Structure reinforcing method and reinforcing system for actively repairing steel structure cracks through iron-based shape memory alloy based on rubber bolt mixed connection

Abstract

The invention discloses a structure reinforcing method and system for actively repairing steel structure cracks through an iron-based shape memory alloy based on rubber bolt mixed connection. The system comprises a to-be-reinforced thin-wall steel member with cracks; an iron-based shape memory alloy (Fe-SMA) plate is pre-tensioned; the bolts are connected with the structural adhesive layer. The pre-tensioned Fe-SMA plate is cooperatively connected to a crack area of the thin-wall steel member to be reinforced through bolts and structural adhesive, and the Fe-SMA plate introduces local prestress to the reinforced thin-wall steel member through heating excitation. According to the method, development of cracks is actively inhibited by introducing prestress, local rigidity is improved through additional plates, and cold repair and performance improvement of an in-service structure are achieved. The method has the advantages of being good in universality, simple in construction process, low in manufacturing cost, free of introduction of residual stress and the like, the advantages of bolt connection and cementation connection are fused, the shackle of the durability of structural adhesives and the fatigue resistance of bolts is broken through, and meanwhile higher activation temperature can be borne.

Description

Technical Field

[0001] This invention relates to the field of building and civil engineering technology, and in particular to a prestressed active maintenance method for steel structures based on a hybrid connection of Fe-SMA and adhesive plugs for reinforcing and repairing cracks in thin-walled steel members. Background Technology

[0002] Steel structures inevitably experience performance degradation during long-term service, with steel bridges being particularly prone to crack initiation and propagation due to prolonged fatigue loads. Current mainstream methods for repairing steel structure cracks include installing crack arresting holes, bonding steel plates, and bonding fiber composite materials. These passive repair methods can control crack evolution to some extent, but their effectiveness is limited, and some methods may even lead to secondary cracking.

[0003] In recent years, active crack repair methods based on the application of local prestress have been applied in actual bridge engineering, such as CFRP / SMA composite patches, Fe-SMA bonding, and Fe-SMA bonding with crack arresting holes. These active maintenance methods rely on the shape memory effect of shape memory alloys. Through reliable connections, the prestress generated during the activation process of the pre-tensioned SMA is transferred to the thin-walled steel member being reinforced, while crack arresting holes release stress at the crack tip. This technology can effectively inhibit crack propagation, prevent secondary cracking, and significantly improve the fatigue life of cracked steel structures.

[0004] Common connection methods on the market include bolted connections, adhesive bonding, and welding. Bolted connections offer relatively reliable connection capabilities, but their fatigue resistance is poor. Welded connections are simple to operate, but the high-temperature treatment introduces residual stress, which is detrimental to fatigue bearing capacity. Adhesive bonding, with its better fatigue resistance and the advantage of non-destructive reinforcement, is widely used in engineering applications involving active maintenance and crack repair. However, the durability of adhesive bonding in humid and hot environments is unsatisfactory.

[0005] To overcome the drawbacks of the aforementioned connections, a novel connection method is urgently needed to achieve more reliable active maintenance and repair of steel structure cracks. Among these, a hybrid connection method combining bolted and adhesive connections can impart better fatigue resistance to the bolted connections while providing a reliable protection mechanism against the degradation of the adhesive layer under long-term environmental influences. Furthermore, this connection method is convenient to construct, causes low damage, and is highly efficient, making it suitable as a novel connection method for Fe-SMA active maintenance of steel structure cracks. Summary of the Invention

[0006] Objective: To overcome the problems of complex construction and the trade-off between fatigue resistance and durability in existing crack repair methods for thin-walled steel components, this invention provides a structural reinforcement method and system based on iron-based shape memory alloys for actively repairing cracks in steel structures using adhesive-bolt hybrid connections. This method offers a structurally sound, convenient, damage-controllable, and highly effective approach for actively repairing and reinforcing cracks in thin-walled steel components. The invention utilizes pre-tensioned Fe-SMA plates, which are connected to the cracked areas of the thin-walled steel component using adhesive-bolt hybrid connections. Then, the Fe-SMA plates are heated and stimulated, introducing pre-compression stress into the cracks through the shape memory effect, thus inhibiting crack propagation.

[0007] Technical solution: The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloy with adhesive-bolt hybrid connection described in this invention involves covering a pre-tensioned Fe-SMA plate with bolt holes on a structural adhesive layer, connecting the pre-tensioned Fe-SMA plate to the crack area of ​​the thin-walled steel member to be reinforced, and introducing local prestress into the thin-walled steel member by heating and stimulating the Fe-SMA plate.

[0008] Furthermore, steel balls are arranged within the adhesive layer to control its thickness.

[0009] Furthermore, crack arrest holes are provided at the crack tips of thin-walled steel components to release the stress at the crack tips.

[0010] Furthermore, when three or more bolts are used to connect in the crack propagation direction, the bolts are arranged in a non-linear manner that is anti-symmetrical to the stress on the adhesive layer, so as to uniformly distribute the stress in the non-pre-stretched direction of the Fe-SMA plate.

[0011] Furthermore, the Fe-SMA plate uses iron-based shape memory alloy Fe-SMA, which undergoes pre-stretching before use, with a strain range of 2%-8%.

[0012] Furthermore, the Fe-SMA plate completely covers the crack and the crack arrestor hole, and its pretensioning direction is perpendicular to the crack.

[0013] Furthermore, the heating temperature range of the Fe-SMA plate in the non-bolted connection area is 150-400℃.

[0014] The aforementioned structural reinforcement method for actively repairing steel structure cracks using iron-based shape memory alloys based on adhesive-bolt hybrid connections is also applicable to the reinforcement and repair of cracks in the positive bending moment zone of bending members, in which case a single-sided Fe-SMA plate connection is sufficient.

[0015] Another aspect of the present invention provides a reinforcement system comprising a thin-walled steel member with cracks to be reinforced, a pre-tensioned shape memory alloy Fe-SMA plate, structural adhesive, and bolts, wherein a structural adhesive layer is coated between the Fe-SMA plate and the thin-walled steel member to be reinforced, and the Fe-SMA plate and the thin-walled steel member to be reinforced are connected by bolts and bolt holes.

[0016] In the above technical solution:

[0017] The pre-tensioned Fe-SMA plate is bonded to the cracked area of ​​the thin-walled steel member using structural adhesive and bolts. Prestress is introduced into the thin-walled steel member by heating and stimulating the Fe-SMA plate in the non-bolted area, and crack arrest holes are created to effectively alleviate stress at the crack tip. Bolt holes are provided on both the Fe-SMA plate and the thin-walled steel member for mechanical connection. Crack arrest holes are created at the crack tip of the thin-walled steel member. The Fe-SMA plate is pre-stretched to a strain of 2%-8%. The structural adhesive is a civil engineering grade adhesive used for non-mechanical connection between the Fe-SMA and the thin-walled steel member. The bolts are high-strength bolts used for mechanical connection between the Fe-SMA and the thin-walled steel member. The Fe-SMA can be heated using methods such as a hot air gun, flamethrower, or resistance heating.

[0018] The specific steps include: locating the crack in the thin-walled steel component to be reinforced and marking the bonding area; drilling bolt holes on both sides of the crack in the thin-walled steel component to be reinforced; polishing and cleaning the surface of the thin-walled steel component to be reinforced until it is glossy; applying a structural adhesive layer to the marked area of ​​the thin-walled steel component to be reinforced; covering the adhesive layer with a pre-tensioned Fe-SMA connecting plate with bolt holes and clamping the Fe-SMA plate to the thin-walled steel component using wood clamps; assembling the bolts into the bolt holes, applying pre-tightening force, and scraping off excess structural adhesive; after curing for 7 days, activating the Fe-SMA plate by heating with a hot air gun or other heating methods; and after cooling, applying anti-corrosion treatment to the entire glued bolt connection structure.

[0019] in,

[0020] The reinforcement structure of the Fe-SMA plate for cracks in thin-walled steel components includes, but is not limited to, the coverage mode in which the Fe-SMA pretensioning direction is perpendicular to the crack, as shown in this application example.

[0021] The hybrid connection structure of Fe-SMA and the thin-walled steel structure to be reinforced with adhesive plugs includes, but is not limited to, the Fe-SMA + bolt + structural adhesive structure described in this application example.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention employs a connection method that combines bolts and structural adhesive, thereby providing the connection with good fatigue resistance and reliable durability.

[0024] 2. The Fe-SMA plate actively applies prestress to the thin-walled steel component to be reinforced and is equipped with crack arrest holes. The coupling of these two mechanisms can effectively alleviate the stress at the crack tip and prevent secondary cracking.

[0025] 3. It avoids the use of heavy jacks, significantly improving the feasibility and versatility of construction operations.

[0026] 4. For steel members subjected to bending, single-sided connection can be used to introduce prestress and increase the cross-sectional stiffness, effectively improving the bending resistance and fatigue resistance of the steel members subjected to bending.

[0027] 5. When the number of bolts in the width direction of the Fe-SMA plate is greater than 2, this invention suggests using a nonlinear arrangement of bolts with an antisymmetric distribution curve of adhesive layer stress to uniformly mix the stress flow of the connection. Attached Figure Description

[0028] Figure 1 It is a thin-walled steel component that develops cracks;

[0029] Figure 2 This is an assembly diagram of thin-walled steel components reinforced with Fe-SMA adhesive plugs.

[0030] Figure 3 These are disassembled diagrams of thin-walled steel components reinforced with Fe-SMA adhesive plugs. (a) is an axonometric projection view, and (b) is a side view.

[0031] Figure 4 This is a nonlinear bolt arrangement diagram used when the crack is relatively long;

[0032] Figure 5 This is an assembly diagram of a steel member subjected to bending reinforced using a hybrid connection of Fe-SMA adhesive plugs. Detailed Implementation

[0033] For ease of description, the relative positions of the components and the dimensions of the parts are based on the layout of the accompanying drawings and do not limit the structure of this patent. All technologies implemented based on the content of this invention fall within the scope of this invention.

[0034] Figure 1 This is a partial view of a thin-walled steel structure with a crack: a crack at the transverse diaphragm of an orthotropic steel bridge deck, with a crack length of 60mm. The treatment method is to use prestressed Fe-SMA plates with crack arresting holes and a mixed connection of adhesive and bolts for reinforcement and repair. The steps are as follows:

[0035] Step S1: Locate the crack in the thin-walled steel component to be reinforced and draw lines to determine the bonding area. Determine the bolt diameter and quantity according to relevant specifications. In this case, 12.9 grade high-strength bolts with a diameter of 10mm are selected, arranged in a 2×2 linear pattern on one side. Accordingly, the Fe-SMA plate with dimensions of 2×75×250mm is selected and pre-stretched by 4%. The activation recovery performance of the Fe-SMA plate used is shown in Table 1.

[0036] Table 1. Activation recovery performance of Fe-SMA plates

[0037]

[0038] Step S2: Drill bolt holes on both sides of the crack in the thin-walled steel component to be reinforced and at corresponding positions on the 4% pre-stretched Fe-SMA plate. The hole spacing is 30mm, the end-to-end distance of the holes on the Fe-SMA plate is 20mm, and the edge distance is 22.5mm. The hole diameter is 1mm larger than the bolt diameter to ensure assembly feasibility. Then, according to the specifications, drill anti-crack holes at the crack tip.

[0039] The diameter of the stop hole is 16mm, and its center is located at the tip of the crack.

[0040] Step S3: Use a grinder to grind the marked area of ​​the reinforced thin-walled steel component and the side of the Fe-SMA plate to be bonded until the surface is shiny. Then use alcohol to clean the surface of the thin-walled steel component and the side of the Fe-SMA plate to be bonded.

[0041] Step S4: After the surface treatment is completed, apply a structural adhesive layer evenly to the marked area of ​​the thin-walled steel component to be reinforced, and arrange small steel balls of the same diameter evenly, discretely and in small quantities within the adhesive layer. In this case, the diameter of the small steel balls is 2mm to control the thickness of the adhesive layer to 2mm.

[0042] Step S5: Cover the structural adhesive layer with a 4% pre-stretched Fe-SMA board and clamp the Fe-SMA board to the thin-walled steel component to be reinforced using wood clamps.

[0043] Step S6: Install the bolts into the bolt holes respectively, apply the pre-tightening force in two stages, the initial tightening torque is 50% of the final tightening torque, and tighten to the target torque in the second stage. At this time, the excess structural adhesive will be squeezed out from the side by the pressure of the Fe-SMA plate. Use a scraper to remove the excess structural adhesive.

[0044] Step S7: After 7 days of curing, use a hot air gun or other heating equipment to heat and activate the middle 100mm length of the non-bolt-connected section of the Fe-SMA plate, maintaining the temperature at approximately 200℃ for 5 minutes. At this time, the pre-stretched Fe-SMA plate exerts its shape memory effect, shrinking after complete cooling. The compressive stress generated during the shrinkage process is transferred to the reinforced thin-walled steel component through the bolts and structural adhesive layer, thereby introducing a compressive stress of at least 60MPa at the crack tip region. This method significantly reduces the stress amplitude at the edge of the crack arrest hole under load and alleviates stress concentration, achieving efficient crack arrest. In addition, the additional Fe-SMA plate enhances the local stiffness of the reinforced area, offsetting the adverse effect of local stiffness degradation after crack initiation, thereby synergistically improving the fatigue resistance of the reinforced thin-walled steel component.

[0045] Step S8: After cooling to room temperature, perform anti-corrosion treatment on the entire glue plug hybrid connection structure.

[0046] When the crack length is long, a non-linear arrangement of multiple bolts can be used, such as... Figure 4 As shown. When the thin-walled steel member being reinforced is a bending member, single-sided reinforcement can be used. In this case, crack tip arresting holes can be opened as needed, such as... Figure 5 As shown.

[0047] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A structural reinforcement method for actively repairing cracks in steel structures using iron-based shape memory alloys based on adhesive-bonded hybrid connections, characterized in that... The pre-tensioned Fe-SMA plate (2) with bolt holes is covered on the structural adhesive layer (3). The pre-tensioned Fe-SMA plate (2) is connected to the crack area of ​​the thin-walled steel member (1) to be reinforced, and local prestress is introduced into the thin-walled steel member to be reinforced by heating the Fe-SMA plate.

2. The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloys using adhesive-plug hybrid connections, as described in claim 1, is characterized in that: Steel balls are placed inside the adhesive layer to control its thickness.

3. The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloys using adhesive-bonded hybrid connections, as described in claim 1, is characterized in that: When three or more bolts (4) are used to connect in the direction of crack propagation, the bolts (4) are arranged in a non-linear manner that is anti-symmetrical to the stress on the adhesive layer, so as to uniformly distribute the stress in the non-pre-stretched direction of the Fe-SMA plate (2).

4. The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloys using adhesive-bonded hybrid connections, as described in claim 1, is characterized in that: The Fe-SMA plate (2) uses iron-based shape memory alloy Fe-SMA and undergoes pre-stretching before use, with a strain range of 2%-8%.

5. The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloys using adhesive-bonded hybrid connections, as described in claim 1, is characterized in that: The crack tip of the thin-walled steel component to be reinforced is provided with a crack-stopping hole.

6. The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloys using adhesive-plug hybrid connections, as described in claim 5, is characterized in that: The Fe-SMA plate (2) completely covers the crack and the crack arresting hole, and its pretensioning direction is perpendicular to the crack.

7. The structural reinforcement method for actively repairing steel structure cracks based on iron-based shape memory alloys using adhesive-plug hybrid connections, as described in claim 1, is characterized in that: The heating temperature range of the Fe-SMA plate (2) in the non-bolt (4) connection area (5) is 150-400℃.

8. A reinforcement system for use in the method according to any one of claims 1-7, characterized in that: The device includes a cracked thin-walled steel member to be reinforced (1), a pre-tensioned shape memory alloy Fe-SMA plate (2), structural adhesive (3), bolts (4), and an activation area (5). The Fe-SMA plate (2) and the thin-walled steel member to be reinforced (1) are coated with a structural adhesive layer (3), and the Fe-SMA plate (2) and the thin-walled steel member to be reinforced (1) are connected by bolts (4) and bolt holes.

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