JP2001215178A - Method and apparatus for detecting crack of structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus especially suited to a large- sized welded structure such as a bridge or the like and capable of detecting whether a crack is generated early, certainly and easily. SOLUTION: A crack detector is equipped with a mechanism for feeding air to the interior 11a of a structural member 11 under pressure to hermetically seal the same in the structural member, a pressure sensor for measuring the internal air pressure of the structural member and a display part for displaying the internal air pressure. The structural member 11 is constituted of a hollow base material 16 and the end members 17a, 17b for closing both ends of the hollow base material 16 and the measured value P of the internal air pressure of the structural member 11 measured by the pressure sensor 4 is monitored. When a crack is generated in the structural member 11 and pierces the wall of the structural member 11, the internal air pressure lowers and the measured value P thereof lowers. The change of the measured value P displayed on a display part 15 is judged from the display of the display part 15 to detect the generation of the crack.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a crack in a structure having a closed space and an apparatus for detecting the crack.

[0002]

2. Description of the Related Art Vehicles and the like travel through structures such as bridges for a long period of time. Each time, a repeated load is applied to the structural material constituting the structure, and a fatigue crack may occur. Such fatigue cracks gradually grow and may eventually lead to serious accidents such as breakage of the structure.

[0003] Therefore, it is necessary to detect and repair fatigue cracks at an early stage. For this purpose, regular inspections and crack detection are performed. Periodic inspections are mainly performed by visual inspection.

[0004] Penetration inspection (PT) and magnetic particle inspection (M) are available for small cracks and cracks that are difficult to detect by visual inspection.
T), so-called non-destructive inspection such as ultrasonic flaw detection (UT) is used in combination depending on the purpose.

Further, in order to detect the occurrence of fatigue cracks, the magnitude and frequency of the stress generated in the structure are continuously measured, and the relationship between the number of repetitions of the stress obtained in advance through tests and the like and the fatigue life of the material is calculated as follows. Various proposals have been made for diagnosing the remaining life of a structure.

Alternatively, a fatigue life prediction sensor (sacrifice test piece) is provided at a position where a crack is predicted to occur and a crack is generated earlier than a structure and grows, and the crack of the predictive sensor is detected. Accordingly, a method for estimating the degree of fatigue deterioration of a structure has been proposed (Japanese Patent Laid-Open No. Hei 1 (1998)).
0-068679).

[0007]

In a large-sized welded structure such as a bridge, fatigue cracks are generally likely to occur in stress-concentrated portions such as welds. In addition, the access to the inspection points is not easy, and the number of inspection points is enormous, so that the above-mentioned visual inspection often misses fatigue cracks.

[0008] Even if a nondestructive inspection such as ultrasonic flaw detection is performed, much time and labor is required for installation and inspection of equipment, and inspection of a welded portion and the like must be performed for each location. It takes a lot of time to become.

In addition, stress measurement and detection of a fatigue crack using a predictive sensor do not detect the fatigue crack itself generated in the structure, so that even if an indication of the degree of deterioration due to fatigue is obtained, Whether or not a fatigue crack has actually occurred is not clear unless checked by other means.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and particularly suitable for a large-sized welded structure such as a bridge, and can quickly, reliably and easily detect the presence or absence of a crack. It is an object to provide a method and its sensing device.

[0011]

According to the first aspect of the present invention, for a structure having a closed space, the pressure inside the closed space is maintained at a pressure exceeding or less than the atmospheric pressure, and the internal pressure is reduced. A method for detecting a crack in a structure, comprising measuring the change in the measured value and detecting the occurrence of a crack in the closed space structure.

According to a second aspect of the present invention, there is provided an apparatus for detecting a crack in a structure having a closed space, wherein a mechanism for injecting gas into the closed space and sealing it, a pressure sensor for measuring the internal pressure,
A structural member crack detection device comprising a display unit for displaying an internal pressure.

According to a third aspect of the present invention, there is provided an apparatus for detecting a crack in a structure having a closed space, comprising a mechanism for maintaining the pressure inside the closed space below atmospheric pressure and a display unit for displaying the internal pressure. Characteristic crack detector for structural materials. According to the present invention, for a structure having a closed space, the air pressure inside the closed space is measured, and the presence or absence of crack generation of the structure having the closed space is determined early from the change in the measured value, reliably and It can be easily detected.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. 4A and 4B show an example of a structure having a closed space to which the present invention is applied, and FIG. 4A is a side view,
FIG. 2B is a partial front view taken along line AA of FIG.

The pipe truss bridge 30 includes a bridge girder 31 and a pier 27
And a floor slab 28. Bridge girder 31 is lower chord material 31
a, diagonal member 31b, upper chord member 31c, and a steel pipe is used for each of them, and both ends of the steel pipe are closed,
It has a closed space.

FIG. 1 is a side view showing an embodiment of the present invention. The structural member 11 is a structural member corresponding to the upper chord material or the lower chord material of the pipe truss bridge, which is a structure having a closed space shown in FIG.

[0017] The crack detecting device is provided inside the structural member 11.
The apparatus is provided with a mechanism for pressure-feeding and sealing gas into a, a pressure sensor for measuring the internal pressure, and a display unit for displaying the internal pressure. The structural member 11 includes a hollow substrate 16 and a hollow substrate 1.
6 is composed of end members 17a and 17b that close both ends.

Although a steel pipe is used for the hollow base material 16, the present invention is not limited to this, and any hollow base material such as a hollow square member can be used.

The structural member 11 is provided with an opening 18 penetrating through the interior 11a, and a mechanism is connected to the opening 18 for pressurizing gas to be sealed therein. An air feeding / sealing mechanism 12 is used as the gas pressure feeding / sealing mechanism.

Air is practically inexpensive and easy to handle. However, the present invention is not limited to this, and a gas such as nitrogen can be used. Here, the case where air is used will be described.

The air feeding / sealing mechanism 12 includes a nozzle 19, a valve 13, an air supply pipe 20, and a compressor 21, and the nozzle 19 is inserted into the opening 18 of the structural member 11 and fixed. The air compressed by the compressor 21 to a pressure exceeding the atmospheric pressure is supplied to the air supply pipe 20.
The pressure is fed into the structural member 11 via the valve 13 and hermetically closed, and the pressure inside the closed space of the structural member 11 is maintained at a pressure exceeding the atmospheric pressure.

The pressure sensor 14 measures the internal air pressure of the structural member 11, and is mounted on the end member 17a in this embodiment, but is not limited to this, and may be mounted on the hollow substrate 16.

The internal pressure measured by the pressure sensor 14 is displayed on a display unit 15.

The display unit 15 monitors the displayed internal air pressure as needed by an inspector at the time of inspection of the structure to monitor for the occurrence of cracks.

A method for monitoring the occurrence of cracks will be described below. The measured value P of the internal air pressure of the structural member 11 measured by the pressure sensor 14 is displayed on the display unit 15 and is appropriately monitored. When a crack occurs in the structural member 11 and the crack penetrates the plate thickness, the internal air pressure decreases, and the measured value of the internal air pressure P
Decrease. The occurrence of a crack is detected by determining from the display on the display unit 15 that a change in P displayed on the display unit 15 has occurred.

Further, P is recorded continuously or intermittently at appropriate intervals, and the record is displayed on the display unit 15. By monitoring the display, the occurrence of a change in P is detected, and the occurrence of a crack is detected.

Further, P fluctuates in accordance with the fluctuation of the internal air temperature of the structural member. A value of P exceeding the fluctuation range of P corresponding to the temperature change is set in advance as a threshold value Ps. It is determined from the display of the display unit 15 that a change in P exceeding the threshold value Ps has occurred, and the occurrence of a crack is detected.

Further, if the display unit 15 is installed at a position easily accessible to an inspector who inspects the structural member 11, for example, under a bridge girder in a bridge, it is not necessary to temporarily provide a scaffold, and the crack generation can be easily monitored. be able to.

Further, if the signal of the pressure sensor 14 is remotely transmitted by the transmission means and the display unit 15 is installed in a place apart from the structural member 11, for example, in a management office of a road including a bridge, it is possible to monitor the occurrence of cracks from a remote place. Can be easily performed.

Further, by adding the alarm function 29, the inspector can easily monitor the occurrence of cracks.

Further, the occurrence of cracks may be detected by using an air suction mechanism such as a vacuum pump to maintain the inside of the closed space of the structural member at a pressure lower than the atmospheric pressure.

In order to confirm the effect of the present invention, a test specimen having a closed space was subjected to a three-point bending fatigue test using a fatigue test apparatus as shown in FIG.

FIG. 2 is a plan view showing a fatigue test apparatus used for a fatigue test of a structural member having a closed space used in the present invention, and FIG. 3 is a view showing the relationship between the internal air pressure and the number of load repetitions during the fatigue test. It is.

The specimen S uses a steel pipe for the hollow base member 16.
Using flanges for the end members 17a and 17b, flanges are welded to both ends of the steel pipe to seal the inside. Specimen S has a length L of 2610 mm, an outer diameter of 450 mm, and a thickness of 25 mm
It is.

In the fatigue test apparatus 22, reaction walls 23a, 23b, and 23c are arranged as fixed walls in three directions, and a test piece S is pin-joined to opposing reaction walls 23a and 23b.
a, 24b. On the other hand, the reaction wall 23c
The fatigue tester 22a is attached to the
a on the other side of the connecting jig via the pin joint 24c.
5 are attached. A steel ring 26 is welded to the outside of the center of the test body S so as to be integrated with the load jig 25.

Before the fatigue test, a pressure sensor 1 was attached to the specimen S.
4 was provided, an opening 18 having a diameter of 14 mm was provided, the internal air pressure was increased to 0.05 MPa based on the atmospheric pressure, and then the container was sealed. In the test, a repeated load was applied to the test piece S via the load jig 25.

As a result, fatigue cracks were generated from the weld toe at the steel pipe side of the central welded portion, which is the stress concentrated portion, and propagated in the thickness direction of the specimen S to penetrate the specimen S. During the fatigue test, the internal air pressure of the test sample S was measured by the pressure sensor 14 at every constant number of load repetitions.

FIG. 3 is a graph in which the number of load repetitions in the above test is shown on the horizontal axis, and the measured internal air pressure is plotted on the vertical axis. From the observation of the fatigue cracks performed at the same time, the fatigue cracks penetrated the plate thickness of the test piece S at 328,000 load repetitions, and the number of load repetitions and the number of load repetitions at which the internal air pressure sharply decreased were often one. As a result, the present invention can detect a fatigue crack with extremely high accuracy.

Next, a case where the crack detecting device of the present invention is used for a bridge girder of a bridge will be described in detail with reference to FIG. (A)
The drawing is a side view, and the drawing (b) is a partial front view taken along line AA of the drawing (a).

The pipe truss bridge 30 includes a bridge girder 31 and a pier 27
And a floor slab 28. Bridge girder 31 is lower chord material 31
a, a diagonal member 31b, and an upper chord member 31c, each of which is made of a steel pipe, and both ends of the steel pipe are closed to form a closed space.

Lower chord 31a, diagonal 31b, upper chord 31c
And a pressure sensor 14 for measuring the internal air pressure, and a pressure sensor 14 for measuring the internal air pressure.
Is arranged, and it is confirmed whether or not a fatigue crack has occurred in the lower chord material 31a, the diagonal material 31b, and the upper chord material 31c.

The compressor 21 of the air feeding mechanism 12,
If the display unit 15 is arranged at a position distant from the bridge girder 31, for example, at the base of the bridge girder 27, there is no need to provide a scaffold for accessing the bridge girder 31, and it is possible to confirm the occurrence of fatigue cracks. Air is supplied by the air supply mechanism 12 and the bridge girder 3
The internal air pressure of the closed space 1 is maintained at a pressure exceeding the atmospheric pressure. By monitoring the internal air pressure in the closed space of the bridge girder 31, the occurrence of fatigue cracks can be detected.

According to the crack detecting device of the present invention, the bridge girder 31
Even a large-sized structure having a complicated structure as described above, it is possible to quickly and surely and easily confirm whether or not a fatigue crack has occurred, and to take appropriate action promptly. Although the embodiment has been described in detail about the pressurized feeding, the same crack can be monitored by setting the internal pressure to a negative pressure from the atmospheric pressure using a vacuum pump.

[0044]

As described above, according to the present invention, in a structure having a closed space, the air pressure inside the closed space is measured, and the presence or absence of a crack in the closed space structure is detected from a change in the measured value. Therefore, the presence or absence of crack generation can be detected early, reliably and easily, particularly for large-sized welded structures such as bridges. Therefore, appropriate measures can be taken against crack generation.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment according to the present invention.

FIG. 2 is a plan view showing a fatigue test apparatus used for a test piece of a structural material having a closed space used in the present invention.

FIG. 3 is a diagram showing a relationship between a measured internal air pressure and a number of load repetitions during a test according to the present invention.

FIG. 4 is a view showing a bridge girder of a bridge to which the crack detection device according to the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Structural member 11a Inside 12 Gas supply mechanism 13 Valve 14 Pressure sensor 15 Display part 16 Hollow base member 17a, 17b End member 18 Opening 19 Nozzle 20 Air supply pipe 21 Compressor 22 Fatigue test device 22a Fatigue tester 23a, 23b, 23c Reaction wall 24a, 24b, 24c Pin joint 25 Applying jig 26 Ring 27 Pier 28 Floor slab 29 Warning function 30 Pipe truss bridge 31 Bridge girder 31a Lower chord 31b Diagonal 31c Upper chord S

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shunji Ueda 1-2-2 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 2G024 AD34 CA16 FA11 2G067 AA19 DD02 EE11

Claims (3)

[Claims] 1. A structure having a closed space, the pressure inside the closed space is maintained at a pressure higher than or lower than the atmospheric pressure, and the internal pressure is measured. A method for detecting a crack in a structure, comprising detecting occurrence of a crack in the structure. 2. A crack detecting device for a structure having a closed space, wherein a mechanism for pressure-feeding a gas into the closed space and sealing the same is provided.
An apparatus for detecting a crack in a structural material, comprising: a pressure sensor for measuring an internal air pressure; and a display unit for displaying the internal air pressure. 3. A structure crack detecting device for a structure having a closed space, comprising: a mechanism for keeping the pressure inside the closed space below atmospheric pressure; and a display unit for displaying the internal pressure. Crack detection device.