Prestressed SMA-FRP composite tendon structure and preparation method thereof

Abstract

The application discloses a prestressed SMA-FRP composite tendon structure and a preparation method thereof, and comprises at least three coaxially arranged tendon sections, wherein the tendon sections are SMA unit tendons or FRP unit tendons, and the at least three tendon sections comprise SMA unit tendons and FRP unit tendons; a connecting assembly comprises an outer connecting sleeve and an inner connecting sleeve, the two ends of the inner connecting sleeve are sleeved on the end portions of two tendon sections respectively, the outer connecting sleeve is sleeved on the outer portion of the inner connecting sleeve, a gap is formed between the wall of the inner connecting sleeve and the wall of the outer connecting sleeve, the two ends of the outer connecting sleeve extend to the outer portion of the exposed portion of the tendon section respectively, and the two ends of the outer connecting sleeve are connected with end sealing plates for sealing the gap between the outer connecting sleeve and the exposed portion of the tendon section to form a closed cavity, the closed cavity is filled with expanded adhesive, and the expanded adhesive covers the tendon section. The application solves the problem that the prestress loss of prestressed FRP material during the service period cannot be conveniently supplemented.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, specifically to a prestressed SMA-FRP composite reinforcement structure and its preparation method. Background Technology

[0002] Shape memory alloys (SMAs) are special alloy materials composed of martensite and austenite crystal structures. These two crystal structures can transform into each other under specific conditions, macroscopically manifesting as a change in the shape of the SMA. In its parent state, an SMA is composed of austenite. When a specific temperature is reached, the austenite crystal structure transforms into martensite through changes in atomic positions; this process is called martensitic transformation. Besides temperature-induced transformation, applying an external load to induce a certain degree of pre-deformation in the SMA can also induce martensitic transformation. When the pre-deformed SMA is subjected to high temperatures, the martensite produced by the martensitic transformation reverts to austenite; macroscopically, the deformation of the SMA is recovered. This process is called reverse martensitic transformation or austenitic transformation. This shape recovery phenomenon caused by the crystal structure phase transformation is called the shape memory effect (SME), one of the most prominent characteristics of SMAs.

[0003] In the field of structural engineering, shape memory alloys can be classified according to their constituent materials into nickel-titanium shape memory alloys (Ni-TiSMA) and iron-based shape memory alloys (Fe-SMA), among others. However, early research was mainly based on Ni-TiSMA. Due to its high cost and unstable recovery stress, Ni-TiSMA did not yet have the potential for large-scale application as a prestressed material in civil engineering. Fe-SMA, developed in the 1980s, offers lower production costs and more stable recovery stress, making it more likely to be widely used in civil engineering than Ni-Ti shape memory alloys. With continuous optimization of Fe-SMA materials, products in the form of ribbed steel bars, thin plates, and round bars are now available.

[0004] Currently, most prestressing tendons use a single metallic material (such as high-strength steel wire or steel strand). These materials are susceptible to corrosion in specific environments (such as highly corrosive environments), affecting the durability and safety of the structure. These prestressing tendons are inadequate in handling complex and variable engineering environments, limiting their application in some specialized fields (such as marine engineering and chemical equipment). Furthermore, traditional prestressing tendons are prone to fatigue damage under repeated loading, leading to prestress loss and affecting the long-term stability and safety of the structure. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, a prestressed SMA-FRP composite reinforcement structure and its preparation method are provided to solve the problem that the prestress loss of prestressed FRP materials during service life cannot be easily replenished.

[0006] To achieve the above objectives, a prestressed SMA-FRP composite reinforcement structure is provided, comprising:

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

[0008] The connecting assembly includes an outer sleeve and an inner sleeve. The two ends of the inner sleeve are respectively fitted onto the ends of two rib sections. The outer sleeve is fitted onto the outside of the inner sleeve. A gap is formed between the wall of the inner sleeve and the wall of the outer sleeve. The two ends of the outer sleeve extend to the outside of the exposed portion of the rib section. The two ends of the outer sleeve are connected to end-sealing plates for sealing the gap between the outer sleeve and the exposed portion of the rib section to form a closed cavity. The closed cavity is filled with an expanding adhesive, which covers the rib section.

[0009] Furthermore, the at least three reinforcement segments include two SMA unit reinforcement segments and one FRP unit reinforcement segment, with the FRP unit reinforcement segment disposed between the two SMA unit reinforcement segments.

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

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

[0012] Furthermore, the expanding binder is expanding cement mortar.

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

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

[0015] At least three joint segments should be coaxially arranged;

[0016] The two ends of the inner sleeve of the connecting component are respectively fitted onto the ends of the two adjacent stiffeners;

[0017] The outer sleeve of the connecting assembly is fitted over the inner sleeve, and a gap is formed between the wall of the inner sleeve and the wall of the outer sleeve. Both ends of the outer sleeve extend to the outside of the exposed portion of the rib joint.

[0018] An expanding adhesive is injected into the external connecting sleeve, the expanding adhesive filling the gap and covering the rib joint;

[0019] End-sealing plates are connected to both ends of the external connecting sleeve to seal the exposed portion between the external connecting sleeve and the reinforcing joint.

[0020] The beneficial effects of the present invention are that the SMA unit reinforcement of the prestressed SMA-FRP composite reinforcement structure of the present invention has excellent shear strength, which can resist the high clamping force generated by the steel wedge anchor, and is compatible with the steel wedge anchor for prestressing anchorage, ensuring that the SMA unit reinforcement can be stably 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 magnitude of the recovery stress of the SMA.

[0022] The prestressed SMA-FRP composite reinforcement structure of this invention utilizes SMA unit reinforcements, whose special material composition gives them corrosion resistance close to that of stainless steel, enabling them to resist corrosive media to a certain extent. Meanwhile, FRP unit reinforcements, as non-metallic materials, possess natural corrosion resistance. The combination of these two materials to form the prestressed SMA-FRP composite reinforcement structure of this invention improves the structure's durability and service life.

[0023] When the prestressed SMA-FRP composite reinforcement structure of the present invention acts on the structure and constrains its deformation, the recovery stress generated in the SMA unit reinforcement will be converted into prestress on the structure. This prestress is caused by the phase transformation of the SMA crystal structure itself. By inducing the phase transformation of the SMA unit reinforcement through external excitation, there is no need to apply prestress on the construction site with the help of tensioning equipment, which greatly simplifies the construction process. It can also perform secondary excitation on the SMA unit reinforcement to realize timely replenishment and adjustment of the prestress loss of the structure. Attached Figure Description

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

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

[0026] Figure 2 This is a schematic diagram of the connection component according to an embodiment of the present invention. Detailed Implementation

[0027] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

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

[0030] Specifically, there are at least three segments of ligament 1. These at least three segments of ligament 1 are coaxially arranged.

[0031] Reinforcing joint 1 is either SMA element a or FRP element b. Multi-segment reinforcing joint 1 includes both SMA element a and FRP element b. The end reinforcement joints of at least three segments are SMA element reinforcements.

[0032] In this embodiment, at least three reinforcement segments 1 include two SMA unit reinforcement segments a and one FRP unit reinforcement segment b. The FRP unit reinforcement segment b is disposed between the two SMA unit reinforcement segments a.

[0033] The connecting component 2 includes an outer connecting sleeve 21, an inner connecting sleeve 22, an end cap 23, and an expansion adhesive 24.

[0034] Specifically, the two ends of the inner sleeve 22 are respectively fitted onto the ends of the two reinforcing joints 1. The outer sleeve 21 is fitted onto the outside of the inner sleeve 22. A gap is formed between the wall of the inner sleeve 22 and the wall of the outer sleeve 21.

[0035] In a preferred embodiment, the inner sleeve 22 and the outer sleeve 21 are coaxially arranged. 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 portion of the rib joint 1.

[0036] Both ends of the external connecting sleeve 21 are connected to end sealing plates 23. The end sealing plates 23 are used to seal the exposed part between the external connecting sleeve 21 and the reinforcing joint 1 so that the gap forms a closed cavity.

[0037] In this embodiment, the end cap is annular. The end of the rib passes through the inner annular hole of the end cap.

[0038] The closed cavity is filled with an expanding adhesive 24. The expanding adhesive 24 covers the reinforcing joint 1. In a preferred embodiment, the expanding adhesive 24 is an expanding cement mortar.

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

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

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

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

[0043] S1. Set at least three joints 1 coaxially.

[0044] S2. The two ends of the inner sleeve 22 of the connecting component 2 are respectively fitted onto the ends of the two adjacent stiffeners 1.

[0045] S3. The outer sleeve 21 of the connecting component 2 is fitted over the inner sleeve 22, and a gap is formed between the wall of the inner sleeve 22 and the wall of the outer sleeve 21. The two ends of the outer sleeve 21 extend to the outside of the exposed part of the rib joint 1.

[0046] S4. Inject expansion adhesive 24 into the outer sleeve 21. The expansion adhesive 24 fills the gap and covers the rib joint 1.

[0047] S5. Connect end plates 23 to both ends of the external connecting sleeve 21 to seal the exposed part between the external connecting sleeve 21 and the reinforcing joint 1.

[0048] In some embodiments, when the external connecting sleeve has a grout outlet and a grout injection port, the end cap can be first sealed between the exposed portion of the external connecting sleeve 21 and the reinforcing joint 1, and then the expansion adhesive can be injected into the external connecting sleeve through the grout injection port.

[0049] In the prestressed SMA-FRP composite reinforcement structure of the present invention, the front and rear ends of the connecting component of the outer sleeve are sealed by end-sealing plates. A grout outlet and a grout injection port are respectively provided on the same axis on the outer side of the outer 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. 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 aligned 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 effect.

[0051] The SMA unit reinforcement, FRP unit reinforcement, inner sleeve and centering rod are inserted into the outer sleeve while maintaining the aforementioned state. Then, the inner ring hole of the end plate is passed through the SMA unit reinforcement and FRP unit reinforcement respectively and tightly attached to the front and rear ends of the outer sleeve.

[0052] Adhesive tape is used to tightly attach the end cap plate to the external connecting sleeve to ensure the alignment of the SMA unit reinforcement and the FRP unit reinforcement.

[0053] Expandable binder is injected into the external sleeve through the grouting hole until it overflows from the outlet. At this point, the external sleeve is filled with expandable binder. Once the expandable binder has completely hydrated and solidified, the SMA and FRP unit bars are completely bound by it. The expanded binder, after hydration and expansion, generates strong expansion pressure due to its volume expansion. The SMA and FRP unit bars are fully connected and transmit force, achieving efficient force transfer and synergistic work, forming a prestressed SMA-FRP composite reinforcement.

[0054] On the construction site, steel clamp-type anchors are used to clamp and anchor the SMA unit bars at both ends of the SMA-FRP composite reinforcement. When an electric current is applied to one end of the SMA unit bar, the SMA unit bar will shrink in length. Because the SMA-FRP composite reinforcement is clamped and anchored by the steel clamp-type anchors, the deformation of the SMA is suppressed and converted into prestress applied to the structure.

[0055] By using steel clamp-type anchors to prestress the SMA unit bars at the ends of the prestressed SMA-FRP composite reinforcement structure of the present invention, the SMA unit bars are prestressed and anchored. These anchors, with their high-strength clamping force, ensure the SMA unit bars are firmly fixed during prestressing application, thereby effectively transferring the prestress to the entire composite reinforcement structure. Simultaneously, heating the SMA unit bars causes a phase transformation (from martensite to austenite), accompanied by changes in shape and size. This phase transformation process generates a significant mechanical response, causing the SMA unit bars to contract and release the prestress. The clamping action of the steel clamp-type anchors locks the prestress within the prestressed SMA-FRP composite reinforcement structure of the present invention, generating prestress in the structure. If the structural prestress of the prestressed SMA-FRP composite reinforcement structure of the present invention is lost due to long-term use or environmental factors, the SMA unit bars can be re-heated and stimulated to undergo another phase transformation. During this process, the SMA unit reinforcement will re-shrink and generate prestress, thereby compensating for and restoring 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 SMA unit reinforcement allow for on-site prestressing without the need for tensioning equipment, enabling timely replenishment and free adjustment of prestress loss in the structure. Meanwhile, the lightweight and high-strength characteristics of FRP unit reinforcement reduce the structure's self-weight. The combination of these two materials forms the prestressed SMA-FRP composite reinforcement structure of this invention. This avoids the incompatibility between traditional steel clamp anchors and FRP unit reinforcement, utilizes the high elongation of SMA to alleviate the poor ductility of FRP prestressed structures, and solves the problem of the inability to replenish prestress loss in later stages of the structure. This increases the practicality of building materials and makes them suitable for various applications, which is the key point of this invention's technical solution.

[0057] The SMA unit reinforcement of the prestressed SMA-FRP composite reinforcement structure of the present invention has excellent shear strength and can resist the high clamping force generated by the steel wedge anchor. It is compatible with the steel wedge anchor for prestressing anchorage, ensuring that the SMA unit reinforcement can be stably 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 magnitude of the recovery stress of the SMA.

[0059] The prestressed SMA-FRP composite reinforcement structure of the present invention has SMA unit reinforcements with corrosion resistance close to that of stainless steel due to their special material composition, which can resist the erosion of corrosive media to a certain extent; while FRP unit reinforcements, as non-metallic materials, have natural corrosion resistance. The combination of the two to form the prestressed SMA-FRP composite reinforcement structure of the present invention eliminates concerns about corrosion, effectively solves the problem of easy corrosion of traditional prestressed reinforcements, and improves the durability and service life of the structure.

[0060] Meanwhile, if the SMA unit reinforcement in the prestressed SMA-FRP composite reinforcement structure of the present invention is constrained when the shape memory effect occurs, the energy generated by its phase transformation will exist in the form of stress, called recovery stress. When the prestressed SMA-FRP composite reinforcement structure of the present invention acts on the structure and constrains its deformation (e.g., embedded in concrete), the recovery stress generated in the SMA unit reinforcement will be transformed into prestress on the structure. This prestress is caused by the phase transformation of the SMA's own crystal structure. By inducing the phase transformation of the SMA unit reinforcement through external excitation, there is no need to apply prestress on the construction site using tensioning equipment, which greatly simplifies the construction process. It can also be used to perform secondary excitation on the SMA unit reinforcement to achieve timely replenishment and adjustment of the prestress loss in the structure.

[0061] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A prestressed SMA-FRP composite reinforcement structure, characterized in that, include: At least three stiffening segments are coaxially arranged, wherein the stiffening segments are SMA unit stiffening segments or FRP unit stiffening segments, and the at least three stiffening segments include the SMA unit stiffening segments and the FRP unit stiffening segments, and the stiffening segments at the ends of the at least three stiffening segments are the SMA unit stiffening segments; A connecting assembly includes an outer sleeve and an inner sleeve. The two ends of the inner sleeve are respectively fitted onto the ends of two rib sections. The outer sleeve is fitted onto the outside of the inner sleeve. A gap is formed between the wall of the inner sleeve and the wall of the outer sleeve. The two ends of the outer sleeve extend to the outside of the exposed portion of the rib section. The two ends of the outer sleeve are connected to end-sealing plates for sealing the gap between the outer sleeve and the exposed portion of the rib section to form a closed cavity. The closed cavity is filled with an expanding adhesive, which covers the rib section. Once the expandable binder is fully hydrated and solidified, the SMA and FRP unit bars are completely bound by it. The expanded binder, due to its volume expansion, generates strong expansion pressure, effectively connecting and transmitting force between the SMA and FRP unit bars, achieving efficient force transfer and synergistic work to form a prestressed SMA-FRP composite reinforcement. Steel clamp-type anchors are used to clamp and anchor the SMA unit bars at both ends of the SMA-FRP composite reinforcement. Electrical excitation is applied to one end of the SMA unit bar, causing it to retract in length. Because the SMA-FRP composite reinforcement is clamped and anchored by the steel clamp-type anchors, the deformation of the SMA is suppressed and converted into prestress applied to the structure. The prestress level of the structure is adjusted by changing the excitation temperature of the SMA unit bars in the SMA-FRP composite reinforcement to regulate the magnitude of the SMA's recovery stress.

2. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that, The at least three reinforcement segments include two SMA unit reinforcement segments and one FRP unit reinforcement segment, with the FRP unit reinforcement segment disposed between the two SMA unit reinforcement segments.

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

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

5. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that, The expanding binder is expanding cement mortar.

6. The prestressed SMA-FRP composite reinforcement structure according to claim 1, characterized in that, The external connecting sleeve has a slurry outlet and a slurry outlet at both ends.

7. A method for preparing a prestressed SMA-FRP composite reinforcement structure as described in any one of claims 1 to 6, characterized in that, Includes the following steps: At least three joint segments should be coaxially arranged; The two ends of the inner sleeve of the connecting component are respectively fitted onto the ends of the two adjacent stiffeners; The outer sleeve of the connecting assembly is fitted over the inner sleeve, and a gap is formed between the wall of the inner sleeve and the wall of the outer sleeve. Both ends of the outer sleeve extend to the outside of the exposed portion of the rib joint. An expanding adhesive is injected into the external sleeve. The expanding adhesive fills the gap and covers the reinforcing joint. When the expanding adhesive is completely hydrated and solidified, the SMA unit reinforcement and the FRP unit reinforcement are completely wrapped by the expanding adhesive. The expanding adhesive generates strong expansion pressure due to the volume expansion after hydration and expansion. The SMA unit reinforcement and the FRP unit reinforcement are fully connected and transmit force, realizing efficient force transmission and collaborative work, forming a prestressed SMA-FRP composite reinforcement. End-sealing plates are connected to both ends of the external connecting sleeve to seal the exposed portion between the external connecting sleeve and the reinforcing joint; Steel clamp anchors are used to clamp and anchor the SMA unit bars at both ends of the SMA-FRP composite reinforcement. When the SMA unit bar at one end is electrically excited, the SMA unit bar will shrink in length. Because the SMA-FRP composite reinforcement is clamped and anchored by the steel clamp anchors, the deformation of the SMA is suppressed and converted into prestress applied to the structure.

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