Prestressed SMA-FRP combined rib structure and preparation method thereof

Abstract

The invention discloses a prestressed SMA-FRP combined rib structure and a preparation method thereof.The prestressed SMA-FRP combined rib structure comprises at least three rib sections which are coaxially arranged, the rib sections are SMA unit ribs or FRP unit ribs, and the at least three rib sections comprise the SMA unit ribs and the FRP unit ribs; the connecting assembly comprises an outer connecting sleeve and an inner connecting sleeve, the two ends of the inner connecting sleeve are arranged at the ends of the two rib sections in a sleeving mode respectively, the outer connecting sleeve is arranged outside the inner connecting sleeve in a sleeving mode, a gap is formed between the pipe wall of the inner connecting sleeve and the pipe wall of the outer connecting sleeve, and the two ends of the outer connecting sleeve extend to the outer portions of the exposed portions of the rib sections respectively. The two ends of the external connection sleeve are connected with end sealing plates which are used for sealing the space between the external connection sleeve and the exposed part of the rib joint so that the gap can form a sealed cavity, the sealed cavity is filled with an expansion binding material, and the rib joint is wrapped with the expansion binding material. The problem that the prestress loss in the service period of the prestress FRP material cannot be conveniently supplemented is solved.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, and in particular to a prestressed SMA-FRP composite reinforcement structure and a preparation method thereof. Background Art

[0002] Shape memory alloy (SMA) is a special alloy material composed of two crystal structures, martensite and austenite. These two crystal structures can transform into each other under certain circumstances, which is manifested as a change in the shape of the SMA on a macro scale. The SMA in the parent state is composed of an austenite crystal structure. When a certain temperature is reached, the austenite crystal structure will transform into a martensite crystal structure through atomic position changes. This process is called martensitic phase transformation. In addition to temperature induction, applying an external load to cause a certain pre-deformation of the SMA can also induce martensitic phase transformation. When the pre-deformed SMA experiences high temperature, the martensite produced by the martensitic phase transformation will transform back into austenite. On a macro scale, the SMA deformation has been restored. This process is called martensitic reverse phase transformation or austenitic phase transformation. The above-mentioned shape recovery phenomenon caused by the crystal structure phase transformation is called shape memory effect (SME), which is one of the most important characteristics of SMA.

[0003] In the field of structural engineering, shape memory alloys can be divided into nickel-titanium-based shape memory alloys (Ni-TiSMA) and iron-based shape memory alloys (Fe-SMA) according to their constituent materials. However, early research was mainly based on Ni–TiSMA. Due to its high price and unstable recovery stress, Ni-TiSMA does not yet have the potential for large-scale application in the field of civil engineering as a prestressed material. Fe-SMA was successfully developed in the 1980s. Its low production price and stable recovery stress make it more likely to be used on a large scale in civil engineering than Ni-Ti shape memory alloys. With the continuous optimization of Fe-SMA materials, products in the form of ribbed steel bars, thin plates, and round bars have been launched.

[0004] Currently, most prestressed tendons are made of a single metal material (such as high-strength steel wire, steel strand, etc.). These materials are susceptible to corrosion in certain environments (such as highly corrosive environments), affecting the durability and safety of the structure. These prestressed tendons are unable to cope with complex and changing engineering environments, limiting their application in some special fields (such as marine engineering, chemical equipment, etc.). In addition, traditional prestressed tendons are prone to fatigue damage under repeated loads, resulting in prestress loss, affecting the long-term stability and safety of the structure. Summary of the invention

[0005] In order to overcome the defects of the prior art, a prestressed SMA-FRP composite reinforcement structure and a preparation method thereof are provided to solve the problem that the prestress loss of the prestressed FRP material during service period cannot be conveniently supplemented.

[0006] In order to achieve the above object, a prestressed SMA-FRP composite reinforcement structure is provided, comprising:

[0007] At least three sections of ribs are coaxially arranged, wherein the ribs are SMA unit ribs or FRP unit ribs, the at least three sections of ribs include the SMA unit ribs and the FRP unit ribs, and the ribs at the ends of the at least three sections of ribs are the SMA unit ribs;

[0008] A connecting assembly comprises an outer connecting sleeve and an inner connecting sleeve, wherein the two ends of the inner connecting sleeve are respectively sleeved on the ends of two ribs, the outer connecting sleeve is sleeved on the outside of the inner connecting sleeve, a gap is formed between the tube wall of the inner connecting sleeve and the tube wall of the outer connecting sleeve, the two ends of the outer connecting sleeve respectively extend to the outside of the exposed part of the rib, the two ends of the outer connecting sleeve are connected with end sealing plates for sealing between the outer connecting sleeve and the exposed part of the rib to form a closed cavity in the gap, the closed cavity is filled with expansion adhesive, and the expansion adhesive is coated on the rib.

[0009] Furthermore, the at least three sections of ribs include two sections of the SMA unit ribs and one section of the FRP unit ribs, and one section of the FRP unit ribs is arranged between the two sections of the SMA unit ribs.

[0010] Furthermore, the inner sleeve and the outer sleeve are coaxially arranged.

[0011] Furthermore, centering rods are formed on opposite sides of the tube wall of the inner sleeve, respectively. The centering rods are arranged along the radial direction of the inner sleeve, and the two pairs of centering rods are coaxially arranged.

[0012] Furthermore, the expansive adhesive is expansive cement mortar.

[0013] Furthermore, two ends of the external connection sleeve are respectively provided with a slurry outlet and a slurry outlet.

[0014] The present invention provides a method for preparing a prestressed SMA-FRP composite reinforcement structure, comprising the following steps:

[0015] At least three rib segments are arranged coaxially;

[0016] The two ends of the inner sleeve of the connection assembly are respectively sleeved on the ends of two adjacent ribs;

[0017] The outer sleeve of the connection assembly is sleeved on the outside of the inner sleeve, a gap is formed between the tube wall of the inner sleeve and the tube wall of the outer sleeve, and both ends of the outer sleeve extend to the outside of the exposed part of the rib respectively;

[0018] Injecting expansion adhesive into the outer sleeve, the expansion adhesive fills the gap and covers the rib joint;

[0019] End plates are connected to both ends of the external connection sleeve to seal the space between the external connection sleeve and the exposed portion of the rib joint.

[0020] The beneficial effect of the present invention is that the SMA unit reinforcement of the prestressed SMA-FRP composite reinforcement structure of the present invention has excellent shear strength, can resist the high-strength clamping force generated by the steel clip-type anchor, and is suitable for the steel clip-type anchor for prestressed anchoring, ensuring that the SMA unit reinforcement can be firmly fixed during the prestressing process, thereby effectively transferring the prestress to the entire composite reinforcement structure.

[0021] In the prestressed SMA-FRP composite reinforcement structure of the present invention, the prestress level of the structure is adjusted by changing the excitation temperature of the SMA unit reinforcement in the SMA-FRP composite reinforcement to adjust the recovery stress of the SMA.

[0022] The SMA unit bar in the prestressed SMA-FRP composite bar structure of the present invention has a corrosion resistance close to that of stainless steel due to its special material composition, and can resist the erosion of corrosive media to a certain extent. As a non-metallic material, the FRP unit bar has natural corrosion resistance. The combination of the two to form the prestressed SMA-FRP composite bar structure of the present invention improves the durability and service life of the structure.

[0023] When the prestressed SMA-FRP composite reinforcement structure of the present invention acts on the structure and constrains its deformation, the restoring stress generated in the SMA unit reinforcement will be converted into prestress on the structure. The prestress is caused by the phase change of the crystal structure of the SMA itself. By inducing the phase change of the SMA unit reinforcement through external excitation, there is no need to apply prestress with the help of tensioning equipment at the construction site, which greatly simplifies the construction process. The SMA unit reinforcement can also be subjected to secondary excitation to achieve timely supplementation and adjustment of the prestress loss of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0025] Figure 1 Schematic diagram of the structure of the prestressed SMA-FRP composite reinforcement structure according to an embodiment of the present invention.

[0026] Figure 2 Schematic diagram of the structure of the connection assembly of an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] Reference Figure 1 and Figure 2 As shown, the present invention provides a prestressed SMA-FRP composite reinforcement structure, including: a reinforcement segment 1 and a connection component 2.

[0030] Specifically, there are at least three rib segments 1. At least three rib segments 1 are coaxially arranged.

[0031] The rib segment 1 is an SMA unit rib a or an FRP unit rib b. The multi-segment rib segment 1 includes an SMA unit rib a and an FRP unit rib b. The rib segments at the ends of at least three rib segments are SMA unit ribs.

[0032] In this embodiment, at least three sections of ribs 1 include two sections of SMA unit ribs a and one section of FRP unit ribs b. The one section of FRP unit ribs b is disposed between the two sections of SMA unit ribs a.

[0033] The connection assembly 2 includes an outer connection sleeve 21 , an inner connection sleeve 22 , an end sealing plate 23 , and an expansion adhesive 24 .

[0034] Specifically, the two ends of the inner sleeve 22 are respectively sleeved on the ends of the two ribs 1. The outer sleeve 21 is sleeved outside the inner sleeve 22. A gap is formed between the tube wall of the inner sleeve 22 and the tube wall of the outer sleeve 21.

[0035] As a preferred embodiment, the inner sleeve 22 is coaxially arranged with the outer sleeve 21. The length of the outer sleeve is greater than the length of the inner sleeve. Both ends of the outer sleeve 21 extend to the outside of the exposed part of the rib 1 respectively.

[0036] End plates 23 are connected to both ends of the external connection sleeve 21. The end plates 23 are used to block the gap between the external connection sleeve 21 and the exposed part of the rib 1 so that the gap forms a closed cavity.

[0037] In this embodiment, the end plate is annular, and the ends of the ribs are inserted into the inner annular holes of the end plate.

[0038] The closed cavity is filled with an expansion adhesive 24. The expansion adhesive 24 is coated on the rib section 1. As a preferred embodiment, the expansion adhesive 24 is an expansion cement mortar.

[0039] As a preferred embodiment, centering rods 27 are respectively formed on opposite sides of the tube wall of the inner sleeve 22. The centering rods 27 are arranged along the radial direction of the inner sleeve 22, and the two centering rods 27 are coaxially arranged.

[0040] In this embodiment, two centering rods on the outer side of the tube wall of the inner sleeve penetrate the inner sleeve and are connected as one.

[0041] As a preferred embodiment, two ends of the external connection sleeve 21 are respectively provided with a slurry outlet 25 and a slurry outlet 26 .

[0042] The present invention provides a method for preparing a prestressed SMA-FRP composite reinforcement structure, which is characterized by comprising the following steps:

[0043] S1. Coaxially arrange at least three segments of ribs 1.

[0044] S2. The two ends of the inner sleeve 22 of the connecting assembly 2 are respectively sleeved on the ends of two adjacent ribs 1.

[0045] S3. The outer connecting sleeve 21 of the connecting assembly 2 is sleeved on the outside of the inner connecting sleeve 22, a gap is formed between the tube wall of the inner connecting sleeve 22 and the tube wall of the outer connecting sleeve 21, and both ends of the outer connecting sleeve 21 extend to the outside of the exposed part of the rib 1 respectively.

[0046] S4, pouring the expansion adhesive 24 into the external connection sleeve 21, the expansion adhesive 24 fills the gap and covers the rib 1.

[0047] S5. Connect end plates 23 to both ends of the external connection sleeve 21 to seal the space between the external connection sleeve 21 and the exposed portion of the rib 1.

[0048] In some embodiments, when a grout outlet and a grouting port are formed on the external connection sleeve, the end plate can be first sealed between the external connection sleeve 21 and the exposed part of the rib 1, and then the expansion adhesive can be poured into the external connection sleeve through the grouting port.

[0049] The front and rear ends of the external connection sleeve of the connection assembly in the prestressed SMA-FRP composite reinforcement structure of the present invention are sealed with two pipe openings of the external connection sleeve by end-sealing plates. A grout outlet and a grouting port are respectively arranged on the same axis outside the external connection sleeve.

[0050] When preparing the prestressed SMA-FRP composite reinforcement structure of the present invention, one end of the SMA unit reinforcement and the FRP unit reinforcement are inserted into the inner sleeve, and then a centering rod with a length slightly smaller than the inner diameter of the outer sleeve is nailed into the middle of the inner sleeve, so that the SMA unit reinforcement and the FRP unit reinforcement are centered inside the outer sleeve (the SMA unit reinforcement and the FRP unit reinforcement are coaxially arranged with the outer sleeve), thereby ensuring good force transmission and anchoring effects.

[0051] Insert the SMA unit ribs, FRP unit ribs, inner sleeve and centering rod into the outer sleeve while maintaining the above state, and then pass the inner ring holes of the end plate through the SMA unit ribs and FRP unit ribs respectively to close to the front and rear ends of the outer sleeve.

[0052] Adhesive tape is used to tightly fit the end plate to the external connection sleeve to ensure that the SMA unit reinforcement and the FRP unit reinforcement are aligned.

[0053] Inject the expansion adhesive into the external connection sleeve from the grouting hole until the expansion adhesive overflows from the grout outlet. At this time, the external connection sleeve is already full of expansion adhesive. When the expansion adhesive is completely hydrated and solidified, the SMA unit bar and the FRP unit bar are completely wrapped by the expansion adhesive. The expansion adhesive after hydration and expansion generates strong expansion pressure due to volume expansion. The SMA unit bar and the FRP unit bar are fully connected to transmit force, achieving efficient force transmission and coordinated work, forming prestressed SMA-FRP composite bars.

[0054] Only at the construction site are steel clip-type anchors used to clamp and anchor the SMA unit bars at both ends of the SMA-FRP composite bars. The SMA unit bars at one end are electrified to cause the SMA unit bars to shrink in length. Because the SMA-FRP composite bars are clamped and anchored by the steel clip-type anchors, the deformation of the SMA is suppressed and converted into prestress applied to the structure.

[0055] By using a steel clip anchor to prestress the SMA unit bars at the ends of the prestressed SMA-FRP composite bar structure of the present invention, this anchor ensures that the SMA unit bars can be firmly fixed during the prestressing process through a high-strength clamping force, thereby effectively transferring the prestress to the entire composite bar structure. At the same time, the SMA unit bars are heated and excited, and they undergo a phase change (from the martensite phase to the austenite phase), accompanied by changes in shape and size. This phase change process can produce a significant mechanical response, causing the SMA unit bars to contract and release the prestress, and the clamping effect of the steel clip anchor is used to lock the prestress in the prestressed SMA-FRP composite bar structure of the present invention, thereby generating prestress on the structure. After the structural prestress of the prestressed SMA-FRP composite bar structure of the present invention is lost due to long-term use or environmental factors, the SMA unit bars can be heated and excited again to cause them to undergo a phase change again. During this process, the SMA unit tendons will shrink again and generate prestress, thereby compensating for the lost prestress. The temperature of the heating excitation can be adjusted as needed to maintain or adjust the required prestress level.

[0056] The material properties of the SMA unit bar can make it possible to apply prestress at the construction site without the help of tensioning equipment, and can also achieve timely supplementation and free adjustment of the prestress loss of the structure, while the light weight and high strength characteristics of the FRP unit bar can reduce the dead weight of the structure. The combination of the two forms the prestressed SMA-FRP composite bar structure of the present invention, so as to avoid the problem that the traditional steel clip anchor is not compatible with the FRP unit bar, and can use the high elongation of SMA to alleviate the problem of poor ductility of the FRP prestressed structure, and solve the problem that the prestress loss of the structure cannot be supplemented again in the later stage, which increases the practicality of the building material and can be used in a variety of occasions, which is the key point of the technical solution of the present invention.

[0057] The SMA unit reinforcement of the prestressed SMA-FRP composite reinforcement structure of the present invention has excellent shear strength, can resist the high-strength clamping force generated by the steel clip-type anchor, and is suitable for the steel clip-type anchor for prestressed anchoring, ensuring that the SMA unit reinforcement can be firmly fixed during the prestressing process, thereby effectively transferring the prestress to the entire composite reinforcement structure.

[0058] In the prestressed SMA-FRP composite reinforcement structure of the present invention, the prestress level of the structure is adjusted by changing the excitation temperature of the SMA unit reinforcement in the SMA-FRP composite reinforcement to adjust the recovery stress of the SMA.

[0059] The SMA unit bars in the prestressed SMA-FRP composite bar structure of the present invention have a corrosion resistance close to that of stainless steel due to their special material composition, and can resist the erosion of corrosive media to a certain extent; and the FRP unit bars, as non-metallic materials, have natural corrosion resistance. The combination of the two forms the prestressed SMA-FRP composite bar structure of the present invention, which does not need to worry about corrosion problems, can effectively solve the problem of easy corrosion of traditional prestressed bars, and improves the durability and service life of the structure.

[0060] At the same time, if the SMA unit bar in the prestressed SMA-FRP composite bar structure of the present invention is constrained when the shape memory effect occurs, the energy generated by its phase change will exist in the form of stress, which is called recovery stress. When the prestressed SMA-FRP composite bar structure of the present invention acts on the structure and constrains its deformation (for example: embedded in concrete), the recovery stress generated in the SMA unit bar will be converted into prestress on the structure. The prestress is caused by the phase change of the crystal structure of the SMA itself. The SMA unit bar is induced to undergo phase change by external excitation, and there is no need to apply prestress with the help of tensioning equipment at the construction site, which greatly simplifies the construction process. The SMA unit bar can also be secondary excited to achieve timely supplementation and adjustment of the prestress loss of the structure.

[0061] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A prestressed SMA-FRP composite reinforcement structure, characterized in that: include: At least three sections of ribs are coaxially arranged, wherein the ribs are SMA unit ribs or FRP unit ribs, the at least three sections of ribs include the SMA unit ribs and the FRP unit ribs, and the ribs at the ends of the at least three sections of ribs are the SMA unit ribs; A connecting assembly comprises an outer connecting sleeve and an inner connecting sleeve, wherein the two ends of the inner connecting sleeve are respectively sleeved on the ends of two ribs, the outer connecting sleeve is sleeved on the outside of the inner connecting sleeve, a gap is formed between the tube wall of the inner connecting sleeve and the tube wall of the outer connecting sleeve, the two ends of the outer connecting sleeve respectively extend to the outside of the exposed part of the rib, the two ends of the outer connecting sleeve are connected with end sealing plates for sealing between the outer connecting sleeve and the exposed part of the rib to form a closed cavity in the gap, the closed cavity is filled with expansion adhesive, and the expansion adhesive is coated on the rib.

2. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that: The at least three sections of ribs include two sections of the SMA unit ribs and one section of the FRP unit ribs, and one section of the FRP unit ribs is arranged between the two sections of the SMA unit ribs.

3. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that: The inner sleeve is coaxially arranged with the outer sleeve.

4. The prestressed SMA-FRP composite reinforcement structure according to claim 3, characterized in that: Centering rods are respectively formed on opposite sides of the tube wall of the inner sleeve. The centering rods are arranged along the radial direction of the inner sleeve, and the two pairs of centering rods are coaxially arranged.

5. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that: The expansion bonding material is expansion cement mortar.

6. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that: The two ends of the external connection sleeve are respectively provided with a slurry outlet and a slurry outlet.

7. A method for preparing a prestressed SMA-FRP composite reinforcement structure as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: At least three rib segments are arranged coaxially; The two ends of the inner sleeve of the connection assembly are respectively sleeved on the ends of two adjacent ribs; The outer sleeve of the connection assembly is sleeved on the outside of the inner sleeve, a gap is formed between the tube wall of the inner sleeve and the tube wall of the outer sleeve, and both ends of the outer sleeve extend to the outside of the exposed part of the rib respectively; Injecting expansion adhesive into the outer sleeve, the expansion adhesive fills the gap and covers the rib joint; End plates are connected to both ends of the external connection sleeve to seal the space between the external connection sleeve and the exposed portion of the rib joint.

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