JPH04310857A - Method for detecting development of crack of steel bridge structure using ae method - Google Patents

Abstract

PURPOSE:To obtain a AE inspection method monitoring the development of a crack in order to ensure safety in an existing bridge structure having a crack of a degree exerting no effect on strength. CONSTITUTION:A plurality of AE sensors S1-S4 are respectively arranged in the vicinity of the leading end position of the crack of a bridge structural member in a preliminarily estimated crack developing direction so as to form spatitial filters to provide limited monitor regions. Only the AE signals generated within the monitor regions are extracted from the repeated load generated by a running vehicle and the development state of the crack is estimated from the state with the elapse of time thereof.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to the diagnosis of steel bridge structures using the AE method (acoustic emission method). AE with removal means
This paper relates to a method for highly accurate inspection using the method.

0002

[Prior Art] The AE method is an inspection method that utilizes the phenomenon that when a solid deforms or breaks, the strain energy stored until then is released and propagates as elastic waves. There are many examples where it has been used for testing. This testing method detects a large number of AEs in a product after it is completed.
A sensor is attached to the product to detect (orient) the occurrence and location of cracks based on the AE signal generated by the released energy when an external force such as water pressure is gradually applied to the product. In this AE test, it is important to extract only the desired AE signal, which generally has a lot of noise. Conventionally, several methods have been proposed for noise removal. For example, "Basics and Applications of Acoustic Emission"
There are three spatial filter methods described in (Coronasha Co., Ltd., published December 25, 1976). In this method, (a) a gate AE sensor is installed outside the measurement AE sensor, and when the gate AE sensor receives noise such as mechanical vibration from outside the monitoring area, the gate circuit is closed and the measurement AE sensor outputs the noise. How not to let it happen, (
b) Only waves that reach two AE sensors almost simultaneously A
(c) A method in which a waveform with a slow rise is removed as a noise signal from a distance, etc.

0003

[Problem to be Solved by the Invention] The present inventors have conducted research on using the AE method for crack diagnosis in existing bridges.
Unlike conventional AE inspections of tanks, pressure vessels, etc., bridge structures have complex shapes with bolted joints and footings, and are subject to repeated loads from moving vehicles, so they are subject to extremely noisy environments. It was found that it was difficult to detect unknown cracks in advance using the AE method. Furthermore, even if the location of a crack has been confirmed, it has not been possible to inspect the growth of the crack using only the conventional spatial filter method. In other words, noise from outside the monitoring area can be removed, but within the monitoring area, in addition to the AE signal due to the released energy caused by the generation of new cracks caused by the external force of the repeated load from the traveling vehicle, there is also the AE signal caused by the cracks that have already formed. Since apparent AE signals (noise) are generated due to contact and rubbing, a correlation with crack growth could not be obtained from signals within the monitoring area alone.

0004

[Means for Solving the Problems] The present invention provides an AE inspection method for monitoring the progress of cracks in order to ensure safety in existing bridge structures that have minute cracks that do not affect the strength. The purpose is to provide a limited number of AE sensors by arranging multiple AE sensors to form a spatial filter in the vicinity of the crack tip position of the bridge structural member and in each of the predicted direction of crack propagation. Then, only the AE signals generated within each monitoring area are extracted from the repeated loads caused by the running vehicle, and the progress of cracks is estimated from the changes over time.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 5 are drawings for explaining a spatial filter according to the present invention. To configure the spatial filter, four AE sensors S1 to S4 are used, of which AE sensor S1 is installed at the crack or in the direction of crack growth and serves as a measurement sensor, and the other three AE sensors S
2 to S4 are provided at arbitrary distances in three directions around the AE sensor S1. In addition, three AE sensors S2 ~
S4 may be provided equidistantly in three directions around the AE sensor S1. The monitoring area is formed around the AE sensor S1, and its range Δl can be arbitrarily determined by setting the reception time range Δt in relation to the sound velocity V of the subject. That is, for example, if the object to be detected is steel and V=3000m
/s, if the setting time range Δt=10μs, Δ
l=V×Δt=3cm. The AE signal measurement is performed using the received wave of the AE sensor S1 as a reference, as shown in FIG.
A set time range Δt is provided after =l4/v. Only when all three AE sensors S2 to S4 receive the signal within this set time, the AE signal generated from within the monitoring area,
That is, it is an AE signal due to a crack. FIG. 3 shows a case where each of the AE sensors S2 to S4 receives a signal from point a within the monitoring area, and each of the AE sensors S2 to S4 receives the signal within a set time range. Also, Figures 4 and 5 show noise generated from points b and c outside the monitoring area, and three AE
This shows an example in which the sensors S2 to S4 are not all satisfied with receiving data within the set time range. As described above, the spatial filter can detect only the AE signals generated only within a specific monitoring area around the AE sensor S1 and remove other noises.

Next, a method for monitoring crack growth will be explained with reference to FIGS. 6 to 9. As described above, the monitoring area A forming a spatial filter is provided near the tip of the crack 1 in the bridge web 3, which has been confirmed in advance by visual inspection, color check, ultrasonic inspection, etc. In addition, a plurality of similar monitoring areas B are provided in the predicted growth direction 2 of the crack 1. The crack propagation direction 2 is a direction perpendicular to the maximum tensile principal stress and can be estimated from stress analysis. For example, in a simple bridge main girder, cracks tend to propagate along the edges of longitudinal stiffeners, and the cracks tend to propagate toward the web, so it can be easily predicted. To monitor crack growth, monitor area A where cracks have already formed and at least 1 area in the direction of crack growth.
It is sufficient to provide a monitoring area B at each location, but if you want to know in detail how the crack is progressing, it is preferable to provide a plurality of monitoring areas B at appropriate intervals. FIG. 6 shows an example in which the monitors are provided in two monitoring areas B1 and B2. In FIG. 6, 4 is the lower flange of the bridge.

FIGS. 7 to 9 show examples in which the crack growth detection method of the present invention was confirmed by fatigue tests. At first, many AE signals are seen in monitoring area A (near the crack), and almost none are observed in monitoring area B. However, as the number of repetitions increases, the AE signal in monitoring area A decreases, and the AE signal in monitoring area B1 increases. It increases rapidly and then decreases. Next, the AE signal in monitoring area B2 is rapidly increasing. That is, when the AE signals in the monitoring areas B1 and B2 suddenly increase, this indicates that a crack has developed in each monitoring area. In addition, monitoring areas A and B
After the crack has passed through, no new crack will occur, so A
Although no E signal should be generated, it is presumed that the reason why the AE signal is measured is due to the crack surfaces hitting each other.

[0008]

[Effects of the Invention] According to the present invention, by removing noise with a spatial filter and further providing a monitoring area in the direction of predicted crack growth, crack growth can be accurately monitored even when a large amount of noise is included. This is an excellent way to ensure safety monitoring of bridges.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the arrangement relationship between a monitoring area and an AE sensor.

FIG. 2 is a diagram showing reception time range settings for each sensor.

FIG. 3 is a diagram showing an example of receiving signals from points a, b, and c.

FIG. 4 is a diagram showing another example of receiving signals from points a, b, and c.

FIG. 5 is a diagram showing another example in which signals from points a, b, and c are received.

FIG. 6 is a diagram showing the arrangement of monitoring areas for inspecting crack growth according to the present invention.

FIG. 7 is a diagram showing data of an AE signal in monitoring area A obtained according to the present invention.

FIG. 8 is a diagram showing data of the AE signal of the monitoring area B1 obtained according to the present invention.

FIG. 9 is a diagram showing data of the AE signal in the monitoring area B2 obtained according to the present invention.

[Explanation of symbols]

S1 AE sensor (first AE signal reception sensor)
S2 AE sensor (second receiving sensor) S3
AE sensor (third receiving sensor) S4 AE sensor (fourth receiving sensor) S Signal wave Δt Reception time range A Crack tip monitoring area B1 Crack growth monitoring area B2 Crack growth monitoring area 1 Crack 2 Crack growth direction 3 Bridge web 4 Bottom flange

Claims (1)

[Claims] Claim 1: A limited monitoring area is provided by arranging a plurality of AE sensors to form a spatial filter in the vicinity of the crack tip position of the bridge structural member and in each of the predicted direction of crack propagation. AE whose source is within each monitoring area from the vibration caused by
A method for detecting crack growth in steel bridge structures using the AE method, which is characterized in that only signals are extracted and the progress of cracks is estimated from the state of changes over time.