CN105136359A - Method for calculating work load based on beam surface strain values measured by optical fiber sensors - Google Patents

Abstract

The invention discloses a method for calculating the working load based on the strain value of the beam surface measured by an optical fiber sensor. Bending or torsional working load data. The present invention utilizes FBG strain sensors, which are pasted on the beam structure at certain intervals, so the beam is divided into multiple regions. The present invention can calculate the torque, bending moment and shear force of the section at the optical fiber sensor, and then use the shear force of two adjacent sections to calculate the working load value of this area. The present invention proposes a specific implementation plan to verify the present invention the accuracy. Compared with other current methods for measuring the working load of beams, the present invention has the advantages of anti-interference, time and cost saving, high efficiency and the like.

Description

Method for Calculating Working Load Based on Beam Surface Strain Values Measured by Fiber Optic Sensors

technical field

The invention relates to a method for calculating a working load based on beam surface strain values measured by an optical fiber sensor, and belongs to the technical field of optical fiber sensing.

Background technique

Currently, the industry employs a rigorous but time-consuming design approach that relies heavily on computational methods, such as finite element modeling (FEM), to obtain the operating loads on beam structures. But finite element modeling is a method that consumes a lot of manpower and economic cost.

Further, for real-time loads associated with aircraft wings, the method used is a relatively extensive "strain gauge/load calibration" method developed in the 1950s. First, a series of discrete traditional strain gauges are installed inside the wing structure, and a series of concentrated loads are applied to the wing surface to calibrate the response of the strain gauges under these loads, which is called the influence coefficient. Then input the measured value of the strain gauge into the software, and run the load formula in real time to get the result. Wherein this method is time-consuming and labor-intensive when installing the sensor, and the cost is relatively high.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies in the prior art and provide a method for calculating the working load based on the beam surface strain value measured by the optical fiber sensor. load.

Another object of the invention is to reduce the time to acquire the working loads acting on the beam in real time.

A still further object of the present invention is to reduce the economic costs associated with acquiring the working load on the beam in real time.

The technical solution of the present invention: a method for calculating the working load based on the strain value of the beam surface measured by the optical fiber sensor. Both. The implementation steps are as follows:

(1) Install multiple optical fiber sensors on the beam structure. When measuring the bending load, the optical fiber sensor is pasted along the axial direction of the beam; when measuring the torsional load, the optical fiber sensor should be 45° to the axis of the beam;

(2) After the fiber optic sensor is arranged, apply a bending load or torsional load, apply a known single point load or a force couple at the free end of the beam, and obtain the strain value at each fiber optic sensor;

(3) After arranging the optical fiber sensor and applying a known load, the beam is calibrated and tested to obtain the structural performance of the beam at each optical fiber sensor. The structural performance includes bending stiffness and torsional stiffness; and a section is defined here Coefficient s _i , so that where I _i is the moment of inertia of the section at the i-th sensor, and c _i is the distance of the i-th sensor from the neutral axis. According to the relationship formula between bending moment M _i and strain ε _i at the i-th sensor (E _i is the Young's modulus at the i-th sensor), after deformation, it is brought into the section coefficient, and the formula M _i = (ES) _i ε _i is obtained, then (ES) _i is the proportional coefficient of the bending moment and the strain value, Determine the relationship between bending moment and strain after calibration;

(4) Calculate the torque and bending moment by using the calibrated structural characteristics and the strain value measured by the optical fiber sensor;

(5) The shear force is obtained by using the bending moment between two adjacent optical fiber sensors, and then the real-time working load of the beam is calculated by using the shear force.

The optical fiber sensor is a Fiber Bragg Grating (FBG) sensor.

The calibration method is as follows, the length of the calibrated cantilever beam is l, the fiber optic sensor has been arranged on the beam before calibration, and a known single point load P is applied to the free end of the beam, then the beam will bend, and the beam will It is discretized into multiple regions by the fiber optic sensor, the length of each region is Δl, and the bending moment at the section x= _xi is M=P(li△l), which is brought into the formula , get the formula The bending stiffness of the beam is determined at each measurement location; the strain value is measured at each fiber optic sensor, according to the calibration formula Obtain the bending stiffness at each fiber optic sensor.

In the step (4), the process of calculating the bending moment by utilizing the structural characteristics of the calibration and the strain value recorded by the optical fiber sensor is: the calibration result of the step (3) obtains the bending stiffness at each optical fiber sensor, according to the formula: That is, the relationship between the bending moment and the strain is determined, and the strain value is measured by each optical fiber sensor, so the bending moment on the beam section where each optical fiber sensor is located is determined.

In the step (5), the bending moment between two adjacent optical fiber sensors is used to obtain the shear force, and then the process and formula for obtaining the working load by the shear force are:

According to the principle of moment balance, the shear force V _i at the section x= _xi can be determined, and the calculation formula is According to the force balance principle, the working load P _i at the section x= _xi can be determined, and the calculation formula is P _i =-△V _i .

The advantage of the present invention compared with prior art is:

(1) The present invention reduces the complexity of finite element modeling, that is, compared with finite element modeling, the present invention is simple and has high calculation efficiency.

(2) The optical fiber sensor adopted in the present invention has the advantages of light weight, small size, easy networking, and anti-electromagnetic interference, which overcomes the shortcomings of traditional strain gauges and has the advantages of saving time and effort.

(3) The present invention greatly reduces the time and cost required for completing structural analysis, increasing accuracy and the like.

Description of drawings

Fig. 1 is the arrangement diagram of the sensor on the constant section beam;

In the figure, 1-beam; 2-FBG sensor (to measure torsional strain); 3-axis of beam; 4-FBG sensor (to measure bending strain); 5-sensor interval; 6-c (sensor to neutral axis or neutral axis face distance); 7-beam length. The bending strain optical fiber sensor is mounted along the axial direction of the beam, and the torsional strain optical fiber sensor is mounted along the axial direction of the beam at an angle of 45° to the axis.

Detailed ways

The implementation object is a cantilever beam structure as shown in Figure 1, the left end is fixedly supported, and the right end is the free end of the beam, in Figure 1, 1-beam; 2-FBG sensor (measuring torsional strain); 3-axis of the beam; 4-FBG sensor (measuring bending strain); 5-sensor interval △l; 6-c (distance from sensor to neutral axis or neutral plane); 7-beam length l. The bending strain optical fiber sensor is mounted along the axial direction of the beam, and the torsional strain optical fiber sensor is mounted along the axial direction of the beam at an angle of 45° to the axial direction.

The present invention is specifically realized as follows:

(1) Install multiple optical fiber sensors on the beam structure. When measuring the bending load, stick it along the axial direction of the beam; when measuring the torsional load, the optical fiber sensor should be at 45° to the axis of the beam;

(2) After the fiber optic sensor is arranged, apply a bending load or torsional load, that is, act on a known single point load or a force couple at the free end of the beam, and obtain the strain value at each fiber optic sensor;

(3) After arranging the optical fiber sensor and applying a known load, a simple calibration experiment is carried out on the beam to obtain the structural performance of the beam at each optical fiber sensor, and the structural performance includes bending stiffness and torsional stiffness;

(4) Calculate the bending moment and torque by using the calibrated structural characteristics and the strain value measured by the optical fiber sensor;

(5) The shear force is obtained by using the bending moment between two adjacent optical fiber sensors, and then the real-time working load of the beam is calculated by using the shear force.

Further, the present invention installs a set of optical fiber sensor network with reasonable spatial resolution on the beam. In order to obtain the structural characteristics of the section at the sensor, for the bending condition of the beam, a single point load is applied to the free end of the beam to obtain the beam’s bending properties. Similarly, a couple is applied at the free end of the beam to obtain the torsional structural properties of the beam.

The present invention provides an improved method for calculating operating loads based on beam surface strain values measured by fiber optic sensors. Usually, multiple fiber optic sensors are arranged on the beam in a grid-like, regular pattern. Optical fiber sensors have the characteristics of small size and light weight, so a large number of optical fiber sensors are used. These sensors actually divide the beam into zones, which are the sections between two adjacent sensors. The invention assumes that these regions have constant structural properties, but the structural properties of different regions may be different. Since strain values are measured at both edges of each zone, the zones can be the same or different in length.

The invention adopts optical frequency domain reflection technology, uses gratings with low reflectivity of the same central wavelength, and tunable lasers. Hundreds of FBGs in a string. A common configuration is to use 480 sensors, glued at 1FBG/cm on a fiber about 6m long. The number of sensors depends on the length of the beam, for example, for the wing, the user can stick one at about 1.27cm. Compared with other current methods, the method of the present invention has higher spatial resolution.

After the fiber optic sensor is mounted on the beam, bending and torsional loads can be applied as described below. For bending loads, an applied out-of-plane single point load, with a known load, acts on the free end of the beam, usually along the main axis of the wing. Similarly, for torsional loading, a known couple acts on the free ends of the structure. Next, subject the beam to the working load. During the loading period, using the structural performance information of each part and the strain value measured from the sensor, according to the time interval set by the user, the torque, bending moment, shear force and load at each area can be calculated come out.

The theoretical method of determining the bending load is described in more detail below, because the derivation theory and formulas of bending and torsion have similar characteristics, so the torsion situation can be obtained by analogy.

This approach is based on the classical bending equations for a uniform beam:

$\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; the\; y</span>}}{{\mathrm{<span\; class="notranslate">\; dx</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

where y is the vertical displacement, x is the axial coordinate of the beam, M(x) is the bending moment, E is Young's modulus (or modulus of elasticity), and I is the moment of inertia Equation (1) can be written as form:

$\frac{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

where ε(x) is the strain value and c(x) is the distance from the sensor to the neutral axis, both are functions of the beam axis x.

The beam structure is divided into many regions by the sensor, each region can be defined as a part of the beam whose length is Δl, formula (2) can be written as an equation for each strain, for example, the equation at section x= _xi is as follows

$\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The subscript i is the number of the sensor at section x= _xi .

If the section coefficient is defined:

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Substituting formula (4) into formula (3) is:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The next step is to perform a simple calibration with a known single point load.

The length of the beam being calibrated is l, which is discretized into multiple regions by the sensor, each region has a length of Δl, and the bending moment at the cross-section x= _xi is M=P(li△l), and the formula is brought into (3) formula, the bending stiffness of the beam is determined at each measurement location. After bringing in:

${<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

The product of elastic modulus and section coefficient in formula (5) can be obtained by calibration with the following formula:

${<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In order to obtain the working load data of the beam, the strain value ε is measured in the experiment, and the bending stiffness (EI) is obtained through the single-point load calibration experiment, so under any load in the experiment, the bending moment at each region can be Sure:

${\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Then formula (5) is:

M _i ＝(ES) _i ε _i (9)

According to the principle of moment balance, the shear load at section x= _xi can be determined as:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; \&cong;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;M</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Finally, according to the balance of forces principle, the working load can be determined:

P _i ＝-△V _i (11)

The invention utilizes the in-plane strain measurement value of the beam surface provided by the fiber Bragg grating (FBG) technology to calculate the plane applied bending and torsional loads in real time and with super high efficiency.

In order to illustrate the present invention, a specific example is as follows

(1) FBG strain sensors are pasted on a cantilever beam with equal cross-section along the axial direction at a certain interval.

(2) Apply a known single-point load force P on its free end, and then complete the bending stiffness calibration experiment at each sensor according to formula (6).

(3) The performance of the calibrated equal-section beam can be compared with the calculation results of the following formula:

${<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; Ebh</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

(4) Then use the calibrated bending stiffness and strain values to calculate the bending moment, shear force, working load, etc. using formulas (8), (10), and (11) in the present invention.

(5) apply an equivalent load on the position where the sensor is arranged on the above-mentioned beam, record the beam to measure the strain value under the action of an equidistant uniform load, then bring into the formula (8), (10), (11) in the present invention Calculate bending moments, shear forces, working loads, and more.

(6) Compare the calculated load with the actual applied working load to calculate the accuracy.

(7) When the beam is a beam with a gradual cross-section, analogous to the case of a beam with a uniform cross-section, the values of the bending moment, shear force, and load of the beam at the sensor are respectively loaded with a single point load and a uniform load.

The correctness of the calibration results of the bending stiffness under the conditions of a single-point load and a uniformly distributed load can be verified through the above-mentioned specific implementation scheme. In addition, the in-plane strain value of the beam surface and the calibrated structural performance can be used to calculate the plane applied bending load in real time, and the accuracy error can be determined by comparing with the applied known load. An analogy can be obtained for torsional loads.

Although the illustrative specific embodiments of the present invention have been described above, so that those skilled in the art can understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, As long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are included in the protection list.

Claims (5)

1. A method for calculating the working load based on the beam surface strain value recorded by the optical fiber sensor, characterized in that: the beam is an equal section cantilever beam or a section gradient cantilever beam, and the working load is a bending load, a torsional load, or both Both are available, and the implementation steps are as follows: (1) Install multiple optical fiber sensors on the beam structure. When measuring the bending load, the optical fiber sensor is pasted along the axial direction of the beam; when measuring the torsional load, the optical fiber sensor should be 45° to the axis of the beam; (2) After the fiber optic sensor is arranged, apply a bending load or torsional load, apply a known single point load or a force couple at the free end of the beam, and obtain the strain value at each fiber optic sensor; (3) After arranging the optical fiber sensor and applying a known load, the beam is calibrated and tested to obtain the structural performance of the beam at each optical fiber sensor. The structural performance includes bending stiffness and torsional stiffness; and a section is defined here Coefficient s _i , so that Where I _i is the moment of inertia of the section at the i-th sensor, and c _i is the distance between the i-th sensor and the neutral axis, according to the relationship formula between the bending moment M _i and the strain ε _i at the i-th sensor E _i is the Young's modulus at the i-th sensor, which is brought into the section coefficient after deformation, and the formula M _i = (ES) _i ε _i is obtained, then (ES) _i is the proportional coefficient between the bending moment and the strain value, and the calibration Then the relationship between bending moment and strain is determined; (4) Calculate the torque and bending moment by using the calibrated structural characteristics and the strain value measured by the optical fiber sensor; (5) The shear force is obtained by using the bending moment between two adjacent optical fiber sensors, and then the real-time working load of the beam is calculated by using the shear force. 2. The method for calculating the working load based on the beam surface strain value measured by the optical fiber sensor according to claim 1, characterized in that: the optical fiber sensor is a Fiber Bragg Grating (FBG) sensor. 3. the method for calculating the working load based on the beam surface strain value recorded by the optical fiber sensor according to claim 1, is characterized in that: the calibration method is as follows, the length of the cantilever beam of calibration is 1, and has been in The fiber optic sensor is arranged on the beam, and a known single point load P acts on the free end of the beam, then the beam will bend, and the beam is discretized into multiple regions by the fiber optic sensor, the length of each region is Δl, and the section x= _xi The bending moment at is M=P(li△l), which is brought into the formula , get the formula The bending stiffness of the beam is determined at each measurement location; the strain value is measured at each fiber optic sensor, according to the calibration formula Obtain the bending stiffness at each fiber optic sensor. 4. the method for calculating the working load based on the beam surface strain value recorded by the optical fiber sensor according to claim 1, characterized in that: the structural characteristics of the calibration and the strain value calculated by the optical fiber sensor are used in the step (4) The process of bending moment is: the step (3) calibration result obtains the bending stiffness at each optical fiber sensor, according to the formula: That is, the relationship between the bending moment and the strain is determined, and the strain value is measured by each optical fiber sensor, so the bending moment on the beam section where each optical fiber sensor is located is determined. 5. a kind of method based on the beam surface strain value that optical fiber sensor records according to claim 1 calculates working load, it is characterized in that: in described step (5), utilize the bending moment between adjacent two optical fiber sensors The process and formula for obtaining the shear force and then using the shear force to obtain the working load are: The formula for calculating the shear force V _i at the section x= _xi is The formula for calculating the working load P _i at the section x= _xi is P _i =-△V _i .