A prestressed FRP tendon for clip anchoring and a preparation method thereof

Abstract

The present invention discloses a prestressed FRP tendon that can be used for clip anchoring and a preparation method thereof, wherein the middle section is FRP tendons, and the two ends are transitioned from FRP tendons to steel strands through a transition zone. The middle section FRP tendons are made of a resin matrix and a fiber reinforced composite material through a pultrusion process; the inner core of the transition zone is a prestressed steel strand, and the outer portion is wrapped with FRP fiber filaments; the two ends are steel strands or high-strength steel wires, forming a new type of prestressed FRP tendons that can be used for clip anchoring. The invention can be used as a prestressed tendon, and when anchoring, the steel strands or high-strength steel wires at the two ends are anchored. Its mechanical properties have all the advantages of FRP tendons, and avoid the problem of difficult anchoring of FRP tendons due to low shear strength.

Description

Technical Field

[0001] The invention relates to the technical field of prestressed fasteners, and in particular to a prestressed FRP tendon that can be used for clip anchoring and a preparation method thereof. Background Art

[0002] At present, plates, bars, cables, etc. have been widely used in civil engineering. In existing research, there are many ideas to apply FRP materials to large-span and super-large-span bridges. The light weight and high strength of FRP materials can effectively solve the sag effect caused by the deadweight of steel cables and greatly increase the theoretical limit span of bridges. At the same time, FRP cables are more suitable for harmful environments such as across rivers and seas, where humidity and high chloride ion concentration are high.

[0003] However, due to the low shear strength of FRP materials (fiber reinforced composite materials), its anchoring has always been a bottleneck problem restricting its application in the field of prestressed cables. At present, the anchoring system of FRP cables can be divided into two categories based on the anchoring force mechanism: mechanical clamping type and bonding type. Mechanical clamping anchors are similar to steel strand clip anchors. They rely on the pressure exerted by the clips on the FRP bars to produce clamping effects. The advantages are flexible design and convenient construction. The disadvantages are that the clips are prone to produce concentrated stress during the clamping process, causing damage to the FRP bars and causing shear failure of the FRP bars in the anchoring area, while the ideal failure mode should not occur in the anchoring area. Bonding anchors are filled with resin or other bonding materials in a sleeve-like device, and the shear force is transmitted through the bonding force, friction and mechanical bite force between the bonding material and the FRP cable. The advantages are mature technology and high anchoring reliability. The disadvantages are that the anchor is long and not suitable for large loads and light round bars.

[0004] In the current public technology, FRP is generally wrapped along the entire longitudinal length of the steel strand or steel bar, taking advantage of the high strength, low elastic modulus, light weight, and corrosion resistance of FRP, which complements the low strength, high elastic modulus, large weight, and corrosion resistance of steel. Through the principle of material mixing, a composite reinforcement material with high strength, high elastic modulus, medium quality, and corrosion resistance is formed. It can be seen that the purpose of the invention of the hybrid reinforcement is mainly to solve the defects of the low elastic modulus of FRP materials and the defects of the corrosion resistance of steel. The mechanical properties of the finished product have both the properties of steel and FRP materials.

[0005] However, the inner core of the above-mentioned FRP-steel composite reinforcement is steel, and the outer surface is wrapped with FRP material. When used in prestressed structures, anchors matching the FRP material are required, which cannot solve the FRP anchoring problem. Summary of the invention

[0006] The purpose of the present invention is to propose a new type of prestressed FRP tendon that can be used for clip anchoring and a preparation method thereof, and to replace the end of the FRP material with a steel cable segment by utilizing the material mixing principle and the bonding principle, so as to give full play to the respective advantages of FRP and steel strands, make up for the mechanical and chemical property defects of each material, and solve the anchoring problem of the FRP cable.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] A prestressed FRP tendon that can be used for clip anchoring, characterized in that it includes a middle FRP segment, steel cable segments at both ends, and a transition segment connecting the FRP segment and the steel cable segment; the FRP segment is formed by FRP fiber bundles being dipped in a resin matrix and heated and cured; the transition segment is formed by bonding the steel cable at the end of the steel cable segment to the FRP fiber bundle at the end of the FRP segment, the steel cable is located at the center of the FRP fiber bundle, and the FRP fiber bundle is evenly bonded around the steel cable along the central axis of the steel cable, and the bonding method is heated and cured. The ratio of steel strands and FRP can be designed according to different usage targets.

[0009] As a preferred technical solution of the present invention, in the transition section, the FRP fiber filaments surrounding the steel cable are arranged in layers from the inside to the outside, and progressive bonding overlap is adopted. The overlap length of the inner layer of FRP fiber filaments is longer than that of the outer layer, that is, the overlap length of the FRP fiber filaments close to the core material is long, and the farther from the core material in the diameter direction, the shorter the overlap length, which can effectively prevent peeling.

[0010] Furthermore, a wrapping tape may be included, wherein the wrapping tape is an FRP wrapping wire, an FRP wrapping bundle or an FRP wrapping tape, or other matching materials, which is wrapped around the outside of the transition section. The bonding method is heat curing, and the purpose is also to prevent peeling.

[0011] Wherein, the FRP fiber bundle is a bundle of carbon fiber, glass fiber, aramid fiber or basalt fiber material.

[0012] Furthermore, the resin matrix is ​​a thermosetting resin matrix or a thermoplastic resin matrix.

[0013] Furthermore, the steel cable segment may be a high-strength steel wire or a high-strength steel bar.

[0014] In addition, the present invention also provides a method for preparing the above-mentioned prestressed FRP tendons that can be used for clip anchoring, which is characterized by comprising the following steps:

[0015] Step 1: Yarn feeding: pull the FRP raw yarn bundle out from the yarn feeding frame;

[0016] Step 2: Dipping: Place the resin matrix in the dipping tank, and fully soak the pulled FRP raw yarn bundle through the dipping tank;

[0017] Step 3: Pass the yarn through the yarn plate: pass the fully soaked fiber raw yarn through the yarn through the yarn plate;

[0018] Step 4: FRP reinforcement forming: The fiber raw yarn passes through the yarn threading plate and enters the forming mold to form the FRP reinforcement;

[0019] Step 5: Heat and solidify to prepare FRP segments: The formed FRP bars are heated and solidified by a heating device to form FRP segments;

[0020] Step 6: Add steel strands: When the middle FRP section reaches the specified length, insert the steel strands into the middle of the threading plate. At this time, the FRP tow will be wrapped around the outside of the steel strands and extruded through the forming die together;

[0021] Step 7: Transition section forming: The formed steel strand and the transition section composed of the FRP tow wrapped around the outside of the steel strand are solidified and formed together through a heating device;

[0022] Step 8, stop feeding the FRP tow: when the transition section reaches the designed length, cut off the fiber raw tow and stop feeding the FRP tow;

[0023] Step 9: Cutting the steel strands: Continue to feed the steel strands until the cable segment reaches the specified length and then cut the steel strands. At this point, the preparation of the prestressed FRP tendons is completed.

[0024] The ultimate tensile bearing capacity of the FRP segment reinforcement is F FRP , the ultimate bearing capacity of the cable segment F Steel , the ultimate tensile bearing capacity of the transition section is F T , the three satisfy F T >F Steel >F FRP .

[0025] The main working principle of the present invention is to utilize the bonding performance between the steel strand and the FRP resin matrix to transition the FRP to the steel strand at the end through the transition zone, which can solve the problem of difficult FRP anchoring. The anchoring of the cable is achieved by anchoring the high-strength steel wires or steel strands at both ends, and the FRP section and the high-strength steel wire or steel strand are transitioned through an overlap section. The axial tension of the cable is transmitted through the bonding force of the overlap section. Through the transition section, the FRP material is transitioned to steel, and the anchoring of the steel replaces the anchoring of the FRP material, which completely avoids the anchoring problem of the FRP cable.

[0026] Compared with the prior art, the technical advantages of the present invention are:

[0027] The present invention does not mix steel and FRP along the entire length of the reinforcement, but only transitions the FRP to steel strands through a transition zone at the end of the FRP. The cable of the present invention has all the performance advantages of the FRP material, and only needs to anchor the steel strand material instead of the FRP in the end anchoring area.

[0028] The reinforcement material of the present invention can be used for materials such as prestressed bridge cables that require anchoring at the ends. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or other aspects and advantages of the present invention will become clearer and easier to understand through the detailed description made in conjunction with the following drawings, which are only exemplary and do not limit the present invention, wherein:

[0030] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0031] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0032] Figure 3 This is a structural diagram of Example 3 of the present invention.

[0033] Reference numerals: 1 - FRP segment, 2 - steel cable segment, 3 - transition segment, 4 - winding belt. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the prestressed FRP tendons that can be used for clip anchoring and the preparation method thereof of the present invention will be described with reference to the accompanying drawings. The embodiments described herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention, are illustrative and exemplary, and should not be interpreted as limiting the embodiments of the present invention and the scope of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims and the specification of this application, including technical solutions that adopt any obvious replacement and modification of the embodiments described herein.

[0035] The drawings of this specification are schematic diagrams, which assist in explaining the concept of the present invention and schematically show the shapes of various parts and their mutual relationships. Please note that in order to clearly show the structures of various components of the embodiments of the present invention, the drawings are not drawn according to the same scale. The same reference numerals are used to represent the same parts.

[0036] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. Figure 1The present invention is a structural schematic diagram of embodiment 1, a prestressed FRP tendon that can be used for clip anchoring, including a middle FRP segment 1, steel cable segments 2 at both ends, and a transition segment 3 connecting the FRP segment 1 and the steel cable segment 2; the FRP segment 1 is formed by FRP fiber bundles 4 being dipped in a resin matrix and heated and cured; the transition segment 3 is formed by bonding the steel cable at the end of the steel cable segment 2 and the FRP fiber bundle at the end of the FRP segment 1, the steel cable is located at the center of the FRP fiber bundle, the FRP fiber bundle is uniformly bonded around the steel cable along the central axis of the steel cable, and is longitudinally wrapped along the steel strand, and the bonding method is heated and cured. The ratio of the steel strand and the FRP can be designed according to different usage targets. The FRP fiber bundle is a bundle of carbon fiber, glass fiber, aramid fiber or basalt fiber material. The resin matrix is ​​a thermosetting and thermoplastic resin matrix. The steel cable segment 2 is a high-strength steel wire or a high-strength steel bar.

[0037] like Figure 2 This is a structural schematic diagram of Example 2 of the present invention. In the transition section 3 of this embodiment, the FRP fiber filaments surrounding the steel cable are arranged in layers from the inside to the outside, and a progressive bonding overlap is adopted. The overlap length of the inner layer of FRP fiber filaments is longer than that of the outer layer. That is, the overlap length of the FRP close to the core material is long, and the farther away from the core material in the diameter direction, the shorter the overlap length is to prevent peeling.

[0038] like Figure 3 This is a structural schematic diagram of Example 3 of the present invention. In addition to all the structures of Example 1, this embodiment also includes a wrapping tape 4, which is an FRP wrapping wire, FRP wrapping bundle or FRP wrapping tape, or other matching materials, wrapped around the outside of the transition section 3, and the bonding method is heating and curing.

[0039] The ratio of steel strands to FRP should be designed based on tensile strength so that the ultimate tensile bearing capacity of FRP segment 1 is FRP Lower than the ultimate bearing capacity F of cable segment 2 Steel , as shown in formula (1), so that the damage does not occur in the steel strand area.

[0040] F FRP <F Steel (1)

[0041] The length of the transition section should be designed based on the bond strength so that the bond strength is higher than the strength of the steel cable section 2 and the FRP section 1, as shown in formula (2), so that failure does not occur in the transition area.

[0042] F T >F Steel >F FRP (2)

[0043] The present application can be manufactured by the following method, and the middle FRP segment 1 can adopt the common FRP reinforcement manufacturing process, that is, yarn feeding, dipping, molding and heating curing. The specific steps are: ① Pull out the FRP raw yarn bundle from the yarn rack; ② Place the resin matrix in the dipping tank, and fully infiltrate the pulled FRP raw yarn bundle through the dipping tank; ③ Pass the fully infiltrated fiber raw yarn through the yarn feeding plate; ④ After the fiber raw yarn passes through the yarn feeding plate, it enters the forming mold for molding; ⑤ The formed FRP reinforcement is heated and cured by a heating device to form the FRP segment 1; ⑥ When the middle FRP segment 1 is made to a specified length, the steel strand is inserted into the middle of the yarn feeding plate, at this time, the FRP strand will be wound around the outside of the steel strand, and together through the molding die extrusion molding; ⑦ The transition segment composed of the formed steel strand and the FRP strand wound around the outside of the steel strand is cured and formed together by a heating device; ⑧ When the transition segment 3 reaches the designed length, the fiber raw yarn bundle is cut off, and the feeding of the FRP strand is stopped; ⑨ The steel strand is continuously fed until the specified length is reached and then the steel strand is cut off.

[0044] In the transition section 3, the steel strand and the FRP fiber bundle that has been impregnated are simultaneously fed into the forming mold, and the steel strand in the center of the transition section and the surrounding FRP fiber bundles are combined into one by pultrusion and heating curing. When the length of the transition section is met, the FRP fiber bundle is stopped from being fed into the mold, and the steel strand is continuously fed to a certain length, and finally a wrapping belt 4 can be added on the outermost side.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A prestressed FRP tendon that can be used for clip anchoring, characterized in that: The invention comprises a middle FRP section (1), steel cable sections (2) at both ends, and a transition section (3) connecting the FRP section (1) and the steel cable section (2); the FRP section (1) is formed by dipping an FRP fiber bundle in a resin matrix and heating and curing; the transition section (3) is formed by bonding a steel cable at the end of the steel cable section (2) to an FRP fiber bundle at the end of the FRP section (1); the steel cable is located at the center of the FRP fiber bundle, and the FRP fiber bundle is uniformly bonded to the periphery of the steel cable along the central axis of the steel cable, and the bonding method is heating and curing; in the transition section (3), the FRP fiber filaments surrounding the steel cable are arranged in layers from the inside to the outside, and are overlapped by progressive bonding, and the overlap length of the inner layer of the FRP fiber filament layer is longer than that of the outer layer; and the invention also comprises a winding belt (4).

2. A prestressed FRP tendon for clip anchoring according to claim 1, characterized in that: The wrapping tape (4) is an FRP wrapping wire, an FRP wrapping bundle or an FRP wrapping tape that is wrapped around the outside of the transition section (3), and the bonding method is heating and curing.

3. The prestressed FRP tendon that can be used for clip anchoring according to claim 1, characterized in that: The FRP fiber bundle is a bundle of carbon fiber, glass fiber, aramid fiber or basalt fiber material.

4. The prestressed FRP tendon that can be used for clip anchoring according to claim 1, characterized in that: The resin matrix is ​​a thermosetting resin matrix and a thermoplastic resin matrix.

5. The prestressed FRP tendon that can be used for clip anchoring according to claim 1, characterized in that: The steel cable segment (2) is a high-strength steel wire or a high-strength steel bar.

6. A method for preparing a prestressed FRP tendon for clip anchoring according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: Yarn feeding: pull the FRP raw yarn bundle out from the yarn feeding frame; Step 2: Dipping: Place the resin matrix in the dipping tank, and fully soak the pulled FRP raw yarn bundle through the dipping tank; Step 3: Pass the yarn through the yarn plate: pass the fully soaked fiber raw yarn through the yarn through the yarn plate; Step 4: FRP reinforcement forming: The fiber raw yarn passes through the yarn threading plate and enters the forming mold to form the FRP reinforcement; Step 5: Heating and curing: The formed FRP ribs are heated and cured by a heating device to form FRP segments; Step 6: Add steel strands: When the middle FRP section reaches the specified length, insert the steel strands into the middle of the threading plate. At this time, the FRP tow will be wrapped around the outside of the steel strands and extruded through the forming die together; Step 7: Forming the transition section (3): The formed steel strand and the transition section composed of the FRP strands wound around the outside of the steel strand are cured together by a heating device; Step 8, stop feeding the FRP tow: when the transition section (3) reaches the designed length, cut off the fiber raw tow and stop feeding the FRP tow; Step 9: Cutting the steel strands: Continue to feed the steel strands until the cable segment reaches the specified length and then cut the steel strands. At this point, the preparation of the prestressed FRP tendons is completed.

7. The method for preparing a prestressed FRP tendon that can be used for clip anchoring according to claim 6, characterized in that: The ultimate tensile bearing capacity of the FRP segment reinforcement is F FRP , the ultimate bearing capacity F of the cable segment (2) Steel , the ultimate tensile bearing capacity of the transition section is F T , the three satisfy F T＞ F Steel＞ F FRP .

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