A pressure type FRP anchor rod system based on SMA self-sensing and thermal shrinkage self-locking

Abstract

This application relates to the field of anchor bolt technology and discloses a pressure-type FRP anchor bolt system based on SMA self-sensing and heat-shrink self-locking. The anchor bolt system is installed in a borehole in the soil and includes multiple anchor bolts and splicing sleeves. The multiple anchor bolts are coaxially arranged to form the anchor bolt body, which is installed in the borehole and extends at least partially outside the borehole. The anchor bolts and splicing sleeves are connected by threads, and adjacent anchor bolts are connected by splicing sleeves made of shape memory alloy. The splicing sleeve has a first terminal and a second terminal, both of which are connected to wires. When the splicing sleeve is energized, it has a first state and a second state. When the splicing sleeve is in the first state, it contracts and deforms under the action of current to lock the splicing sleeve and the anchor bolts. When the splicing sleeve is in the second state, the resistance of the splicing sleeve is calculated by the voltage and current connected to the splicing sleeve to determine the deformation state of the splicing sleeve.

Description

Technical Field

[0001] This application relates to the field of anchor bolt technology, and in particular to a pressure-type FRP anchor bolt system based on SMA self-sensing and heat-shrink self-locking. Background Technology

[0002] Fiber-reinforced polymer (FRP) anchors have been widely used in geotechnical engineering fields such as slope protection, foundation pit support, tunnel reinforcement, and anti-buoyancy engineering due to their excellent properties, including lightweight, high strength, corrosion resistance, and electromagnetic insulation. However, FRP anchors face two long-standing technical challenges in engineering applications: First, FRP materials have a low elastic modulus and significant creep characteristics, making it difficult to establish effective long-term prestress using traditional prestressing techniques, thus limiting the load-bearing capacity of FRP anchors in demanding support scenarios. Second, FRP is a linearly elastic brittle material, and its joints (including anchor ends and reinforcement splice nodes) experience significant stress concentration due to geometric abrupt changes and interlocking of the clamps. When the stress at the joint exceeds the material's limit, FRP anchors often experience sudden radial splitting or shear brittle fracture without obvious warning, posing a serious threat to engineering safety.

[0003] Existing monitoring methods struggle to cover the critical area of ​​the connection point. Distributed fiber optic strain sensors can be deployed in the hollow walls of FRP hollow anchor bolts to output multi-point deformation information; however, sensors such as fiber optic gratings cannot withstand the enormous compressive stress generated by the interlocking of the anchoring section clips, making them highly susceptible to damage during installation. This results in the connection point becoming a "blind spot" for traditional monitoring. Furthermore, the inner anchor head of FRP anchor bolts is typically buried deep within the rock and soil, and its stress and deformation state is concealed. Traditional monitoring methods cannot directly obtain real-time stress data of the inner anchor head, failing to meet the need for in-situ monitoring of the stress state throughout the entire life cycle of the anchoring device.

[0004] Furthermore, most existing FRP anchors require connection via splicing sleeves. To ensure the stability of the connection between the FRP anchor and the splicing sleeve, a locking structure is usually installed between the splicing sleeve and the FRP anchor to prevent relative rotation and improve the service life of the entire anchoring device. However, this method of locking the splicing sleeve and the FRP anchor via a locking structure greatly increases the structural complexity of the anchoring device and increases construction costs. Summary of the Invention

[0005] This application provides a pressure-type FRP anchor system based on SMA self-sensing and heat-shrink self-locking, which facilitates the locking of anchor bolts and splicing sleeves, reduces the construction cost of the anchor system, and allows for in-situ stress detection of the anchoring device.

[0006] To achieve the above objectives, the main technical solutions adopted in this application include: This application provides a pressure-type FRP anchor system based on SMA self-sensing and heat-shrink self-locking. The anchor system is installed in a borehole in the soil and includes multiple anchors and splicing sleeves. The multiple anchors are coaxially arranged to form the anchor body, which is installed in the borehole and extends at least partially outside the borehole. The anchors and splicing sleeves are connected by threads, and adjacent anchors are connected by splicing sleeves made of shape memory alloy. The splicing sleeve has a first terminal and a second terminal, both of which are connected to wires. When the splicing sleeve is energized, it has a first state and a second state. When the splicing sleeve is in the first state, it shrinks and deforms under the action of current to lock the splicing sleeve and the anchors. When the splicing sleeve is in the second state, the resistance of the splicing sleeve is calculated by the voltage and current connected to the splicing sleeve to determine the deformation state of the splicing sleeve.

[0007] Furthermore, the splicing sleeve includes a bolt and two interlocking semicircular sleeves, which are connected by the bolt. Each semicircular sleeve has an internal thread. A first terminal and a second terminal are connected to each of the two semicircular sleeves.

[0008] Furthermore, the anchor system also includes a sleeve, with at least a portion of the anchor body and the splicing sleeve located inside the sleeve.

[0009] Furthermore, the anchor system also includes an inner anchor head and an outer anchor head. Along the axial direction of the anchor, the inner anchor head and the outer anchor head are respectively connected to the anchor body, and the inner anchor head and the outer anchor head are located at both ends of the casing, with the outer anchor head located outside the soil.

[0010] Furthermore, both the inner and outer anchor heads are made of shape memory alloys.

[0011] Furthermore, the anchor system also includes a grouting cylinder, which is sleeved on the outside of the casing, with the inner anchor head and the outer anchor head respectively abutting against the grouting cylinder.

[0012] Furthermore, the anchor system also includes a base, which is fitted onto the outside of the anchor body, and the outer anchor head abuts against the grouting cylinder through the base.

[0013] Furthermore, the inner wall of the splicing sleeve is coated with structural adhesive.

[0014] Furthermore, the anchor bolt is made of glass fiber reinforced plastic or carbon fiber reinforced plastic.

[0015] By connecting the anchor bolt and the shape memory alloy splicing sleeve to an external power source, it is convenient to drive the anchor bolt and the splicing sleeve to lock together via an external power source, thereby reducing the construction cost of the anchor bolt system. On the other hand, it is convenient to detect the shrinkage of the splicing sleeve via an external power source, so as to meet the needs of in-situ stress monitoring of the anchor bolt system. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a structural schematic diagram of the anchor system provided in this application.

[0018] Figure 2 yes Figure 1 The diagram shows the structural schematic of the splicing sleeve of the anchor bolt system.

[0019] Explanation of reference numerals in the attached drawings: Soil 1, Drill hole 101, Anchor bolt 2, Splicing sleeve 3, First terminal 301, Second terminal 302, Bolt 303, Semi-circular sleeve 304, Casing 4, Inner anchor head 5, Outer anchor head 6, Grouting cylinder 7, Platform 8, Wire 9. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] like Figure 1 and Figure 2 As shown, as one implementation method, this application provides a pressure-type FRP anchor system based on SMA self-sensing and heat-shrink self-locking, including multiple anchors 2, splicing sleeves 3, inner anchor heads 5 and outer anchor heads 6. Multiple anchors 2 are used to splice to form the anchor body, and splicing sleeves 3 are used to connect two adjacent anchors 2. The anchor system is installed in the borehole 101 of the soil 1.

[0022] It should be noted that SMA refers to shape memory alloy.

[0023] Specifically, multiple anchor bolts 2 are coaxially arranged and interconnected to form an anchor bolt body, which is installed inside the borehole 101.

[0024] At least a portion of the anchor body extends outside the borehole 101 to facilitate the connection of the outer anchor head 6 with the anchor body. The inner anchor head 5 is installed at the end of the anchor body located in the borehole 101. The tension of the anchor body is transmitted to the soil 1 through the inner anchor head 5 and the outer anchor head 6.

[0025] It should be noted that under the action of the anchor bolt body tension, the inner anchor head 5 and the outer anchor head 6 move closer to each other, thereby transferring the anchor bolt body tension to the soil 1.

[0026] Anchor bolt 2 and splicing sleeve 3 are connected by threads, and adjacent anchor bolts 2 are connected by splicing sleeve 3 to form the anchor bolt body.

[0027] It should be noted that the anchor system includes two or more anchors 2, and two adjacent anchors 2 are connected by splicing sleeves 3.

[0028] The splicing sleeve 3 is made of shape memory alloy. Shape memory alloy has the ability to shrink when heated, and its resistance value changes over a large range after being heated.

[0029] When the splicing sleeve 3 is heated and deformed, both its radial and axial dimensions decrease. The reduction in the radial dimension of the splicing sleeve 3 locks the splicing sleeve 3 and the anchor rod 2 together, preventing relative rotation between the splicing sleeve 3 and the anchor rod 2 and improving the stability of the anchor rod body. At the same time, the reduction in the axial dimension of the splicing sleeve 3 reduces the distance between adjacent anchor rods 2. The splicing sleeve 3 applies axial tension to the anchor rod 2, thereby applying multi-point distributed prestress along the axial direction of the anchor rod 2 to the anchor rod body.

[0030] The splicing sleeve 3 has a first terminal 301 and a second terminal 302. Both the first terminal 301 and the second terminal 302 are connected to wires 9. The wires 9 are connected to an external power source, and an excitation current or a micro-current is applied to the splicing sleeve 3 through the external power source.

[0031] When the splicing sleeve 3 is energized, it has a first state and a second state.

[0032] An external power source applies an excitation current to the splicing sleeve 3, causing it to be in its first state. Under the action of the excitation current, the splicing sleeve 3 heats up, causing it to shrink and deform. Under the radial shrinkage of the splicing sleeve 3, the internal thread of the splicing sleeve 3 and the external thread of the anchor rod 2 are tightly engaged, thereby locking the splicing sleeve 3 and the anchor rod 2. At the same time, under the axial shrinkage of the splicing sleeve 3, the splicing sleeve 3 applies a tensile force to the anchor rod 2, thereby anchoring the anchor rod body.

[0033] An external power source applies a detection micro-current to the splicing sleeve 3, causing the splicing sleeve 3 to be in a second state. The resistance of the splicing sleeve 3 is calculated by the voltage and current connected to the splicing sleeve 3 to determine the deformation state of the splicing sleeve 3. This meets the requirement of in-situ monitoring of the stress state throughout the entire life cycle of the anchoring device. At the same time, it can detect local stress concentration and early signs of brittle fracture at the connection of the anchor rod 2, thereby improving the stability of the anchor rod system.

[0034] To more clearly illustrate the technical solution of this application, the following definitions are provided: Figure 1 The upward and downward directions are shown. The axial direction of anchor rod 2 is... Figure 1 The up and down directions are shown.

[0035] like Figure 2 As shown, as one implementation method, along the axial direction of the anchor rod 2, the first terminal 301 and the second terminal 302 are located at both ends of the splicing sleeve 3, which facilitates the differentiation of the first terminal 301 and the second terminal 302 and improves the wiring convenience of the splicing sleeve.

[0036] like Figure 2 As shown, as one implementation method, the splicing sleeve 3 includes a bolt 303 and two semi-circular sleeves 304. The two semi-circular sleeves 304 that are spliced ​​together are connected by the bolt 303, which facilitates the assembly of the splicing sleeve 3 with the anchor rod 2 and improves the assembly efficiency of the anchor rod system.

[0037] Both semicircular sleeves 304 have internal threads, and the internal threads of the two semicircular sleeves 304 are joined together to form a complete internal thread, ensuring that the anchor rod 2 can be installed in the splicing sleeve 3 through the thread.

[0038] It should be noted that bolt 303 and the two semi-circular sleeves 304 are both shape memory alloys, which ensure that bolt 303 and semi-circular sleeves 304 shrink at the same time, thereby ensuring the connection stability of splicing sleeve 3.

[0039] As one implementation, each of the two semicircular sleeves 304 is connected to a first terminal 301 and a second terminal 302, so that an external power supply can be connected to the two semicircular sleeves 304 respectively, ensuring that the two semicircular sleeves 304 contract simultaneously or are detected simultaneously.

[0040] As one implementation method, the inner wall of the splicing sleeve 3 is coated with structural adhesive, which is a modified epoxy resin structural adhesive.

[0041] When the splicing sleeve 3 is in the first state, the splicing sleeve 3 heats up, causing the structural adhesive to melt and fill the gap between the external thread of the anchor rod 2 and the internal thread of the splicing sleeve 3. After the splicing sleeve 3 cools down, it solidifies to form a chemical bond, further improving the connection stability between the anchor rod 2 and the splicing sleeve 3.

[0042] Meanwhile, structural adhesive can fill the gaps between the semi-circular sleeves 304, improving the connection stability between the semi-circular sleeves 304.

[0043] As one implementation method, in the initial state (without excitation current heating), the pitch of the internal thread of the splicing sleeve 3 is consistent with the pitch of the external thread of the anchor rod 2, and there is a certain gap between the internal thread sidewall of the splicing sleeve 3 and the external thread sidewall of the anchor rod 2, so as to ensure that the anchor rod 2 can be stably installed into the splicing sleeve 3.

[0044] like Figure 1 As shown, in one implementation, the anchor bolt system also includes a sleeve 4, with at least a portion of the anchor bolt body and the splicing sleeve 3 located inside the sleeve 4. The sleeve 4 protects the anchor bolt body and the splicing sleeve 3, ensuring that the splicing sleeve 3 can be stably connected to an external power source.

[0045] Sleeve 4 is a PVC sleeve.

[0046] It should be noted that the inner diameter of the sleeve 4 is slightly larger than the outer diameter of the splicing sleeve 3 to ensure that the wire can pass through the gap between the sleeve 4 and the splicing sleeve 3.

[0047] like Figure 1 As shown, in one implementation method, along the axial direction of the anchor rod 2, the inner anchor head 5 and the outer anchor head 6 are respectively connected to the anchor rod body, and the inner anchor head 5 and the outer anchor head 6 are located at both ends of the sleeve 4, while the outer anchor head 6 is located outside the soil 1.

[0048] As one implementation method, both the inner anchor head 5 and the outer anchor head 6 are made of shape memory alloy.

[0049] Similarly, both the inner anchor head 5 and the outer anchor head 6 are connected to terminals so that the wire 9 can be connected to the inner anchor head 5 and the outer anchor head 6, so that the inner anchor head 5 and the outer anchor head 6 can deform or be tested simultaneously with the splicing sleeve 3.

[0050] It should be noted that both terminals of the inner anchor head 5 are located at the end of the inner anchor head 5 facing the sleeve 4, so as to protect the terminals of the inner anchor head 5 through the sleeve 4.

[0051] As one implementation method, both the inner anchor head 5 and the outer anchor head 6 are disc-shaped structures.

[0052] like Figure 1 As shown, as one implementation method, the anchor system also includes a grouting cylinder 7, which is sleeved on the outside of the sleeve 4, and the inner anchor head 5 and the outer anchor head 6 respectively abut against the grouting cylinder 7.

[0053] The strength of the connection between the soil 1 and the anchor system is increased by the grouting cylinder 7, which makes it easier to anchor the anchor to the soil 1.

[0054] It should be noted that the grouting cylinder 7 is formed between the sleeve 4 and the soil 1 by concrete grouting. After the grouting cylinder 7 is constructed, the concrete grouting wraps around the outside of the inner anchor head 5, so that one end of the anchor system is fixed to the grouting cylinder 7.

[0055] like Figure 1 As shown, as one implementation method, the anchor system also includes a base 8, which is sleeved on the outside of the anchor body, and the outer anchor head 6 abuts against the grouting cylinder 7 through the base 8, which facilitates the connection between the outer anchor head 6 and the grouting cylinder 7, thereby realizing the anchoring of the anchor system and the grouting cylinder 7.

[0056] It should be noted that the diameter of the pedestal 8 is larger than the diameter of the grouting cylinder 7, ensuring that the outer ring of the pedestal 8 can come into contact with the soil 1.

[0057] As one implementation method, the anchor bolt 2 is made of glass fiber reinforced plastic or carbon fiber reinforced plastic.

[0058] The working principle of the anchor bolt system is as follows: Step S1: During installation, insert the anchor rod 2 into the sleeve 4. Apply modified epoxy resin structural adhesive to the inner wall of the hole used to install the anchor rod 2 in the inner anchor head 5. Pre-install the inner anchor head 5 at the bottom of the bottommost anchor rod 2. Apply an excitation current to the inner anchor head 5 to make it heat-shrink and tightly hug the bottom end of the anchor rod 2.

[0059] Step S2: Apply modified epoxy resin structural adhesive to the inner wall of the semi-circular sleeve 304 (unshrinkable), then attach the two semi-circular sleeves 304 to the end of the anchor rod 2. The internal thread of the semi-circular sleeve 304 initially engages with the external thread of the anchor rod 2, and the two semi-circular sleeves 304 are fixedly connected by bolts 303.

[0060] In this step, the semi-circular sleeve 304 is in an unretracted state to ensure that the anchor rod body together with the sleeve 4 is smoothly lowered into the borehole 101 to achieve the connection of multiple anchor rods 2.

[0061] Step S3: After the anchor bolt body and the casing 4 are in place, concrete grout is poured between the casing 4 and the borehole 101.

[0062] After the concrete grout reaches the design strength, the base 8 is set on the outside of the anchor rod body. Then, the inner wall of the installation hole of the outer anchor head 6 is coated with modified epoxy resin structural adhesive. The outer anchor head 6 is then fitted onto the top of the anchor rod body. An excitation current is passed through the outer anchor head 6 to make it thermally shrink and tightly hug the top of the anchor rod body.

[0063] In step S4, an excitation current is applied to the splicing sleeve 3, causing the splicing sleeve 3 to contract and thus tightly grip the anchor rod 2. At the same time, the modified epoxy resin structural adhesive melts during the heating and activation process, filling the gap between the splicing sleeve 3 and the anchor rod 2. After cooling, it solidifies to form a chemical bond.

[0064] When the splicing sleeve 3 contracts, it applies an axial tensile force to the anchor rod 2, thereby achieving the application of prestress to the anchor rod 2. When multiple splicing sleeves 3 are distributed along the axial direction of the anchor rod 2, distributed prestress application to the main body of the anchor rod can be achieved.

[0065] Step S5, during the service phase, a detection microcurrent is connected to the splicing sleeve 3, inner anchor head 5, and outer anchor head 6 via wire 9 to perform real-time resistance monitoring using the piezoresistive effect of shape memory alloy. The deformation state of the inner anchor head 5 and outer anchor head 6 can reflect the stress state of the anchor head, and the deformation state of the splicing sleeve 3 can reflect the axial tensile stress of the anchor rod 2. Based on this, the service status of the anchor rod device is assessed and an early warning is given.

[0066] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A pressure-type FRP anchor system based on SMA self-sensing and heat-shrinkable self-locking, wherein the anchor system is installed in a borehole (101) in the soil (1), characterized in that, The anchor system includes: Multiple anchor rods (2) are coaxially arranged to form an anchor rod body, which is installed in the borehole (101); The splicing sleeve (3) is used to connect the anchor rod (2) and the splicing sleeve (3) by thread. Adjacent anchor rods (2) are connected by the splicing sleeve (3). The material of the splicing sleeve (3) is a shape memory alloy. The splicing sleeve (3) has a first terminal (301) and a second terminal (302). Both the first terminal (301) and the second terminal (302) are connected to wires. When the splicing sleeve (3) is energized, the splicing sleeve (3) has a first state and a second state. When the splicing sleeve (3) is in the first state, the splicing sleeve (3) shrinks and deforms under the action of current to lock the splicing sleeve (3) and the anchor rod (2). When the splicing sleeve (3) is in the second state, the resistance of the splicing sleeve (3) is calculated by the voltage and current of the splicing sleeve (3) to determine the deformation state of the splicing sleeve (3).

2. The pressure-type FRP anchor system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 1, characterized in that, The splicing sleeve (3) includes a bolt (303) and two semi-circular sleeves (304) that are spliced ​​together. The two semi-circular sleeves (304) that are spliced ​​together are connected by the bolt (303). Each semi-circular sleeve (304) has an internal thread. The first terminal (301) and the second terminal (302) are connected to both of the two semi-circular sleeves (304).

3. The pressure-type FRP anchor system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 1, characterized in that, The anchor system also includes a sleeve (4), with at least a portion of the anchor body and the splicing sleeve (3) located inside the sleeve (4).

4. A pressure-type FRP anchor system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 3, characterized in that, The anchor system also includes an inner anchor head (5) and an outer anchor head (6). Along the axial direction of the anchor (2), the inner anchor head (5) and the outer anchor head (6) are respectively connected to the anchor body, and the inner anchor head (5) and the outer anchor head (6) are respectively located at both ends of the sleeve (4), and the outer anchor head (6) is located outside the soil (1).

5. A pressure-type FRP anchor system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 4, characterized in that, The materials of the inner anchor head (5) and the outer anchor head (6) are both shape memory alloys.

6. A pressure-type FRP anchor bolt system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 4, characterized in that, The anchor system also includes a grouting cylinder (7), which is sleeved on the outside of the sleeve (4), and the inner anchor head (5) and the outer anchor head (6) respectively abut against the grouting cylinder (7).

7. A pressure-type FRP anchor bolt system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 6, characterized in that, The anchor system also includes a base (8), which is fitted on the outside of the anchor body, and the outer anchor head (6) abuts against the grouting cylinder (7) through the base (8).

8. A pressure-type FRP anchor bolt system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 1, characterized in that, The inner wall of the splicing sleeve (3) is coated with structural adhesive.

9. A pressure-type FRP anchor bolt system based on SMA self-sensing and heat-shrinkable self-locking as described in claim 1, characterized in that, The anchor rod (2) is made of glass fiber reinforced plastic or carbon fiber reinforced plastic.

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