JP2013147834A - Crack monitoring method and system for bridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack monitoring method and system which can monitor cracks in a bridge with little labor and cost to prevent an increase in labor and cost for bridge repair.SOLUTION: A K-value sensor 7 is installed to a crack 77 generated from a weld bead 41 to a trough 4 in a steel floor slab 1, and a measurement terminal 8 connected to the K-value sensor 7 is fixed on the side surface of the trough 4. Measurement information of the K-value sensor 7 is read by a receiving terminal through a USB memory 83 connected to the measurement terminal 8, and a developing speed and developing length of the crack 77 are estimated by an analysis software. When the developing speed of the crack 77 is larger than a reference value, a crack sensor is installed to the crack 77, and measurement information of the crack sensor is received by the receiving terminal through the measurement terminal 8 to measure a developing length. When the developing length of the crack 77, measured by the crack sensor, exceeds a reference value, the crack 77 is determined as a repair candidate.

Description

  The present invention relates to a method and a system for monitoring a crack generated in a bridge such as a highway.

  Since many highways were constructed during the period of high growth, damage to structures with age has been increasing recently. In urban expressways, steel bridges with floor slabs and piers constructed of steel materials are often used, but fatigue cracks and corrosion are the main damages that occur in steel bridges. Of these, fatigue cracks often have a direct adverse effect on the structure, so strict measures must be taken. The main reason for the occurrence and progression of cracks is the repeated loading of vehicles, but in recent years, traffic on urban highways has increased and the size of vehicles has been increasing. It is thought to be one of the factors that promote the increase of damage.

  Under such circumstances, conventionally, in order to deal with cracks in the steel bridge, a visual inspection is performed in which an inspector approaches the steel bridge and visually detects the crack. The visual inspection is performed by using a scaffold installed on the steel bridge or a special vehicle stopped on the road because the inspector needs to approach the steel bridge. When cracks are found by visual inspection, basically all repairs are performed to repair all in the order of discovery.

  In order to detect cracks at an early stage and repair them at an early stage, it is necessary to frequently inspect substantially all parts of the steel bridge. Therefore, the scaffolds are frequently installed over a wide range, and there is a problem that the labor and cost of inspection increase. In addition, it is necessary to secure the stop position of the special vehicle, and road regulation is frequently performed, which has a problem of having a great influence on road traffic.

  By the way, in steel bridges, it is known that a relatively large number of cracks occur in the welded portions of the members constituting the main girder and the deck plate. Therefore, conventionally, a crack sensor is installed at the welded part of a steel bridge, the detection information of the crack sensor is transmitted to a personal computer with a data logger, the detection information is displayed on a display with a personal computer, and a crack is generated at a remote location. Has been proposed (see Patent Document 1). The crack sensor is formed by fixing one continuous ultrafine wire to the welded portion with an adhesive, and if the welded portion is cracked, the ultrafine wire is broken and the resistance value of the resulting ultrafine wire is thereby broken. It detects the change of the crack and detects the crack. According to this crack monitoring method, after the crack sensor is installed, the crack can be detected without approaching the steel bridge, so the frequency of installing the scaffold and the frequency of regulating the road can be reduced.

JP 2003-75301 A

  However, the above conventional crack monitoring method does not always cause a crack at the position where the crack sensor is installed, and may cause a crack at a position where no crack sensor is installed, so the crack detection accuracy is low. There is a problem. If it is going to detect all the cracks which arise in a steel bridge, it will be necessary to install a crack sensor in every member, and the effort and cost concerning installation and monitoring will become excessive, and it is not realistic.

  In addition, cracks that occur in steel bridges, such as those that greatly progress in a short time after they occur, and those that stop progressing when reaching a certain length, are often different depending on the crack, There is no elucidated method for reliably predicting the mode of progress. In other words, it is difficult to accurately predict the occurrence and progress of cracks in steel bridges. Conventionally, in order to elucidate the mechanism of cracks in steel bridges, attempts have been made to install strain sensors on steel bridge members and monitor changes in stress, but methods for predicting cracks have been established. Not.

  In addition, the policy of discovering cracks by visual inspection and repairing all of the cracks in sequence is the effort required to monitor and repair cracks in the near future, considering that damage to bridges is expected to increase over time. There is a problem that the cost increases significantly.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a crack monitoring method and a crack monitoring system that can monitor a crack in a bridge with less effort and cost, and can prevent an increase in labor and cost for repairing the bridge.

In order to solve the above problems, a bridge crack monitoring method of the present invention includes a step of installing a strain sensor in a bridge crack,
Estimating a crack growth rate based on the measurement value of the strain sensor;
Identifying a crack having a growth rate greater than a reference value;
Installing a crack propagation sensor in the identified crack;
Determining a crack having a measured value of the crack propagation sensor larger than a reference value as a repair candidate.

  According to the above configuration, the strain sensor is installed in the crack of the bridge, the crack propagation speed is estimated based on the measurement value of the strain sensor, and the crack whose progress speed is larger than the reference value is specified. In this way, by determining the progress rate of a crack generated in the bridge and specifying a crack whose progress rate is larger than the reference value, it is possible to extract a crack with a high degree of urgent repair. Here, since the growth rate estimated based on the measurement value of the strain sensor is the crack growth rate when the measurement by the strain sensor is performed, the growth of the crack is reduced or increased after the measurement by the strain sensor. There is a case. Further, the progress rate estimated based on the measurement value of the strain sensor is obtained by calculation and is not a direct measure of the rate at which the crack progresses. Therefore, a crack propagation sensor is installed in the crack specified based on the propagation speed, and the actual amount of crack propagation is measured by the crack propagation sensor. A crack whose measured value of the crack propagation sensor is larger than a reference value is determined as a repair candidate. In this way, the urgency of repair is actually high by narrowing the cracks in the bridge step by step based on the growth rate estimated based on the measurement value of the strain sensor and the measurement value of the crack growth sensor. A crack to be repaired preferentially can be identified with high accuracy. By repairing the cracks thus identified, it is possible to prevent fatal damage to the bridge with less effort and cost than repairing all the cracks that have been discovered.

  In the present invention, the strain sensor refers to a sensor having a function of detecting a target strain based on, for example, a change in electrical resistance, and has one detection element for detecting strain or a plurality of detection elements. For example, various types of sensors are applicable. As a strain sensor, it has a conductive linear detector formed on the surface of the insulating film so as to extend in the direction in which strain is detected, and the value of electrical resistance that changes as the linear detector is deformed It is possible to use one that detects a distortion value based on the above. The crack propagation sensor is a sensor having a function of detecting the length of a crack based on, for example, a change in electric resistance. As a crack growth sensor, a conductive detection part having a plurality of intersections intersecting with a crack is formed on the surface of the insulating film, and the detection changes by sequentially cutting the plurality of intersections according to the progress of the crack. What detects the progress length of a crack based on the value of the electrical resistance of a part can be used.

In the method for monitoring a crack in a bridge according to an embodiment, the step of estimating the crack growth rate based on the measurement value of the strain sensor obtains a stress intensity factor from the measurement value of the strain sensor by the following equation (1). The crack growth rate is predicted based on the frequency distribution of the obtained stress intensity factors.
K _I = C ₁ (ε ₁ + ε ₂ ) (1)
However, K _I is perpendicular stress intensity factor of progress surface cracks, C ₁ is a coefficient determined based on the Young's modulus and Poisson's ratio of the length of the crack, cracked member, epsilon ₁ developments surface crack The strain in the direction perpendicular to the progress plane measured on one side of the crack, and ε ₂ is the strain in the direction perpendicular to the progress plane measured on the other side of the crack progress plane.

According to the above embodiment, the strain around the tip of the crack in the cracked member is measured by the strain sensor, and the stress intensity factor is obtained from the measured value of the strain sensor by the above equation (1). A plurality of stress intensity factors are calculated based on a plurality of strain values obtained within a predetermined period. From these multiple stress intensity factors, the frequency distribution of the difference between the maximum and minimum values of the stress intensity factor (hereinafter referred to as the stress intensity factor range) can be obtained, and the crack growth rate can be estimated from the stress intensity factor range. . In addition, by accumulating the stress intensity factor range, the crack growth length can be predicted. When the measured strain is only the strain ε _{1 in the} direction perpendicular to the development plane on one side of the crack, the strain ε ₂ in the direction perpendicular to the development plane on the other side is changed to the strain ε ₂ in the direction perpendicular to the development plane on the one side. it may be considered to be the same as the strain ε _1. In this case, K _I = 2C ₁ ε ₁ .

  In one embodiment of the bridge crack monitoring method, the strain sensor is a K-value sensor having a strain gauge that is installed at the tip of the crack and detects strain in a direction perpendicular to at least a crack propagation surface.

  According to the said embodiment, the value for estimating the progress speed of a crack can be effectively measured with the K value sensor installed in the front-end | tip part of a crack. Here, the K-value sensor is a sensor that measures a stress intensity factor at the peripheral portion of the crack tip in a cracked member, and has at least a strain gauge that detects strain in a direction perpendicular to the crack progress surface. . The K-value sensor preferably has two or more strain gauges that are arranged on both sides of the crack propagation surface and detect strain perpendicular to the propagation surface, and more preferably, are arranged on both sides of the crack propagation surface. And having two or more strain gauges for detecting strain in a direction parallel to the progress surface.

The bridge crack monitoring system of the present invention is a crack monitoring system for performing the above-described bridge crack monitoring method,
A measurement terminal that is installed in the vicinity of the crack occurrence position of the bridge, is connected to a sensor installed in the crack and performs measurement related to the crack, and a reception terminal that receives information from the measurement terminal by wireless communication,
The measuring terminal
A control unit for controlling and operating the strain sensor and / or the crack propagation sensor;
A wireless transmission unit for transmitting detection information of the strain sensor and / or crack propagation sensor by wireless communication;
And a power supply unit that supplies power to the control unit and the wireless transmission unit.

  According to the above configuration, the strain sensor and / or crack propagation sensor is installed in the crack of the bridge, and the control of the measurement terminal in which these strain sensor and / or crack propagation sensor is installed in the vicinity of the crack occurrence position of the bridge. The measurement information about the cracks can be obtained. Measurement information from the strain sensor and / or crack propagation sensor is transmitted to the receiving terminal by the wireless transmission unit. The control unit and the wireless transmission unit operate when power is supplied from a power supply unit. As described above, when a crack occurs in the bridge, the strain sensor and / or the crack progress sensor is installed in the crack, and the strain sensor and / or the crack progress sensor is connected only by installing the measurement terminal near the crack. Thus, it is possible to easily perform the measurement related to the crack with a simple apparatus configuration without connecting the power supply line or the information transmission line, and collect the measurement information in the receiving terminal. As measurement information transmitted from the measurement terminal to the reception terminal, information specifying the sensor that has performed the measurement, information indicating the time or position at which the measurement was performed, and the like, along with the information on the measurement value measured by the sensor May be included.

  In the bridge crack monitoring system according to an embodiment, the measurement terminal includes a connection terminal to which the storage unit is detachably connected.

  According to the above embodiment, the storage unit is connected to the connection terminal of the measurement terminal, the measurement information of the strain sensor and / or the crack propagation sensor is stored in the storage unit, and then the storage unit is removed and connected to another device. By doing so, the measurement information regarding a crack can be easily collected. Therefore, even if the amount of measurement information of the sensor is large, measurements related to cracks can be collected with a simple device configuration without connecting an information transmission line. Here, a USB memory having a USB (Universal Serial Bus) terminal can be used as the storage unit. In addition to the measurement value of the sensor, the storage unit may store information specifying the sensor that has performed the measurement, information indicating the time or position at which the measurement was performed, and the like. Further, the measurement terminal may incorporate a non-detachable storage unit, and the measurement information may be temporarily stored in the built-in storage unit.

  In the bridge crack monitoring system according to an embodiment, the receiving terminal includes a registration unit that registers information received from the measuring terminal with a server through a computer network.

  According to the embodiment, the measurement information related to the crack received from the measurement terminal is registered in the server through the computer network by the registration unit of the reception terminal. Therefore, it is possible to easily and quickly collect the crack measurement values registered in the server at a position away from the bridge to know the progress of the crack. In addition, by installing multiple measurement terminals corresponding to multiple bridge cracks and registering measurement information from these measurement terminals in the server, information related to multiple bridge cracks can be collected and managed collectively. Analysis can be performed efficiently.

It is a figure which shows a mode that the steel bridge which monitors a crack was observed from the bottom face side. It is a flowchart which shows the crack monitoring method of a bridge. It is a top view which shows a K value sensor. It is a figure which shows the relationship between the constant for calculating | requiring K value from the distortion output of a K value sensor, and the length of a crack. It is a figure which shows the relationship between the progress rate of a crack, and a stress intensity factor range. It is a figure which shows the relationship between the progress rate of a crack, and a stress intensity factor range. It is a schematic diagram which shows a mode that the K value sensor and the measurement terminal were installed in the generation | occurrence | production position of the crack of steel bridges. It is a figure which shows the crack monitoring system of a bridge.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a view showing a state where a steel bridge as a bridge for monitoring cracks is observed from the bottom surface side of a floor slab. This steel bridge is a viaduct of an urban highway, and is constructed by supporting a steel floor slab 1 with a steel or concrete pier. The steel floor slab 1 has a deck plate 2 and a pavement 3 laid on the upper surface of the deck plate 2. On the lower surface of the deck plate 2, as a reinforcing member, a trough 4 having a U-shaped cross section and extending in the bridge axis direction, and a main girder or a longitudinal rib having an I-shaped cross section extending in parallel with the trough 4 5 and cross beams or horizontal ribs 6 extending in a direction perpendicular to the bridge axis and having an I-shaped cross section are provided. The deck plate 2, trough 4, main girder or vertical rib 5 and cross girder or horizontal rib 6 are made of steel, and the trough 4, main girder or vertical rib 5, and horizontal girder or horizontal rib 6 are the deck plate 2. It is fixed by welding. In a steel bridge, many cracks occur in the welded portions of the deck plate 2 of the steel floor slab 1, the deck plate 2 and the trough 4, the main girder or vertical rib 5, and the cross beam or horizontal rib 6.

  FIG. 2 is a flowchart illustrating the bridge crack monitoring method according to the embodiment. The method for monitoring cracks in a bridge according to the present embodiment estimates the progress rate of a crack generated in a bridge based on the amount of strain measured at the tip of the crack, and further confirms by measuring the actual progress rate of the crack. By doing so, the crack to be repaired is determined.

  In the bridge crack monitoring method of the present embodiment, first, a scaffold (not shown) is installed on the bottom or side of the steel floor slab 1 of the steel bridge, and an inspector visually checks the steel floor slab 1 from the scaffold. Explore. When the inspector finds a crack, a K-value sensor as a strain sensor is installed in all the found cracks (step S1). As will be described in detail later, the K-value sensor has four gauge elements and measures the amount of strain in two directions on both sides of the crack propagation surface. In addition to the K value sensor, at least one strain sensor that measures the strain in the direction perpendicular to the progress surface of the crack may be used.

  When K value sensors are installed in all cracks of the bridge, lead wires of the K value sensor are connected to measurement terminals described in detail later, and the measurement terminals are installed in the vicinity of the cracks to measure strain. The distortion measurement by the K value sensor is performed over a predetermined period (step S2). The period during which strain is measured by the K-value sensor can be set between 24 hours and 168 hours (ie, 7 days), and is preferably 72 hours. A crack stress intensity factor is calculated based on the strain value measured by the K-value sensor, and a crack growth rate is estimated based on the calculated stress intensity factor value (step S3).

It is determined whether or not the estimated growth rate of the crack is greater than a predetermined reference value (step S4). If the growth rate is greater than the reference value, a crack sensor as a crack growth sensor is attached to the crack. Install (step S5). The reference value of the progress rate can be set to 1 × 10 ⁻⁷ (m / cycle), for example. If the progress rate is smaller than the reference value, the crack is removed from the repair candidate and the current monitoring is terminated. For a crack whose progress rate is smaller than the reference value, the distortion by the K value sensor is measured again in the next monitoring. The time interval between the current monitoring and the next monitoring can be set to any of 3 to 8 years. The monitoring time interval is preferably 3 to 5 years for steel slabs, and preferably 5 to 8 years for concrete slabs. Any time interval from 3 to 8 years may be set for the entire structure of the bridge including the pier. As described above, a change in the crack growth rate can be detected by repeating the measurement by the K-value sensor for the crack whose growth rate is smaller than the reference value.

  The crack in which the crack sensor is installed is measured over a predetermined period (step S6), and the actual progress length of the crack is obtained based on the measurement result (step S7). The measurement period by the crack sensor can be set between 3 months and 6 months, and is preferably 6 months. The measurement period by the crack sensor is preferably set so as to include a summer period from June to September in which cracks tend to progress. For the measurement result of the crack sensor, it is determined whether or not the progress length of the crack is larger than a predetermined reference value (step S8). If the progress length is larger than the reference value, the crack is repaired. A candidate is determined (step S9). The reference value of the progress length can be set to 600 (mm), for example. If the progress length is smaller than the reference value, the crack is removed from the repair candidate and the current monitoring is terminated. For cracks whose progress length is smaller than the reference value, distortion is again measured by the K-value sensor in the next monitoring. The time interval between the current monitoring and the next monitoring can be set to any of 3 to 8 years. The monitoring time interval is preferably between 3 and 5 years for steel slabs, and preferably between 5 and 8 years for concrete slabs, but the overall structure of the bridge including the piers. For, any time interval from 3 to 8 years may be set. As described above, by measuring the growth rate again for a crack having a growth rate larger than the reference value and a growth length smaller than the reference value, a change in the crack growth rate can be detected.

  In this way, the growth rate is estimated based on the measured value of the K-value sensor, limited to cracks whose growth rate exceeds the reference value, and the actual growth length is measured by the crack sensor to determine the repair candidate crack. Therefore, it is possible to accurately identify cracks that are actually urgently repaired. Therefore, it is possible to eliminate unnecessarily unnecessary repairs without reducing the safety of the bridge, and to effectively reduce the repair cost of cracks, rather than repairing all found cracks. In addition, K value sensors that can be used multiple times are installed in all cracks and measurements are performed, while crack sensors that can be used only once are installed in a limited crack and measurement is performed. Rather than installing a crack sensor in the crack, useless use of the sensor can be reduced, and the cost of measurement can be reduced. Here, with respect to the cracks determined as repair candidates, the crack repair order may be determined based on the progress speed and the progress length.

  The estimation of the crack growth rate is performed according to linear fracture mechanics based on the measured value by the K value sensor shown in FIG.

As shown in FIG. 3, the K-value sensor 7 has gauge elements 71, 72, 73, 74 formed of a conductor printed on a sheet-like gauge base 70 formed of an insulating resin. . The gauge elements 71, 72, 73, and 74 are a first gauge element 71 and a second gauge element 72 that measure strain in a direction perpendicular to the progress surface of the crack 77, and a third gauge that measures strain in the parallel direction of the progress surface. An element 73 and a fourth gauge element 74 are included. The first gauge element 71 and the second gauge element 72 are linear metals that form a meandering pattern of one stroke so that a plurality of linear portions extending in one direction are arranged in parallel in a substantially semicircular belt-like region. It is made of foil. The first gauge element 71 and the second gauge element 72 are arranged to face each other so as to be arranged on a concentric circle with a space between them. The third gauge element 73 and the fourth gauge element 74 are each a linear metal that forms a meandering pattern of one stroke so that a plurality of straight line portions extending in the other direction are arranged in parallel in a substantially semicircular belt-like region. It is made of foil. The third gauge element 73 and the fourth gauge element 74 are spaced apart from each other, and the first gauge element 71 and the second gauge element 72 are disposed inside the first gauge element 71 and the second gauge element 72. Opposing to be arranged on concentric circles. Lead terminals 11, 11, 12, 12, 13, 13, 14, and 14 are provided at both ends of the first gauge element 71, the second gauge element 72, the third gauge element 73, and the fourth gauge element 74, respectively. Is provided. The K value sensor 7 includes a tip 77a of the crack 77 positioned at the center of the gauge elements 71, 72, 73, 74, and straight portions of the first and second gauge elements 71, 72 are perpendicular to the progress surface. And it affixes on the front-end | tip part of the crack 77 so that the linear part of the 3rd and 4th gauge elements 73 and 74 may make a parallel with an extended surface. Assuming that the strain output of the first gauge element 71 of the K value sensor 7 is ε ₁ and the strain output of the second gauge element 72 is ε ₂ , the stress of mode I, which is the deformation in the opening direction of the crack 77, as the K value. the intensity factor K _I, can be obtained by the following equation (1).
K _I = C ₁ (ε ₁ + ε ₂ ) (1)
Also, the strain output of the third gauge element 73 of the K value sensor 7 and epsilon _3, when the strain output of the fourth gauge element 74 and epsilon _4, as K values, mode II is the modification of the shear direction crack 77 the stress intensity factor K _II on deformation of the can be determined by the following equation (2).
K _II = −C ₂ (ε ₃ −ε ₄ ) (2)
Here, C ₁ and C ₂ are coefficients determined based on the length of the crack 77 and the Young's modulus and Poisson's ratio of the member in which the crack 77 has occurred. The unit of the stress intensity factors K _I and K _II and the coefficients C ₁ and C ₂ is MPa√m.

FIG. 4 is a diagram showing the relationship between the length of a crack 77 and C ₁ and C ₂ in a steel sheet having a Young's modulus of 2.06 × 10 ² GPa and a Poisson's ratio of 0.3. In FIG. 4, the horizontal axis represents the length a (mm) of the crack 77, and the vertical axis represents C ₁ and C ₂ (MPa√m). As shown in FIG. 4, the value of C ₁ increases while the rate of increase decreases as the length a of the crack 77 increases. That, C ₁ is increased while converging towards the fixed asymptotic value. When the length a of a crack 77 is 10 mm, _{C 1} is 1.45MPa√m, when the length a of a crack 77 is 50 mm, _{C 1} is 1.7MPa√m. On the other hand, the value of C ₂ decreases as the length a of the crack 77 increases and the decrease rate decreases. That, C ₂ is reduced while converging towards the fixed asymptotic value. When the length a of the crack 77 is 10 mm, C ₂ is 1.5 × 10 ⁴ MPa√m, and when the length a of the crack 77 is 50 mm, C ₂ is 1.2 × 10 ⁴ MPa√ m.

A K value sensor 7 is installed on a test piece having a crack 77 whose analytical value of the stress intensity factor is known, and the stress intensity factor is calculated from the above equations (1) and (2) based on the strain output of the K value sensor 7. was calculated K _I and K _II, calculated value was confirmed to be errors of 10% or less with respect to the analysis value.

In crack monitoring method bridges in this embodiment, among the stress intensity factor K _I and K _II Mode I and Mode II, the only stress intensity factor K _I Mode I, used to estimate the propagation rate of the crack 77. Measurement results over a predetermined period of strain output epsilon ₁ and epsilon ₂ of the K value sensor 7 and from the above expression (1), by Rainflow Mean method is the difference between the maximum value and the minimum value of the stress intensity factor K _I and the stress intensity factor range [Delta] K, obtaining the frequency distribution of the average value K _mean the stress intensity factor K _I. From the frequency distribution of the stress intensity factor range ΔK and the mean value K _mean , the growth rate of the crack 77 is estimated in consideration of the stress ratio, and the growth length of the crack is predicted by linearly accumulating the growth rate. The progress rate may be estimated based only on the mode I stress intensity factor range ΔK, or the progress rate may be estimated based on the mode I stress intensity factor range ΔK and the mode II stress intensity factor range ΔK. May be.

An equation for estimating the crack growth rate based on the stress expansion respect number range ΔK can be expressed as the following equation (3).
da / dN = C (ΔK ⁿ −ΔK _th ⁿ ) (3)
Here, da / dN is the crack growth rate (m / cycle), C and n are constants, ΔK is the stress intensity factor range (MPa√m), and ΔK _th ⁿ is the lower limit stress intensity factor The range (MPa√m). When ΔK ⁿ ≦ ΔK _th ⁿ , da / dN = 0.

Alternatively, the equation for estimating the crack growth rate can be expressed as in the following equations (4) and (5).
da / dN = C (ΔK) ⁿ , ΔK> ΔK _th (4)
da / dN = 0, ΔK ≦ ΔK _th (5)
Here, da / dN is the crack growth rate (m / cycle), C and n are constants, ΔK is the stress intensity factor range (MPa√m), and ΔK _th is the lower limit stress intensity factor range. (MPa√m). The above equation (4) is applied to the range of ΔK> ΔK _th , and the equation (5) is applied to the range of ΔK ≦ ΔK _th .

Or the estimation formula of the growth rate of a crack can be expressed like the following formula (6).
da / dN = C (ΔK) ⁿ (6)
In the above formula (6), da / dN is the crack growth rate (m / cycle), C and n are constants, and ΔK is the stress intensity factor range (MPa√m).

The constants and the lower limit stress intensity factor range of the above formulas (3) to (6) are the values shown in the following table according to the Japan Steel Structure Association edited by the Japan Steel Structure Association The combination of can be adopted. Here, in any of the above formulas (3) to (6), the application limit is ΔK ≦ 100 MPa√m.

FIG. 5A shows cracks estimated corresponding to the stress intensity factor range when the constants C and n and the lower limit stress intensity factor range ΔK _th in the above table are applied to the equations (3) to (5). It is a graph which shows progress speed. In FIG. 5A, the horizontal axis represents the stress intensity factor range ΔK (MPa√m), and the vertical axis represents the crack growth rate da / dN (m / cycle). The horizontal and vertical axes are displayed on a logarithmic scale. As shown in FIG. 5, when the constants C and n of design 1 and the lower limit stress intensity factor range ΔK _th are applied, the crack growth rate da / dN and the stress intensity range ΔK are curves corresponding to Equation (3). A ₁₁ , a straight line A ₁₂ corresponding to Expression (4), and a straight line A ₁₃ corresponding to Expression (5) are included. 5A, the portion ΔK is above about 5MPa√m linear _{A 12} is overlapped with the curve _{A 11.} Further, when the constants C and n of design 2 and the lower limit stress intensity factor range ΔK _th in the above table are applied, the crack growth rate da / dN and the stress intensity range ΔK are expressed by the curve A ₂₁ corresponding to the equation (3). Or, there is a relationship such as a straight line A ₂₂ corresponding to Expression (4) and a straight line A ₂₃ corresponding to Expression (5). In FIG. 5A, a portion where ΔK of the straight line A ₂₂ is about 7.5 MPa√m or more overlaps with the curve A ₂₁ . As shown in FIG. 5A, the growth rate of the crack is determined by the equation (4) represented by the straight line A ₁₂ and the straight line A ₂₂ rather than the equation (3) represented by the curved line A ₁₁ and the curved line A _21. formula represented by a ₁₃ and the straight line _{a 23} better by the (5), the estimation results of the safety side is obtained.

FIG. 5B shows the crack growth rate estimated corresponding to the stress intensity factor range when the constants C and n and the lower limit stress intensity factor range ΔK _th in the above table are adopted in the above equation (6). It is a graph. In FIG. 5B, the horizontal axis represents the stress intensity factor range ΔK (MPa√m), and the vertical axis represents the crack growth rate da / dN (m / cycle). The horizontal and vertical axes are displayed on a logarithmic scale. As shown in FIG. 5B, when the constants C and n of design 1 and the lower limit stress intensity factor range ΔK _th are applied, the crack growth rate da / dN and the stress intensity range ΔK are straight lines corresponding to Equation (6). as in the a _14, it has a linear relationship in logarithmic. Further, when the constants C and n of design 2 and the lower limit stress intensity factor range ΔK _th are employed, the crack growth rate da / dN and the stress intensity range ΔK are expressed as a straight line A ₂₄ corresponding to the equation (6). Have a linear relationship in logarithmic representation. The growth rate of the crack is based on the equation (3) represented by the curve A ₁₁ and the curve A ₂₁ in FIG. 5A and the straight line A ₁₂ according to the equation (6) represented by the curve A ₁₄ and the curve A ₂₄ in FIG. In addition, the estimation result on the safe side is obtained as compared with the equation (4) represented by the straight line A ₂₂ and the equation (5) represented by the straight line A ₁₃ and the straight line A ₂₃ .

  From these facts, the equation for estimating the crack growth rate is calculated based on the importance of the bridge, the characteristics of the cracked member, the action state of the load, and the like. It can be appropriately selected from (5) and formula (6).

In addition, as for the crack growth rate, it is better to adopt the constants C and n of the design 1 and the lower limit stress intensity factor range ΔK _th than the constants C and n of the design 2 and the lower limit stress intensity factor range ΔK _th. A safer result is obtained. For example, the constants C and n of the design 1 and the lower limit stress intensity factor range ΔK _th are preferably used when performing calculations related to an actual bridge. The constants C and n of the design 2 and the lower limit stress intensity factor range ΔK _th is preferably employed when normal calculation of the fatigue life and fatigue strength of an average member is performed. The constants C and n and the lower limit stress intensity factor range ΔK _th may be other values depending on the composition of the cracked member, the frequency at which the load acts, and the like.

The values of constants C and n and the lower limit stress intensity factor range ΔK _{th in} the above table are used to estimate the growth rate of cracks occurring in relatively high tensile residual stress fields, such as in the vicinity of weld beads and welds. The constants C and n are preferably corrected by the stress ratio, which is the ratio of the maximum value of the stress intensity factor to the minimum value, for cracks that occur in a portion having a low tensile residual stress such as a non-welded portion. .

Further, the stress intensity factor K _I and K _II as K value varies in accordance with growth of the crack 77, the crack 77 length when measuring K value was a ₀ has grown to a length of a If, corrects by multiplying {square root} a / {square root} a ₀ to K values.

In the above embodiment, the stress intensity factor KI of the mode _I is obtained from the strain output of the first gauge element 71 of the K value sensor 7 as ε ₁ and the strain output of the second gauge element 72 as ε _2. the only strain output epsilon ₁ of the first gauge element 71 value sensor, may be determined stress intensity factor K _I mode I. In this case, it is assumed that the strain output ε ₂ measured by the second gauge element 72 is the same as the strain output ε ₁ of the first gauge element 71, and K _I = 2C ₁ ε ₁ . In addition to the K-value sensor 7, a strain sensor that measures strain in a direction perpendicular to the progress surface of the crack 77 is installed similarly to the first gauge element 71, and the stress intensity factor is calculated based on the output of the strain sensor. The progress rate and length of the crack 77 may be calculated.

  FIG. 6 is a diagram showing a state in which the K value sensor 7 and the measurement terminal 8 for monitoring the crack growth rate are installed on the steel bridge. Hereinafter, the case where the crack 77 which arose in the welding part of the deck plate 2 of the steel floor slab 1 and the trough 4 is monitored is demonstrated.

  As shown in FIG. 6, a weld bead 41 is formed at a welded portion between the deck plate 2 and the trough 4, and a crack 77 that has propagated along the weld bead 41 is bent at a predetermined position to be trough 4. Progressing towards the bottom of When the crack 77 is found, the K value sensor 7 is installed at the tip of the crack 77, a plurality of lead wires connected to the K value sensor 7 are connected to the measurement terminal 8, and the measurement terminal 8 is connected to the side surface of the trough 4. Fixed to. The K-value sensor 7 functions as a strain sensor that measures the variation of the strain around the tip of the crack 77 generated in the trough 4. As will be described in detail later, the measurement terminal 8 includes a control unit that controls and operates various sensors including the K value sensor 7, a storage unit that stores measurement information of the sensor, and a wireless communication unit that transmits measurement information. Etc. are built in the terminal body 81. A battery 87 that supplies power to the control unit, the storage unit, the wireless communication unit, and the like is connected to the terminal body 81. The terminal body 81 is provided with a connection terminal to which a USB memory 83 as a storage unit is detachably connected, and an antenna 82 connected to the wireless communication unit. Note that the terminal main body 81 may be removably connected with a USB memory 83 as a storage unit, or may include a storage device such as a flash memory as a storage unit. The terminal body 81 may have both a connection terminal to which the USB memory 83 can be attached and detached and a built-in storage device. Further, the battery 87 may be built in the terminal main body 81.

  Since the measurement terminal 8 is driven by the battery 87 and transmits the measurement information of the K value sensor 7 by the wireless communication unit, it is possible to measure and collect information on the crack 77 without being connected to a commercial power supply line or an information transmission line. It has become. The measuring terminal 8 may be directly fixed to the trough 4 of the steel floor slab 1, the main girder, or the longitudinal rib 5 with a magnet, or a bolt nut or the like is attached to a scaffold (not shown) installed on the steel floor slab 1. It may be fixed. In any case, it is only necessary to connect the sensor and the measurement terminal 8 with a lead wire, so that the installation position of the measurement terminal 8 can be selected with a high degree of freedom. In addition to the K value sensor 7, a crack propagation sensor or a strain sensor may be connected to the measurement terminal 8, and one or more sensors may be connected to the measurement terminal 8.

  FIG. 7 is a block diagram illustrating the crack monitoring system of the embodiment. This monitoring system includes the measurement terminal 8, the receiving terminal 9, and the server 10. The receiving terminal 9 is installed in the vicinity of the bridge where the measuring terminal 8 is installed, receives measurement information from the measuring terminal 8 by wireless communication, and analyzes the crack propagation speed and length. The server 10 is connected to the receiving terminal 9 via the network N, and collects and stores measurement information and analysis results regarding cracks. The network N that connects the receiving terminal 9 and the server 10 can use various information communication networks such as the Internet, a telephone line, and a dedicated line.

  As shown in FIG. 7, the measurement terminal 8 includes a terminal main body 81, an antenna 82 protruding from the terminal main body 81, a connection terminal for connecting the USB memory 83 to the terminal main body 81, and a bridge connected to the K value sensor 7. A drive amplifier 84 constituting the circuit, a CPU 85 for controlling the operation of the measurement terminal 8, a wireless I / F (interface) 86 for wirelessly transmitting measurement information of the K value sensor 7, and a power supply for the measurement terminal 8 A battery 87 is provided. The terminal body 81 is formed so that a crack sensor and other sensors can be connected in addition to the K value sensor 7, and the drive amplifier 84 is formed so as to be able to drive other sensors. The CPU 85 is configured to control operations of the drive amplifier 84, the wireless I / F 86, the USB memory 83, and the like according to a program stored in a memory (not shown). The CPU 85 and the drive amplifier 84 correspond to a control unit that controls and operates the sensor. The CPU 85 is configured to control operations of the drive amplifier 84, the wireless I / F 86, the USB memory 83, and the like according to a command received from the receiving terminal 9 through the wireless I / F 86. The battery 87 is composed of a lithium ion battery and can perform a measurement operation for a long time.

  When the K value sensor 7 is connected to the measurement terminal 8 and measurement is performed to estimate the progress rate of the crack 77, the measurement information from the K value sensor 7 is stored in the USB memory 83 because the data amount is relatively large. When the period of measurement by the K value sensor 7 ends, the USB memory 83 is collected by an inspector who has approached the measurement terminal 8 through the scaffold. On the other hand, when a crack sensor is connected to the measuring terminal 8 and the progress length of the crack 77 is measured, the measurement information from the crack sensor is transmitted to the receiving terminal 9 through the wireless I / F 86 in real time because the data amount is relatively small. To do.

  The receiving terminal 9 includes a terminal main body 91 configured with a personal computer or the like, a wireless unit 92 connected to the terminal main body 91, and analysis software 93 stored in a storage device of the terminal main body 91. The receiving terminal 9 is configured by connecting a wireless unit 92 that performs wireless communication with the measuring terminal 8 and installing analysis software 93 to a terminal main body 91 formed of a versatile device such as a personal computer. The wireless unit 92 performs wireless communication with the measurement terminal 8 and receives measurement information of the sensor connected to the measurement terminal 8. The analysis software 93 processes the measurement information received from the measurement terminal 8 to calculate an estimated value of the progress rate and progress length of the crack 77, and a function to organize the actual measurement values of the progress rate and progress length. And a function of outputting the result of information processing. The terminal main body 91 has a connection terminal of a storage device, is connected to a USB memory 83 in which measurement information is stored by the measurement terminal 8, reads the measurement information in the USB memory 83, and performs information processing by the analysis software 93. It is possible. The receiving terminal 9 has a network communication function for connecting to the network N and communicating with other devices, and can upload measurement information and analysis results of the crack 77 to the server 10. This network communication function corresponds to the registration unit.

  The server 10 is configured by a personal computer or the like, and stores the measurement information and analysis results received from the receiving terminal 9 via the network N in the database 11, and the stored information in the database 11 can be distributed via the network N. Is formed. For example, predetermined information can be distributed to the connection terminal 12 connected to the network N in response to a request from the connection terminal 12. As a result, the bridge crack can be monitored through the connection terminal 12 at a position remote from the cracked bridge, the analysis result regarding the crack can be browsed, and the analysis regarding the crack can be performed. Can do.

  According to the crack monitoring system having the above configuration, measurement information can be stored in the USB memory 83, and the K value sensor 7 and the crack sensor are connected to the measurement terminal 8 capable of wirelessly transmitting the measurement information and installed in the vicinity of the crack. Therefore, it is possible to reduce the size of the equipment installed at the crack occurrence site. Therefore, it is possible to reduce the height work on the bridge and facilitate the installation work of the measuring device. In addition, since the measurement information is transmitted from the measurement terminal 8 to the reception terminal 9, and the reception terminal 9 can upload the measurement information and analysis information to the server 10 through the network N, the crack of the bridge is remote from the bridge where the crack occurs. Can be monitored and analyzed.

  In the above embodiment, the measurement information of the K value sensor 7 is stored in the USB memory 83, and the USB memory 83 is collected by the inspector and connected to the receiving terminal 9 to read the measurement information. The information may be transmitted to the receiving terminal 9 by wireless communication via the wireless I / F 86.

  Further, in the above embodiment, the bridge crack monitoring system is used for the purpose of determining the repair priority by monitoring the progress of cracks. Good. The cracked portion of the bridge may be cracked again due to an increase in load or repeated action of the load even after the repair is completed. Therefore, by installing a K-value sensor 7 at the crack repair completion part and collecting measurement information at the measurement terminal 8, it is possible to observe the stress state of the crack repair completion part and detect the recurrence of the crack. Can do.

  Moreover, although the said embodiment demonstrated the case where the crack which arose on the viaduct of a city highway was monitored, this invention is applicable also to the crack which arose in the steel member of another bridge.

1 Steel floor slab 2 Deck plate 4 Trough 7 K value sensor 8 Measuring terminal 9 Receiving terminal 10 Server 77 Crack N Network

Claims (6)

Installing a strain sensor in the crack of the bridge;
Estimating a crack growth rate based on the measurement value of the strain sensor;
Identifying a crack having a growth rate greater than a reference value;
Installing a crack propagation sensor in the identified crack;
And a step of determining a crack having a measured value of the crack growth sensor larger than a reference value as a repair candidate. In the bridge crack monitoring method according to claim 2,
The step of estimating the crack growth rate based on the measured value of the strain sensor obtains the stress intensity factor from the measured value of the strain sensor by the following equation (1), and based on the frequency distribution of the obtained stress intensity factor. A method for monitoring cracks in a bridge characterized by predicting the growth rate of cracks.
K _I = C ₁ (ε ₁ + ε ₂ ) (1)
However, K _I is perpendicular stress intensity factor of progress surface cracks, C ₁ is a coefficient determined based on the Young's modulus and Poisson's ratio of the length of the crack, cracked member, epsilon ₁ developments surface crack The strain in the direction perpendicular to the progress plane measured on one side of the crack, and ε ₂ is the strain in the direction perpendicular to the progress plane measured on the other side of the crack progress plane. In the bridge crack monitoring method according to claim 1,
The bridge crack monitoring method, wherein the strain sensor is a K-value sensor that is installed at a crack tip and has a strain gauge that detects strain in a direction perpendicular to at least a crack propagation surface. A crack monitoring system for performing the method for monitoring cracks in a bridge according to claim 1,
A measurement terminal that is installed in the vicinity of the crack occurrence position of the bridge, is connected to a sensor installed in the crack and performs measurement related to the crack, and a reception terminal that receives information from the measurement terminal by wireless communication,
The measuring terminal
A control unit for controlling and operating the strain sensor and / or the crack propagation sensor;
A wireless transmission unit for transmitting detection information of the strain sensor and / or crack propagation sensor by wireless communication;
A crack monitoring system comprising: a power supply unit that supplies power to the control unit and the wireless transmission unit. In the bridge crack monitoring system according to claim 4,
The measurement terminal has a connection terminal to which the storage unit is detachably connected. In the bridge crack monitoring system according to claim 4,
The crack monitoring system, wherein the receiving terminal includes a registration unit that registers information received from the measuring terminal with a server through a computer network.

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