CN110715614B - Spiral optical fiber sensing strain testing device and method for prestressed FRP (fiber reinforced Plastic) ribs - Google Patents
Spiral optical fiber sensing strain testing device and method for prestressed FRP (fiber reinforced Plastic) ribs Download PDFInfo
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- 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
- G01B11/165—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of a grating deformed by the object
Abstract
A device for testing the sensing strain of spiral optical fibre for prestressed FRP rib is composed of a spiral sensing optical fibre embedded in said FRP rib, a photosensitive signal conversion system for capturing the photosensitive parameter variation of said sensing optical fibre, a computer data processing system for outputting and recording the axial strain value of said FRP rib, and a computer data processing system for amplifying and converting the ring-down spectrum signal of said spiral cavity, the accurate assessment of the structural prestress loss provides basic data.
Description
Technical Field
The invention belongs to the technical field of experimental mechanics measurement of bridge engineering, is suitable for strain test of a prestressed FRP (fiber reinforced Plastic) bar, and particularly relates to a device and a method for testing the strain of a spiral optical fiber sensor of the prestressed FRP bar.
Background
At present, concrete structures adopting prestressed FRP ribs are more and more widely applied to civil engineering and building engineering, and the FRP main framework ribs or the prestressed ribs which are used as main bearing members are key links which relate to the safety of the whole structure and the objective evaluation of the use performance in strain (stress) monitoring and identification under the service state of the FRP main framework ribs or the prestressed ribs, and are especially important in the health monitoring and operation maintenance practice of large-span bridge engineering. However, the most mature and extensive steel string strain gauges applied to traditional reinforced concrete and prestressed concrete structure monitoring depend on a large number of welding connections in the arrangement mode, the typical inorganic non-metallic materials such as fiber reinforced fabric prestressed FRP ribs cannot be considered, and only another type of surface attachment type strain testing technology can be selected to be applied to the strain testing of the prestressed FRP ribs.
Therefore, a series of bottleneck problems restricting the testing precision of the surface-attached strain testing technology are derived, and the bottleneck problems are mainly reflected in the following three aspects: firstly, the attached strain elements (strain gauges and strain gauges) are arranged on the surface of the prestressed FRP rib, and after concrete is vibrated, the strain elements are mechanically damaged, so that the survival rate of the test elements is seriously influenced; the second step, in the practice of structural engineering operation and maintenance, the conventional test method shows that, even for the same test area, the strain test elements arranged on the upper edge and the lower edge of the prestressed FRP rib show larger difference in numerical value for the beam and column members which are deformed in a press bending or stretch bending composite stress state, the reason for this is that the radial effect (stress and deformation) has obvious influence on the axial strain, and the effect is more obvious for the prestressed FRP rib with larger diameter; and thirdly, the traditional surface-attached strain testing element is arranged on the surface of the FRP to be tested in a reciprocating winding mode, a plurality of straight line sections and semi-circular arc sections exist, and during strain testing, as the strain change states of the straight line sections and the circular arc sections are obviously different, and in a subsequent long-term monitoring period, the traditional surface-attached strain testing element is greatly influenced by working environments such as temperature and humidity, and the like, and the strain testing precision is greatly influenced.
In summary, based on the optical fiber signal transmission and conduction mechanism, in order to make up for the defects of the traditional surface-attached strain testing technology in the strain state test of the prestressed FRP bar, an embedded-type layout method is adopted as a substitute scheme, and the improvement of a corresponding parameter calibration method is a necessary way for realizing higher-precision strain monitoring.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a spiral optical fiber sensing strain testing device and a method for a prestressed FRP rib, and the device and the method are designed aiming at the surface geometric topological shape characteristics of the prestressed FRP rib, an embedded spiral sensing optical fiber testing device is provided, and a strain precision optical measurement method matched with the embedded spiral sensing optical fiber testing device is provided, so that the high-precision measurement of the strain change value of the prestressed FRP rib is realized by analogy to a spring axial expansion working mechanism, the prestress loss and the permanent stress state of the prestressed FRP rib can be further known in real time with high precision, and the device and the method are of great importance for the service performance evaluation of members such as beams, columns and the like.
In order to achieve the purpose, the invention adopts the technical scheme that:
the utility model provides a spiral optic fibre sensing of prestressing force FRP muscle meets an emergency testing arrangement, including spiral embedded spiral sensing optic fibre 1 who twines in prestressing force FRP muscle 4, spiral sensing optic fibre 1 passes through optical fiber network device 5 and inserts photosensitive signal conversion processing system 2, after beam column structure takes place the coordinated deformation with prestressing force FRP muscle 4, photosensitive signal conversion processing system 2 catches the photosensitive parameter change that spiral sensing optic fibre 1 took place, and through the spiral chamber ring down the spectral signal amplification, after the conversion, by 3 terminal output of computer data processing system and record the axial strain value of prestressing force FRP muscle 4 that corresponds.
The surface of the prestressed FRP rib 4 is provided with a spiral groove, the spiral sensing optical fiber 1 is embedded and wound in the groove to realize stable and fixed connection, and after winding and laying preparation are completed, the spiral sensing optical fiber is packaged and fixed by materials such as epoxy resin glue.
The spiral sensing optical fiber 1 is made of optical fiber materials made of quartz or plastics. Noting that the change in Bragg wavelength of the sensing fiber is Δ λBFor the magnitude of the strain change Δ ε can be measured by Δ λB＝KεΔε+KTΔ T was tested. In the formula, KεIs the strain sensitive coefficient, Kε＝λBo(1-ρα)；KTIs a coefficient of thermal expansion, KT＝λBo(α + ξ); and delta T is a temperature change value. Wherein rho alpha, alpha and xi are respectively the elasto-optic coefficient, the thermal expansion coefficient and the thermo-optic coefficient of the spiral sensing fiber (1).
The invention also provides a method for testing the spiral optical fiber sensing strain of the prestressed FRP rib, wherein the spiral sensing optical fiber 1 is spirally embedded and wound on the prestressed FRP rib 4, the spiral sensing optical fiber 1 is connected to the photosensitive signal conversion processing system 2 through an optical fiber networking device 5, after the beam column structure and the prestressed FRP rib 4 are subjected to coordinated deformation, the photosensitive signal conversion processing system 2 captures the photosensitive parameter change of the spiral sensing optical fiber 1, and after the amplification and conversion of the ring-down spectrum signal of the spiral cavity, the computer data processing system 3 outputs and records the corresponding axial strain value of the prestressed FRP rib 4.
The photosensitive signal conversion processing system 2 is based on the fiber spiral cavity ring-down spectroscopy technology and algorithm, and the conversion relation formula for the axial strain test is delta lambdaB＝KεΔε+KTΔ T, where Δ λBΔ ε is the change in strain for the change in Bragg wavelength, Δ T represents the change in temperature, KεIs the strain sensitive coefficient, KTThe thermal expansion coefficient is determined according to the concrete type of the prestressed FRP rib 4 and the arrangement mode of the spiral sensing optical fiber 1,
the differential, lambda, of the length L of the test area of the prestressed FRP tendon 4BWavelength, λ, of the sensing fiber 1 being spiral-shapedB＝2neffΛ, where λBIs a wavelength, neffThe effective refractive index of the laser when propagating in the optical fiber, and the lambda is the variation period of the refractive index of the optical fiber.
The strain sensitivity coefficient Kε＝λBo(1-. rho.alpha.), coefficient of thermal expansion KT＝λBo(α + ξ) where λBoAs the initial central wavelength, rho, alpha and xi are respectively an elasto-optical coefficient, a thermal expansion coefficient and a thermo-optical coefficient.
The specific test calculation of the invention is integrated in the photosensitive signal conversion processing system 2, and the first specific test method comprises the following steps:
only one section of spiral sensing optical fiber 1 is wound in the measuring area of the prestress FRP rib 4, so that epsilon1For the strain generated by the spiral sensing optical fiber 1 on the lower edge of the beam body, after the prestressed FRP rib 4 arranged on the lower edge of the beam body is stretched and deformed, the change of the corresponding wavelength signal is reflected on the demodulator as follows: Δ λ ═ Kεε1In which K isε＝λBo(1-rho alpha), and outputting and recording corresponding strain through a computer data processing system 3 terminal based on the formula through signal conversion, wherein the strain is the axial real-time strain value of the prestressed FRP rib 4.
The second specific test method comprises the following steps:
winding two sections of spiral sensing optical fibers 1 up and down in a measuring area of the prestressed FRP rib 4, keeping the lengths of the two sections of spiral sensing optical fibers 1 arranged on the measuring area the same, and enabling epsilon to be1Strain of the lower section spiral sensing fiber 1 on the lower edge of the beam body is caused to be epsilon2Strain generated on the lower edge of the beam body by the upper section of the spiral sensing optical fiber 1 is generated, because the upper section of the spiral sensing optical fiber and the lower section of the beam body are symmetrically arranged, epsilon1＝ε2After the prestressed FRP ribs 4 arranged on the lower edge of the beam body are subjected to tensile deformation, the change of the wavelength signal is reflected on the demodulator as follows: Δ λ ═ Kε(ε1+ε2)＝2Kεε1Based on the formula, the computer data processing system 3 outputs and records the corresponding strain through signal conversion, and the strain change of the actual prestressed FRP rib 4 is 0.5 times of the output strain.
The third specific test method comprises the following steps:
winding two sections of spiral sensing optical fibers 1 up and down in a measuring area of the prestressed FRP rib 4, keeping the lengths of the two sections of spiral sensing optical fibers 1 arranged on the measuring area the same, and enabling epsilon to be1Strain of the lower section spiral sensing fiber 1 on the lower edge of the beam body is caused to be epsilon2For the strain generated by the upper section of the spiral sensing fiber 1 on the lower edge of the beam body, let Δ T be the temperature change on the lower section of the spiral sensing fiber 1, and then the change of the corresponding wavelength is reflected on the demodulator as follows: Δ λ ═ Kε(ε1+ε2)+KTΔ T. Due to temperature effectThe interference that should, the total accuracy of meeting an emergency that the optic fibre strainometer surveyed is lower, utilizes FBG demodulation appearance to carry out temperature compensation to sensing optical fiber, so can get rid of the influence that the temperature changes to prestressing force FRP muscle strain under this test, improves the precision that spiral optic fibre sensing meets an emergency and tests. The obtained wavelength change is input into an optical fiber strain gauge to measure the total strain epsilon, and under the test of the method, the corresponding total strain epsilon can be output and recorded by a computer data processing system 3 terminal through signal conversion based on the formula.
Compared with the prior art, the invention has the beneficial effects that:
(1) the arrangement and test method of the spiral sensing optical fiber effectively solves the problem of test deviation caused by radial effect in the beam and column members deformed in a bending or stretching composite stress state, and remarkably improves the test precision.
(2) The grooves on the surfaces of the prestressed FRP ribs are matched with the epoxy resin for fixed packaging, so that the spiral sensing optical fibers are effectively protected, the sensing optical fibers are prevented from being damaged by concrete pouring, vibration and other construction operations, the survival rate of a test element is guaranteed, meanwhile, the temperature and humidity working environment of the sensing optical fibers of a subsequent structure in a long service period is effectively solidified, and the test stability is improved.
(3) The embedded arrangement of the sensing optical fiber is convenient for operation, has less working procedures, does not need welding operation, and is more suitable for typical inorganic non-metallic materials such as prestressed FRP ribs.
(4) The technical defects of sensitive noise error and poor test robustness in a straight line arrangement mode in the traditional attached strain test technology are effectively overcome.
(5) The technical defect that the deformation of a straight line section and a semi-arc section is asynchronous in the reciprocating winding arrangement mode of a test element on the surface of the FRP to be tested in the traditional attached strain test is effectively overcome.
(6) The length of the testing section and the spiral optical fiber winding configuration can be flexibly adjusted according to the structural characteristics of the prestressed FRP rib, and the method has better adaptability in variable field environments.
(7) Due to the sensitivity of the sensing optical fiber material, compared with a common resistance strain wire, the sensing optical fiber has higher accuracy and better flexibility in the using process, is more beneficial to fitting the prestress FRP rib, and improves the measurement accuracy.
The invention can not only eliminate the interference of radial effect on the response of strain change when the deformable body member is in a composite stress state, but also effectively overcome the technical defects that strain elements (strain gauges and strain gauges) are arranged on the surface of the prestressed FRP rib, the survival rate is low after concrete is vibrated, the difference of test results is large, and the deformation of the straight line section and the semi-circular arc section is not synchronous. Through technical improvement, the difficulty of arranging the sensors in prestress FRP rib strain monitoring is obviously reduced, the survival rate and the test precision of the sensors are effectively guaranteed, the method can be widely applied to the technical fields of bridge structure load tests, health monitoring and the like in civil and architectural engineering, and has positive engineering significance and application value for realizing the service performance evaluation of the bridge structure and guaranteeing the integral safe operation of the structure.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a schematic diagram of the structure of the optical fiber sensing system.
FIG. 3 is a schematic diagram of the implantable helical sensing fiber embedded deployment of the present invention.
FIG. 4 is a schematic diagram of the layout parameters of the spiral sensing optical fiber.
FIG. 5 is a schematic diagram of a strain change test of a prestressed FRP rib of a simply supported beam bridge.
FIG. 6 is a schematic diagram of a spiral fiber-optic sensing strain measurement system according to the present invention.
FIG. 7 is a schematic diagram of a two-stage optical fiber strain testing system according to the present invention.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the drawings and examples.
As shown in figure 1, the spiral optical fiber sensing strain testing device for the prestressed FRP rib is characterized in that a main stressed member prestressed FRP rib 4 arranged in a concrete beam and a concrete column is embedded and wound in the spiral optical fiber 1 by means of a groove formed by extrusion on the surface of the prestressed FRP rib, an optical fiber networking device 5 is led out and connected into a photosensitive signal conversion processing system 2 in parallel, and the optical fiber sensing strain testing device is tested, converted and then transmitted to a computer data processing system 3 to be analyzed and realize real-time output of a strain change value of the prestressed FRP rib 4.
The structural principle of the optical fiber sensing system is shown in fig. 2, the spiral sensing optical fiber 1 comprises a cladding 11, a grating 12 and a fiber core 13, the arrangement mode is shown in fig. 3, and after the arrangement is completed, the arrangement shape can be abstracted to the spiral geometry shown in fig. 4.
The sensing optical fiber measurement adopts the principle that the elasto-optic effect of the optical fiber is utilized, and the refractive index of the fiber core 13 is permanently and periodically changed due to the elasto-optic effect, so that the grating pitch of the grating 12 is changed. Therefore, after the optical signal with a certain frequency width enters the fiber grating, the light with a specific wavelength returns along the original path, the optical signals with the other wavelengths are directly transmitted out, when the fiber grating generates strain or is subjected to the change of external temperature, the reflected central wavelength moves, and the fiber grating and the central wavelength have a certain relationship. Therefore, the change of the strain can be obtained by measuring the moving distance of the central wavelength.
The working principle of the fiber grating is that the wavelength meeting the fiber grating Bragg condition is as follows:
λB＝2neff·Λ (1)
wherein λBIs the Bragg wavelength, neffThe effective refractive index of the laser propagating in the optical fiber, and the lambda is the variation period of the Bragg grating refractive index.
Besides, the change of the optical fiber strain can affect the effective refractive index and the change period, because the thermo-optic effect exists, the change period of the refractive index changes along with the change of the temperature, and the change period is specifically shown as the formula (2).
ΔλB＝λBo(1-ρα)Δε+λBo(α+ξ)ΔT (2)
In the formula, Δ λBFor changes in bragg wavelength, ρ α, and ξ are the elasto-optic coefficient, the thermal expansion coefficient, and the thermo-optic coefficient, respectively, Δ ∈ is the change in strain, and Δ T represents the change in temperature.
Let Kε＝λBo(1-ρα)，KT＝λBo(α + ξ) in which K isεIs called the strain sensitive coefficient, KTReferred to as the coefficient of thermal expansion, then:
ΔλB＝KεΔε+KTΔT (3)
an included angle theta is formed between the sensing optical fiber and the pre-strain FRP rib when the sensing optical fiber is wound on the pre-strain FRP rib, as shown in figure 3, the strain along the axial direction of the optical fiber is taken as axial strain, and the strain along the cross section direction of the optical fiber is called transverse strain. When the pre-strain FRP rib generates strain, the radial direction and the transverse direction of the optical fiber are affected, so that the working principle of the optical fiber is analyzed to achieve the purpose of accurately measuring the strain change rule.
Axial strain epsilon on preset strain FRP ribFStrain epsilon in the axial direction of the optical fiberZ＝εFcos θ, fiber transverse strain εJ＝εF sinθ。
(1) Fiber grating characteristic analysis under axial strain
Differentiating two sides of the fiber bragg grating equation to obtain:
dλB＝2Λ·dneff+2neff·dΛ (4)
obtained by dividing formula (1) by formula (2):
for the prestressed FRP reinforcement material, the deformation thereof conforms to the linear elasticity, so that there are:
ε in the above formula represents the axial strain of the fiber.
Only the influence of axial deformation on the refractive index of the optical fiber is considered under axial strain, while the influence of radial deformation on the refractive index of the optical fiber is ignored, so that the influence of axial strain on the change of the refractive index of the optical fiber is as follows:
in the above formula C11And C12Refers to the axial and transverse refractive index changes caused by axial strain, called the elasto-optic coefficient; v in the above formula means the poisson's ratio.
Order to
The following can be obtained:
let alphaε＝λB(1-C), then alphaεThe sensitivity coefficient is taken as the relation between the axial strain of the optical fiber and the wavelength change, so that the mathematical relation between the two is shown as a formula (9).
ΔλB＝αεε (9)
(2) Fiber grating characteristic analysis under transverse strain
Under transverse strain and when shear strain is negligible, only the effect of transverse strain on the refractive index of the optical fiber is considered, while the effect of axial strain on the refractive index of the optical fiber is ignored, so the effect of transverse strain on the change of the refractive index of the optical fiber is as follows:
order for doing the same
Then it can be obtained:
all together make alpha'ε＝λB(1-C'), then alphaεThe sensitivity coefficient of the fiber as the relationship between the transverse strain and the wavelength variation can be obtainedThe mathematical relationship between them is shown in formula (12).
ΔλB＝α'εε (12)
Assuming that the total length of the optical fiber spiral line is T, the sectional area is A, and the sensitivity k of the optical fiber material, the transmission efficiency is expressed as:
when the fiber is under tension or compression, the helix T, A, k changes, fully differentiates the above equation, and after finishing, has
The cross section of the sensing optical fiber is circular
D1For the diameter of the fiber, there are:
it is known from material mechanics that the Poisson ratio is v1The relationship between the transverse deformation and the axial deformation of the optical fiber is
For a diameter of D2L length of test area and v Poisson ratio2The relationship between the transverse deformation and the axial deformation of the prestressed FRP rib is
From the length of the helix
In the formula
L is the length of the test area and S is the pitch. Differentiating the formula (18), and arranging the formula (17) as follows:
by substituting formula (15) and formula (16) for formula (19)
By substituting formula (19) and formula (20) into formula (14)
Order to
The conversion equation for the axial strain test is thus obtained:
k is the sensitivity coefficient of the optical fiber test, and the sensitivity coefficient calibration can be realized according to the concrete type of the prestressed FRP rib and the arrangement mode of the spiral sensing optical fiber for the actual structural engineering.
The following describes the technical solutions of the present invention in further detail by way of examples with reference to fig. 5 to 7, but the present invention is not limited to these embodiments.
Before pouring and manufacturing the simply supported prestressed FRP reinforced concrete beam shown in FIG. 5, namely selecting a span section with the largest bending moment effect in a certain range as a test area, and performing spiral sensing optical fiber surrounding arrangement by matching with a surface groove configuration of an extrusion type Fiber Reinforced Plastic (FRP) rib. Uniformly coating epoxy resin in a measuring area range for encapsulation and fixation, connecting the optical fiber networking device 5 and a lead after the epoxy resin is hardened, and simultaneously determining key test parameters: and testing the length L of the area, the pitch S and the number n of winding turns, and carrying out sensitivity coefficient K calibration. The normal operation state of the bridge is simulated, the illustrated simply supported beam generates bending deformation under the condition of bearing radial symmetrical load F, and the vertical force F is generalized equivalent load and can represent the dead weight of the bridge, the pavement of a bridge deck and the static load of accessory facilities in the service state, the dynamic load of vehicles periodically acting on the beam body and the like. Under the action, the prestressed FRP rib arranged on the lower edge of the section is subjected to tensile deformation, and the generated static or dynamic strain along the axial direction of the prestressed FRP rib can be monitored in real time by applying a spiral optical fiber testing device and a method.
As shown in fig. 6, in a specific testing method of the present invention, the connection optical fiber networking device 5 is connected to the optical fiber strain testing system through a wire, and is integrated in the photosensitive signal conversion processing system 2 for testing.
Only one section of spiral sensing optical fiber 1 is wound in the measuring area of the prestress FRP rib 4, so that epsilon1In order to sense the strain generated by the optical fiber on the lower edge of the beam body, after the prestressed FRP rib arranged on the lower edge of the beam body is stretched and deformed, the change of the corresponding wavelength signal obtained by the formula (3) is reflected on a demodulator as follows:
Δλ＝Kεε1+KTT1 (24)
since the test temperature remains constant for controlling a single variable during the test, equation (24) above can be expressed as:
Δλ＝Kεε1 (25)
wherein Kε＝λBo(1-rho alpha), the corresponding strain epsilon can be output and recorded by a computer data processing system (3) terminal through signal conversion based on the formula (3)1Namely, the axial real-time strain value of the prestressed FRP rib is obtained.
As shown in fig. 7, in another specific testing method of the present invention, the connection optical fiber networking device 5 is connected to the optical fiber strain testing system through a wire, and is integrated in the photosensitive signal conversion processing system 2 for testing.
Winding two sections of spiral sensing optical fibers 1 up and down in a measuring area of the prestressed FRP rib 4, keeping the lengths of the two sections of spiral sensing optical fibers 1 arranged on the measuring area the same, keeping the lengths of the two sections of spiral sensing optical fibers arranged on the measuring area the same, and enabling the length of the epsilon to be the same1For sensing the strain of the optical fiber on the lower edge of the beam body, let ε2For sensing the strain generated by the optical fiber on the lower edge of the beam body, since the two are symmetrically arranged, epsilon1＝ε2. After the prestressed FRP ribs arranged on the lower edge of the beam body are stretched and deformed, the change of wavelength signals is reflected on a demodulator as follows:
Δλ＝Kε(ε1+ε2)＝2Kεε1 (26)
based on the formula (26), the corresponding strain epsilon can be output and recorded by a computer data processing system 3 terminal through signal conversion1The axial strain of the actual prestressed FRP rib is 0.5 times of the output strain.
As shown in fig. 7, in the third specific testing method of the present invention, the connection optical fiber networking device 5 is connected to the optical fiber strain testing system through a wire, and is integrated in the photosensitive signal conversion processing system 2 for testing.
Winding two sections of spiral sensing optical fibers 1 up and down in a measuring area of the prestressed FRP rib 4, keeping the lengths of the two sections of spiral sensing optical fibers 1 arranged on the measuring area the same, keeping the lengths of the two sections of spiral sensing optical fibers arranged on the measuring area the same, and enabling the length of the epsilon to be the same1For sensing the strain of the optical fiber on the lower edge of the beam body, let ε2If Δ T is a temperature change in the sensing fiber 2 for the strain of the sensing fiber 2 generated on the lower edge of the beam body, the corresponding wavelength change is reflected in the demodulationThe instrument is as follows:
Δλ＝Kε(ε1+ε2)+KTΔT (27)
the obtained wavelength change is input into the optical fiber strain gauge to measure the total strain epsilon, under the test of the method, the signal can be converted based on the formula (27), but the total strain precision measured by the optical fiber strain gauge is poor due to the interference of the temperature effect, so the FBG demodulator is used for carrying out temperature compensation on the sensing optical fiber, and the change of the corresponding wavelength is reflected on the demodulator as follows:
Δλ＝Kε(ε1+ε2)＝Kεε (28)
therefore, the influence of temperature on the axial strain of the prestressed FRP rib can be eliminated under the test, the precision of the spiral optical fiber sensing strain test is improved, and the corresponding total strain epsilon is output and recorded by the computer data processing system 3 terminal.
In summary, the invention implements the longitudinal strain test on the pre-embedded prestressed FRP bars in beam and column structures under typical composite stress states such as bending or stretching through the embedded spiral sensing optical fiber matched with the surface geometric topological shape of the prestressed FRP bars, can effectively eliminate the interference of bending radial effect (deformation and stress) on the longitudinal strain target test result, can implement strain continuous monitoring on the prestressed FRP bars with higher precision, and provides basic data for real-time mastering the working state of the effective prestress of the prestressed FRP bars and accurately evaluating the structure prestress loss. Compared with the traditional testing device, the invention has the advantages of simple structure, convenient operation, strong environmental adaptability and difficult damage in field installation. Compared with a resistance strain test method, the sensing optical fiber has higher test stability, is convenient to install and use due to the flexibility of the material and has the functions of transmission, sensing and the like, and the efficiency of measuring data is higher.
The embodiments of the present invention described herein are not intended to be all limiting, and any modifications, equivalent alterations and the like, which are made by those skilled in the art, are intended to be included within the scope of the present invention, all of which are within the spirit and scope of the inventive concept.
Claims (8)
1. A spiral optical fiber sensing strain testing device of a prestressed FRP rib is characterized by comprising a spiral sensing optical fiber (1) which is spirally embedded and wound in the prestressed FRP rib (4), wherein a spiral groove is formed in the surface of the prestressed FRP rib (4), the spiral sensing optical fiber (1) is embedded and wound in the groove and is packaged and fixed by epoxy resin adhesive and other materials, the spiral sensing optical fiber (1) is made of a light-guide fiber material made of quartz or plastics, the spiral sensing optical fiber (1) is connected into a photosensitive signal conversion processing system (2) through an optical fiber networking device (5), after a beam column structure and the prestressed FRP rib (4) are in coordinated deformation, the photosensitive signal conversion processing system (2) captures photosensitive parameter changes generated by the spiral sensing optical fiber (1), and after amplification and conversion of ring-down spectrum signals through a spiral cavity, the axial strain value of the corresponding prestress FRP rib (4) and the sensitivity coefficient of the optical fiber test are output and recorded by a computer data processing system (3) terminal
Where eta is the transmission efficiency of the optical fiber helix,
t is the total length of the optical fiber spiral line, A is the sectional area of the optical fiber spiral line, k is the sensitivity of the optical fiber material, v1Is the Poisson ratio of the optical fiber, L is the length of the testing area of the prestressed FRP rib, v2Is the poisson ratio of prestressed FRP rib, D2The diameter of the prestressed FRP rib is,
s is the pitch.
2. The method for testing the sensing strain of the spiral optical fiber of the prestressed FRP rib is characterized in that the spiral sensing optical fiber (1) is spirally embedded and wound on the prestressed FRP rib (4), a spiral groove is formed in the surface of the prestressed FRP rib (4), the spiral sensing optical fiber (1) is embedded and wound in the groove, and the method is used for testing the sensing strain of the spiral optical fiber of the prestressed FRP ribThe spiral sensing optical fiber (1) is made of optical fiber materials made of quartz or plastics, the spiral sensing optical fiber (1) is connected into a photosensitive signal conversion processing system (2) through an optical fiber networking device (5), after a beam column structure and a prestress FRP rib (4) are subjected to coordinated deformation, photosensitive parameter change generated by the spiral sensing optical fiber (1) is captured by the photosensitive signal conversion processing system (2), and after amplification and conversion of a spiral cavity ring-down spectrum signal, the axial strain value of the corresponding prestress FRP rib (4) is output and recorded by a computer data processing system (3) terminal, and the sensitivity coefficient of an optical fiber test is fixed
Where eta is the transmission efficiency of the optical fiber helix,
t is the total length of the optical fiber spiral line, A is the sectional area of the optical fiber spiral line, k is the sensitivity of the optical fiber material, v1Is the Poisson ratio of the optical fiber, L is the length of the testing area of the prestressed FRP rib, v2Is the poisson ratio of prestressed FRP rib, D2The diameter of the prestressed FRP rib is,
s is the pitch.
3. The method for testing the helical optical fiber sensing strain of the prestressed FRP tendon as claimed in claim 2, wherein the photosensitive signal conversion processing system (2) is based on an optical fiber helical cavity ring-down spectroscopy technology and algorithm.
4. The method for testing the helical optical fiber sensing strain of the prestressed FRP rib according to claim 2 or 3, wherein the conversion relation for the axial strain test in the photosensitive signal conversion processing system (2) is Δ λB＝KεΔε+KTΔ T, where Δ λBΔ ε is the change in strain for the change in Bragg wavelength, Δ T is the change in temperature，KεIs the strain sensitive coefficient, KTThe thermal expansion coefficient is determined according to the concrete type of the prestressed FRP rib (4) and the arrangement mode of the spiral sensing optical fiber (1),
is the differential of the length L of the test area of the prestressed FRP rib (4), lambdaBWavelength, lambda, of a helically shaped sensing fiber (1)B＝2neffΛ, where λBIs the Bragg wavelength, neffThe effective refractive index of the laser when propagating in the optical fiber, and the lambda is the variation period of the refractive index of the optical fiber.
5. The method for testing the spiral optical fiber sensing strain of the prestressed FRP rib of claim 4, wherein the strain sensitivity coefficient K isε＝λBo(1-. rho.alpha.), coefficient of thermal expansion KT＝λBo(α + ξ) where λBoAs the initial central wavelength, rho, alpha and xi are respectively an elasto-optical coefficient, a thermal expansion coefficient and a thermo-optical coefficient.
6. The method for testing the spiral optical fiber sensing strain of the prestressed FRP tendon as claimed in claim 4, wherein only one section of the spiral sensing optical fiber (1) is wound in the testing area of the prestressed FRP tendon (4) so that epsilon1For the strain generated by the spiral sensing optical fiber (1) on the lower edge of the beam body, after the prestressed FRP rib (4) arranged on the lower edge of the beam body is stretched and deformed, the change of the corresponding wavelength signal is reflected on a demodulator as follows: Δ λ ═ Kεε1In which K isε＝λBo(1-rho alpha), and outputting and recording corresponding strain through a computer data processing system (3) terminal based on the formula through signal conversion, wherein the strain is the axial real-time strain value of the prestressed FRP rib (4).
7. The method for testing the spiral optical fiber sensing strain of the prestressed FRP tendon as claimed in claim 4, wherein two sections of spiral sensing optical fibers (1) are wound up and down in the testing area of the prestressed FRP tendon (4) to maintain the two sections of spiral sensing optical fibers in the testing areaThe lengths of the sensing optical fibers (1) are the same, so that epsilon1Strain of the lower section spiral sensing fiber (1) on the lower edge of the beam body is caused to be epsilon2Strain generated on the lower edge of the beam body by the upper section of the spiral sensing optical fiber (1) is generated, and because the two are symmetrically arranged, epsilon1＝ε2After the prestressed FRP ribs (4) arranged on the lower edge of the beam body are stretched and deformed, the change of the wavelength signal is reflected on a demodulator as follows: Δ λ ═ Kε(ε1+ε2)＝2Kεε1Based on the formula, through signal conversion, the corresponding strain is output and recorded by a computer data processing system (3) terminal, and the strain change of the actual prestress FRP rib (4) is 0.5 times of the output strain.
8. The method for testing the spiral optical fiber sensing strain of the prestressed FRP tendon as claimed in claim 4, wherein two sections of spiral sensing optical fibers (1) are wound up and down in the measurement area of the prestressed FRP tendon (4), the lengths of the two sections of spiral sensing optical fibers (1) in the measurement area are kept the same, and epsilon is made1Strain of the lower section spiral sensing fiber (1) on the lower edge of the beam body is caused to be epsilon2For the strain generated by the upper section of the spiral sensing optical fiber (1) on the lower edge of the beam body, making delta T be the temperature change on the lower section of the spiral sensing optical fiber (1), and then the corresponding wavelength change is reflected on the demodulator as follows: Δ λ ═ Kε(ε1+ε2)+KTΔ T, using the FBG demodulator to perform temperature compensation on the sensing fiber, wherein the change of the corresponding wavelength is reflected on the demodulator as: Δ λ ═ Kε(ε1+ε2)＝KεAnd epsilon, inputting the obtained wavelength change into an optical fiber strain gauge to measure the total strain epsilon, and outputting and recording the corresponding total strain epsilon by a computer data processing system (3) terminal through signal conversion based on the formula under the test of the method.
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