Steel, reinforced concrete pile reinforced structure and method

Abstract

The application discloses a kind of for steel, reinforced concrete pile reinforcing structure and method, structure includes: FRP sleeve, FRP sleeve is at least by two arc FRP sheet splicing and is formed into;Sleeve fixing assembly, sleeve fixing assembly is used to install on the pile body to be reinforced, and sleeve fixing assembly is connected with FRP sleeve, and FRP sleeve is fixed;Plugging plate, it is set in the bottom of FRP sleeve, for the opening of FRP sleeve bottom plugging. Utilize the lightweight high-strength characteristics of FRP material, sheet unit light weight, easily carry, greatly reduce the dependence on large hoisting equipment, especially suitable for tidal area and other construction window short, operation space limited harsh environment.FRP material inherent corrosion resistance makes sleeve can resist seawater chloride ion erosion for a long time, avoids the corrosion problem of steel formwork or reinforcing member.Field assembly mode improves construction flexibility, can realize fast assembly, significantly improve the efficiency, durability and comprehensive economy of reinforcing engineering.

Description

Technical Field

[0001] This invention relates to the field of composite material applications, and in particular to a structure for reinforcing steel and reinforced concrete piles. Background Technology

[0002] In ports, wharves, cross-sea bridges, and near-shore structures, steel piles and reinforced concrete piles serve as foundation load-bearing components, and their long-term durability and safety directly affect the service life and operational safety of the entire project. However, these structures are subjected to the harsh dual challenges of the marine environment: first, chemical and electrochemical corrosion from chloride ions, oxygen, and microorganisms in seawater; and second, physical erosion and fatigue loads from waves, ice floes, and ship impacts. Extensive engineering practice and research have shown that pile foundation damage exhibits distinct regional characteristics. Pile sections located in areas of fluctuating water levels (especially tidal zones and splash zones) experience a much higher corrosion rate than sections that are constantly submerged underwater or exposed to the atmosphere, often becoming the weakest link in the overall structural safety.

[0003] Currently, the repair and reinforcement of such damaged pile foundations traditionally relies on the following methods, but all of them have significant limitations: 1. Traditional cross-section enlargement method: This requires binding steel bars around the old pile, erecting formwork, pouring concrete, and curing. In tidal areas, construction is limited by water levels, requiring the construction of expensive temporary cofferdams, resulting in short effective working time and a long construction period. The newly added concrete layer itself faces the risk of chloride ion penetration and steel bar corrosion in the marine environment, failing to fundamentally solve the durability problem and potentially creating a cycle of "reinforcing after damage." Significantly increasing the pile cross-section may require a reassessment of the foundation bearing capacity. 2. Steel plate bonding method: The steel plate itself requires extremely strict anti-corrosion treatment, and in humid and salt spray environments, the anti-corrosion layer is easily damaged, and the steel plate will rust rapidly, resulting in a short lifespan of reinforcement and high subsequent maintenance costs. It requires high standards for pile foundation surface treatment, and the bonding quality is easily affected by the humid environment and construction process, posing a risk of peeling. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a structure for reinforcing steel and reinforced concrete piles.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a structure for reinforcing steel and reinforced concrete piles, comprising: FRP sleeve, wherein the FRP sleeve is formed by splicing two arc-shaped FRP sheets end to end; A casing fixing assembly is used to install on the pile body to be reinforced, and the casing fixing assembly is connected to the FRP casing to fix the FRP casing. A sealing plate is installed at the bottom of the FRP sleeve to seal the bottom opening of the FRP sleeve.

[0006] The above technical solution, which uses at least two curved FRP sheets assembled on-site to form an FRP sleeve, solves the problems of difficult transportation and inability to install in confined spaces inherent in traditional integral sleeves. This solution fully leverages the lightweight and high-strength properties of FRP material; the sheet units are lightweight and easy to handle, significantly reducing reliance on large hoisting equipment, making it particularly suitable for harsh environments with short construction windows and limited working space, such as tidal zones. Simultaneously, the inherent corrosion resistance of FRP material allows the sleeve to withstand long-term chloride ion corrosion from seawater, fundamentally avoiding the corrosion problems of steel formwork or reinforcement components. The on-site assembly method not only improves construction flexibility, adapting to different pile diameters and shapes, but also enables rapid assembly through modular design, significantly improving the efficiency, durability, and overall economic benefits of reinforcement projects.

[0007] As a preferred embodiment of the present invention, the inner wall of the arc-shaped FRP sheet is provided with protruding ribs, and the ribs and the arc-shaped FRP sheet are integrally formed.

[0008] The above technical solution, which integrally forms raised ribs on the inner wall of the curved FRP sheet, has a dual effect: Firstly, the ribs act as reinforcing ribs, significantly enhancing the axial and circumferential stiffness of the FRP sheet itself, making it less prone to deformation during handling, installation, and under the lateral pressure of concrete, thus ensuring the geometric stability of the reinforced structure. Secondly, after concrete is poured, these ribs embed into the concrete, forming a strong mechanical interlocking effect, effectively preventing interface slippage between the FRP sleeve and the concrete filling layer under complex loads, ensuring that the new and old materials can work together under the same load.

[0009] As a preferred embodiment of the present invention, insert blocks and slots are respectively provided at both ends of the circumferential direction of the arc-shaped FRP sheet. When two adjacent arc-shaped FRP sheets are spliced, the splicing is completed by inserting the insert blocks into the slots.

[0010] The above technical solution, employing a tongue-and-groove connection between inserts and slots, provides a rapid and precise positioning benchmark for the on-site assembly of FRP sheets. Preliminary assembly and fixation of the sheets can be achieved before tightening the bolts, simplifying high-altitude or underwater operations and improving construction efficiency. This tortuous joint path, combined with sealing materials, forms multiple leak-proof barriers, effectively preventing the loss of cement grout during grouting, ensuring the density of the filled concrete, and thus guaranteeing the integrity and final strength of the reinforced structure.

[0011] As a preferred embodiment of the present invention, the sleeve fixing component includes a clamp for fixing to the pile body to be reinforced. A plurality of connecting plates are also provided in the circumference of the clamp, and the connecting plates are also connected to the ribs of the inner wall of the arc-shaped FRP sheet.

[0012] By using the above technical solution, and by setting up a sleeve fixing assembly that includes clamps and connecting plates, and connecting the connecting plates to the ribs on the inner wall of the FRP sheet, not only can the FRP sleeve be reliably fixed on the old pile, preventing it from floating or shifting during concrete pouring, but it can also transfer the horizontal force (such as wave force) borne by the old pile to the FRP sleeve and the filling concrete through the connecting plates, so that the three form a whole to jointly resist bending moment and shear force, greatly improving the overall stiffness and bearing capacity of the reinforced pile foundation.

[0013] As a preferred embodiment of the present invention, a connecting hole is provided on the rib, and a waist-shaped hole is provided on the connecting plate, wherein the connecting plate and the rib are fixedly connected by bolts.

[0014] The above technical solution involves setting connection holes on the ribs and oblong holes on the connecting plate. Bolts are used for connection, and the oblong holes allow for a certain range of relative movement between the connecting plate and the ribs before bolt tightening. This allows workers to precisely adjust the circumferential position and verticality of the FRP sleeve, ensuring its concentricity with the existing pile and resulting in a uniform thickness of the surrounding infill concrete layer. This not only optimizes the load-bearing performance but also simplifies the installation process and reduces installation difficulty.

[0015] As a preferred embodiment of the present invention, one end of the connecting plate is fixedly connected to the rib, and the other end is rotatably connected to the clamp, and can be locked with the clamp.

[0016] The above technical solution designs the connecting plate and clamp as a rotatable connection, allowing the connecting plate to swing freely within a certain angle range. This effectively adapts to potential unevenness on the surface of the old pile or compensates for minor deviations that are unavoidable during installation. It ensures that even when the pile body is not a perfectly cylindrical shape, the connecting plate maintains good contact with the ribs on the inner wall of the FRP sleeve, achieving an effective connection and improving the reliability of the project.

[0017] As a preferred embodiment of the present invention, the sealing plate includes two semi-circular base plates, which are further connected to the clamp via a connecting rod.

[0018] The above technical solution connects the sealing plate to the clamp via a connecting rod, allowing the installation of the sealing plate and the clamp to be carried out simultaneously, simplifying the operation. When closing the clamp, the connecting rod can drive the sealing plate to be accurately positioned and pressed against the bottom of the pile, effectively sealing the opening at the bottom of the FRP sleeve and preventing concrete grout leakage. This not only eliminates the cumbersome process of separately installing and fixing the base plate, but also improves the reliability of the bottom seal and construction efficiency.

[0019] As a preferred embodiment of the present invention, the semi-circular base plate is provided with a positioning groove for installing the FRP sleeve.

[0020] The above technical solution involves setting a V-shaped positioning groove on the bottom plate of the sealing plate. When the FRP sleeve is lowered, its bottom will naturally embed into the V-shaped groove, achieving automatic centering and ensuring the concentricity of the FRP sleeve and the old pile. At the same time, the V-shaped structure has better guiding and supporting functions, which can more effectively transfer the weight of the FRP sleeve to the bottom plate, enhancing the stability during installation.

[0021] This invention also discloses a method for reinforcing steel and reinforced concrete piles, comprising the following steps: Step S01: Clean the surface of the pile to be reinforced; Step S02: Install the sleeve fixing assembly on the surface of the reinforced pile; install the sealing plate at the lowest point of the pile to be reinforced. Step S03: Prepare at least two curved FRP sheets for splicing, splice the curved FRP sheets into an FRP sleeve, and fit it onto the outer periphery of the pile to be reinforced. Step S04: Abut the lower end of the assembled FRP sleeve against the sealing plate, and fix the FRP sleeve to the sleeve fixing assembly; Step S05: Inject concrete or resin concrete into the cavity formed between the FRP sleeve and the pile to be reinforced.

[0022] Through the above technical solution, the reinforcement method solves most of the technical difficulties in the factory by cleaning, installing fixing components and sealing plates, assembling FRP sleeves, and finally fixing and grouting. The on-site operation process is clear and simple, which significantly reduces the stringent requirements on the technical level of workers and the on-site working environment. It is particularly suitable for safe, efficient and reliable pile foundation reinforcement in marine environments with short time windows and harsh conditions, such as tidal zones.

[0023] As a preferred embodiment of the present invention, in step S05, the FRP sleeve is fixed to the sleeve fixing assembly by connecting the ribs on the inner wall of the FRP sleeve to the sleeve fixing assembly.

[0024] The above technical solution connects the FRP sleeve's inner wall ribs to the sleeve fixing components, ensuring that shear force can be effectively transferred between the old and new structures. This tightly integrates the FRP sleeve, filling concrete, and old pile into a composite whole, allowing them to jointly bear the load.

[0025] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention employs spliced ​​FRP sleeves for reinforcement. FRP material itself possesses excellent resistance to chloride ion and salt spray corrosion, providing a robust protective sleeve for the internal old pile and filling concrete. This fundamentally prevents re-corrosion of the reinforced section and addresses the durability shortcomings of traditional steel reinforcement. This structure, through the mechanical interlocking of ribs and concrete, and the shear-resistant connection of clamps and connecting plates, tightly integrates the FRP sleeve, filling concrete, and old pile into a cohesive composite pile. This structure not only effectively restores the cross-sectional stiffness lost due to corrosion but also, through the circumferential constraint of the FRP sleeve, places the core concrete under triaxial compression, thereby significantly improving the pile's compressive bearing capacity and deformation capacity (ductility). This allows it to more effectively resist accidental loads such as waves and ship impacts, ensuring the long-term reliability of the reinforcement effect.

[0026] 2. This invention solves the construction challenges of pile foundation reinforcement in harsh marine environments such as tidal zones and splash zones by using prefabricated sheets and modular tooling. The main manufacturing processes are completed in the factory, producing high-quality curved FRP sheets, clamp fixing components, and sealing plates, among other standard components. On-site construction is simplified to clear steps: cleaning, tooling installation, assembly, fixing, and grouting. This construction method requires less reliance on large lifting equipment, significantly reduces operation time, and fully utilizes the brief construction window during low tide. It reduces the difficulty of underwater or high-altitude operations and the stringent skill requirements for workers, thereby significantly improving construction efficiency, safety, and adaptability to complex environments while ensuring the final structural quality. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of steel and reinforced concrete pile reinforcement.

[0028] Figure 2 This is a top view of the structure of the present invention used for reinforcing steel and reinforced concrete piles.

[0029] Figure 3 This is a schematic diagram of the structure of the arc-shaped FRP sheet of the present invention.

[0030] Figure 4 This is the present invention. Figure 3 Enlarged view of part A.

[0031] Figure 5 This is a schematic diagram of the structure after the sleeve fixing assembly is installed on the pile to be reinforced.

[0032] Figure 6 This is the present invention. Figure 5 Enlarged view of part B.

[0033] Explanation of reference numerals in the attached drawings: 1. FRP sleeve; 2. Sleeve fixing assembly; 3. Pile to be reinforced; 4. Foundation; 5. Sealing plate; 11. Curved FRP sheet; 12. Rib; 13. Slot; 14. Insert block; 15. Connecting hole; 21. Clamp; 22. Connecting plate; 23. Waist-shaped hole; 24. Connecting rod; 51. Base plate; 52. Positioning groove. Detailed Implementation

[0034] The following is in conjunction with the appendix Figure 1-6 The present invention will be described in further detail below.

[0035] Example 1: This embodiment discloses a structure for reinforcing steel and reinforced concrete piles, mainly used for reinforcing support piles in ports, wharves, cross-sea bridges, and near-shore structures, such as... Figure 1 As shown, the upper end of the pile body 3 that needs to be reinforced is connected to the pile cap 4, and the lower end is driven into the foundation on the seabed. The part that needs to be reinforced is a distance above and below the water surface. This part is located in the water level fluctuation zone. Due to the harsh environment of alternating wet and dry conditions, rich oxygen, and concentrated salt, the corrosion rate of the pile body is much higher than that of sections that are submerged underwater for a long time or exposed to the atmosphere.

[0036] like Figures 2 to 6 This embodiment of a structure for reinforcing steel and reinforced concrete piles includes an FRP sleeve 1, a sleeve fixing assembly 2, and a sealing plate 5.

[0037] The FRP sleeve 1 is formed by splicing two curved FRP sheets 11 circumferentially end to end. The curved FRP sheets 11 are integrally formed using a pultrusion process to ensure high strength and high corrosion resistance. (Reference) Figure 3 and Figure 4 Each curved FRP sheet 11 has two axially extending raised ribs 12 on its inner wall. These ribs 12 are formed in one step with the sheet body during the pultrusion process, greatly enhancing the rigidity of the curved FRP sheet 11. In this embodiment, the rib 12 has a T-shaped cross-section. The T-shaped rib 12 not only enhances the rigidity of the curved FRP sheet 11, but also ensures that when concrete is poured between the FRP sleeve 1 and the pile 3 to be reinforced, the concrete can be tightly bonded to the curved FRP sheet 11, preventing the curved FRP sheet 11 from slipping off the concrete layer.

[0038] A continuous slot 13 is formed on one longitudinal edge of the curved FRP sheet 11, and an insert 14 matching the shape of the slot 13 is formed on the other longitudinal edge. During assembly, the insert 14 of one curved FRP sheet 11 is aligned and inserted into the slot 13 of the adjacent curved FRP sheet 11, which can achieve rapid initial positioning and closing, and effectively prevent grout leakage during subsequent injection.

[0039] like Figure 5 and Figure 6 As shown, the sleeve fixing assembly 2 includes clamps 21. Each clamp 21 consists of two semi-circular steel rings fastened to a predetermined height on the pile body 3 to be reinforced by high-strength bolts. The number of clamps 21 is determined by the length of the curved FRP sheet 11. If the curved FRP sheet 11 is long and heavy, multiple clamps can be used. In this embodiment, two clamps 21 are provided on the pile body 3 to be reinforced. In this embodiment, multiple (10 in this embodiment) connecting plates 22 are evenly connected to the outer circumferential wall of the clamps 21 above the pile body 3 via hinges. Each connecting plate 22 has an elongated waist-shaped hole 23. Correspondingly, connecting holes 15 are pre-drilled on the ribs 12 of the inner wall of each curved FRP sheet 11. The waist-shaped holes 23 on the connecting plates 22 are fixed to the connecting holes 15 by bolts, thereby fixing the curved FRP sheet 11 to the pile body 3 to be reinforced.

[0040] A connecting rod 24 is fixed to the clamp 21 below the pile 3 to be reinforced. One end of the connecting rod 24 is fixed to the clamp 21, and the other end is connected to the sealing plate 5. The sealing plate 5 consists of two semi-circular base plates 51. The upper surface of each base plate 51 is provided with an arc-shaped positioning groove 52, the curvature of which matches the outer diameter of the FRP sleeve 1, for supporting and limiting the FRP sleeve 1. The cross-section of the positioning groove 52 is a V-shaped structure (large opening at the upper end and small opening at the lower end).

[0041] During assembly, first fasten the two clamps 21 to the pile body 3 respectively, and then lower the two bottom plates 51 of the sealing plate 5 through the connecting rod 24 to close at the bottom of the pile.

[0042] Then, two arc-shaped FRP sheets 11 are wrapped around the pile body and initially assembled using the interlocking of inserts 14 and slots 13 to form an FRP sleeve 1. The lower end of the sleeve is placed in the positioning groove 52 of the base plate 51. Next, the position of the FRP sleeve 1 is adjusted so that the connecting holes 15 on its ribs 12 align with the oblong holes 23 on the connecting plate 22. Bolts are then inserted and tightened. The oblong hole 23 allows for fine-tuning during installation to ensure that the FRP sleeve 1 is concentric with the old pile body 3. Finally, high-strength micro-expansion cement mortar, or resin-containing concrete, is injected into the cavity between the FRP sleeve 1 and the old pile body 3. After curing and hardening, a robust composite reinforcement structure that works in tandem with the original pile is formed.

[0043] Example 2: This embodiment details a method for reinforcing steel and reinforced concrete piles based on the structure described in Embodiment 1. This method is particularly suitable for reinforcing corroded reinforced concrete piles in tidal environments, and specifically includes the following steps: Step S01, Cleaning and treatment of pile surface: When the pile body is exposed at low tide, use a high-pressure water gun or mechanical tools to thoroughly clean the surface of the reinforced section of the pile body 3, removing attached marine organisms, loose concrete, corrosion products, and old coatings until a solid base layer is exposed. For exposed reinforcing bars, rust removal and rust prevention treatment are required.

[0044] Step S02: Install the sleeve fixing assembly and sealing plate: As attached Figure 5 and 6 As shown, at the designed elevation of the cleaned pile body 3 (usually located 1 meter below the estimated maximum corrosion depth), the sleeve fixing assembly 2 is installed. First, the two semi-circular rings of the clamp 21 are fitted onto the pile body, and the connecting bolts are initially tightened. Then, the two semi-circular bottom plates 51 of the sealing plate 5 are tightly closed as the clamp 21 below closes, forming a bottom seal. At this time, the two clamps 21, the connecting rod 24, and the sealing plate 51 form a temporary support frame.

[0045] Step S03, Assembly and placement of FRP sleeve: As attached Figure 2 , 3 As shown in Figure 4, the prefabricated curved FRP sheet 11 is transported to the site. Workers wrap two FRP sheets 11 around the pile body and precisely slide the insert 14 on one curved FRP sheet 11 into the slot 13 of the other sheet. This process utilizes tongue-and-groove joints to achieve rapid initial positioning and assembly. After assembly and assembly, a complete FRP sleeve 1 is formed, which is slowly lowered so that its bottom rests stably in the positioning groove 52 of the sealing plate 51.

[0046] Step S04, Final fixing of FRP sleeve and fixing components: This is a crucial step in ensuring the overall structural integrity. (See attached image) Figure 6 As shown, adjust the circumferential and axial positions of the FRP sleeve 1 so that the connecting hole 15 on its inner wall rib 12 aligns with the slotted hole 23 on the connecting plate 22. Due to the adjustment margin provided by the slotted hole 23, the final position of the FRP sleeve 1 can be fine-tuned to ensure its concentricity with the existing pile body 3. Then, insert high-strength stainless steel bolts and tighten them with a torque wrench to the preset torque, thereby firmly fixing the FRP sleeve 1 to the pile body 3. This mechanical connection not only serves a positioning function but is also an important shear-resistant connection.

[0047] Step S05: Injecting filler material: A grouting port and a vent hole are provided at the top of the FRP sleeve 1. High-strength cement-based grout or resin concrete with high fluidity, micro-expansion, and corrosion resistance is pressure-injected into the cavity between the FRP sleeve 1 and the old pile body 3 through the grouting port. The grouting should be continuous until grout overflows from the vent hole, ensuring the cavity is densely filled without voids.

[0048] Step S06, Curing and Shaping: After grouting is completed, the grout is cured underwater using conventional methods. Once its strength reaches the design requirements, the reinforcement structure is considered complete. The FRP sleeve 1 serves as a permanent formwork and protective layer, and together with the internal concrete filling and the original pile body, forms a composite pile foundation with significantly improved bearing capacity and durability.

[0049] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A structure for reinforcing steel and reinforced concrete piles, characterized in that, include: FRP sleeve (1), the FRP sleeve is made of at least two arc-shaped FRP sheets (11) spliced ​​end to end; Sleeve fixing assembly (2), the sleeve fixing assembly (2) is used to be installed on the pile body (3) to be reinforced, and the sleeve fixing assembly (3) is connected to the FRP sleeve (1) to fix the FRP sleeve (1); A sealing plate (5) is provided at the bottom of the FRP sleeve (1) to seal the bottom opening of the FRP sleeve (1).

2. The structure for reinforcing steel and reinforced concrete piles according to claim 1, characterized in that: The inner wall of the arc-shaped FRP sheet (11) is provided with protruding ribs (12), and the ribs (12) and the arc-shaped FRP sheet (11) are integrally formed.

3. The structure for reinforcing steel and reinforced concrete piles according to claim 1 or 2, characterized in that: Insertion blocks (14) and slots (13) are respectively provided at both ends of the circumferential direction of the arc-shaped FRP sheet (11). When two adjacent arc-shaped FRP sheets (11) are spliced, the splicing is completed by inserting the insertion blocks (14) into the slots (13).

4. The structure for reinforcing steel and reinforced concrete piles according to claim 2, characterized in that: The sleeve fixing component (2) includes a clamp (21), which is used to fix the pile body (3) to be reinforced. Multiple connecting plates (22) are also provided in the circumference of the clamp (21). The connecting plates (22) are also connected to the ribs (12) on the inner wall of the arc-shaped FRP sheet (11).

5. The structure for reinforcing steel and reinforced concrete piles according to claim 4, characterized in that: A connecting hole (15) is provided on the rib (11), and a waist-shaped hole (23) is provided on the connecting plate (22). The connecting plate (22) and the rib (12) are fixedly connected by bolts.

6. The structure for reinforcing steel and reinforced concrete piles according to claim 5, characterized in that: One end of the connecting plate (23) is fixedly connected to the rib (12), and the other end is rotatably connected to the clamp (21).

7. The structure for reinforcing steel and reinforced concrete piles according to claim 4, characterized in that: The sealing plate (5) includes two semi-circular base plates (51), which are also connected to the clamp (21) by a connecting rod (24).

8. The structure for reinforcing steel and reinforced concrete piles according to claim 7, characterized in that: The semi-circular base plate (51) is provided with a positioning groove (52) for installing FRP sleeves.

9. A method for reinforcing steel and reinforced concrete piles, characterized in that, Includes the following steps: Step S01: Clean the surface of the pile (3) to be reinforced; Step S02: Install the sleeve fixing assembly (2) on the surface of the reinforced pile (3); install the sealing plate (5) at the bottom of the reinforced position of the pile (3); Step S03: Prepare at least two curved FRP sheets (11) for splicing, splice the curved FRP sheets (11) into an FRP sleeve (1), and fit it onto the outer periphery of the pile body (3) to be reinforced; Step S04: Abut the lower end of the spliced ​​FRP sleeve (1) against the sealing plate (5), and fix the FRP sleeve (1) to the sleeve fixing assembly (2); Step S05: Pour concrete or resin concrete into the cavity formed between the FRP sleeve (1) and the pile body (3) to be reinforced.

10. The method for reinforcing steel and reinforced concrete piles according to claim 9, characterized in that: In step S05, the FRP sleeve (1) is fixed to the sleeve fixing assembly (2) by connecting the ribs (12) on the inner wall of the FRP sleeve (1) to the sleeve fixing assembly (2).

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