JP7208622B2 - Strain measuring device for metal structure and method for detecting deterioration damage of metal structure - Google Patents

Description

The present invention relates to a metal structure strain measuring device and a metal structure degradation damage detection method for measuring the strain of a metal structure that changes due to fatigue cracks caused by repeated dynamic external forces.

In metal structures such as steel bridges, which are subjected to repeated dynamic external forces, there is a danger that fatigue cracks will occur from welds and eventually lead to fatigue failure. Conventionally, as a deterioration damage detection method to prevent such a danger, a strain gauge is arranged near the welded part and the change in the amplitude of the strain signal is monitored when an external force such as the load of the vehicle acts. method is known. By determining that there is an abnormality when the amount of change in the amplitude of the distorted signal exceeds the threshold value, it is possible to take measures such as inspection and repair.

For example, a strain gauge that converts the stress generated in a steel structure into an electrical signal and detects it, and the detected value and reference of the amplitude of the stress signal obtained by amplifying and A/D converting the detection signal detected by the strain gauge A CPU that controls signal processing such as comparison with values, a memory unit and USB that record data, an LED display unit that receives the output from these and displays the judgment result, and a power supply unit that supplies power to each unit. , a CPU, an LED display unit, and a housing accommodating a power supply unit are known (Patent Document 1). The monitoring time zone of this stress monitoring device is assigned to a limited time zone during which at least one train train is passing in one day, and is assigned once every several days.

Further, there is known a crack diagnosis apparatus including strain sensors installed in two areas determined to be crack diagnosis targets and an arithmetic unit (Patent Document 2). In this crack diagnosis device, stress analysis (stress analysis with external force applied) using an analysis model without cracks and an analysis model with cracks, which is the target of crack diagnosis, is performed to determine the strain signal associated with the occurrence of cracks. Two regions are obtained in which the relative rate of change in the amount of change in amplitude is equal to or greater than a set value, and strain sensors are installed in regions corresponding to these two regions. The arithmetic unit statistically processes the diagnostic data group based on the data input from each strain sensor at the time of crack diagnosis and the normal data group accumulated when the crack diagnosis target is in a normal state where no crack has occurred. A relative comparison is made, and based on the comparison result, the presence or absence of crack generation in the crack diagnosis target is determined.

Japanese Patent Application Laid-Open No. 2017-49112 (published on March 9, 2017) Japanese Patent Application Laid-Open No. 2017-187327 (published on October 12, 2017)

However, the conventional technology described above is a method of monitoring changes in the amplitude of a strain signal when an external force such as the load of a passing vehicle acts. It must be measured by sampling. Therefore, there is a problem that expensive measuring equipment is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a strain measuring device for metal structures and a method for detecting deterioration damage to metal structures, which can inexpensively and easily detect deterioration damage to metal structures that are subjected to repeated dynamic external forces. It is in.

In order to solve the above problems, a strain measuring device for a metal structure according to the present invention is a strain measuring device for a metal structure to which a dynamic external force is repeatedly applied, wherein a strain signal representing the strain of the metal structure and a strain gauge installed on the metal structure to output the dynamic external force from the strain gauge to detect changes in internal stress due to fatigue cracks occurring in the metal structure. a measuring unit for continuously measuring a base value related to the internal stress of the metal structure at predetermined time intervals based on the dynamic response process of the output strain signal.

According to this feature, based on the dynamic response process of the strain signal, by continuously measuring the base value related to the internal stress of the metal structure at predetermined time intervals, the fatigue strain generated in the metal structure can be determined. Changes in internal stress due to cracks can be detected. Therefore, expensive measuring equipment for measuring strain that changes in a short period of time at high speed is not required, and degradation damage to metal structures that are repeatedly subjected to dynamic external forces can be detected easily and inexpensively.

In the strain measuring device for a metal structure according to the present invention, the base value is a value that becomes a starting point of the dynamic response process of the strain signal, and when the external force is continuously applied in both directions, the strain signal including the median value of the amplitude of the strain signal when the external force is applied continuously in one direction, including the maximum value or the minimum value of the amplitude of the strain signal, and when the external force is applied intermittently, the starting point of the fluctuation of the strain signal and includes the value of the strain signal when the external force is not applied.

According to the above configuration, it is possible to detect the base value from the strain signal according to the state of action of the external force.

In the strain measuring apparatus for a metal structure according to the present invention, the base value is obtained from a predetermined number of sampled values and a minimum value selected from a plurality of sampled values of the strain signal sampled in a certain period in descending order from the maximum value. It is preferable to include a predetermined number of sampled values selected in ascending order and an average value of the remaining sampled values excluding the sampled values.

According to the above configuration, noise in the strain signal output from the strain gauge can be eliminated.

In the strain measuring device for a metal structure according to the present invention, the base value is the center of a plurality of sampled values of strain signals sampled in a certain period when the dynamic external force is repeatedly applied in both directions. It preferably contains a value.

According to the above configuration, since the median value of the plurality of sampling values of the strain signal represents the internal stress generated in the metal structure, deterioration damage of the metal structure can be detected by detecting a change in the median value. can.

In the strain measuring device for a metal structure according to the present invention, the base value is the maximum of a plurality of sampled values of the strain signal sampled in a certain period when the dynamic external force is repeatedly applied in one direction. It is preferred to include values or local minima.

According to the above configuration, the maximum value or the minimum value of the plurality of sampling values of the strain signal represents the internal stress generated in the metal structure. Damage can be detected.

In the strain measuring apparatus for a metal structure according to the present invention, it is preferable that the base value includes a sampling value of the strain signal sampled for a certain period when the dynamic external force is not applied.

According to the above configuration, there is no need to measure a change in strain when an external force such as a load of a vehicle acts, so there is no need to measure strain occurring in a short time at high speed.

In the strain measuring device for a metal structure according to the present invention, it is preferable that the strain signal has a sampling frequency of 0.1 Hz or more and 10 Hz or less.

According to the above configuration, high-speed sampling of the distorted signal becomes unnecessary.

The strain measuring apparatus for a metal structure according to the present invention further comprises another strain gauge installed on the metal structure for outputting another strain signal representing another strain of the metal structure, The gauge is installed at a location where the internal stress is tensile stress due to welding of the metal structure, and the other strain gauge is installed at a location where the internal stress is compressive stress due to welding of the metal structure. preferably.

According to the above configuration, it is possible to accurately detect the deterioration damage of the metal structure according to the change in the internal stress generated when the metal structure is damaged.

The strain measuring apparatus for a metal structure according to the present invention further comprises another strain gauge installed on the metal structure for outputting another strain signal representing another strain of the metal structure, A structure has a first metal material, a second metal material, and a weld that joins the first and second metal materials, and the strain gauge is generated in the metal structure by the weld. and the other strain gauge is positioned in a weld zone where there is an internal tensile stress in the opposite direction, and the other strain gauge is located in a region of the weld where there is an internal compressive stress in the opposite direction that balances the internal tensile stress created by the weld. is preferably placed in the

According to the above configuration, it is possible to accurately detect the deterioration damage of the metal structure according to the change in the internal stress generated when the metal structure is damaged.

In the strain measuring device for a metal structure according to the present invention, the metal structure includes a first metal plate, a second metal plate, and welding for joining the surface of the first metal plate and the surface of the second metal plate. and the strain gauge is installed on the back surface of the first metal plate.

According to the above configuration, deterioration damage of the metal structure can be accurately detected according to the change in internal stress between the front surface and the back surface of the first metal plate that occurs when the metal structure is damaged.

The strain measuring apparatus for a metal structure according to the present invention further comprises another strain gauge installed on the metal structure for outputting another strain signal representing another strain of the metal structure, It is preferable that a gauge is installed on the surface of the metal structure and the other strain gauge is installed on the back surface of the metal structure.

According to the above configuration, it is possible to accurately detect the deterioration damage of the metal structure according to the change in the internal stress between the front surface and the back surface of the first metal plate when the metal structure is damaged.

The strain measuring apparatus for a metal structure according to the present invention further comprises another strain gauge installed on the metal structure for outputting another strain signal representing another strain of the metal structure, A strain of the metal structure corresponding to the gauge is a strain along a first direction, and another strain of the metal structure corresponding to the other strain gauge is a strain along a second direction orthogonal to the first direction. Preferably, the strain gauge and the other strain gauge are installed so that the measuring directions are orthogonal to each other.

According to the above configuration, it is possible to accurately detect the deterioration damage of the metal structure according to the direction in which the internal stress generated when the metal structure is damaged.

In order to solve the above problems, a method for detecting deterioration damage to a metal structure according to the present invention is a method for detecting deterioration damage to a metal structure to which a dynamic external force is repeatedly applied. Based on the dynamic response process of the strain signal output from the strain gauge, the base value related to the internal stress that changes due to fatigue cracks occurring in the metal structure is continuously measured at predetermined time intervals. a measuring step of determining the amount of change in the base value over time; a comparison step of comparing the amount of change in the base value over time obtained in the measuring step with a predetermined default value; and a judgment step of judging whether or not deterioration damage has occurred in the metal structure based on a result of comparison between the amount of change over time of and the predetermined value.

According to this feature, based on the dynamic response process of the strain signal, by continuously measuring the base value related to the internal stress that changes due to fatigue cracks occurring in the metal structure at predetermined time intervals, Changes in internal stress due to deterioration damage of metal structures can be detected. Therefore, expensive measuring equipment for measuring strain generated in a short period of time at high speed is not required, and degradation damage of metal structures subjected to repeated dynamic external forces can be detected inexpensively and simply.

In the method for detecting deterioration damage of a metal structure according to the present invention, the amount of change over time in the base value obtained in the measurement step is between the value of the strain signal and the initial value of the strain signal at the start of measurement. It preferably contains a difference value.

According to the above configuration, it is possible to determine whether deterioration damage has occurred in the metal structure based on the amount of change in the base value.

In the method for detecting deterioration damage of a metal structure according to the present invention, the amount of change over time in the base value obtained in the measuring step preferably includes the amount of change in the base value per unit time.

According to the above configuration, it is possible to determine whether deterioration damage has occurred in the metal structure based on the amount of change in the base value.

In the method for detecting deterioration damage of a metal structure according to the present invention, the amount of change over time in the base value obtained in the measuring step is a predetermined amount of change in the base value continuously measured at the predetermined time interval. It is preferable that the amount of change showing a different trend of change be included in the range of or more.

According to the above configuration, it is possible to determine whether deterioration damage has occurred in the metal structure based on the amount of change in the base value.

ADVANTAGE OF THE INVENTION This invention is effective in the ability to detect deterioration damage of a metal structure which receives a dynamic external force repeatedly at low cost and simply.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic perspective view which shows the structure of the strain measuring apparatus of the steel structure which concerns on embodiment. (a) to (c) are waveform diagrams showing the concept of the base value measured by the strain measuring device for the steel structure. (a) and (b) are graphs for explaining changes in the base values in fatigue tests. (a) is a perspective view showing the main part of the steel structure, and (b) to (d) show the number of repetitions of the load applied to each main part of the steel structure and the average strain of each main part. is a graph showing the relationship between (a) to (f) are images showing the results of thermal stress analysis of changes in internal stress due to crack initiation in the main part of the steel structure. FIG. 4 is a schematic perspective view showing an example of the balance and boundaries of internal stress generated by welding in the steel structure. (a) is a schematic perspective view showing fatigue cracks and strain gauges generated in the main part of the steel structure, and (b) is a graph showing the strain range and average strain based on the fatigue cracks. FIG. 4 is a schematic perspective view showing fatigue cracks and a pair of strain gauges generated in the main part of the steel structure; It is a figure which shows an example of the arrangement|positioning aspect of several strain gauges provided in the strain measuring apparatus of the said steel structure.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.

FIG. 1 is a schematic perspective view showing the configuration of a strain measuring device 1 for a steel structure 2 according to an embodiment. A strain measuring device 1 measures strain generated in a steel structure 2 (metal structure) to which a dynamic external force is repeatedly applied. The steel structure 2 includes, for example, a rectangular plate-shaped steel member 5 (first metal member) and a rectangular plate-shaped steel member 6 (second metal member) vertically joined to the steel member 5 by a weld 8 at one end of the steel member 5 . ) and a trapezoidal plate-shaped steel 7 joined to the steels 5 and 6 by a weld 11 so as to reinforce the joint between the steels 5 and 6 . However, the steel structure 2 shown in FIG. 1 shows an example for easy understanding, and is not limited to the structure shown in FIG.

The strain measuring device 1 includes a strain gauge 3 arranged on the surface of the steel material 5 to output a strain signal representing the strain of the steel material 5 and an internal strain gauge 3 caused by a fatigue crack 16 generated in the steel material 5 based on a dynamic external force. Based on the dynamic response process of the strain signal output from the strain gauge 3, a base value related to the internal stress of the steel material 5 measured in the absence of external forces is determined to detect changes in stress. and a measuring device 10 for continuously measuring at time intervals of .

In this specification, the "base value" is a value related to internal stress generated by welding of the steel structure 2, a value that is the starting point of the dynamic response process of the strain signal, and has the same magnitude. When the external force is continuously applied to the steel structure 2 in both directions, it corresponds to the median value of the amplitude of the strain signal, and when the external force is continuously applied to the steel structure 2 in one direction, the external force is zero. When the external force is intermittently applied to the steel structure 2, it corresponds to the starting point of the fluctuation of the strain signal and the external force is the steel structure It corresponds to the value of the distortion signal when the object 2 is not attached.

This base value excludes a predetermined number of sampled values selected in descending order from the maximum value and a predetermined number of sampled values selected in descending order from the minimum value from the plurality of sampled values of the distortion signal sampled in a certain period. An average of the remaining sampled values can be included.

This base value can include a median value of a plurality of sampled values of the strain signal sampled for a certain period when the dynamic external force is repeatedly applied in both directions.

This base value can include a maximum value or a minimum value of a plurality of sampling values when the dynamic external force of the strain signal sampled in a certain period is repeatedly applied in one direction.

This base value can include a sampling value of the strain signal sampled for a certain period of time when the dynamic external force is not applied.

It is preferable that the sampling frequency of the distortion signal sampled in a certain period is 0.1 Hz or more and 10 Hz or less.

The strain measuring device 1 preferably comprises a strain gauge 4 placed on the surface of the steel 5 to output another strain signal representing another strain of the steel 5 . It is preferable that the strain gauge 3 is installed at a location where tensile stress is generated in the steel material 5 by welding, and the strain gauge 4 is installed at a location where compressive stress is generated in the steel material 5 by welding.

The steel materials 5 and 6 of the steel structure 2 have a weld region R1 corresponding to the internal stress (e.g., tensile stress) generated in the welds 8 and 11 and an opposite direction to balance the internal stress generated in the welds 8 and 11. and a boundary line 9 that separates the weld region R1 and the reverse stress region R2. The strain gauge 3 is preferably arranged in the weld region R1 and the strain gauge 4 is preferably arranged in the reverse stress region R2.

The strain gauges 3 and 4 may be installed on the surface of the steel material 5 opposite to the steel material 7, or may be installed on both the surface of the steel material 5 on the steel material 7 side and the surface on the opposite side of the steel material 7. .

The direction of strain detected by the strain gauge 4 may be the same direction as the direction of strain detected by the strain gauge 3, or may be a different direction, for example, an orthogonal direction.

Based on the dynamic response process of the strain signals output from the strain gauges 3 and 4 installed on the surface of the steel material 5 of the steel structure 2, the measuring device 10 measures the internal stress related to the welding of the steel material 5. A base value measurement unit 13 for continuously measuring a value at predetermined time intervals to obtain the amount of change over time in the base value, and the amount of change over time in the base value obtained by the base value measurement unit 13. is compared with a predetermined default value, and based on the result of comparison between the amount of change over time in the base value and the default value, the occurrence of deterioration damage of the steel material 5 is determined. and a deterioration damage determination unit 15 that determines the presence or absence of damage.

The amount of change over time in the base value obtained by the base value measuring unit 13 may include a difference value between the value of the strain signal output from the strain gauge 3 and the initial value of the strain signal at the start of measurement. and may include the amount of change in the base value per unit time, or the amount of change showing a different trend of change over a predetermined range among the amounts of change in the base value continuously measured at the predetermined time intervals. may include

The strain measuring device 1 according to the embodiment measures deterioration/damage such as occurrence of fatigue cracks 16 in the steel structure 2 which is subjected to repeated dynamic external forces by measuring the magnitude of the amount of deformation with respect to the magnitude of the external force (load), i.e. , the amplitude of the strain signal is measured, and when the amplitude of the strain signal exceeds a certain level with respect to the external force, it is judged that deterioration damage has occurred. 2 focused on the balance of internal stress due to welding.

The internal stress of the steel structure 2 is generated and distributed throughout the steel structure 2, not only in the vicinity of the member fastening portions, so as to balance the tensile stress due to the welds 8 and 11. In addition, the residual stress initially generated by the tightening of member fastening portions such as bolts at the time of construction also becomes internal stress.

Therefore, when deterioration damage occurs in the steel structure 2 , for example, cracks occur in the welded portions 8 and 11 , the internal stress balance of the entire steel structure 2 changes due to the fatigue cracks 16 . In other words, if the change in internal stress can be efficiently detected, deterioration damage of the steel structure 2 can be detected.

In addition to the above findings, the present embodiment has a new finding that changes in the internal stress balance can be detected from changes in the base value based on the dynamic response process of the strain signal while measuring the strain that changes due to external force. It is based on knowledge. The strain measuring device 1 according to this embodiment does not measure the amount of deformation (amplitude of the strain signal) when an external force is applied, but continuously measures the base value based on the dynamic response process of the strain signal in time series. , the amount of change over time (the amount of change over time in the base value) is detected instead of the absolute value of the internal stress.

By comparing the amount of change over time in the base value with a predetermined default value, it is possible to determine whether or not deterioration damage has occurred in the steel structure 2 . The “predetermined value” is a value determined in advance based on a model experiment or the like that reflects various parameters such as mechanical properties of the target steel structure 2, and damage caused by dynamic external force. is determined from the correlation between the degree of and the base value of the strain response process.

According to such a strain measuring device for a metal structure and a deterioration damage detection method for a metal structure, high-frequency sampling is not required, and the measurement period can be lengthened. In addition, the measurement can be performed several times a day, and long-term operation using a battery is possible. Therefore, a simple monitoring system that does not require expensive measurement equipment can be realized.

2(a) to (c) are waveform diagrams showing the concept of the base values B1, B2, and B3 measured by the strain measuring device 1 for the steel structure 2. FIG. The base value of the dynamic response process of the strain signals S1, S2, and S3 output from the strain gauge 3 is the starting point of the dynamic variation of the strain (when the external force is zero).

As shown in FIG. 2(a), when the external force is equally applied to the steel structure 2 in both directions, the median value of the amplitude of the strain signal S1 output from the strain gauge 3 is the base value when the external force is zero. value B1. As shown in FIG. 2(b), when an external force is applied to the steel structure 2 in one direction, the maximum value of the strain signal S2 output from the strain gauge 3 is the base value B2 when the external force is zero. . When the external force acts in one direction from the opposite direction, the minimum value instead of the maximum value becomes the base value B2 when the external force is zero. As shown in FIG. 2(c), when an external force is intermittently applied to the steel structure 2, the base value B3 is the starting point of fluctuation and the value when no external force is applied.

FIGS. 3(a) and 3(b) are graphs for explaining changes in the base values in the fatigue test. FIG. 4(a) is a perspective view showing the main part of the steel structure 2, and (b) to (d) show the number of repetitions of the load applied to each main part of the steel structure 2 and the average of each main part. 4 is a graph showing the relationship between strain. 5(a) to (f) are images showing the results of thermal stress analysis of changes in internal stress due to the occurrence of fatigue cracks 16 in the main part of the steel structure 2. FIG. FIG. 6 is a schematic perspective view showing an example of the balance of internal stress generated by the welded portions 8 and 11 in the steel structure 2 and boundary lines.

As shown in FIGS. 3(a) and 3(b), the present inventors conducted a fatigue test in which a cyclic load was applied to a steel structure 2, which is a specimen, and found that the strain under no load over a long period of time (average strain) As a result of examining whether it is possible to detect damage from changes in , the change curve of the strain under no load (average strain) detected by the strain gauge 3 when the number of repetitions reaches a certain number is shown in Fig. 4(b). , and found that it is closely related to the initiation and propagation of the fatigue crack 16 shown in FIG. 4(a). The validity of the result is that the thermal stress analysis of the change in internal stress due to the generation of the fatigue crack 16 shows that the fatigue crack 16 is generated and propagates as shown in FIGS. , was confirmed by the change in the strain under no load (mean strain, residual stress). The steel structure 2 has a weld area R1 corresponding to tensile stress and a reverse stress area corresponding to compressive stress, as shown in FIG. R2 is generated. Therefore, when the fatigue crack 16 occurs and the internal stress changes, the base value of the strain gauge 3 attached to the weld region R1 becomes the strain on the compression side (Fig. 4(b)), and the reverse stress region R2 The base value of the strain gauge 4 affixed to is the strain on the tensile side (Fig. 4(c)).

The present embodiment is based on such knowledge, and instead of measuring the amount of change (amplitude of the strain signal) when an external force is applied as in the conventional method, it is based on the dynamic response process of the strain signal. By continuously measuring the value (base value) in chronological order, the magnitude of change in internal stress over time is detected instead of the absolute value of internal stress that changes due to deterioration damage of the steel structure 2. It is. By comparing the amount of change over time in the base value with a predetermined default value, it can be determined that deterioration damage has occurred in the steel structure 2 .

FIG. 7(a) is a schematic perspective view showing a fatigue crack 16 generated in the main part of the steel structure 2 and the strain gauge 3, and FIG. 4 is a graph showing changes in range and average strain; Conventionally, the presence or absence of the fatigue crack 16 was generally evaluated by the change in the amplitude of the strain signal due to the action of the load. As shown by the curve L2 showing the change, the present invention is based on the knowledge that the strain under no load (average strain) reacts more sensitively to the generation of the fatigue crack 16 than the change in the strain range due to the action of the load. they found. The above knowledge can be applied to any portion of the steel structure 2 within the range where the internal stress (residual stress) generated by the welded portions 8 and 11 affects the steel structure 2 .

The conventional monitoring system for detecting deterioration and damage of the steel structure 2 is real-time monitoring, and mechanically, it is an evaluation based on the response to an external load, and requires a constant power supply or has a limited measurement period. was In addition, the mechanical behavior and vibration characteristics due to damage were verified in laboratory experiments.

On the other hand, the monitoring system using the strain measuring device 1 according to the embodiment is a monitoring system that only needs to accumulate data for a certain period of time. may be transferred once a day or once a week. Therefore, the power consumption of measuring equipment and communication equipment is much less than that of the conventional monitoring system. This eliminates the need for a constant power supply and enables long-term measurement over several years using only a battery.

The strain measuring device 1 according to the embodiment can measure strain data in a state where no external force or the like is acting on the steel structure 2 . The object to be measured is not limited to the steel structure 2, and may be any other metal structure or a concrete structure that partially uses metal as long as the structure changes the balance of internal stress when damage occurs. good.

When damage occurs, the balance of internal stress changes in the object to be measured by the strain measuring device 1 according to the embodiment, so the strain measuring device 1 does not need to apply a dynamic external force to detect damage.

FIG. 8 is a schematic perspective view showing a fatigue crack 16 generated in a main part of the steel structure 2 and a pair of strain gauges 3 and 4. FIG. A pair of strain gauges 3 and 4 may be installed at different locations where fatigue cracks 16 generated in the steel structure 2 cause internal stresses (for example, compressive stress and tensile stress) in different directions. Then, by measuring the strain in a state where no external force (load) acts on the steel structure 2 for the fatigue crack 16 that has occurred, the fatigue crack 16 due to repeated dynamic external forces on the steel structure 2 is measured. Progress can be monitored.

Although an example in which the strain gauges 3 and 4 are installed on the steel structure 2 has been shown, the present invention is not limited to this. Instead of using the strain gauges 3 and 4, it is possible to monitor the progress of the fatigue crack 16 by an eddy current inspection or the like in which an alternating current is applied to the coil.

Although an example of detecting the fatigue crack 16 of the steel structure 2 has been shown, the present invention is not limited to this. A strain gauge may be installed on the head or shaft of a bolt provided on the steel structure 2 to measure the strain when no external force (load) acts on the steel structure 2 . In addition, if the change in the base value of the strain at the position where the internal stress (residual stress) generated by welding of the steel structure 2 changes due to corrosion can be measured over time, it is possible to detect the progress of corrosion of the steel structure 2. Alternatively, if the angle of the steel structure 2 can be measured using an accelerometer or a displacement meter, it is possible to detect damage related to the displacement/angle of the steel structure 2 .

The strain measuring device 1 according to the embodiment can also detect damage that changes the internal stress balance due to damage to RC (reinforced concrete) and PC (prestressed concrete). For example, by measuring the distortion of the nut portion near the fixing portion of the PC cable, it is possible to detect the damage of the PC cable.

Although an example in which the strain measuring device 1 detects changes in internal stress due to fatigue cracks 16 generated in the steel structure 2 has been described, the present invention is not limited to this. The target to be detected by the strain measuring device 1 may be an index that changes due to damage occurring in the steel structure 2 . Further, the measured values of the strain measuring device 1 may be measured values in a state where no load is applied, and there is no need for frequent measurements. The strain measuring device 1 can detect damage to the steel structure 2 by continuing to acquire data during normal times when no load is applied.

FIG. 9 is a diagram showing an example of arrangement of a plurality of strain gauges 3 provided in the strain measuring device 1 for the steel structure 2. As shown in FIG. The steel structure 2 can be, for example, a bridge, as shown in FIG. A plurality of strain gauges 3 are installed at predetermined intervals on steel plates provided on the bridge. Each strain gauge 3 wirelessly transmits a strain signal representing the strain of the steel plate to the measuring device 10 .

As described above, the strain measuring device for metal structures and the deterioration damage detection method for metal structures according to the present embodiment can be used to measure changes in internal stress balance due to deterioration damage that occurs in metal structures that are repeatedly subjected to dynamic external forces. can be detected, thereby detecting the occurrence of structural deterioration damage such as fatigue cracks in welds.

This embodiment further has the following features.

(1) Measurement of physical quantities other than strain is not required.

(2) Damage can be detected not only in the vicinity of the welded portion, but also at any position where variation in internal stress balanced in the entire structural unit of the metal structure due to deterioration damage can be detected.

(3) Sampling at a high frequency is not required, and measurement intervals can be lengthened.

(4) It is possible to detect damage in places that are not visible to the naked eye.

(5) Sensitivity of detection is better than conventional determination of magnitude of strain for dynamic load.

The deterioration of the large-scale social infrastructure built during Japan's high-growth period has become a major problem. Under such social conditions, there is an increasing demand for solutions to this social problem. In addition, expectations are rising for the advancement of technologies such as the Internet of Things (IoT) and high-speed, high-capacity communications (5G (5th Generation mobile communication system, 5th ^Generation ) standards, etc.), and new technologies will be applied. It is desired to develop a technology that This embodiment meets these social demands.

This embodiment can be applied to metal structures and structures that partially use metal that are subject to repeated dynamic external forces for deterioration and damage. For example, highways, road bridges, bridges over rivers, It can be applied to steel towers, iron bridges, large suspension bridges through which vehicles can pass, bogie parts of railroad vehicles, and the like.

The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.

1 strain measuring device 2 steel structure (metal structure)
3 strain gauge 4 strain gauge 5 steel material (first metal material)
6 Steel material (second metal material)
7 Steel material 8 Welded part (Fastening part)
9 boundary line 10 measuring device (measuring unit)
11 Welded portion 13 Base value measurement portion 14 Base value change amount comparison portion 15 Degradation damage determination portion 16 Fatigue cracks S1, S2, S3 Strain signals B1, B2, B3 Base value R1 Welded region R2 Reverse stress region

Claims (15)

A strain measuring device for a metal structure to which a dynamic external force is repeatedly applied,
a strain gauge mounted on the metal structure for outputting a strain signal representing the strain of the metal structure;
In order to detect degradation damage caused to the metal structure by the dynamic external force using changes in the internal stress of the metal structure, the strain gauge is measured when the external force becomes zero. and a measuring unit for continuously measuring a base value , which is the value of the strain signal of the metal structure, at predetermined time intervals. The base value includes the median value of the amplitude of the strain signal at which the external force is zero when the external force is continuously applied in both directions, and when the external force is continuously applied in one direction, the external force is It includes the maximum value or the minimum value of the amplitude of the distortion signal that becomes zero, is the starting point of fluctuation of the distortion signal when the external force is applied intermittently, and is the value of the distortion signal when the external force is not applied. 2. The strain measuring device for a metal structure according to claim 1, comprising: The base value excludes a predetermined number of sampled values selected in descending order from the maximum value and a predetermined number of sampled values selected in ascending order from the minimum value from the plurality of sampled values of the distortion signal sampled in a predetermined period. 2. A strain measuring apparatus for a metal structure according to claim 1, which includes an average value of the remaining sampling values. 2. The metal structure according to claim 1, wherein the base value includes a median value of a plurality of sampling values of strain signals sampled in a certain period when the dynamic external force is repeatedly applied in both directions. Strain measuring device. 2. The metal according to claim 1, wherein the base value includes a maximum value or a minimum value of a plurality of sampling values of strain signals sampled in a certain period when the dynamic external force is repeatedly applied in one direction. Structural strain measurement device. 2. The apparatus for measuring strain of a metal structure according to claim 1, wherein the base value includes a sampling value of the strain signal sampled for a certain period when the dynamic external force is not applied. The strain measuring device according to any one of claims 3 to 6, wherein the distortion signal has a sampling frequency of 0.1 Hz or more and 10 Hz or less. 2. The apparatus for measuring strain of a metal structure according to claim 1, further comprising another strain gauge installed on said metal structure for outputting another strain signal representing another strain of said metal structure. . The metal structure has a first metal plate material, a second metal plate material, and a weld portion that joins the surface of the first metal plate material and the surface of the second metal plate material,
2. A strain measuring apparatus for a metal structure according to claim 1, wherein said strain gauge is installed on the rear surface of said first metal plate. further comprising another strain gauge mounted on the metal structure for outputting another strain signal representing another strain of the metal structure;
The strain gauge is installed on the surface of the metal structure,
2. A strain measuring apparatus for a metal structure according to claim 1, wherein said another strain gauge is installed on the back surface of said metal structure. further comprising another strain gauge mounted on the metal structure for outputting another strain signal representing another strain of the metal structure;
strain of the metal structure corresponding to the strain gauge is strain along a first direction;
the other strain of the metal structure corresponding to the other strain gauge is strain along a second direction orthogonal to the first direction;
2. A strain measuring apparatus for a metal structure according to claim 1, wherein said strain gauge and said another strain gauge are installed so that their measuring directions are perpendicular to each other. A deterioration damage detection method for a metal structure to which a dynamic external force is repeatedly applied, comprising:
Deterioration caused in the metal structure due to the dynamic external force based on a strain signal output from a strain gauge installed on the surface of the metal structure and using a change in internal stress of the metal structure. In order to detect damage, a base value, which is the value of the strain signal of the metal structure measured by the strain gauge when the external force becomes zero, is continuously measured at predetermined time intervals. a measuring step of determining the amount of change in value over time;
a comparing step of comparing the amount of change over time of the base value obtained in the measuring step with a predetermined default value;
and a determination step of determining whether or not deterioration damage has occurred in the metal structure based on the result of comparison between the amount of change over time in the base value and the predetermined value. Degradation damage detection method. 13. The metal structure according to claim 12, wherein the amount of change over time in the base value obtained in the measuring step includes a difference value between the value of the strain signal and the initial value of the strain signal at the start of measurement. Degradation damage detection method. 13. The method for detecting deterioration and damage to a metal structure according to claim 12, wherein the amount of change over time in the base value obtained in the measuring step includes the amount of change in the base value per unit time. The amount of change over time in the base value obtained in the measuring step includes an amount of change showing a different trend of change over a predetermined range among the amounts of change in the base value continuously measured at the predetermined time intervals. The method for detecting deterioration damage of a metal structure according to claim 12.

Images