JPH0374785B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention predicts the risk of fatigue damage in structures such as bridges before fatigue cracks occur in the structure body. It is about the method.

[Prior Art and its Problems] The following method can be considered as a conventional method for predicting the risk of fatigue damage that can be applied to structures such as bridges.

First, the first method is to apply stress measurement using a strain gauge. That is, this is a method in which a strain gauge is affixed to a region that is at risk of fatigue damage, the degree of stress is calculated from the output of the gauge, and the degree of damage is estimated from the magnitude.

However, with this method, it is difficult to affix strain gauges to existing elevated structures, the painted area must be treated before and after the strain gauge is affixed, and information can only be obtained from the area where the strain gauge is affixed. There were problems such as not being able to obtain

A second method is acoustic wave measurement using acoustic emission. In materials such as steel, this is due to plastic deformation or cracking of the material.
Taking advantage of the fact that sound, or elastic waves, are generated during propagation, an acoustic emission wave receiver is installed in a dangerous area, and the risk of damage is determined from the signal.

However, with this method, the elastic wave output due to plastic deformation before crack initiation is not large and difficult to detect, and the detection limit is generally set at a crack length of about 3 mm, in which case it cannot be predicted. There was a problem.

Furthermore, a third method includes visual inspection and non-destructive inspection. This is a periodic inspection to detect whether or not fatigue cracks have occurred in dangerous areas by visual inspection and non-destructive inspection.

However, this method has the problem that the inspection environment for elevated structures such as bridges is generally poor, making it difficult to apply highly accurate non-destructive inspection methods, or requiring a large amount of man-hours to prepare scaffolding for inspection. . In addition, since cracks cannot be predicted as a result of inspection if they have already occurred, there is a problem in that inspections must be carried out frequently from a very early stage.

[Object of the Invention] In order to solve the above problems, the present invention has the following objectives: (a) it is applicable to structures such as bridges with poor inspection environments, the installation work is not so difficult, and (b) accuracy and detection are improved. It is an object of the present invention to provide a method for predicting fatigue damage of a structure, which has good properties and (c) does not cause the risk of crack propagation to the structure body.

[Structure of the Invention] In order to achieve this object, the fatigue damage prediction method according to the present invention has a notch in a structure and an inner part located at a position an appropriate distance from the tip of the notch in the depth direction. A prediction piece with a hole filled with a colored liquid is attached by welding, a crack occurs in the prediction piece before the structure, and the occurrence of a crack in the prediction piece is recognized by visually observing the colored liquid seeping out on the surface of the prediction piece. This method consists of a method of predicting the lifespan of a structure based on the occurrence of cracks in the prediction piece.

[Operation of the Invention] In the fatigue damage prediction method as described above, since the prediction piece is attached to the structure by welding, the load applied to the structure due to the strain generated in the structure is reliably transmitted to the prediction piece. Since a notch is provided in the prediction piece, fatigue cracks will occur in the prediction piece before cracks occur in the structure itself, and only the prediction piece can be observed with a telescope to investigate whether or not cracks have occurred. This makes it possible to predict the degree of fatigue damage to a structure. Since the prediction piece has a hole, a crack that starts from the tip of the notch will grow and stop at the hole, and even though the prediction piece is welded to the structure, the crack in the prediction piece will not grow. It will not propagate to the structure through the weld.

In addition, since the colored liquid is sealed in the sealing hole, when a crack occurs in the prediction piece, the crack leads to the hole, and the sealed colored liquid leaks to the surface of the prediction piece, preventing the occurrence of cracks in the prediction piece. It can be easily identified with the naked eye, improving convenience and identifiability.

[Example] A preferred example of the fatigue damage prediction method of the present invention will be described below with reference to the drawings.

Figure 1 shows a case where a bridge is used as an example of a structure. In the figure, 1 is a structure, which is supported on a foundation support 8. In such a structure 1, a large tensile stress due to bending stress is generated at the lower edge of the structure 1, and is repeatedly applied due to the passage of vehicles, railway vehicles, etc. through the bridge. Therefore, the lower edge portion of the structure 1 becomes a dangerous area where fatigue cracks may occur. A prediction piece 2, which will be described below, is attached to a fatigue crack-prone area of the structure 1. Installation is by welding.

The prediction piece 2 is made of the same material as the main body of the structure 1, and is made of a plate member having a notch 3, as shown in FIGS. 2 and 3. Notch 3
is provided on the lower side where the maximum bending stress is applied when the prediction piece 2 is subjected to bending stress from the structure 1. The prediction piece 2 has a hole 4 having a smooth curved inner diameter surface at a position facing the notch 3 and at a position away from the notch 3, that is, at a position separated from the tip of the notch 3 by an appropriate distance in the depth direction.
is formed. The hole 4 is a sealed hole as shown in FIG. 5, and a colored liquid 7 is sealed therein. The prediction piece 2 is attached to the structure 1 by welding 5, and the welding part 5 has a smooth curve,
Finished to prevent notches from forming.

As shown in FIGS. 4 and 5, the prediction piece 2 has an opening angle α of the notch 3 and a curvature of the tip of the notch 3.
By appropriately selecting r ² , the distance d between the notch 3 and the hole 4, and the curvature r ¹ provided on the left and right sides of the notch 3 of the prediction piece 2 so as to continue to the welding part 5, The ease with which cracks form from the notch 3 is controlled.

FIG. 7 relates to a different embodiment from FIG. 4,
A case is shown in which a notch 3' is also provided in the prediction piece 2 on the opposite side of the notch 3 from the hole 4. By doing so, it is ensured that cracks will not occur in the prediction piece 1. However, the notch 3' must be provided in a direction in which the crack does not propagate toward the main body of the structure 1.

In order to predict fatigue damage in the structure 1 using the prediction pieces 2, first, the prediction pieces 2 are attached to appropriate fatigue damage-prone parts of the structure. The attachment may be done in advance before construction of the structure 1, or may be attached to the existing structure 1.

The structure 1 is subjected to repeated loads, and the prediction piece 2 is also subjected to repeated stresses. Between the prediction piece 2 and the structure 1, fatigue cracks begin in the prediction piece 2 with the notch 3 first from the notch 3 portion. Notch 3
Even if a crack 6 occurs from the hole 4, the crack 6 stops at the hole 4. Since the hole 4 has a smooth inner diameter surface, the notch effect is small and prevents the crack 6 from propagating into the main body of the structure 1.

By detecting the occurrence of cracks 6 in the prediction piece 2, the degree of fatigue damage of the structure 1 can be known before harmful cracks occur in the structure 1. When the crack 6 generated from the notch 3 penetrates the hole 4, the colored liquid 7 in the hole 4 seeps onto the surface of the prediction piece 2, and by visually observing it from a distance with a telescope, it is easy to detect the occurrence of the crack. Therefore, the degree of damage to the structure 1 can be known. In other words, if there is a color change on the surface of the prediction piece 2, it is determined based on the margin E whether or not to perform a complete inspection, and if there is no color change, it is considered that there is sufficient safety against fatigue damage. good. Therefore, fatigue damage to the main body of the structure 1 can be easily predicted by observing only the color change.

FIG. 8 shows the relationship between the fatigue properties of the prediction piece 2 and the main body of the structure 1, particularly the occurrence of cracks at locations A, B, and C in FIG. 4. At a portion A where the prediction piece 2 is not attached, cracks occur in the main body of the structure 1 according to the characteristic line A in FIG. Prediction piece 2 and structure 1
When finishing r ¹ and the welded portion 5 of the main body to avoid stress concentration as much as possible, the welded portion 5 cracks according to characteristic line B. Although part B near the weld 5 may crack earlier than part A, it is finished so that it has the same lifespan as A as much as possible. C
Due to the degree of stress concentration determined by the opening angle α of the notch 3 and the curvature ^r2 of the notch tip, cracks occur fairly quickly. The crack that occurred in part C is the distance d to hole 4.
There is a lifespan to spread the message. This is the characteristic line C'.
The degree of margin from when a crack penetrates to hole 4 until a crack occurs in the main body of structure 1 is shown by E in Figure 6, and r ¹ , r ² , α, d, r ³ of prediction piece 2, etc. It is possible to freely adjust the margin depending on the dimensions and shape of the.

In the above description, a bridge is used as an example of the structure 1, but it may be any other structure, such as a steel tower or a crane.

[Effects of the Invention] According to the present invention, since the prediction piece 2 having the notch 3 and the hole 4 and having the colored liquid sealed in the hole 4 is attached to the structure 1 by welding, cracks do not occur in the structure body. Fatigue cracks can be generated in the prediction piece 2 before the cracks are inspected, and the cracks can be applied to structures with poor inspection environments without propagating the cracks to the structure itself. Since it is only necessary to visually observe the liquid using a telescope, etc., it is possible to obtain the effect that the degree of fatigue damage of the structure can be determined with good detectability.

[Brief explanation of drawings]

FIG. 1 is an overall front view of a structure to which an embodiment of the present invention is applied, FIG. 2 is a partial cross-sectional view of the structure near the predictive piece attachment part, FIG. 3 is a side view of FIG. 2, and FIG. The figures are a partial sectional view of the predicted piece part in Fig. 2, Fig. 5 is a side view of the part in Fig. 4, Fig. 6 is a sectional view of the crack part in Fig. 4, and Fig. 7 is a partial sectional view of the part of the prediction piece in Fig. 4. FIG. 8 is a partial cross-sectional view of the predicted piece portion of the example, and a fatigue characteristic diagram. 1...Structure, 2...Predicted piece, 3...Notch, 4...Hole, 5...Welded part, 6...Crack,
7...Color liquid.

Claims (1)

[Claims] 1. A prediction piece having a notch and a hole filled with a colored liquid inside is attached to the structure by welding at a position an appropriate distance from the tip of the notch in the rearward direction, and the prediction piece is attached to the structure by welding. Fatigue characterized by generating cracks in the piece, visually observing the colored liquid seeping out on the surface of the prediction piece, recognizing the occurrence of cracks in the prediction piece, and predicting the life of the structure from the occurrence of cracks in the prediction piece. Damage prediction method.