A steel bridge fatigue crack reinforcement composite structure

Abstract

The utility model discloses a kind of steel bridge fatigue crack reinforcing composite structures, comprising: the steel bridge plate with crack, the two sides area of crack on steel bridge plate is respectively first hammering area, second hammering area, the position of crack on steel bridge plate is third hammering area, shape memory alloy reinforcing batten and carbon fiber reinforcing cloth are successively laid and pasted from below to above at crack on steel bridge plate.The reinforcing composite structure guarantees reinforcing effect at the same time, gives consideration to construction feasibility and economy, by forming "closed-inhibit-enhance" triple protection, long-acting reinforcement to railway bridge key structure crack can be realized.

Description

Technical Field

[0001] This utility model relates to the field of steel bridge crack reinforcement technology, and more specifically to a composite structure for fatigue crack reinforcement of steel bridges. Background Technology

[0002] Fatigue cracking has always been a prominent problem in the design and maintenance of railway steel bridges. During long-term service, critical components such as welded joints are prone to fatigue cracks due to cyclic loading, seriously affecting structural safety. Therefore, how to effectively strengthen steel bridges to address fatigue cracks in the long term is of great research significance and engineering value for ensuring the safe operation of railway steel bridges.

[0003] Traditional repair methods, such as welding reinforcement, easily introduce residual stress, leading to secondary cracking. Among existing technologies, the pneumatic impact crack closure (ICR) reinforcement method is convenient and quick to implement, rapidly closing cracks through pneumatic impact, but its reinforcement effect is limited and cannot achieve long-term reinforcement. Shape memory alloys (SMA) can generate prestressed crack closure through thermal excitation, but when used alone, the interface between the reinforcement layer and the substrate is prone to peeling. Carbon fiber reinforced polymers (CFRP), while improving local strength, have limited crack closure effects and cannot actively inhibit crack propagation. Furthermore, surface treatment processes before crack closure (such as grinding and shot peening) are insufficient to completely eliminate stress concentration at the crack tip. Currently, there are reinforcement schemes that combine SMA and CFRP by drilling crack arresting holes, but this scheme has certain limitations. Critical structures in railway bridges are generally much thicker in steel plate thickness than those in highway bridges, making the drilling of crack arresting holes relatively difficult, and it can easily affect the original structural stiffness. Utility Model Content

[0004] In view of this, this utility model addresses the problems existing in the current steel bridge fatigue crack repair technology, such as poor crack closure effect, insufficient synergy between reinforcement materials and the matrix, low long-term stability, and high construction difficulty. It proposes a composite structure for steel bridge fatigue crack reinforcement, which closes the crack through pneumatic impact pretreatment, combined with SMA to provide long-term prestress compensation and gradient CFRP high-strength coverage, to achieve active crack repair, stress redistribution, and long-term structural enhancement.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A composite structure for fatigue crack reinforcement of steel bridges includes: a steel bridge plate with cracks, wherein the areas on both sides of the crack on the steel bridge plate are respectively a first impact zone and a second impact zone, and the area directly above the crack on the steel bridge plate is a third impact zone, and shape memory alloy reinforcing strips and carbon fiber reinforcing cloth are sequentially laid on the steel bridge plate from bottom to top at the crack.

[0007] Furthermore, the carbon fiber reinforcing fabric fully covers the shape memory alloy reinforcing strip.

[0008] Furthermore, the carbon fiber reinforcing fabric comprises a lower layer of high-modulus carbon fiber fabric, a middle layer of medium-high modulus carbon fiber fabric, and an upper layer of standard modulus carbon fiber fabric laid in sequence.

[0009] Furthermore, the high-modulus carbon fiber cloth is M40J grade with a modulus ≥380 GPa, the medium-high modulus carbon fiber cloth is T800 grade with a modulus of 294 GPa, and the standard modulus carbon fiber cloth is T300 grade with a modulus of 230 GPa.

[0010] The implementation steps of the above-mentioned reinforced composite structure are as follows:

[0011] Step 1: Pneumatic Impact Closure of Crack Surface. The crack surface is impacted three times using pneumatic equipment. The first and second impact zones on either side of the fatigue crack are treated with the first and second impacts, respectively. These two impacts close the crack from both sides towards the center. A third impact is then applied to the third impact zone above the fatigue crack to deepen the crack closure and enhance the reinforcement effect. This step initially closes the crack, achieving the first stage of reinforcement.

[0012] Step Two: Applying SMA (Shape Memory Alloy) Strips and Pressure Curing. First, mark the approximate area for structural adhesive application. The application area should be larger than the SMA strip to prepare for subsequent application of high-carbon fiber reinforcement. Clean and roughen the application area. Then, use a loader to pre-stretch the SMA strip. Next, level the cracked surface after the first reinforcement treatment with leveling adhesive to ensure a smooth surface. Apply structural adhesive evenly to the application area. The structural adhesive used is a high-performance two-component steel bonding adhesive, prepared at a 2:1 mass ratio. When applying the SMA strip, first use a small spatula to evenly apply the structural adhesive to the application area, ensuring no gaps. Then, perform edge corner treatment. Afterward, use a strong magnetic magnet for pressure curing for at least 5 days. Finally, use a digital display hot air gun to heat and activate the area, recording temperature changes during the process. Control the maximum activation temperature to approximately 200℃, and the heating time for each strip is 5 minutes. This step utilizes the shape memory effect of the shape memory alloy to provide long-term prestress compensation for the steel plate, achieving a second layer of reinforcement.

[0013] Step 3: Apply multiple layers of carbon fiber cloth with different elastic moduli. A first layer of high-modulus carbon fiber cloth (M40J grade, modulus ≥380 GPa) is applied to the surface of the SMA after the second reinforcement. The high-modulus fibers bear the tensile stress at the crack tip, reducing the stress intensity factor, decreasing crack opening displacement (COD), and delaying fatigue propagation. Next, a second layer of medium-high modulus carbon fiber cloth (T800 grade, modulus ≈294 GPa) is applied, serving as a buffer between the high-modulus inner layer and the low-modulus outer layer, balancing stress transfer and dispersing energy. Finally, a third layer of standard modulus carbon fiber cloth (T300 grade, modulus ≈230 GPa) is applied. This low-modulus layer absorbs external impact energy, protects the inner structure, covers undamaged areas, expands the load transfer range, and reduces the overall stress level. The three layers of carbon fiber fabric are bonded together with structural adhesive of 0.3–0.5 mm thickness. After each layer is bonded, a debubbling roller is used to roll the carbon fiber fabric multiple times along the fiber direction to ensure the CFRP fabric is straight, extended, and free of air bubbles, and to allow the structural adhesive to fully penetrate. After bonding, the CFRP is pressure-cured using clamps for 5 days. The length of the carbon fiber fabric should be greater than the length of the SMA (Structured Aluminum Mesh) to ensure that the carbon fiber fabric fully covers the SMA strips. This step allows the CFRP and the reinforced structure to work together to increase overall stiffness, achieving a third layer of reinforcement.

[0014] This invention employs ICR (Insulated Crack Reinforcement) as the first step. ICR technology is simple to construct and effective against non-penetrating cracks on steel plate surfaces, making it suitable for the relatively thick critical structures of railway bridges. However, ICR reinforcement alone has limited effectiveness; after a period of loading, the cracks will reopen. Therefore, SMA (Solid Molybdenum Mesh) is used as the second layer of reinforcement, providing long-term prestress compensation. This prestress effectively counteracts the tensile stress generated by external loads, improving the structure's load-bearing capacity and stiffness. Finally, a third layer of reinforcement is applied by bonding gradient CFRP (Chemical Fluorescent Reinforced Polymer) fabric. Optimized fiber orientation disperses stress, inhibits crack opening displacement, and enhances overall strength. The use of a bonded gradient CFRP layer for this third layer of reinforcement optimizes stress distribution, strengthens interface properties, and significantly improves fatigue life. This composite reinforcement structure ensures effective reinforcement while considering construction feasibility and economy. By forming a triple protection of "closure-inhibition-reinforcement," it achieves long-term reinforcement of cracks in critical structures of railway bridges. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0016] Figure 1 This utility model provides a structural schematic diagram of a steel bridge plate with cracks in a composite structure for strengthening fatigue cracks in steel bridges.

[0017] Figure 2 This invention provides a schematic diagram of the hammering zone in a composite structure for strengthening fatigue cracks in a steel bridge. Figure (a) is a schematic diagram of the first hammering zone, Figure (b) is a schematic diagram of the second hammering zone, and Figure (c) is a schematic diagram of the third hammering zone.

[0018] Figure 3 This is a schematic diagram of a steel bridge fatigue crack reinforcement composite structure provided by this utility model, in which shape memory alloy reinforcing strips and carbon fiber reinforcing cloth are laid.

[0019] Figure 4 This is a schematic diagram showing the completed reinforcement of a steel bridge fatigue crack reinforcement composite structure provided by this utility model.

[0020] Figure 5 This is a schematic diagram of a pneumatic device. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] For long-term reinforcement of fatigue cracks in key components of railway bridges, a composite reinforcement structure is proposed, comprising three aspects:

[0026] (1) Pneumatic impact crack closure technology (ICR) induces plastic deformation around fatigue cracks in steel bridge decks through high-energy pneumatic impact. The compressive residual stress generated by the impact closes the crack and inhibits its propagation. After the impact, the surface roughness of the crack increases, the crack closure area expands, the stress intensity factor at the crack tip decreases, and the impact area undergoes work hardening due to plastic deformation, thereby improving local stiffness and fatigue resistance.

[0027] (2) The reinforcement principle of shape memory alloy (SMA) is mainly based on its unique shape memory effect and superelasticity. Shape memory effect refers to the ability of SMA (Structured Aluminum Molecular Weighted Material) to recover its original shape after plastic deformation at low temperatures by heating to a specific temperature (above the austenitic transformation temperature). Based on this, SMA materials can be pre-stretched, fixed to the structure requiring reinforcement, and then heated above the transformation temperature. The SMA attempts to recover its original shape, but due to being fixed to the structure, it generates recovery stress (prestress). This prestress can effectively offset the tensile stress generated by external loads, improving the load-bearing capacity and stiffness of the structure. When the structure deforms due to load or damage, the prestress of the SMA can be dynamically adjusted by heating, achieving adaptive repair or reinforcement. Hyperelasticity refers to the characteristic of SMA to undergo large deformation through stress-induced martensitic transformation (SIM) when subjected to external forces at room temperature (austenitic phase), and then completely recover its original shape after unloading. During repeated loading and unloading processes, SMA absorbs energy through phase transformation (hysteresis energy dissipation), reducing structural vibration and dynamic response. SMA has a long hyperelastic cycle life (up to millions of cycles), making it suitable for long-term dynamic reinforcement needs.

[0028] (3) The reinforcement principle of carbon fiber reinforced composite (CFRP) is mainly based on its high strength, high modulus, lightweight and corrosion-resistant properties. Through interfacial bonding and stress transfer, it significantly improves the load-bearing capacity, stiffness and durability of the structure. The tensile strength of carbon fiber can reach 3000~7000 MPa and the elastic modulus is about 200~600 GPa, which is far greater than that of steel. It can effectively bear the tensile stress of the structure. The resin matrix bonds the fibers into a whole and transfers the stress to the structure. CFRP is tightly bonded to the surface of the structure through adhesive, forming a "composite material-matrix" synergistic stress system. Under the action of external force, CFRP transfers the load to the structure through interfacial shear stress, delays crack propagation and improves the overall stiffness.

[0029] The specific implementation method is as follows:

[0030] This utility model discloses a composite structure for strengthening fatigue cracks in steel bridges, comprising: a steel bridge plate 1 with cracks 11, the areas on both sides of the cracks 11 on the steel bridge plate 1 being a first impact zone 12 and a second impact zone 13, the area directly above the cracks 11 on the steel bridge plate 1 being a third impact zone 14, and shape memory alloy reinforcing strips 2 and carbon fiber reinforcing cloth 3 being sequentially laid on the steel bridge plate 1 from bottom to top at the cracks 11.

[0031] Carbon fiber reinforced fabric 3 fully covers shape memory alloy reinforcing strip 2.

[0032] The carbon fiber reinforcing fabric 3 includes a lower layer of high modulus carbon fiber fabric 31, a middle layer of medium-high modulus carbon fiber fabric 32, and an upper layer of standard modulus carbon fiber fabric 33, which are laid in sequence.

[0033] High-modulus carbon fiber cloth 31 is M40J grade with a modulus ≥380 GPa, medium-high modulus carbon fiber cloth 32 is T800 grade with a modulus of 294 GPa, and standard modulus carbon fiber cloth 33 is T300 grade with a modulus of 230 GPa.

[0034] The specific reinforcement process is as follows:

[0035] Figure 1 The selected steel bridge plate 1 to be reinforced is a flat butt-welded structure with equal thickness and width. Crack 11 occurred at the weld. Before reinforcement, the weld reinforcement was ground down. Figure 5 The ICR pneumatic device 100 consists of four parts: an air compressor 1001, an air guide pipe 1002, a pneumatic hammer 1003, and an impact head 1004. The air compressor 1001 provides power to the pneumatic hammer 1003, which drives the impact head 1004 to perform a hammering motion. This device is used to perform the first stage of reinforcement on the crack, i.e., according to... Figure 2The operation is performed in the order shown in Figures (a), (b), and (c). First, two impacts are applied to both sides of the crack, and finally a third impact is applied above the crack. The impact time is not less than 30 seconds, which can achieve initial crack closure. Next, SMA strips are pasted to implement the second layer of reinforcement. First, the area for applying structural adhesive is roughly marked, and the position for subsequent CFRP pasting needs to be reserved in advance. The area is roughened by grinding. Then, the SMA strips are pre-stretched. Since ICR treatment will cause depressions on the surface of the steel bridge deck, the reinforced surface needs to be leveled with leveling adhesive to ensure a smooth surface. The structural adhesive is evenly applied to the pasting area. High-performance two-component steel bonding adhesive is prepared at a ratio of 2:1 by weight. When bonding SMA strips, first use a small spatula to evenly apply the structural adhesive to the bonding area, ensuring no gaps. Then, bond the pre-stretched SMA strips to the marked positions and apply pressure with a strong magnet for curing. The curing time should be at least 5 days. After the structural adhesive has cured, use a hot air gun to heat-activate the center area of ​​the SMA strips, inducing restoring stress and providing long-term prestress compensation. It is important to note that the SMA activation temperature should be higher than the curing temperature of the structural adhesive. Finally, apply high-elasticity modulus CFRP fabric for a third layer of reinforcement. Apply a 0.3–0.5 mm thick layer of adhesive to the surface of the SMA after the second layer of reinforcement. Apply a 0.3-0.5mm thick layer of structural adhesive to the first layer of high-modulus CFRP, then apply a second layer of medium-high modulus carbon fiber cloth. Use a debubbling roller to roll the cloth multiple times along the fiber direction to ensure the CFRP cloth is straight, extended, and free of air bubbles, and to allow the structural adhesive to fully penetrate. Apply a 0.3-0.5mm thick layer of structural adhesive to the surface of the first high-modulus CFRP layer, then apply a second layer of medium-high modulus carbon fiber cloth. Use a debubbling roller to roll the cloth multiple times along the fiber direction. Finally, apply a 0.3-0.5mm thick layer of structural adhesive to the second medium-modulus CFRP layer, then apply a third layer of standard modulus carbon fiber cloth. Use a debubbling roller to roll the cloth multiple times along the fiber direction to form a gradient CFRP layer. The gradient CFRP is as follows: Figure 3 As shown in the image. After the adhesive is applied, clamps are used to apply pressure and cure the CFRP for 5 days. Once the structural adhesive has cured, the clamps are removed, thus completing the reinforcement composite solution. The final reinforcement effect is shown in the image. Figure 4 As shown.

[0036] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0037] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those 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 to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite structure for fatigue crack reinforcement of steel bridges, characterized in that, include: A steel bridge plate (1) with cracks (11) has a first hammering zone (12) and a second hammering zone (13) on both sides of the cracks (11), and a third hammering zone (14) on the steel bridge plate (1) directly above the cracks (11). Shape memory alloy reinforcing strips (2) and carbon fiber reinforcing cloth (3) are sequentially laid on the steel bridge plate (1) from bottom to top at the cracks (11).

2. The steel bridge fatigue crack reinforcement composite structure according to claim 1, characterized in that, The carbon fiber reinforcing fabric (3) fully covers the shape memory alloy reinforcing strip (2).

3. The steel bridge fatigue crack reinforcement composite structure according to any one of claims 1-2, characterized in that, The carbon fiber reinforcing fabric (3) includes a lower layer of high modulus carbon fiber fabric (31), a middle layer of medium-high modulus carbon fiber fabric (32), and an upper layer of standard modulus carbon fiber fabric (33) laid in sequence.

4. The steel bridge fatigue crack reinforcement composite structure according to claim 3, characterized in that, The high modulus carbon fiber cloth (31) is M40J grade with a modulus ≥380GPa, the medium-high modulus carbon fiber cloth (32) is T800 grade with a modulus of 294GPa, and the standard modulus carbon fiber cloth (33) is T300 grade with a modulus of 230GPa.

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