Method for acquiring bridge information and bridge information acquisition system

Abstract

Get information about bridges. [Solution] The method for acquiring bridge information includes step S11 of applying input light to an optical fiber 11 placed in a strain measurement area 91S set on the bridge 91, step S12 of acquiring return light caused by the input light while a vehicle 95 is passing over the bridge 91, and step S13 of acquiring measured strain information D91a that indicates the distribution of strain occurring in the strain measurement area 91S due to the passage of the vehicle 95 by applying processing based on optical frequency domain reflectometry (OFDR) to the return light; and by repeating step S12 of acquiring return light and step S13 of acquiring measured strain information D91a while the vehicle 95 is passing over the bridge 91, multiple pieces of measured strain information D91a are acquired.

Description

[Technical Field]

[0001] The present invention relates to a method for acquiring bridge information and a bridge information acquisition system. [Background technology]

[0002] The lifespan of a bridge depends on the type and number of vehicles passing through it. For example, if the traffic volume of large vehicles or freight vehicles is higher than expected, the lifespan of bridge components such as deck slabs and girders may be shorter than expected. Therefore, to maintain the safety of bridges, periodic inspections and repair work are carried out on bridges. For example, Patent Documents 1 to 6 disclose techniques for evaluating structures including bridges.

[0003] Patent Document 1 discloses a monitoring system that estimates the deterioration state of a structure. The technology in Patent Document 1 detects road surface displacement of a travel path and obtains the axle load of a vehicle from the road surface displacement and the displacement coefficient of the travel path. The technology in Patent Document 1 then estimates the degree of deterioration of the structure using the axle load distribution obtained from the axle load. Patent Document 2 discloses a technology for predicting the remaining lifespan of a bridge. The technology in Patent Document 2 predicts the remaining lifespan based on the progression of bridge damage and formulates an appropriate maintenance and repair plan.

[0004] Patent Document 3 discloses an optical fiber sensor for detecting vehicle weight. The fiber sensor of Patent Document 3 is a vehicle weight sensor with a simple structure that measures the weight of a vehicle while it is moving. Patent Document 4 discloses technology related to a method for measuring the weight of a vehicle traveling on a bridge. The technology of Patent Document 4 measures the live load of a bridge by indirectly measuring the axle load of a vehicle traveling on the bridge via the structural members of the bridge. Patent Document 5 discloses technology for obtaining the displacement of a structure caused by multiple moving objects moving in series. Patent Document 6 discloses a system for detecting changes in the characteristics of a structure. The system of Patent Document 6 performs the process from measuring changes in the characteristics of a structure to calculating the load fully automatically and in real time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6883768 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-44116 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-024427 [Patent Document 4] Patent No. 5153572 [Patent Document 5] Patent No. 7396139 [Patent Document 6] Patent No. 3896465 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the technology disclosed in the above patent documents, it is possible to obtain information such as strain for evaluating the condition of a bridge. However, due to limitations arising from the measurement principle and limitations when applying the technology to the field, the information that can actually be obtained is only a portion of the overall bridge information. Therefore, there has been a demand in this technical field for a method and system that can obtain even more information for evaluating the condition of a bridge.

[0007] An object of the present invention is to provide a method and system for acquiring bridge information that can obtain information about bridges. [Means for solving the problem]

[0008] A method for acquiring bridge information, which is one form of the present invention, includes the steps of: providing input light to an optical fiber placed in a strain measurement area set on the bridge; obtaining return light caused by the input light while a vehicle is passing over the bridge; and applying processing based on optical frequency domain reflectometry (OFDR) to the return light to obtain measured strain information that indicates the distribution of strain occurring in the strain measurement area due to the passage of the vehicle.By repeating the steps of obtaining return light and obtaining measured strain information while the vehicle is passing over the bridge, multiple pieces of measured strain information are obtained.

[0009] This method for acquiring bridge information uses a technique that applies processing based on optical frequency domain reflectometry (OFDR) to obtain information about strain occurring in the strain measurement area while a vehicle is passing over the bridge. Processing based on optical frequency domain reflectometry (OFDR) makes it possible to obtain information showing the distribution of strain occurring in the strain measurement area multiple times while a vehicle is passing over the bridge. As a result, information about the bridge can be obtained by using multiple pieces of measured strain information.

[0010] The method for acquiring bridge information may further include a step of evaluating deterioration of the strain measurement area using multiple pieces of measured strain information. The step of evaluating deterioration may include a step of preparing reference strain information that indicates the distribution of strain that occurs in the strain measurement area when a vehicle passes over a bridge that is considered to be free of deterioration, and a step of determining whether deterioration has occurred in the strain measurement area using the difference between the reference strain information and the measured strain information. This method makes it possible to evaluate deterioration of the strain measurement area.

[0011] The method for acquiring bridge information may further include a step of predicting the lifespan of the bridge using a plurality of pieces of measured strain information. The step of predicting the lifespan may include a step of obtaining, for each stress section set according to the magnitude of the measured stress converted from the measured strain, stress occurrence frequency information indicating the number of times that measured stresses of magnitudes included in each of a plurality of stress sections occurred, using the plurality of pieces of measured strain information, and a step of predicting the lifespan of the bridge by applying processing based on the cumulative fatigue damage law to the stress occurrence frequency information. This method makes it possible to predict the lifespan of the bridge.

[0012] The method for acquiring bridge information may further include a step of evaluating a vehicle passing over a bridge using a plurality of pieces of measured strain information, the step of evaluating the vehicle including a step of preparing judged strain information indicated by the maximum value of strain generated in the strain measurement area when a reference vehicle of a reference weight passes over the bridge, and a step of determining that the vehicle is in an overloaded state exceeding the reference weight when the measured waveforms of the strain distributions indicated by the plurality of pieces of measured strain information deviate from the judged waveforms of the strain distributions indicated by the judged strain information. This method makes it possible to detect that an overloaded vehicle has passed over a bridge.

[0013] The method for acquiring bridge information may further include a step of evaluating a vehicle passing over the bridge using a plurality of pieces of measured strain information, the step of evaluating the vehicle including a step of preparing judged strain information indicated by the maximum value of strain occurring in the strain measurement area when a reference vehicle of a reference weight passes over the bridge, and a step of determining that a vehicle accident has occurred when one of the measured waveforms of the strain distributions indicated by the plurality of pieces of measured strain information deviates from the judged waveform of the strain distribution indicated by the judged strain information. This method makes it possible to detect an accident on a bridge.

[0014] Another form of the present invention, a bridge information acquisition system, comprises a light source unit that provides input light to an optical fiber placed in a strain measurement area set on the bridge, a light receiving unit that obtains returned light resulting from the input light while a vehicle is passing over the bridge, and an acquisition unit that applies processing based on optical frequency domain reflectometry (OFDR) to the returned light to obtain measured strain information that indicates the distribution of strain occurring in the strain measurement area due to the passage of the vehicle.By repeating the process of obtaining the returned light by the light receiving unit and the measurement strain information by the acquisition unit while the vehicle is passing over the bridge, multiple pieces of measured strain information are obtained.

[0015] This system can obtain information showing the distribution of strain occurring in the strain measurement area multiple times while a vehicle is passing over the bridge. As a result, information about the bridge can be obtained by using the multiple measured strain information. [Effects of the Invention]

[0016] According to the present invention, there are provided a method and a system for acquiring bridge information, which are capable of obtaining information about bridges. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an illustration of the main steps of the disclosed method for obtaining bridge information. [Figure 2] FIG. 2 is a flowchart of the method for acquiring bridge information according to the first embodiment. [Figure 3] Fig. 3(a) is a schematic diagram showing a small vehicle passing over a bridge, and Fig. 3(b) is an example of measured strain information acquired while the small vehicle was passing over the bridge. [Figure 4] Fig. 4(a) is a schematic diagram showing a large vehicle passing over a bridge, and Fig. 4(b) is an example of measured strain information acquired while the large vehicle was passing over the bridge. [Figure 5]Figure 5(a) is a schematic diagram showing a large vehicle passing over a bridge with cracks, and Figure 5(b) is an example of measured strain information acquired while a large vehicle is passing over a bridge with cracks. [Figure 6] FIG. 6 is a flowchart of a method for acquiring bridge information according to the second embodiment. [Figure 7] Fig. 7(a) is a schematic diagram showing a vehicle passing over a bridge, and Fig. 7(b) is an example of measured strain information acquired while the vehicle is passing over the bridge. [Figure 8] 8(a) and 8(b) are diagrams for explaining the step of converting the maximum measured strain value into a measured stress value. [Figure 9] Figure 9(a) is an example of a stress-strain diagram described in the Standard Specifications for Concrete, and Figure 9(b) is a graph showing the relationship between stress amplitude and the number of cycles leading to fatigue failure (damage cycle number). [Figure 10] FIG. 10 is an example of a histogram showing stress. [Figure 11] FIG. 11 is a flowchart of a method for acquiring bridge information according to the third embodiment. [Figure 12] FIG. 12 is a diagram for explaining the processing executed in the step of obtaining information indicating whether or not a vehicle is overloaded, which is an example of information related to a passing vehicle, and the step of obtaining information indicating whether or not an accident has occurred. [Figure 13] FIG. 13 is a functional block diagram of a system for acquiring bridge information according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0019] FIG. 1 is a diagram showing the relationship between the main steps of the method for acquiring bridge information of the present disclosure. In the method of the present disclosure, a bridge 91 (see FIG. 3(a)) is the target object. Input light is applied to an optical fiber 11 installed on the bridge 91, and return light based on the input light is obtained. The return light contains information corresponding to strain occurring in the bridge 91. The information corresponding to strain obtained from this return light is used to obtain several pieces of bridge information.

[0020] A key step in the method for acquiring bridge information is step S1 of acquiring a plurality of pieces of measured strain information D91a. ​​A feature of the method for acquiring bridge information of the present disclosure is step S1 of acquiring a plurality of pieces of measured strain information D91a, ​​and three pieces of bridge information are acquired using the plurality of pieces of measured strain information D91a acquired in step S1. The bridge information includes information indicating the condition of the bridge 91 itself. For example, the bridge information can include the degree of deterioration of the bridge 91 and the fatigue life of the bridge 91. Furthermore, the bridge information includes not only the condition of the bridge 91 itself but also information about vehicles passing over the bridge 91. For example, the information about vehicles includes information identifying overloaded vehicles among vehicles passing over the bridge 91. Furthermore, the information about vehicles includes information about whether or not a vehicle passing over the bridge 91 has caused an accident.

[0021] Therefore, the method of acquiring bridge information of the present disclosure includes three steps for acquiring the three pieces of bridge information exemplified above. Specifically, the method of acquiring bridge information includes step S2 of performing a deterioration assessment of the bridge 91, step S3 of predicting the fatigue life of the bridge 91, and step S4 of acquiring information about passing vehicles.

[0022] The method for acquiring bridge information of the present disclosure may include at least one of step S1 of acquiring a plurality of pieces of measured strain information D91a, ​​step S2 of performing a deterioration assessment of the bridge 91, step S3 of predicting the fatigue life of the bridge 91, and step S4 of acquiring information about passing vehicles. In the first embodiment described below, a method including step S1 of acquiring a plurality of pieces of measured strain information D91a and step S2 of performing a deterioration assessment of the bridge 91 is exemplified. In the second embodiment, a method including step S1 of acquiring a plurality of pieces of measured strain information D91a and step S3 of predicting the fatigue life of the bridge 91 is exemplified. Furthermore, in the third embodiment, a method including step S1 of acquiring a plurality of pieces of measured strain information D91a and step S4 of acquiring information about passing vehicles is exemplified.

[0023] First Embodiment In the first embodiment, a method for acquiring bridge information including a process for evaluating deterioration is illustrated. The method for acquiring bridge information according to the first embodiment is implemented according to the flow shown in FIG. 2. First, the strain response caused by the passage of a vehicle 95 while a bridge 91 is in service is measured using an optical fiber 11. Next, based on the waveform of the obtained strain distribution, a position where a strain distribution different from the expected strain distribution is obtained is identified. Then, it is determined that deterioration such as a crack has occurred at the identified position. Then, by storing the strain and its position, information on the occurrence of deterioration and the position where the deterioration has occurred are identified.

[0024] First, multiple pieces of measured strain information D91a are acquired (S1). A strain measurement area 91S is set on the bridge 91, and optical fibers 11 are laid in the strain measurement area 91S. The optical fibers 11 are laid on at least one side track in the direction of vehicle passage on the bridge 91. In this case, it is desirable to lay the optical fibers 11 in locations where damage such as cracks is likely to occur, such as the concrete deck 91a or the underside of the girder, as shown in FIG. 3(a) and other figures. The strain measurement area 91S may be, for example, between the first bearing portion 91b and the second bearing portion 91c. Then, in this step S1, the distribution of strain occurring in the strain measurement area 91S is obtained. The strain distribution is composed of strain values ​​occurring at multiple measurement points. The strain distribution obtained in this step S1 may be considered to be continuous data across the entire strain measurement area 91S from a macroscopic perspective.

[0025] Furthermore, in step S1, the measured strain information D91a is acquired multiple times while the vehicle 95 is passing over the bridge 91. For example, the acquisition of the measured strain information D91a may be started when the vehicle 95 passes over the first bearing portion 91b. The acquisition of the measured strain information D91a may then be ended when the vehicle 95 passes over the second bearing portion 91c. As a result, multiple pieces of measured strain information D91a are acquired while one vehicle 95 passes over the bridge 91. Furthermore, the measured strain information D91a may be continuously acquired at a predetermined interval regardless of whether the vehicle 95 is passing over the bridge 91. Here, "multiple" means that the information is discrete in time. In this case, it can be said that step S1 acquires information about strain that is discrete in time but continuous in space. Furthermore, because the information is discrete in time, it can also be said that the multiple pieces of measured strain information D91a indicate changes over time in the strain distribution occurring in the bridge 91.

[0026] 3 and 4 are examples of measured strain information D91a. ​​FIG. 3(b) is an example of measured strain information D91a obtained when a small vehicle 95A passes over the bridge 91 as shown in FIG. 3(a). FIG. 4(b) is an example of measured strain information D91a obtained when a large vehicle 95B passes over the bridge 91. The horizontal axis in FIGS. 3(b) and 4(b) indicates the position on the bridge 91. Specifically, the horizontal axis indicates the distance from the first support portion 91b, with the position of the first support portion 91b being used as the reference. The vertical axis in FIGS. 3(b) and 4(b) indicates the strain value.

[0027] For example, graph G31 in FIG. 3(b) is a waveform showing the strain distribution that occurred in the strain measurement area 91S of the bridge 91 when the small vehicle 95A was at position P31. Similarly, graphs G32 to G38 are waveforms showing the strain distribution that occurred in the strain measurement area 91S of the bridge 91 when the small vehicle 95A was at positions P32 to P38, respectively. Referring to graphs G31 to G38, as the small vehicle 95A moves, the strain distribution waveform also changes accordingly. In other words, graphs G31 to G38 show the change over time in the strain distribution that occurs in the strain measurement area 91S of the bridge 91 when the small vehicle 95A is passing over the bridge 91. The strain is greatest where the small vehicle 95A is located. Then, by identifying the peaks of the graphs G31 to G38, it is possible to estimate the position of the small vehicle 95A when each of the graphs G31 to G38 was acquired.

[0028] Similarly, graphs G41 to G48 in Figure 4(b) are waveforms showing the strain distribution that occurred in strain measurement area 91S of bridge 91 when large vehicle 95B was at positions P41 to P48. Graphs G41 to G48 also show the change over time in the strain distribution that occurs in strain measurement area 91S of bridge 91 when large vehicle 95B is passing over bridge 91. By identifying the peaks of graphs G41 to G48, the position of large vehicle 95B when graphs G41 to G48 were acquired can be estimated.

[0029] Furthermore, when the vertical axis of Fig. 3(b) is compared with the vertical axis of Fig. 4(b), the magnitude of the distortion caused when large vehicle 95B passes is greater than the magnitude of the distortion caused when small vehicle 95A passes. Therefore, the peak values ​​of graphs G31 to G38 and G41 to G48 can be used to estimate the attributes of the vehicles that passed over bridge 91.

[0030] There are several known methods for measuring strain using the optical fiber 11. Among them, optical frequency domain reflectometry (OFDR) is used to obtain information about strain that is discrete in time and continuous in space.

[0031] In the OFDR method, continuous light (incident light) with a linearly swept wavelength is input to the optical fiber 11. The incident light generates Rayleigh scattered light within the optical fiber 11. After detecting this Rayleigh scattered light, predetermined signal processing is performed to obtain information about the position on the optical fiber 11 and the spectrum of the Rayleigh scattered light specific to that position. It is assumed that the strain occurring in the optical fiber 11 is equivalent to the strain occurring in the bridge 91. The strain occurring in the optical fiber 11 is proportional to the amount of shift in the spectral waveform of the Rayleigh scattered light. Therefore, first, the spectrum of the Rayleigh scattered light is acquired when a vehicle 95 is not passing over the bridge 91 and stored as a reference spectrum. Then, the spectrum of the Rayleigh scattered light is acquired when a vehicle 95 is passing over the bridge 91 and stored as a measurement spectrum. The cross-correlation between the reference spectrum and the measurement spectrum is then calculated, and the strain is calculated by multiplying the shift at which the correlation coefficient is maximized by the strain coefficient.

[0032] Optical Time Domain Reflectometry (OTDR), a Rayleigh measurement method using pulsed light, is limited by input peak power due to nonlinear optical effects, and strain is measured by averaging over several seconds or more. On the other hand, OFDR uses continuous light, which alleviates input power limitations and allows for a single measurement in an observation time of several milliseconds. Therefore, with OFDR, it is possible to set the sampling frequency to, for example, 10 to 20 Hz. Assuming that the bridge 91 is 120 m long and the vehicle 95 is traveling at a speed of 60 km / h, 72 to 144 measurements can be taken while the vehicle 95 is passing over the bridge 91. In other words, the OFDR method can quasi-dynamically capture the strain distribution as the vehicle 95 passes over the bridge 91. The OFDR method can achieve a sampling frequency sufficient to capture the strain that occurs on the bridge 91 due to the vehicle 95 passing over it. Setting the sampling frequency to a range of 10 to 20 Hz reduces the amount of data required on the server to store the measured strain information D91a and the operational effort required, which is also effective in reducing measurement costs.

[0033] Here, we compare OFDR with other strain measurement techniques that use optical fibers. Examples of measurement techniques other than OFDR include the so-called Rayleigh method and Brillouin method. The Rayleigh method shares a commonality with OFDR in that it uses Rayleigh scattered light. The Rayleigh method also shares a commonality with OFDR in that it obtains the scattered light source position by measuring the time it takes for the scattered light to return. However, the Rayleigh method differs from OFDR in that it observes the intensity of the Rayleigh scattered light as a function of time and requires averaging by injecting optical pulses several thousand times or more.

[0034] Furthermore, the Brillouin metrology method measures strain by measuring the frequency shift of Brillouin scattered light. Like the Rayleigh metrology method, the Brillouin metrology method requires averaging by injecting optical pulses several thousand times. This averaging process requires time before a strain measurement value is output. In other words, the Rayleigh and Brillouin metrology methods cannot perform measurements that can be considered dynamic, as can the OFDR method.

[0035] Another method for measuring strain using optical fiber is the distributed acoustic sensing (DAS). Unlike the Rayleigh and Brillouin sensing methods mentioned above, DAS is capable of measuring dynamic vibrations. However, the magnitude of the strain measured by DAS is small compared to the strain that actually occurs in the structure.

[0036] The OFDR method discussed so far and other measurement techniques (Rayleigh measurement method, Brillouin measurement method, and DAS measurement method) are summarized in Table 1. [Table 1]

[0037] <Deterioration assessment of Bridge 91> Next, a deterioration assessment of the bridge 91 is carried out (S2). Here, "deterioration assessment" refers to, for example, determining whether or not cracks 93a, 93b (see FIG. 5(a)) have occurred in the bridge 91. Furthermore, "deterioration assessment" here also includes, for example, determining whether or not the overall rigidity of the bridge 91 has decreased. The deterioration assessment of the bridge 91 is carried out by comprehensively assessing the presence or absence of these cracks 93a, 93b, the degree of decrease in rigidity, and the like. The result of the deterioration assessment may be a choice such as "deterioration present" or "no deterioration," or may be a numerical evaluation of the degree of deterioration such as a "deterioration index."

[0038] Graph G51 in Figure 5(b) is reference strain information D91b when large vehicle 95B is positioned approximately in the center of bridge 91, which does not have cracks 93a, 93b and has no reduction in rigidity. Graph G52 in the same figure is measured strain information D91a when large vehicle 95B is positioned approximately in the center of bridge 91, which has cracks 93a, 93b and has a reduction in rigidity.

[0039] Compared to graph G51, graph G52 shows that the waveform of the strain response is larger overall. This is thought to be due to an overall decrease in the rigidity of bridge 91, resulting in larger strains. Therefore, a decrease in rigidity can be detected by calculating the strain response in a healthy state through analysis, or by measuring the strain response in advance at a point when the bridge is considered healthy and comparing it with that. In other words, the degree of decrease in rigidity can be evaluated based on the overall increase in the strain response waveform.

[0040] Furthermore, when a large vehicle 95B passes over bridge 91 on which cracks 93a and 93b have occurred, the strain response increases locally at positions L1 and L2 where cracks 93a and 93b have occurred. Referring to graph G52, it can be seen that peaks G52a and G52b, where the strain response has increased locally, appear corresponding to the positions of cracks 93a and 93b. By detecting such peaks G52a and G52b from measured strain information D91a, ​​it is possible to know that cracks 93a and 93b have occurred in bridge 91. Furthermore, it is also possible to know the positions L1 and L2 on bridge 91 where cracks 93a and 93b have occurred.

[0041] It is important to note that the passage of the large vehicle 95B applies a load to the bridge 91, causing cracks 93a and 93b occurring in the bridge 91 to become apparent as peaks in the strain distribution. Furthermore, even if a peak in the strain distribution occurs, the peak must be captured by measurement. If the interval between strain measurement points is large, it may not be possible to capture the peak. However, the OFDR method applied in this embodiment makes it possible to capture the strain as a distribution. Therefore, strain peaks G52a and G52b occurring as abrupt changes in a narrow range are not overlooked. As a result, cracks 93a and 93b occurring in the bridge 91 can be reliably detected, enabling highly accurate deterioration assessment of the bridge 91.

[0042] That is, in step (S2) of evaluating the deterioration of the bridge 91, the cracks 93a and 93b locally increase strain at their locations, making it possible to detect the cracks by setting a threshold value. There are no particular restrictions on the conditions for determining the strain distribution as indicating deterioration.

[0043] In short, in step S2, first, reference strain information D91b is prepared (S20). Next, it is determined whether there is a local change in shape in the waveform indicated by measured strain information D91a (S21). If it is determined that there is a change in shape (S21: YES), it is determined that deterioration has occurred in the bridge 91 (S22). Note that in step S22, the type of deterioration may be identified depending on the type of change in shape. Specifically, it may be identified whether the type of deterioration is cracks 93a, 93b or an overall decrease in rigidity of the bridge 91. If it is determined that there is no change in shape (S21: NO), the deterioration assessment process is terminated.

[0044] <Action and effect> The method for acquiring bridge information includes step S11 of applying input light to an optical fiber 11 placed in a strain measurement area 91S set on the bridge 91, step S12 of acquiring return light caused by the input light while a vehicle 95 is passing over the bridge 91, and step S13 of acquiring measured strain information D91a that indicates the distribution of strain occurring in the strain measurement area 91S due to the passage of the vehicle 95 by applying processing based on optical frequency domain reflectometry (OFDR) to the return light.By repeating step S12 of acquiring return light and step S13 of acquiring measured strain information D91a while the vehicle 95 is passing over the bridge 91, multiple pieces of measured strain information D91a are acquired.

[0045] In this method of acquiring bridge information, a technique that applies processing based on optical frequency domain reflectometry (OFDR) is used to obtain measured strain information D91a related to strain occurring in strain measurement area 91S while a vehicle 95 is passing over bridge 91. Processing based on optical frequency domain reflectometry (OFDR) makes it possible to obtain information indicating the distribution of strain occurring in strain measurement area 91S multiple times while a vehicle 95 is passing over bridge 91. As a result, by using the multiple pieces of measured strain information D91a, ​​bridge information related to bridge 91 can be obtained.

[0046] The method for acquiring bridge information includes step S2 of evaluating deterioration of the strain measurement area 91S using multiple pieces of measured strain information D91a. ​​Step S2 of evaluating deterioration includes step S20 of preparing reference strain information D91b that indicates the distribution of strain that occurs in the strain measurement area 91S when a vehicle 95 passes over a bridge 91 that is considered to be free of deterioration, and step S21 of determining whether deterioration has occurred in the strain measurement area 91S using the difference between the reference strain information D91b and the measured strain information D91a. ​​This method makes it possible to evaluate deterioration of the strain measurement area 91S.

[0047] Second Embodiment In the second embodiment, a method for acquiring bridge information including a process for predicting a fatigue life will be exemplified. The method for acquiring bridge information according to the second embodiment is carried out according to the flow chart of FIG.

[0048] 6, a plurality of pieces of measured strain information D91a are obtained (S1). This step S1 is the same as that described in the first embodiment, and therefore a detailed description thereof will be omitted.

[0049] Next, the fatigue life of the bridge 91 is predicted (S3). In this step S3, a threshold value for strain that affects fatigue damage to the concrete deck slab 91a is set. Next, the maximum value of strain that exceeds the threshold value is obtained. Next, the maximum value of strain is converted into stress. This stress is then used to calculate the damage level D, which will be described later, to predict the fatigue life. Details of the fatigue life prediction of the bridge 91 (S3) are described below.

[0050] <Prediction of fatigue life of bridge 91> The fatigue life prediction (S3) of the bridge 91 uses the cumulative fatigue damage law. The cumulative fatigue damage law is calculated by dividing the damage level D and the stress amplitude (σ k ) and the number of repetitions (n k ) and a function including the above is used. Equation (1) is described in, for example, the Standard Specifications for Concrete. For example, when a concrete slab 91a constituting a bridge 91 is subjected to a certain stress amplitude (σ k ) is the load indicated by N k It is assumed that fatigue failure occurs as a result of repeated stresses. k ) is the number of repetitions of the load corresponding to k The damage level D of a deck slab subjected to repeated stresses of all amplitude levels can be expressed by formula (1). When this damage level D is 1 or greater, fatigue failure occurs.

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[0051] First, it is determined whether or not a measured strain equal to or greater than a threshold value is detected (S31). This step S31 is for determining whether or not to update the damage level D used in the fatigue life prediction step (S36) before executing the step.

[0052] If a measured strain equal to or greater than the threshold is not detected (S31: NO), a step (S36) of predicting a fatigue life is executed without updating the damage level D. If a measured strain equal to or greater than the threshold is detected (S31: YES), a series of steps (S33 to S35) of updating the damage level D is executed, and then a step (S36) of predicting a fatigue life is executed using the updated damage level D. Next, a series of steps S33 to S35 of updating the damage level D will be described.

[0053] First, the maximum measured strain value is obtained (S33). Specifically, the maximum strain value is extracted from each of the multiple pieces of measured strain information D91a, ​​and this maximum value is used as the maximum measured strain value. The multiple pieces of measured strain information D91a can be obtained at different positions on the component to be measured. For example, when there are n pieces of measured strain information D91a, ​​the number of maximum measured strain values ​​is also n, and the maximum measured strain values ​​are organized at each of the n positions.

[0054] First, as shown in Figure 7(a), the maximum measured strain value during the event (hereinafter referred to as the "event") is obtained from multiple measured strain information D91a measured within the time when the vehicle 95C that caused the detection of measured strain above the threshold passes over the bridge 91 (S33).

[0055] Specifically, first, a time history waveform (D91f) of strain change at a point of interest (a point where the degree of fatigue damage is evaluated) is obtained from multiple pieces of measured strain information D91a measured during the event. FIG. 7(b) is an example of the time history waveform (D91f) of strain change. The horizontal axis of FIG. 7(b) indicates time relative to when the vehicle 95C begins to pass over the bridge 91. The vertical axis of FIG. 7(b) indicates strain value. For example, graph G71 shown in FIG. 7(b) is the time history of strain occurring at point P71 on the bridge 91. Similarly, graphs G72 to G77 are the time history of strain occurring at points P72 to P77 on the bridge 91.

[0056] Next, the maximum strain values ​​at points P71 to P77 are extracted from each of graphs G71 to G77 included in the time history waveform (D91f) of strain change, and the extracted maximum values ​​are used as the maximum measured strain values ​​for that event and that point.

[0057] The plurality of pieces of measured strain information D91a includes strain information at different positions within each element (such as a steel girder or concrete slab) that constitutes the bridge 91, so it is possible to obtain the maximum measured strain values ​​at each of the plurality of points of interest. For example, when there are a total of n points of interest in an element such as a steel girder or concrete slab, it is possible to obtain n maximum measured strain values ​​at each of the points of interest from the plurality of pieces of measured strain information D91a.

[0058] The maximum measured strain value is converted to a measured stress value (S34). The main elements that make up the bridge 91 are, for example, steel girders and concrete deck slabs. Therefore, in this step S34, the measured steel girder stress value and the measured deck slab stress value are presented as two examples of measured stress values, and the calculation to obtain the measured steel girder stress value from the maximum measured strain value and the calculation to obtain the measured deck slab stress value from the maximum measured strain value are explained.

[0059] In the case of steel girders, repeated tensile stress has a significant impact on fatigue damage. The stress value generated in the steel girder (measured steel girder stress value) can be obtained using the following equation (2).

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[0060] A method for calculating the measured deck stress value will be explained below. The concrete deck 91a is composed of concrete 91a1 and reinforcing bars 91a2 (see FIG. 8(a)). Therefore, in the concrete deck 91a, the compressive stress generated in the concrete 91a1 and the tensile stress generated in the reinforcing bars 91a2 have a significant effect on fatigue damage. Therefore, an example will be given of a method for obtaining the compressive stress generated in the concrete 91a1 and the tensile stress generated in the reinforcing bars 91a2 when an optical fiber 11 is installed on the underside of the concrete deck 91a.

[0061] First, we will discuss the compressive stress occurring in the concrete 91a1. According to the assumption of maintaining a flat surface shown in Figures 8(a) and 8(b), it can be seen that the strain in the member cross section changes in the height direction. Then, the strain in the compressive edge of the concrete 91a1 (ε c ) and the strain at the position of the tension rebar (ε s ) can be obtained.

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[0062] The position of the neutral axis may be obtained by carrying out a fiber model analysis or the like. The stress generated in the reinforcing bars 91a2 constituting the concrete floor slab 91a is calculated by the strain (ε s ) by the Young's modulus of the reinforcing bar (see equation (5)).

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[0063] The stress occurring at the compression edge of concrete 91a1 may be obtained using the stress-strain diagram G91 shown in Figure 9(a). Figure 9(a) is an example of the stress-strain diagram G91 described in the Standard Specifications for Concrete. Furthermore, equations (6) to (8) show the stress-strain relationship of concrete 91a1. The curved portion G91a in Figure 9(a) is expressed by equation (9).

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[0064] The above calculation is performed for each measured maximum strain value at n points of interest. For example, if there are J points of interest within the steel girders and L points of interest within the concrete slab (J + L = n), the total n measured maximum strain values ​​can be used to obtain the maximum tensile stress occurring in the J steel girders, the maximum compressive stress occurring in the L concrete 91a1, and the maximum tensile stress acting on the L reinforcing bars 91a2. Using these, a histogram G10 (stress occurrence frequency information D91c) is obtained for each of the n points of interest, as shown in FIG. 10. Specifically, the count of the section corresponding to the maximum stress obtained in the event is added to the data on the number of occurrences for each stress section obtained since the start of measurement. In the histogram G10 in FIG. 10, the horizontal axis represents the stress section, and the vertical axis represents the number of occurrences of the stress corresponding to that stress section.

[0065] Then, the damage degree D is updated at each of the n different positions of the component to be measured (S35). First, attention is paid to the first stress section shown in the histogram G10. The stress amplitude (σ k ) and the stress amplitude (σ k ) occurrence count (n k ) is obtained. Next, the stress amplitude (σ k ) is the number of cycles (N k ) is obtained. k ) can be obtained using Figure 9(b). In Figure 9(b), the horizontal axis represents the number of repetitions (N k ) and the vertical axis is the stress amplitude (σ k ) Graph G92 (Number of iterations required to calculate the damage level D (Nk ) indicates the state where the damage level D is 1. For example, the stress amplitude (σ k ) and the number of repetitions (N k ) and the coordinates indicated by are on the graph G92. This means that the stress amplitude (σ k ) is repeated for a number of times (N k ) is the number of cycles required for fatigue damage to occur. k ) is the damage cycle number (N k ) Then, in the first stress section, the stress amplitude (σ k ), the stress amplitude (σ k ) occurrence count (n k ), and the number of damage cycles (N k ) is a known value. k ) occurrence count (n k ) is the number of occurrences since the system of this embodiment was applied. In calculating the damage level D, the number of occurrences of the stress amplitude (i k ) is required to obtain the stress amplitude (σ k ) occurrence count (n k ) is measured during T1, and the period from the opening of the bridge to the introduction of this system is T2. k can be calculated as follows:

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[0066] Then, based on these values, the damage level D in the kth stress section is calculated using equation (11). k can be obtained.

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[0067] By the above procedure, the damage level D kThe damage degree D of the target location can be obtained by adding up the damage degrees in the first to Nth stress sections included in the histogram G10.

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[0068] <Steps for predicting fatigue life> Next, the fatigue life BL is predicted (S36). If the damage level D is 1 or greater (D>1), it is understood that the fatigue life BL has already been reached. If the damage level D is less than 1 (D<1), it is understood that the fatigue life BL has not yet been reached. The fatigue life BL is expressed by equation (13). Equation (13) is used to obtain the fatigue life BL under the assumption that the "fatigue strength accumulated per unit time" is the same. The fatigue life BL can be obtained for each position of the component to be measured, i.e., at n locations. The fatigue life BL can be calculated for each measurement location of the component.

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[0069] <Action and effect> However, a large vehicle 95B or an overloaded vehicle carrying a load greater than the expected load may pass over the bridge 91. In this case, the bridge 91 is subjected to a large repeated load. Furthermore, the number of vehicles 95 passing over the bridge 91 may be greater than expected. It is known that when such a load greater than expected repeatedly acts on the bridge 91, the fatigue life of components such as the concrete deck 91a and girders of the bridge 91 becomes shorter than expected. Therefore, it is important to quantitatively grasp the damage level D of these components. Furthermore, cracks and deterioration of the concrete deck 91a and girders are detected through periodic inspections. However, given the expected future financial difficulties, it is necessary to reduce the burden and cost of inspection work. The method for acquiring bridge information of this embodiment can solve these problems.

[0070] The method for acquiring bridge information of the second embodiment includes step S3 of predicting the fatigue life of the bridge 91 using multiple pieces of measured strain information D91a. ​​Step S3 of predicting the fatigue life includes steps S33 and S34 of obtaining stress occurrence frequency information D91c indicating the number of times measured stresses of magnitudes included in each of multiple stress sections set according to the magnitude of measured stress converted from the measured strain, using the multiple pieces of measured strain information D91a, ​​and step S36 of predicting the fatigue life of the bridge 91 by applying processing based on the cumulative fatigue damage law to the stress occurrence frequency information D91c. According to this method, the fatigue life of the bridge 91 can be predicted.

[0071] Third Embodiment The third embodiment illustrates a method for acquiring bridge information, which includes a process for acquiring information about passing vehicles. The method for acquiring bridge information according to the third embodiment is performed according to the flow shown in Fig. 11. As shown in Fig. 11, the method for acquiring bridge information according to the third embodiment includes step S1 for acquiring a plurality of pieces of measured strain information D91a and step S4 for acquiring information about passing vehicles.

[0072] First, it is determined whether or not the vehicle 95 has passed the first bearing portion 91b of the bridge 91 (S91). The first bearing portion 91b roughly corresponds to one end of the strain measurement area 91S. In other words, the fact that the vehicle 95 has passed the first bearing portion 91b means that the vehicle 95 has entered the strain measurement area 91S. Note that the criterion for determining whether or not the vehicle 95 has entered the strain measurement area 91S is not limited to the first bearing portion 91b. It may be selected appropriately depending on the state of the bridge 91 in question.

[0073] If it is not determined that the vehicle 95 has passed (S91: NO), the operation (S1) of acquiring the measured strain information D91a is not started, and the determination operation (S91) is performed again after a predetermined period has elapsed. If it is determined that the vehicle 95 has passed (S91: YES), the operation (S1) of acquiring the measured strain information D91a is started. In other words, the determination operation (S91) is repeatedly performed until it is determined that the vehicle 95 has passed.

[0074] Next, a plurality of pieces of measured strain information D91a are obtained (S1). This step S1 is the same as that explained in the first embodiment, so a detailed explanation will be omitted.

[0075] Next, it is determined whether the vehicle 95 is overloaded (S41). The measured waveforms G12b and G12c indicated by the measured strain information D91a acquired in step S1 are compared with a previously acquired threshold waveform G12a (determined strain information D91d) (see FIG. 12). Specifically, it is determined whether the measured waveforms G12b and G12c deviate from the threshold waveform G12a. For example, if the peaks K12b and K12c of the measured waveforms G12b and G12c exceed the threshold waveform G12a, it may be determined that there is a "deviation." Alternatively, the "deviation" may be determined based on other conditions.

[0076] When it is determined that the measured waveforms G12b and G12c deviate from the threshold waveform G12a (S41: YES), the passing vehicle 95 is determined to be an overloaded vehicle (S42). Then, necessary processing for the overloaded vehicle may be performed. For example, the manager of the bridge 91 may be notified that an overloaded vehicle has passed. When it is not determined that the measured waveforms G12b and G12c deviate from the threshold waveform G12a (S41: NO), the process proceeds to the next step S43.

[0077] Next, it is determined whether an accident has occurred (S43). It is determined whether the peaks K12b and K12c of the measurement waveforms G12b and G12c indicated by the measured strain information D91a acquired in step S1 exceed the threshold information (accident detection threshold information G12s) for detecting the presence or absence of an accident that has been acquired in advance.

[0078] When it is determined that the peaks K12b and K12c of the measurement waveforms G12b and G12c deviate from the threshold waveform G12a (S43: YES), it is determined that an accident has occurred due to a passing vehicle 95 (S44). Then, necessary processing in response to the occurrence of the accident may be performed. For example, the occurrence of the accident may be notified to the manager of the bridge 91. When it is not determined that the peaks K12b and K12c of the measurement waveforms G12b and G12c deviate from the threshold waveform G12a (S43: NO), the process proceeds to the next step S92.

[0079] Next, it is determined whether the vehicle 95 has passed the second support portion 91c of the bridge 91 (S92). The second support portion 91c roughly corresponds to the other end of the strain measurement area 91S. In other words, the fact that the vehicle 95 has passed the second support portion 91c means that the vehicle 95 has exited the strain measurement area 91S. Note that the criterion for determining whether the vehicle 95 has exited the strain measurement area 91S is not limited to the second support portion 91c. It may be selected appropriately depending on the state of the bridge 91 in question.

[0080] If it is not determined that the vehicle 95 has passed (S92: NO), this means that the vehicle 95 is still passing through the strain measurement area 91S. In this case, the following steps are executed: acquiring measured strain information D91a again (S1), determining whether the vehicle 95 is overloaded (S41), determining whether an accident has occurred (S43), and determining whether the vehicle 95 has passed the second support portion 91c of the bridge 91 (S92).

[0081] It is possible that while the vehicle 95 is passing through the strain measurement area 91S, an accident may not occur at some point, but an accident may occur at some point thereafter. Therefore, the determination of whether an accident has occurred (S43) is repeatedly executed until the vehicle 95 leaves the strain measurement area 91S.

[0082] On the other hand, it is normally impossible for the vehicle 95 to be not overloaded at a certain point while passing through the strain measurement area 91S, but to change to an overloaded state at a later point in time. Therefore, in the process of determining whether the vehicle 95 is overloaded (S41), if the vehicle 95 is not determined to be "overloaded" in the first determination (S41), the determination (S41) may be omitted in the second and subsequent repeated operations.

[0083] <Action and effect> The method for acquiring bridge information according to the third embodiment includes step S4 of evaluating a vehicle 95 passing over a bridge 91 using a plurality of pieces of measured strain information D91a. ​​Step S4 of evaluating the vehicle 95 may include step S40 of preparing judgment strain information D91d indicated by the maximum value of strain occurring in the strain measurement region 91S when a reference vehicle having a reference weight passes over the bridge 91, and step S41 of determining that the vehicle 95 is in an overloaded state exceeding the reference weight if the measured waveforms of the strain distributions indicated by the plurality of pieces of measured strain information D91a deviate from the judgment waveform of the strain distribution indicated by the judgment strain information D91d. This method makes it possible to detect that an overloaded vehicle 95 has passed over the bridge 91.

[0084] <Fourth embodiment> The fourth embodiment is a bridge information acquisition system 1 for the method of acquiring bridge information according to the first, second and third embodiments.

[0085] 13, the bridge information acquisition system 1 has an optical fiber 11. The optical fiber 11 having a predetermined length is attached to the bridge 91 as already described.

[0086] Furthermore, the bridge information acquisition system 1 has a light processing unit 12 and an information processing device 13. The light processing unit 12 inputs measurement light into the optical fiber 11. Furthermore, the light processing unit 12 obtains Rayleigh scattered light emitted from the optical fiber 11. The information processing device 13 obtains a plurality of pieces of measured strain information D91a using the Rayleigh scattered light obtained by the light processing unit 12. Furthermore, the information processing device 13 uses the plurality of pieces of measured strain information D91a to perform a deterioration assessment of the bridge 91 (S2), a fatigue life prediction of the bridge 91 (S3), and acquisition of information regarding passing vehicles (S4).

[0087] The optical processing unit 12 includes a light source section 121 , an optical circulator 122 , and a light receiving section 123 .

[0088] The light source unit 121 generates measurement light for obtaining the measured strain information D91a and inputs the measurement light into the optical fiber 11. A laser diode, for example, may be used as the source of the measurement light. The information processing device 13 operates based on a control signal provided by the light source unit 121.

[0089] The optical circulator 122 is connected to the light source unit 121, the optical fiber 11, and the light receiving unit 123. The optical circulator 122 inputs the input light generated by the light source unit 121 into the optical fiber 11. The optical circulator 122 also outputs the Rayleigh scattered light emitted from the optical fiber 11 to the light receiving unit 123.

[0090] The light receiving unit 123 receives the Rayleigh scattered light emitted by the optical circulator 122. Specifically, the light receiving unit 123 performs predetermined signal processing on the change in amplitude of the Rayleigh scattered light detected during the wavelength sweep, and calculates the intensity (spectrum) for each frequency at each position.

[0091] The information processing device 13 obtains measured strain information D91a using the change in amplitude of the Rayleigh scattered light output from the light receiving unit 123. For example, the information processing device 13 generates a graph showing the magnitude of strain at each location on the optical fiber 11. The information processing device 13 executes an operation to obtain measured strain information D91a every time a predetermined time elapses. For example, the information processing device 13 executes an operation to obtain measured strain information D91a N times while the vehicle 95 is passing over the bridge 91.

[0092] The information processing device 13, which is a computer 40, performs a process (S1) of obtaining multiple pieces of measured strain information D91a, ​​and using the multiple pieces of measured strain information D91a, ​​performs a deterioration assessment of the bridge 91 (S2), predicts the fatigue life of the bridge 91 (S3), and obtains information about passing vehicles (S4).

[0093] The information processing device 13 includes, as its main components, a processor 13P and a memory 13M. The processor 13P executes a program stored in the memory 13M, whereby the processor 13P realizes several functional components.

[0094] The information processing device 13 includes, as functional components realized by the processor 13P, a deterioration assessment unit 131, a lifespan prediction unit 132, and a passing vehicle information acquisition unit 133. The deterioration assessment unit 131 performs the deterioration assessment of the bridge 91 described above (S2). The lifespan prediction unit 132 performs the lifespan prediction of the bridge 91 described above (S3). The passing vehicle information acquisition unit 133 performs the acquisition of information about passing vehicles described above (S4). The operations performed by these functional components are as described in detail in the first, second, and third embodiments.

[0095] The bridge information acquisition system 1 includes a light source unit 121 that provides input light to an optical fiber 11 arranged in a strain measurement area 91S set on the bridge 91, a light receiving unit 123 that obtains return light resulting from the input light while a vehicle 95 is passing over the bridge 91, and an information processing device 13 that applies processing based on optical frequency domain reflectometry (OFDR) to the return light to obtain measured strain information D91a that indicates the distribution of strain occurring in the strain measurement area due to the passage of the vehicle 95. The process of obtaining the return light by the light receiving unit 123 (S12) and obtaining the measured strain information D91a by the information processing device 13 (S13) is repeated while the vehicle 95 is passing over the bridge 91, thereby acquiring multiple pieces of measured strain information D91a.

[0096] This bridge information acquisition system 1 can obtain information indicating the distribution of strain occurring in the strain measurement area 91S multiple times while a vehicle 95 is passing over the bridge 91. As a result, by using multiple pieces of measured strain information D91a, ​​bridge information regarding the bridge 91 can be obtained.

[0097] <Modification> The method of acquiring bridge information according to the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0098] For example, the method for acquiring bridge information according to the present disclosure may include any one selected from step S1 of acquiring a plurality of pieces of measured strain information, step S2 of performing a deterioration assessment of the bridge 91, step S3 of predicting the fatigue life of the bridge 91, and step S4 of acquiring information about passing vehicles. Specifically, as a first example, the method for acquiring bridge information according to the present disclosure may include step S1 of acquiring a plurality of pieces of measured strain information and step S2 of performing a deterioration assessment of the bridge 91. As a second example, the method for acquiring bridge information according to the present disclosure may include step S1 of acquiring a plurality of pieces of measured strain information and step S3 of predicting the fatigue life of the bridge 91. Furthermore, as a third example, the method for acquiring bridge information according to the present disclosure may include step S1 of acquiring a plurality of pieces of measured strain information and step S4 of acquiring information about passing vehicles.

[0099] Furthermore, the method for acquiring bridge information according to the present disclosure may include two steps selected from step S1 of acquiring a plurality of pieces of measured strain information, step S2 of conducting a deterioration assessment of the bridge 91, step S3 of predicting the fatigue life of the bridge 91, and step S4 of acquiring information about passing vehicles. Specifically, as a fourth example, the method for acquiring bridge information according to the present disclosure may include step S1 of acquiring a plurality of pieces of measured strain information, step S2 of conducting a deterioration assessment of the bridge 91, and step S3 of predicting the fatigue life of the bridge 91. As a fifth example, the method for acquiring bridge information according to the present disclosure may include step S1 of acquiring a plurality of pieces of measured strain information, step S2 of conducting a deterioration assessment of the bridge 91, and step S4 of acquiring information about passing vehicles. Furthermore, as a sixth example, the method for acquiring bridge information according to the present disclosure may include step S1 of acquiring a plurality of pieces of measured strain information, step S3 of predicting the fatigue life of the bridge 91, and step S4 of acquiring information about passing vehicles.

[0100] Furthermore, as a seventh example, the method of obtaining bridge information of the present disclosure may include three steps: step S1 of obtaining multiple pieces of measured strain information, step S2 of performing a deterioration assessment of the bridge 91, step S3 of performing a fatigue life prediction of the bridge 91, and step S4 of obtaining information about passing vehicles.

[0101] When predicting the fatigue life of a bridge 91, a threshold value may be set for the strain that affects fatigue damage, and a strain response above the threshold value may be evaluated as affecting fatigue damage. There are no particular limitations on the method for determining this threshold. For example, if it is assumed that fatigue damage will be affected when the weight of a large vehicle or an overloaded vehicle acts on the bridge, the threshold value may be determined by obtaining a strain value through analysis using the weight of the large vehicle or the overloaded vehicle as an input value and the target bridge as a model.

[0102] In the second embodiment, information on whether the vehicle is overloaded and information on whether an accident involving the vehicle has occurred are exemplified as information on the vehicle. As described above, the measured strain information D91a can be used to estimate the position of a vehicle on the bridge 91, and traffic congestion information or information on whether a wrong-way vehicle is present may be obtained as information on the vehicle. Furthermore, traffic congestion information may be used to perform traffic congestion prediction. [Explanation of symbols]

[0103] 1...bridge information acquisition system, 11...optical fiber, 12...optical processing unit, 13...information processing device, 13M...memory, 13P...processor, 40...computer, 91...bridge, 91a...concrete deck, 91a1...concrete, 91a2...reinforcing bar, 91b...first support portion, 91c...second support portion, 91S...measurement area, 93a, 93b...cracks, 95...vehicle, 95A...small vehicle, 95B...large vehicle, 95C...vehicle, 121...light source unit, 122...optical circulator, 123...light receiving unit, 131...deterioration evaluation unit, 132...life expectancy prediction unit, 133...passing vehicle information acquisition unit, BL...fatigue life, D...damage level for each stress section, D k...Damage level in the kth stress interval, D91a...Measured strain information, D91b...Reference strain information, D91c...Stress occurrence frequency information, D91d...Judgment strain information, D92...Information on the number of repetitions required to calculate the damage level D, G10...Histogram, G12a...Threshold waveform, G12b, G12c...Measured waveform, G31 to G38...Graph, G41 to G48...Graph, G51, G52...Graph, G52a, G52b...Peak, G71 to G77 ...graph, G91...stress-strain diagram, G91a...curve section, G92...graph, K12b, K12c...peak, L1, L2...location of cracks 93a, 93b, P31~P38...position of small vehicle on bridge, P41~P48...position of large vehicle on bridge, P71~P77...location of vehicle on bridge, S1...step of obtaining multiple measured strain information, S2...step of evaluating deterioration, S3...step of predicting bridge fatigue life , S4...step of obtaining information about passing vehicles, S11...step of applying input light to an optical fiber, S12...step of obtaining returned light by a light receiving unit, S13...step of obtaining measured strain information, S20...step of preparing reference strain information, S21...step of determining whether there is a local change in shape in the waveform indicated by the measured strain information, S22...step of determining whether deterioration has occurred in the bridge, S31...step of determining whether a measured strain greater than a threshold has been detected, S33...step of obtaining the maximum measured strain value, S34...step of converting the maximum measured strain value to a measured stress value, S35...step of updating the damage level, S36...step of predicting fatigue life, S40...step of preparing judgment strain information, S41...step of determining whether an overloaded state has occurred, S43...step of determining whether an accident has occurred, S92...step of determining whether a vehicle has passed through the second support portion, T1...step.

Claims

1. providing input light to an optical fiber arranged in a strain measurement area set on the bridge; obtaining return light resulting from the input light during a period when a vehicle is passing over the bridge; and applying processing based on optical frequency domain reflectometry (OFDR) to the returned light to obtain measured strain information indicating a distribution of strain occurring in the strain measurement area due to the passage of the vehicle, A method for acquiring bridge information, wherein the step of acquiring the returned light and the step of acquiring the measured strain information are repeated while the vehicle is passing over the bridge, thereby acquiring a plurality of pieces of the measured strain information.

2. The method further includes a step of evaluating deterioration of the strain measurement region using a plurality of pieces of measured strain information, The step of assessing the deterioration includes: preparing reference strain information indicating a distribution of strain occurring in the strain measurement area when the vehicle passes over the bridge that is considered to be free of deterioration; The method for acquiring bridge information according to claim 1 , further comprising: a step of determining whether or not deterioration has occurred in the strain measurement area using a difference between the measured strain information and the reference strain information.

3. The method further includes a step of predicting a lifespan of the bridge using a plurality of pieces of measured strain information; The step of predicting the life span includes: a step of obtaining, using the plurality of pieces of measured strain information, stress occurrence frequency information indicating the number of times that the measured stress having a magnitude included in each of the plurality of stress sections has occurred, for each stress section set according to the magnitude of the measured stress converted from the measured strain; The method for acquiring bridge information according to claim 1, further comprising a step of predicting the lifespan of the bridge by applying processing based on a cumulative fatigue damage rule to the stress occurrence frequency information.

4. further comprising a step of evaluating the vehicle passing through the bridge using a plurality of pieces of measured strain information; The step of evaluating the vehicle includes: preparing judgment strain information indicated by the maximum value of strain occurring in the strain measurement area when a reference vehicle having a reference weight passes over the bridge; 2. The method for acquiring bridge information according to claim 1, further comprising a step of determining that the vehicle is in an overloaded state exceeding the reference weight when the measured waveforms of the strain distributions indicated by the plurality of pieces of measured strain information deviate from the judged waveforms of the strain distributions indicated by the judged strain information.

5. further comprising a step of evaluating the vehicle passing through the bridge using a plurality of pieces of measured strain information; The step of evaluating the vehicle includes: preparing judgment strain information indicated by the maximum value of strain occurring in the strain measurement area when a reference vehicle having a reference weight passes over the bridge; 2. A method for acquiring bridge information as described in claim 1, comprising a step of determining that an accident involving the vehicle has occurred when one of the measured waveforms of each strain distribution indicated by the plurality of pieces of measured strain information deviates from the judged waveform of the strain distribution indicated by the judged strain information.

6. a light source unit that provides input light to an optical fiber arranged in a strain measurement area set on the bridge; a light receiving unit that receives return light resulting from the input light while the vehicle is passing over the bridge; an acquisition unit that acquires measured strain information indicating a distribution of strain occurring in the strain measurement area due to the passage of the vehicle by applying processing based on optical frequency domain reflectometry (OFDR) to the returned light, A bridge information acquisition system that acquires multiple pieces of measured strain information by repeating the process of obtaining the returned light using the light receiving unit and obtaining the measured strain information using the acquisition unit while the vehicle is passing over the bridge.

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