Intelligent cable for monitoring temperature and humidity of main cable of suspension bridge and monitoring method

Abstract

The invention discloses an intelligent cable for monitoring the temperature and humidity of a main cable of a suspension bridge and a monitoring method.The intelligent cable comprises a main cable strand and an intelligent cable strand embedded into the main cable strand, and the intelligent cable strand comprises a plurality of intelligent cable wires wound around the same cable strand in the main cable strand; the intelligent cable wire comprises a temperature and humidity fiber grating sensing unit, a spiral armored protection layer and a protection sleeve which are sequentially arranged from inside to outside. The temperature and humidity FBG sensing unit comprises a plurality of temperature and humidity FBG pairs, and each temperature and humidity FBG pair is composed of a temperature FBG and a humidity FBG; the humidity FBG is coated with a high-concentration polyimide sensibilization solution, the temperature and humidity FBG is sleeved with a double-layer capillary sleeve, and the double-layer capillary sleeve is used for isolating stress generated by the main cable strand; the spiral armored protection layer is of a stainless steel strip spiral winding structure. The intelligent rope can realize the temperature and humidity monitoring of the suspension bridge main cable in the full life cycle on the premise of overcoming the interference of the main cable stress on the temperature and humidity sensor.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering health monitoring technology, and in particular to an intelligent cable and monitoring method for monitoring the temperature and humidity of the main cable of a suspension bridge. Background Technology

[0002] The main cable of a long-span suspension bridge is the core load-bearing component of the bridge structure, and its service performance directly determines the safety and service life of the bridge. Under the coupled effects of multiple factors such as humidity, heat, and force, the high-strength steel wires of the main cable are prone to fatigue, corrosion, and even breakage. The internal temperature and humidity of the main cable are key environmental factors that induce corrosion of the steel wires. Residual rainwater from construction, external rainwater during operation, and the intrusion of acidic gases can lead to increased humidity inside the main cable, accelerating the corrosion of the steel wires (such as the Inoshima Ohashi Bridge in Japan and the High and Low Coast Bridge in Sweden, which both required maintenance or cable replacement due to corrosion of the main cable, and the Myaung Mya Bridge in Myanmar, which collapsed due to corrosion of the main cable).

[0003] Existing methods for monitoring the temperature and humidity of main cables have significant drawbacks: First, traditional sensors (such as resistive humidity sensors and single-layer encapsulated fiber Bragg grating sensors) are easily affected by stress in the main cable, resulting in low accuracy in temperature and humidity measurement and insufficient humidity sensitivity (the sensitivity of traditional humidity sensors with polyimide surface coating is only below 2 pm / %RH); Second, the sensor protection structure is weak and easily damaged under conditions such as main cable strand manufacturing (high temperature of hot-cast anchors), erection (traction and torsion), and service (cable clamp extrusion, cable saddle extrusion), making long-term stable monitoring impossible; Third, the monitoring range is limited, and the measurement points are scattered, making it difficult to cover the entire length of the main cable (usually more than 1 km), and it is impossible to obtain full-section temperature and humidity distribution data. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes an intelligent cable and monitoring method for monitoring the temperature and humidity of the main cable of a suspension bridge. This intelligent cable can achieve temperature and humidity monitoring of the main cable of a suspension bridge throughout its entire life cycle while overcoming the interference of the main cable stress on the temperature and humidity sensor. It features high measurement accuracy, long monitoring distance, and safety and reliability.

[0005] A smart cable for monitoring the temperature and humidity of the main cable of a suspension bridge includes a main cable strand and smart strands embedded in the main cable strand. Each smart strand comprises multiple smart wires wound around the same strand within the main cable strand. Each smart wire includes, from the inside out, a temperature and humidity fiber optic grating sensing unit, a spiral armored protective layer, and a protective sleeve. The temperature and humidity fiber optic grating sensing unit includes multiple pairs of temperature and humidity FBG gratings, each pair consisting of a temperature FBG grating and a humidity FBG grating. The humidity FBG grating is coated with a high-concentration polyimide sensitizing solution, and the temperature and humidity FBG grating is covered with a double-layer capillary sleeve to isolate stress generated by the main cable strand. The spiral armored protective layer is a spirally wound structure of stainless steel strip, and the protective sleeve has air circulation holes.

[0006] As a preferred embodiment of the above technical solution, the intelligent cable strand is embedded in the cable strand located on the side of the cable saddle in the main cable strand.

[0007] As a preferred embodiment of the above technical solution, the temperature and humidity FBG gratings of a single smart cable are arranged at intervals, and the temperature and humidity FBG gratings of two adjacent smart cables are staggered.

[0008] As a preferred embodiment of the above technical solution, the double-layer capillary tube includes an inner sleeve and an outer steel tube. The inner sleeve limits and straightens the optical fiber, and the outer steel tube is used to isolate external stress.

[0009] As a preferred embodiment of the above technical solution, the inner sleeve, the outer steel pipe, and the protective sleeve are all made of stainless steel.

[0010] As a preferred embodiment of the above technical solution, the temperature and humidity FBG grating pair is prepared using laser direct writing technology.

[0011] A method for monitoring the temperature and humidity of the main cable of a smart cable based on any one of the above-mentioned methods, the specific process of which is as follows:

[0012] S1, prepare intelligent cable wire, and sequentially complete temperature and humidity FBG grating writing, polyimide sensitizing coating, double-layer capillary steel tube stress isolation, spiral armor and stainless steel sleeve installation.

[0013] S2, the smart cable wire is embedded into the designated strand of the main cable to form a smart cable strand. Before the smart cable wire enters the anchorage area, a hole is opened to lead out the sensing optical fiber. The stainless steel sleeve participates in the hot casting anchor. Demodulators are set in the anchorage chambers on both sides of the suspension bridge.

[0014] S3, the demodulator acquires grating wavelength offset data, calculates the main cable temperature ΔT based on the temperature FBG grating, and calculates the relative humidity RH based on the humidity FBG grating after simultaneously removing the influence of temperature on humidity, where:

[0015] ΔT = ΔλT / 9.8

[0016] RH=(ΔλH-ΔλT) / 4

[0017] ΔλT represents the wavelength offset of the temperature FBG grating, and ΔλH represents the wavelength offset of the humidity FBG grating.

[0018] As a preferred embodiment of the above technical solution, in step S2, a backup demodulation interface is set at the top of the middle bridge tower of the suspension bridge and connected to a backup demodulator. The backup demodulation interface is formed by cutting the smart cable and leading out the sensing optical fiber.

[0019] As a preferred embodiment of the above technical solution, in step S3, when the smart cable breaks, the backup demodulator is activated to collect temperature and humidity data from the measuring points behind the break.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. High measurement accuracy: The humidity FBG grating is coated with high-concentration polyimide, with a sensitivity of 4pm / %RH, which is more than 100% higher than the traditional coating method; the double-layer capillary steel tube stress isolation structure can effectively eliminate the interference of main cable stress on the grating, with temperature measurement accuracy of ±0.5℃ and humidity measurement accuracy of ±2%RH.

[0022] 2. Strong environmental adaptability: The intelligent cable adopts a double-layer protection of "spiral armor + stainless steel sleeve". The 316L stainless steel sleeve can withstand the design load of the cable clamp and the compressive strength of the cable saddle. It is undamaged under cable strand traction, torsion and hot casting anchor conditions, meeting the requirements of long-term service.

[0023] 3. Comprehensive monitoring range: By staggering the gratings of two intelligent cable strands, full-section monitoring of the main cable can be achieved, solving the problem of scattered measuring points in traditional methods.

[0024] 4. High reliability: The design of demodulators at both ends and backup demodulation interface in the middle avoids monitoring interruption caused by fiber breakage; the fiber lead-out process at the anchor head has been experimentally verified, and the survival rate of the fiber is 100%. Attached Figure Description

[0025] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] A smart cable for monitoring the temperature and humidity of the main cable of a suspension bridge includes a main cable strand and smart strands embedded in the main cable strand. Each smart strand comprises multiple smart wires wound around the same strand within the main cable strand. Each smart wire includes, from the inside out, a temperature and humidity fiber optic grating sensing unit, a spiral armored protective layer, and a protective sleeve. The temperature and humidity fiber optic grating sensing unit includes multiple pairs of temperature and humidity FBG gratings, each pair consisting of a temperature FBG grating and a humidity FBG grating. The humidity FBG grating is coated with a high-concentration polyimide sensitizing solution, and the temperature and humidity FBG grating is covered with a double-layer capillary sleeve to isolate stress generated by the main cable strand. The spiral armored protective layer is a spirally wound structure of stainless steel strip, and the protective sleeve has air circulation holes.

[0028] The temperature and humidity FBG grating is fabricated using laser direct writing technology, eliminating the need to remove the fiber coating. The fiber has a tensile strength ≥100kpsi and can withstand a maximum strain of 20000με. The grating has a center wavelength of 1500-1600nm, a wavelength spacing of 2nm, and a grating length of 5mm. The temperature FBG grating is coated with a thermoplastic material for temperature measurement and humidity data compensation, with a temperature sensitivity of 9.8pm / ℃. The humidity FBG grating has a humidity sensitivity of 4pm / %RH.

[0029] The outer diameter of the steel strip in the spiral armor protective layer is 3-4mm, which is used to resist the traction and torsional forces during the cable strand erection process and protect the internal sensing unit.

[0030] The protective sleeve is made of 316L stainless steel with an outer diameter of 6.35mm and a wall thickness of 0.89mm. It has 1mm diameter air circulation holes on its surface to allow air to pass through the inside and outside of the sleeve, ensuring synchronized temperature and humidity. The ultimate elongation of the stainless steel sleeve is ≥4.0%, and it remains in the elastic stage under the design load, which can withstand the clamping force of the cable and the compressive force of the cable saddle.

[0031] In this embodiment, the smart cable strand is embedded in the main cable strand located on the side of the cable saddle.

[0032] In this embodiment, the temperature and humidity FBG gratings of a single smart cable are spaced apart, and the temperature and humidity FBG gratings of two adjacent smart cables are staggered.

[0033] Specifically, the temperature and humidity FBG grating pairs of a single smart cable strand are spaced 100m apart, and the grating pairs of two adjacent smart cable strands are staggered by 50m along the main cable axis.

[0034] In this embodiment, the double-layer capillary tube includes an inner sleeve and an outer steel tube. The inner sleeve limits and straightens the optical fiber, and the outer steel tube is used to isolate external stress.

[0035] In this embodiment, the inner sleeve, outer steel pipe, and protective sleeve are all made of stainless steel.

[0036] like Figure 1 The method for monitoring the temperature and humidity of the main cable of a smart cable based on any one of the above-mentioned features is as follows:

[0037] S1, prepare intelligent cable wire, and sequentially complete temperature and humidity FBG grating writing, polyimide sensitizing coating, double-layer capillary steel tube stress isolation, spiral armor and stainless steel sleeve installation.

[0038] S2, the smart cable wire is embedded into the designated strand of the main cable to form a smart cable strand. Before the smart cable wire enters the anchorage area, a hole is opened to lead out the sensing optical fiber. The stainless steel sleeve participates in the hot casting anchor. Demodulators are set in the anchorage chambers on both sides of the suspension bridge.

[0039] S3, the demodulator acquires grating wavelength offset data, calculates the main cable temperature ΔT based on the temperature FBG grating, and calculates the relative humidity RH based on the humidity FBG grating after simultaneously removing the influence of temperature on humidity, where:

[0040] ΔT = ΔλT / 9.8

[0041] RH=(ΔλH-ΔλT) / 4

[0042] ΔλT represents the wavelength offset of the temperature FBG grating, and ΔλH represents the wavelength offset of the humidity FBG grating.

[0043] In this embodiment, in step S2, a backup demodulation interface is set on the top of the middle bridge tower of the suspension bridge and connected to a backup demodulator. The backup demodulation interface is formed by cutting the smart cable and leading out the sensing optical fiber.

[0044] In this embodiment, in step S3, when the smart cable breaks, the backup demodulator is activated to collect temperature and humidity data at the measuring point behind the break.

[0045] The following uses the Cangrong Xunjiang Bridge in Guangxi (the world's first three-tower space cable ground anchorage suspension bridge with a main span exceeding 500 meters) as an example to illustrate the implementation process of this invention in detail:

[0046] 1. Intelligent cable fabrication parameters

[0047] Sensing fiber: It adopts ultraviolet direct writing type fiber, and the coating layer is a thermoplastic material with a tensile strength ≥100kpsi;

[0048] Temperature and humidity FBG grating: center wavelength 1550nm, wavelength interval 2nm, grating length 5mm; temperature grating is coated with hot melt material, humidity grating is coated with high concentration polyimide;

[0049] Stress isolation structure: inner steel pipe with an outer diameter of 2.5mm, outer steel pipe with an outer diameter of 3mm;

[0050] Spiral armored steel strip: 304 stainless steel, outer diameter 4mm;

[0051] Stainless steel sleeve: 316L stainless steel, outer diameter 6.35mm, wall thickness 0.89mm, air vent spacing 50cm, vent diameter 1mm.

[0052] 2. Intelligent thread-locking implantation

[0053] Each main cable of the Xunjiang Bridge contains 37 strands, each strand containing 127 Φ6mm high-strength steel wires. The 7th and 32nd strands (on the side of the cable saddle, where the compressive force is the least) are selected to be implanted with intelligent cable wires.

[0054] The intelligent cable is 1.5km long, and each intelligent cable is equipped with 15 sets of temperature and humidity grating pairs (100m apart). The grating pairs of two intelligent cables are staggered by 50m along the axial direction to form 30 measuring points, covering the entire length of the main cable.

[0055] 3. Monitoring system installation

[0056] Demodulator: A narrow-bandwidth fiber Bragg grating demodulator (wavelength resolution 0.1 pm) is used, and is installed in the anchor chambers on both banks;

[0057] Anchor head fiber optic cable lead-out: 1m before the smart cable enters the anchoring area, a Φ3mm hole is opened on the stainless steel sleeve, and the armored sensing fiber optic cable is led out and extended to the anchor chamber through the pre-embedded steel pipe. The stainless steel sleeve continues to extend into the anchoring area and is hot-cast into the anchor together with other steel wires.

[0058] Intermediate backup: Cut the smart cable at the top saddle of the middle tower, lead out the sensing fiber, and reserve the demodulator interface.

[0059] 4. Verification of monitoring effectiveness

[0060] Temperature and humidity performance test: In the constant temperature and humidity test chamber, the humidity was adjusted from 40% to 80% at 30℃. The wavelength of the humidity grating showed a linear relationship with the humidity change (R²=0.9998), which meets the design requirements.

[0061] Cable clamping test: A compressive force of 38.1kN (equivalent cable clamping force) was applied to a 60mm long stainless steel sleeve. The maximum stress of the sleeve was 317MPa (less than the tensile strength of 485MPa of 316L stainless steel), and no plastic deformation was observed.

[0062] On-site monitoring: After the bridge was put into operation, the demodulator collected data in real time. The temperature and humidity distribution of the main cable was uniform and the data from the measuring points was stable.

[0063] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A smart cable for monitoring temperature and humidity in the main cable of a suspension bridge, characterized in that: The system includes a main cable strand and smart strands embedded within it. Each smart strand comprises multiple smart wires wound around the same strand within the main cable strand. Each smart wire includes, from the inside out, a temperature and humidity fiber optic grating sensing unit, a spiral armored protective layer, and a protective sleeve. The temperature and humidity fiber optic grating sensing unit includes multiple pairs of temperature and humidity FBG gratings, each pair consisting of a temperature FBG grating and a humidity FBG grating. The humidity FBG grating is coated with a high-concentration polyimide sensitizing solution, and a double-layer capillary sleeve is fitted over it to isolate stress generated by the main cable strand. The spiral armored protective layer is a stainless steel strip spirally wound structure, and the protective sleeve has air circulation holes.

2. The intelligent cable for monitoring temperature and humidity of the main cable of a suspension bridge according to claim 1, characterized in that: The intelligent cable strand is embedded in the main cable strand located on the side of the cable saddle.

3. The intelligent cable for monitoring temperature and humidity of the main cable of a suspension bridge according to claim 3, characterized in that: The temperature and humidity FBG gratings of a single smart cable are arranged at intervals, and the temperature and humidity FBG gratings of two adjacent smart cables are staggered.

4. The intelligent cable for monitoring temperature and humidity of the main cable of a suspension bridge according to claim 1, characterized in that: The double-layer capillary tube includes an inner sleeve and an outer steel tube. The inner sleeve limits and straightens the optical fiber, and the outer steel tube is used to isolate external stress.

5. The intelligent cable for monitoring temperature and humidity of the main cable of a suspension bridge according to claim 4, characterized in that: The inner sleeve, outer steel pipe, and protective sleeve are all made of stainless steel.

6. The intelligent cable for monitoring temperature and humidity of the main cable of a suspension bridge according to claim 1, characterized in that: The temperature and humidity FBG grating pair was fabricated using laser direct writing technology.

7. A method for monitoring the temperature and humidity of the main cable of a smart cable according to any one of claims 1-6, characterized in that: The specific process is as follows: S1, prepare intelligent cable wire, and sequentially complete temperature and humidity FBG grating writing, polyimide sensitizing coating, double-layer capillary steel tube stress isolation, spiral armor and stainless steel sleeve installation. S2, the smart cable wire is embedded into the designated strand of the main cable to form a smart cable strand. Before the smart cable wire enters the anchorage area, a hole is opened to lead out the sensing optical fiber. The stainless steel sleeve participates in the hot casting anchor. Demodulators are set in the anchorage chambers on both sides of the suspension bridge. S3, the demodulator acquires grating wavelength offset data, calculates the main cable temperature ΔT based on the temperature FBG grating, and calculates the relative humidity RH based on the humidity FBG grating after simultaneously removing the influence of temperature on humidity, where: ΔT = ΔλT / 9.8 RH=(ΔλH-ΔλT) / 4 ΔλT represents the wavelength offset of the temperature FBG grating, and ΔλH represents the wavelength offset of the humidity FBG grating.

8. The method for monitoring the temperature and humidity of the main cable of an intelligent cable according to claim 7, characterized in that: In step S2, a backup demodulation interface is set on the top of the middle tower of the suspension bridge and connected to a backup demodulator. The backup demodulation interface is formed by cutting the smart cable and leading out the sensing optical fiber.

9. The method for monitoring the temperature and humidity of the main cable of an intelligent cable according to claim 8, characterized in that: In step S3, when the smart cable breaks, the backup demodulator is activated to collect temperature and humidity data from the measuring points behind the break.

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