CN107830898B - Corrosion environment monitoring device based on optical fiber sensing and monitoring method thereof - Google Patents

Abstract

The invention discloses a corrosion environment monitoring device and a monitoring method, wherein the monitoring device includes a monitoring steel bar, a steel bar support frame, a sensor, a demodulator and a monitoring data processor; the steel bar support frame includes two baffles, located at two The support column between the two baffles and the anchors located outside the two baffles, the monitoring steel bars pass through the two baffles and are fixed to the baffles by the anchors; the sensors include FBG temperature sensors and FBG stress sensor, wherein the FBG temperature sensor is used as a temperature compensation sensor, the FBG temperature sensor and the FBG stress sensor are arranged on the support column; the FBG temperature sensor and the FBG stress sensor are connected in series with the monitoring device through the demodulator processor connection. The invention can realize the accurate, high-precision, in-situ monitoring of the corrosion degree of the prestressed tendons and predict the development of the corrosion without interfering with the development and development of the corrosion. Using the device has small error, high precision, and can monitor the rust environment for a long time.

Description

Corrosion environment monitoring device and monitoring method based on optical fiber sensing

technical field

The invention relates to a corrosion environment monitoring device, in particular to a corrosion environment monitoring device based on optical fiber sensing and a monitoring method thereof, belonging to the field of civil engineering structure health monitoring.

Background technique

Steel, as a very widely used building material today, is not only used in various steel structures, oil and gas pipelines and steel bridges, but also in the form of reinforced concrete composite materials together with concrete in bridges and highways around the world. , high-rise buildings, fortifications and other industrial, civil and military applications. Generally speaking, steel has a series of advantages such as high strength, good plasticity and toughness, stable performance and mechanical properties during service, but at the same time there are some problems that need to be solved. It is easily affected by the environment and corroded, which greatly affects its performance. Especially in severe environments such as the seaside humid environment, corrosion develops rapidly; or in hidden situations such as reinforced concrete structures, the corrosion of steel bars is difficult to detect, and it is often difficult to recover when found, which seriously affects the durability of engineering structures. Safety and security are the key issues that experts and scholars have devoted their efforts to studying and trying to solve.

The reason why the corrosion of steel bars has received so much attention is that, on the one hand, the corrosion of steel bars will reduce the effective cross-sectional area of the steel bars, reduce its strength, and cause damage to the structure, especially in reinforced concrete. The volume of the rusted part will expand to 2 to 4 times of the original volume, resulting in rust expansion force, and at the same time, it will also destroy the friction and grip between the steel bar and the concrete. Swelling or even falling off as a whole will eventually lead to failure and damage of the concrete structure; on the other hand, the rust produced by the corrosion will accelerate the corrosion process of the unrusted steel bars, and the safety performance and service life of the structure will be seriously affected. If the corrosion is not monitored at any time The development of the situation, timely detection and removal of rust products, so that the structure misses the best maintenance period, the difficulty of repair and repair costs will increase exponentially, and even failure to detect the hidden safety hazards in time, which will lead to the collapse of the structure and cause serious damage. Economic losses and casualties. Therefore, in order to effectively solve such problems, develop effective steel corrosion monitoring technology to correctly grasp the current situation of steel corrosion, predict the subsequent development of steel corrosion, evaluate the durability life of structures, make maintenance and reinforcement decisions, and protect people's lives. Property safety is of great significance, with great practical significance and social and economic benefits.

At present, for the corrosion of steel bars at home and abroad, the main method of regular inspection is adopted. The main inspection methods are: 1. Battery potential method: By measuring the change of the corrosion potential of the steel bar before and after corrosion, the corrosion state of the steel bar is judged. This method can only judge the basic corrosion situation of the steel bar, find out the corrosion part of the steel bar, but cannot judge the corrosion rate of the steel bar, and is affected by many factors, such as polarization, humidity and temperature, etc. 2. Linear polarization method: Based on the Stern-Geary formula, when a small voltage is applied to the steel bars in the concrete, the balance potential of the steel bars will shift, and the overpotential and polarization current caused by polarization will be in the micro-polarization region. a linear relationship. The method is greatly affected by the environment and has a small scope of application. When the environmental conditions change, the detection results may produce serious errors. 3. Electrochemical noise (ECN) testing technology is one of the important means of corrosion research, which is usually used in industrial field corrosion monitoring. ECN devices generally consist of three pre-embedded electrodes, in which the size, material and surface state of the two working electrodes are exactly the same. Along with the corrosion process, the potential and current of the two electrodes fluctuate, and this fluctuation is called electrochemical noise. Electrochemical noise test equipment is simple, low cost, and can measure the location (area) of corrosion, such as the measurement of pitting corrosion. However, the measured data is not stable, resulting in inaccurate resistance, and the processing of data and spectrum is difficult. How to reasonably interpret the data obtained by analysis and describe the characteristics of the data is also the difficulty of ECN test. In addition, there are other detection methods such as resistance probe and galvanostatic method. These methods are difficult to control the corrosion degree of steel bars in real time, nor can they predict and judge the degree of corrosion development well. They are greatly interfered by the outside world, waste manpower and material resources, and cannot be practically applied in engineering.

Some scholars have also studied some methods of using fiber grating for corrosion monitoring. Most of their ideas are to judge the corrosion degree of steel bars by monitoring the rust expansion force generated when steel bars are corroded. However, because optical fibers are easily damaged, it is only suitable for early monitoring. In the later stage, it is easy to break due to environmental factors, rust expansion force and other reasons, and because the optical fiber covers the surface of the steel bar, it will affect the corrosion process of the steel bar, and it is difficult to apply it to engineering practice. The field monitoring technology of steel corrosion is still the focus of research on steel corrosion in concrete.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a corrosion environment monitoring device based on optical fiber sensing and a monitoring method thereof. The monitoring device does not directly contact the steel bars to be monitored. Monitoring, thereby obtaining the corrosion status of steel bars, can achieve accurate, high-precision and in-situ monitoring of the corrosion degree of steel bars without interfering with the development of corrosion, and predict the corrosion status and its development. Using the device has small error and high precision, and can monitor the corrosion degree and changes of steel bars in situ for a long time.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A rust environment monitoring device is characterized in that: comprising—monitoring steel bars, steel support frames, sensors, demodulators and monitoring data processors; the steel steel support frames include two baffles, and a A support column and an anchor located outside the two baffles, the monitoring steel bars pass through the two baffles and are fixed to the baffles by the anchors; the sensors include a FBG temperature sensor and a FBG stress sensor, the FBG temperature The sensor and the FBG stress sensor are arranged on the support column; the FBG temperature sensor and the FBG stress sensor are connected in series with the monitoring device processor through the demodulator, and the demodulator is used to obtain the FBG The wavelength variation of the temperature sensor and the FBG stress sensor, the monitoring device processor obtains the cross-sectional area of the monitoring steel bar used for judging the corrosion condition of the corrosion environment according to the wavelength variation obtained by the demodulator.

The monitoring bar cross-sectional area s _t obtained by the monitoring device processor is:

In the formula, λ _f is the original wavelength of the FBG stress sensor; λ _ft is the data measured by the FBG stress sensor at time t; λ _p is the original wavelength of the FBG temperature sensor; λ _pt is the measured time of the FBG temperature sensor at time t r is the radius of the support column; E is the elastic modulus of the support column, _n is the number of the support column; μ is the strain parameter;

A foot for adjusting the height is arranged at the lower end of the baffle, and a tightening nut is arranged on the foot.

A rust environment monitoring method using the above-mentioned monitoring device, the steps are:

Step 1. Installation and fixation of the monitoring device, including:

Pass the monitoring steel bar through the two baffles, so that the middle section of the monitoring steel bar is in the steel support frame, tension the monitoring steel bar and anchor the monitoring steel bar on the baffle outside the baffle;

Connect the FBG stress sensor and the FBG temperature sensor in series with optical fibers, and install them on the surface of the support column, wherein the wavelength of the FBG stress sensor is λ _f , and the wavelength of the FBG temperature sensor is λ _p ;

Place the monitoring device near the pre-embedded steel under tension in the concrete formwork to be poured, maintain the level of the monitoring steel bar and adjust the height of the monitoring steel bar to be the same as the embedded steel bar before fixing;

Connect the FBG stress sensor and the FBG temperature sensor to the demodulator with an optical fiber;

Step 2, pouring the embedded steel bar and the monitoring steel bar into one body through concrete and curing;

Step 3: Corrosion monitoring, including:

According to the data λ _ft and λ _pt of the FBG stress sensor and FBG temperature sensor measured at different times, calculate the strain size Δε _t and the applied force F _{t at each corresponding time point t} :

F _t =nΔε _t Eπr ²

Among them, μ is the strain parameter, n is the number of support columns; E is the elastic modulus of the support columns; r is the radius of the support columns.

Then, the monitored steel bar area s _{t at each time point t is calculated by F t :}

Among them, σ _t is the stress of the prestressed tendon after the prestress loss of the time t.

By comparing the cross-sectional area of the steel bar at different monitoring time points, the corrosion condition of the internal environment of the concrete can be judged.

By comparing the cross-sectional area of the steel bar at each adjacent time point, the corrosion situation and corrosion speed of the concrete internal environment were judged.

The working principle of the present invention is as follows: the prestressed tendons used for monitoring in the device are corroded under the action of the corrosive environment. During the corrosion process, the effective cross-sectional area of the reinforcing bars decreases, resulting in a decrease in the overall stiffness of the prestressed tendons, while the size of the prestressed tendons is reduced. Therefore, the stress of the monitored steel bar increases in the axial direction, and the strain also increases, and the strain will be transmitted to the support column through the left and right baffles of the prestressed steel support frame. Strain-sensitive, under the combined action of temperature and stress, the grating is deformed, and its central reflection wavelength changes (wavelength drift). A sufficient length of optical fiber is reserved inside the tube, and the optical fiber reserved for the FBG temperature sensor will offset the strain change, so that the Bragg grating is only affected by temperature and produces wavelength drift. By monitoring the wavelength drift of the two reflection peaks, two binary linear equations are established according to the sensitivity coefficients of the temperature and strain responses of the two sensors, and the temperature and strain at the moment are calculated, and the strain results obtained by monitoring the initial moment As a benchmark, compare the data at each time point in the later period to obtain the speed of strain change in each time period, that is, to monitor the corrosion environment by monitoring the prestressed tendons, master the corrosion situation, and quantify the corrosion rate.

In the present invention, the specific installation process of the device is as follows: first, pass the monitoring steel bars through the holes of the left and right baffles of the prestressed reinforcement support frame, so that the middle section of the steel bars is in the steel frame, and the steel bars are tensioned and placed on the outside of the baffle plates. Anchor the steel bars on the baffle, connect the FBG stress sensor and the FBG temperature sensor in series with optical fibers, and install them on the surface of the upper roof; then, except for the prestressed tendons, other parts of the device are coated with inorganic polymer elastic coatings, and the device is installed. Place it near the tension steel in the concrete formwork to be poured, screw the 4 threaded feet into the prestressed reinforcement support frame from the reserved internal threaded holes of the support column, pay attention to keep the prestressed reinforcement horizontal and adjust the height to monitor the reinforcement and tension. The steel bars are at the same height, and then the nut is screwed from the root of the foot to prevent the foot thread from slipping; finally, before the concrete is poured, the FBG stress sensor and the FBG temperature sensor are connected to the demodulator with optical fiber for concrete pouring and curing.

In the present invention, the function of the prestressed tendons is to sense and reflect the rusting environment inside the concrete; the function of the FBG stress sensor is to monitor the change of the strain and temperature of the steel strip; the function of the FBG temperature sensor is to eliminate the monitoring caused by the temperature change error, and improve the monitoring accuracy; in the prestressed rib support frame, the function of the left and right baffles is to transmit the stress of the prestressed rib to the upper top plate, and used to install the threaded feet, and the function of the support column is to paste the FBG stress sensor and FBG temperature At the same time, the sensor also has the function of bearing the prestress of the prestressed tendons; the function of the threaded feet is to adjust the height of the monitoring prestressed tendons to make them at a suitable monitoring height; the function of the set nut is to prevent the thread of the feet and the prestressed tendons. The internal thread sliding wire of the support frame causes the device to be tilted or damaged; the function of the inorganic polymer elastic coating is to protect the sensor from being damaged during the concrete pouring process, and at the same time, the components of the prestressed tendon support frame are not directly contacted with the concrete, so that the free strain is not affected. Restricted to improve monitoring accuracy; the role of optical fiber is to transmit data; the role of demodulator and computer is to demodulate signal and data analysis.

Compared with the prior art, the monitoring device of the present invention has the following beneficial technical effects:

1. It is not in contact with the steel bars in the structure, and does not affect the natural development process of steel bar corrosion. At the same time, the rust expansion effect of steel bar corrosion has no effect on the monitoring results, which greatly reduces the system error.

2. The fiber grating has the advantages of good corrosion resistance and high sensitivity, and can realize high-precision and long-term monitoring of the corrosion of prestressed bars.

3. The cost is low, and the materials used are relatively cheap, which is convenient for large-scale application in engineering practice and reduces the cost of corrosion monitoring.

4. It can completely monitor the whole stage from the beginning of corrosion on the mechanism to the later stage of corrosion, the degree of corrosion rate development, the development rate and other important factors, so as to evaluate the durability of the structure, predict the remaining service life and provide reinforcement and maintenance. reliable basis. It solves the problem that other sensors can only monitor the rust rate in the early stage of rust, which is difficult to apply in engineering practice.

Description of drawings

Fig. 1 is a kind of structural schematic diagram of a 4-support column device based on optical fiber sensing corrosion environment monitoring according to the present invention;

2 is a schematic structural diagram of a 2 support column device based on optical fiber sensing corrosion environment monitoring according to the present invention;

Fig. 3 is the vertical sectional view of the FBG stress sensor and the FBG temperature sensor in the monitoring device of the present invention;

Fig. 4 is the vertical sectional view of the device of the present invention when working in concrete;

Reference numerals: 1: Monitoring steel bar; 2: FBG stress sensor; 3: FBG temperature sensor; 4: Prestressed tendon support frame; 5: Anchor; 6: Threaded foot; Molecular elastic coating; 9: Transmission optical fiber; 10: Demodulator and computer; 11: Concrete; 12: Rebar in structure; 201: Adhesive; 202: Strain grating; 301: Metal tube; 302: Rubber; 303: Temperature grating; 401: Left baffle; 402: Right baffle; 403: Support column.

Detailed ways

The patent of the present invention will be further explained below in conjunction with the accompanying drawings.

The present invention is based on an optical fiber sensing corrosion environment monitoring device. As shown in FIG. 1 , the monitoring device includes a monitoring steel bar 1 , a FBG stress sensor 2 , a FBG temperature sensor 3 , a prestressed tendon support frame 4 , an anchor 5 , and a threaded foot 6 . , Fastening nut 7, inorganic polymer elastic coating 8 and transmission optical fiber 9. Use anchors 5 to stretch the monitoring steel bar 1 and anchor it on the prestressed tendon support frame 4. The lower end of the prestressed tendon support frame is connected to the threaded foot 6. Use the thread on the foot to adjust the height of the monitoring steel bar, and tighten the nut 7. Fixed feet. Except for monitoring steel bar 2, other parts of the device are evenly coated with inorganic polymer elastic paint. The FBG stress sensor 2 and the FBG temperature sensor 3 are connected in series with the optical fiber 9 , installed on the support column 403 of the prestressed tendon support frame, and connected to the demodulator and the computer 10 .

The prestressed tendon support frame 4 is composed of a support column 403 , a left baffle 401 and a right baffle 402 . The support column is connected with the left and right baffles. The left and right baffles can be cuboid stainless steel plates, there are through holes in the middle, and through holes with internal threads are arranged at the bottom.

The material selected for the prestressed support frame is stainless steel, steel or other light-weight and high-strength materials.

The number of holes on the prestressed rib support frame is 4, which are distributed on the four corners of the bottom of the left and right baffles.

The hole thread on the prestressed rib support frame adopts a single-line helix, the major diameter is 3-5mm, the minor diameter is 1-3mm, and the pitch is 0.5-0.7mm.

The number of support columns on the prestressed tendon support frame is 2, which are respectively arranged at the middle position of the left and right baffles near the upper and lower sides, see Figure 2. The distance between the support column 403 and the upper and lower sides is 10-20mm. Or the number of support columns is four, and they are arranged at the four corners of the left and right baffles, and the distance between them is 10-20mm from the adjacent two sides.

The radius of the support column on the prestressed tendon support frame is 15-20mm.

The length of the support column on the prestressed tendon support frame is 300mm-400mm.

The thickness of the left and right baffles of the prestressed tendon support frame is 5-20mm, more preferably 10-15mm.

The length of the left and right baffles of the prestressed tendon support frame is 100-250mm, the width is 100-250mm, more preferably, it is a rectangle, and the side length is 150-200mm.

The diameter of the holes in the middle of the left and right baffles of the prestressed tendon support frame is 20-30mm.

The monitoring steel bars are specially set up to monitor the corrosion environment inside the concrete. The monitoring steel bars are passed across the holes of the left and right baffles of the prestressed tendon support frame, and the monitoring steel bars are tensioned on the outside of the baffles by anchors, and then Secure the anchor to the outside of the baffle.

The diameter of monitoring steel bars is 15-30mm.

The length of the monitoring steel bars is 400mm-500mm.

FBG stress sensor is a wavelength modulation sensor, which is made by using a part of the optical fiber for communication using the ultraviolet exposure method of the nonlinear absorption effect of the germanium-doped fiber, and is packaged with an adhesive.

The FBG temperature sensor is a specially treated FBG stress sensor. It is packaged in a tube type. The inside of the metal tube is not filled. A sufficient length of optical fiber is reserved in the tube, and the left and right ends of the tube are sealed and fixed.

The two gratings of the FBG stress sensor and the FBG temperature sensor use different grating pitches.

With threaded feet, the upper 3/4 part of the feet is a cylinder with external threads, which can be screwed into the inner threaded hole of the support column of the prestressed rib support frame and fixed on the prestressed rib support frame, and the lower 1/4 part is a cone body.

The monitoring device includes 4 adjustment feet.

The height of the threaded feet is 20mm-40mm.

The upper part of the thread of the threaded foot adopts a single-line helix, the major diameter is 3-5mm, the minor diameter is 1-3mm, and the pitch is 0.5-0.7mm, and its parameters are consistent with the inner thread of the support column hole.

Tighten the nut and screw it into the fixed prestressing tendon support frame from the lower half of the adjusting foot.

The major diameter of the nut thread is 3-5mm, the minor diameter is 1-3mm, and the pitch is 0.5-0.7mm, and its parameters are consistent with the inner thread of the support column hole.

Inorganic polymer elastic coating, evenly applied to other parts of the device except monitoring steel bars.

Inorganic polymer elastic coatings use alkali metal silicate or silica sol.

The coating thickness of the inorganic polymer elastic coating is 1-5mm, more preferably 2-3mm. The transmission optical fiber adopts armored optical cable.

Example 1:

It is used to monitor the corrosion environment of reinforced concrete.

First, pass the monitoring steel bar 1 through the holes of the left and right baffles (401, 402) of the prestressed reinforcement support frame 4, so that the middle section of the steel bar is in the steel frame, tension the steel bar and anchor the steel bar on the outside of the baffle plate On the baffle, select suitable FBG stress sensor 2 and FBG temperature sensor 3 with large wavelength difference, wherein the wavelength of the FBG stress sensor is λ _f , and the wavelength of the FBG temperature sensor is λ _p . Connect the FBG stress sensor 2 and the FBG temperature sensor 3 in series with an optical fiber 9, and install them on the surface of the support column; then, except for the prestressed tendons, other parts of the device are coated with an inorganic polymer elastic coating 8, and the device is placed in the waiting area. Near the tensile steel bars in the pouring concrete formwork, screw the four threaded legs 6 into the prestressed rib support frame from the reserved internal threaded holes of the left and right baffles (401, 402) of the prestressed rib support frame 4, as shown in Figure 4 , pay attention to keep the prestressing tendon level and adjust the height of the prestressing tendon to be the same as the tension bar, then screw the set nut 7 from the root of the foot into the thread to prevent the foot from slipping; finally, before pouring concrete, connect the FBG stress sensor with an optical fiber And the FBG temperature sensor is connected to the demodulator for concrete pouring and curing. After curing, record the data λ _ft and λ _pt measured by the FBG stress sensor and FBG temperature sensor at each time point, and calculate the wavelength drift of each sensor:

Δλ _ft =λ _ft -λ _f (1a)

or Δλ _pt =λ _pt -λ _p

(1b)

According to the principle of FBG stress sensor, the calculation formula can be obtained:

Δλ _ft = μΔε _t +γΔT (2)

Among them, Δλ _ft is the wavelength drift of the FBG stress sensor at time t, μ is the strain parameter, γ is the temperature parameter, both μ and γ are determined by the characteristics of the fiber grating material and are known quantities, Δε _t is the axial direction of the grating at time t Strain, ΔT is the amount of temperature change at time t.

The FBG temperature sensor is not affected by stress through special packaging, and its calculation formula is:

Δλ _pt = γΔT (3)

Among them, λ _ft is the monitoring data of the FBG stress sensor at time t, and λ _pt is the monitoring data of the FBG temperature sensor at time t.

Substitute into formulas (1) and (2) respectively, we can get:

Δλ _ft =λ _ft -λ _f = μΔε _t +γΔT (4)

Δλ _pt =λ _pt -λ _p =γΔT (5)

Δλ _ft -Δλ _pt = μΔε _t (6)

The relationship between wavelength drift and prestressing tendon strain can be established. According to the first group of data monitored when the maintenance is completed, the actual force on the prestressed tendons can be calculated:

F _t =nΔε _t Eπr ² (7)

Among them, F _t is the magnitude of the force acting on the prestressed tendon at time t, r is the radius of the support column, E is the elastic modulus of the support column, and n is the number of the support column.

After that, according to the above-mentioned data collection process and calculation process, the monitoring data is extracted at corresponding time intervals, and the strain sizes Δε ₂ , Δε ₃ , Δε ₄ at each corresponding time point are calculated ... and then the prestress size and formula are:

σ _t =σ ₀ -(σ _l1 +σ _l2 +σ _l3 +σ _l4t +σ _l5t ) (8)

Among them, σ _t is the stress of the prestressed tendon after the prestress loss of time t; _{σ 0} is the tensile stress of the prestressed tendon; σ _l2 is the prestress loss value caused by the friction of the prestressing tendons; σ _l3 is the prestressing loss value caused by the temperature difference between the anchor and the prestressing tendons during concrete heating and curing; σ _l4t is the prestressing relaxation caused by the time t σ _l5t is the prestress loss value caused by the shrinkage and creep of the prestress at time t; for the detailed calculation method of σ _l1 ~σ _l5t, please refer to "Specification for Concrete Design GB 50010-2010".

After calculating the steel bar area s _t at each time point, the cross-sectional area of the steel bar at each monitoring time point can be obtained. By comparing the cross-sectional area of the steel bar at each adjacent time point, the corrosion situation and corrosion rate of the concrete internal environment can be judged.

Example 2:

Used to monitor the wet conditions of structures on the seashore.

Example 1 is repeated, except that the device does not need to be pre-embedded in the concrete, and is placed in the natural environment next to the structure to be monitored.

Claims (7)

1. a corrosion environment monitoring device, is characterized in that: comprise a monitoring steel bar, steel bar support frame, sensor, demodulator and monitoring device processor; Described steel bar support frame comprises two baffles, is located between two baffles. The support column between the two baffles and the anchors located outside the two baffles, the monitoring steel bars pass through the two baffles and are fixed with the anchors and the baffles; the sensors include a FBG temperature sensor and a FBG stress sensor, and the The FBG temperature sensor and the FBG stress sensor are arranged on the support column; the FBG temperature sensor and the FBG stress sensor are connected in series with the monitoring device processor through the demodulator, and the demodulator is used to obtain all the The wavelength variation of the FBG temperature sensor and the FBG stress sensor, and the monitoring device processor obtains the cross-sectional area of the monitoring steel bar used for judging the corrosion condition of the monitored corrosion environment according to the wavelength variation obtained by the demodulator. 2 . The rust environment monitoring device according to claim 1 , wherein the number of the FBG stress sensors is two and is located on different support columns, and the number of the FBG temperature sensors is one and is located where one of the FBG stress sensors is located. 3 . Hold on. 3. rust environment monitoring device according to claim 2, is characterized in that: described FBG temperature sensor and FBG stress sensor are all fiber grating sensors, and two gratings of described FBG stress sensor and FBG temperature sensor select different grating pitches for use . 4. The corrosion environment monitoring device according to any one of claims 1-3, characterized in that: the monitoring steel bar cross-sectional area s _t obtained by the monitoring device processor is:

where λ _f is the original wavelength of the FBG stress sensor; λ _ft is the wavelength measured by the FBG stress sensor at time t; λ _p is the original wavelength of the FBG temperature sensor; λ _pt is the measured wavelength of the FBG temperature sensor at time t r is the radius of the supporting column; E is the elastic modulus of the supporting column, _n is the number of supporting columns; μ is the strain parameter; 5 . The corrosion environment monitoring device according to claim 4 , wherein a support foot for adjusting the height is provided at the lower end of the baffle, and a tightening nut is provided on the support foot. 6 . 6. A method for monitoring the corrosion environment of steel bars in concrete using the monitoring device described in any one of claims 1-5, wherein the steps are: Step 1. Installation and fixation of the monitoring device; Step 2, pouring the embedded steel bar and the monitoring steel bar into one body through concrete and curing, and the diameter, arrangement direction and prestress size of the monitoring steel bar are the same as the embedded steel bar; Step 3: Corrosion monitoring, including: According to the wavelength λ _ft of the FBG stress sensor and the wavelength λ _pt of the FBG temperature sensor measured at different times, calculate the strain size Δε _t and the force F _{t at each corresponding time point t} :

F _t =nΔε _t Eπr ² Among them, μ is the strain parameter, n is the number of support columns; E is the elastic modulus of the support column; r is the radius of the support column; λ _f is the original wavelength of the FBG stress sensor; λ _p is the original wavelength of the FBG temperature sensor; Then, the monitored steel bar area s _{t at each time point t is calculated by the prestress F t :}

Among them, σ _t is the stress of the prestressed tendon after the prestress loss of the time t. 7. The method for monitoring the corrosion environment of steel bars in concrete according to claim 6, wherein the installation and fixation of the monitoring device specifically comprises: Pass the monitoring steel bar through the two baffles, so that the middle section of the monitoring steel bar is in the steel support frame, tension the monitoring steel bar and anchor the monitoring steel bar on the baffle outside the baffle; Connect the FBG stress sensor and the FBG temperature sensor in series with optical fibers, and install them on the surface of the support column; Place the monitoring device near the pre-embedded steel under tension in the concrete formwork to be poured, maintain the level of the monitoring steel bar and adjust the height of the monitoring steel bar to be the same as the embedded steel bar before fixing; Connect the FBG stress sensor and FBG temperature sensor to the demodulator with optical fibers.

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