CN111289474A - Intelligent anchorage device for monitoring corrosion fracture of prestressed steel strand - Google Patents

Abstract

The invention provides an intelligent anchor for monitoring corrosion fracture of a prestressed steel strand, and belongs to the technical field of structural health monitoring. The intelligent anchorage device for monitoring the corrosion fracture of the steel strand comprises the steel strand, a working clamping piece, a working anchor ring, a groove cover, an anchor gasket, a spiral rib, a corrugated pipe, a photonic crystal fiber sensor and a rubber hose. The intelligent anchorage device is based on the working principle of a photonic fiber interferometer, adopts a special packaging method, and utilizes the characteristic that optical signals in photonic crystal fibers are sensitive to local uneven pressure change, so that the pretightening force change on the working anchor ring surface is monitored in real time under the condition that the normal work of the steel strand anchorage device is not influenced, and the condition of corrosion fracture of the steel strand is accurately reflected. The method has the advantages of high sensitivity, simple operation, strong practicability, wide application prospect and wide popularization market.

Description

An intelligent anchor for monitoring corrosion and fracture of prestressed steel strands

technical field

The invention relates to an intelligent anchor for monitoring corrosion and fracture of prestressed steel strands, belonging to the field of structural health monitoring, in particular for monitoring corrosion and fracture of prestressed steel strands.

Background technique

In the development of the construction industry in recent years, steel strands have been widely used in bridge cables and prestressed anchors. Steel strand not only has very high tensile strength, but also has good relaxation, which plays an irreplaceable role in the construction industry. However, like ordinary steel bars, steel strands will also corrode, the bearing capacity of the corroded steel strands is greatly reduced, and the severely corroded steel strands may even break, seriously endangering the safety of building structures. Therefore, it is necessary to monitor the performance of the steel strands in real time, and take safety protection measures in time for the steel strands that are corroded and fractured to avoid engineering accidents and casualties.

At present, the commonly used methods for monitoring corrosion and fracture of prestressed steel strands include acoustic emission method, ultrasonic guided wave method, magnetic flux sensor monitoring method, frequency meter method and strain gauge monitoring method. The monitoring range of the acoustic emission method and the ultrasonic guided wave method is not easy to determine, and the collected signal is easily disturbed by environmental factors, which reduces the measurement accuracy. The magnetic fields between the inner coils of the magnetic flux sensor interfere with each other, and the measurement accuracy is not high. The frequency meter monitoring method requires that the measured object only vibrates slightly and has no lateral external thrust, which is easily affected by end constraints such as dampers, and its application is limited. Strain gauge monitoring is a widely used method at present, but in practical applications, it has the disadvantages of poor durability and short service life, and it is difficult to realize the force monitoring of the structure during operation.

Optical fiber sensors are small in size, light in weight, resistant to electromagnetic interference, and strong in corrosion resistance, and some optical fiber-based sensors are also used to monitor corrosion fractures in steel strands. Compared with the traditional steel strand corrosion and fracture monitoring method, the intelligent anchorage for prestressed steel strand corrosion and fracture monitoring based on photonic crystal fiber is simple to manufacture, has high sensitivity, reliable measurement results and low production cost, and does not affect the production cost. The monitoring results of the normal operation of the steel strand can provide an important basis for the durability evaluation and reinforcement maintenance of the steel strand.

SUMMARY OF THE INVENTION

In view of the problems in the prior art, the present invention provides an intelligent anchor for monitoring corrosion and fracture of prestressed steel strands. The intelligent anchor is made based on a photonic crystal optical fiber sensor. Sensitive to pressure changes, the corrosion fracture of steel strands can be indirectly monitored by changes in the local pressure exerted on it. The measurement results of the device are reliable and can provide an important basis for the durability evaluation of steel strands and reinforcement and maintenance.

Technical scheme of the present invention:

An intelligent anchor for monitoring corrosion and fracture of prestressed steel strands, including steel strands 1, working clips 2, working anchor rings 3, groove covers 4, anchor washers 5, spiral bars 6, bellows 7 , photonic crystal optical fiber pressure sensor 8 and rubber hose 9; wherein photonic crystal optical fiber pressure sensor 8 is formed by fusion of first single-mode optical fiber 10, photonic crystal optical fiber 11 and second single-mode optical fiber 12; wherein the first single-mode optical fiber 10 and the second single-mode fiber 12 includes a core 13, a cladding layer 14, a coating layer 15 and a plastic protective sheath 16; the photonic crystal fiber 11 includes a core 17, a cladding layer 18, a coating layer 19, a plastic protective sheath 20 and a plastic sheath Layer air channel 21;

Both ends of the photonic crystal fiber 11 are respectively fused with the first single-mode fiber 10 and the second single-mode fiber 12; one end of the first single-mode fiber 10 is fused with the photonic crystal fiber 11, and the other end is a free end , used to connect the light source transmitter and the spectrum analyzer; one end of the second single-mode fiber 12 is welded with the photonic crystal fiber 11, and a layer of gold film 25 is evenly deposited on the end face of the other end;

The grooves 23 are evenly cut around the contact surface of the working anchor ring 3 and the anchor gasket 5, and the groove positions correspond to the distribution positions of the steel strands 1 one-to-one;

The groove cover 4 is an annular cover, and a hole is reserved in the center to ensure the smooth passage of the steel strand; and the lower surface of the groove cover 4 is fixed with a serrated tooth that engages with the groove 23 on the working anchor ring 3. twenty four;

The gap between the working anchor ring 3 and the groove cover 4 is sealed with a thin rubber skin;

The photonic crystal optical fiber pressure sensor 8 is placed in the groove 23 of the working anchor ring 3, and the groove 23 and the serrated teeth 24 on the groove cover 4 are pressed against each other, and the photonic crystal optical fiber sensor 8 in the middle is formed. pressure;

A ring-shaped groove 27 is drilled around the groove 23 near the steel strand 1 and communicated with the groove 23 for placing the transmission single-mode optical fiber 10 at the end of the sensor, and a plurality of transmission single-mode optical fibers extend concave The grooves 27 lead together to the outside of the anchor ring.

The uncompressed part of the first single-mode optical fiber 10 is packaged and protected by a plastic hose 9 .

There is a certain angle between the anchor ring groove 23 and the radius of the anchor ring 3 to avoid breakage of the photonic crystal fiber sensor 8 during the winding process.

The photonic crystal fiber sensor 8 is sensitive to local uneven pressure changes, and can sensitively monitor the pressure changes between the anchor ring groove 23 and the serrated teeth 24 .

The thin rubber skin 26 is used to seal the gap between the groove cover 4 and the working anchor ring 3, and the thin rubber skin 26 has good elasticity to ensure the normal operation of the intelligent anchor.

The sizes of the teeth 6 on the groove cover and the grooves 7 on the anchor ring ensure that a sufficient force can be transmitted to the photonic crystal fiber sensor 8 without being damaged by pressure.

The groove cover teeth 6 are serrated, and apply partial pressure to the photonic crystal fiber part of the photonic crystal fiber sensor 8; epoxy resin glue or glass fiber cloth 26 is used for the uncompressed part of the photonic crystal fiber sensor 8. fixed.

The slot position and the groove spacing on the anchor ring 3 are adjusted according to the distribution of steel strands, the number of steel strands and the sensitivity requirements of the photonic crystal fiber pressure sensor.

The probe length of the photonic crystal fiber pressure sensor 8 is adjusted according to the size of the anchor ring 3 and the monitoring sensitivity requirements.

The working principle of the intelligent anchorage for monitoring corrosion and fracture of prestressed steel strands:

The core principle of the present invention is the working principle of the photonic crystal fiber interferometer, as shown in FIG. 6 . In the present invention, the light source emitted by the light source transmitter is transmitted to the core 13 of the first single-mode optical fiber 10. As can be seen from FIG. 6(a), when the light propagating in the single-mode optical fiber reaches a 11) When there is an air bubble in the splicing area, part of the light is reflected back; another part of the light passes through the bubble, and the air bubble acts as a diffusing lens to diffract the light, and part of the light is excited into the cladding for transmission, forming a cladding mode. The two modes of light continue to be transmitted to the second single-mode fiber (12) to the end of the second single-mode fiber (12). The gold film at the end of the second single-mode fiber acts as a mirror to reflect the light back, and the light intensity returned to the first single-mode fiber is

I _R =I ₁ +I ₂ +2(I ₁ ×I ₂ ) ^1/2 cos(Δφ) (1)

Among them, I ₁ and I ₂ are the light intensities of the light in the core 17 and the cladding 18 of the photonic crystal fiber 11, respectively. Δφ is the total phase difference, and the calculation method is

Δφ=2πΔnL _f /λ (2)

where Δn=n ₁ −n ₂ , n ₁ and n ₂ are the refractive indices of the core 17 and cladding 18 of the photonic crystal fiber 11 , respectively, L _f is the length of the photonic crystal fiber 11 , and λ is the wavelength of the light source light. Finally, the result obtained can be represented by the visibility v of the light

V=-10·log ₁₀ [1-2(k) ^1/2 /(1+k)] (3)

where k=I ₂ /I ₁ .

In the present invention, when the anchor ring 3 and the anchor spacer 5 are stacked against each other, the preload force F generated by the anchor spacer will be transmitted to the groove cover 4, and then the groove cover 4 will transmit it to the photonic crystal fiber by pressure The sensor 8 is forced to cause the tiny holes 21 to collapse. Figure 6(a) after compressive collapse and Figure 6(b) before compressive collapse. After the tiny hole 21 collapses, the propagating light beam transmitted from the transmission single-mode fiber 10 to the photonic fiber 11 propagates along the fiber core 17, and receives the optical signal v ₀ reflected back by the mirror 25, which represents that the steel strand does not appear corrosion cracking.

When the steel strand is corroded and fractured, the preload force F of the photonic crystal fiber sensor buried in the nearby groove is lost, and the pressure transmitted by the groove cover tooth 24 to the photonic fiber sensor 8 becomes smaller F', which collapses under compression. The tiny holes 21 become larger, changing the refractive index of the cladding 18 , which affects the light beam propagating in the core 17 , resulting in changes in the optical signal output by the single-mode fiber 10 . There is a certain mathematical relationship between the preload force F and the reflected light signal v:

F=f(v) (4)

The functional relationship in formula (4) can be fitted by experiment. According to formula (4), the corrosion and fracture of the steel strand can be inferred according to the change degree of the optical signal.

Beneficial effects of the present invention:

1. The present invention can monitor the corrosion and fracture of steel strands in real time by monitoring the pressure of the photonic optical fiber;

2. The sensing principle of the present invention is a photonic crystal fiber interferometer, which has high sensitivity, faster acquisition of monitoring data, and is more authentic and reliable;

3. The present invention is easy to operate, and is not affected by external factors such as the environment, and the measurement results are more accurate and reliable;

4. The photonic crystal optical fiber sensor in the present invention is small in size, and when it is embedded in the working anchor ring, the normal operation of the steel strand anchorage will not be affected, and the non-destructive monitoring of the corrosion and fracture of the steel strand can be realized;

5. The present invention has simple operation, convenient sensor arrangement and low cost, is suitable for promotion, and has a high application prospect.

Description of drawings

Fig. 1 is the schematic diagram of the intelligent anchorage used for monitoring the corrosion and fracture of steel strand according to the present invention;

Fig. 2 is the B-B cross-sectional view of the intelligent anchorage for monitoring corrosion and fracture of steel strands according to the present invention;

Fig. 3 is the A-A cross-sectional view of the intelligent anchorage for monitoring corrosion and fracture of steel strands according to the present invention;

4 is a detailed view of the working anchor ring groove of the intelligent anchor for monitoring corrosion and fracture of steel strands according to the present invention;

5 is a schematic diagram of a photonic crystal fiber pressure sensor based on the present invention, (a) a schematic diagram of a photonic crystal fiber pressure sensor; (b) a cross-sectional view of the photonic crystal fiber pressure sensor C1-C1; (c) a cross-sectional view of the photonic crystal fiber pressure sensor C2-C2 ;

6 is a schematic diagram of the working mechanism of the intelligent anchor for monitoring the corrosion and fracture of steel strands according to the present invention, (a) before corrosion and fracture of steel strands; (b) after corrosion and fracture of steel strands; (c) schematic diagram of incident spectrum and transmission spectrum ;

7 is a schematic diagram of the relationship between pressure and reflected light intensity based on a photonic crystal fiber pressure sensor of the present invention;

In the figure: 1 steel strand; 2 working clip; 3 working anchor ring; 4 groove cover; 5 anchor gasket; 6 spiral rib; 7 corrugated tube; 8 photonic crystal fiber pressure sensor; 9 plastic hose; 10 1 single-mode fiber; 11 photonic crystal fiber; 12 second single-mode fiber; 13 single-mode fiber core; 14 single-mode fiber cladding; 15 single-mode fiber coating; 16 single-mode fiber plastic protective sheath; 17 core ; 18 cladding; 19 coating layer; 20 plastic protective cover; 21 cladding air channel; 23 anchor ring groove; 24 serrated teeth; 25 gold film; 26 thin rubber skin, epoxy resin glue or glass fiber cloth .

Detailed ways

In order to make the objectives, features and advantages of the present invention more intuitive and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the following descriptions The embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in Figures 1-7, the present invention provides a smart anchor for monitoring corrosion and fracture of prestressed steel strands, characterized in that the smart anchor for monitoring corrosion and fracture of prestressed steel strands based on photonic optical fibers The tool includes a steel strand 1, a working clip 2, a working anchor ring 3, a groove cover 4, an anchor gasket 5, a spiral rib 6, a corrugated tube 7, a photonic crystal fiber sensor 8 and a rubber hose 9; among which the photonic crystal fiber The pressure sensor is formed by splicing a first single-mode fiber 10, a photonic crystal fiber 11, and a second single-mode fiber 12; wherein the first single-mode fiber 10 and the second single-mode fiber 12 include a core 13, a cladding 14, a coating layer 15 and plastic protective sheath 16; photonic crystal fiber (PCF) 11 includes core 17, cladding layer 18, coating layer 19, plastic protective sheath 20 and cladding air channel 21;

Two ends of the photonic crystal fiber 11 are respectively fused with the first single-mode fiber 10 and the second single-mode fiber 12; one end of the first single-mode fiber 10 is fused with the photonic crystal fiber 11, and the other end is a free end for communication A light source transmitter and a spectrum analyzer; one end of the second single-mode fiber 12 is welded to the photonic crystal fiber 11, and a layer of gold film 25 is uniformly deposited on the end face of the other end;

The grooves 23 are evenly cut around the contact surface of the working anchor ring 3 and the anchor gasket 5, and the groove positions correspond to the distribution positions of the steel strands 1 one-to-one;

The groove cover 4 is an annular cover, and a hole is reserved in the center to ensure that the steel strand can pass through smoothly; and the lower surface of the groove cover 4 is fixed with a zigzag tooth (24) that engages with the groove 23 of the working anchor ring 3;

The gap between the working anchor ring 3 and the groove cover 4 is sealed with a thin rubber skin;

The photonic crystal fiber sensor 4 is placed in the groove 23 of the working anchor ring, and the groove 23 and the serrated teeth 24 on the groove cover 4 are pressed against each other to form a pre-pressure for the photonic crystal fiber sensor 4 in the middle.

An annular groove 27 is drilled around the groove 23 near the steel strand 1 and communicated with the groove 23 to place the transmission single-mode optical fiber 10 at the end of the sensor, and a plurality of transmission single-mode optical fibers extend the groove 27 are led out together to the outside of the anchor ring.

The uncompressed portion of the first single-mode optical fiber is packaged and protected by a plastic hose 9 .

There is a certain angle between the anchor ring groove 23 and the radius of the anchor ring 3 to prevent the photonic crystal fiber sensor 8 from being broken during the winding process.

The photonic crystal fiber sensor 4 is sensitive to locally unevenly distributed pressure, and can sensitively monitor the pressure change between the groove 23 of the anchor ring and the serrated teeth 24 .

Further, the thin rubber skin 26 is used to seal the gap between the groove cover 4 and the working anchor ring 3, and the thin rubber skin 26 has good elasticity and can ensure the normal operation of the smart anchor.

Further, the size of the groove cover teeth 6 and the groove 7 on the anchor ring are appropriate, which can not only transmit a sufficient force to the photonic crystal fiber sensor 8, but also prevent it from being damaged by pressure.

Further, the groove cover teeth 6 are serrated, and apply partial pressure to the photonic crystal fiber part of the optical fiber sensor 8; use epoxy resin glue or glass fiber cloth 26 to fix the appropriate position of the uncompressed part of the sensor. .

Further, the slot position and groove spacing on the anchor ring 3 are adjusted according to the distribution of steel strands, the number of steel strands and the sensitivity requirements of the photonic crystal fiber pressure sensor.

Further, the probe length of the photonic crystal fiber pressure sensor 8 is adjusted according to the size of the anchor ring 3 and the monitoring sensitivity requirements.

Monitor the corrosion and fracture of the steel strand, install the photonic crystal fiber pressure sensor according to the distribution position of the steel strand in the steel strand anchor, and cover the buckle groove on the surface of the working anchor ring, so that the teeth on the groove cover are in contact with each other. The grooves on the surface of the anchor ring are engaged with each other, and the gap between the groove cover and the working anchor ring is sealed with a thin rubber strip, and the anchor ring and the anchor gasket are tightened to receive the reflected light signal of the photonic crystal fiber at this time. This optical signal is monitored. If the optical signal changes, it means that there is a loss of preload, and measures need to be taken to protect it.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The recorded technical solutions are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. An intelligent anchor for monitoring corrosion and fracture of prestressed steel strand, it is characterized in that, this smart anchor for monitoring corrosion and fracture of pre-stressed steel strand comprises steel strand (1), working clip (1). 2), working anchor ring (3), groove cover (4), anchor gasket (5), spiral rib (6), bellows (7), photonic crystal fiber pressure sensor (8) and rubber hose (9) ); wherein the photonic crystal fiber pressure sensor (8) is formed by splicing a first single-mode fiber (10), a photonic crystal fiber (11) and a second single-mode fiber (12); wherein the first single-mode fiber (10) and The second single-mode fiber (12) includes a core (13), a cladding (14), a coating (15) and a plastic protective sheath (16); the photonic crystal fiber (11) includes a core (17), a cladding (18), a coating layer (19), a plastic protective cover (20) and a cladding air channel (21); Both ends of the photonic crystal fiber (11) are respectively fused with the first single-mode fiber (10) and the second single-mode fiber (12); one end of the first single-mode fiber (10) is fused with the photonic crystal fiber (11) welding, and the other end is a free end, which is used to connect the light source transmitter and the spectrum analyzer; one end of the second single-mode fiber (12) is welded with the photonic crystal fiber (11), and the end face of the other end is uniformly deposited with a layered gold film (25); The grooves (23) are evenly cut around the contact surface of the working anchor ring (3) and the anchor washer (5), and the positions of the grooves correspond one-to-one with the distribution positions of the steel strands (1); The groove cover (4) is an annular cover, and a hole is reserved in the center to ensure smooth passage of the steel strand; and the groove (23) on the lower surface of the groove cover (4) is fixed with the groove (23) on the working anchor ring (3). ) serrated teeth (24) engaging with each other; The gap between the working anchor ring (3) and the groove cover (4) is sealed with a thin rubber skin; The photonic crystal optical fiber pressure sensor (8) is placed in the groove (23) of the working anchor ring (3), and the groove (23) and the serrated teeth (24) on the groove cover (4) are mutually abutted. tight, to form a pre-pressure on the photonic crystal fiber sensor (8) in the middle; An annular groove (27) is excavated around the groove (23) near the steel strand (1) and communicated with the groove (23) for placing the transmission single-mode optical fiber (10) at the end of the sensor. ), a plurality of transmission single-mode optical fibers are led out together along the groove (27) to the outside of the anchor ring. 2. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 1, wherein a plastic hose (9) is used for the uncompressed part of the first single-mode optical fiber (10). Encapsulation protection. 3. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 1 or 2, characterized in that, between the anchor ring groove (23) and the radius of the anchor ring (3) There is a certain included angle to avoid breakage of the photonic crystal fiber sensor (8) during the winding process. 4. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 3, wherein the photonic crystal fiber sensor (8) is sensitive to local uneven pressure changes, and can monitor anchors sensitively The pressure change between the ring groove (23) and the serrated teeth (24). 5. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 1, 2 or 4, characterized in that the thin rubber skin (26) is used to seal the groove cover (4) In the gap between the working anchor ring (3) and the thin rubber skin (26), the elasticity is good, so as to ensure the normal operation of the intelligent anchor. 6. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 5, characterized in that, the groove (6) on the groove cover and the groove (7) on the anchor ring are connected The size ensures that sufficient force can be delivered to the photonic crystal fiber sensor (8) without causing it to be damaged by pressure. 7. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 1, 2, 4 or 6, characterized in that the groove cover teeth (6) are serrated, Part of the photonic crystal optical fiber in the photonic crystal optical fiber sensor (8) is partially pressurized; epoxy resin glue or glass fiber cloth (26) is used to fix the unpressed part of the photonic crystal optical fiber sensor (8). 8. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 7, characterized in that, the slot positions and groove spacings on the anchor ring (3) are based on the thickness of the steel strands. The distribution, the number of strands, and the sensitivity of the photonic crystal fiber pressure sensor require adjustment. 9. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 1, 2, 4, 6 or 8, characterized in that the probe length of the photonic crystal fiber pressure sensor (8) Adjust according to the size of the anchor ring (3) and the monitoring sensitivity requirements. 10. The intelligent anchor for monitoring corrosion and fracture of prestressed steel strands according to claim 7, wherein the length of the probe of the photonic crystal fiber pressure sensor (8) is based on the size of the anchor ring (3) and monitoring sensitivity requirements to adjust.

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