A composite anchor for FRP bars and its preparation method

Abstract

This invention relates to the field of anchoring technology and discloses a composite anchor for FRP (fiberglass reinforced plastic) bars and its manufacturing method. The composite anchor includes an outer sleeve, an anchor ring, a clamping plate, and a pre-tightening device. The anchor ring and clamping plate have coaxial through holes, with the clamping plate positioned within the through hole of the anchor ring. The outer sleeve and anchor ring are fixed by grooves and protrusions. The pre-tightening device includes a column with an open end and a cavity, and a planar bearing. The cavity is used to hold adhesive. The bottom surface of the column has a positioning hole, an injection hole, and a vent hole. The FRP bar passes through the through hole of the anchor ring, the through hole of the clamping plate, and the positioning hole. A protruding annular baffle is provided on the inner wall of the open end of the column. The planar bearing is positioned outside the baffle, and its tightening ring is fixedly connected to the end face of the open end of the column. The pre-tightening device is threadedly connected to the outer sleeve, and the loosening ring of the planar bearing contacts the end face of the anchor ring. The composite anchor prevents the FRP bar from exhibiting a cutting effect during anchoring, resulting in high anchoring efficiency. The clamping plate exerts a large axial force, further improving anchoring efficiency.

Description

Technical Field

[0001] This invention relates to the field of anchoring technology, and specifically to a composite anchor for FRP bars and its preparation method. Background Technology

[0002] Carbon fiber reinforced polymer (FRP) composites possess advantages such as corrosion resistance, acid and alkali resistance, high specific strength, and high specific modulus, making them widely used in the construction, monitoring, and maintenance of roads, bridges, and buildings. While FRP bars have high tensile strength, their transverse shear strength is lower than that of steel. Traditional anchorages for anchoring prestressed steel bars are unsuitable for FRP bars, leading to premature failure due to the low transverse strength of the FRP bars. Studies have shown that in anchorage structures using FRP bars, the anchorage has a greater impact on the final load-bearing capacity of the anchorage structure.

[0003] Existing anchorages for FRP (Fiberglass Reinforced Plastic) tendons mainly include clamping anchorages and bonded anchorages. Clamping anchorages rely on clamps or cone plugs to generate circumferential pressure on the FRP tendons, thus clamping and anchoring the prestressed tendons. However, clamping anchorages are prone to shearing effects when operating under large fatigue stress amplitudes for extended periods, leading to shear failure of the FRP tendons. Bonded anchorages primarily consist of a cylindrical metal sleeve, bonded to the FRP tendons using resin or other adhesives. Once the adhesive reaches its design strength, prestress is applied to the FRP tendons by tensioning the metal sleeve with a jack. Bonded anchorages have a longer anchorage length, a long adhesive curing time, and poor creep resistance, making them unsuitable for locations requiring rapid anchoring or in confined construction spaces.

[0004] Composite anchors combine clamping and bonding anchors, overcoming the aforementioned drawbacks. Patent CN108532837A provides a composite double-sleeve anchor for FRP bars, solving the notch effect and adhesive creep problems that occur during FRP bar anchoring. However, when applying pre-tightening force, the pre-tightening device requires tightening two tension bolts separately. The force applied to the two bolts during tightening is difficult to be completely uniform, leading to uneven force distribution on the inner sleeve or anchor ring, causing the FPR to be subjected to radial shear force and still potentially damaged. Patent CN113374177B replaces multiple tension bolts with a single clamping screw, whose end face contacts the wedge, solving the problem of uneven force distribution on the inner sleeve or anchor ring. However, when the clamping screw is screwed in, it puts force on the conical wedge, causing it to rotate with the clamping screw and become damaged, subsequently damaging the anchor ring. While a fixing ring can prevent slight rotation by placing a fixing ring between the conical wedge and the anchor ring, under greater force, the fixing ring may damage or the conical wedge may deform and become damaged, severely affecting the use of the anchor. Furthermore, existing anchors often struggle to advance multiple wedges simultaneously, resulting in uneven force distribution among the wedges and a small axial force, leading to low anchoring efficiency. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a composite anchor for FRP reinforcement and its preparation method. In this composite anchor, there is no relative movement between the outer sleeve and the anchor ring, or between the anchor ring and the wedges; no load is generated between the outer sleeve and the anchor ring, or between the anchor ring and the wedges; the FRP reinforcement experiences low transverse shear force, resulting in high anchor strength; the wedges are evenly stressed, leading to high axial force on the FRP reinforcement and high anchoring efficiency.

[0006] To achieve the above objectives, the present invention employs the following technical solutions.

[0007] A composite anchor for FRP reinforcement includes an outer sleeve, an anchor ring, a clamp, and a pre-tightening device; the anchor ring and the clamp are provided with coaxial through holes, and the clamp is disposed in the through hole of the anchor ring, the shape of which is adapted to the through hole of the anchor ring;

[0008] The inner wall of the outer sleeve has multiple grooves along the axial direction at one end and internal threads at the other end; the outer wall of the anchor ring has protrusions that match the grooves, and the outer sleeve and the anchor ring are fixed by the grooves and protrusions.

[0009] The pre-tightening device includes a column with a cavity and an open end, and a plane bearing. The cavity is used to hold adhesive. The closed end of the column has a positioning hole coaxial with the through hole of the anchor ring. An injection hole and an vent hole are respectively provided on both sides of the positioning hole. The FPR bar passes through the through hole of the anchor ring, the through hole of the clamping piece, and the positioning hole. The outer wall of the open end of the column is provided with external threads, and the inner wall of the open end of the column is provided with a protruding annular baffle. The height of the annular baffle is the same as the thickness of the plane bearing. The plane bearing is located outside the annular baffle, and its tight ring is fixedly connected to the end face of the open end of the column.

[0010] The pre-tightening device is connected to the outer sleeve by a thread. The stress of the FRP rib is adjusted by adjusting the pre-tightening device. When the pre-tightening device is tightened, the loose ring of the plane bearing contacts the end face of the anchor ring.

[0011] Preferably, the clip is formed by combining three clip bodies, each clip body has staggered tooth blocks on both sides, and the tooth blocks on both sides of two adjacent clip bodies mesh with each other.

[0012] More preferably, the inner surface of the clamp body is provided with internal threads. When the three clamp bodies are combined into a clamp, the inner surface of the clamp body forms a through hole with internal threads, and the inner diameter of the through hole is the same as the inner diameter of the FPR rib.

[0013] More preferably, the thread pitch of the internal thread of the clamping plate through hole is 10mm.

[0014] Preferably, both the outer sleeve and the cylinder are regular hexagonal prisms.

[0015] Preferably, the groove is a dovetail groove, and a stop block is detachably provided at the end of the dovetail groove for limiting the position of the dovetail groove.

[0016] Preferably, there are two planar bearings, namely a first planar bearing and a second planar bearing, wherein the outer diameter of the second planar bearing is smaller than the inner diameter of the first planar bearing; the second planar bearing is located in the inner ring of the first planar bearing.

[0017] Composite anchorages for FRP bars are prepared by the following method:

[0018] S1. Create a 3D solid model of the outer sleeve, and then 3D print the 3D solid model to obtain the outer sleeve;

[0019] S2, using the method in step 1, 3D print the anchor ring, clamping plate and pre-tightening device respectively;

[0020] S3, pass the FPR bar through the through hole of the anchor ring and the positioning hole of the pre-tightening device;

[0021] S4, connect the outer sleeve to the anchor ring through the groove and the convex strip, and insert the clamp into the through hole of the anchor ring 2 for anchoring;

[0022] S5, adjust the pre-tightening device to apply pre-tightening force until the pre-tightening device is tightened to the point that it cannot rotate;

[0023] S6, inject adhesive through the injection hole, and after the adhesive cures, a composite anchor is obtained.

[0024] Preferably, 3D printing includes the following steps:

[0025] S11. Use modeling software to create a model of the outer jacket and export the model as an STL file.

[0026] S12: Import the STL format file into the 3D printing slicing software for slicing processing to obtain slicing data; print the slicing data using a 3D printer to obtain the final product.

[0027] Preferably, the 3D printing material is carbon fiber composite material; the binder is epoxy resin.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The FRP bars of the composite anchor will not exhibit a notch effect during the anchoring process, have a long service life, good creep resistance, and high anchoring efficiency; the axial sliding distance of the wedge body in the anchor ring remains consistent, which reduces the transverse shear force on the FRP bars and increases the axial force, thereby improving the anchoring efficiency.

[0030] A planar bearing is installed between the pre-tightening device and the anchor ring of the composite anchor to prevent the anchor ring from rotating and generating load when adjusting the pre-tightening force of the FRP reinforcement by tightening the pre-tightening device, which could damage the anchor. The outer sleeve and the column of the pre-tightening device are regular hexagonal prisms, which facilitates the connection and reinforcement of the anchor to the main beam, improves stability, facilitates the application of pre-tightening force with a wrench, and makes it easy to position.

[0031] The composite anchor of the present invention is made of carbon fiber composite material, with its outer sleeve, anchor ring, clamping plate and pre-tightening device all made of fused wire 3D printing technology. It has the advantages of light weight, high strength, corrosion resistance and aging resistance. The preparation method of the present invention can realize the one-piece molding of complex models, with high processing accuracy and short preparation cycle. Attached Figure Description

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1 This is a cross-sectional schematic diagram of a composite anchor.

[0034] Figure 2 This is a cross-sectional view of the outer sleeve;

[0035] Figure 3 This is the left view of the outer jacket.

[0036] Figure 4 This is a cross-sectional schematic diagram of the anchor ring;

[0037] Figure 5 This is the left view of the anchor ring;

[0038] Figure 6 This is a front view of the clip body;

[0039] Figure 7 This is a side view of the clip body;

[0040] Figure 8 This is a cross-sectional schematic diagram of the pre-tightening device;

[0041] Figure 9 Left view of the pre-tightening device;

[0042] Figure 10 This is a schematic diagram of a 3D printer structure.

[0043] The attached figures are labeled as follows:

[0044] 1. Outer sleeve; 2. Anchor ring; 3. Clamping piece; 4. Pre-tightening device; 5. Adhesive; 6. FPR rib; 7. 3D printer; 11. Groove; 12. Stop block; 21. Raised strip; 31. Clamping piece body; 32. Through hole; 41. Column; 42. Surface bearing; 411. Positioning hole; 412. Injection hole; 413. Vent hole; 414. Annular baffle; 71. Feed box; 72. Feed roller; 73. Heat sink; 74. Hot end; 75. Molded printing filament; 76. Printer nozzle; 77. Molded printing filament; 78. Building platform. Detailed Implementation

[0045] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0046] Figure 1 This is a cross-sectional schematic diagram of a composite anchor. The composite anchor for FRP reinforcement of the present invention includes an outer sleeve 1, an anchor ring 2, a clamping plate 3, and a pre-tightening device 4; the anchor ring 2 and the clamping plate 3 are provided with coaxial through holes, the through hole of the anchor ring 2 is frustoconical, and the clamping plate 3 is disposed in the through hole of the anchor ring 2, the shape of which matches the through hole of the anchor ring 2;

[0047] like Figure 2 and Figure 3 As shown, the inner wall of the outer sleeve has multiple grooves 11 along the axial direction at one end and an internal thread at the other end; as Figure 4 and Figure 5 The outer wall of the anchor ring 2 is provided with a protrusion 21 that matches the groove; the outer sleeve and the anchor ring are fixed by the groove 11 and the protrusion 21. To achieve a better fixing effect, the groove is a dovetail groove and the protrusion is a dovetail protrusion.

[0048] In this embodiment, the length of the internal thread section on the inner wall of the outer sleeve is 100mm, and the pitch of the internal thread is 3mm.

[0049] like Figure 8 As shown, the pre-tightening device 4 includes a column 41 with one end open and a cavity, and a plane bearing 42. The cavity is used to place the adhesive 5 to fix the FRP reinforcement. Figure 9 As shown, the bottom surface of the column has a positioning hole 411 coaxial with the through hole of the anchor ring 2. The FPR rib 6 passes through the through hole of the anchor ring 2, the through hole of the clamping piece 3 and the positioning hole 411. An injection hole 412 and an exhaust hole 413 are respectively provided on both sides of the positioning hole for injecting adhesive into the cavity.

[0050] The outer wall of the open end of the column is provided with external threads, and the inner wall of the open end of the column is provided with a protruding annular baffle 414. The height of the annular baffle is the same as the thickness of the planar bearing 42. The planar bearing is located outside the baffle, and its retaining ring is fixedly connected to the end face of the open end of the column. The retaining ring is used to separate the adhesive from the planar bearing, preventing the adhesive from contacting the planar bearing and affecting its operation. In this embodiment, the length of the external thread section on the outer wall of the open end of the column is 100mm, and the pitch of the external thread is 3mm.

[0051] The pre-tightening device is connected to the outer sleeve by threads. The stress of the FRP reinforcement is adjusted by adjusting the pre-tightening device. When the pre-tightening device is tightened, the tight ring of the flat bearing rotates with the pre-tightening device, while the loose ring of the flat bearing does not rotate. The loose ring moves towards the anchor ring and contacts the end face of the anchor ring. As the pre-tightening device continues to rotate, the loose ring of the flat bearing axially presses against the end face of the anchor ring, causing axial movement of the anchor ring and increasing the stress of the FRP reinforcement. This prevents the anchor ring from rotating and generating load when adjusting the pre-tightening force of the FRP reinforcement by tightening the pre-tightening device, which could damage the anchor.

[0052] As a preferred embodiment of the present invention, such as Figure 6 and Figure 7 As shown, the clamping piece 3 is formed by combining three clamping piece bodies 31. Each clamping piece body 31 has staggered toothed blocks on both sides, and the toothed blocks on both sides of adjacent clamping piece bodies mesh with each other. The axial sliding distance of the clamping piece body within the anchor ring remains consistent, reducing the transverse shear force on the FPR reinforcement and increasing the axial force, thereby improving the anchoring efficiency.

[0053] The inner surface of the clamping body is provided with internal threads. When three clamping bodies are combined to form a clamping plate, the inner surfaces of the three clamping bodies are connected and closed, forming a through hole 32 with internal threads on the inner surface of the clamping plate. The inner diameter of the through hole is the same as the inner diameter of the FPR rib. The diameters at both ends of the clamping plate are 10mm and 40mm respectively, and the internal thread spacing on the inner surface is 10mm. The internal threads make the FPR rib clamped more securely.

[0054] As a preferred embodiment, both the outer sleeve and the column are regular hexagonal prisms, which facilitates the connection and reinforcement of the anchor and the main beam, improves stability, makes it easy to apply pre-tightening force with a wrench, and facilitates their positioning.

[0055] In a preferred embodiment of the present invention, a stop block is detachably provided at the end of the dovetail groove for limiting the dovetail groove. When the dovetail protrusion is inserted into the dovetail groove, the stop block is inserted at the end of the dovetail groove to prevent the dovetail protrusion from sliding out of the dovetail groove when the anchor ring moves under force.

[0056] As a preferred embodiment, two planar bearings are used: a first planar bearing and a second planar bearing. The outer diameter of the second planar bearing is smaller than the inner diameter of the first planar bearing. The second planar bearing is located within the inner ring of the first planar bearing. Using two planar bearings increases the stress-bearing area of ​​the anchor ring, resulting in more even stress distribution when the pre-tightening device is tightened.

[0057] The axial sliding distance of the clamping body in this invention remains consistent within the anchor ring, reducing the transverse shear force on the FRP reinforcement and increasing the axial force, thus improving anchoring efficiency. A plane bearing is installed between the pre-tightening device and the anchor ring in the composite anchor to prevent the anchor ring from rotating and generating loads when adjusting the pre-tightening force of the FRP reinforcement by tightening the pre-tightening device, which could damage the anchor. The outer sleeve and the column of the pre-tightening device are regular hexagonal prisms, facilitating the connection and reinforcement of the anchor to the main beam, improving stability, and making it easy to apply pre-tightening force with a wrench and for easy positioning. The FRP reinforcement of the composite anchor has a long service life, good creep resistance, and high anchoring efficiency during anchoring.

[0058] The method for preparing the above-mentioned composite anchor includes the following steps:

[0059] S1. Create a 3D solid model of the outer sleeve, and then 3D print the 3D solid model to obtain the outer sleeve;

[0060] The material used in 3D printing is carbon fiber composite material, and the specific method is as follows:

[0061] Use modeling software such as CAD or 3DS MAX to create a model of the outer sleeve, and export the model as an STL file; then import the STL file into 3D printing slicing software for slicing to obtain slicing data; use a 3D printer to print the slicing data to obtain the outer sleeve.

[0062] 3D printing uses the fused filament method, which manufactures thermoplastic parts by heating and extruding carbon fiber composite materials and depositing the melt layer by layer onto a heated platform. For example... Figure 10As shown, during the printing process, filaments made of thermoplastic carbon fiber composite material in the feed hopper 71 of the 3D printer 7 are fed into the hot end 74 via feed rollers 72 and heat sinks 73, and heated to above the glass transition temperature in the heating chamber, becoming molten. These molten printing filaments 75 are then extruded through the printer nozzle 76 and guided to lay side-by-side on the build platform (xy plane) along a predetermined path, forming a two-dimensional plane composed of a series of discrete straight lines. After cooling, the molten printing filaments 75 solidify together. Subsequently, the printer nozzle 76 or the build platform 78 shifts out-of-plane to deposit the next layer. Before the previous layer completely cools, the shaped printing filaments 77 of different layers are interconnected. The process from filament to layer to volume continues from bottom to top until the three-dimensional object is completed. Each volume component of the printed three-dimensional object consists of layers, each layer composed of individually extruded shaped printing filaments 77.

[0063] S2, using the method in step 1, 3D print the anchor ring, clamping plate and pre-tightening device respectively;

[0064] S3, pass the FPR bar through the through hole of the anchor ring and the positioning hole of the pre-tightening device;

[0065] S4, connect the outer sleeve to the anchor ring through the groove and the convex strip, and insert the clamp into the through hole of the anchor ring for anchoring;

[0066] S5, adjust the pre-tightening device to apply pre-tightening force until the pre-tightening device is tightened to the point that it cannot rotate;

[0067] S6, inject adhesive through the injection hole, and after the adhesive cures, a composite anchor is obtained.

[0068] In this embodiment, epoxy resin is selected as the adhesive.

[0069] Anchorages are fabricated using fused filament 3D printing technology, enabling the one-piece molding of complex models and improving the precision of composite anchorages. Composite anchorages use carbon fiber composite materials instead of steel, offering advantages such as light weight, high strength, corrosion resistance, and aging resistance. Furthermore, the stiffness matching between the carbon fiber composite material and the FRP reinforcement avoids the notch effect, ensuring the normal use of the composite anchorage.

[0070] Although the present invention has been described in detail in this specification with general description and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A composite anchor for FRP bars, characterized in that, It includes an outer sleeve (1), an anchor ring (2), a clamping plate (3), and a pre-tightening device (4); the anchor ring and the clamping plate are provided with coaxial through holes, and the clamping plate is located in the through hole of the anchor ring, and its shape is adapted to the through hole of the anchor ring; The clip is formed by combining three clip bodies (31), and each clip body has staggered tooth blocks on both sides, and the tooth blocks on both sides of two adjacent clip bodies mesh with each other; The inner wall of the outer sleeve has multiple grooves (11) along the axial direction at one end and internal threads at the other end; the outer wall of the anchor ring is provided with a protrusion (21) that matches the grooves, and the outer sleeve and the anchor ring are fixed by the grooves and the protrusion. The pre-tightening device includes a column (41) with a cavity and an open end and a plane bearing (42). The cavity is used to place adhesive (5). The closed end of the column has a positioning hole (411) coaxial with the through hole of the anchor ring. An injection hole (412) and an exhaust hole (413) are respectively provided on both sides of the positioning hole. The FPR rib (6) passes through the through hole of the anchor ring, the through hole of the clamping piece and the positioning hole. The outer wall of the open end of the column is provided with an external thread, and the inner wall of the open end of the column is provided with a protruding annular baffle (414). The height of the annular baffle is the same as the thickness of the plane bearing. The plane bearing is located outside the annular baffle, and its tight ring is fixedly connected to the end face of the open end of the column. The pre-tightening device is connected to the outer sleeve by a thread. The stress of the FRP rib is adjusted by adjusting the pre-tightening device. When the pre-tightening device is tightened, the loose ring of the plane bearing contacts the end face of the anchor ring.

2. The composite anchorage according to claim 1, characterized in that, The inner surface of the clamp body is provided with internal threads. When the three clamp bodies are combined into a clamp, a through hole (32) with internal threads is formed on the inner surface of the clamp body. The inner diameter of the through hole is the same as the inner diameter of the FPR rib.

3. The composite anchorage according to claim 2, characterized in that, The thread pitch of the internal thread of the clamp through hole is 10mm.

4. The composite anchorage according to claim 1, characterized in that, Both the outer sleeve and the cylinder are regular hexagonal prisms.

5. The composite anchorage according to claim 1, characterized in that, The groove is a dovetail groove, and a stop block (12) is detachably provided at the end of the dovetail groove for limiting the position of the dovetail groove.

6. The composite anchorage according to claim 1, characterized in that, The number of planar bearings is two, namely a first planar bearing and a second planar bearing. The outer diameter of the second planar bearing is smaller than the inner diameter of the first planar bearing. The second planar bearing is located in the inner ring of the first planar bearing.

7. The method for preparing the composite anchorage according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Create a 3D solid model of the outer sleeve, and then 3D print the 3D solid model to obtain the outer sleeve; S2, using the method in step 1, 3D print the anchor ring, clamping plate and pre-tightening device respectively; S3, pass the FPR bar through the through hole of the anchor ring and the positioning hole of the pre-tightening device; S4, connect the outer sleeve and the anchor ring through the groove and the convex strip, and insert the clip into the through hole of the anchor ring (2) for anchoring; S5, adjust the pre-tightening device to apply pre-tightening force until the pre-tightening device is tightened to the point that it cannot rotate; S6, inject adhesive through the injection hole, and after the adhesive cures, a composite anchor is obtained.

8. The preparation method according to claim 7, characterized in that, The 3D printing includes the following steps: S11. Use modeling software to create a model of the outer jacket and export the model as an STL file. S12: Import the STL format file into the 3D printing slicing software for slicing processing to obtain slicing data; print the slicing data using a 3D printer to obtain the final product.

9. The preparation method according to claim 7, characterized in that, The 3D printing material is carbon fiber composite material, and the binder is epoxy resin.

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