CN214250869U - Distributed optical fiber sensing device capable of monitoring steel beam cracks - Google Patents
Distributed optical fiber sensing device capable of monitoring steel beam cracks Download PDFInfo
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- CN214250869U CN214250869U CN202120402881.5U CN202120402881U CN214250869U CN 214250869 U CN214250869 U CN 214250869U CN 202120402881 U CN202120402881 U CN 202120402881U CN 214250869 U CN214250869 U CN 214250869U
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Abstract
The utility model relates to a distributed optical fiber sensing device capable of monitoring cracks of a steel beam, which comprises a sensing optical fiber to be detected, wherein the sensing optical fiber to be detected is a photonic crystal optical fiber, the outside of the photonic crystal optical fiber is wrapped by epoxy resin adhesive glue and is pasted on the upper surface of the steel beam along the length direction of the steel beam, the photonic crystal optical fiber is electrically connected with a BOTDA strain analyzer, and the bottom of the steel beam is provided with a bracket; the two ends of the steel beam are provided with hooks; and arranging the fiber bragg grating at the joint of the steel beam. The utility model discloses replace the single mode with photonic crystal fiber and carry out girder steel structure health monitoring, than traditional single mode fiber crowning 2 orders of magnitude's brillouin gain, be favorable to the detection to brillouin signal. In addition, another sensing parameter can be separated from the cladding structure of the photonic crystal fiber, so that a new sensing function can be expanded, and the reliability and the expandability of the detection system are improved.
Description
Technical Field
The utility model belongs to the technical field of the structural health monitoring, especially, relate to a can monitor fissured distributed optical fiber sensing device of girder steel.
Background
With the planning and construction of a large number of urban infrastructures, China becomes the region with the fastest global economic development and the largest engineering construction scale. Against this background, the quality requirements of people on construction engineering are constantly increasing. Modern engineering faces the problems of more difficulty, high difficulty, large investment and the like, and building structures develop towards super high-rise, large space and large span. Therefore, the safety requirements of people are gradually increased. However, in the using stage of a building, due to a plurality of factors such as stress action, fatigue effect, environmental temperature and humidity, aging corrosion and the like, a plurality of signs are presented before many safety accidents occur, and structural damage and resistance performance decline all cause catastrophic accidents. At present, a steel beam structure is a framework structure of a building and is widely applied to civil engineering. Before an accident occurs, the construction steel beams are cracked. Therefore, the method has great significance for monitoring and researching the cracks of the steel beam.
The existing structure health monitoring technologies mainly comprise a ground monitoring method, a ground photogrammetry method, a GPS deformation monitoring technology, a satellite remote measuring technology and the like, however, the methods are high in cost, only can be used for monitoring the surface health, and cannot be used for effectively monitoring the internal health. The optical fiber sensor has the advantages of small volume, high precision, electromagnetic interference resistance, remote measurement and the like, and is taken as a first-choice sensitive element for structural health monitoring. At present, three types of optical fiber sensors for structural health monitoring are mainly used, namely a Fabry-perot (Fabry-perot) cavity interference type sensor, a Fiber Grating (FG) sensor and a Brillouin scattering (Brillouin scattering) sensor. In contrast, the brillouin scattering sensor is not only simple in structure, but also can realize remote and distributed measurement.
Brillouin time-domain analysis (BOTDA) technology, which is one kind of Brillouin scattering, has been widely applied to structural health monitoring, and has the advantages of high sensitivity, long distance, distribution and the like. However, crack monitoring is currently achieved primarily through single mode fiber brillouin peak change detection. The method has two disadvantages, firstly, the single-mode optical fiber is a total internal reflection waveguide structure with a fiber core doped with germanium ions, and when the temperature is too high, the thermal motion of the ions can cause the waveguide structure to be invalid. Second, external disturbances can cause peak instability to a large extent, and thus cracks cannot be accurately predicted. Therefore, it is very important to research and use special optical fibers to replace single modes and improve the measurement method for monitoring the structural health of the steel beam.
SUMMERY OF THE UTILITY MODEL
The utility model provides a not enough to prior art exists, the utility model provides a can monitor fissured distributed optical fiber sensing device of girder steel, with the brillouin frequency spectrum that meets an emergency that BOTDA strain analysis appearance obtained, through the peak area proportion of the brillouin frequency spectrum that the analysis crack part corresponds to the prediction crackle, have that measurement accuracy is high, interference immunity is strong and lay advantages such as simple.
A distributed optical fiber sensing device capable of monitoring cracks of a steel beam comprises a sensing optical fiber to be detected, wherein the sensing optical fiber to be detected is a photonic crystal optical fiber, the outside of the photonic crystal optical fiber is wrapped by epoxy resin adhesive glue and is adhered to the upper surface of the steel beam along the length direction of the steel beam, the photonic crystal optical fiber is electrically connected with a BOTDA strain analyzer, and a support is arranged at the bottom of the steel beam; the two ends of the steel beam are provided with hooks; and arranging the fiber bragg grating at the joint of the steel beam.
The utility model has the advantages that:
considering that the single-mode optical fiber is doped with germanium ions, when the temperature is too high, the thermal motion of the ions can cause the waveguide structure to be invalid, and the Brillouin signal cannot be detected; the utility model provides a replace the single mode with special optic fibre and carry out girder steel structure health monitoring. The optical fiber used for monitoring the crack of the steel beam is a photonic crystal optical fiber. The cladding of the photonic crystal fiber is formed by air holes with a regular photonic crystal structure, and has stronger limiting capacity on light passing through the fiber core, so that the photonic crystal fiber not only has narrower Brillouin dispersion line width than common fiber, but also has 2 orders of magnitude higher Brillouin gain than the traditional single-mode fiber, and is favorable for detecting Brillouin signals. In addition, another sensing parameter can be separated from the cladding structure of the photonic crystal fiber, so that a new sensing function can be expanded, and the reliability and the expandability of the detection system are improved.
The utility model discloses a mark girder steel both ends and exert stress and the relation that optic fibre met an emergency to and the peak area proportion of the brillouin frequency spectrum that meets an emergency that analysis crack part corresponds, monitoring girder steel crack position and trend. When the steel beam has cracks, the Brillouin strain spectrum of the sensing optical fiber to be measured has peak values at positions corresponding to the cracks. When the crack grows, the peak value becomes larger, and the corresponding peak value area also increases. The width of the crack is more easily predicted by probing the area of the peak region.
Drawings
Fig. 1 is a schematic view of a distributed optical fiber sensing device capable of monitoring cracks of a steel beam according to an embodiment of the present invention;
fig. 2 is a strain distribution curve of a photonic crystal fiber on a 15m long steel beam according to an embodiment of the present invention;
FIG. 3 is a graphical representation of a Brillouin area calculation variable for peak one of the strain profiles of the photonic crystal fiber of FIG. 2;
fig. 4 is a change curve of a fiber grating measured value of a crack i and a brillouin peak area according to an embodiment of the present invention;
fig. 5 is a comparison diagram of the measured value and the calculated value of the fiber grating of the second crack provided by the embodiment of the present invention;
wherein the content of the first and second substances,
the optical fiber strain measurement device comprises a 1-BOTDA strain analyzer, 2-to-be-measured sensing optical fibers, 3-epoxy resin adhesive glue, 4-steel beams, 5-supports and 6-fiber gratings.
Detailed Description
For better explanation of the present invention, the following detailed description of the embodiments of the present invention will be made with reference to the accompanying drawings for better understanding.
As shown in fig. 1, a distributed optical fiber sensing device capable of monitoring a steel beam crack comprises a sensing optical fiber 2 to be detected, wherein the sensing optical fiber 2 to be detected is a photonic crystal optical fiber, the outside of the photonic crystal optical fiber is wrapped by epoxy resin adhesive 3 and is adhered to the upper surface of a steel beam 4 along the length direction of the steel beam 4, the photonic crystal optical fiber is electrically connected with a BOTDA strain analyzer 1, a support 5 is arranged at the bottom of the steel beam 4, and the support 5 supports the steel beam 4 from the bottom; the two ends of the steel beam 4 are provided with hooks for hanging the iron bucket and filling sand and soil with different weights into the iron bucket, so that the application of different forces is realized; and a fiber grating 6 is arranged at the joint of the two steel beams 4 for measuring the width of the crack. In this embodiment, the total length of the steel beam 4 is 15m, three steel beams and two steel beam joints are provided, the joints of the two steel beams 4 are respectively located at positions 4.6m away from two end portions of the steel beam 4, and the joints of the steel beams 4 are provided with fiber gratings 6, namely a first fiber grating and a second fiber grating.
Taking the steel beam 4 with the length of 15m as an example, a monitoring method of a distributed optical fiber sensing device capable of monitoring the crack of the steel beam 4 is described and verified, and the method specifically comprises the following steps:
the method comprises the following steps: hanging iron barrels at hooks at two ends of the steel beam 4, sequentially adding sandy soil with different weights into the barrels, and enabling the stress applied to the left end or the right end of the beam to be 98N, 196N, 294N and 392N respectively;
step two: the measurements of cracks produced by the steel beam 4 applying the four stresses described above, measured by the fiber grating 6, were recorded: the first crack of the fiber grating is FBG1 ═ (30 μm, 60 μm, 80 μm and 110 μm), and the second crack of the steel beam 4 is FBG1 ═ (39 μm, 80 μm, 130 μm and 190 μm);
step three: strain distribution of the photonic crystal fiber covered on the steel beam 4 is acquired through a BOTDA acquisition technology of the BOTDA strain analyzer 1, as shown in fig. 2, for a strain distribution curve of the photonic crystal fiber on the steel beam 4 with a length of 15m provided in this embodiment, a peak value is generated at a crack position by the strain curve, the peak value of the crack one is a peak value one, the peak value of the crack two is a peak value two, and the brillouin peak areas of the two cracks in this embodiment are δ as shown in fig. 2COD1And deltaCOD2Shown, peak area δCODI.e. the crack width can be expressed as:
wherein epsiloniIs the strain of the ith sample point,. epsilonFIs the average value of strain in the flat area between the peak value and the peak value, δ s is the resolution, L is the length of the peak value generated by the optical fiber deformation, and n is L/δsThe number of sampling points is specifically shown as the calculation variable of the brillouin peak area of peak one in the embodiment of fig. 3.
In the embodiment, δ s is selected to be 2.5cm, and the Brillouin peak area of the first peak value and the second peak value which can be calculated through the formula (1) is respectively δCOD1(25.47,57.27,89.21,139.5) and δCOD2＝(24.16,68.99,105.26,229.85)；
Step four: determining a change curve of the measured value of the fiber grating 6 and the brillouin peak area, as shown in fig. 4, the change curve of the measured value of the fiber grating 6 and the brillouin peak area of the first crack shows that the measured value of the fiber grating 6 and the brillouin peak area are in a better linear relationship, and the relationship between the measured value of the fiber grating 6 and the brillouin peak area of the first crack is fitted to be deltaFBG10.6847x +1.6605, and the coefficient of linear regression is R2＝0.9635；
Step five: and calculating the position, the variation trend and the crack width of the second crack of the steel beam 4 based on the relation curve between the measured value of the first crack of the fiber bragg grating 6 and the Brillouin peak area.
Calculating the relationship between the measured value of the fiber grating 6 fitted by the first crack and the Brillouin peak area, wherein the ratio of the Brillouin peak area of the second peak to the Brillouin peak area of the first peak is lambda deltaCOD2/δCOD1Then the calculated value of crack two is deltaFcod2＝λ*δFBG1And calculating the crack calculated value of the second crack under the pressure value.
In order to verify the feasibility of the method, the calculation result is compared with the measured value of the second crack measured by the second fiber grating, as shown in fig. 5, which is a comparison point between the measured value and the calculated value of the second crack fiber grating 6, it can be seen that the measured value and the calculated value of the second crack fiber grating 6 show the same variation trend. The average error Eorror of the calculated value and the measured value of the fiber grating 6 is:
where i is the number of calculations, δFBG2The fiber grating 6 measurement for crack two. By calculation, the result showed that the average error value was only 9.5%. Thus, the position and width of the crack can be measured using this method.
Claims (1)
1. The utility model provides a can monitor cracked distributed optical fiber sensing device of girder steel which characterized in that: the optical fiber strain analyzer comprises a to-be-detected sensing optical fiber, wherein the to-be-detected sensing optical fiber is a photonic crystal optical fiber, the outside of the photonic crystal optical fiber is wrapped by epoxy resin adhesive glue and is adhered to the upper surface of a steel beam along the length direction of the steel beam, the photonic crystal optical fiber is electrically connected with a BOTDA strain analyzer, and a support is arranged at the bottom of the steel beam; the two ends of the steel beam are provided with hooks; and arranging the fiber bragg grating at the joint of the steel beam.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112857227A (en) * | 2021-02-24 | 2021-05-28 | 沈阳建筑大学 | Distributed optical fiber sensing device capable of monitoring steel beam cracks and monitoring method |
| CN112857227B (en) * | 2021-02-24 | 2024-05-24 | 沈阳建筑大学 | Distributed optical fiber sensing device capable of monitoring cracks of steel beam and monitoring method |
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