 18 is reserved for the connection between the pile sleeve 70 and the end plate 10. It is formed as a whole by welding and pressing, which restrains and protects the pile head concrete, and enhances the pile head strength and impact resistance. Specifically, during installation, the sleeve 70 is placed on the end plate 10 and gently tapped with a hammer to ensure that the mating surfaces of the sleeve 70 and the end plate 10 are tightly attached to the entire circumference. Then, the sleeve 70 is welded and pressed into the end plate 10 to form an integral whole.

[0078] The headplate 20 has a first side surface 21 and a second side surface 22. A central tensioning hole 23 is provided in the center of the headplate 20, and an internal tensioning thread 231 is provided inside the central tensioning hole 23. The headplate 20 has multiple headplate screw holes 24 evenly distributed around the central tensioning hole 23 for fixing the constraint screw 40. Specifically, the internal thread of the central tensioning hole 23 is configured as Tr80×8, which matches and connects with the external thread of the tensioning bolt for applying prestress. Further, the thickness of the headplate 20 is increased around the central tensioning hole 23 on the first side surface 21, and the thread depth of the central tensioning hole 23 is lengthened. An arc-shaped connecting groove 25 is provided at the thickened part of the headplate 20, connecting with the outer peripheral wall of the headplate 20 and the right-angle groove wall provided on the first side surface 21. Further, a sealing baffle 232 is welded to the central tensioning hole area on the second side surface 22 of the headplate, and the outer diameter of the sealing baffle 232 is larger than the diameter of the central tensioning hole 23 of the headplate 20. Specifically, the outer diameter of the head plate 20 is the same as the outer diameter of the end plate 10. During operation, the sealing baffle 232 can be positioned by using the head plate 20 and the thin steel plate as the same center. The sealing baffle 232 is welded to the second side 22 of the head plate through the weld 233 to prevent the concrete from overflowing from the tensioning hole 23 in the center of the head plate when the concrete pile is centrifuged after the concrete is placed.

[0079] The tail plate 30 has a through-hole 31 in its center. During operation, a rubber plug is inserted into the tail plate center hole 31 to prevent concrete from overflowing from the center hole during centrifugation after the concrete pile is placed. After centrifugation, the rubber plug is removed to empty the slurry inside the pile. The tail plate 30 has multiple tail plate screw holes 32 evenly distributed around the center hole 31 for fixing the constraint screws 40. Specifically, the outer diameter of the tail plate 30 is larger than the pile shape.

[0080] The constraint bolts 40 located at both ends of the FRP reinforcement cage 60 pass through the head plate bolt holes 24 and the tail plate bolt holes 32, respectively, and are detachably connected to the end plate tensioning holes 15 located at both ends of the FRP reinforcement cage 60. Specifically, the constraint bolts 40 are hexagonal bolts, and each constraint bolt 40 is equipped with a fastening nut 90 that abuts against the head plate bolt holes 24 and the tail plate bolt holes 32 for relative fixation. Further, the head plate bolt holes 24 and the tail plate bolt holes 32 are both larger than the inner diameter of the tensioning holes 15 and the outer diameter of the constraint bolts 40. The hexagonal head 44 of the constraint bolt 40 is larger than the inner diameter of the head and tail plate bolt holes 24, the diameter of the bolt body 42 is larger than the thread type of the constraint bolt 40, and the length of the bolt body 42 is greater than the height of the anchoring sleeve 51. The external thread of the constraint screw 40 is divided into upper and lower parts. The lower thread 41 of the constraint screw 40 starts from the tail and its thread height is consistent with the thickness of the end plate 10. The upper thread 45 of the constraint screw 40 starts from the height of the head / tail plate below the washer, and its height is consistent with the thickness of the fastening nut 90. A fastening nut is installed on the upper part of the constraint screw 40 for fixing the screw to the head plate or tail plate. To avoid stress concentration caused by uneven prestressing, all constraint screws are of the same model and have the same height as the lower thread 41. The constraint screw 40 is made of high-strength steel, and its length, diameter, and pitch can be designed or adjusted according to actual needs. The constraint screw 40 is equipped with a fastening nut 90 for fixing the constraint screw 40 to the head plate 20 and tail plate 30. Washers 43 are installed at the connection between the fastening nut and the head plate, and at the connection between the constraint nut and the tail plate. During operation, the constraint screw 40 passes through the head plate screw hole 24 on the first side 21 of the head plate. After screwing the fastening nut 90 into the rod body 42, the lower thread 41 is installed and locked to the tension hole 15 on the first side 12 of the end plate. Then, the fastening nut 90 is installed and locked to the upper thread 45 so that it is tightly attached to the head plate 20 on the second side 22 of the head plate. Similarly, the constraint screw 40 passes through the tail screw hole 32. After screwing the fastening nut 90 into the rod body 42, the lower thread 41 is installed and locked to the tension hole 15 on the first side 12 of the end plate. Then, the fastening nut 90 is installed and locked to the upper thread 45 so that it is tightly attached to the tail plate 30. The constraint screw head plate connection 80, constraint screw end plate connection 81, FRP main rib end plate connection 82, and constraint screw tail plate connection 83 are as follows: Figure 12 and Figure 13 As shown.

[0081] Example 2

[0082] The second objective of this invention is to provide a method for preparing pre-tensioned FRP-reinforced concrete pipe piles, comprising the following steps:

[0083] S1. Forming the FRP reinforcement cage 60: Cut the FRP reinforcement 52, prepare the adhesive and inject it into the anchoring sleeve from the head end; insert one end of the FRP reinforcement 52 with the injected adhesive 53 into the anchoring sleeve 51, ensuring that the FRP reinforcement 52 and the anchoring sleeve 21 are coaxial, so that the adhesive 53 fully fills the gap between the anchoring sleeve and the FRP reinforcement and the gap between the through hole and the FRP reinforcement, forming the anchoring end of the FRP main reinforcement 50, and promptly clean up any excess adhesive; then, make FRP stirrups according to the required size, and use non-metallic tensioning straps to tie the FRP main reinforcement 50 and FRP stirrups to form the FRP reinforcement cage 60. The finished FRP reinforcement cage is similar in appearance to a traditional steel cage.

[0084] S2. Fabrication and installation of hoop plate 70: After aligning 2 to 4 pieces of plate material neatly, roll them into a circular hoop 70 by machine and hammer the two ends together to be aligned and welded. The weld should be flat and there should be no missing welds or weld penetration. Put the rolled hoop 70 on the end plate 10 and tap it lightly with a hammer to ensure that the mating surface of the hoop and the end plate is tightly attached to the entire circumference. Press the reserved groove 18 between the hoop 70 and the end plate into the entire circumference. The insertion should be uniform and firm.

[0085] S3. Install FRP reinforcement cage 60: Pass the anchor sleeve 51 at the end of the FRP main reinforcement 50 in the prepared FRP reinforcement cage 60 through the tension hole 15, rotate the end plate 10 so that the FRP main reinforcement 50 is screwed into the anchor hole 17 through the reinforcement hole 16, pull the end plates 10 at both ends so that the anchor sleeve 51 is assembled and clamped to the groove 171 on the first side of the anchor hole 17 for positioning.

[0086] S4. FRP reinforcement cage 60 is placed into the mold: The prepared FRP reinforcement cage 60, end plate 10, head plate 20 and tail plate 30 are placed in the lower half mold of the centrifugal pipe pile. The constraint screws 40 are installed and locked through the head plate screw hole 24 and the tail plate screw hole 32 respectively and the tension hole 15 of the end plate 10. The fastening nut 90 is installed and locked with the upper external thread 45 so that it is tightly attached to the head plate 20 and the tail plate 30. The tail plate 30 is tightly attached to the tail of the steel mold.

[0087] S5. Concrete placement: Use a forced concrete mixer to prepare fresh concrete with a low slump of 2-5cm. The concrete strength grade should not be lower than C80. According to the usage requirements of each centrifugal pipe pile, fill the lower half of the mold with fresh concrete evenly. When placing the concrete, follow the order of "first the middle - then both ends - then the middle again" to ensure that the concrete is evenly distributed in the steel mold.

[0088] S6. Mold Closure: Clean both sides of the mold edge, place the grout-stopping rope, close the upper half of the centrifugal pipe pile mold, and use a pneumatic wrench to symmetrically tighten the mold closing bolts from one end to the other or from the middle to both ends to ensure a tight seal and that the mold does not loosen or the concrete does not leak during high-speed centrifugal operation.

[0089] S7. Prestressing tensioning: Move the jack to align it with the center of the steel mold, align and fasten the tensioning nut and tensioning sprite head, and tension the FRP rib cage 60 after the mold is closed. Control the oil valve to make the movement smooth and slow, pausing at least 3 times. After reaching the specified parameters, maintain a stable pressure (e.g., not less than 10 seconds), then lock the tensioning nut and release the oil pressure.

[0090] S8. Centrifugal molding: The tensioned and anchored pipe pile mold is hoisted above the centrifuge and accelerated step by step. Through the centrifugal compaction molding process, the fresh concrete is uniformly compacted around the centrifugal pipe pile mold, and a cavity is formed inside the pipe pile. After centrifugation, the rubber plug in the center hole 31 of the tail plate is removed, and the surface quality of the inner wall of the pipe pile is checked. The excess slurry is poured out.

[0091] S9. Normal pressure curing: After centrifugation, the pipe pile with mold is hoisted into the steam curing tank. The steam curing process is generally divided into four stages: static stop, heating, constant temperature and cooling. The heating rate is about 25℃ / h. The constant temperature stage is 4 to 8 hours to make the concrete strength reach the specified level.

[0092] S10. Demolding: Following the “symmetrical cross method”, first remove the tail plate 30 and then the template bolts. Loosen the tension nuts and remove the tension baffle. Lift the cover mold. Remove the tension rods. Loosen the constraint screws 40 and fastening nuts 90 between the end plate 10 and the head plate 20 and tail plate 30. Cut off the excess FRP reinforcement ends 51 of the end plate 10. Lift the pile out of the mold.

[0093] S11. Autoclaving: After the pipe piles are demolded, marked, printed, and inspected for quality, they are hoisted onto a car and pulled into an autoclave for secondary curing. The autoclaving process is divided into four stages: pressurization, constant pressure, depressurization, and cooling. During the constant pressure stage, the gauge pressure should generally be maintained above 0.90 MPa and the temperature should be around 180°C. When the pressure inside the autoclave drops to 0 MPa, the autoclave doors at both ends are opened to allow ventilation and cooling of the pipe piles. The pipe piles should be removed from the autoclave when the temperature difference with the outdoor temperature is no more than 80°C. After curing, the piles are pulled out of the autoclave and hoisted for transport and stacking according to regulations.

[0094] The positional relationships shown in the figures are for illustrative purposes only and should not be considered as limitations on this patent. The embodiments listed above are illustrative examples for the purpose of clearly and explicitly explaining the relevant content of this invention and are not intended to specifically limit the embodiments of this invention. Those skilled in the art will be able to make various other variations or adjustments based on the above description. It is neither necessary nor possible to list all possible embodiments in detail here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection covered by the claims of this invention.

Claims

1. A prestressing application device for pre-tensioned FRP-reinforced concrete pipe piles, characterized in that, The device is applied to the FRP main reinforcement bars extending from both ends of the FRP reinforcement cage skeleton, and includes end plates, head plates, tail plates, restraining screws, and sleeves. The end plates, head plates, restraining screws, and sleeves are set at one end of the FRP reinforcement cage skeleton, and the other end of the FRP reinforcement cage skeleton is also provided with end plates, tail plates, restraining screws, and sleeves. Straight cylindrical anchoring sleeves are respectively fitted at both ends of the FRP main reinforcement bars, and the anchoring sleeves are filled with adhesive to bond them to the FRP reinforcement bars to form anchoring ends. The end plates, head plates, and tail plates are all made of circular substrates. The end plate has a first side and a second side. The first side is located away from the FRP reinforcement cage, and the second side is located closer to the FRP reinforcement cage. A through-hole is provided in the center of the end plate. Multiple tension holes are provided around the center hole. Connecting through holes and anchor holes are provided on the sides of the tension holes. The anchor holes are used to anchor the FRP main reinforcement. A countersunk groove is provided on the side of the anchor hole away from the FRP reinforcement cage; the countersunk groove has a flat opening. The through holes connect the corresponding anchor holes and tension holes. The anchor holes and tension holes are on concentric circles, and the line connecting the center lines of the tension holes, through holes, and anchor holes is an arc centered on the center hole of the end plate. A pre-drilled groove is machined around the periphery of the first side of the end plate for connecting a hoop. The head plate has a first side and a second side, and a through central tensioning hole is provided in the middle of the head plate. A tensioning internal thread is provided inside the central tensioning hole, and a plurality of head plate screw holes are provided on the head plate evenly distributed around the central tensioning hole. The tail plate has a through-hole in the middle and multiple tail plate screw holes evenly distributed around the circumference of the tail plate center hole. The constraint screw is a hexagonal bolt, and the constraint screw is equipped with fastening nuts that abut against the screw holes of the head plate and the screw holes of the tail plate for relative fixation; The anchoring end of the FRP main reinforcement passes through the tensioning hole from the second side of the end plate and then through the corresponding reinforcement hole before being inserted into the anchoring hole. The anchoring sleeve is inserted into the groove of the anchoring hole. The constraint screws located at both ends of the FRP stiffener cage skeleton pass through the head plate screw holes and tail plate screw holes respectively and are detachably connected to the end plate tensioning holes located at both ends of the FRP stiffener cage skeleton. The head plate, tail plate and end plate are connected by constraint screws and fastening nuts to limit and fix them, giving the FRP anchoring end sufficient space to avoid damage to the FRP reinforcement due to shear stress concentration caused by the anchoring device.

2. The prestressing application device for pre-tensioned FRP reinforced concrete pipe piles according to claim 1, characterized in that, The periphery of the first side of the end plate is provided with a welding groove. The welding groove has an arc-shaped groove wall and an inclined groove wall. The arc-shaped groove wall is connected to the first side of the end plate, and the inclined groove wall is located between the arc-shaped groove wall and the outer peripheral wall of the end plate.

3. The prestressing application device for pre-tensioned FRP reinforced concrete pipe piles according to claim 2, characterized in that, The head plate screw hole and the tail plate screw hole are both larger than the inner diameter of the tensioning hole and the outer diameter of the constraint screw.

4. The prestressing application device for pre-tensioned FRP-reinforced concrete pipe piles according to claim 3, characterized in that, The outer diameter of the tail plate is larger than that of the pipe pile, and the outer diameter of the head plate is the same as that of the end plate.

5. The prestressing application device for pre-tensioned FRP reinforced concrete pipe piles according to claim 4, characterized in that, A sealing baffle is welded to the center of the second side of the head plate, and the outer diameter of the sealing baffle is larger than the diameter of the central tension hole of the head plate.

6. A method for preparing pre-tensioned FRP-reinforced concrete pipe piles, characterized in that, Using the prestressing application device as described in claim 5 and the following steps: S1. Forming of FRP Reinforcing Cage: Cut FRP reinforcing material, insert one end of the FRP reinforcing material into the anchor sleeve after injecting adhesive, ensure that the FRP reinforcing material and the anchor sleeve are coaxial, and make the adhesive fully fill the gap to form the anchor end of the FRP main reinforcement; use non-metallic tensioning bands to tie the FRP main reinforcement and FRP stirrups to form the FRP reinforcing cage. S2. Hoop fabrication and installation: Press and roll 2 to 4 pieces of sheet material into a circular hoop, and hammer the two ends together to align and weld them. Place the pressed hoop on the end plate and press the hoop into the reserved groove on the entire circumference. S3. Install FRP reinforcement cage: Pass the anchor sleeves at the ends of the FRP main reinforcements in the prepared FRP reinforcement cage through the tensioning hole, rotate the end plate to make the FRP main reinforcements screw into the anchor hole through the reinforcement hole, pull the end plates at both ends to make the anchor sleeves fit and lock into the groove on the first side of the anchor hole for positioning. S4. FRP reinforcement cage installation: Place the fabricated FRP reinforcement cage, end plate, head plate and tail plate into the lower half of the centrifugal pipe pile mold. The constraint screws are installed and locked through the screw holes of the head plate, the screw holes of the tail plate and the tensioning holes of the end plate respectively. The fastening nuts are installed and locked with the upper threads to make them fit tightly against the head plate and tail plate. The tail plate is in close contact with the tail of the steel mold. S5. Concrete placement: Use a forced concrete mixer to produce concrete with a strength grade of not less than C80. According to the usage requirements of each centrifugal pipe pile, fill the lower half of the mold with freshly mixed concrete evenly. S6. Mold closing: Clean both sides of the mold edge, place the grout-stopping rope, close the upper half of the centrifugal pipe pile mold and tighten the mold closing bolts; S7. Prestressing tensioning: Tensioning the FRP rib cage skeleton after mold closing, locking the tensioning nut, maintaining stable pressure after reaching the specified parameters, and then releasing the pressure by returning oil. S8. Centrifugal molding: The tensioned and anchored pipe pile mold is hoisted to the centrifuge for centrifugal compaction. After centrifugation, the rubber plug in the center hole of the tail plate is removed and the excess slurry is poured out. S9. Normal pressure curing: After centrifugation, the pipe piles with molds are hoisted into the steam curing tank to make the concrete strength reach the specified level. S10. Demolding: First remove the tail plate, then remove the template bolts, loosen the tension nuts and remove the tension baffle, and lift the cover mold. Remove the tension rods, loosen the constraint bolts and fastening nuts between the end plate and the head and tail plates, cut off the excess FRP reinforcement ends of the end plates, and lift the pile out of the formwork; S11. Autoclaving: The pipe piles are hoisted onto the autoclave car and pulled into the autoclave for secondary curing. After curing, the piles are pulled out of the autoclave and transported and stacked according to regulations.

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