Multi-metal thermal expansion matching type FRP-concrete connecting screw and connecting structure

Abstract

The invention discloses a multi-metal thermal expansion matching type FRP-concrete connecting screw and a connecting structure, the screw comprises an alloy steel anchoring drill rod, and the alloy steel anchoring drill rod comprises a drill bit section used for being tapped into a concrete member and a screw rod section used for anchoring the concrete member; the invar steel transition connecting rod is coaxially fixed to the end, close to the lead screw section, of the alloy steel anchoring drill rod, and the invar steel transition connecting rod is arranged in the prefabricated through hole of the FRP component in a small clearance fit mode. The thermal expansion coefficient of the invar transition connecting rod is smaller than or equal to that of the FRP component, and temperature difference expansion stress generated between the FRP component and the invar transition connecting rod can be avoided; and the stainless steel screw head is coaxially fixed to the end, away from the alloy steel anchoring drill rod, of the invar steel transition connecting rod, the FRP component and the concrete component which are secondarily anchored through the screw are more stable and reliable, and interface stripping failure of the FRP component and the concrete component under the long-term dynamic load, temperature circulation or humidity change environment is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of fastener manufacturing and use, and in particular relates to a multi-metal thermal expansion matching FRP-concrete connecting screw and a connecting structure. Background Art

[0002] Fiber-reinforced polymer (FRP) systems have become one of the key technologies for strengthening concrete structures due to their high specific strength, corrosion resistance, and ease of construction. The American Concrete Institute (ACI) clearly stated in the "Guide to Design and Construction of Fiber-Reinforced Polymer (FRP) Systems for Reinforced Concrete Structures" (ACI 440.2R-17) published in 2017 that the connection between FRP and concrete structures mainly relies on bonding technology (such as epoxy resin bonding). However, pure bonding connections are prone to interfacial debonding failure under long-term dynamic loads, temperature cycles, or humidity changes. Especially in application scenarios with large temperature differences, the durability of the bonding interface faces severe challenges. In order to improve the reliability of the reinforcement system, a composite method of bonding and mechanical connection can be adopted, that is, secondary anchoring by bolts is performed on the basis of bonding to enhance the collaborative working performance of FRP and concrete.

[0003] Current connecting bolts and FRP components suffer from a significant mismatch in thermal expansion coefficients. For example, stainless steel, due to its greater thermal expansion coefficient than FRP, can cause the originally designed clearance fit to become an interference fit when the temperature rises. The resulting expansion stress can directly act on the FRP hole walls, causing matrix cracking, fiber breakage, or interlaminar delamination. Over time, this expansion-contraction cycle can also lead to relaxation at the metal-composite interface, ultimately causing bolt loosening and even connection failure.

[0004] Therefore, how to provide a multi-metal thermal expansion matching FRP-concrete composite connecting screw and connecting structure is a problem that those skilled in the art urgently need to solve. Summary of the Invention

[0005] In view of this, the present invention provides a multi-metal thermal expansion matching FRP-concrete composite connecting screw and connection structure to ensure the connection reliability between FRP components and concrete components, and avoid interface delamination failure between FRP components and concrete components under long-term dynamic loads, temperature cycles or humidity changes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a multi-metal thermal expansion matching FRP-concrete connecting screw for improving the connection reliability between FRP components and concrete components, comprising:

[0007] An alloy steel anchor drill rod, comprising a drill bit section for drilling into a concrete member and a screw section for anchoring the concrete member;

[0008] An Invar steel transition connecting rod, the Invar steel transition connecting rod being coaxially fixed to one end of the alloy steel anchor drill rod near the screw rod section, the Invar steel transition connecting rod being fitted with a small clearance within a prefabricated through hole of the FRP component, the Invar steel transition connecting rod having a thermal expansion coefficient less than or equal to that of the FRP component and capable of avoiding thermal expansion stress generated between the FRP component and the Invar steel transition connecting rod;

[0009] A stainless steel screw head is coaxially fixed to the end of the Invar steel transition connecting rod away from the alloy steel anchor drill rod.

[0010] The beneficial effects of the present invention are as follows: the screw of the present invention is used to enhance the connection reliability between FRP components and concrete components, and belongs to a secondary anchoring method. The screw uses an alloy steel anchor drill rod to effectively penetrate the concrete component, and based on the engagement of the screw segment with the hole wall of the concrete component, an anchoring effect is generated. The Invar steel transition connecting rod is matched with the prefabricated through hole of the FRP component, wherein the thermal expansion coefficient of the Invar steel transition connecting rod is less than or equal to the thermal expansion coefficient of the FRP component, thereby avoiding the loosening problem between the Invar steel transition connecting rod and the prefabricated through hole of the FRP component caused by temperature difference changes, and also avoiding the expansion stress generated by the screw directly acting on the FRP hole wall, causing matrix cracking, fiber breakage or interlayer delamination problems, thereby ensuring the secondary anchoring effect of the FRP component and the concrete component, and the stainless steel screw head has sufficient corrosion resistance, thereby improving the reliability of the component connection.

[0011] Preferably, the outer wall surface of the Invar steel transition connecting rod is provided with a rough textured surface, and the rough textured surface is passivated to form a passivation film layer.

[0012] The resulting technical effect is: before connection, glue is applied to the outer wall of the Invar steel transition connecting rod, and a roughened surface is set on the outer wall of the Invar steel transition connecting rod, which can increase the adhesion of the bond and improve the assembly and fastening effect with the prefabricated through-hole of the FRP component. The passivation treatment can improve the corrosion resistance of the screw surface and avoid potential corrosion.

[0013] Preferably, the stainless steel screw head is a hexagonal flange screw head, and the stainless steel screw head is formed from austenitic stainless steel.

[0014] The resulting technical effect is that the hexagonal flange screw head facilitates the transmission of torque on the one hand, and on the other hand, the larger flange surface can disperse the compressive stress and prevent FRP lamination damage.

[0015] Preferably, the alloy steel anchor drill rod is formed from 35CrMo steel.

[0016] The resulting technical effect is that the alloy steel anchor drill rod formed from 35CrMo steel has greater hardness and wear resistance.

[0017] The present invention also discloses a connection structure of a multi-metal thermal expansion matching FRP-concrete connecting screw, comprising the above-mentioned screw, an FRP component and a concrete component, wherein the FRP component is bonded to the outer surface of the concrete component, a prefabricated through-hole is provided on the FRP component, the alloy steel anchor drill rod passes through the prefabricated through-hole and is hammered into the concrete component, the invar steel transition connecting rod is located in the prefabricated through-hole and a dense bonding layer is formed between the outer wall of the invar steel transition connecting rod and the prefabricated through-hole, and the stainless steel screw head covers the opening of the prefabricated through-hole.

[0018] The resulting technical effect is that, in addition to traditional bonding fixation, FRP components and concrete components are anchored secondary with screws, thus avoiding interface debonding failure between FRP components and concrete components under long-term dynamic loads, temperature cycles or humidity changes, thereby improving the connection reliability between FRP components and concrete components.

[0019] Preferably, a flange surface is provided on a side of the stainless steel screw head close to the FRP component, and a diameter of the flange surface is larger than an inner diameter of the prefabricated through hole.

[0020] The resulting technical effect is that the flange surface can cover the prefabricated through-holes of the FRP component to prevent external water vapor from penetrating into the prefabricated through-holes, and the flange surface can also disperse the compressive stress to prevent FRP lamination damage.

[0021] Preferably, a sealant layer is provided around the contact area between the stainless steel screw head and the FRP component.

[0022] The resulting technical effect is: by providing a sealing layer to isolate water vapor from entering the prefabricated through hole, potential corrosion of the Invar steel transition connecting rod is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural diagram of a multi-metal thermal expansion matching FRP-concrete composite connecting screw of the present invention;

[0024] Figure 2 This is a schematic diagram of the connection structure of a multi-metal thermal expansion matching FRP-concrete composite connecting screw of the present invention;

[0025] Figure 3 This is a schematic diagram of a countersunk connection state of a multi-metal thermal expansion matching FRP-concrete composite connecting screw of the present invention;

[0026] Figure 4 for Figure 3 Schematic diagram of countersunk screw seal;

[0027] Figure 5This is a schematic diagram of a non-countersunk head connection state of a multi-metal thermal expansion matching FRP-concrete composite connecting screw of the present invention;

[0028] Figure 6 for Figure 5 Sealing diagram of non-countsunk screws.

[0029] 1 alloy steel anchor drill rod, 11 drill bit section, 12 screw section, 2 Invar steel transition connecting rod, 21 rough textured surface, 3 stainless steel screw head, 31 flange surface, 4 FRP component, 5 concrete component, 6 bonding layer, 7 sealant layer. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] See the attached Figures 1 to 6 According to an embodiment of the present invention, a multi-metal thermal expansion matching FRP-concrete connecting screw is used to improve the connection reliability between the FRP component 4 and the concrete component 5, which includes:

[0032] An alloy steel anchor drill rod 1, comprising a drill bit section 11 for drilling into a concrete member 5 and a screw section 12 for anchoring the concrete member 5;

[0033] An invar steel transition link 2 is coaxially fixed to one end of the alloy steel anchor drill rod 1 near the screw segment 12. The invar steel transition link 2 fits within a prefabricated through hole of the FRP component 4 with a small clearance. The thermal expansion coefficient of the invar steel transition link 2 is less than or equal to the thermal expansion coefficient of the FRP component 4, thereby preventing thermal expansion stress from being generated between the FRP component 4 and the invar steel transition link 2.

[0034] The stainless steel screw head 3 is coaxially fixed to the end of the Invar steel transition connecting rod 2 away from the alloy steel anchor drill rod 1.

[0035] The alloy steel anchor drill rod 1, the Invar steel transition connecting rod 2 and the stainless steel screw head 3 are connected by friction welding, resistance welding or laser welding.

[0036] The metal material of the Invar steel transition connecting rod 2 is mainly composed of Invar steel, and no thread is required to be made on it.

[0037] The thermal expansion coefficient of Invar steel is a=1.6×10 -6 / ℃. Close to or less than the expansion coefficient of the FRP material, this ensures that when the temperature changes, the prefabricated through-holes of the FRP components will not expand, and thus will not generate the expansion force of the interference fit that may cause cracking of the hole edge matrix, fiber breakage or delamination.

[0038] In some embodiments, the outer wall of the Invar steel transition link 2 is roughened to form a rough roughened surface 21. The Invar steel transition link 2 is coated with epoxy resin when connected to the inner hole wall of the FRP component. In order to improve the firmness of the bonding, the Invar steel is roughened, which can significantly improve the adhesion of the bonding and improve the fastening effect.

[0039] The rough, textured surface is passivated to form a passivation film layer. Due to the inherently weak corrosion resistance of Invar steel, it is prone to contact with the inner pore walls of the FRP material, causing electrostatic corrosion. Although the textured surface is adhered to an adhesive, it is also susceptible to electrostatic corrosion once moisture penetrates. Therefore, the textured Invar steel surface needs to be further passivated to improve the corrosion resistance of the screw surface.

[0040] In other embodiments, the stainless steel screw head 3 is a hexagonal flange screw head formed from austenitic stainless steel. This portion of the metal is primarily composed of austenitic stainless steel. The screw head section is typically exposed to air. Therefore, the use of austenitic stainless steel ensures sufficient corrosion resistance. Furthermore, the hexagonal flange surface structure of the screw head section allows for transmission of tightening torque while distributing compressive stress and preventing damage to the FRP laminate.

[0041] More specifically, the alloy steel anchor drill rod 1 is machined from 35CrMo steel, a material with exceptional hardness and wear resistance. The drill bit features a drill tail design, adding a cutting edge or drill point to the end of the screw, making penetration easier and more efficient. The threads engage the concrete hole wall, generating friction and preventing the screw from pulling out or loosening.

[0042] The present invention also discloses a connection structure of a multi-metal thermal expansion matching FRP-concrete connecting screw, comprising the above-mentioned screw, an FRP component 4 and a concrete component 5. The FRP component 4 is bonded to the outer surface of the concrete component 5. A prefabricated through-hole is provided on the FRP component 4. An alloy steel anchor drill rod 1 passes through the prefabricated through-hole and is hammered into the concrete component 5. An invar steel transition connecting rod 2 is located in the prefabricated through-hole and a dense bonding layer 6 is formed between the outer wall of the invar steel transition connecting rod 2 and the prefabricated through-hole. A stainless steel screw head 3 covers the opening of the prefabricated through-hole.

[0043] Specifically, a flange surface 31 is provided on one side of the stainless steel screw head 3 close to the FRP component 4 . The diameter of the flange surface 31 is larger than the inner diameter of the prefabricated through hole so as to cover the opening of the FRP prefabricated through hole.

[0044] There are two types of screw connections in practice: countersunk and non-countersunk. Figure 3-6 .

[0045] More specifically, a sealant layer 7 is provided around the contact area between the stainless steel screw head 3 and the FRP component 4 to prevent moisture from penetrating into the prefabricated through-hole of the FRP component and to avoid potential corrosion of the Invar steel transition link 2. The present invention adopts multiple means to avoid corrosion of the Invar steel transition link 2, including but not limited to the sealant layer 7 and the adhesive layer 6.

[0046] This product's screws address the problem of cracking of FRP hole walls and interface relaxation caused by mismatched thermal expansion coefficients of traditional bolts. It adopts a three-section heterogeneous metal composite structure: the anchor drill rod is made of high-strength alloy steel and has a self-drilling tail structure to achieve concrete anchoring; the transition connecting rod adopts a thermal expansion coefficient of 1.6×10 -6 / ℃ Invar steel is passivated with nitric acid to inhibit potential corrosion with FRP, and its expansion coefficient matches that of FRP to eliminate temperature difference stress; the stainless steel screw head is an austenitic stainless steel hexagonal flange surface structure, which has both anti-corrosion function and compressive stress dispersion ability. The three sections are formed into a whole by friction welding or resistance welding. The flange surface covers the edge of the FRP prefabricated hole to prevent lamination damage, and the contact surface between the screw head and FRP is isolated from environmental corrosion by sealant. The present invention solves the problem of interface failure of adhesive-mechanical composite connection through thermal expansion matching design and multi-material collaboration, and significantly improves the long-term reliability of FRP-concrete structure in temperature cycle and corrosive environment.

[0047] As for the devices and methods of use disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the methods.

[0048] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-metal thermal expansion matching FRP-concrete connecting screw for improving the connection reliability between an FRP component (4) and a concrete component (5), characterized in that: include: An alloy steel anchor drill rod (1), comprising a drill bit section (11) for drilling into a concrete member (5) and a screw rod section (12) for anchoring the concrete member (5); An Invar steel transition connecting rod (2), the Invar steel transition connecting rod (2) is coaxially fixed to one end of the alloy steel anchor drill rod (1) close to the screw rod section (12), the Invar steel transition connecting rod (2) is fitted with a small clearance in the prefabricated through hole of the FRP component (4), the thermal expansion coefficient of the Invar steel transition connecting rod (2) is less than or equal to the thermal expansion coefficient of the FRP component (4), and the generation of temperature differential expansion stress between the FRP component (4) and the Invar steel transition connecting rod (2) can be avoided; A stainless steel screw head (3) is coaxially fixed to the end of the Invar steel transition connecting rod (2) away from the alloy steel anchor drill rod (1).

2. The multi-metal thermal expansion matching FRP-concrete connecting screw according to claim 1, characterized in that: The outer wall of the Invar steel transition connecting rod (2) is provided with a rough textured surface (21), and the rough textured surface (21) is passivated to form a passivation film layer.

3. The multi-metal thermal expansion matching FRP-concrete connecting screw according to claim 1, characterized in that: The stainless steel screw head (3) is a hexagonal flange screw head, and the stainless steel screw head (3) is formed from austenitic stainless steel.

4. The multi-metal thermal expansion matching FRP-concrete connecting screw according to claim 1, characterized in that: The alloy steel anchor drill rod (1) is formed from 35CrMo steel.

5. A connection structure of a multi-metal thermal expansion matching FRP-concrete connection screw, comprising a screw according to any one of claims 1 to 4, an FRP component (4) and a concrete component (5), characterized in that: The FRP component (4) is bonded to the outer surface of the concrete component (5); a prefabricated through hole is provided on the FRP component (4); the alloy steel anchor drill rod (1) passes through the prefabricated through hole and is drilled into the concrete component (5); the Invar steel transition connecting rod (2) is located in the prefabricated through hole, and a bonding layer (6) is densely formed between the outer wall of the Invar steel transition connecting rod (2) and the prefabricated through hole; and the stainless steel screw head (3) covers the opening of the prefabricated through hole.

6. The connection structure of the multi-metal thermal expansion matching FRP-concrete connection screw according to claim 5, characterized in that: A flange surface (31) is provided on one side of the stainless steel screw head (3) close to the FRP component (4), and the diameter of the flange surface (31) is larger than the inner diameter of the prefabricated through hole.

7. The connection structure of a multi-metal thermal expansion matching FRP-concrete connection screw according to claim 5, characterized in that: A sealing rubber layer (7) is provided on the peripheral side of the contact area between the stainless steel screw head (3) and the FRP component (4).

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