CN109443231B - Stress-free meter based on optical fiber sensing - Google Patents
Stress-free meter based on optical fiber sensing Download PDFInfo
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- CN109443231B CN109443231B CN201811575816.1A CN201811575816A CN109443231B CN 109443231 B CN109443231 B CN 109443231B CN 201811575816 A CN201811575816 A CN 201811575816A CN 109443231 B CN109443231 B CN 109443231B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
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Abstract
The invention provides an optical fiber sensing-based stress-free meter, which comprises an inner barrel, an outer barrel and an optical fiber sensor, wherein the inner barrel and the outer barrel are both of a hollow structure with an open top end, the inner barrel is sleeved inside the outer barrel, the edge of the top end of the inner barrel extends outwards to be connected with an extension part, the extension part is in contact connection with the edge of the top end of the outer barrel, a plurality of first small holes are formed in the barrel wall of the inner barrel, two symmetrical second small holes are formed in the extension part, the optical fiber sensor firstly penetrates through one second small hole to reach between the inner barrel and the outer barrel, then sequentially penetrates through all the first small holes and finally penetrates out of the other second small hole, and the optical fiber sensor is used for measuring. When the stress-free meter provided by the invention generates free volume deformation in concrete in the inner barrel, the optical fiber sensor embedded in the stress-free meter can sense the strain and temperature information of different positions of the inner barrel, and the three-dimensional distribution information of the strain and temperature of a concrete test piece is obtained, so that the free volume deformation of the concrete can be accurately obtained.
Description
Technical Field
The invention relates to the technical field of stress-free meters for measuring concrete autogenous volume deformation, in particular to a stress-free meter based on optical fiber sensing.
Background
The risk of failure of a high concrete dam is essentially caused by the fact that the stress of the dam foundation or the dam body exceeds the strength of the material, and therefore stress-strain monitoring of the dam is necessary. In the stress-strain observation of large-volume concrete structures, a stress-free gauge is generally used to measure the deformation of concrete under external force due to physicochemical factors and temperature and humidity changes of the concrete itself, and the deformation generated by the non-external stress is also called free volume deformation. Further, the deformation measured by the non-stress meter includes four parts: (1) under the conditions of constant temperature and no humidity and no external force, the concrete is deformed only due to the physical and chemical factors of the concrete, namely the self-generated volume deformation; (2) expansion and contraction deformation of concrete due to temperature change, namely free temperature deformation; (3) temperature stress, i.e. temperature stress deformation, is generated due to non-uniform temperature distribution in the concrete; (4) volume deformation, i.e., humidity deformation, due to changes in humidity within the concrete specimen.
The calculation of the concrete self-generated volume deformation is generally to measure the free volume deformation of a test piece by a stress-free meter and then deduct the free temperature deformation, the temperature stress deformation and the humidity deformation of the concrete. The free temperature deformation is obtained according to the volume deformation generated by temperature drop in a short time; the humidity deformation is generally ignored due to the fact that the moisture conductivity of the stress-free sleeve and the concrete is low; temperature stress deformation is often ignored by monitoring personnel because the current equipment cannot realize multipoint temperature measurement and cannot establish temperature gradient change in the concrete test piece.
At present, the indoor test of concrete self-generated volume deformation is generally carried out according to the relevant regulations of hydraulic concrete test regulations (S L352-2006), the same double-layer sleeve device is adopted in an engineering field to be buried in a concrete structure, and a strain gauge is vertically buried in the center.
The indoor test can well control the temperature and humidity conditions of a test piece, but the temperature field condition of the environment where the stress meter is not located is difficult to be comprehensively known on a project site, particularly in dam projects, the temperature distribution in a dam body is often uneven, the unevenness can cause concrete to generate temperature stress deformation, at the moment, whether the deformation is generated due to temperature stress or self-generated volume deformation is difficult to distinguish from a measurement result, and the measurement result is often fluctuated and irregularly changed. In addition, the vibrating wire type strain gauge adopted in the conventional stress-free gauge can only sense one strain value and one temperature value, and cannot obtain a monitoring result of three-dimensional strain distribution of concrete in the stress-free barrel, so that the measurement result of the conventional stress-free gauge is generally considered to be irrelevant to external force, but a certain stress transition area is inevitably formed in an open area where the concrete in the barrel is contacted with the surrounding concrete, the influence range of the transition area cannot be determined at present, the measurement result of the strain gauge can be influenced, and the influence degree of the equipment recommended in the hydraulic concrete test regulations (S L352-2006) cannot be evaluated at present.
In order to more accurately know the self-generated volume deformation of concrete, the three-dimensional temperature and strain information of a concrete sample in the stress-free sleeve barrel need to be comprehensively known, and the optical fiber sensing technology is mature day by day and can provide help for the improvement of a stress-free meter device. Firstly, the optical fiber sensor has high sensitivity and can completely meet the measurement requirement; secondly, distributed measurement can be realized by the distributed optical fiber sensing technology, the temperature and the strain of each point on the optical fiber can be obtained, and the spatial resolution can reach 1 mm; finally, the optical fiber is very fine and can be easily implanted into a concrete structure without influencing the structure.
Disclosure of Invention
In view of the above, the present invention provides a stress-free meter based on optical fiber sensing, which can obtain reliable concrete self-generated volume deformation data.
The invention provides an optical fiber sensing-based stress-free meter, which comprises an inner barrel, an outer barrel and an optical fiber sensor, wherein the inner barrel and the outer barrel are both of a hollow structure with an open top end, the inner barrel is sleeved inside the outer barrel, the edge of the top end of the inner barrel extends outwards to be connected with an extension part, the extension part is in contact connection with the edge of the top end of the outer barrel, a plurality of first small holes are formed in the barrel wall of the inner barrel, two symmetrical second small holes are formed in the extension part, the optical fiber sensor firstly penetrates through one second small hole to reach between the inner barrel and the outer barrel, then sequentially penetrates through all the first small holes, and finally penetrates out of the other second small hole, and the optical fiber sensor is used for measuring the temperature and strain information of concrete.
Furthermore, the first small hole and the second small hole are provided with water isolating plugs, each water isolating plug comprises a bolt and a nut which is connected with the bolt in a matched mode, the bolt is fastened by the nut after being inserted into the first small hole or the second small hole, the center of the bolt is provided with a through hole, and the through hole allows the optical fiber sensor to penetrate through the through hole.
Furthermore, epoxy resin glue is filled between the through hole and the optical fiber sensor, and the optical fiber sensor is sealed and fixed by the epoxy resin glue.
Further, the optical fiber sensor comprises an optical fiber temperature sensor and an optical fiber strain sensor, the optical fiber temperature sensor is used for measuring the temperature information of the concrete contained in the inner barrel, and the optical fiber strain sensor is used for measuring the strain information of the concrete contained in the inner barrel.
Furthermore, the optical fiber temperature sensor and the optical fiber strain sensor are both packaged in the sheath, the optical fiber temperature sensor is placed in the hollow tube, the optical fiber temperature sensor can move in the hollow tube, the hollow tube is attached to the sheath, and the optical fiber strain sensor is directly attached to the sheath.
Further, the optical fiber sensor positioned in the inner barrel is in a linear straightening state, and the optical fiber sensor positioned outside the inner barrel is in a free extension state.
The technical scheme provided by the invention has the beneficial effects that: the stress-free meter based on the optical fiber sensing has the advantages that through the design of the outer barrel and the inner barrel, when external force extrusion occurs, the outer barrel can play a role in supporting and protecting the inner barrel, the inner barrel cannot be influenced by slight deformation of the outer barrel, and the outer barrel cannot be influenced by deformation of the inner barrel; when the concrete in the inner barrel is subjected to free volume deformation, the optical fiber sensor embedded in the inner barrel can sense the strain and temperature information of different positions of the inner barrel, so that the three-dimensional distribution information of the strain and temperature of the concrete in the inner barrel is obtained, and the autogenous volume deformation of the concrete is analyzed more accurately; the stress-free meter based on the optical fiber sensing provided by the invention has the advantages that the water-isolating plug is arranged, so that the slurry leakage can be prevented when the optical fiber sensor passes through the inner barrel and the extension part of the inner barrel, and the optical fiber sensor can be fixed.
Drawings
Fig. 1 is a schematic structural diagram of a stress-free meter based on optical fiber sensing.
Fig. 2 is a cross-sectional schematic view of a stress-free meter based on optical fiber sensing according to the present invention.
Fig. 3 is a front view of a bolt without a stress gauge based on optical fiber sensing.
Fig. 4 is a left side view of a bolt of an optical fiber sensing based stress-free gauge of the present invention.
Fig. 5 is a left side view of a nut of an unstressed meter based on optical fiber sensing of the present invention.
FIG. 6 is a cross-sectional schematic view of an optical fiber sensor based on optical fiber sensing without a strain gauge.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings.
Referring to fig. 1 and 2, an embodiment of the present invention provides an optical fiber sensing-based stress-free meter, including an inner barrel 1, an outer barrel 2 and an optical fiber sensor 3, where the inner barrel 1 and the outer barrel 2 may be cylindrical, circular truncated cone, rectangular parallelepiped, and the like, the inner barrel 1 and the outer barrel 2 are both hollow structures with open top ends, the inner barrel 1 is located inside the outer barrel 2, the top end edge of the inner barrel 1 extends outwards to connect an extension portion 11, the extension portion 11 and the top end edge of the outer barrel 2 are sealed by welding, the top end of the inner barrel 1 is flush with the top end of the outer barrel 2, the height of the inner barrel 1 is smaller than the height of the outer barrel 2, the outer diameter of the inner barrel 1 is smaller than the inner diameter of the outer barrel 2 so that a certain distance is formed between the inner barrel.
The outer barrel 2 can be made of materials with high strength and rigidity, so that the outer barrel 2 has certain extrusion resistance and deformation resistance, and is not damaged due to deformation under high confining pressure.
The inner barrel 1 is made of a material with low rigidity, the inner wall of the inner barrel 1 can be a smooth curved surface or a corrugated curved surface, a flexible waterproof material with certain thickness can be sprayed or stuck on the barrel wall of the inner barrel 1, the flexible waterproof material can absorb the volume space change caused by the free volume deformation of concrete, and the concrete in the inner barrel 1 can be moisturized.
A plurality of first small holes 12 are formed in the wall of the inner barrel 1, two symmetrical second small holes 13 are formed in the extending part 11, the two second small holes 13 take the center of the top end of the inner barrel 1 as a symmetrical center, and the water-insulating plugs 4 are mounted at the first small holes 12 and the second small holes 13.
Referring to fig. 1, 3, 4 and 5, the water stop plug 4 includes a bolt 41 and a nut 42 cooperatively connected with the bolt 41, a through hole 411 is formed in the center of the bolt 41, the length of the through hole 411 is equal to the length of the bolt 41, the through hole 411 penetrates through the whole bolt 41, the through hole 411 allows the optical fiber sensor 3 to pass through, the bolt 41 is fastened by the nut 42 after being inserted into the first small hole 12 or the second small hole 13, the size of the first small hole 12 and the size of the second small hole 13 are matched with the size of the screw portion of the bolt 41, the nut 42 is located on the outer wall of the inner barrel 1, two water stop gaskets 43 are arranged between the bolt 41 and the nut 42, and the two water stop gaskets 43 are respectively located on the inner side and.
The optical fiber sensor 3 can be a fiber grating sensor or a distributed optical fiber sensor; the optical fiber sensor 3 has the capability of detecting temperature and strain; the detection technology of the optical fiber sensor 3 may be based on various optical principles including fiber bragg grating, brillouin optical time domain reflection technology (BOTDR), brillouin optical time domain analysis technology (BOTDA), brillouin frequency domain analysis technology (BOFDA), and the like.
Referring to fig. 6, the optical fiber sensor 3 includes an optical fiber temperature sensor 31 and an optical fiber strain sensor 32, the optical fiber temperature sensor 31 is used to measure temperature information of concrete contained in the inner tub 1, the optical fiber strain sensor 32 is used to measure strain information of concrete contained in the inner tub 1, the optical fiber temperature sensor 31 and the optical fiber strain sensor 32 are both enclosed in the sheath 5, the optical fiber temperature sensor 31 is disposed in the hollow tube 6, and optical fiber temperature sensor 31 can freely move in hollow tube 6, hollow tube 6 and sheath 5 are tightly attached together, optical fiber strain sensor 32 is directly tightly attached together with sheath 5, reinforcing bar 7 is implanted in sheath 5 to increase tensile strength of optical fiber sensor 3, pattern 51 is arranged on the surface of sheath 5, pattern 51 can increase contact friction between sheath 5 and concrete, and strain transfer can be more effective.
When the stress-free meter provided by the invention is used for monitoring the self-generated volume deformation of concrete, when an inner barrel 1 and an outer barrel 2 are both cylinders, as shown in figure 1, three first small holes 12 are punched at the positions of 1/4, 1/2 and 3/4 of the inner barrel 1, then a row of same first small holes 12 are punched at intervals of 90 degrees around the barrel wall of the inner barrel 1, then two second small holes 13 are symmetrically punched on an extension part 11 of the inner barrel 1, bolts 41 of a water-proof plug 4 are inserted into the corresponding first small holes 12 and second small holes 13, then the bolts are fastened by nuts 42, then an optical fiber sensor 3 packaged in a sheath 5 firstly passes through one water-proof plug 4 on the extension part 11 to reach a pore space between the inner barrel 1 and the outer barrel 2, then sequentially passes through all water-proof plugs 4 on the barrel wall of the inner barrel 1 according to a certain sequence rule, and finally passes out of the other water-proof plug 4 on the extension part 11, the optical fiber sensor 3 inside the inner barrel 1 is ensured to be in a linear extension state, and the optical fiber sensor 3 outside the inner barrel 1 is in a free extension state, so that a monitoring net capable of monitoring the temperature and strain of each part inside concrete in the inner barrel 1 is formed; the through holes 411 of all the bolts 41 are filled with epoxy resin glue, the epoxy resin glue plays a role in sealing and fixing the optical fiber sensor 3, the whole inner barrel 1 is placed into the outer barrel 2 after the epoxy resin glue is solidified, the top end edges of the extension part 11 and the outer barrel 2 are sealed and welded, a complete stress-free meter based on optical fiber sensing is formed, concrete with the same specification as that adopted in engineering construction is poured into the inner barrel 1 after particles with the diameter larger than 40mm are removed, the concrete is vibrated lightly and uniformly, the stress-free meter is placed in the corresponding position of the engineering for long-term monitoring, a plurality of stress-free meters based on optical fiber sensing can be measured in series, and monitoring results of all the stress-free meters based on optical fiber sensing can be obtained through one-time measurement.
The optical fiber sensor 3 in the inner barrel 1 can simultaneously obtain the temperature and strain information of each point in the concrete structure body, can be used for identifying the reason of concrete strain, separating interference factors and obtaining more reliable concrete autogenous volume deformation data, for example: when the temperature of the concrete in the inner barrel 1 is measured to be uniform, but the upper part of the concrete in the inner barrel 1 has large strain, and the lower part of the concrete has no strain basically, the strain is caused by the stress transmission of the external concrete; when the concrete has a temperature gradient in a certain direction and the difference of strain in the direction is large, the strain is greatly influenced by temperature stress deformation, and the strain value in the direction with the small temperature gradient is selected as much as possible and the free temperature deformation value is removed to obtain the concrete autogenous volume deformation.
According to the stress-free meter based on the optical fiber sensing, due to the design of the outer barrel 2 and the inner barrel 1, when external force extrusion occurs, the outer barrel 2 can play a role in supporting and protecting the inner barrel 1, the inner barrel 1 cannot be influenced by slight deformation of the outer barrel 2, and the outer barrel 2 cannot be influenced by deformation of the inner barrel 1; when the concrete in the inner barrel 1 is subjected to free volume deformation, the optical fiber sensor 3 embedded in the inner barrel can sense the strain and temperature information of different positions of the inner barrel, so that the three-dimensional distribution information of the strain and temperature of a concrete test piece is obtained, and more accurate concrete autogenous volume deformation information is obtained; the stress-free meter based on optical fiber sensing provided by the invention can prevent slurry leakage and fix the optical fiber sensor 3 when the optical fiber sensor 3 passes through the inner barrel 1 and the extension part 11 thereof by arranging the water-proof plug 4.
In this document, the terms front, back, upper and lower are used to define the components in the drawings and the positions of the components relative to each other, and are used for clarity and convenience of the technical solution. It is to be understood that the use of the directional terms should not be taken to limit the scope of the claims.
The features of the embodiments and embodiments described herein above may be combined with each other without conflict.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (5)
1. The stress-free meter based on the optical fiber sensing is characterized by comprising an inner barrel, an outer barrel and an optical fiber sensor, wherein the inner barrel and the outer barrel are both of a hollow structure with an open top end, the inner barrel is sleeved inside the outer barrel, the edge of the top end of the inner barrel extends outwards to be connected with an extension part, the extension part is in contact connection with the edge of the top end of the outer barrel, a plurality of first small holes are formed in the barrel wall of the inner barrel, two symmetrical second small holes are formed in the extension part, the optical fiber sensor firstly penetrates through one second small hole to reach between the inner barrel and the outer barrel, then sequentially penetrates through all the first small holes, and finally penetrates out of the other second small hole, and the optical fiber sensor is used for measuring the temperature and strain information of concrete contained in; the optical fiber sensor positioned in the inner barrel is in a linear extension state, and the optical fiber sensor positioned outside the inner barrel is in a free extension state, so that a monitoring net capable of monitoring the temperature and strain of each part in the concrete in the inner barrel is formed.
2. The non-stress meter based on optical fiber sensing according to claim 1, wherein a water-proof plug is installed at each of the first small hole and the second small hole, the water-proof plug comprises a bolt and a nut connected with the bolt in a matching manner, the bolt is fastened by the nut after being inserted into the first small hole or the second small hole, and a through hole is formed in the center of the bolt and allows the optical fiber sensor to pass through.
3. The fiber sensing-based strain-free gauge according to claim 2, wherein an epoxy glue is filled between the through hole and the fiber sensor.
4. The fiber sensing-based non-stress gauge according to claim 1, wherein the fiber sensor comprises a fiber temperature sensor for measuring temperature information of concrete contained in the inner barrel and a fiber strain sensor for measuring strain information of concrete contained in the inner barrel.
5. The fiber optic sensing based strain gauge of claim 4, wherein the fiber optic temperature sensor and the fiber optic strain sensor are both enclosed within a sheath, the fiber optic temperature sensor is disposed within a hollow tube, the fiber optic temperature sensor is movable within the hollow tube, the hollow tube is attached to the sheath, and the fiber optic strain sensor is attached directly to the sheath.
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| CN112632676B (en) * | 2020-12-23 | 2022-10-11 | 华能澜沧江水电股份有限公司 | Concrete dam stress gradient monitoring method |
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