JP2013250120A - Damage detection method for structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a damage detection method for a structure that has a relatively high degree of freedom of installation.SOLUTION: For a damage detection method for a structure, a first base 10 and a second base 10 are fixed on a surface of a structure apart from each other, and a detection member 50 is arranged between the first base 10 and second base 10 while applied with predetermined tension. Then an output of a strain gauge 51 provided to the detection member 50 is compared with a prepared reference value to detect damage to the structure. Each base 10 has relatively narrow area and can be fixed to a concrete-made or steel-made surface etc., with a concrete screw, so even if a surface state of a surface to be inspected is inferior, a fittable place is found and the base can be fitted. The distance between the bases can be varied by adjusting the length of the detection member 50, so the method is applicable to a relatively wide surface to be inspected.

Description

  The present invention relates to deterioration and damage (breaking) of structures and structures such as concrete and steel bridge girders due to salt damage, alkali aggregate reaction (in the case of concrete), fatigue and corrosion (in the case of steel), etc. , Cracks, peeling, etc.).

  In reinforced concrete and steel bridge girders, damage such as breakage, cracks (cracks), peeling of concrete, exposure of reinforcing bars, etc. occurs due to deterioration over time (for example, several decades after cross-linking), salt damage, and corrosion. . Such damage causes a change in the behavior of the structure, and if the behavior change becomes large, measures such as traffic restrictions may be taken. For this reason, it is necessary to monitor such a behavior change and deal with it promptly when an abnormality appears. Specifically, the behavior change appears as an increase in the amount of displacement or vibration of the structure. Since it is difficult to directly measure the amount of displacement, distortion may be measured.

  In addition, the RC structure (reinforced concrete) is designed to give tensile strength to the internal reinforcing bars instead of concrete in the tensile region (lower flange side in the bridge). For this reason, on the tension side, not the distortion of the surface of the concrete, but the surface of the concrete is shaved to expose the reinforcing bar, and a strain gauge or the like is attached thereto to measure the strain.

  A strain gauge or a surface strain gauge is used as an apparatus for measuring the strain on the surface of an object. Moreover, a pie gauge is known as an apparatus for measuring the width of a crack. The strain gauge has a flat plate shape and is used by directly attaching to an object. For this reason, when a crack etc. generate | occur | produce in an attachment location, there exists a possibility that a gauge may be damaged. In addition, it is difficult to attach to a portion where the surface is corroded or originally cracked. The surface strain gauge requires a temporary material for mounting the jig and requires a welding operation, so that it takes time to handle. Further, since the distance between the jigs is fixed, the installation place is limited. Since the pie gauge is installed so as to straddle existing cracks, it is necessary to predict the occurrence of cracks. A plurality of cracks are required for a wide range of cracks.

  On the other hand, there is also known a method in which a measuring instrument is not directly attached to a test surface, but a member fixed to the test surface and the measurement meter are separated from each other, and a distortion or the like is measured with the measuring instrument via a fixed object. As such a method, an apparatus for detecting strain using an optical fiber is disclosed (for example, see Patent Document 1). This device has a gauge base having a pair of rigid plate-like main body portions and a flexible portion for connecting the main body portions, and is fixed by winding an optical fiber between projections standing on each main body portion. The main body is attached to the structure to be measured. When the structure is distorted, the distance between the protrusions of each main body changes, and the change is concentrated on the central flexible part, and the distortion is expanded and transmitted to the optical fiber. For this reason, it is said that distortion can be detected with higher sensitivity.

JP 2003-254723 A

In the apparatus described in Patent Document 1 described above, it is described that a flexible part is formed between the main body parts to make the whole as a whole, thereby facilitating handling in the attachment process. However, since it is an integrated object, it is necessary to design the gauge base according to the size of the installation location, the shape of damage, and the like. Furthermore, a relatively large installation area is required, and the detection location may be limited. In addition, there is a flexible part between the main body parts, but in order to see changes in the relative position of the main body parts, there is nothing between the main body parts that gives resistance to displacement, or there is resistance. It is preferable that it is as low as possible.
An object of the present invention is to provide a damage detection method for a structure having a relatively high degree of freedom in installation.

In order to solve the above-described problem, in the damage detection method for a structure of the present invention, the first base and the second base are provided at the first place and the second place that are separated from each other on the surface of the structure. The detection member is disposed in a state where a predetermined tensile force is applied between the first base and the second base, and the output of the strain gauge provided on the detection member is set in advance. The damage of the structure is detected by comparing with a prepared reference value.
In this invention, it is good also as detecting damage based on the residual distortion in the no external force state of the said structure measured with the said strain gauge.

According to the present invention, when the relative position of the first base and the second base changes, the displacement is measured by a strain gauge from each base via the detection member. Each base has a relatively small area and can be fixed to a concrete or steel surface with concrete screws, bolts / nuts, adhesives, etc. Can be found and installed. Furthermore, since the distance between the bases can be varied by adjusting the length of the detection member, it is possible to cope with a relatively wide test surface. Furthermore, since the base is separate and the detection member disposed between the bases can use a cable or the like, the resistance given to the displacement between the bases can be relatively low.
Further, as the detection member, it is possible to use a material whose Young's modulus (elastic coefficient) is several orders different from that of the base member. The base member is not substantially deformed, and the first portion of the structure and the first member All of the relative displacement with respect to the second portion can be detected as distortion of the detection member. This makes it possible to acquire the average surface strain between the first location and the second location of the structure. At this time, by bringing the position of the detection member closer to the measurement surface of the structure, it is possible to reduce measurement errors caused by deformation caused by the couple (moment) acting on the base member.
Furthermore, by setting a predetermined tensile force on the detection member, it is possible to detect distortion with higher sensitivity, and to prevent resonance when it is likely to resonate (if resonance occurs, change the tension. Perform zero point correction). Furthermore, it is possible to measure the distortion on the compression side.
Therefore, it is possible to provide a method with relatively high installation flexibility and capable of detecting damage to the structure with high sensitivity.

In the present invention, the detection member may be an optical fiber incorporating an optical strain detection means.
In this case, it can be used instead of the detection member and the strain gauge, and the number of parts can be reduced. As the optical fiber, FBG, OTDR, BOTDR, or the like can be used.

In the present invention, the first base and the second base are fixed to the structure with a fixing jig for substantially fixing a relative position, and then the fixing jig is removed. Is preferred.
By using a fixing jig, the cable can be transported as a set so that the cable does not get entangled with each base. Furthermore, since the fixing jig is removed after fixing the first base and the second base to the structure with the fixing base mounted on the fixing jig, each base can be easily maintained while maintaining an appropriate positional relationship. It can be attached to the test surface.

In the present invention, the structure is preferably a concrete or steel bridge girder as an example.
In addition, it can be applied to plant piping, pressure vessels, concrete retaining walls (breakwaters, etc.) and jacket structures (steel towers, etc.).

In the present invention, it is more preferable that the reference value is made different based on an output of a weight measuring unit that measures the weight of a vehicle traveling on the bridge girder.
Since the measured strain value differs according to the weight of the vehicle, more realistic and accurate damage detection can be performed by setting a reference value according to the weight.

  In this invention, the said structure can also be comprised by the prestressed concrete to which the compressive stress was provided by the stress provision member arrange | positioned inside. In this case, a defect of the stress applying member can be detected based on an increase in strain detected by the strain gauge.

  As described above, according to the present invention, since the first base and the second base are provided at locations separated from each other, the area of the portion fixed to the test surface can be made relatively small. Even if the surface state of the surface to be inspected is bad, it is possible to find and attach a place that can be attached so as to straddle a place where the surface state is bad. Furthermore, since the distance between the bases can be varied by adjusting the length of the detection member, it is possible to cope with a relatively wide test surface. Therefore, it is possible to provide a method capable of detecting damage to a building having a relatively high degree of freedom in installation.

It is a figure explaining the example of application of the damage detection method of the building concerning an embodiment of the invention. It is a figure which shows the structure of the damage detection apparatus used for the damage detection method of FIG. 1, FIG. 2 (A) is a side view, FIG.2 (B) is a top view, FIG.2 (C) is a front view. It is the front view which decomposed | disassembled and showed the base part of the damage detection apparatus of FIG. It is a figure explaining the jig | tool which fixes the base of the damage detection apparatus of FIG. It is a graph which shows an example of the distortion measured value by the damage detection method of the present invention.

Hereinafter, a damage detection method for a building (structure) according to an embodiment of the present invention will be described with reference to the drawings.
The damage detection method for a building can also be used as a method for measuring the surface distortion of a building (structure).

FIG. 1 is a diagram for simply explaining a damage detection method for a building according to an embodiment of the present invention.
The damage detection method of the present invention detects, for example, cracks or peeling of the lower surface of the bridge girder B arranged between the piers F in the reinforced concrete or steel bridge structure shown in FIG. The damage detection device 1 is attached to the lower surface of the bridge to detect damage to the bridge girder B.
The surface on which the device 1 is mounted (surface to be tested) is not damaged to the extent that rapid countermeasures are required, such as large cracks or peeling, for example, where the deterioration is expected to progress in the future, This is a place where a large load is applied or a place where environmental conditions are severe. Moreover, the side surface of the bridge girder B and the side surface of the pier F can also be detected.
Actually, many existing bridges are deteriorated, and cracks and peeling occur in many places. Although there are places where the weight of passing vehicles has already been regulated, there is an urgent need to monitor the damage situation because there is concern about the progress of deterioration in the future.
Since many of these structures, such as concrete and steel bridges, that have been deteriorated are difficult to directly install strain gauges due to surface conditions, the method of this embodiment is extremely difficult. Useful.

2A and 2B are diagrams for explaining the structure of the damage detection apparatus, in which FIG. 2A is a side view, FIG. 2B is a plan view, and FIG. 2C is a front view (some parts omitted). .
The damage detection apparatus 1 includes a pair of first base 10 and second base 10 that are fixed to a test surface, and a detection member 50 that is disposed between the first base 10 and the second base 10. And a strain gauge 51 provided on the detection member 50. The first base portion 10 and the second base portion 10 have the same structure, and are installed facing each other on a straight line (X axis in FIG. 2B).

First, the structure of the base 10 will be described with reference to FIGS. FIG. 3 is an exploded front view of the base. The depth direction in FIG. 3 is the X-axis direction.
The base portion 10 includes a fixing portion 20 that is fixed to a surface to be examined and a grip portion 30 that grips the detection member 50.
As shown in FIG. 2C and FIG. 3, the fixing portion 20 has a π shape in the front shape, a shape symmetrical to the X axis, a pair of fixing pieces 21 that are long in the X axis direction, and both fixing pieces. 21 and a higher mounting piece 22.
Each fixing piece 21 is fixed to the surface to be inspected by, for example, a concrete screw 80 (a bolt and a nut when the structure is made of steel) when the structure is made of concrete.
A grip portion 30 is attached to the upper surface of the attachment piece 22. As shown in FIG. 2B, the mounting piece 22 has a parallel guide hole 24 extending in the X-axis direction. Further, a plate-like holding piece 26 that holds the detection member 50 and a member (tension holding member 60) that applies tension to the detection member 50 rises from one end edge of the attachment piece 22. As shown in FIGS. 2C and 3, the holding piece 26 has a hole 27 through which the tension holding member 60 is inserted and a hole 28 through which the detection member 50 is inserted side by side. It has been.
The fixing part 20 can be produced, for example, by pressing a stainless plate having a thickness of about 2 mm.

  The grip portion 30 is a rectangular parallelepiped block shape having a shape symmetrical to the X axis, and is attached to the upper surface of the attachment piece 22 of the base portion 20. The grip part 30 is composed of an upper piece 31 and a lower piece 32 which are divided into upper and lower parts. As shown in FIG. 3, a groove 33 extending along the X axis is formed on the lower surface of the upper piece 31. In this example, the cross-sectional shape of the groove 33 is a triangle, but there is no particular limitation as long as the detection member can be gripped. A groove 34 extending along the X axis is also formed on the upper surface of the lower piece 32. The cross-sectional shape of the groove 34 is a triangle. When the upper and lower pieces 31 and 32 are overlapped, the grooves 33 and 34 face each other and penetrate the grip portion 30 along the X axis. The detection member 50 is gripped between the grooves 33 and 34. The height between the grooves 33 and 34 is substantially the same as the height of the detection member through hole 28 formed in the support piece 26 of the fixed portion 20.

  As shown in FIG. 3, the upper piece 31 has a screw hole 36 extending along the X axis. The height of the screw hole 36 is the same as the height of the tension applying member through hole 27 opened in the support piece 26 of the fixing portion 20.

  The upper piece 31 and the lower piece 32 are positioned by a dowel 38 formed on the lower surface of the upper piece 31. After the detection member 50 is held between the grooves 33 and 34 of the upper and lower pieces 31 and 32, the upper and lower pieces 31 and 32 are fixed by a plurality of screws, and the detection member 50 is fastened and fixed to the holding portion 30.

A screw hole 41 for fixing a fixing jig 70 described later is formed on the upper surface of the grip portion 30. The screw holes 41 can be opened, for example, at four positions symmetrical to the X axis.
Further, the grip portion 30 is provided with two guide bolts 43 protruding from the lower surface. When the grip portion 30 is installed on the attachment piece 22 of the fixed portion 20, each guide bolt 43 engages with each guide hole 24 formed in the attachment piece 22. The grip portion 30 can slide along the guide hole 24, that is, both in the X-axis direction.
The grip part 30 is made of a resin such as Duracon, for example.

The detection member 50 can be a cable made of a material (for example, a steel wire, an optical fiber, etc.) that has flexibility and allows predetermined elastic deformation (stretching) with respect to tensile stress. By making the radius of the cable larger than the depth of the grooves 33, 34 formed in the upper and lower pieces 31, 32 of the grip portion 30, the cable can be more reliably held between the grooves of the upper and lower pieces 31, 32. Cables of various lengths may be prepared in advance, or the length of the test surface that is expected to be the widest may be used.
Near the center of the detection member 50, a strain gauge 51 is attached with an adhesive or the like. As the strain gauge 51, for example, a FLA series manufactured by Tokyo Sokki Kenkyujo Co., Ltd. can be used according to the thickness of the detection member 50.

As the tension applying member 60, a bolt (with SW) can be used. The bolt 60 is passed through the tension applying member through hole 27 of the support piece 26 of the fixing portion 20 and screwed into the screw hole 36 formed in the grip portion 30. Since the guide bolt 43 engages with the guide hole 24 of the fixed portion 20 and is prevented from rotating, the grip 30 is rotated along the guide hole 24, that is, X. Slide in the axial direction.
The slide length of the grip portion 30 in one base 10 is preferably about 25 mm. That is, as the entire apparatus, the distance between the gripping portions 30 can be increased up to about 50 mm, and a sufficient tension adjustment width can be obtained.

As shown in FIGS. 2A and 2B, each base 10 is arranged on the X-axis so that the gripping portion 30 is opposed. At this time, if necessary, the tension of the detection member 50 can be adjusted by rotating the tension applying bolt 60 and sliding the grip portion 30 in the X-axis direction.
When the relative position of both bases 10 changes, this change is transmitted to the detection member 50 and detected by the strain gauge 51.

Next, an example of a fixing jig that substantially fixes the relative position between the first base 10 and the second base 10 will be described with reference to FIG.
The fixing jig 70 is for fixing the first base portion 10 and the second base portion 10 in a state where the first base portion 10 and the second base portion 10 are arranged on the X-axis. In this example, a plate-like member attached between the grip portions 30 of both base portions 10 can be used. The fixing jig 70 has a width equal to the width of the grip portion 30 and a predetermined length extending in the X-axis direction. If the length is about the length of the test surface that is expected to be the widest, a single jig 70 can correspond to test surfaces of various widths. A plurality of long holes 71 parallel to the X axis are formed in the fixing jig 70 along two lines parallel to the X axis. The long holes 71 on each line are alternately arranged in the longitudinal direction.

  The fixing jig 70 is bridged between the upper surfaces of the gripping portions 30 of the base portions 10 arranged to face each other. Then, screws are passed through the long holes 71 of the fixing jig 70 and screwed into the screw holes 41 on the upper surface of the gripping portion 30. Thereby, both the base parts 10 are hold | maintained at the fixing jig 70 with the attitude | position along the X-axis. That is, both bases 10 can be stored or transported while being held in a posture along the X axis.

Next, an example of a method for attaching the damage detection apparatus 1 to the test surface using the fixing jig 70 will be described.
The dimensions of the test surface are measured in advance. Then, one end of the detection member 50 having a length adaptable to this dimension is gripped by the grip portion 30 of the first base portion 10. Thereafter, the grip portion 30 is placed on the mounting piece 22 of the fixed portion 20, and the bolt 60 as a tension applying member is screwed into the screw hole 36 of the grip portion 30 through the insertion hole 27 of the support piece 26 of the fixed portion 20. Then, the fixed portion 20 and the grip portion 30 are connected. Here, the gripping part 30 is positioned in front of the attachment piece 22 of the fixing part 20 (in the direction facing the second base part). Similarly, the other end of the detection member 50 coming out of the grip 30 of the first base 10 is gripped by the second base 10. Thus, the space | interval (length of the detection member 50) between the fixing | fixed parts 20 can be adjusted according to the width of a to-be-tested surface.
The detection member 50 coming out from the rear surface of the grip portion 30 of each base portion 10 is passed through the detection member insertion hole 28 of the support piece 26 of the fixed portion 20.

  The first base portion 10 and the second base portion 20 are separated from each other so that the detection member 50 is tensioned, and the fixing jig 70 is bridged between the upper surfaces of the grip portions 30 of the base portions 10. And the long hole 71 of the fixing jig 70 and the screw hole 41 formed in the upper surface of each holding part 30 are aligned, and the fixing jig 70 and the holding part 30 are fixed with a screw. As a result, the first base 10 and the second base 20 are positioned on the X axis and fixed to the fixing jig 70.

Then, the fixing piece 21 of the fixing portion 20 is fixed to the test surface with the concrete screw 80 while both the base portions 10 are fixed to the fixing jig 70. At this time, since the area of the fixing portion 20 is relatively small, even if the state of the test surface is poor, it is possible to search for and fix the place where it can be attached.
Thereafter, the fixing jig 70 is removed from both base portions 10. As a result, both base portions 10 are fixed to the test surface in a posture positioned on the X axis. At this time, when it is desired to increase the tension of the detection member 50, the bolt 60 is rotated to slide the base grip portion 30 backward (outward) by an appropriate distance. As described above, the tension adjustable distance is about 50 mm. When a predetermined tensile force is applied to the detection member 50, strain can be detected with higher sensitivity. Further, by preloading the tensile force in this way, even when a strain in the direction in which both the base portions 10 are close to each other occurs, the detection member 50 is prevented from being slackened, and the strain can be detected appropriately. Can be done.
Then, the strain gauge 51 is fixed near the center of the detection member 50 by bonding or the like. The input / output lines of the strain gauge 51 are electrically connected to a processing apparatus installed in the vicinity of the test surface, and the measured value is monitored by the processing apparatus.
When cracks or peeling occurs between the bases 10 on the surface to be tested, the relative positions of the bases 10 change. This change is transmitted to the detection member 50 and detected by the strain gauge 51. The detected value is compared with a reference value prepared in advance, and it is determined that some damage or abnormality has occurred when the difference exceeds a threshold value.

FIG. 5 is a graph showing an example of the distortion measurement value. The vertical axis represents the strain value, and the horizontal axis represents time.
In this example, the damage detection apparatus 1 of the present invention is installed on a test body obtained by bonding and synthesizing steel fiber reinforced concrete, and the result of performing a static tensile test while observing cracks is schematically shown.
The distortion value increases almost linearly with time. When cracks are observed visually (portion surrounded by broken lines in the figure), the value of strain increases while increasing or decreasing rapidly until the load reaches a maximum. After releasing the load, the strain value decreased almost linearly and residual strain associated with cracking was detected.
Incidentally, when cracks are generated on the surface in this way, in the conventional technique in which a strain gauge is directly attached to a structure, the strain gauge is destroyed and measurement cannot be measured.
In this way, a reference value that causes damage or abnormalities such as cracks is measured in advance by preliminary tests, etc., and the measured value is compared with the reference value. To detect. Alternatively, it is possible to detect the occurrence of cracks by numerically processing the values in consideration of increasing and decreasing during cracking.
Furthermore, it is possible to detect cracks by picking up by a method using such a threshold and measuring and examining the residual strain under no external force (for example, a state where no automobile etc. is on the bridge). it can.
In addition, damage such as cracks and cracks generated on the side opposite to the side on which the detection member is disposed in the structure can be detected as compressive strain on the side on which the detection member is disposed.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) The detection member may be an optical fiber with an optical strain detection means built therein. In this case, an optical fiber can be used for the detection member, the cable and the strain gauge. As such an optical fiber, an optical strain meter (FBG), an optical loss meter (OTDR), an optical strain distribution meter (BOTDR) or the like can be used. In particular, the FBG is a narrow region (50 mm or less) on the optical fiber. This is preferable in that the distortion can be measured at intervals of 1 m or more on the same optical fiber. In addition, when a plurality of strain detection means are installed in the longitudinal direction of a long structure, if an electrical strain gauge is used, a pair of cables are wired at each installation location, which is difficult to handle. If an optical fiber is used, measurement can be performed with a single optical fiber, so installation is easy.

(2) The reference value can be varied based on the output of the weight measuring means for measuring the weight of the vehicle traveling on the bridge girder. The heavier the weight, the larger the strain value. If a constant value is used as a reference value, the actual situation may not be grasped. For this reason, it is preferable to set a reference value according to the weight of the vehicle. As the weight measuring means, for example, those described in Japanese Patent No. 3896465 can be used.

(3) As a process of the distortion measurement value, for example, a value when the same vehicle is run once a month can be compared. In this case, it can be determined that damage has occurred when the displacement of the value suddenly increases.

(4) Although the damage detection method of the present invention is mainly applied to structures such as reinforced concrete or steel bridge girders, prestressed concrete (PC) to which compressive stress is applied by a stress applying member disposed inside. It is applicable also to the structure comprised by. In this case, if the detected strain is constantly monitored, the strain value increases when one of the internal stress applying members breaks. And after a fracture | rupture, compared with before the fracture | rupture, a change arises in the value of distortion in normal times. Based on the change of this value, the defect of the stress applying member can be determined.

DESCRIPTION OF SYMBOLS 1 Damage detection apparatus 10 Base 20 Fixing part 21 Fixing piece 22 Mounting piece 24 Guide hole 26 Supporting piece 27 Tension member insertion hole 28 Detection member insertion hole 30 Gripping part 31 Upper piece 32 Lower piece 33, 34 Groove 36 Screw hole 38 Dowel 41 Screw hole 43 Guide bolt 50 Detection member 51 Strain gauge 60 Tension applying member (bolt)
70 Fixing jig 71 Long hole

Claims (7)

A method for detecting damage to a structure,
The first base and the second base are respectively fixed to the first and second locations separated from each other on the surface of the structure,
Between the first base and the second base, the detection member is arranged with a predetermined tensile force applied,
A damage detection method for a structure, wherein the damage of the structure is detected by comparing an output of a strain gauge provided on the detection member with a reference value prepared in advance. 2. The damage detection method for a structure according to claim 1, wherein damage is detected based on residual strain of the structure measured by the strain gauge in an external force state. The structure detection method according to claim 1, wherein the detection member is an optical fiber in which an optical strain detection unit is built. The first base and the second base are fixed to the structure in a state in which a fixing jig for substantially fixing a relative position is mounted, and then the fixing jig is removed. The damage detection method according to any one of claims 1 to 3. The structure damage detection method according to any one of claims 1 to 4, wherein the structure is a concrete or steel bridge girder. 6. The reference value according to claim 1, wherein the reference value is made different based on an output of a weight measuring unit that measures a weight of a vehicle traveling on the bridge girder. Structure damage detection method. The structure is composed of prestressed concrete that has been subjected to compressive stress by a stress applying member disposed therein,
The structure damage detection method according to any one of claims 1 to 6, wherein a defect of the stress applying member is detected based on an increase in strain detected by the strain gauge.

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