Device for monitoring steel bar corrosion expansion radial strain distribution

Abstract

The invention provides a device for monitoring steel bar corrosion expansion radial strain distribution, and belongs to the technical field of structural health monitoring. The device for monitoring the corrosion expansion radial strain distribution of the reinforcing steel bar comprises a semi-annular stainless steel shell, a semi-annular stainless steel shell cover, a semi-annular stainless steel shell bottom, a fan-shaped hollow convex extrusion block, a single-mode optical fiber, a Fabry-Perot cavity, a protective soft sleeve, a butterfly-shaped hand-screwing rubber head screw and a rivet. The device is based on a multiplexing intrinsic Fabry-Perot interferometer and the principle that the length of a Fabry-Perot cavity can be changed due to steel bar corrosion expansion, when a steel bar is corroded and expanded, the tensile strain of the Fabry-Perot cavity is increased, the increase amount is in direct proportion to the radial strain of the steel bar corrosion expansion, and the tensile strain of the Fabry-Perot cavity is measured by monitoring the increase amount of the tensile strain of the Fabry-Perot cavity. The real-time, quantitative and nondestructive monitoring on the radial strain distribution of the corrosion expansion of the reinforcing steel bar is realized. The device is easy to manufacture, low in economic cost, capable of greatly reducing the manual operation amount, convenient to install and convenient to put into use on a large scale.

Description

Technical Field

[0001] The invention relates to a device for monitoring radial strain distribution of steel bar corrosion expansion based on a multiplexed intrinsic Fabry-Perot interferometer, belongs to the technical field of structural health monitoring, and is used for monitoring radial strain distribution of steel bar corrosion expansion in concrete structures. Background Art

[0002] Reinforced concrete structure has many advantages such as simple construction procedures, high construction efficiency and short construction period, and high cost performance in long-term use. It is a very economical structural form. It is widely used in industrial and civil buildings and is currently one of the most widely used structural types in the construction industry around the world. However, with the passage of time and the complexity of the service environment of engineering structures, the durability problem of reinforced concrete structures has become increasingly prominent, and steel corrosion has led to premature destruction of concrete structures. In addition, in projects such as bridges or ports near the coast, due to corrosion, reinforced concrete structures have experienced earlier damage after they were built, and they cannot reach the designed service life, reducing the original economy. Therefore, in order to ensure the safe and normal operation of the structure, it is essential to monitor the radial strain distribution of steel corrosion expansion in the structure.

[0003] At present, the commonly used detection methods for steel bar corrosion and expansion are divided into two categories: damage detection and non-destructive testing. Among them, damage detection is to chisel open the structure and make a judgment by visually observing the leaked steel bars. This method is generally carried out when the steel bar corrosion is serious. At this time, it is already in the middle and late stages of structural damage and cannot achieve the effect of real-time monitoring. Non-destructive testing includes resistance rod method, eddy current detection method, acoustic emission detection method, corrosion potential method, etc. On the one hand, due to high cost, inability to monitor in real time for a long time, and being restricted by installation conditions, on-site environment and other factors, these methods are currently difficult to apply on a large scale in actual projects; on the other hand, steel bar corrosion in concrete structures is mostly local corrosion with uneven distribution along the length and circumference, and these methods cannot detect the unevenness of steel bar corrosion.

[0004] In recent years, optical fiber has been highly valued in structural health monitoring due to its advantages such as small size, light weight, corrosion resistance, electromagnetic interference resistance, real-time monitoring, networking and reliable data. Among them, the Fabry-Perot interferometer fiber sensor realizes the interference between light beams by constructing a Fabry-Perot cavity on the optical fiber. When the measured physical quantity changes, the phase difference between the two coherent lights also changes, and the interference spectrum drifts. Compared with distributed optical fibers, traditional Fabry-Perot interferometer fiber sensors have higher resolution, which can reach the nanometer level, but the disadvantage is that they can only measure a single position. The multiplexed intrinsic Fabry-Perot interferometer fiber sensor has multiple Fabry-Perot cavities, which can realize monitoring of multiple positions, making up for the shortcomings of the traditional ones. This type of sensor has high resolution and sensitivity, and can be used for health detection of reinforced concrete structural components. It has great development space in the field of steel corrosion and expansion monitoring.

[0005] Therefore, it is particularly important to provide a highly sensitive, real-time, and non-destructive monitoring device from a new technical perspective for monitoring the annular strain distribution of steel bar corrosion expansion in reinforced concrete structures, thereby providing important guarantees for the safe service of reinforced concrete structures. Summary of the invention

[0006] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a device for monitoring the radial strain distribution of steel bar corrosion expansion, with the aim of achieving real-time monitoring of the radial strain distribution of steel bar corrosion expansion, accurately determining the health status of the structure, and thus ensuring the safety of the structure.

[0007] The technical solution of the present invention:

[0008] A device for monitoring the radial strain distribution of steel bar corrosion expansion, comprising a semi-circular stainless steel shell 1, a semi-circular stainless steel shell cover 2, a semi-circular stainless steel shell bottom 3, a fan-shaped hollow convex extrusion block 4, a single-mode optical fiber 5, a Fabry-Perot cavity 6, a protective soft cover 7, a butterfly-shaped hand-tightened rubber head screw 8, and a rivet 9;

[0009] The semi-circular stainless steel shell 1 is composed of a semi-circular stainless steel shell cover 2 and a semi-circular stainless steel shell bottom 3. Figure 1 As shown, epoxy resin glue is used for bonding during splicing;

[0010] The inner semicircular side of the semi-circular stainless steel shell 1 is open, and there is a convex part at the edge;

[0011] The fan-shaped hollow convex extrusion block 4 is made of PA12 nylon material and is manufactured by multi-jet melting 3D printing technology;

[0012] A plurality of fan-shaped hollow convex extrusion blocks 4 are placed along the circumference of the semi-annular stainless steel shell 1;

[0013] The fan-shaped hollow convex extrusion block 4 is placed in the semi-circular stainless steel shell 1, and the concave arc surface on the outside is blocked by the convex part of the semi-circular side edge of the semi-circular stainless steel shell 1, and will not slide out;

[0014] The convex arc top of the outer side of the fan-shaped hollow convex extrusion block 4 contacts the inner wall of the semi-circular stainless steel shell 1 and is bonded with cyanoacrylate glue, and the other contact parts are all ordinary contacts without any bonding and fixing;

[0015] The height of the fan-shaped hollow convex extrusion block 4 is the same as the height of the inner space of the semi-circular stainless steel shell 1;

[0016] A plurality of Fabry-Perot cavities 6 are generated on the single-mode optical fiber 5 by femtosecond laser technology;

[0017] The single-mode optical fiber 5 passes through the midpoint of the intersection of the plane and the arc surface of the fan-shaped hollow convex extrusion block 4. Figure 2 As shown;

[0018] The contact portion between the fan-shaped hollow convex extrusion block 4 and the single-mode optical fiber 5 is bonded with cyanoacrylate glue;

[0019] The Fabry-Perot cavity 6 on the single-mode optical fiber 5 is located in the middle of the hollow part of the fan-shaped hollow convex extrusion block 4;

[0020] The portion of the single-mode optical fiber 5 extending out of the semi-circular stainless steel housing 1 is protected by a protective soft cover 7;

[0021] When the two semi-circular stainless steel shells 1 are assembled, one end is riveted by a rivet 9 to support the rotation of the device and cannot be disassembled. The other end is connected by a butterfly hand-tightened rubber head screw 8 to open the device;

[0022] The size of the semi-circular stainless steel shell 1 and the number and size of the fan-shaped hollow convex extrusion blocks 4 are adjusted according to the actual diameter of the steel bar to be tested.

[0023] Working principle of the present invention:

[0024] The principle of the device for monitoring the radial strain distribution of steel bar corrosion expansion based on multiplexed intrinsic Fabry-Perot interferometer is as follows Fig. 9As shown, when the steel bar corrodes and expands, the expansion object will apply radial extrusion force to the fan-shaped hollow convex extrusion block 4, at which time the radial strain of the fan-shaped hollow convex extrusion block 4 will decrease, while the annular strain will increase. Since the contact part of the fan-shaped hollow convex extrusion block 4 and the single-mode optical fiber 5 is bonded with cyanoacrylate glue, the single-mode optical fiber 5 will elongate with the increase of the annular strain of the fan-shaped hollow convex extrusion block 4, which also causes the cavity length of the Fabry-Perot cavity 6 to extend from l to l', thereby causing the tensile strain of the Fabry-Perot cavity 6 to increase. By establishing the relationship between the annular strain of the fan-shaped hollow convex extrusion block 4 and the increase in the tensile strain of the Fabry-Perot cavity 6, real-time monitoring of the radial strain distribution of the steel bar corrosion expansion is achieved.

[0025] like Fig. 9 As shown, before the steel bar corrodes, the upper half of the hollow part of the fan-shaped hollow convex extrusion block 4 can be regarded as an isosceles triangle with a side length of a and a base angle of θ. At this time, the length l of the optical fiber at the hollow part of the fan-shaped hollow convex extrusion block 4 is

[0026] l=2acosθ (1)

[0027] When the steel bar corrodes, the volume expansion causes the radius at a certain point along the circumference to increase by x. At this time, the waist length of the upper half of the hollow part of the fan-shaped hollow convex extrusion block 4 remains unchanged, and the height is reduced. As a result, the fiber is stretched by hoop strain, and the length l' is

[0028]

[0029] The elongation deformation of the optical fiber in this part is Δ l for

[0030]

[0031] Then the strain ε of the optical fiber is

[0032]

[0033] Based on the principle of Rayleigh scattering distributed optical fiber strain sensing, when the strain changes, the back-scattering spectrum of the optical signal in the optical fiber will shift in frequency, and the magnitude of the shift is proportional to the change in strain, that is,

[0034] v′=v 0 +C·ε (5)

[0035] Where, ν 0 and ν′ are the spectral frequency shifts before and after steel bar corrosion, respectively; C is the strain coefficient (dv / dε); ε is the optical fiber strain.

[0036] Since the relationship between the radial strain ε′ and the increase x at a certain point along the circumference of the steel bar is

[0037]

[0038] Where r is the original radius of the steel bar.

[0039] Substituting equation (4) into equation (5), and then substituting equation (6), we can obtain the relationship between the spectral frequency shift and the radial strain ε′ at a certain point along the circumference of the steel bar:

[0040]

[0041] Therefore, the radial strain ε′ of the steel bar at a certain point along the circumference after corrosion can be obtained by using the spectral frequency shift measured by the optical fiber according to equation (7).

[0042] Therefore, based on the above-mentioned inventive principle, we can monitor whether the steel bar is corroded by measuring the spectral frequency shift through continuous optical fiber, and calculate the radial strain distribution of each point along the circumference after the steel bar corrodes and expands.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The present invention monitors the radial strain distribution of steel bar corrosion expansion by monitoring the changes in the spectral signal in the optical fiber.

[0045] (2) The present invention is more sensitive to the extrusion force generated by steel bar corrosion expansion products, has higher sensitivity and stable performance.

[0046] (3) The present invention can monitor the radial strain distribution of steel bar corrosion expansion in real time, online and non-destructively, thereby providing early warning maintenance for structural safety.

[0047] (4) The present invention is simple to manufacture and has low economic cost, which greatly reduces the workload of manual labor. It is also easy to install and is convenient for large-scale use. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of a semi-circular stainless steel housing of a device for monitoring the radial strain distribution of steel bar corrosion expansion according to the present invention;

[0049] Figure 2 It is a schematic diagram of a fan-shaped hollow convex extrusion block of the device for monitoring the radial strain distribution of steel bar corrosion expansion of the present invention;

[0050] Figure 3 It is a schematic structural diagram of a device for monitoring radial strain distribution of steel bar corrosion expansion according to the present invention;

[0051] Figure 4 A top view of the radial strain distribution device for monitoring corrosion expansion of steel bars according to the present invention;

[0052] Figure 5 It is a cross-sectional view of the AA section of the device for monitoring the radial strain distribution of steel bar corrosion expansion of the present invention;

[0053] Figure 6 It is a front view of the radial strain distribution device for monitoring corrosion expansion of steel bars of the present invention;

[0054] Figure 7 It is a BB cross-sectional view of the device for monitoring the radial strain distribution of steel bar corrosion expansion of the present invention;

[0055] Figure 8 It is a schematic diagram of the arrangement of the present invention for monitoring the radial strain distribution of actual steel bar corrosion expansion;

[0056] Fig. 9 Schematic diagram of the monitoring principle of the present invention.

[0057] In the figure: 1 semi-circular stainless steel shell; 2 semi-circular stainless steel shell cover; 3 semi-circular stainless steel shell bottom; 4 fan-shaped hollow convex extrusion block; 5 single-mode optical fiber; 6 Fabry-Perot cavity; 7 protective soft cover; 8 butterfly-shaped hand-tightened rubber-head screws; 9 rivets; 10 optical fiber sensing device for monitoring radial strain distribution of steel bar corrosion expansion; 11 steel bars; 12 concrete. DETAILED DESCRIPTION

[0058] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] like Figures 1 to 9 As shown, the present invention provides a device for monitoring the radial strain distribution of steel bar corrosion expansion, comprising a semi-annular stainless steel shell 1, a semi-annular stainless steel shell cover 2, a semi-annular stainless steel shell bottom 3, a fan-shaped hollow convex extrusion block 4, a single-mode optical fiber 5, a Fabry-Perot cavity 6, a protective soft cover 7, a butterfly-shaped hand-tightened rubber head screw 8, and a rivet 9;

[0060] The semi-circular stainless steel shell 1 is composed of a semi-circular stainless steel shell cover 2 and a semi-circular stainless steel shell bottom 3. Figure 1 As shown, epoxy resin glue is used for bonding during splicing;

[0061] The inner semicircular side of the semi-circular stainless steel shell 1 is open, and there is a convex part at the edge;

[0062] The fan-shaped hollow convex extrusion block 4 is made of PA12 nylon material and is manufactured by multi-jet melting 3D printing technology;

[0063] A plurality of fan-shaped hollow convex extrusion blocks 4 are placed in the semi-circular stainless steel shell 1;

[0064] The fan-shaped hollow convex extrusion block 4 is placed in the semi-circular stainless steel shell 1, and the concave arc surface on the outside is blocked by the convex part of the semi-circular side edge of the semi-circular stainless steel shell 1, and will not slide out;

[0065] The convex arc top of the outer side of the fan-shaped hollow convex extrusion block 4 contacts the inner wall of the semi-circular stainless steel shell 1 and is bonded with cyanoacrylate glue, and the other contact parts are all ordinary contacts without any bonding and fixing;

[0066] The height of the fan-shaped hollow convex extrusion block 4 is the same as the height of the inner space of the semi-circular stainless steel shell 1;

[0067] A plurality of Fabry-Perot cavities 6 are generated on the single-mode optical fiber 5 by femtosecond laser technology;

[0068] The single-mode optical fiber 5 passes through the midpoint of the intersection of the plane and the arc surface of the fan-shaped hollow convex extrusion block 4. Figure 2 As shown;

[0069] The contact portion between the fan-shaped hollow convex extrusion block 4 and the single-mode optical fiber 5 is bonded with cyanoacrylate glue;

[0070] The Fabry-Perot cavity 6 on the single-mode optical fiber 5 is located in the middle of the hollow part of the fan-shaped hollow convex extrusion block 4;

[0071] The portion of the single-mode optical fiber 5 extending out of the semi-circular stainless steel housing 1 is protected by a protective soft cover 7;

[0072] When the two semi-circular stainless steel shells 1 are assembled, one end is riveted by a rivet 9 to support the rotation of the device and cannot be disassembled. The other end is connected by a butterfly hand-tightened rubber head screw 8 to open the device;

[0073] The size of the semi-circular stainless steel shell 1 and the number and size of the fan-shaped hollow convex extrusion blocks 4 are adjusted according to the actual diameter of the steel bar to be tested.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for monitoring the radial strain distribution of steel bar corrosion expansion, characterized in that: The device for monitoring the radial strain distribution of steel bar corrosion expansion comprises a semi-circular stainless steel housing (1), a semi-circular stainless steel housing cover (2), a semi-circular stainless steel housing bottom (3), a fan-shaped hollow convex extrusion block (4), a single-mode optical fiber (5), a Fabry-Perot cavity (6), a protective soft cover (7), a butterfly-shaped hand-tightened rubber head screw (8), and a rivet (9); The semi-circular stainless steel housing (1) is composed of a semi-circular stainless steel housing cover (2) and a semi-circular stainless steel housing bottom (3); The inner semicircular side of the semi-circular stainless steel shell (1) is open, and a convex portion is provided at the edge; The fan-shaped hollow convex extrusion block (4) is made of PA12 nylon material and is manufactured by multi-jet melting 3D printing technology; A plurality of fan-shaped hollow convex extrusion blocks (4) are arranged along the circumference of the semi-annular stainless steel shell (1); The inner concave arc surface on the outer side of the fan-shaped hollow convex extrusion block (4) is blocked by the convex part of the inner semicircular side edge of the semi-circular stainless steel shell (1) and will not slide out; The convex arc top of the outer side of the fan-shaped hollow convex extrusion block (4) contacts the inner wall of the semi-circular stainless steel shell (1) and is bonded with cyanoacrylate glue, while the remaining contact parts are all in ordinary contact without any bonding and fixing; The height of the fan-shaped hollow convex extrusion block (4) is the same as the height of the inner space of the semi-circular stainless steel shell (1); A plurality of Fabry-Perot cavities (6) are generated on the single-mode optical fiber (5) by femtosecond laser technology; The Fabry-Perot cavity (6) on the single-mode optical fiber (5) is located in the middle of the hollow portion of the fan-shaped hollow convex extrusion block (4); The single-mode optical fiber (5) passes through a fan-shaped hollow convex extrusion block (4) placed along the circumference in the semi-annular stainless steel housing (1); The portion of the single-mode optical fiber (5) extending out of the semi-annular stainless steel housing (1) is protected by a protective soft sleeve (7); When the two semi-circular stainless steel shells (1) are assembled, one end is riveted by a rivet (9) to support the rotation of the device and cannot be disassembled. The other end is connected by a butterfly-shaped hand-tightened rubber head screw (8) to open the device.

2. The device for monitoring radial strain distribution of steel bar corrosion expansion according to claim 1, characterized in that: When splicing the two parts of the semi-circular stainless steel shell cover (2) and the semi-circular stainless steel shell bottom (3) of the semi-circular stainless steel shell (1), epoxy resin glue or anti-corrosion, waterproof glue with high strength after curing is used.

3. The device for monitoring radial strain distribution of steel bar corrosion expansion according to claim 1, characterized in that: The contact portion between the fan-shaped hollow outwardly convex extrusion block (4) and the single-mode optical fiber (5) is bonded with cyanoacrylate glue.

4. The device for monitoring radial strain distribution of steel bar corrosion expansion according to claim 1, characterized in that: The size of the semi-annular stainless steel shell (1) and the number and size of the fan-shaped hollow convex extrusion blocks (4) are adjusted according to the actual diameter of the steel bar to be tested.

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