An energy collection device arranged at a bridge expansion joint, a design method and a bridge expansion joint monitoring mechanism

Abstract

The present application relates to the technical fields of intelligent sensing of bridges, and particularly relates to an energy collection device arranged at a bridge expansion joint, a design method and a bridge expansion joint monitoring mechanism, comprising: a conversion unit arranged in a bridge expansion joint structure, capturing the strain of the structure after being stressed, and generating an alternating flexoelectric signal; a base layer located between the conversion unit and the bridge expansion joint, adjusting the strain distribution of the conversion unit; a rectification unit integrated with an impedance matching circuit, connected with the conversion unit, converting the alternating flexoelectric signal into a direct current, and delivering it to an energy storage unit; compared with the prior art, the beneficial effects of the present application are: the present application relates to a monitoring mechanism of a bridge expansion joint, the device has a self-powered structure based on the flexoelectric effect, without external power supply, significantly reducing the wiring and maintenance cost, at the same time, the monitoring unit realizes millimeter level displacement resolution and real-time structure health assessment, ensuring the structural safety of the bridge expansion joint.

Description

Technical Field

[0001] This invention relates to the field of intelligent sensing technology for bridges, specifically to an energy harvesting device and design method for bridge expansion joints, and a bridge expansion joint monitoring mechanism. Background Technology

[0002] Modular expansion joints for highway bridges are key dynamic connection components in bridge structures, used to accommodate longitudinal displacement at the beam ends caused by temperature changes, concrete shrinkage and creep, and vehicle loads. Traditional modular expansion joints typically consist of a center beam, cross beams, displacement boxes, and support blocks. The center beam often uses I-shaped steel sections to directly withstand wheel impacts and undergo bending deformation; the cross beams transfer loads to the main beams; and the support blocks provide low-friction support for the cross beams.

[0003] The vibrations and impacts generated when vehicles pass through expansion joints contain a significant amount of mechanical energy, which is currently dissipated primarily as heat. This not only leads to energy waste but also induces structural fatigue. Furthermore, as vulnerable components, the health of expansion joints is crucial to the overall safety of the bridge. Existing monitoring technologies largely rely on external power supplies and wired sensors, which suffer from problems such as complex installation, high maintenance costs, and insufficient long-term reliability.

[0004] The flexoelectric effect refers to the physical phenomenon of polarization of materials under non-uniform strain fields. However, in practical applications, the flexoelectric effect often suffers from problems such as low conversion efficiency and inability to increase the strain gradient. In order to pursue a large strain gradient, making the structure very thin or with sharp notches will sacrifice the mechanical strength and durability of the material, resulting in a reduction in service life. Therefore, how to achieve a balance between strength and reliability, and find the optimal balance point of the structure in accordance with the application scenario, is the technical problem to be solved by this application.

[0005] Therefore, developing an energy harvesting device and design method for bridge expansion joints, as well as a bridge expansion joint monitoring mechanism, not only has urgent research value, but also has good economic benefits and industrial application potential. This is the driving force and foundation for the completion of this invention. Summary of the Invention

[0006] In order to overcome the defects of the prior art mentioned above, the technical problem to be solved by the present invention is to provide an energy harvesting device and design method for bridge expansion joints, and a bridge expansion joint monitoring mechanism, so as to solve the technical problems of monitoring and energy loss of modular expansion joints in bridges.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] An energy harvesting device disposed at a bridge expansion joint includes:

[0009] The conversion unit, arranged in the bridge expansion joint structure, captures the strain of the structure after it is subjected to stress and generates an alternating flexural electrical signal.

[0010] The base layer, located between the transfer unit and the bridge expansion joint, adjusts the strain distribution of the transfer unit;

[0011] The rectifier unit, which integrates an impedance matching circuit, is connected to the conversion unit to convert the alternating flexural electrical signal into direct current and deliver it to the energy storage unit.

[0012] The energy storage unit, which is a supercapacitor or a miniature lithium battery, stores the converted electrical energy.

[0013] In this invention, as an improvement, the conversion unit is provided with an upper electrode, a semiconductor active layer and a lower electrode in sequence. The lower electrode is connected to the substrate layer, and the substrate layer is attached to the beam structure of the bridge expansion joint. The substrate layer has a gradient lattice structure.

[0014] In this invention, as an improvement, the conversion unit and the base layer are arranged in the middle beam and cross beam of the bridge expansion joint, specifically on the upper surface of the upper and lower flanges of the middle beam and both sides of the web, as well as on the upper surface of the cross beam at the connection between the cross beam and the middle beam.

[0015] A monitoring mechanism for bridge expansion joints with an energy harvesting device includes:

[0016] The monitoring unit, comprising several sensor components, is arranged in the expansion joint and the bridge structure on both sides of the expansion joint to monitor the deformation and stress of the bridge expansion joint.

[0017] The power supply device uses a conversion unit located in the bridge expansion joint to capture the bending strain of the structure after it is subjected to stress, generate an alternating flexural electrical signal, which is converted into direct current by a rectifier unit and then transmitted to the energy storage unit. The energy storage unit then supplies power to the sensor components in the monitoring unit.

[0018] A design method for an energy harvesting device, comprising:

[0019] S1: Based on the flexural electrical effect, select a suitable conversion unit material for bridge expansion joints and design the interface to achieve the corresponding conversion coefficient;

[0020] S2: A base layer is set between the beam and the transfer unit. The base layer structure is designed using a topology optimization method to enhance the gradient stress distribution of the transfer unit.

[0021] S3: Based on the characteristics of bridge expansion joints, the conversion unit and base layer are arranged in the bridge expansion joint;

[0022] S4: The integrated impedance matching circuit forms a rectifier unit, which converts the alternating flexural electrical signal into direct current and sends it to the energy storage unit;

[0023] S5: The energy storage unit is connected to the sensor components in the monitoring unit via a connection line, and supplies power to the sensor components.

[0024] In this invention, as an improvement, the conversion unit adopts a flexible thin-film composite material based on the structural properties of the bridge expansion joint. The overall thickness is 2-4 mm, and it is attached to the beam structure of the expansion joint. Specifically, it includes an upper electrode, a lower electrode, and a semiconductor active layer sandwiched between the upper and lower electrodes. The semiconductor active layer is barium titanate oxygen-reduced or n-type doped silicon, and the thickness is 0.5-2 mm.

[0025] In this invention, as an improvement, the interface between the semiconductor active layer and the upper electrode is designed as a corrugated or micro / nano structure with spaced trenches. The trench depth or the distance from the trough to the interface is 10 μm, and the period of the corrugations and trenches at the interface is 100 μm.

[0026] In this invention, as an improvement, the base layer structure design includes:

[0027] The design is based on a uniformly distributed gradient lattice structure.

[0028] Analyze the stress distribution of the beam at the location of the conversion unit, and calculate the strain gradient of the beam based on the stress distribution.

[0029] The gradient lattice structure of the substrate was optimized by comparing the strain gradient of the beam.

[0030] In this invention, as an improvement, optimizing the gradient lattice structure includes adjusting the lattice porosity by dividing the region into regions by the beam, wherein the lattice porosity is positively correlated with the strain of the beam.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) The present invention relates to a monitoring mechanism for bridge expansion joints. The device has a self-powered structure based on flexural electrical effect, which does not require an external power source, significantly reducing wiring and maintenance costs. At the same time, the monitoring unit achieves millimeter-level displacement resolution and real-time structural health assessment, ensuring the structural safety of bridge expansion joints.

[0033] (2) The present invention adopts a flexural electrical conversion unit suitable for bridge expansion joints. Through structural design and material optimization, the conversion efficiency is increased by 20-50% compared with the traditional piezoelectric mechanism, the power output is higher, and the power consumption of the monitoring unit is longer. In use, it is compatible with the existing expansion joint system, does not affect the original function of the structure, realizes integrated installation and maintenance, and has no polarization degradation problem and excellent resistance to mechanical fatigue. Attached Figure Description

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0035] Figure 1 This is a schematic diagram of the conversion unit of the present invention installed in an expansion joint;

[0036] Figure 2 This is a schematic diagram of the structure of the conversion unit of the present invention at the installation positions of the middle beam and the cross beam;

[0037] Figure 3 This is a top view of the conversion unit of the present invention at the installation position on the crossbeam;

[0038] Figure 4 This is a schematic diagram of the conversion unit and the base layer of the present invention;

[0039] Figure 5 This is a schematic diagram of the design process of the base layer of the present invention;

[0040] In the figure: 1. Substrate layer, 2. Protective layer, 3. Conversion unit, 301. Upper electrode, 302. Semiconductor active layer, 303. Lower electrode, 6. Middle beam, 7. Crossbeam. Detailed Implementation

[0041] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0042] like Figure 1-2 As shown, an energy harvesting device arranged in a bridge expansion joint includes a conversion unit 3, a base layer 1, a rectifier unit, and an energy storage unit. The conversion unit 3, the rectifier unit, and the energy storage unit constitute an energy conversion-storage system. The conversion unit 3 is arranged in the bridge expansion joint to capture the strain of the structure after it is subjected to stress and generate an alternating flexural electrical signal.

[0043] By monitoring the stress and deformation of the bridge expansion joint structure, it was found that the structure with large bending strain after being stressed includes the middle beam 6 and the cross beam 7. The middle beam 6 is made of I-beam steel, and the cross beam 7 is supported below the middle beam 6. The transfer unit 3 is installed on the upper surface of the upper and lower flanges of the middle beam 6 and both sides of the web, as well as on the upper surface of the cross beam at the connection between the cross beam 7 and the middle beam 6. In order to avoid excessive wear of the transfer unit 3, a protective layer 2 is covered on the outside of the transfer unit 3. The protective layer 2 is a thin sheet-like PDMS layer with a thickness of 100μm. The total thickness of the protective layer 2, the transfer unit 3 and the base layer 1 is between 2-5mm.

[0044] like Figure 3 As shown, the conversion unit 3 is provided with an upper electrode 301, a semiconductor active layer 302 and a lower electrode 303 in sequence. The semiconductor active layer 302 is barium oxygen-reduced titanate or n-type doped silicon, with a thickness of 0.5~2 mm.

[0045] The semiconductor active layer 302, which is barium titanate with oxygen reduction, was prepared by sol-gel method and RTP rapid thermal treatment. The thermal treatment parameters were 650°C for 30 min.

[0046] The semiconductor active layer 302 is made of n-type doped silicon by chemical vapor deposition (CVD) or ion implantation.

[0047] By adjusting the material and thickness of the semiconductor active layer 302 as described above, the interfacial polarization effect is enhanced in the contact between the semiconductor active layer 302 and the upper electrode 301, achieving an effective flexural coefficient of not less than 100 μC / m.

[0048] Based on the material and thickness of the semiconductor active layer, a corrugated micro / nano structure or a micro / nano structure with spaced trenches is designed at the contact interface between the semiconductor active layer 302 and the upper electrode 301 to improve the concentration of the structural strain gradient, clarify the balance relationship between the structural strain gradient and the strength, and determine the setting parameters of the semiconductor active layer 302 micro / nano structure. The setting period of the corrugations and trenches at the interface is adjusted to 100μm, that is, the distance from one peak to the adjacent valley is 100μm, the distance between the bottoms of two adjacent trenches is 100μm, and the trench depth and the distance from the valley to the interface are 10μm.

[0049] The surface of the semiconductor active layer 302 structure is replicated in batches by photolithography and reactive ion etching, and nanoimprinting is used to achieve the replication of surface texture.

[0050] The design of materials and structure in the above-mentioned conversion unit serves two purposes: first, to ensure that the conversion unit is properly installed in the bridge expansion joint; and second, to improve the strain gradient and flexural electro-electric conversion efficiency through material design.

[0051] like Figure 3 As shown, the conversion unit 3 is arranged on the beam structure through the base layer 1, which is a gradient lattice structure. The gradient lattice structure of the base layer is designed based on topology optimization.

[0052] The specific design method for the above energy harvesting device is as follows:

[0053] S1: Based on the flexural electrical effect, select a conversion unit material suitable for bridge expansion joints, enhance the effective flexural electrical coefficient through material selection, and conduct interface design to improve the degree of strain gradient concentration, thereby increasing the energy conversion factor by 4 to 8 times.

[0054] S2: A base layer is set between the beam and the transfer unit. The base layer structure is designed using a topology optimization method to enhance the gradient stress distribution of the transfer unit.

[0055] S3: Based on the characteristics of bridge expansion joints, the conversion unit and base layer are arranged in the bridge expansion joint. The conversion unit is arranged in the stress gradient concentration area of ​​the bridge expansion joint, including the upper surface of the upper and lower flanges of the middle beam and both sides of the web, as well as the upper surface of the crossbeam at the connection between the crossbeam and the middle beam. According to the size of the conversion unit, the arrangement position can extend from the connection between the crossbeam and the middle beam to the surrounding upper surface area of ​​the crossbeam.

[0056] S4: The integrated impedance matching circuit forms a rectifier unit, which converts the alternating flexural electrical signal into direct current and sends it to the energy storage unit;

[0057] S5: The energy storage unit is connected to the sensor components in the monitoring unit via a connection line, and supplies power to the sensor components.

[0058] The base layer structure design includes:

[0059] The initial design was based on a uniformly distributed gradient lattice structure, and the lattice structure was adjusted accordingly.

[0060] Based on the different locations of the conversion units, the stress distribution of the beam at the location of the conversion units is analyzed, and the strain gradient of the beam is calculated based on the stress distribution. The finite element method is used to analyze and calculate the stress and strain gradient of the beam structure.

[0061] The gradient lattice structure of the substrate was optimized by comparing the strain gradient of the beam.

[0062] Optimizing the lattice structure involves adjusting the porosity of the structure according to the strain gradient of the beam, so that the gradient lattice porosity is positively correlated with the strain gradient of the beam, and adjusting the distribution of the strain gradient by adjusting the lattice to achieve a seamless transition of the strain boundary.

[0063] The relationship between porosity and strain gradient is mainly reflected in the control of material mechanical properties. By adjusting the gradient lattice porosity, the effective elastic modulus and strength of the material can be affected. Higher porosity will lead to a decrease in material stiffness, making it easier to deform under the same load, thus corresponding to higher local strain. However, the distribution of porosity is not unlimited and needs to correspond to the strain gradient. Therefore, the lattice structure needs to be adjusted according to the strain gradient region of the beam.

[0064] In the expansion joint beam, the measured strain gradient range is 0.1-1 m⁻¹, corresponding to bending deformation with a curvature radius of 1-10 m. As a dividing threshold, the region with a strain gradient <0.5 m⁻¹ is the low gradient region, in which the corresponding gradient lattice has a uniform material distribution, and the region with a strain gradient >0.5 m⁻¹ is the high gradient region, which requires gradient lattice strengthening to optimize power density and voltage output.

[0065] In fatigue testing, the stress range is based on dynamic amplification and horizontal load ratio. When dividing the region, the strain gradient threshold can be set to 50% of the fatigue limit to ensure uniform strain within the region and avoid cracking.

[0066] In topology optimization, region partitioning is performed at the cell scale, and the strain gradient threshold is based on the minimum correlation score of the filter homogenization model to exclude low-correlation regions.

[0067] In this application, the adjustments to the pore density and size of the crystal lattice are as follows:

[0068] 1) Local stiffness control: Reducing pore size and increasing density improves local modulus and strength, allowing the region to withstand higher loads while generating less strain; conversely, increasing pore size and decreasing density makes the material softer, allowing for greater deformation to absorb energy. In the beam of a modular expansion joint, the lattice is adjusted according to the strain gradient, so that high-strain regions use large pores and low-strain regions use small pores, achieving a positive correlation distribution and smoothing the strain gradient. For example, for a strain gradient of 0.1-1 m⁻¹, regions with small radii of curvature use 70% pores, and low-strain regions use 30% pores.

[0069] 2) Deformation behavior optimization: Adjusting the pore size can induce layer-by-layer collapse or segmented deformation, starting from the high-porosity region and gradually transitioning to the low-porosity region, avoiding overall shear failure and improving energy absorption efficiency by 20%-148%. This is particularly effective under longitudinal compression, enabling the strain gradient to gradually change along the thickness or length direction, enhancing the fatigue resistance and power density of the structure.

[0070] 3) Seamless transition and performance improvement: By adjusting the porosity through continuous or stepped gradients, such as linear, quadratic or S-shaped functions, weak layers or discontinuous elements are avoided, achieving seamless strain transition, reducing stress concentration, and reducing modulus loss by 19%-72% at the transition point.

[0071] Experiments have verified that the linear inverse relationship with the strain gradient can significantly improve compressive strength by 14%-50% and energy absorption without sacrificing overall porosity.

[0072] A monitoring mechanism for bridge expansion joints is provided, which adds a monitoring unit to the above-mentioned energy harvesting device. The monitoring unit includes several monitoring sensors to monitor the stress and deformation of the bridge expansion joint. In the displacement monitoring of the bridge expansion joint structure, the resolution reaches the millimeter level. In damage detection, abnormal signals are identified through spectrum analysis to detect damage such as cracks and fatigue.

[0073] The conversion unit also has sensing and monitoring functions. Using the data from the conversion unit, the stress distribution and strain gradient of the beam can be monitored, and vehicle load information for different lanes and axle loads can be obtained.

[0074] Specific implementation of the conversion unit:

[0075] Flexural electrical conversion units are arranged on both sides of the web and the upper surface of the lower flange of the I-beam. The structure includes:

[0076] The substrate is a 50 μm polyimide (PI) film; the lower electrode is a 200 nm sputtered gold (Au) film; the active layer is a 1 mm thick BaTiO3-δ film prepared by the sol-gel method with an oxygen vacancy concentration of 10¹. 8 ~10¹ 9 cm⁻³; the upper electrode is a 200 nm aluminum (Al) film forming a Schottky contact; the protective layer is a 100 μm polydimethylsiloxane (PDMS).

[0077] The surface of the active layer is laser-processed to form a sinusoidal ripple microstructure with a period of 100 μm and a depth of 10 μm.

[0078] After being placed in the bridge expansion joint, under vehicle load, the test showed that the radius of curvature of the middle beam was 1~10 m, the strain gradient was 0.1~1 m⁻¹, the measured output voltage was 5~10 V, and the volume power density reached 100 μW / cm³.

[0079] Specific embodiments of conversion units with sensing and monitoring functions:

[0080] A transition unit is installed on the upper surface of the crossbeam at mid-span and at the connection with the middle beam. The structure includes:

[0081] The active layer is n-type doped silicon with a concentration of 10¹ 6 cm⁻³, thickness 0.5 mm; the electrode is a Pt / Ti bilayer structure, and the size is a flexible sheet of 40 mm × 20 mm; the gradient lattice is prepared by 3D printing, with a porosity gradient of 0–70%.

[0082] When the beam is subjected to load and bending, the output voltage is linearly related to the bending moment, with a calibration coefficient of 0.2 V ( / kN·m). Load distribution and modal identification can be achieved through multi-unit deployment. After 30 days of continuous monitoring, the load characteristics of vehicles with different lanes and axle loads were successfully obtained.

[0083] Specific implementation of the monitoring unit:

[0084] In the monitoring unit, the rectifier unit uses a Schottky diode 1N5819 with VF=0.3 V, the energy storage unit consists of a 100 μF supercapacitor + a 3.7 V lithium battery, and the wireless transmission module is a LoRa module with a transmission distance >1 km. The spectrum identification settings are 100 Hz for normal operation and 1 Hz for energy-saving mode. The system has a built-in adaptive threshold algorithm that can identify spectrum abrupt changes (such as new resonance peaks) and trigger high-frequency sampling and early warning. In a 6-month field test on a highway bridge, it successfully provided early warning for two cases of abnormal vibration caused by aging of the sealing strip.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A design method for an energy harvesting device arranged in a bridge expansion joint, characterized in that, The energy harvesting device specifically includes: The conversion unit captures the strain of the structure after it is subjected to force and generates an alternating flexural electrical signal; Base layer, adjust the strain distribution of the conversion unit; The rectifier unit, which integrates an impedance matching circuit, is connected to the conversion unit to convert the alternating flexural electrical signal into direct current and deliver it to the energy storage unit. The energy storage unit, which is a supercapacitor or a miniature lithium battery, stores the converted electrical energy. The conversion unit is provided with an upper electrode, a semiconductor active layer and a lower electrode in sequence. The lower electrode is connected to the base layer. The base layer is attached to the beam structure of the bridge expansion joint. The beam structure includes the upper surface of the upper and lower flanges of the middle beam of the bridge expansion joint and both sides of the web plate, as well as the upper surface of the crossbeam at the connection between the crossbeam and the middle beam of the bridge expansion joint. The design methodology for energy harvesting devices specifically includes: S1: Based on the flexural electrical effect, select a suitable conversion unit material for bridge expansion joints and design the interface to achieve the corresponding conversion coefficient; S2: A base layer is set between the beam structure and the transfer unit. The base layer structure is designed using a topology optimization method to enhance the gradient stress distribution of the transfer unit. S3: Based on the characteristics of bridge expansion joints, the conversion unit and base layer are arranged in the bridge expansion joint; S4: The integrated impedance matching circuit forms a rectifier unit, which converts the alternating flexural electrical signal into direct current and sends it to the energy storage unit; S5: The energy storage unit is connected to the sensor assembly in the monitoring unit via a connection line, and supplies power to the sensor assembly; The conversion unit is based on the structural properties of bridge expansion joints and adopts a flexible thin-sheet composite material with an overall thickness of 2-5 mm. The semiconductor active layer is barium titanate oxygen reduction or n-type doped silicon with a thickness of 0.5-2 mm. The base layer has a gradient lattice structure.

2. A bridge expansion joint monitoring mechanism applying the design method of claim 1, characterized in that, include: The monitoring unit, comprising several sensor components, is arranged in the expansion joint and the bridge structure on both sides of the expansion joint to monitor the deformation and stress of the bridge expansion joint. The power supply unit captures the bending strain of the structure after it is subjected to stress by the conversion unit, generates an alternating flexural electrical signal, which is converted into DC power by the rectifier unit and then sent to the energy storage unit, which in turn supplies power to the sensor components in the monitoring unit.

3. The design method of the energy harvesting device arranged in the bridge expansion joint according to claim 1, characterized in that: The interface between the semiconductor active layer and the upper electrode is designed as a corrugated or spaced-out micro / nano structure. The trench depth or the distance from the trough to the interface is 10 μm, and the period of the corrugations and trenches at the interface is 100 μm.

4. The design method of the energy harvesting device arranged in the bridge expansion joint according to claim 1, characterized in that: The design of the base layer structure includes: The design is based on a uniformly distributed gradient lattice structure. Analyze the stress distribution of the beam structure at the location of the conversion unit, and calculate the strain gradient of the beam structure based on the stress distribution; The gradient lattice structure of the substrate layer was optimized by comparing the strain gradient of the bridge expansion joint beam structure.

5. The design method of the energy harvesting device arranged in the bridge expansion joint according to claim 4, characterized in that: Optimizing the gradient lattice structure of the substrate involves adjusting the density and size of the lattice pores based on the strain gradient of the beam structure, wherein the density and size of the lattice pores are positively correlated with the strain gradient of the beam structure.

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